The effects of canal preparation and filling on the incidence of dentinal defects

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The effects of canal preparation and filling on the incidence of dentinal defects Article in International Endodontic Journal · April 2009 DOI: 10.1111/j.1365-2591.2008.01502.x · Source: PubMed

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SOURCE, OR PART OF THE FOLLOWING SOURCE: Type Dissertation Title New insights into the root canal wall Author H. Shemesh Faculty Faculty of Dentistry Year 2009 Pages 83

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Vo l u m e 0 1

issue 01

October 2009

www.shemesh.nl

SHEMESH New insights into the root canal wall

THE GLUCOSE PENETRATION MODEL 15-47 Feasibility, limitations and results

NOVEL IMAGING METHODS 49-65 Optical coherence tomography, Ultrasound

DENTINAL DEFECTS 67-77

Incidence, causes and development endodontic procedures

NEW INSIGHTS INTO THE ROOT CANAL WALL

Hagay Shemesh

This thesis is supplemented by a website:

www.shemesh.nl

NEW INSIGHTS INTO THE ROOT CANAL WALL

ACADEMISCH PROEFSCHRIFT Ter verkrijging van de graad van doctor aan de Universiteit van Amsterdam op gezag van de Rector Magnificus Prof. dr. D.C van den Boom ten overstaan van een door het college voor promoties ingestelde commissie, in het openbaar te verdedigen in de Agnietenkapel op vrijdag 23 oktober 2009, te 14:00 uur

door

Hagay Shemesh Geboren te Beer Yaakov, Israel

Promotor:

Prof. dr. P.R. Wesselink

Copromotors:

dr. M.– K. Wu dr. L.W.M van der Sluis

Faculteit der Tandheelkunde

This thesis was prepared at the Department of Endodontology Academic Centre for Dentistry Amsterdam (ACTA), University of Amsterdam and VU University Amsterdam, the Netherlands.

This thesis is dedicated to Paul Wesselink and Min-Kai Wu for their unprecedented contribution to endodontology in the last 3 decades.

Contents

9

Chapter I

General introduction

Chapter II

Permeability of the root canal wall and leakage

17

Leakage along apical root fillings using two different leakage models

26

Glucose and fluid transport through coronal root structure and filled roots

33

Influence of passive ultrasonic irrigation on the seal of root canal fillings

39

Comparability of results from two leakage models

44

Glucose reactivity with different filling materials

Chapter III

Novel imaging methods

51

High frequency ultrasound imaging of a single-species biofilm

57

The ability of optical coherence tomography to characterize the root canal walls

62

Diagnosis of vertical root fracture with optical coherence tomography

Chapter IV

Inspection of dentinal defects in the root canal wall

69

Effects of canal preparation and filling on the incidence of dentinal defects

75

The ability of different Ni-Ti rotary instruments to induce dentinal damage

79

Chapter V

Summary and conclusions Samenvatting en conclusies Acknowledgements

9

Chapter I Introduction

10

11

New insights into the root canal wall Introduction Endodontology is concerned with the study of the form, function and health of, injuries to and diseases of the dental pulp and periradicular region, and the prevention and treatment of apical periodontitis, caused by infection (European Society of Endodontology, 2006). The technical aim of the endodontic treatment is the shaping and cleaning of the root canal system and the filling of the canals as if to prevent coronal leakage and entomb remaining microorganisms, preventing them from irritating the periapical tissues (Sundqvist et al.1998). Recent evidence show that endodontic therapy may not always result in favorable and predictable outcomes.

Moreover, it seems that clinical endodontic research neglected important issues concerning the outcome of the treatment like low sensitivity of conventional radiographs in detecting periapical lesions and low recall rates (Wu et al. in print).

In order to investigate the effectiveness of procedures during endodontic therapy, two major approaches could be taken: randomized clinical studies comparing the results of treatments and in vitro / ex vivo investigations. Randomized clinical studies have a higher level of evidence when compared to other studies but are difficult to perform not only because of the need to standardize conditions but also because experimenting on human beings requires a set of preconditions which are nowadays hard to meet. When human subjects are difficult to investigate and control, animals may provide more relevant information on the outcomes of different treatments. Experimenting with animals is controversial in most countries and strict rules and requirements make these investigations time consuming and expensive.

The next step in considering an investigation method is in vitro studies. These laboratory tests aim at investigating different materials and methods in laboratory conditions using models, extracted teeth and special machinery.

The common substrate for all endodontic procedures is the root canal itself, but different aspects of the root canal treatment from the root canal wall perspective were seldom addressed. The root canal wall is made of dentine which has a complex relationship between morphology and

function (Kishen et al. 2000). This could possibly affect procedures we use during root canal treatment, which are roughly divided into two important steps: Cleaning of the root canal system (including mechanical instrumentation) and filling. These pose challenges to the clinician and researcher while there is still no consensus as to the preferred method or material of choice.

Cleaning and instrumentation of the canal The objective of mechanical instrumentation is to remove the main bulk of infected material and its nutritional supply, facilitate irrigation and appropriately shape the canal for the filling procedure (HĂźlsmann et al. 2005). There are numerous problems associated with the preparation procedures and their effect on the root canal walls: 1. A debate exists as to the formation, importance and faith of the smear layer which is created during the preparation procedures (Ĺžen et al.

1995). This debate is addressed in a few studies in this thesis checking the influence of the removal of the smear layer on the effectiveness of the filling to prevent leakage, and the propagation of light through the dentinal tubules.

2. In infected root canals microorganisms could be attached to the root canal walls in the form of biofilms (Svensäter & Bergenholtz 2004, Chavez de Paz 2007) which are resistant to cleaning procedures and disinfectants. Biofilms are difficult to image and investigate, and existing investigation methods involve preparation procedures that damage the structure and vitality of the biofilm. This thesis checks the ability of an ultrasound scan to image the 3D structure of biofilms nondestructively.

3. The canal anatomy is complex and often longoval in form (Wu et al. 2000). Efficient instrumentation and cleaning of such canals is extremely challenging. It is important to visualize and to have knowledge of internal anatomy relationships before undertaking endodontic therapy. This thesis explores the

12

feasibility of optical coherence tomography as a non destructive method to look at the anatomy of the root canals and associated structures.

The root canal filling The purpose of filling the root canal is to prevent the growth of bacteria remaining after canal preparation and the passage of fluids and bacterial elements from the pulp cavity into the periapical tissues (Sundqvist et al.1998). However, it seems that current filling materials and techniques fail to provide a leak-free seal (Wu & Wesselink 1993, Eldeniz & Ă˜rstavik 2009).

A variety of laboratory-based experimental models are used to detect and measure leakage along root fillings. The fluid transport set-up is often used to measure leakage of water through root canal fillings (Wu et al. 1993). Xu et al. (2005) proposed and used a new model that measures the leakage of glucose molecules. The glucose leakage model is relatively easy to assemble and use and could give quantitative leakage measurements which are based on a chemical reaction between specific enzymes and glucose. This reaction is very sensitive, measured by a spectrophotometer and could detect minute concentration changes of glucose. This thesis uses the glucose penetration model in order to compare the sealing ability of various materials and methods and to further assess the advantages and limitations of this model.

Both mechanical instrumentation and obturation of the root canal could introduce defect in the root canal wall (Wilcox et al. 1997). These defects could eventually propagate into vertical root fractures and might have clinical significance. The procedures that mostly cause these defects are debatable (Lertchirakarn et al. 1999). Evidence exists as to the role of lateral compaction of gutta percha in the formation of vertical root fracture (Dang and Walton 1989), but the ability of other endodontic procedures to cause dentinal defects was not studied yet. The recent introduction of different Ni-Ti files used with engine-driven mechanical forces to endodontics could be a contributing factor in the formation of such defects. This thesis explores the influence of different endodontic procedures on the formation of defects like craze lines and vertical root fractures in the root canal wall.

Objectives of the thesis The aim of this thesis was to suggest new methodologies to measure, image and explore the root canal walls and related interfaces and to present new insights into the root canal wall associated with endodontic treatment procedures. Specifically, 3 approaches were taken: 1. Leakage measurements using the penetration of glucose through root canal fillings as a new model for assessing the sealing ability of different materials and methods.

2. The application of novel imaging technologies for non destructive high resolution characterization of the root canal wall and related structures.

3. Studies into the ability of different types of files and filling methods to inflict defects on the root canal wall.

Outline of the thesis - In chapter II, the glucose penetration model for leakage tests is tried. Different experiments are presented using this model and its ability to detect leakage patterns through different materials, set ups and conditions. Comparison between performance of different materials and methods as observed with this new model and the already established fluid transport model were also made. The limitations of this model to reliably detect leakage through root canal fillings are discussed.

- In chapter III new endodontic applications for novel imaging techniques are suggested. Ultrasound scans for imaging live biofilm without damaging its delicate 3D structures and vitality. Optical coherence tomography for intra-canal imaging, showing the root canal walls and related structures nondestructively and without using ionized radiation.

- In chapter IV the formation and incidence of dentinal defects in the root canal wall after different preparation and filling procedures are discussed.

Comparison is made between the lateral compaction technique and a non compaction technique, and between the use of hand files and different rotary Ni-Ti systems.

13

References: Quality guidelines for endodontic treatment: consensus report of the European Society of Endodontology.(2006) International Endodontic Journal 39, 921-930.

Chavez de Paz LE. (2007) Redefining the persistent infection in root canals: possible role of biofilm communities. Journal of endodontics 33,652-62.

Dang DA, Walton RE (1989) Vertical root fracture and root distortion: effect of spreader design.

Journal of Endodontics 15, 294-301.

Eldeniz AU, Ørstavik D (2009) A laboratory assessment of coronal bacterial leakage in root canals filled with new and conventional sealers.

International Endodontic Journal 42:303-12.

Hülsmann M, Peters OA, Dummer PMH (2005) Mechanical preparation of root canals: shaping goals, techniques and means. Endodontic Topics 10, 30-76.

Kishen A, RamamurtyU, Asundi A (2000) experimental studies on the nature of property gradients in the human dentine. Journal of Biomarials research 51: 650-9.

Lertchirakarn V, Palamara JE, Messer HH (1999) Load and strain during lateral condensation and vertical root fracture. Journal of Endodontics 25 99-104. Şen BH, Wesselink PR, Türkün M (1995) The smear layer: a phenomenon in root canal therapy.

International Endodontic Journal 28,141-8.

Sundqvist G, Figdor D, Persson S, Sjögren U (1998) Microbiologic analysis of teeth with failed endodontic treatment and the outcome of conservative re-treatment. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 85,86-93.

Svensäter G, Bergenholtz G (2004) Biofilms in endodontic infections. Endodontic Topics 9, 2736.

Wilcox LR, Roskelley C, Sutton T (1997) The relationship of root canal enlargement to finger spreader induced vertical root fracture. Journal of Endodontics 23, 533-4.

Wu MK, De Gee AJ, Wesselink PR, Moorer WR (1993) Fluid transport and bacterial penetration along root canal fillings. International Endodontic Journal 26:203-8.

Wu MK, Wesselink PR (1993) Endodontic leakage studies reconsidered. Part I. Methodology, applications and relevance. International endodontic journal 26, 203-8.

Wu MK, R'oris A, Barkis D, Wesselink PR (2000) Prevalence and extent of long oval canals in the apical third. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 89,739-43.

Wu MK, Shemesh H, Wesselink PR (2009) Limitations of previously published systematic reviews evaluating the outcome of endodontic treatment. International Endodontic Journal inprint Xu Q, Fan MW, Fan B, Cheung GS, Hu HL (2005) A new quantitative method using glucose for analysis of endodontic leakage. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 99,107-11.

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15

Chapter II Permeability of the root canal wall and leakage

This chapter is enhanced by additional high-resolution images available on www.shemesh.nl

1. Leakage along apical root fillings with and without smear layer using two different leakage models: a two-month longitudinal ex vivo study. Shemesh H, Wu MK, Wesselink PR. Int Endod J. 2006 Dec;39(12):968-76.

2. Glucose penetration and fluid transport through coronal root structure and filled root canals. Shemesh H, van den Bos M, Wu MK, Wesselink PR. Int Endod J. 2007 Nov;40(11):866-72.

3. An evaluation of the influence of passive ultrasonic irrigation on the seal of root canal fillings. van der Sluis LW, Shemesh H, Wu MK, Wesselink PR. Int Endod J. 2007 May;40(5):356-61.

4. Comparability of results from two leakage models. Souza EM, Wu MK, Shemesh H, Bonetti-Filho I, Wesselink PR. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2008 Aug;106(2):309-13.

5. Glucose reactivity with filling materials as a limitation for using the glucose leakage model. Shemesh H, Souza EM, Wu MK, Wesselink PR. Int Endod J. 2008 Oct;41(10):869-72.

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17 doi:10.1111/j.1365-2591.2006.01181.x

Leakage along apical root fillings with and without smear layer using two different leakage models: a two-month longitudinal ex vivo study

H. Shemesh, M.-K. Wu & P. R. Wesselink Department of Cariology Endodontology Pedodontology, Academic Centre for Dentistry Amsterdam (ACTA), Amsterdam, The Netherlands

Abstract Shemesh H, Wu M-K, Wesselink PR. Leakage along apical root fillings with and without smear layer using two different leakage models: a two-month longitudinal ex vivo study.

International Endodontic Journal, 39, 968–976, 2006.

Aim To compare two different experimental models when measuring leakage along root fillings with or without smear layer.

Methodology One hundred and twenty singlerooted teeth were prepared to size 50 and allocated to two groups: fluid transport model (n ¼ 60) and glucose penetration model (n ¼ 60). The roots in each group were divided into three subgroups of 20 teeth each.

Smear layer was left in place in group 1 but removed in groups 2 and 3. In groups 1 and 2 canals were filled with laterally compacted gutta-percha cones and AH 26. Group 3 was laterally compacted with Resilon cones and Epiphany sealer. The coronal portion of the filling was removed to assure only 4 mm of filling remained in the canal. Leakage of glucose was evaluated by measuring its concentration once a week for a total period of 56 days using a glucose penetration model. Fluid transport was evaluated by measuring the movement of an air-bubble using a fluid transport model, 1 and 8 weeks after canal filling. Differences

Introduction The purpose of a root filling is to prevent bacterial growth and penetration of fluid and antigenic agents

Correspondence: H. Shemesh, Department of Cariology Endodontology Pedodontology, ACTA, Louwesweg 1, 1066 EA Amsterdam, The Netherlands (Tel.: 3120 518 8549; fax 3120 669 2881; e-mail: h.shemesh@acta.nl).

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International Endodontic Journal, 39, 968–976, 2006

between the groups in glucose concentrations and fluid transport were statistically analysed with the Kruskal– Wallis and the Mann–Whitney tests. The level of significance was set at a ¼ 0.05.

Results Glucose penetration was significantly different between the three groups after the first 8 days (P < 0.05). Resilon leaked the most throughout the experiment period. No significant difference (P > 0.05) existed between the two gutta-percha groups at all time intervals (Mann–Whitney test). In the fluid transportation model, no statistically significant differences were observed between all three experimental groups (P > 0.05) at either 1 or 8 weeks after filling (Kruskal– Wallis test).

Conclusions Under the conditions of this study, the glucose penetration model was more sensitive in detecting leakage along root fillings. Removing the smear layer before filling did not improve the sealing of the apical 4 mm of filling. Resilon allowed more glucose penetration but the same amount of fluid transport as the gutta-percha root fillings.

Keywords: gutta-percha, canal filling, smear layer.

leakage,

Resilon,

root

Received 20 March 2006; accepted 13 June 2006

between the canal and periapical tissues (Sundqvist et al. 1998).

A variety of laboratory-based experimental models are used to detect and measure leakage along root fillings. Dye leakage, fluid transport and bacterial penetration are currently the methods used most often.

Recently Xu et al. (2005) discussed a new model that measures the leakage of glucose molecules. The model consists of a tube containing concentrated glucose

ª 2006 International Endodontic Journal

18 Shemesh et al. Leakage of apical root fillings

solution that is connected to the coronal aspect of the tooth, whilst the apical region is dipped in water.

Glucose that accumulates in the apical chamber is measured with a spectrophotometer following an enzymatic reaction. Glucose has a low molecule weight of 180 Da, and may be used as an indication for toxins that might penetrate the canal (Xu et al. 2005).

Leakage studies consistently show bacterial penetration through root fillings. Torabinejad et al. (1990) reported that 50% of filled single-rooted teeth were contaminated along the whole length of the canal after 19 and 42 days of exposure depending on the infecting microorganism. Khayat et al. (1993) reported that all root canals filled with laterally or vertically condensed gutta-percha were contaminated in less than 30 days after exposure to human saliva.

One of the methods previously described for improving the seal and for minimizing leakage is the removal of the smear layer before filling (Clark-Holke et al.

2003). This has been claimed to improve sealer penetration inside the dentinal tubules, achieving a potentially greater adherence to the canal wall (Kokkas et al. 2004). Indeed, some studies that investigated the removal of the smear layer concluded that a better seal was achieved when the smear layer was removed (Kennedy et al. 1986, Cergneux et al. 1987, Taylor et al. 1997, Clark-Holke et al. 2003, C¸obankara et al.

2004). Other studies have suggested that removing the smear layer increases dentine permeability and might impair the sealing ability, and even allow bacteria to grow inside the dentinal tubules (Pashley et al. 1981, Drake et al. 1994, Galvan et al. 1994, Love 1996). Two review articles on the clinical implications of the smear layer in endodontics (S¸ en et al. 1995, Torabinejad et al.

2002) confirmed the uncertainty and debate relating to the removal of smear layer before filling. More recently Gulabivala et al. (2005) discussed the effects of mechanical and chemical procedures including the removal of the smear layer on the seal and stated that the mechanisms leading to successful root canal treatment remained to be determined.

Current filling materials and techniques fail to provide a leak-free seal (Wu & Wesselink 1993, Wu et al. 1993). Gutta-percha is the most popular filling material and has been used for this purpose for many years. Systems like warm injection and carrier-coated root fillings have been developed but have been shown to leak to a certain extent (Mannocci et al. 1999, Abarca et al. 2001, Wu et al. 2003, Chu et al. 2005).

Recently, a new thermoplastic synthetic polymerbased root filling material was introduced (Resilon;

ª 2006 International Endodontic Journal

Pentron Clinical Technologies, Wallingford, CT, USA).

This material resembles gutta-percha in appearance, has similar handling properties and is available both in cone format and in pellets for warm injection. The corresponding sealer (Pentron Clinical Technologies) is a dual curable dental resin composite. This so-called ‘Epiphany’ system (Resilon and sealer combined with self-etching of the canal wall) is claimed to form a ‘monoblock’ which adheres to the dentine walls, prevents leakage and increases resistance to fracture (Shipper et al. 2004, Teixeira et al. 2004).

The purpose of this study was to compare two different experimental models in measuring leakage along apical root fillings with and without the smear layer.

Materials and methods Selection and preparation of teeth One hundred and sixty recently extracted single-rooted human teeth were selected and stored in 0.2% sodium azide, NaN3 (E. Merck, Darmstadt, Germany) at +4 C until use. Mandibular incisors were excluded because of their morphological diversity (Kaffe et al. 1985). Premolars were used only when a radiograph indicated a single canal. Teeth with open apices or large carious lesions were excluded.

The coronal portions of all teeth were removed so that each root specimen was 15 mm long. A diamond bur (FG 173 Horico, Berlin, Germany) was used to gain straight-line entry to the root canal. A size 20 K-Flexofile (Dentsply Maillefer, Ballaigues, Switzerland) was inserted into the canal to verify patency (Kuttler 1955). All samples were examined under a microscope (Zeiss Stemi SV6, Jena, Germany) to exclude cracks. The coronal 4 mm of the root specimens were then embedded in acryl (Vertex; Dentimex BV, Zeist, the Netherlands) to form an acrylic cylinder around the root and enable intimate contact between the rubber tube used to connect the specimen during the leakage phase of the study and the root specimen. All procedures and treatments were preformed by one individual.

Instrumentation and obturation of root canals The working length was determined by subtracting 1 mm from the total length of the root. The apical portion of the canal was instrumented to a size 50 master file using the balanced force technique (Roane & Sabala 1985) with K-Flexofiles (Dentsply Maillefer). A

International Endodontic Journal, 39, 968–976, 2006

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19 Leakage of apical root fillings Shemesh et al.

step-back flaring technique was then performed at 1 mm increments with Gates Glidden burs number 2–6 (Dentsply Maillefer) making the taper 0.2 mm mm)1 (Wu et al. 2002). The purpose of this preparation regimen was to create a uniform size of canal and to overcome the variation in natural morphology. Each canal was irrigated with freshly prepared 2% NaOCl with a 27-gauge needle after every instrument and ensuring patency by extrusion of the solution beyond the apical foramen. A minimum of 10 mL NaOCl solution was used for each root. The prepared roots were randomly divided into three experimental groups of 40 roots, and two control groups of 20 roots each.

root. Three paper points size 50 were used to remove excess primer after 1 min from each root. Roots were then filled with lateral compaction of Resilon cones and Epiphany sealer (Pentron Clinical Technologies) in the same way as in group 1. The filling was removed from the coronal portion of the canal in the same manner as group 1, leaving 4 mm of the apical filling intact.

Group 1 After preparation was completed, canals were rinsed with an additional 5 mL 2% NaOCl solution and then with 5 mL deionized water. Each canal was dried using paper point size 50.

A size 50 gutta-percha master cone coated with AH 26 sealer (Dentsply Maillefer) was inserted into the canal. Light pumping motions were used to fill the canal with sealer and bring the cone to full working length. Lateral compaction was achieved using a size C finger spreader (Dentsply Maillefer) and size 25 accessory gutta-percha cones that initially reached to within 1 mm of the working length. The tip of each accessory cone was lightly coated with sealer, placed and compacted laterally. The process was repeated until cones could not be inserted more than 10 mm into the canal. An estimation of the total amount of sealer used was achieved by using a 0.5 cm · 0.5 cm square of mixed sealer for each tooth.

The coronal gutta-percha was removed with a hot plugger (0.5 mm diameter, Dentsply Maillefer) and vertically packed, leaving the apical 4 mm of root filling subjected to the leakage test (Fan et al. 1999).

Negative control group All roots were sealed with laterally compacted guttapercha and AH 26 for the whole length of the canal and completely covered with nail varnish.

After filling all specimens were maintained for 1 week at 37 C and 100% humidity to allow the materials to set. Specimens in each group were then divided equally between the two different models, glucose penetration and fluid transport.

Group 2 After completion of preparation canals were rinsed with 5 mL 17% EDTA for 3 min to remove the smear layer (Hu¨lsmann et al. 2003) and then rinsed with 5 mL deionized water. The filling was completed in the same way as group 1.

Group 3 All canals were rinsed with 5 mL 17% EDTA for 3 min and then with 5 mL deionized water. After drying, a self-etching primer (Epiphany primer; Pentron Clinical Technologies) was placed into the canal with a 26gauge needle. Two drops of primer were used for each

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Positive control group Canals were filled using lateral compaction of guttapercha cones without any sealer. No warm vertical forces were used and the whole length of the filling remained.

Glucose penetration model – preparation and measurements The difference between the current version of the glucose penetration model and the original model introduced by Xu et al. (2005) lies mainly in the environment in which the equipment was stored: in order to overcome evaporation of fluids, specimens were placed in a closed jar with 100% humidity. From a pilot study it was concluded that this method would eliminate the effect of fluid evaporation on glucose concentration measurements.

The resin block around the coronal part of each root was connected to a rubber tube with stainless steel wires, which was in itself connected to a 16 cm long pipette (Pyrex, Acton, MA, USA). The assembly was then placed in a sterile glass bottle with a screw cap and sealed with sticky wax. A uniform hole was drilled in the screw cap with a diamond bur (No.173 Horico, Berlin, Germany) to assure an open system at all times (Fig. 1). Two millilitres of 0.2% NaN3 solution were inserted into the glass bottle, such that the root samples were immersed in the solution. NaN3 was used to inhibit the growth of microorganisms that might influence the glucose readings. The tracer used in the present study was 1 mol L)1 glucose solution (pH 7.0).

Glucose has a low molecular weight and is hydrophilic

ª 2006 International Endodontic Journal

20 Shemesh et al. Leakage of apical root fillings

Glucose solution

Glass tube

Open system

14 cm

Rubber tube

Acrylic cylinder Metal wire

33, 40, 48 and 56 days. The same amount of fresh 0.2% NaN3 was added to the glass bottle reservoir to maintain a constant volume of 2 mL. The sample was then analysed with a Glucose kit (Megazyme, Wicklow, Ireland) in a spectrophotometer (Molecular Devices, Spectra max 384 plus) at a wavelength of 340 nm.

Concentrations of glucose in the lower chamber were presented in mmol L)1 at each time interval following filling. The lowest glucose level for which the current procedure is believed to be accurate is 0.003 mmol L)1 which derives from an absorbance difference of 0.02 (d-Glucose-HK assay procedure; Megazyme, 2004).

Below this level, the absorbance readings become relatively small, and results are subject to greater error from technique variables. Concentrations smaller than this were thus ignored. Similarly, once leakage exceeded 21 mmol L)1 samples were no longer observed as the glucose concentration in the lower chamber suggested substantial leakage had occurred.

Root specimen 0.2% NaN3 solution

Figure 1 Glucose penetration model.

and chemically stable. About 4.5 mL of the glucose solution, containing 0.2% NaN3, was injected into the pipette until the top of the solution was 14 cm higher than the top of gutta-percha in the canal, which created a hydrostatic pressure of 1.5 kPa or 15 cm H2O (Xu et al. 2005). All specimens were then returned to the incubator at 37 C for the duration of the observation period. A total of 25 lL of solution was drawn from the glass bottle using a micropipette at 8, 13, 20,

Fluid transport model – preparation and measurements Roots were mounted in the fluid transport device (Fig. 2) previously described by Wu et al. (1993). The pipettes used were 22 mm long 1 mL glass pipettes (Witeg, Wertheim, Germany). All connections were tightly closed by twisting pieces of stainless steel wire in a water bath at 20 C. Fluid transport along the root filling was measured under a headspace pressure of 30 kPa (0.3 atm) and after 3 h the volume of fluid transport was recorded. The results were expressed as lL min)1. After measurements teeth were carefully disconnected from the assembly, placed in 0.2% NaN3 solution and returned to the incubator for a period of 8 weeks. The medium was changed with a fresh NaN3

Headspace pressure Silicon tube

Water bath (20°) Filled root

Standard capillary Air bubble

Silicon tube

Figure 2 Fluid transport model.

ª 2006 International Endodontic Journal

Wire connections

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21 Leakage of apical root fillings Shemesh et al.

Glucose concentration mmol L–1

solution every week. After 8 weeks the roots were mounted again and checked for fluid transport in the same way.

Statistical analysis The differences between the groups with regard to glucose concentrations and fluid transport were statistically analysed with the Kruskal–Wallis and the Mann–Whitney tests (version 12.0.1, SPSS, Chicago, IL, USA). The level of significance was set at a ¼ 0.05.

GP+AH26, SL present Negative control

GP+AH26, SL removed Positive control

Resilon-Epiphany

30 40 20 Days after obturation

50

26 22 18 14 10 6 2 0

10

60

Figure 3 Median glucose penetration in mmol L)1 after

Results

2 months.

GP+AH26, SL present Negative control

Percent leakaing samples

The results for the glucose model are shown in Table 1 and Figs 3 and 4. The positive control group had substantial leakage of glucose from the first day which increased over time. After 2 weeks all samples had maximum leakage (21 mmol L)1). In the negative control group no glucose was detected in the apical reservoirs throughout the experiment. Glucose concentrations in the experimental groups revealed that after the first 8 days the difference between the three groups was significant (Kruskal–Wallis test, P < 0.05).

Resilon laterally compacted had the most leakage at all time intervals. However, no significant difference existed between the two gutta-percha groups (Mann– Whitney test, P > 0.05) at all time intervals. The statistical significance of the differences between all three groups is summarized in Table 2.

The results of the fluid transport model are shown in Table 3. The positive control group had bubble movement that exceeded the pipette length after 3 h and was impossible to measure. The negative control group had no movement of the bubble. No significant difference

100 90 80 70 60 50 40 30 20 10 0 –10 0

10

GP+AH26, SL removed Positive control

ResilonEpiphany

20 30 40 Day after obturation

50

60

Figure 4 Percentage of leaking samples in the glucose penetration model – after 2 months.

(P > 0.05) existed between the three experimental groups at both time intervals, 1 and 8 weeks, after filling (Kruskal–Wallis test).

Table 1 Mean and median of glucose leakage in mmol L)1 at different times after obturation Day Group

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GP AH 26 (smear layer present) Mean (SD) 3.1 (6.0) Median (range) 0 (0–21) Percentage leaking 30 GP AH 26 (smear layer removed) Mean (SD) 3.2 (6.6) Median (range) 0 (0–21) Percentage leaking 30 Resilon–Epiphany (smear layer removed) Mean (SD) 3.5 (5.6) Median (range) 1.4 (0–13.5) Percentage leaking 55

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13

20

33

40

4.1 (7.3) 0 (0–21) 40

4.6 (7.9) 0 (0–21) 40

5.1 (7.9) 0 (0–21) 45

5.5 (8.0) 0.2 (0–21) 50

6.0 (8.4) 0.8 (0–21) 50

7.3 (8.7) 2.2 (0–21) 70

3.6 (6.8) 0 (0–21) 35

4.5 (7.3) 0 (0–21) 40

4.8 (7.5) 0 (0–21) 40

6.3 (8.7) 1.5 (0–21) 55

6.8 (9.0) 2.0 (0–21) 55

7.0 (9.0) 2.5 (0–21) 55

6.2 (7.0) 2.4 (0–21) 90

6.6 (7.0) 2.9 (0–21) 90

8.0 (7.2) 4.4 (0–21) 90

9.6 (7.4) 7.2 (0–21) 90

12.0 (8.0) 12.3 (0–21) 90

12.8 (7.9) 12.9 (0–21) 90

International Endodontic Journal, 39, 968–976, 2006

48

56

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22 Shemesh et al. Leakage of apical root fillings

Table 2 P values – statistical signifi-

cance of the difference in glucose concentrations between the groups at specific time intervals

Kruskal–Wallis test

Mann–Whitney test

Time after filling (days)

P (groups 1–3)

P (groups 1 and 2)

P (groups 1 and 3)

P (groups 2 and 3)

8 13 20 33 40 48 56

0.415 0.012 0.026 0.034 0.031 0.020 0.035

– 0.799 0.989 0.799 0.799 0.820 0.738

– 0.015 0.020 0.038 0.023 0.013 0.035

– 0.013 0.033 0.026 0.030 0.026 0.024

Table 3 Average fluid transportation and percentage of leak-

ing samples 1 and 8 weeks after obturation Average fluid transport in lL (percentage leaking samples) Group

1 week

8 weeks

GP/AH26 (smear layer present; n ¼ 20) GP/AH26 (smear layer removed; n ¼ 20) Resilon/Epiphany (smear layer removed; n ¼ 20)

0.5 (20)

0.2 (10)

0.1 (15)

0.05 (5)

0.0 (0)

0.0 (0)

Discussion Several test methods have been described to evaluate the sealing quality of filled root canals. In the present study, two different models were used: the fluid transport model (Wu et al. 1993) and the glucose penetration model (Xu et al. 2005). The latter can be seen as a further development of the fluid transportation concept: both measure passage of fluid along root filled teeth after subjecting them to constant pressure.

However, the glucose model allows measurements of diffusion of the marker molecules as well. The glucose test might be more sensitive than the measurement of air-bubble movement, not only because the detected threshold measurement by eye is higher than that of the spectrophotometer, but also because the convective fluid transport was combined with glucose molecule diffusion.

Time difference is an important factor when comparing the results from the two different models. In the glucose penetration model the tooth is continuously subjected to the pressure of the glucose solution in the coronal chamber for a period of 2 months. The fluid penetration model detects leakage after subjecting the filling to pressure for 3 h. This enormous time difference might result in detection of smaller voids in the

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filling, making the glucose test more sensitive. Furthermore, summated glucose leakage during 2 months was measured whereas fluid transportation was measured for 3 h and observed at two different time intervals, 1 and 8 weeks after filling.

Evaporation of fluids during the 56 days experiment duration could alter the glucose concentrations both in the apical and the coronal chambers. Evaporation will inevitably occur as these two compartments have to have an opening to release pressure build-up and cannot be closed hermetically in order to allow leakage to occur. Xu et al. (2005) refers only to evaporation from the apical chamber, compensating it with water according to a representative sample. The method used here, storing the models in a closed humid jar, addresses the evaporation factor from both chambers and proved to be effective in initial pilot studies.

The effect of the removal of smear layer before obturation has been the subject of extensive debate.

According to the current findings, the smear layer did not affect the seal with gutta-percha and AH 26 in the apical 4 mm, when checked with the fluid transport or the glucose penetration models. These results are in agreement with those of Saunders & Saunders (1994a) who found no significant difference in dye leakage after 4 months between root fillings when the smear layer was removed or present. Saunders & Saunders (1994b) assessed dye leakage of Thermafil fillings and laterally condensed gutta-percha with glass–ionomer sealer no significant difference was observed after 4 months between any of the groups. Madison & Krell (1984) and Evans & Simon (1986) also found no difference in leakage when the smear layer was removed or not.

Although dye-leakage results have debatable relevancy (Wu & Wesslink 1993) they were the most frequently used to assess the influence of smear layer. In contrast to these findings, Clark-Holke et al. (2003) checked a mixed culture of bacteria penetrating through root fillings. A total of 30 teeth were used, amongst which

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23 Leakage of apical root fillings Shemesh et al.

10 served as controls. During the 2-month observation period, leakage was not observed in the group where smear layer was removed, whilst 60% of the specimen having a smear layer leaked. In spite of the small number of specimen and the authors’ own claim that leakage could occur after the 2-month observation period, it was suggested that removing the smear layer decreased bacterial leakage. Similarly, Kennedy et al.

(1986) and Cergneux et al. (1987) observed that smear layer removal reduced dye leakage. These conflicting reports might be attributed to difference in the type of sealer and filling technique, the method of producing and removing the smear layer and different laboratory procedures to check the leakage (S¸ en et al. 1995). More recently, Paque´ et al. (2006) found no effect of the smear layer on dye penetration through root dentine, and suggested that tubular sclerosis rather than the smear layer that influences penetrability.

Resilon is a new root filling material that consists of a composite that may be bonded to the wall of the canal.

Results from the current experiment indicate that the apical 4 mm of Resilon–Epiphany root canal fillings allowed more glucose penetration than gutta-percha.

Shipper et al. (2004) detected more rapid bacterial leakage in gutta-percha and AH 26 fillings when compared with Resilon–Epiphany during a period of 31 days when the whole length of the root canal was filled with laterally or vertically compacted material. In the current experiment only the 4 apical mm of filling were checked. The dentinal tubules configuration which is less dense in the apical part than the coronal part (Fogel et al. 1988) might lead to compromised bonding apically. Tay et al. (2005a) observed in a transmission electron micrograph gaps of about 2 lm between the root dentine and the Resilon primer. These imperfections in the bonding might be too small to be detected by bacterial penetration models, as the average length of bacteria varies from 0.2 to more than 10 lm, the width from 0.2 to 1.5 lm (Hobot 2002).

The influence of the geometric variables involved in the use of adhesive sealers was previously discussed by Feilzer et al. (1993) and more recently by Tay et al.

(2005a). The latter study simulated different scenarios and appraised the C-factors that arise from thin resin films. In a Class I cavity, the bonded surface area is five times more than the unbonded surface area (C-factor is 5). As the unbonded surface area becomes smaller, as in a root canal, the C-factor becomes much higher, there is insufficient stress relief by flow and a high probability that one or more bonded areas will debond.

The probability of imperfect dentine bonding in a root

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International Endodontic Journal, 39, 968–976, 2006

canal during polymerization might exceed the bond strength, and a high volumetric shrinkage of the sealer might occur when it polymerizes. In cross-sections of filled roots, gaps were observed between the dentine and the Epiphany layer (Tay et al. 2005a). These imperfections in the bonding to the walls of the canal might be too small to be detected by bacterial penetration models.

The dimensional stability of Resilon should also be addressed. Preliminary unpublished studies have shown that Resilon cones discharged a coloured substance to the surrounding medium it, that may affect the measurements of optical density. As this colour (pink) is not absorbed at the same wavelength that is assessed by the glucose kit, the results were not compromised. However, every new material that is about to be checked with this method, should be assessed for its colour properties when it is immersed in fluid for an extended period. Gutta-percha and AH 26 on the other hand, did not show any colour discharge when soaked in water.

Tay et al. (2005b,c) discussed the susceptibility of Resilon to degradation in two different studies: in the first, 15 mm diameter Resilon and gutta-percha discs were immersed in sodium etoxide for 20 and 60 min.

The treated discs were then examined with a scanning electronic microscope and dispersive X-ray analysis. The surface of the Resilon discs was hydrolysed after 20 min exposing the filler, whilst gutta-percha discs were unaffected. The second experiment examined 15 mm diameter discs of Resilon, gutta-percha and polycaprolactone that were incubated with phosphate-buffered saline, Lipase PS or cholesterol esterase. Resilon and polycaprolactone discs had significant weight loss and surface thinning when compared with the gutta-percha discs. The influence of this phenomenon on glucose penetration may be greater in the current setting than in that of Shipper et al. (2004) because of the longer observation period. These results challenge the claims of the manufacturer (‘Epiphany Newsletter’, July 2005, Pentron Clinical Technologies) that the colour discharge from Resilon cones is only food grade dye ‘leaching out into the tooth’. However, it may provide an explanation for the increased leakage in the Resilon group.

Conclusions • The glucose penetration model is a sensitive method to detect leakage along root fillings.

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24 Shemesh et al. Leakage of apical root fillings

• Under the conditions of this study, no statistically significant difference in glucose penetration or fluid transportation was observed along the 4 mm apical root filling with gutta-percha and AH 26 whether or not the smear layer was removed prior to filling.

• Canals filled with Resilon had more glucose penetration than gutta-percha and AH 26 during a period of 56 days, whilst no statistically significant difference was observed between the Resilon and gutta-percha filled teeth in the fluid transportation model either at 1 or 8 weeks.

References Abarca AM, Bustos A, Navia M (2001) A comparison of apical sealing and extrusion between Thermafil and lateral condensation techniques. Journal of Endodontics 27, 670–2.

Cergneux M, Ciucchi B, Dietschi JM, Holz J (1987) The influence of the smear layer on the sealing ability of canal obturation. International Endodontic Journal 20, 228–32.

Chu CH, Lo EC, Cheung GS (2005) Outcome of root canal treatment using Thermafil and cold lateral condensation filling techniques. International Endodontic Journal 38, 179– 85.

Clark-Holke D, Drake D, Walton R, Rivera E, Guthmiller JM (2003) Bacterial penetration through canals of endodontically treated teeth in the presence or absence of the smear layer. Journal of Dentistry 31, 275–81.

C¸obankara FK, Adanr N, Belli S (2004) Evaluation of the influence of smear layer on the apical and coronal sealing ability of two sealers. Journal of Endodontics 30, 406–9.

Drake DR, Wiemann AH, Rivera EM, Walton RE (1994) Bacterial retention in canal walls in vitro: effect of smear layer. Journal of Endodontics 20, 78–82.

Evans JT, Simon JH (1986) Evaluation of the apical seal produced by injected thermoplasticized Gutta-percha in the absence of smear layer and root canal sealer. Journal of Endodontics 12, 100–7.

Fan B, Wu MK, Wesselink PR (1999) Coronal leakage along apical root fillings after immediate and delayed post space preparation. Endodontics and Dental Traumatology 15, 124–6.

Feilzer AJ, de Gee AJ, Davidson CL (1993) Setting stresses in composites for two different curing modes. Dental Materials 9, 2–5.

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Galvan DA, Ciarlone AE, Pashley DH, Kulild JC, Primack PD, Simpson MD (1994) Effect of smear layer removal on the diffusion permeability of human roots. Journal of Endodontics 20, 83–6.

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Gulabivala K, Patel B, Evans G, Ng YL (2005) Effects of mechanical and chemical procedures on root canal surfaces.

Endodontic Topics 10, 103–22.

Hobot JA (2002) Molecular Medical Microbiology. London, UK: Academic Press, p. 7.

Hu¨lsmann M, Heckendorff M, Lennon A (2003) Chelating agents in root canal treatment: mode of action and indications for their use. International Endodontic Journal 36, 810–30.

Kaffe L, Kaufman A, Littner MM, Lazarson A (1985) Radiographic study of the root canal system of mandibular anterior teeth. International Endodontic Journal 18, 253–9.

Kennedy WA, Walker WA Jr, Gough RW (1986) Smear layer removal effects on apical leakage. Journal of Endodontics 12, 21–7.

Khayat A, Lee SJ, Torabinejad M (1993) Human saliva penetration of coronally unsealed obturated root canals.

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Kokkas AB, Boutsioukis Ach, Vassiliadis LP, Stavrianos CK (2004) The influence of the smear layer on dentinal tubule penetration depth by three different root canal sealers: an in vitro study. Journal of Endodontics 30, 100–2.

Kuttler Y (1955) Microscopic investigation of root apexes.

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Love RM (1996) Adherence of Streptococcus gordonii to smeared and nonsmeared dentine. International Endodontic Journal 29, 108–12.

Madison S, Krell KV (1984) Comparison of ethylenediamine tetraacetic acid and sodium hypochlorite on the apical seal of endodontically treated teeth. Journal of Endodontics 10, 499–503.

Mannocci F, Innocenti M, Bertelli E, Ferrari M (1999) Dye leakage and SEM study of roots obturated with Thermafill and dentin bonding agent. Endodontics and Dental Traumatology 15, 60–4.

Paque´ F, Luder HU, Sener B, Zehnder M (2006) Tubular sclerosis rather than the smear layer impedes dye penetration into the dentine of endodontically instrumented root canals. International Endodontic Journal 39, 18–25.

Pashley DH, Michelich V, Kehl T (1981) Dentin permeability: effects of smear layer removal. Journal of Prosthetic Dentistry 46, 531–7.

Roane JB, Sabala CL (1985) The balanced force concept for instrumentation of curved canals. Journal of Endodontics 11, 203–11.

Saunders WP, Saunders EM (1994a) Coronal leakage as a cause of failure in root-canal therapy: a review. Endodontics and Dental Traumatology 10, 105–8.

Saunders WP, Saunders EM (1994b) Influence of smear layer on the coronal leakage of Thermafil and laterally condensed GP root fillings with a glass ionomer sealer. Journal of Endodontics 20, 155–8.

S¸ en BH, Wesselink PR, Tu¨rku¨n M (1995) The smear layer: a phenomenon in root canal therapy. International Endodontic Journal 28, 141–8.

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Shipper G, Ørstavik D, Teixeira FB, Trope M (2004) An evaluation of microbial leakage in roots filled with a thermoplastic synthetic polymer-based root canal filling material (Resilon). Journal of Endodontics 30, 342–7.

Sundqvist G, Figdor D, Persson S, Sjo¨gren U (1998) Microbiologic analysis of teeth with failed endodontic treatment and the outcome of conservative re-treatment. Oral surgery, Oral Medicine, Oral Pathology, Oral Radiology and Endodontics 85, 86–93.

Tay FR, Loushine RJ, Lambrechts P, Weller RN, Pashley DH (2005a) Geometric factors affecting dentin bonding in root canals: a theoretical modeling approach. Journal of Endodontics 31, 584–9.

Tay FR, Pashley DH, Williams MC et al. (2005b) Susceptibility of a polycaprolactone-based root canal filling material to degradation. I. Alkaline hydrolysis. Journal of Endodontics 31, 593–98.

Tay FR, Pashley DH, Yiu CK et al. (2005c) Susceptibility of a polycaprolactone-based root canal filling material to degradation. II. Gravimetric evaluation of enzymatic hydrolysis.

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Taylor JK, Jeansonne BG, Lemon RR (1997) Coronal leakage: effects of smear layer, obturation technique, and sealer.

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Teixeira FB, Teixeira EC, Thompson JY, Trope M (2004) Fracture resistance of roots endodontically treated with a new resin filling material. Journal of the American Dental Association 135, 646–52.

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Torabinejad M, Ung B, Kettering JD (1990) In vitro bacterial penetration of coronally unsealed endodontically treated teeth. Journal of Endodontics 16, 566–9.

Torabinejad M, Handysides R, Khademi AA, Bakland LK (2002) Clinical implications of the smear layer in endodontics: a review. Oral surgery, Oral Medicine, Oral Pathology, Oral Radiology and Endodontics 94, 658–66.

Wu MK & Wesselink PR (1993) Endodontic leakage studies reconsidered. Part I. Methodology, application and relevance. International Endodontic Journal 26, 37–43.

Wu MK, De Gee AJ, Wesselink PR, Moorer WR (1993) Fluid transport and bacterial penetration along root canal fillings.

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Wu MK, Tigos E, Wesselink PR (2002) An 18-month longitudinal study on a new silicon-based sealer, RSA RoekoSeal: a leakage study in vitro. Oral surgery, Oral Medicine, Oral Pathology, Oral Radiology and Endodontics 4, 499–502.

Wu MK, van der Sluis LW, Ardila CN, Wesselink PR (2003) Fluid movement along the coronal two-thirds of root fillings placed by three different GP techniques. International Endodontic Journal 36, 533–40.

Xu Q, Fan MW, Fan B, Cheung GS, Hu HL (2005) A new quantitative method using glucose for analysis of endodontic leakage. Oral surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontics 99, 107–11.

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26 doi:10.1111/j.1365-2591.2007.01302.x

Glucose penetration and fluid transport through coronal root structure and filled root canals

H. Shemesh, M. van den Bos, M.-K. Wu & P. R. Wesselink ACTA, Amsterdam, The Netherlands

Abstract Shemesh H, van den Bos M, Wu M-K, Wesselink PR. Glucose penetration and fluid transport through coronal root structure and filled root canals. International Endodontic Journal, 40, 866–872, 2007.

Aim To measure glucose penetration and fluid transport through coronal root structure and compare it with leakage along the coronal region of root fillings.

Methodology A total of 50 single-rooted teeth were selected and divided into three groups. Ten roots were sectioned longitudinally and the apical portion was removed leaving a total length of 9 mm. These 20 halfroots served as group 1: root structure (n ¼ 20). The canals of the remaining 40 roots were prepared to size 50 and filled with vertically compacted injectable filling material and sealer. Group 2: Resilon + Epiphany (n ¼ 20) and group 3: gutta-percha + AH26 (n ¼ 20). The apical portion of the root was removed.

Glucose penetration through the coronal root structure and coronal root fillings was checked over a period of

Introduction A variety of laboratory-based experimental models are used to detect and measure leakage along root fillings.

Whilst dye leakage, fluid transport and bacterial penetration were the most frequently used, other methods such as radio-labelled isotopes (Haikel et al.

1999), electromechanical tests (von Fraunhofer et al.

2000) and glucose penetration (Xu et al. 2005) have also been described. These models check penetration of

Correspondence: Hagay Shemesh, DMD Department of Cariology Endodontology Pedodontology, ACTA, Louwesweg 1, 1066 EA Amsterdam, The Netherlands (Tel.: +31 20 5188367; fax: +31 20 6692881; e-mail: hshemesh@acta.nl).

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4 weeks and fluid transport was measured after completion of the glucose penetration test. Differences between the groups were statistically analysed with the Kruskal–Wallis test and the Mann–Whitney test.

Results The three groups presented significantly different glucose penetration (P < 0.05). The two groups of filled canals showed significant glucose leakage whilst the root structure group did not show any leakage. In the fluid transport model, the root structure group also did not show any leakage. No significant difference in leakage existed between the two vertically compacted filling materials, Resilon with Epiphany sealer and gutta-percha with AH26 in both models (P > 0.05).

Conclusion Under the conditions of this study, in both models used, no leakage was observed through root structure. Filled canals were associated with penetration of glucose regardless of the material used.

Keywords: coronal microleakage, fluid transport model, glucose penetration model, root structure.

Received 1 March 2007; accepted 25 April 2007

different tracers through the root canal, assuming it travels along the canal and reaches the apical region.

The clinical relevancy of these studies has been debated. Pitt Ford (1983) showed no correlation between dye penetration through human teeth and periapical tissue response to four different filling materials in dogs. Oliver & Abbott (2001) reported dye penetration through root-filled teeth that had been clinically successful. Karagenc¸ et al. (2006) demonstrated a poor correlation between different leakage model results and concluded that their clinical relevancy was questionable. Pommel et al. (2001) claimed that filtration, diffusion or electrical phenomena governed the outcome of leakage studies in the corresponding models and thus raised doubt on the relevancy of these findings. The size of the tracer might

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27 Shemesh et al. Glucose penetration and fluid transport

also influence the results (Barthel et al. 1999) as well as the potential of the tracer to react or affect the filling material itself. Methylene blue, for example, frequently used in dye leakage studies, might react with different filling materials and calcium hydroxide, making the results from some of these tests unreliable (Wu et al.

1998). A different problem with leakage tests might be that different leakage tracers could penetrate through root dentine and not through the canal. This claim is supported by the findings that dentinal tubules are permeable to bacteria (Love et al. 1996, Perez et al.

1996), adhesive agents (Pashley et al. 1993), cements (C¸alt & Serper 1999, Weis et al. 2004), and fluids (Ozok et al. 2002). Furthermore, dentinal tubules are oriented perpendicular to the root canal walls (Ferrari et al.

2000) and the contact surface area may affect the seal provided by the filling material. As the smear layer is usually removed prior to obturation (Torabinejad et al.

2002), the tubules might be open and allow the tracer used in leakage studies to penetrate through them.

Previously performed leakage studies did not address this issue and used a negative control group of similar filled roots to those checked in the experimental groups, usually coated with nail varnish or sticky wax (Khayat et al. 1993, Taylor et al. 1997, Abarca et al. 2001).

These control groups prevent the tracer from penetrating the canal, but also the dentine itself. If, however, small molecules such as glucose or water can leak through root dentine, it would make results from such leakage studies questionable.

The purpose of this experiment is to compare leakage through root structure with leakage through the coronal part of root-filled canals using both the glucose penetration model and the fluid transport model.

Materials and methods Selection and preparation of teeth Seventy freshly extracted single-rooted teeth were selected and stored in water. Teeth with open apices or large carious lesions were excluded. The roots were randomly divided into two control groups and three experimental groups. The coronal portions of all teeth were removed so that each root specimen was 16 mm long.

Group 1 (n ¼ 20) Ten roots were cut vertically with a diamond-coated bur (H-327, Horico, Berlin, Germany), so 20 half-roots were formed (Fig. 1). The canal area was flattened with a diamond disc and the apical area was removed, leaving a total of 9 mm root structure. A 7-mm thick acrylic cylinder was prepared around the root, which left 1 mm root protruding from each side of the acrylic cylinder. The contact between the acrylic and the root was covered with methacrylate glue (Permacol, Ede, The Netherlands).

9 mm

(c) (a)

(e)

(d)

(b)

Figure 1 Preparation of the experimental groups. Root vertically sectioned (a) to result in two halves where the root canal was polished away (b); apical part removed and embedded in acrylic resin block to form group 1 specimens (c); root canal prepared and filled (d); apical part removed, prepared and embedded in acrylic resin block to from group 2, 3 specimens (e). Both the length of the root canal filling and the halved roots measured 9 mm.

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28 Glucose penetration and fluid transport Shemesh et al.

Preparation of root canals All samples were examined under a microscope (Zeiss Stemi SV6, Jena, Germany) to exclude cracks. A diamond bur (FG 173 Horico, Berlin, Germany) was used to gain straight-line access to the root canal. An ISO size 20 K-Flexofile (Dentsply Maillefer, Ballaigues, Switzerland) was inserted into the canal to verify patency. The coronal 7 mm of the root specimens was embedded in acrylic (Vertex, Dentimex BV, Zeist, The Netherlands) to form a cylinder around the root and enable intimate contact between the root and the rubber tube used to connect the specimen during the leakage phase of the study.

Instrumentation and filling of root canals All teeth were treated by the same operator. The working length was determined by subtracting 1 mm from the total length of the root (16 mm). The apical portion of the canal was instrumented to an ISO size 50 master file using the balanced force technique (Roane et al. 1985) with K-Flexofiles. Step-back flaring was performed at 1 mm increments with Gates Glidden burs numbers 2–6 (Dentsply Maillefer) making the taper 0.2 mm mm)1 (Wu et al. 2002). The purpose of this preparation was to create a uniform size of canal and to overcome variation in natural morphology. Each canal was irrigated with freshly prepared 2% sodium hypochlorite solution (NaOCL) with a 27-gauge needle after every instrument and ensuring patency by extrusion of the solution beyond the apical foramen. A minimum of 10 mL NaOCl solution was used for each root. After preparation, canals were ultrasonically irrigated for 20 s and rinsed with 2 mL of 2% NaOCl. This procedure was repeated thrice (van der Sluis et al. 2006). All canals were then rinsed with 5 mL 17% ethylenediamine tetraacetic acid (EDTA) for 3 min (Scelza et al.

2003) and with 5 mL de-ionized water. Each canal was dried with an ISO size 50 paper point and filled according to the relevant group.

canal with sealer and bring the cone to full working length.

The coronal part of the gutta-percha was removed with a heated System B plugger reaching the apical 5 mm and compacted with a pre-fitted hand plugger.

The coronal section was compacted vertically with gutta-percha using the Obtura II system leaving the coronal 2 mm of the canal empty.

Group 3 (n ¼ 20) Canals were filled with the Resilon–Epiphany system (Pentron Clinical Technologies, Wallingford, CT, USA).

A self-etching primer was placed into the canal with a 26-gauge needle. Two drops of primer were used for each root. Three paper points ISO size 50 were used to remove the excess primer after 1 min from each root.

Roots were filled with Resilon cones and Epiphany sealer with the continuous-wave technique using the System B device and compacted vertically with the Obtura II system. An ISO size 50 Resilon cone coated with Epiphany sealer was inserted into the canal. Light pumping motions were used to fill the canal with sealer and bring the cone to full working length. The coronal part of the filling was removed with a heated System B spreader extending to the apical 5 mm and compacted with a pre-fitted hand plugger. The coronal part was filled with Resilon using the Obtura system, leaving the coronal 2 mm of the canal empty.

Controls The Positive control group (n ¼ 10) consisted of canals that were filled using lateral compaction of guttapercha cones without sealer. No warm vertical forces were used and the whole length of the filling remained intact. The negative control group (n = 10) consisted of roots that were sealed with laterally compacted guttapercha and AH26 for the whole length of the canal and completely covered with nail varnish.

Storage and apical preparation Group 2 (n ¼ 20) Canals were filled with gutta-percha and AH26 (Dentsply Maillefer) using the continuous-wave technique with a System B device and Obtura II system (Obtura Corporation, Fenton, MO, USA). An ISO size 50 guttapercha cone coated with AH26 sealer was inserted into the canal. Light pumping motions were used to fill the

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The filled roots were stored for 1 week at 37 C and 100% humidity to allow the materials to set. The apical 2 mm of the roots were cut with a diamond bur (FG 109 Horico, Berlin, Germany) and 3 mm of the apical root fillings were removed mimicking apical surgery preparation, leaving a total of 9 mm root canal filling (Fig. 1).

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29 Shemesh et al. Glucose penetration and fluid transport

All samples were mounted on a glucose leakage model.

This model was first used by Xu et al. (2005) and was further developed and described in detail in other publications (Shemesh et al. 2006, van der Sluis et al.

2007). The acrylic resin block around the root was connected to a rubber tube with stainless steel wires, which were connected to a 16-cm long pipette (Pyrex, Acton, MA, USA). The assembly was placed in a sterile glass bottle with a screw cap and sealed with sticky wax. A uniform hole was drilled in the screw cap with a diamond bur (No.173 Horico, Berlin, Germany) to assure an open system at all times. Sterile water (2 mL) was injected into the glass bottle, such that the root samples were immersed in the solution. The tracer used in the present study was 1 mol L)1 glucose solution.

Glucose has a low molecular weight and is hydrophilic and chemically stable. About 4.5 mL of the glucose solution was injected into the pipette until the top of the solution was 14 cm higher than the top of the root canal filling, which created an hydrostatic pressure of 1.5 kPa or 15 cm H2O (Xu et al. 2005). All specimens were returned to the incubator at 37 C for the duration of the observation period. A total of 100 lL of the solution was drawn from the glass bottle using a micropipette every week for 4 weeks. The same amount of fresh de-ionized water was added to the glass bottle reservoir to maintain a constant volume of 2 mL. All assemblies were stored in a closed plastic container at 100% humidity to prevent evaporation.

The sample taken every week was analysed with a Glucose kit (Megazyme, Wicklow, Ireland) in a spectrophotometer (Molecular Devices, Spectra max 384 plus) at a wavelength of 340 nm. Concentrations of glucose in the lower chamber were presented in mg L)1 at each time interval. The lowest glucose level for which the current procedure is believed to be accurate is 0.6 mg L)1 which derives from an absorbance difference of 0.02 (d-Glucose HK assay procedure, Megazyme International Limited, 2004).

Below this level, the absorbance readings become relatively small, and results are subjected to greater error from technique variables. Concentrations smaller than this were thus ignored. Similarly, once the optical density reading exceeded 1.2 (corresponds to a glucose concentration of 79.6 mg L)1), samples were no longer observed as the glucose concentration in the lower chamber suggested substantial leakage had occurred.

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Fluid transport model After completion of the glucose penetration, test roots were mounted on a fluid transport model (Wu et al.

1993). Fluid transport was measured under a headspace pressure of 30 kPa (0.3 atm), and after 3 h the movement of an air bubble was recorded and expressed in microlitre.

Statistical analysis The differences between the groups with regard to glucose concentrations and fluid transport were analysed statistically with the Kruskal–Wallis and the Mann–Whitney tests (spss, version 12.0.1, Chicago, IL, USA). The level of significance was set at a ¼ 0.05.

Results The negative control group showed no leakage in either model throughout the experiment period. The positive control group leaked immediately. The results obtained from the experimental groups are summarized in Table 1.

The difference in glucose leakage between the three experimental groups was highly significant (P < 0.0001). Group 1 (root structure) had no leakage, whilst the two other groups (gutta-percha, Resilon) did leak (Fig. 2). Although more roots in the Resilon group showed glucose penetration, there was no statistical significance between them (P ¼ 0.174). In the fluid transport model, no samples leaked at the end of 4 weeks in the Resilon–Epiphany group, and one sample leaked (4 lL) in the gutta-percha group. No

Glucose concentration (mg L–1)

Model assembly and measurements: glucose penetration model

50 40

GP RESILON

30 20 10 0 1 week

Figure 2 Mean 1–4 weeks.

2 week 3 week Time

glucose

penetration

in

4 week

mg L)1

after

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30 Glucose penetration and fluid transport Shemesh et al.

Table 1 Mean glucose leakage in mg L)1 1 week GP and AH26 Mean 0.96 SD 1.23 Median 0.50 Range 0–4.97 % Leaking samples 0 Resilon–Epiphany Mean 8.75 SD 20.45 Median 0.13 Range 0–79.60 % Leaking samples 15 Root structure Mean 0.0 SD 0.0 % Leaking samples 0

2 week

3 week

4 week

3.14 5.58 9.05 4.61 12.22 20.73 1.62 1.13 1.23 0.20–19.30 0–41.46 0–79.60 15 20 20 12.69 24.78 2.88 0–79.60 40 0.0 0.0 0

16.04 16.85 27.76 27.67 4.97 5.67 0–79.60 0–79.60 50 50 0.0 0.0 0

0.0 0.0 0

statistical significance was observed between groups in the fluid transport model (P ¼ 0.368).

Discussion At the end of 4 weeks, both tracers penetrated all 10 roots of the positive control group and none of the negative control group. Root structure showed no penetration of any of the tracers. Overall, 14 of the 40 filled roots allowed glucose to pass through the canal and reach the apical portion.

Most studies in this field found fluid movement or tracer penetration through root-filled teeth regardless of the filling material or filling method used (Abarca et al. 2001, Wu et al. 2003). The current finding that root dentine did not allow fluid movement or glucose penetration is important when assessing the relevancy of such studies. It proves that the tracer passes through the canal and the measurements reflect the ability of the canal filling to prevent tracer penetration through it. Nevertheless, we cannot exclude the possibility that parts of the root dentine might be permeable to the tracer: only if the whole length of the checked root structure (9 mm long) could allow the tracer to pass through it, would we detect leakage at the apical side.

The possibility that certain parts of the root dentine might be permeable is of little concern to the present study, however, as it does not affect the detection of tracer at the other side of the root.

Advances in bonding techniques have led to the development of composite resin root filling materials such as Resilon. Early studies with Resilon have presented a decrease in the amount of bacterial penetration through root canals treated using Resilon

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International Endodontic Journal, 40, 866–872, 2007

when compared with gutta-percha (Shipper et al.

2004) and an increase in the fracture resistance of root-filled teeth (Teixeira et al. 2004). However, Most of the more recent studies comparing Resilon–Epiphany root fillings to more conventional gutta-percha techniques concluded that there is no apparent advantage of using Resilon–Epiphany over gutta-percha with different sealers (Biggs et al. 2006, Onay et al. 2006, Pitout et al. 2006, Sagsen et al. 2006, Baumgartner et al. 2007). Consistent with these reports, the current experiment indicates no statistically significant difference between the two different materials: Resilon with Epiphany sealer or gutta-percha with AH26 in terms of fluid movement and glucose penetration.

The apical portion of root fillings with Resilon or gutta-percha allow glucose penetration when checked with the glucose model (Shemesh et al. 2006). However, the coronal portion of the root canal is wider, more accessible, and it is assumed that the filling of this part of the canal is more efficient than the apical portion. In the case of Resilon, it could be hypothesized that the bond between the filling material and the conditioned canal walls may be stronger in the coronal portion. However, this has not been substantiated. For example, Wu et al. (2003) assessed the coronal twothirds of gutta-percha and RoekoSeal root fillings with the fluid transport model. Comparing their results to a previously published study (Wu et al. 2002) on the same materials and at similar conditions, the coronal portion allowed more fluid movement than the apical portion. In the current experiment, leakage along the coronal portion of the canal was assessed: Resilon allowed more glucose penetration than gutta-percha, but this difference was not statistically significant because of the small group size (n = 20). However, comparing previous reports on the sealing ability of the apical 4 mm of canal filling (Shemesh et al. 2006) to the current findings, Resilon performed better in the coronal part of the canal. This difference could be explained by methodological differences between the two experiments, and possibly by the different location of the filling along the canal. In the present study, the length of the root filling was significantly longer (9 mm as compared with 4 mm in the previous experiment) and the longer the root filling, the less leakage observed (Mattison et al. 1984).

There were differences between results in the two experimental models used. The glucose test may be more sensitive than the measurement of the fluid transport observations: measurements of fluid transportation are carried out by observing an air bubble

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31 Shemesh et al. Glucose penetration and fluid transport

and its movement along a capillary whilst the glucose concentration is determined by a highly sensitive enzymatic reaction measured by the spectrophotometer. Furthermore, the glucose concentration is measured continuously for a period of 4 weeks, whilst specimens in the fluid transport model are subjected to pressure for only 3 h.

Concerns have been raised over the possibility that different filling materials might react with the tracer used. A pilot study was conducted where all filling materials involved in the current experiment were immersed in a glucose solution for up to a month and glucose concentrations were checked periodically.

Resilon, Epiphany, gutta-percha and AH26 did not influence the concentration of glucose over time.

Conclusion Under the conditions of this study, in both models used, samples of coronal root structure did not show any leakage. Root canals filled with vertically compacted Resilon and Epiphany or gutta-percha and AH26 allowed penetration of glucose with no statistical difference between them. However, there was a trend for Resilon–Epiphany-filled roots to allow more penetration of glucose.

Acknowledgement This work was supported, in part, by the ESE research award 2006.

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Baumgartner G, Zehnder M, Paque F (2007) Enterococcus faecalis type strain leakage through root canals filled with gutta-percha/AH plus or Resilon/Epiphany. Journal of Endodontics 33, 45–7.

Biggs SG, Knowles KI, Ibarrola JL, Pashley DH (2006) An in vitro assessment of the sealing ability of resilon/epiphany using fluid filtration. Journal of Endodontics 32, 759–61.

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Scelza MF, Teixeira AM, Scelza P (2003) Decalcifying effect of EDTA-T, 10% citric acid, and 17% EDTA on root canal dentin. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontics 95, 234–6.

Shemesh H, Wu M-K, Wesselink PR (2006) Leakage along apical root fillings with and without smear layer using two different leakage models: a two month longitudinal ex vivo study. International Endodontic Journal 39, 968–76.

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Teixeira FB, Teixeira EC, Thompson JY, Trope M (2004) Fracture resistance of roots endodontically treated with a new resin filling material. Journal of the American Dental Association 135, 646–52. Erratum in: Journal of the American Dental Association 135, 868.

Torabinejad M, Handysides R, Khademi AA, Bakland LK (2002) Clinical implications of the smear layer in endodontics: a review. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontics 94, 658–66. van der Sluis LWM, Gambarini G, Wu M-K, Wesselink PR (2006) The influence of volume, type of irrigant and flushing method on removing artificially placed dentine debris from the apical root canal during passive ultrasonic irrigation. International Endodontic Journal 39, 472–6.

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van der Sluis LWM, Shemesh H, Wu M-K, Wesselink PR (2007) An evaluation of the influence of passive ultrasonic irrigation on the seal of root canal fillings. International Endodontic Journal 40, 356–61. von Fraunhofer JA, Fagundes DK, McDonald NJ, Dumsha TC (2000) The effect of root canal preparation on microleakage within endodontically treated teeth: an in vitro study.

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Weis MV, Parashos P, Messer HH (2004) Effect of obturation technique on sealer cement thickness and dentinal tubule penetration. International Endodontic Journal 37, 653–63.

Wu M-K, De Gee AJ, Wesselink PR, Moorer WR (1993) Fluid transport and bacterial penetration along root canal fillings.

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Wu M-K, Kontakiotis EG, Wesselink PR (1998) Decoloration of 1% methylene blue solution in contact with dental filling materials. Journal of Dentistry 26, 585–9.

Wu M-K, Tigos E, Wesselink PR (2002) An 18-month longitudinal study on a new silicon-based sealer, RSA RoekoSeal: a leakage study in vitro. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontics 4, 499–502.

Wu M-K, van der Sluis LW, Ardila CN, Wesselink PR (2003) Fluid movement along the coronal two-thirds of root fillings placed by three different gutta-percha techniques. International Endodontic Journal 36, 533–40.

Xu Q, Fan MW, Fan B, Cheung GS, Hu HL (2005) A new quantitative method using glucose for analysis of endodontic leakage. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontics 99, 107–11.

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33 doi:10.1111/j.1365-2591.2006.01227.x

An evaluation of the influence of passive ultrasonic irrigation on the seal of root canal fillings

L. W. M. van der Sluis, H. Shemesh, M. K. Wu & P. R. Wesselink Department of Cariology Endodontology Pedodontology, Academic Centre for Dentistry Amsterdam (ACTA), Amsterdam, The Netherlands

Abstract van der Sluis LWM, Shemesh H, Wu MK, Wesselink PR. An evaluation of the influence of passive ultrasonic irrigation on the seal of root canal fillings. International Endodontic Journal, 40, 356–361, 2007.

Aim To evaluate the influence of passive ultrasonic irrigation (PUI) on the seal of root canal fillings.

Methodology A total of 40 mandibular premolars were distributed equally into two groups and the root canals were cleaned and shaped; they were then filled with gutta-percha and AH26 (sealer) using the warm vertical compaction technique with the System B (Analytic Technology, Redmond, WA, USA) device. In one group PUI was applied, after completion of instrumentation and hand-irrigation. In the other group, PUI was not applied. Thereafter, leakage of glucose was

Introduction During passive ultrasonic irrigation (PUI) a small ultrasonically oscillating file or smooth wire (e.g. size 15) is placed in the centre of the root canal following canal shaping (Ahmad et al. 1987). Because the root canal has been enlarged, the irrigant can flow in the root canal and the file or wire can vibrate relatively freely, which will result in more powerful acoustic streaming (Ahmad et al. 1987). PUI with sodium hypochlorite (NaOCl) as the irrigant, removes more dentine debris, planktonic bacteria and pulp tissue from the root canal than the syringe irrigation (Huque et al.

1998, Lee et al. 2004, Gutarts et al. 2005). During PUI,

Correspondence: L.W.M. van der Sluis, Department of Cariology Endodontology Pedodontology, ACTA, Louwesweg 1, 1066 EA Amsterdam, The Netherlands (Tel.: +31 20 5188651; fax: +31 20 6692881; e-mail: l.vd.sluis@acta.nl).

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evaluated by measuring its concentration once a week for a total period of 56 days using a glucose penetration model. Differences between the groups in terms of glucose concentrations were statistically analysed with the Mann–Whitney test; the level of significance was set at P ¼ 0.05.

Results After the first month the root fillings in teeth where PUI had been used, sealed the root canal significantly better than in teeth where no PUI had been used (P ¼ 0.017).

Conclusion Root fillings sealed the root canal better when PUI had been used.

Keywords: irrigation, passive, root fillings, sealing, ultrasonic.

Received 21 August 2006; accepted 18 October 2006

more dentine debris can be removed from the isthmus, oval extensions in the root canal and irregularities from the root canal wall (Goodman et al. 1985, Lee et al.

2004).

It is generally accepted that relatively few dentists use PUI. Remaining dentine debris, which cannot be removed during hand-irrigation, will be packed into oval extensions and irregularities of the root canal (Wu & Wesselink 2001). If oval extensions are filled with dentine debris, the filling material cannot adapt to the canal wall and leakage may ensue (Wu & Wesselink 2001, van der Sluis et al. 2005a) because the filling material and sealer are not compacted against a clean root canal wall but against dentine debris particles, no matter which root filling technique or materials are used.

It is unclear whether root fillings, placed after PUI, seal the root canal better because more dentine debris is removed from the root canal. In the study of Wu et al.

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34 van der Sluis et al. Seal of root fillings after passive ultrasonic irrigation

(2001), the quality of root fillings in oval canals was evaluated using the percentage of gutta-percha (PGP) in the root canal. The mean PGP was 86.6% varying from 47.1–100%. Many oval extensions were not prepared and became filled with dentine debris. PUI was not used for irrigation of the root canals. In another study, where a similar methodology was used, but with PUI, the mean PGP was 98.9% and varied from 94.5–100%. This indicated that PUI removed effectively dentine debris from the oval extensions and thus allowed the gutta-percha to fill more completely the root canal (Ardila et al. 2003).

Healing following root canal treatment is assured through effective infection control (Sjo¨gren et al.

1990). However, it is not clear whether a better sealing root filling leads to less periapical inflammation.

Yamauchi et al. (2006) demonstrated, in an animal experiment, that less periapical inflammation occurred when root fillings were protected against coronal leakage by application of an additional coronal plug of filling material. Because an additional coronal plug leads to less coronal leakage (Chailertvanitkul et al.

1997), these data indicate that less coronal leakage leads to less periapical inflammation.

Different leakage models were used to detect and measure leakage along root fillings (Wu & Wesselink 1993). Leakage tests are improving and recently Xu et al. (2005) reported a new model that measures the leakage of glucose molecules. This model consists of a tube where a concentrated glucose solution is placed and connected to the test element, whilst the apical side of the specimen is dipped in water. Glucose, which leaks through the root canal accumulates in the apical chamber and is measured using an enzymatic reaction with a spectrophotometer. Glucose has a low molecular weight, and may be used as an indication for toxins that might penetrate the canal.

The aim of this study was to evaluate the influence of PUI on the seal of root fillings.

Materials and methods Digital radiographs from bucco-lingual and mesialdistal directions were made of extracted mandibular premolars that had been stored in water with added NaOCl for not more than 1 month. A total of 40 teeth with a single canal that had a long, oval shape at 5 mm coronal to the working length (WL), where the buccolingual diameter was more than twice as large as the mesio-distal diameter, were selected. The curvature of the roots was measured following Schneider’s

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methodology (Schneider 1971). The 40 specimens were divided equally in two anatomically comparable groups taking into account the curvature and the oval shape of the root canals. Two teeth were used as negative controls (the roots were completely covered with nail varnish) and two as positive controls (canals were filled using lateral compaction of Gutta-percha cones without sealer).

The teeth were decoronated and all roots were reduced to a length of 12 mm. WL was determined by inserting a size 15 K-file into the canal until the tip of the file was just visible at the apical foramen. The canals were accessed and prepared to the apical foramen. The coronal aspect of each canal was flared using Gates Glidden drills (Dentsply Maillefer, Ballaigues, Switzerland) sizes 2–4. All the root canals were prepared with the GT rotary system (Dentsply Maillefer) in a crown-down sequence using a series of size 20 and 30, 0.10–0.04 taper. Between the instruments, each canal was irrigated with 2 mL of a 2% NaOCl solution, freshly prepared each day, using a syringe and a 27-gauge needle that was placed 1 mm short of the WL. The NaOCl solution was prepared by diluting a 10% NaOCl solution (Merck, Darmstadt, Germany) and its pH adjusted to 10.8 with 1 N HCl. The concentration of the NaOCl solution was measured iodometrically (Moorer & Wesselink 1982). The final file [master apical file (MAF)] for each root canal at the foramen was size 30, 0.06 taper. After preparation of the root canal, PUI was performed in group 1 (n ¼ 18) with a piezoelectronic unit (PMax:Satelec, Meriganc Cedex, France). After the root canal was filled with 2% NaOCl, using a syringe and a needle, an ultrasonically activated smooth wire of stainless steel size 15, taper 0.02 was inserted in the root canal 1 mm short of WL (van der Sluis et al. 2005b). The irrigant was ultrasonically activated for 1 min. The root canal was then rinsed with 2 mL of 2% NaOCl, using a syringe and a 27-gauge needle that was placed 1 mm short of WL, and the irrigant was again activated ultrasonically for 1 min.

This sequence was repeated thrice resulting in a total irrigation time of 3 min and a total irrigation volume of 6 mL. The oscillation was performed in bucco-lingual direction at power setting ‘blue’ three. According to the manufacturer, the frequency used under these conditions was approximately 30 kHz and the displacement amplitude was 28 lm. The teeth in group two (n ¼ 18) were irrigated with 6 mL of 2% NaOCl by syringe irrigation in place of PUI for the same time period.

After irrigation, the canals were dried and filled with a warm vertical compaction technique. AH26 silverfree root canal sealer (De Trey Dentsply, Konstanz,

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35 Seal of root fillings after passive ultrasonic irrigation van der Sluis et al.

Germany) was mixed manually according to the recommendations of the manufacturer. The sealer was placed in the root canals using an EZ-Fill bi-directional spiral (EDS, Hackensack, NJ, USA), 1 mm short of WL in a pumping motion for 5 s. The complete spiral was coated with sealer. Before the filling procedure the tip of a medium sized non-standardized gutta-percha cone (Autofit, Analytic Endodontics, Glendora, CA, USA) was trimmed until tug-back was achieved 0.5 mm short of the full WL. The trimmed gutta-percha cone, lightly coated with sealer, was placed into the canal 0.5 mm short of the WL. At the level of the cementum–enamel junction the guttapercha was seared off with the tip of an activated heat carrier at 260 (System B, Analytic Technology, Redmond, WA, USA) by placing it in the coronal section of the root canal. After deactivating the heat carrier, the cooled instrument was removed from the canal, bringing out an increment of gutta-percha.

Vertical force was then applied with a cold size 11 handplugger (1.1 mm diameter, Dentsply Maillefer) to compact the gutta-percha in the coronal section of the canal. During the application of the plugger care was taken not to contact the canal wall. This procedure was repeated twice, first to a level 3–4 mm deeper than the cementum–enamel junction, vertically compacting the gutta-percha in the middle section of the canal using a cold size 7 plugger (0.7 mm diameter, Dentsply Maillefer), and secondly to the level 4 mm short of the full WL, vertically compacting the gutta-percha in the apical section of the canal using a cold size 5 plugger (0.5 mm diameter, Dentsply Maillefer). After the apical section the middle and the coronal section were filled using the same technique. During the filling procedure two roots of each group were fractured and discarded.

The remaining teeth were stored in a moist sponge at 37 C for 1 year.

Glucose penetration model – preparation and measurements All samples were examined under a microscope (Zeiss Stemi SV6, Jena, Germany) to exclude those with cracks. The coronal 4 mm of the root specimens were then embedded in Acryl (Vertex, Dentimex BV, Zeist, The Netherlands) to form an acrylic cylinder around the root and enable leak-free contact between the rubber tube and root specimen.

The difference between the current version of the glucose penetration model and the original model introduced by Xu et al. (2005) lies mainly in the

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environment where the models were stored: in order to prevent evaporation of fluids, the models were placed in a closed jar with 100% humidity. From a pilot study it was concluded that this method would eliminate the effect of fluid evaporation on glucose concentration measurements.

The resin block around the coronal part of each root was connected to a rubber tube and the adaptation improved with stainless steel wires. The other end of the tube was similarly connected to a 16-cm long pipette. The assembly was then placed in a sterile glass bottle with a screw cap and sealed with sticky wax, and a uniform hole drilled in the screw cap with a size 173 diamond bur (Horico, Berlin, Germany) to assure an open system at all times. Two mL of a 0.2% NaN3 solution was added into the glass bottle, such that the root samples were immersed in the solution. NaN3 was used to inhibit the growth of microorganisms that might influence the glucose readings. The tracer used in the present study was 1 mol L)1 glucose solution (pH ¼ 7.0). Glucose has a low molecular weight and is hydrophilic and chemically stable. About 4.5 mL of the glucose solution, containing 0.2% NaN3, was injected into the pipette until the top of the solution was 14 cm higher than the top of gutta-percha in the canal, which created a hydrostatic pressure of 1.5 kPa or 15 cm H2O (Xu et al. 2005)(Fig. 1). All specimens were then returned to the incubator at 37 C for the duration of the observation period. A 25 lL increment of solution was drawn from the glass bottle using a micropipette at 5, 14, 21, 37, 48 and 56 days. The same amount of fresh 0.2% NaN3 was added to the glass bottle reservoir to maintain a constant volume of 2 mL. The sample was then analysed with a Glucose kit (Megazyme, Wicklow, Ireland) in a spectrophotometer (Molecular Devices, Spectra max 384 plus, Seattle, Wa, USA) at 340 nm wavelength. Concentrations of glucose in the lower chamber were presented in mg L)1 at that particular time after obturation. The lowest glucose level for which the current procedure is believed to be accurate is 0.663 mg L)1 which derives from an absorbance difference of 0.020 (d-Glucose – HK assay procedure, Megazyme International Limited, 2004).

Below this level, the absorbance readings become relatively small, and results are subject to greater error from technique variables. Concentrations smaller than this were thus ignored. Similarly, once leakage exceeded 1.28 g L)1, samples were no longer tested as the glucose concentration in the lower chamber at this stage was very high and significant leakage had occurred.

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36 van der Sluis et al. Seal of root fillings after passive ultrasonic irrigation

Discussion

Glucose solution

Glass tube

Open system 14 cm

Rubber tube Acrylic cylinder Metal wire Root specimen 0.2% NaN3 solution

Figure 1 The glucose penetration model.

The positive control group (n ¼ 2) was filled using lateral compaction of gutta-percha cones without any sealer. No warm vertical forces were used.

In the negative control group (n ¼ 2) all roots were filled with laterally compacted gutta-percha and AH 26 and completely covered with nail varnish.

The data were statistically analysed with the Mann– Whitney test and P was set at 0.05.

Results The results are shown in Table 1 and 2 and Fig. 2.

After the first month, the root fillings in teeth where PUI had been used, sealed the root canal significantly better than in teeth where PUI had been not used (P ¼ 0.017).

The root fillings placed after PUI allowed significantly less leakage of glucose, which indicates it resulted in a better sealing of the root canal. This can be explained by the fact that more dentine debris can be removed from the oval extensions or irregularities (Lee et al.

2004) and/or more smear layer can be removed from the canal wall using PUI (Cameron 1983, 1987, Alac¸am 1987, Cheung & Stock 1993, Huque et al.

1998). When oval extensions or irregularities of the root canal wall are free of dentine debris they can be filled, which is likely to result in a better seal of the root filling with probability of reduced or no coronal leakage.

Shaping of the root canal in combination with irrigation is more efficient in cleaning the canal than shaping alone (Baugh & Wallace 2005). The present study indicates, that efficient irrigation can also result in significant improvement of the sealing of a root filling. This would suggest that efficient irrigation could decrease coronal leakage of the root fillings and thus reduce the nutrition for the biofilm in the root canal with the potential to reduce the occurrence and severity of apical periodontitis (Yamauchi et al.

2006).

Glucose as a marker in leakage studies has clinical relevance because it is an important nutrient for microorganisms and even at very low concentrations a biofilm is able to survive (Siqueira 2001). Because it is impossible to remove completely the biofilm from the root canal (Ricucci & Bergenholtz 2003, Naı¨r et al.

2005) leakage of very small amounts of glucose could help the biofilm survive or promote its re-growth when left in the root canal after preparation (Siqueira 2001).

In this study, during PUI, 2% NaOCl was placed in the root canal using a syringe in place of a continuous flow. During 3 min of PUI, the 2% solution NaOCl was refreshed every minute using further 2 mL volumes of 2% NaOCl. The results of a previous study showed no significant difference between this method of administration and a continuous flow of irrigant when PUI was used for 3 min (van der Sluis et al. 2006).

Table 1 Mean ± SD of glucose leakage in g L1 at different times Days Use PUI

5

14

21

37

48

57

No (n ¼ 18) Yes (n ¼ 18)

0.19 ± 0.34 0.05 ± 0.08

0.27 ± 0.37 0.14 ± 0.21

0.35 ± 0.48 0.20 ± 0.31

0.61 ± 0.46 0.30 ± 0.42

0.69 ± 0.46 0.40 ± 0.47

0.86 ± 0.37 0.53 ± 0.40

PUI, passive ultrasonic irrigation.

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37 Seal of root fillings after passive ultrasonic irrigation van der Sluis et al.

Table 2 The P-values of statistic analysis after comparing

leakage with and without passive ultrasonic irrigation at the different time intervals Time (days)

P

5 14 21 37 48 57

0.440 0.274 0.970 0.017 0.045 0.014

without PUI with PUI Mean leakage 1.00 0.80 0.60 0.40 0.20 0.00

Day 5

Day 14

Day 21

Day 37

Day 48

Day 57

Figure 2 The mean leakage of glucose over time.

The standard deviation of the leakage results of both groups were large. This may have resulted because of the variation in the oval dimensions of the root canals.

Although the MAF was standardized in all the teeth, the root canal dimension was not standardized; rather the specimens were distributed equally. Another explanation for the large standard deviations in the PUI group can be explained because it is difficult to standardize the positioning of the ultrasonically activated instrument in the centre of the root canal and to standardize the displacement amplitude as any constraint on the wire in the canal will change the amplitude. This will have a direct effect on the efficacy of PUI. This could be overcome by increasing the frequency of the ultrasound, which will reduce the influence of a variation in the displacement amplitude.

In the present study, the modified glucose penetration model was used (Xu et al. 2005, Shemesh et al.

2006). This test can be seen as a further development of the fluid transportation concept (Wu & Wesselink 1993). Both measure penetration of fluid through root fillings after subjecting them to constant pressure; however, the glucose model allows measurements of diffusion of the marker molecules as well. The glucose test might be more sensitive than the measurement of air-bubble movement, not only because the threshold

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International Endodontic Journal, 40, 356–361, 2007

measurement detected by the eye is larger than that of the spectrophotometer, but also because the convective fluid transport was combined with glucose molecule diffusion.

Time difference is an important factor when comparing the two different models. In the glucose penetration model the tooth is continuously subjected to the pressure of the glucose solution in the coronal chamber for a period of 2 months. The fluid penetration model detects leakage usually after subjecting the filling to pressure for 3 h (Shemesh et al. 2006). This enormous time difference might make the glucose test more sensitive, as it may result in detection of smaller voids in the filling.

Some authors claim that PUI removes the smear layer completely (Cameron 1983, 1987, Alac¸am 1987, Huque et al. 1998) or partially from the root canal wall (Cheung & Stock 1993), whereas syringe irrigation of NaOCl does not remove the smear layer from the root canal wall (Cheung & Stock 1993, Huque et al. 1998).

The improved sealing of the root canal filling could also be due to the removal of the smear layer by PUI. However, the reports in the literature on this subject are inconclusive (Sen et al. 1995, Torabinejad et al. 2002).

Leakage along root fillings may increase or decrease with the time following filling. Dissolution of sealer and the smear layer may result in a rise in leakage, whereas swelling of GP may result in diminished leakage (Sen et al. 1995, Kontakiotis et al. 1997). The leakage data measured some time after filling the root canals may be clinically more relevant.

Conclusion Root fillings sealed the root canal better when PUI had been used.

References Ahmad M, Pitt Ford TR, Crum LA (1987) Ultrasonic debridement of root canals: acoustic streaming and its possible role.

Journal of Endodontics 14, 490–9.

Alac¸am T (1987) Scanning electron microscope study comparing the efficacy of endodontic irrigating systems. International Endodontic Journal 20, 287–94.

Ardila CN, Wu MK, Wesselink PR (2003) Percentage of filled canal area in mandibular molars after conventional rootcanal instrumentation and after a noninstrumentation technique (NIT). International Endodontic Journal 34, 591–8.

Baugh D, Wallace J (2005) The role of apical instrumentation in root canal treatment: a review of the literature. Journal of Endodontics 31, 333–40.

ª 2007 International Endodontic Journal

38 van der Sluis et al. Seal of root fillings after passive ultrasonic irrigation

Cameron JA (1983) The use of ultrasonics in the removal of the smear layer: a scanning electron microscope study.

Journal of Endodontics 9, 292–8.

Cameron JA (1987) The synergistic relationship between ultrasound and sodium hypochlorite: a scanning electron microscope evaluation. Journal of Endodontics 13, 541–5.

Chailertvanitkul P, Saunders WP, Saunders EM, MacKenzie D (1997) An evaluation of microbial coronal leakage in the restored pulp chamber of root-canal treated multirooted teeth. International Endodontic Journal 30, 318–22.

Cheung GSP, Stock CJR (1993) In vitro cleaning ability of root canal irrigant with and without endosonics. International Endodontic Journal 26, 334–43.

Goodman A, Reader A, Beck M, Melfi R, Meyers W (1985) An in vitro comparison of the efficacy of the step-back technique versus a step-back/ultrasonic technique in human mandibular molars. Journal of Endodontics 11, 249–56.

Gutarts R, Nusstein J, Reader A, Beck M (2005) In vivo debridement efficacy of ultrasonic irrigation following handrotary instrumentation in human mandibular molars.

Journal of Endodontics 31, 166–70.

Huque J, Kota K, Yamaga M, Iwaku M, Hoshino E (1998) Bacterial eradication from root dentine by ultrasonic irrigation with sodium hypochlorite. International Endodontic Journal 31, 242–50.

Kontakiotis EG, Wu M-K, Wesselink PR. (1997) Effect of sealer thickness on long-term sealing ability: a 2-year follow-up study. International Endodontic Journal 30, 307–12.

Lee S-J, Wu M-K, Wesselink PR (2004) The effectiveness of syringe irrigation and ultrasonics to remove debris from simulated irregularities within prepared root canal walls.

International Endodontic Journal 37, 672–8.

Moorer WR, Wesselink PR (1982) Factors promoting the tissue dissolving capability of sodium hypochlorite. International Endodontic Journal 15, 187–96.

Naı¨r PNR, Henry S, Cano V, Vera J (2005) Microbial status of apical root canal system of human mandibular first molars with primary apical periodontitis after ‘one visit’ endodontic treatment. Oral Surgery, Oral Medicine Oral Pathology, Oral Radiology and Endodontics 99, 231–52.

Ricucci D, Bergenholtz G (2003) Bacterial status in root-filled teeth exposed to the oral environment by loss of restoration and fracture or caries – a histobacteriological study of treated cases. International Endodontic Journal 36, 787–97.

Schneider SW (1971) A comparison of canal preparations in straight and curved root canals. Journal of Oral Surgery 32, 271–5.

ª 2007 International Endodontic Journal

Sen BH, Wesselink PR, Tu¨rku¨n M. (1995) The smear layer: a phenomenon in root canal therapy. International Endodontic Journal 28, 141–8.

Shemesh H, Wu MK, Wesselink PR (2006) Leakage along apical root fillings with and without smear layer using two different leakage models: a two month longitudinal ex vivo study. International Endodontic Journal 39, 968–76.

Siqueira JF (2001) Aetiology of root canal treatment failure: why well-treated teeth can fail. International Endodontic Journal 34, 1–10.

Sjo¨gren U, Ha¨gblund B, Sundqvist G, Wing K (1990) Factors effecting the long-term results on endodontic treatment.

Journal of Endodontics 16, 498–504. van der Sluis LWM, Wu MK, Wesselink PR (2005a) An evaluation of the quality of root fillings in mandibular incisors and maxillary and mandibular canines using different methodologies. Journal of Dentistry 33, 683–8. van der Sluis LWM, Wu MK, Wesselink PR (2005b) A comparison between a smooth wire and a K-file in removing artificially placed dentine debris from root canals in resin blocks during ultrasonic irrigation. International Endodontic Journal 38, 593–6. van der Sluis LWM, Gambarini G, Wu MK, Wesselink PR (2006) The influence of volume, type of irrigant and flushing method on removing artificially placed dentine debris from the apical root canal during passive ultrasonic irrigation. International Endodontic Journal 39, 472–6.

Torabinejad M, Handysides R, Khademi AA, Bakland LK (2002) Clinical implications of the smear layer in endodontics: a review. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology and Endodontics 94, 658–66.

Wu MK, Wesselink PR (1993) Endodontic leakage studies reconsidered. Part: 1. Methodology, application and relevance. International Endodontic Journal 26, 37–43.

Wu MK, Wesselink PR (2001) A primary observation on the preparation and obturation of oval canals. International Endodontic Journal 34, 137–41.

Wu MK, de Schwartz FBC, van der Sluis LWM, Wesselink PR (2001) The quality of root fillings in mandibular incisors after root-end cavity preparation. International Endodontic Journal 34, 613–9.

Xu Q, Fan MW, Fan B, Cheung GS, Hu HL (2005) A new quantitative method using glucose for analysis of endodontic leakage. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology and Endodontics 99, 107–11.

Yamauchi S, Shipper G, Buttke T, Yamauchi M, Trope M (2006) Effect of orifice plugs on periapical inflammation in dogs. Journal of Endodontics 32, 524–6.

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39

Comparability of results from two leakage models Erick Miranda Souza, MSc,a Min-Kai Wu, MD, MSD, PhD,b Hagay Shemesh, DMD,c Idomeo Bonetti-Filho, PhD,d and Paul R. Wesselink, DDS, PhD,e São Paulo, Brazil and Amsterdam, The Netherlands SÃO PAULO STATE UNIVERSITY AND ACADEMIC CENTRE FOR DENTISTRY AMSTERDAM

Objective. The goal of this study was to check whether leakage results of the same specimens measured by 2 different leakage models are similar.

Study design. Canine root canals were prepared and filled with cold gutta-percha cones and 1 of 4 sealers (20 canals for each sealer). The 80 specimens were first connected to a fluid transport model where air-bubble movement was measured. The same specimens were later connected to a glucose penetration model where the concentration of glucose was measured. In both models, a headspace pressure of 30 kPa was used to accelerate leakage.

Results. In both models, 4 sealers ranked the same regarding the leakage they allowed, and a significant correlation between the results of the 2 models was confined (Spearman test coefficient ⫽ 0.65; P ⫽ .000001).

Conclusion. Under the conditions of this study, leakage results of 80 specimens recorded in the fluid transport model and glucose penetration model were similar. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2008;106:309-13)

To achieve periapical healing, root fillings should prevent coronal reinfection and entomb remaining bacteria.1 In a study by Felippe et al.,2 roots of dogs’ teeth and periapical tissues were examined histologically 5 months after different endodontic treatments. Prepared but unfilled canals were associated with severe chronic periapical inflammatory reaction and severe bone and root resorption.

Defective root fillings, which provide pathways for bacteria and toxins to the periapex, are not always identified with 2-dimensional radiographs. A recent treatment outcome study reported reduced success rates when the root filling contained radiographically detectable voids (poor root filling density or dark lines along the filling).3 Therefore, root fillings should present as few voids as possible, and, once present, voids should be as narrow as possible.

Erick Miranda Souza was supported by MEC/CAPES (Foundation for the Coordination of Higher Education and Graduate Training) with an exchange Scholarship. Study conducted at Academic Centre for Dentistry Amsterdam, The Netherlands. a PhD student, Department of Restorative Dentistry, Araraquara Dental School, São Paulo State University. b Senior Scientist, Department of Cariology, Endodontology, and Pedodontology, Academic Centre for Dentistry Amsterdam. c Lecturer, Department of Cariology, Endodontology, and Pedodontology, Academic Centre for Dentistry Amsterdam. d Assistant Professor, Department of Restorative Dentistry, Araraquara Dental School, São Paulo State University. e Professor and Chairman, Department of Cariology, Endodontology, and Pedodontology, Academic Centre for Dentistry Amsterdam.

Received for publication Jan 22, 2008; returned for revision Feb 17, 2008; accepted for publication Feb 19, 2008.

1079-2104/$ - see front matter © 2008 Mosby, Inc. All rights reserved. doi:10.1016/j.tripleo.2008.02.025

Different leakage models, including fluid transport4 and glucose penetration,5 have been used in vitro to determine the presence of voids along the root filling.

Because new materials are continuously developing, so is the need for assessing their sealing ability. Results of different in vitro leakage tests are used to rank various materials. However, it has rarely been studied whether the results of the same specimens recorded in different leakage models are similar.

The purpose of the present study was to investigate the comparability of leakage results of the same specimens recorded in the fluid transport model and glucose penetration model.

MATERALS AND METHODS One hundred recently extracted maxillary and mandibular canines were selected, and proximal radiographs were taken to confirm the presence of a single canal. The coronal parts were removed, leaving roots 15 mm in length.

Instrumentation Canals were prepared with K-files #15 to #50 (Dentsply Maillefer, Ballaigues, Switzerland) to 1 mm short of the apical foramen. This enlargement was chosen following the recommendations of Tronstad.6 A step-back flaring technique was performed at 2-mm increments with Gates-Glidden burs #2 to #6. File #50 was used to smooth the irregularities left by this flaring regimen. Canals were rinsed between each instrument with 2 mL 2% NaOCl solution. One minute of passive ultrasonic irrigation was performed using a #15 Endosonore file (Dentsply Maillefer).7 Because the apical 309

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Fig. 1. Schematic illustration of 2 models. A, Fluid transport. B, Glucose penetration.

diameter of canines could be larger than 0.2 mm,8 a K-file #30 was used to verify patency and assure that the apical foramen was not smaller than #30. Canals were rinsed with NaOCl and dried using paper points.

Roots were randomly divided into 4 experimental groups (20 each) according to the sealers tested—AH26 (Dentsply Detrey, Konstanz, Germany), AH Plus (Dentsply Detrey), RSA (Roeko Dental Products, Langenau, Germany), an experimental castor oil polymer (Polifil; Poliquil Araraquara Polímeros Químicos, Araraquara, Brazil)—and 2 control groups (10 each).

Obturation Polifil is commercially available and consists of a paste (polyester), liquid (biphenyl methane isocyanine), and zinc oxide. The manufacturer’s instructions were followed and 2.5 g of supplied zinc oxide was mixed with 1.0 g of paste and inserted into a plastic syringe.

This was then mixed with the liquid in a 3:1 ratio on a glass plate. The other 3 sealers were also prepared following manufacturer’s recommendations.

Sealers were introduced into the canal twice, 5 s each, using a bidirectional spiral #25 (EDS, Hackensack, NJ). A gutta-percha cone #50 (Henry Schein, Mexico City, Mexico), coated with sealer, was placed into the canal followed by 2 accessory cones #25 placed to a depth where resistance was met. No spreader was used.

Eleven millimeters of the coronal gutta-percha was removed immediately after obturation with a heated plugger, leaving the apical 4 mm to be subjected to the leakage tests.

In the positive control group, lateral compaction of gutta-percha was performed without sealer. Negative controls were filled with 3 gutta-percha cones and AH26, and the external root surface was completely covered with cyanoacrylate.9 To facilitate the leakage setting up, the coronal 8 mm of each specimen was embedded in acrylic resin to form a cylinder around the root. Specimens were then stored for 1 month at 370C and 100% humidity for sealers’ setting.

Fluid transport Roots were mounted on a fluid transport model previously described4 and shown in Fig. 1, A. A 30-kPa (360 cm H2O) headspace pressure was applied, and after 3 h, 6 h, and 24 h, the air bubble movement (in ␮L) in the capillary tube (Fig. 1, A) was recorded.

Glucose penetration Twenty-four hours after finishing fluid transport readings, samples were mounted on a glucose penetration model (Fig. 1, B), where glucose solution was placed in the coronal reservoir. A headspace pressure of 30 kPa was created by connecting the open orifice of the pipette to a pressure source (Fig. 1, B). After 24 h, a sample of 100 ␮L was taken from the apical reservoir and the glucose concentration was measured.

The samples were analyzed using a Glucose kit (Megazyme, Wicklow, Ireland) in a spectrophotometer (Spectra Max 384 Plus; Molecular Devices, Sunnyvale, CA) at a wavelength of 340 nm.5 Glucose concentrations were presented in mg/mL.

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Table I. Leakage of four sealers: fluid transport and glucose penetration Fluid transport (␮L) Sealer AH26 (n ⫽ 20) Median (range) Mean (SD) RSA (n ⫽ 20) Median (range) Mean (SD) AH Plus (n ⫽ 20) Median (range) Mean (SD) Polifil (n ⫽ 20) Median (range) Mean (SD)

Glucose concentration (mg/mL)

3h

6h

24 h

24 h

0 (0-1) 0.2 (0.41)

0 (0-2) 0.25 (0.55)

0 (0-4) 0.85 (1.73)

0.01 (0-1.2) 0.10 (0.30)

0 (0-1) 0.05 (0.22)

0 (0-0.05) 0.01 (0.01)

1 (0-4) 1.20 (1.20)

0.02 (0-1.3) 0.23 (0.43)

0 (0-2) 0.25 (0.55)

0 (0-0.1) 0.02 (0.03)

0 (0-0) 0 (0) 0 (0-1) 0.2 (0.41) 0 (0-0) 0 (0)

0 (0-0) 0 (0) 0 (0-2) 0.35 (0.67) 0 (0-0) 0 (0)

Kruskal-Wallis and Mann-Whitney tests checked differences among the 4 sealer groups and Spearman test verified the correlation between the results of two models (SPSS, version 12.0.1; Chicago, IL). Chi-squared test detected differences in the number of leaking samples demonstrated by the fluid transport model at different time intervals (Sigma Stat, version 3.1; San Jose, CA).

RESULTS In the fluid transport test, no movement of the air bubble was detected in the negative controls. All positive controls showed bubble movement that exceeded the pipette length within 3 h. In the glucose penetration test, no glucose penetration was detected in the negative controls. In all positive controls, glucose penetrated completely to the apical reservoir within 24 h.

Tables I and II show the results of the experimental groups. After 24 h, in both models, RSA showed the best sealing, and AH Plus leaked the most (P ⬍ .01); no significant difference between RSA and Polifil was observed (P ⫽ 0.15, fluid transport; P ⫽ 0.89, glucose penetration).

When the fluid transport model was used, significantly more leaking samples were detected after 24 h than after 3 h or 6 h (Table II; P ⬍ 0.01).

A positive correlation was observed between the results of both models (Fig. 2; coefficient ⫽ 0.65; P ⫽ 0.000001).

DISCUSSION In the original glucose model,5 the headspace pressure was 15 cm of glucose solution. In the present study a higher headspace pressure of 30 kPa (360 cm H2O), was applied to accelerate glucose penetration and create conditions comparable to those for the fluid transport.

Thus, water or glucose solution that moved to the apical chamber under the same headspace pressure was quan-

Table II. Number of leaking samples detected by the fluid transport model at different time intervals Number of leaking samples Sealer

3h

6h

24 h

AH26 (n ⫽ 20) RSA (n ⫽ 20) AH Plus (n ⫽ 20) Polifil (n ⫽ 20) Total (n ⫽ 80)

4 0 4 0 8

4 0 5 0 9

8 1 14 3 26

tified. In fluid transport, air-bubble movement was measured to indicate the volume of water penetration; in glucose penetration, the concentration of glucose in the apical chamber was measured to indicate the volume of glucose solution movement.

Fluid transport and glucose penetration occur only through voids that are completely open, while cul-desac type voids prevent fluid transport or glucose penetration.10,11 It has been shown that neither water nor glucose solution penetrate through root dentin.12 Thus, evidence of fluid transport or glucose penetration demonstrates the existence of at least 1 continuous void along the root filling. A higher value for fluid transport or glucose penetration indicates that the total volume of the voids is bigger.10,11 In this study, 24 h after fluid transport the specimens were connected to the glucose model, where the concentration of glucose was measured. When the same specimens are tested by 2 models, similarity of the results could be considered to be a measure of the models’ reliability. However, one may argue that running the specimens through the fluid transport system under 30 kPa pressure had changed the property of the filling and affected the results of glucose penetration. In a study by Wu et al., the amount of fluid transport along

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Fig. 2. Correlation between the 24 h results of 80 specimens recorded in 2 models (coefficient ⫽ 0.65; P ⫽ .000001).

the same root fillings was examined.13 Fluid transport under headspace pressure of 60 kPa was measured every 2 h. All specimens filled by lateral compaction, vertical compaction, and single cone showed consistent values, indicating that the 60 kPa headspace pressure did not result in detectable damage to the root fillings.

In earlier studies where fluid transport was measured, the headspace pressure was applied for a certain period of time from a few minutes to 24 h.4,14,15 To investigate whether the time of fluid transport plays a role in detection of leaking samples, fluid transport was recorded also after 3 h and 6 h. Significantly more leaking samples were detected after 24 h than after 3 h and 6 h (Table II). Presumably, samples presented with narrow voids required longer pressure time to display detectable fluid accumulation in the apical reservoir. This is supported by the observation that only 1 to 2 ␮L of fluid transport was recorded after 24 h (Table I).

The purpose of this study was to examine whether the same root fillings displayed a similar amount of leakage in 2 different leakage models, not to test specific root filling techniques. Only 3 gutta-percha cones were used to fill each canal to simplify the procedure.

Spreader was not used because of the difficulty to

standardize the spreader load and the number and size of spreader tracks.16,17 Furthermore, using no spreader may prevent root fracture.

Similar techniques, where no compaction forces are used, have been included in several recent studies and in some of them showed a comparable sealing ability to compaction techniques.18-21 Therefore, the results of the present study should provide useful information about the 4 sealers used whenever these noncompaction techniques are accepted.

AH Plus is considered to be a new generation of AH26, having a faster setting time.22 The accelerated setting time may cause shrinkage stress, leading to debonding of sealer from the root canal wall.23,24 In addition, silicon oils present in the sealer have been claimed to affect its sealing properties.24,25 In accordance with other studies, RSA sealer displayed effective sealing,21,26,27 which may be due to its slight expansion during setting28,29 and close adaptation to dentinal walls.30 Polifil is a polyurethane (polyester)31 mixed with zinc oxide. According to our results, Polifil may become a promising endodontic sealer. Similar tissue response has been observed to Polifil and to calcium hydroxide sealer.32

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Under the conditions in this study, results of the same specimens recorded in the fluid transport model and glucose penetration model were similar.

REFERENCES 1. Torabinejad M, Ung B, Kettering JD. In vitro bacterial penetration of coronally unsealed endodontically treated teeth. J Endod 1990;16:566-9.

2. Felippe WT, Felippe MCS, Rocha MJC. The effect of mineral trioxide aggregate on the apexification and periapical healing of teeth with incomplete root formation. Int Endod J 2006;39:2-9.

3. Ørstavik D, Qvist V, Stoltze K. A multivariate analysis of the outcome of endodontic treatment. Eur J Oral Sci 2004;112:224-30.

4. Wu MK, De Gee AJ, Wesselink PR, Moorer WR. Fluid transport and bacterial penetration along root canal fillings. Int Endod J 1993;26:203-8.

5. Xu Q, Fan MW, Fan B, Cheung GS, Hu HL. A new quantitative method using glucose for analysis of endodontic leakage. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2005;99:107-11.

6. Tronstad L. Clinical endodontics. New York: Thieme; 1991. p.

190, 196.

7. van der Sluis LW, Shemesh H, Wu MK, Wesselink PR. An evaluation of the influence of passive ultrasonic irrigation on the seal of root canal fillings. Int Endod J 2007;40:356-61.

8. Wu MK, R’oris A, Barkis D, Wesselink PR. Prevalence and extent of long oval canals in the apical third. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2000;89:739-43.

9. Campos TN, Inoue CH, Yamamoto E, Araki AT, Adachi LK, Rodriguez JE. Evaluation of the apical seal after intraradicular retainer removal with ultrasound or carbide bur. Braz Oral Res 2007;21:253-8.

10. Pashley DH. Dentine permeability: theory and practice. In: Spånberg LSW, editor. Experimental endodontics. Boca Raton, FL: CRC Press; 1990. p. 19-49.

11. Van den Berg HR, Ten Seldam CA, Van der Gulik PS. Compressible laminar flow in a capillary. J Fluid Mech 1993;246:1-20.

12. Shemesh H, van den Bos M, Wu M-K, Wesselink PR. Glucose penetration and fluid transport through coronal root structure and filled root canals. Int Endod J 2007;40:866-72.

13. Wu MK, van der Sluis LWM, Ardila CN, Wesselink PR. Fluid movement along the coronal two-thirds of root fillings placed by three different gutta-percha techniques. Int Endod J 2003;36:533-40.

14. Cobankara FK, Adanir N, Belli S, Pashley DH. A quantitative evaluation of apical leakage of four root-canal sealers. Int Endod J 2002;35:979-84.

15. Pommel L, Camps J. Effects of pressure and measurement time on the fluid filtration method in endodontics. J Endod 2001;27:256-8.

16. Budd CS, Weller RN, Kulild JC. A comparison of thermoplasticized injectable gutta-percha obturation techniques. J Endod 1991;17:260-4.

17. Jarrett IS, Marx D, Covey D, Karmazin M, Lavin M, Gound T. Percentage of canals filled in apical cross sections: an in vitro study of seven obturation techniques. Int Endod J 2004;37:392-8.

Souza et al. 313 18. Dalat DM, Spångberg LS. Comparison of apical leakage in root canals obturated with various gutta-percha techniques using a dye vacuum tracing method. J Endod 1994;20:315-9.

19. Cohen BI, Pagnillo MK, Musikant BL, Deutsch AS. The evaluation of apical leakage for three endodontic fill systems. Gen Dent 1998;46:618-23.

20. Pommel L, Camps J. In vitro apical leakage of System B compared with other filling techniques. J Endod 2001;27:449-51.

21. Wu MK, van der Sluis LW, Wesselink PR. A 1-year follow-up study on leakage of single-cone fillings with RoekoRSA sealer.

Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2006;101:662-7.

22. Cohen BI, Pagnillo MK, Musikant BL, Deutsch AS. An in vitro study of the cytotoxicity of the two root canal sealers. J Endod 2000;26:228-9.

23. Zmener O, Spielberg C, Lamberghini F, Rucci M. Sealing properties of a new epoxy resin-based root-canal sealer. Int Endod J 1997;30:332-4.

24. Miletic I, Anic I, Pezelj-Ribaric S, Jukic S. Leakage of five root canal sealers. Int Endod J 1999;32:415-8.

25. De Moor RJ, De Boever JG. The sealing ability of an epoxy resin root canal sealer used with five gutta-percha obturation techniques. Endod Dent Traumatol 2000;16:291-7.

26. Cobankara FK, Adanir N, Belli S, Pashley DH. A quantitative evaluation of apical leakage of four root-canal sealers. Int Endod J 2002;35:979-84.

27. Roggendorf MJ, Ebert J, Petschelt A, Frankenberger R. Influence of moisture on the apical seal of root canal fillings with five different types of sealer. J Endod 2007;33:31-3.

28. Kazemi RB, Safavi KE, Spångberg LSW. Dimensional changes of endodontic sealers. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1993;76:766-71.

29. Ørstavik D, Nordahl I, Tibballs JE. Dimensional change following setting of root canal sealer materials. Dent Mater 2001;17:512-9.

30. Gençoglu N, Türkmen C, Ahiskali R. A new silicon-based root canal sealer (Roekoseal-Automix). J Oral Rehabil 2003;30: 753-7.

31. Pereira-Júnior OCM, Rahal SC, Iamaguti P, Felisbino SL, Pavan PT, Vulcano LC. Comparison between polyurethanes containing castor oil (soft segment) and cancellous bone autograft in the treatment of segmental bone defect induced in rabbits. J Biomater Appl 2007;21:283-97.

32. Perassi, FT. Tecidual response of EndoRez sealer and a castor oil-based sealer compared to Endofill and Sealapex: a morphologic study (PhD thesis). Araraquara, Brazil: São Paulo State University; 2004.

Reprint requests: Dr. Min-Kai Wu Department of Cariology, Endodontology, and Pedodontology Academic Centre for Dentistry Amsterdam (ACTA) Louwesweg 1 1066 EA Amsterdam The Netherlands m.wu@acta.nl

44 doi:10.1111/j.1365-2591.2008.01440.x

Glucose reactivity with filling materials as a limitation for using the glucose leakage model

H. Shemesh1, E. M. Souza2, M.-K. Wu1 & P. R. Wesselink1 1

Department of Cariology Endodontology Pedodontology, Academic Center for Dentistry Amsterdam (ACTA), Amsterdam, the Netherlands; and 2Department of Dentistry and Endodontics, Araraquara Dental School, Sa˜o Paulo State University, Sa˜o Paulo, Brazil

Abstract Shemesh H, Souza EM, Wu M-K, Wesselink PR. Glucose reactivity with filling materials as a limitation for using the glucose leakage model. International Endodontic Journal, 41, 869–872, 2008.

Aim To evaluate the reactivity of different endodontic materials and sealers with glucose and to asses the reliability of the glucose leakage model in measuring penetration of glucose through these materials.

Methodology Ten uniform discs (radius 5 mm, thickness 2 mm) were made of each of the following materials: Portland cement, MTA (grey and white), sealer 26, calcium sulphate, calcium hydroxide [Ca(OH)2], AH26,Epiphany, Resilon, gutta-percha and dentine. After storing the discs for 1 week at 37 C and humid conditions, they were immersed in 0.2 mg mL)1 glucose solution in a test tube. The concentration of

Introduction A new leakage model was suggested recently (Xu et al.

2005) using glucose as the tracer. Several studies were published using this model (Shemesh et al. 2006, 2007, Kaya et al. 2007, van der Sluis et al. 2007, Zou et al. 2007, Xu et al. 2007, Ozok et al. 2008) and more are being conducted. This model is based on measurements of glucose concentrations in an apical chamber using a sensitive enzymatic reaction. A coloured substance is produced and optical density (OD) is determined by a spectrophotometer, translated

Correspondence: H. Shemesh, Department of Cariology Endodontology Pedodontology, Academic Center for Dentistry Amsterdam (ACTA), Louwesweg 1, 1066 EA, Amsterdam, the Netherlands (Tel.: +31 20 5188651; fax: +31 20 6692881; e-mail: hshemesh@acta.nl).

ª 2008 International Endodontic Journal

glucose was evaluated using an enzymatic reaction after 1 week. Statistical analysis was performed with the anova and Dunnett tests at a significant level of P < 0.05.

Results Portland cement, MTA, Ca(OH)2 and sealer 26 reduced the concentration in the test tube of glucose significantly after 1 week (P < 0.05). Calcium sulphate reduced the concentration of glucose, but the difference in concentrations was not significant (P = 0.054).

Conclusions Portland cement, MTA, Ca(OH)2 and sealer 26 react with a 0.2 mg mL)1 glucose solution.

Therefore, these materials should not be evaluated for sealing ability with the glucose leakage model.

Keywords: glucose, leakage model, optical density, reactivity.

Received 29 January 2008; accepted 10 April 2008

later to concentration units. The advantages of this model are the relative ease of assembly and operation, the availability of the materials and equipment and the great sensitivity of the test (Shemesh et al. 2006).

As leakage studies are constantly being scrutinized for their clinical relevance and reproducibility (Editorial Board of the Journal of Endodontics, 2007), a critical approach to the various leakage models is required.

One of the problems of using a tracer for evaluating leakage is that the tracer itself could chemically react with some materials challenging the reliability of such a test in evaluating sealing ability. For example, methylene blue, which is often used for dye-leakage studies, was previously shown to discolour when in contact with certain filling materials (Wu et al. 1998), whilst root canal fillings might directly inhibit bacteria in bacterial leakage studies (Pitout et al. 2006). The purpose of this study was to determine the reactivity of

International Endodontic Journal, 41, 869–872, 2008

869

45 Reliability of glucose leakage model Shemesh et al.

glucose solution with different dental materials to assess whether glucose is an acceptable tracer for all tested materials.

Materials and methods The following materials were mixed according to the manufacturer’s instructions and inserted into round plastic moulds 2 mm deep with a diameter of 5 mm : Portland cement (Gamma, Leusden, the Netherlands), MTA grey (Angelus, Londrina, Brazil), MTA white (Angelus), Sealer 26 (Dentsply, Petro´polis, Brazil), calcium hydroxide powder (Merck, Darmstadt, Germany), calcium sulphate (Sigma-Aldrich, Steinheim, Germany), AH26 (Dentsply-Maillefer, Tulsa, OK, USA) and Epiphany sealer (Pentron Clinical Technologies, Wallingford, CT, USA). The following thermoplastic materials were adapted into similar moulds with a warm instrument: Resilon cones (Pentron), Gutta-

percha cones (Dentsply De Trey, Konstanz, Germany).

Ten moulds were filled with each material. An additional 10 dentine discs of similar dimensions were created from extracted molar teeth. All moulds and discs were maintained at 37 C and humid conditions.

After 1 week, the set materials were carefully removed from the moulds, forming round discs. Each of the discs was then inserted to a small test tube with 4 mL of glucose 0.2 mg mL)1 solution. Additional 10 test tubes were used as controls and contained only 4 mL of glucose 0.2 mg mL)1 solution. All test tubes were kept at 37 C. A sample of 0.1 mL of the solution was removed after 1 week from each test tube and was analysed with a Glucose kit (Megazyme, Wicklow, Ireland) in a spectrophotometer (Spectra max 384 plus; Molecular Devices, Sunnyvale, CA, USA) at a wavelength of 340 nm. Results were expressed as OD. Statistical analysis was performed with the anova and the Dunnett test at significance level of P < 0.05 (spss version 15.0, SPSS Inc., Chicago, IL, USA).

Table 1 Average optical density (OD), SD and P-value of the

OD measured after 1-week immersion with different materials Material

Average OD ± SD

P-value (compared with glucose solution)

Water Glucose stand.

Dentine Portland cement MTA-grey MTA-white Sealer 26 Ca(OH)2 Calcium sulphate AH26 Epiphany Resilon Gutta-percha

0 0.290 0.293 0 0 0 0 0 0.275 0.282 0.290 0.300 0.297

<0.001 – 0.999 <0.001 <0.001 <0.001 <0.001 <0.001 0.054 0.645 1.000 0.382 0.781

± ± ± ± ± ± ± ± ± ± ± ± ±

0.005 0.010 0.007 0.007 0.004 0.007 0.027 0.005 0.007 0.007 0.017 0.015 0.008

The kit used has a detectable threshold of OD 0.05.

The results are presented in Table 1 and Fig. 1.

The glucose kit used has a detectable threshold of OD 0.05, so all readings lower than 0.05 were ignored. The glucose test tubes with no test material showed the expected OD from a 0.2 mg mL)1 glucose solution (OD 0.3 ± 0.05).

Amongst the materials tested, MTA, Portland cement, sealer 26 and Ca(OH)2 lowered significantly the OD of the solution after 1 week (P < 0.05) .

Dentine, Resilon, Epiphany, AH26 and gutta-percha did not significantly alter the concentration of glucose.

Calcium sulphate reduced the concentration of glucose but the difference in concentrations was not significant (P = 0.054).

Calculated absorption from 0.2 mg mL–1 glucose solution according to the glucose kit used

0.35 0.3

OD values

Results

0.25 0.2 0.15 0.1 0.05

870

se D e Po ntin e rtl an M dc TA .

M -gre TA y -w Se hite al er 2 C a( 6 O C H al ) c.

Su 2 lfa te AH Ep 26 ip ha ny R G es ut ta ilon -p er ch a

co lu

G

W

at

er

0

International Endodontic Journal, 41, 869–872, 2008

Figure 1 The measured optical density (OD) of 0.2 mg mL)1 glucose solution after 1-week immersion with different materials.

ª 2008 International Endodontic Journal

46 Shemesh et al. Reliability of glucose leakage model

Discussion After 1 week in contact with glucose solution, a number of the materials tested reduced significantly the OD of the glucose reaction to the level of water (Fig. 1).

As all published glucose leakage tests checked the penetration of glucose for periods ranging from 20 days (Zou et al. 2007) to 56 days (Shemesh et al. 2006) an observation period of 1 week seems relevant when assessing the reactivity of different materials with the tracer.

Glucose (an aldohexose) in an alkaline solution is slowly oxidized by oxygen, forming gluconic acid: 1 CH2 OH-(CHOH)4 CHO þ O2 2 ! CH2 OH-(CHOH)4 CO2 H In the presence of sodium hydroxide, for example, gluconic acid is converted to sodium gluconate (Sowden & Schaffer 1952). This means that glucose will not be detected by the glucose kit and could thus mask leakage in the glucose leakage model.

Interestingly, Sealer 26 releases Ca(OH)2 (Duarte et al. 2000), whilst MTA contains Ca(OH)2 (Camilleri 2007). It seems that Ca(OH)2 containing products react directly with glucose. This reaction could also be initiated by traces of Ca(OH)2 left in the canal when used as an intra-canal medication. Thus, the leakage measured by glucose concentrations could be influenced by this chemical reaction.

Zou et al. (2007) used the glucose leakage model and concluded that calcium sulphate significantly improved the sealing ability of 1 mm perforations repaired with composite resin. Although the statistical tests used in this study resulted in a nonsignificant influence of calcium sulphate on glucose (P = 0.054), the P-value is small and it cannot be excluded that calcium sulphate might have an influence. Thus, calcium sulphate could be better evaluated for its sealing properties by another tracer or model.

In the glucose leakage model, a 1 mol L)1 glucose solution is used as the tracer and placed in the upper chamber of the model assembly (Xu et al. 2005). This concentration is much higher than the linear range detected by the glucose kits: 4–80 lg of glucose per assay (Glucose–HK assay procedure, Megazyme International Limited, 2004). However, the range of glucose concentrations measured in the apical chamber during a leakage test is dependent on the amount of glucose that penetrated through the canal and can demon-

ª 2008 International Endodontic Journal

strate a large range of concentrations (Shemesh et al.

2006). In this experiment, a glucose concentration of 0.2 mg mL)1 (20 lg per assay) was chosen as it lies within the linear range of detection of the glucose kit used and could give more accurate information on the variations in glucose concentrations after immersion with different materials .

Conclusion The observation that certain materials react with glucose suggests that evaluating these materials with the glucose leakage model might lead to erroneous conclusions. An investigation of the influence of tested materials on glucose should always precede glucose leakage tests to validate the conclusions from such studies.

References Camilleri J (2007) Hydration mechanisms of mineral trioxide aggregate. International Endodontic Journal 40, 462–70.

Duarte MA, Demarchi AC, Giaxa MH, Kuga MC, Fraga SC, de Souza LC (2000) Evaluation of pH and calcium ion release of three root canal sealers. Journal of Endodontics 26, 389–90.

Editorial Board of the Journal of Endodontics (2007) Wanted: a base of evidence. Journal of Endodontics 33, 1401–2.

Kaya BU, Kececi AD, Belli S (2007) Evaluation of the sealing ability of gutta-percha and thermoplastic synthetic polymerbased systems along the root canals through the glucose penetration model. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology and Endodontics 104, 66–73.

Ozok AR, van der Sluis LWM, Wu MK, Wesselink PR (2008) Sealing ability of a new polydimethylsiloxane-based root canal filling material. Journal of Endododontics 34, 204–7.

Pitout E, Oberholzer TG, Blignaut E, Molepo J (2006) Coronal leakage of teeth root-filled with gutta-percha or Resilon root canal filling material. Journal of Endodontics 32, 879–81.

Shemesh H, Wu MK, Wesselink PR (2006) Leakage along apical root fillings with and without smear layer using two different leakage models: a two-month longitudinal ex vivo study. International Endodontic Journal 39, 968–76.

Shemesh H, van den Bos M, Wu MK, Wesselink PR (2007) Glucose penetration and fluid transport through coronal root structure and filled root canals. International Endodontic Journal 40, 866–72. van der Sluis LW, Shemesh H, Wu MK, Wesselink PR (2007) An evaluation of the influence of passive ultrasonic irrigation on the seal of root canal fillings. International Endodontic Journal 40, 356–61.

Sowden JC, Schaffer R (1952) The reaction of d-Glucose, d-Mannose and d-Fructose in 0.035 N Sodium Hydroxide at 35. Journal of the American Chemical Society 74, 499–504.

International Endodontic Journal, 41, 869–872, 2008

871

47 Reliability of glucose leakage model Shemesh et al.

Wu MK, Kontakiotis EG, Wesselink PR (1998) Decoloration of 1% methylene blue solution in contact with dental filling materials. Journal of Dentistry 26, 585–9.

Xu Q, Fan MW, Fan B, Cheung GS, Hu HL (2005) A new quantitative method using glucose for analysis of endodontic leakage. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology and Endodontics 99, 107–11.

Xu Q, Ling J, Cheung GS, Hu Y (2007) A quantitative evaluation of sealing ability of 4 obturation techniques

872

International Endodontic Journal, 41, 869–872, 2008

by using a glucose leakage test. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology and Endodontics 104, 109–13.

Zou L, Liu J, Yin SH et al. (2007) Effect of placement of calcium sulphate when used for the repair of furcation perforations on the seal produced by a resin-based material. International Endodontic Journal 40, 100–5.

ª 2008 International Endodontic Journal

48

49

Chapter III Novel imaging methods

This chapter is enhanced by additional high-resolution images and video available on www.shemesh.nl

1. High frequency ultrasound imaging of a single-species biofilm. Shemesh H, Goertz DE, van der Sluis LW. De Jong N, Wu MK, Wesselink PR. J Dent. 2007 Aug;35(8) 673-8.

2. The ability of optical coherence tomography to characterize the root canal walls.

Shemesh H, van Soest G, Wu MK, van der Sluis LW, Wesselink PR J Endod.

2007Nov;33 (11):1369-73 3. Diagnosis of vertical root fractures with optical coherence tomography Shemesh H, van Soest G, Wu MK, Wesselink PR J Endod. 2008 Jun;34(6):739-42

50

51 journal of dentistry 35 (2007) 673â&#x20AC;&#x201C;678

available at www.sciencedirect.com

journal homepage: www.intl.elsevierhealth.com/journals/jden

High frequency ultrasound imaging of a single-species biofilm H. Shemesh a,*, D.E. Goertz b, L.W.M. van der Sluis a, N. de Jong b, M.K. Wu a, P.R. Wesselink a a

Department of Cariology Endodontology Pedodontology, Academic Centre for Dentistry Amsterdam (ACTA), Louwesweg 1, 1066 EA Amsterdam, The Netherlands b Department of Biomedical Engineering, Erasmus University Medical Center, Dr. Molewaterplein 50, 3015 GE Rotterdam, The Netherlands

article info

abstract

Article history:

Objective: This study evaluated the feasibility of a high frequency ultrasound scan to

Received 27 March 2007

examine the 3D morphology of Streptococcus mutans biofilms grown in vitro.

Received in revised form

Methods: Six 2-day S. mutans biofilms and six 7-day biofilms were grown on tissue culture

21 May 2007

membranes and on bovine dentine discs. A sterile growth medium on the membrane and

Accepted 22 May 2007

disc were used as controls. Surfaces were rinsed and then immersed in sterile saline. Highfrequency ultrasound imaging system was used to scan these surfaces at 55 MHz, and a computer program calculated the average thickness of the biofilm layer from the 3D images.

Keywords:

Results: 3D pictures of the biofilm layers were obtained. Different cross-sections and plains

Biofilm

are easily demonstrated. The average thickness of the 7-day biofilm was significantly bigger

Ultrasound

than the 2-day on both the membranes and dentinal discs. No structures were observed on

Imaging

the sterile membrane or disc.

Conclusion: Three-dimensional structural imaging in situ is possible without damaging the

3D

biofilm layer in a quick and easy manner and can therefore be used to evaluate biofilms longitudinally as a function of time. # 2007 Elsevier Ltd. All rights reserved.

1.

Introduction

Biofilms are communities of microorganism growing on a surface or interface.1 One of the best studied biofilms is dental plaque, which forms on tooth surfaces and causes dental caries.2,3 It is a multi species biofilm dominated by Streptococcus species.4 Biofilm structure has a crucial role in its function and resistance. It has a circulatory system and mixed microbial community that is highly integrated in terms of nutritional needs and output.5 Knowledge of the 3D structure of a biofilm is important in order to understand its special characteristics as well as to monitor the efficacy of procedures to eliminate or

chemically remove it.6 Although various successful attempts to quantify biofilm structure were made,7 producing a clear image of the biofilm or obtaining reliable data about its thickness, density or biomass still presents a challenge.8,9 Laser scanning microscopy is the method most frequently employed for 3D biofilm imaging but its disadvantages are the toxicity of fluorescent markers used, depth of penetration and resolution.10 Recently, nuclear magnetic resonance (NMR) was suggested as a non-invasive method to image live biofilms.11 Ultrasound imaging has been extensively used as a noninvasive diagnostic tool in medicine for over 50 years, and in the majority of applications, it operates in the frequency range

* Corresponding author.

E-mail address: hshemesh@acta.nl (H. Shemesh).

0300-5712/$ â&#x20AC;&#x201C; see front matter # 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jdent.2007.05.007

52 674

journal of dentistry 35 (2007) 673–678

of 1–5 MHz. Ultrasound imaging as a possible diagnostic dental tool has been investigated as far back as the 1960s. Lees and Barber12 were the first to describe a sonic echogram of incisor teeth, and later discussed the difference of echoes received from the dentine-amalgam interface and demineralized dentine.13 They were able to estimate the enamel and dentine thickness at various points, but these measurements could not be representative for the whole tooth. The researchers also neglected to take into account the phase change that occurs when acoustic waves pass through interfaces between materials of different acoustic impedances, thus allowing an error to arise in their measurements.14 More recently, relevant clinical dental applications of ultrasonic scans were discussed,15,16 such as the detection of caries and cracks in the enamel. These studies were imaging hard-tissues, while ultrasound imaging has an excellent capacity to image soft tissues as well. Higher frequency ultrasound systems (20–100 MHz) have lately been developed for specialized biomedical applications, often imaging soft tissues, and offer improved spatial resolution for situations where the imaging probe (transducer) can be brought to within <10 mm from the region of interest.17 The aim of the present study was to evaluate the feasibility of a high frequency ultrasound imaging system to examine the 3D morphology of biofilms. In particular, single-species Streptococcus mutans biofilms on the order of 100–300 mm were non-invasively imaged.

2.

Materials and methods

2.1.

Growth of S. mutans biofilm

S. mutans biofilms were prepared: a frozen stock of S. mutans C180 was plated on Brain Heart Infusion (BHI) agar and grown under anaerobic conditions in gas packed jars for 2 days in 37 8C. One colony was inoculated in 25 ml BHI solution and stored in 37 8C overnight.18 The next morning 0.5 ml of the bacterial suspension was transferred to 25 ml of half strength BHI with pipes buffer (50 mM). 0.1 ml sterile sucrose solution 0.2% was added. This bacterial suspension was pipetted into cell culture inserts (BD Biosciences San Jose, CA, USA) which have a thin (12 mm) membrane on which the biofilm was grown and maintained in anaerobic conditions. The supernatant was carefully removed every day and exchanged with a fresh sterile growth medium containing sucrose. A white layer was visible on the insert’s membrane after 24 h of incubation, indicating biofilm formation. Four different plates of six inserts each were used to generate different biofilms or environments: in plate A (six inserts), biofilms were grown for 7 days before they were ultrasonically scanned, while in plate B (also six inserts) biofilms were grown for only 2 days before scanning. Two other sets of plates were prepared with dentine discs: in plate C, six sterile bovine dentine discs (diameter: 5 mm, uniform thickness of 2 mm) were placed on the insert’s membrane. They were inoculated with 4 ml of bacterial culture and growth medium like the previous plates and the procedure was repeated as in group A. In plate D biofilms were grown on the dentine discs for 2 days. The control plate contained four inserts with

sterile growth medium supplemented with sucrose, two of which contained a sterile bovine dentine disc in it.

2.2.

Ultrasound scan

A commercially available high frequency ultrasound system, designed primarily for use with small animal imaging, was employed in this study (Visualsonics Vevo 770, Toronto, Canada). The 55 MHz probe (#708) was used, which has a single element focused transducer with an aperture of 2 mm and a focal length of 4.5 mm. The estimated 6 dB beam width of this transducer was 62 mm. The nominal bandwidth of the pulses was reported to be 100%, giving pulse duration of approximately 0.02 ms. This type of transducer mechanically scans laterally over a region of interest, and a 2D image is built up using echoes from a series of 384 adjacent transducer beam locations (one pulse per location). 2D images were acquired at 20 frames per second and for an 8 mm lateral image distance, such as that used in this study, the spacing between pulses was 21 mm on average. At a given beam location, the received ultrasound echo is converted into a brightness scale (logarithmically compressed) that is then displayed as one line on the image. The transducer was mounted to the proprietary positioning system, which permitted manual control of the transducer orientation and location relative to an imaging platform. 3D imaging capabilities were enabled with a motorized position axis, which scans the imaging probe through a series of 2D imaging planes to acquire volumetric data.

Before scanning, growth medium was carefully removed and the culture inserts were rinsed and filled with saline, taking care no air bubbles were formed. The inserts were immediately placed on a stable imaging platform and the membrane or dentine surface was manipulated to be in the focal zone of the transducer, and perpendicular to the transducer beam. The configuration is shown in Fig. 1, which indicates that the transducer beam travels through saline before encountering the biofilm. The saline is required as a coupling medium to permit the ultrasound energy to travel into the biofilm. The presence of air, which creates larger echoes, would prohibit ultrasound imaging of the sample.

An image of 8 mm 8 mm 10 mm in the x–y–z directions (Fig. 2) took approximately 10 s to scan. Taking into account

Fig. 1 – Tissue culture insert, and the setting of the scan. A transducer is located inside saline perpendicular to the biofilms’ surface.

53 journal of dentistry 35 (2007) 673–678

675

Fig. 2 – Ultrasound scan output screen: (A) cube view, 3D reconstruction, (B) cross view, (C) transverse view, (D) sagittal view.

the beam width of the transducer, each location was exposed to a maximum of 4 pulses during an individual 2D plane scan and 12 pulses during the 3D scan. The transmit amplitude was set to 10% of the maximum setting. The specific pressure levels employed in this study were not available, but the manufacturer indicated that the peak negative pressure measured using the maximum transmit amplitude for another unit of the same type was 3.3 MPa. The resulting data was presented as a series of standard 2D ultrasound ‘b-scan’ (brightness) images. These data sets then underwent two forms of processing. First, the 3D images were rendered and examined using the internal Vevo 770 system software. This resulted in a 3D visualization of the biofilm surface, which permitted inspection of the biofilm morphology. The images could also be manipulated to look at userselected slices within the volumetric data sets. Second, to perform quantitative analyses, the data sets were transferred to a personal computer and processed using custom software written in a MatlabTM environment (Mathworks Inc., Natick, MA, USA).

Differences between thicknesses of 2-day and 7-day biofilms were statistically analyzed with the Mann–Whitney

tests (SPSS, version 12.0.1, Chicago, IL, USA). The level of significance was set at a = 0.05.

3.

Results

The 3D output shows four different views (Fig. 2). A specific sagittal or transverse image could be generated at the specific plane determined by the cross-view. Sterile dentine discs and membranes immersed in sterile growth medium showed no biofilm growth at all. The membrane itself appeared as a very bright line resulting from a strong echo. In the experimental groups, biofilm structures were clearly visible (Figs. 2–4) as heterogeneous layers above the membrane or dentine discs.

The upper boundary of the biofilm could be delineated due to presence of ‘‘scattered’’ echoes from within the biofilm and the absence of echoes from the overlying saline. The high amplitude membrane reflection could be readily used to identify the lower boundary of the biofilm. Using these boundaries, the average thickness of the biofilm was calculated for both substrates: the membrane and the dentine discs (Table 1). Seven-day biofilms were significantly thicker

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journal of dentistry 35 (2007) 673–678

Table 1 – Average thickness of biofilms grown on different substrates (membrane in tissue culture plates and dentine discs) of 2 and 7 days old

Fig. 3 – Seven-day-old Streptococcus mutans biofilm grown on tissue-culture membrane with mm-scale.

than 2-day biofilms both on the membrane and dentine discs (P = 0.08, P = 0.016, respectively).

4.

Discussion

This study was a preliminary attempt to visualize S. mutans biofilms with an ultrasound imaging system and to assess its validity as a new method in the research of these structures.

The assessment of biofilm was conducted at different growth stages, providing an illustration of its compatibility for

Substrate

Biofilm age days

Average thickness (mm)

S.D.

Membrane

2 7

102 266

11 56

Dentine discs

2 7

92 126

13 16

longitudinal studies. The approach employed was to use a commercially available instrument which has rapid scan time (10 s per sample) and could immediately produce 3D visualization results. These factors are appealing from the perspective of increasing the accessibility of ultrasound techniques to the wider dental biofilm research community.

Ultrasound imaging is widely used for a range of medical applications.19 A short burst of ultrasound is emitted from a transducer and directed into tissue. Echoes are produced as a result of the interaction of sound with tissue, and some of these travel back to the transducer. By timing the period elapsed between the emission of the pulse and the reception of the echo, the distance between the transducer and the tissue can be calculated and an image formed. Echoes are generated when the propagating ultrasound wave encounters an object with different acoustic impedance (product of density and speed of sound). When the ‘object’ is much smaller than the acoustic wavelength, such as in the case of cells within tissue, echo is generated through scattering. This is the origin of the echoes within the biofilm. If the wave encounters an interface that is relatively large with respect to the wavelength, then reflection occurs. This is the situation for the substrate/biofilm interface.

Fig. 4 – Streptococcus mutans biofilm growth on tissue-culture membranes (A–C) and on dentine discs (D–F): (A) sterile membrane (negative control), (B) 2-day-old biofilm, (C) 7-day-old biofilm, (D) sterile dentine disc (negative control), (E) 2-day biofilm, (F) 7-day biofilm.

55 journal of dentistry 35 (2007) 673–678

The biofilms thickness estimates were made based on an assumed ultrasound velocity in biofilm of 1540 m/s.20 It is important to note however that the velocity of sound in biofilm was not measured and although expected to be within the relatively narrow range of velocities found in soft tissues,21 a calculation of this value will allow more precise measurements within the biofilm itself and not only its borders.

According to the results of this experiment, a 7-day biofilm is thicker than a 2-day biofilm regardless of the substrate used.

This is in accordance with previous reports, where an increase in dental plaque thickness was observed, that did not conform to simple growth pattern models.22 The current results however show that the 7-day biofilm was significantly thicker when grown on the membrane. This could be explained by the method applied to grow the biofilm on the dentine discs. Since the discs were not attached to the membrane below them, they constantly moved during the growth medium refreshment every day and it may have dislodged bacteria layering over the disc. Since this problem was not present in the membrane group, a thicker biofilm was able to grow.

There have been two other recent reports of using high frequency ultrasound to image biofilms. Holmes et al.23 imaged non-specific biofilms created in water ponds with a custom 50 MHz system. Placing an immersed transducer below a membrane and detecting reflections from an air/ biofilm interface allowed imaging the surface morphology of these biofilms. The use of air provided a very large reflection signal due to the difference in acoustic properties between air and biofilm. This strong echo, in combination with the signal processing methods applied, permitted the measurement of films of thickness on the order of 10 mm. Unfortunately, this approach has the potential drawback of altering the properties of the biofilm and making longitudinal studies difficult.

Furthermore, such an approach may not be possible to implement if the substrate is dentine rather than a thin membrane. Good et al.24 reported biofilm visualization of bacteria relevant to water pipes using 50 MHz ultrasound. The scanning approach was to discretely move the transducer through a grid, while stopping at each point to acquire a series of signals. Custom software was then used to form 3D images and measure thicknesses. It was also concluded that sound energy is an effective way to investigate biofilms noninvasively.

Microscopy is a highly valuable approach to biofilm investigations, and especially confocal scanning laser microscopy can create accurate 3D reconstructions. However, it cannot be used to visualize unstained (non-fluorescent) material or any other matrix which was not specifically treated.25 Furthermore, the ultrasonic scan of a biofilm takes a few seconds to complete which makes it far easier and more convenient than previous methods. The ultrasound scan can provide an additional tool as a non-invasive method which could be applied repeatedly on the same sample after subjecting is to different treatments or materials without the need of any staining or fixing procedure.

As the number of pulses exposing any given location of the biofilm was very low (<12 over 150 ms) and each pulse was of short duration (<20 ns) and at 20% of the maximum transmit power, it is not expected that any heating, radiation pressure, or bioeffects would be induced during measurements. Cucevic

677

et al.26 used a Visualsonics system (40 MHz) and found temperature rises only when exposing at maximum power with longer pulses (0.4 ms) at high repetition rates (10–20 kHz) sustained over many seconds at the same location.

While in this study we have focused only on morphology and thickness, it should also be noted that the received ultrasound signal may contain more useful information. For example, it has been shown that high frequency ultrasound signals can be sensitive to both tissue structure and cells undergoing apoptosis.27 It may therefore be useful to examine ultrasound signals coming from different biofilm types or during growth and after therapy. Another avenue of investigation would be to examine the use of ultrasound molecular imaging probes which are typically comprised of targeted micro-bubbles.28,29

5.

Conclusion

The present study demonstrated a high frequency ultrasound imaging system that was successfully used to generate 3D computer images of S. mutans biofilm. The biofilm thickness could be calculated from these images. Biofilms on bovine dentine discs were also imaged, proving the method as an effective way to investigate biofilms for dental research.

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26. Cucevic V, Brown AS, Foster FS. Thermal assessment of 40MHz pulsed Doppler ultrasound in human eye. Ultrasound in Medicine & Biology 2005;31:565–73.

27. Czarnota GJ, Kolios MC, Vaziri H, Benchimol S, Ottensmeyer FP, Sherar MD, et al. Ultrasonic biomicroscopy of viable, dead and apoptotic cells. Ultrasound in Medicine & Biology 1997;23:961–5.

28. Dayton PA, Ferrara KW. Targeted imaging using ultrasound.

Journal of Magnetic Resonance Imaging 2002;16:362–77.

29. Goertz DE, van Wamel A, Frijlink ME, de Jong N, van der Steen AF. High frequency nonlinear imaging of targeted microbubble contrast agents. Proceedings of IEEE Ultrasonic Symposium 2005;4:2002–6.

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The Ability of Optical Coherence Tomography to Characterize the Root Canal Walls Hagay Shemesh, DMD,* Gijs van Soest, PhD,† Min-Kai Wu, PhD,* Lucas W.M. van der Sluis, PhD,* and Paul R. Wesselink, PhD* Abstract A detailed understanding of the complexity of root canal systems is imperative to ensure successful root canal therapy. The aim of this study was to evaluate the ability of an optical coherence tomography (OCT) system in imaging root canal walls after endodontic preparation and to correlate these images to histologic sections. Ten extracted mandibular incisors were prepared to size 50 with K-files and Gates Glidden drills. A three-dimensional OCT scan was made with a rotating optical fiber probe inside the root canal. All teeth were sectioned at 5 and 7 mm from the apex and viewed through a microscope. Histologic sections were compared with the corresponding OCT output. All oval canals, uncleaned fins, risk zones, and one perforation that was detected by histology were also imaged by OCT. OCT proves to be a reliable method to image root canals and root dentin in a nondestructive way. This technique holds promise for full in vivo endodontic imaging. (J Endod 2007;33:1369 –1373)

Key Words Histology, intracanal imaging, optical coherence tomography, root canal

From the *Department of Cariology, Endodontology, Pedodontology, Academic Centre for Dentistry Amsterdam (ACTA), Amsterdam, The Netherlands; and †Department of Biomedical Engineering, Thorax Center, Erasmus University Medical Center, Rotterdam, The Netherlands.

Address requests for reprints to Hagay Shemesh, Department of Cariology, Endodontology, Pedodontology, Academic Center for Dentistry Amsterdam (ACTA), Louwesweg 1, 1066 EA Amsterdam, The Netherlands.

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odern imaging techniques are clinically applied during root canal treatment, but important information over inner canal anatomy and dentin thickness is still limited to in vitro observations. Moreover, more than 50% of lower incisors show long-oval form (ratio of long/short canal diameter ⱖ2) 5 mm from the apex (1), which requires special considerations in cleaning and obturation (2). One difficulty in treating oval or curved canals is the chance of strip perforations because of the short distance between the inner canal wall and the periodontal ligament. In these so-called “risk zones,” the clinician is often faced with the challenge to sufficiently clean and enlarge the root canal space while not perforating the mesial or distal wall (3). Current clinical imaging techniques cannot give reliable information on this aspect.

Optical coherence tomography (OCT) is a new diagnostic medical imaging technology that was first introduced in 1991 (4). Since then, it has become a standard tool in ophthalmology and promising imaging method for intracoronary atherosclerosis detection (5). For example, most heart attacks are caused by sudden ruptures of unstable arterial plaques that cannot be detected by using conventional imaging modalities. OCT has the potential to identify these arterial plaques and differentiate stable plaque from unstable. In addition, it is an attractive technique for the early identification of gastrointestinal malignancies, including the esophagus, stomach, and colon (6). Recently, optical in vivo biopsy, providing microscope-quality images in which cell function can be distinguished, is one of the most challenging fields of OCT application (7).

OCT combines the principles of an ultrasound with the imaging performance of a microscope; although an ultrasound produces images from backscattered sound “echoes,” OCT uses infrared light waves that reflect off the internal microstructure within the biological tissues. Using the principle of low-coherence interferometry, it achieves a depth resolution of the order of 10 ␮m and an in-plane resolution similar to the optical microscope. By scanning the probe along the imaged specimen while acquiring image lines, a two-dimensional or three-dimensional image is built up. The OCT light source has a wavelength of 1300 nm. Visible light that has a shorter wavelength is prone to a higher level of scattering and absorption and produces a shallower imaging depth (8). The frequencies and bandwidths of infrared light are significantly higher than medical ultrasound signals, resulting in increased image resolution (9). In endoscopic OCT imaging, near-infrared light is delivered to the imaging site (usually blood vessels) through a thin fiber. The imaging tip contains a lens-prism assembly to focus the beam and direct it toward the vessel wall. The fiber can be retracted inside a catheter sheath to perform a so-called “pullback,” allowing the user to make a stack of cross-sections, scanning the investigated vessel lengthwise. Modern OCT systems reach a 6-mm imaging depth, with 8-␮m resolution, at 50 to 80 frames per second.

OCT potential in dentistry was not overlooked. OCT images of hard and soft tissues in the oral cavity were compared with histologic images using an animal model showing an excellent match (10). In another study, Otis et al (11) discussed the clear depiction of periodontal tissue contour, sulcular depth, connective tissue attachment, and marginal adaptation of restorative materials to dentin, concluding that OCT is a powerful method for generating high-resolution, cross-sectional images of oral structures. Amaechi et al (12) and Baumgartner et al (13) described the recognition of caries with OCT. Recently, Lantis Laser, Inc (Denville, NJ) gained license to LightLab Imaging’s intellectual property portfolio (Westwood, MA) related to OCT in the field of dentistry. OCT could provide dentists with an unprecedented level of image resolution to assist in the evaluation of periodontal disease,

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Basic Research—Technology dental restorations, and in the detection of caries. Commercial development of chair-side OCT dental system is already underway (www.lantislaser. com). The purpose of this experiment was to evaluate the ability of an OCT system to provide important information on the root canal walls using histologic sections as control.

Materials and Methods Preparation of Teeth Ten extracted single-rooted mandibular incisors were selected. A radiograph was taken from two angles to verify a single canal. Teeth with open apices or large carious lesions were excluded. Each tooth was accessed coronally with a diamond bur (FG 173; Horico, Berlin, Germany), and the canal opening was enlarged with Gates Glidden drills #3 and #4, which were inserted 4 and 3 mm into the canal, respectively.

The canal was instrumented to a size 50 stainless steel K-file (Dentsply Maillefer, Ballaigues, Switzerland). Irrigation with 2% NaOCl using a 26-G needle followed after every instrument so that a total of 15 mL of solution was used per tooth. Each canal was then rinsed with sterile saline. For endodontic imaging, the probe’s tip has to be placed inside the root canal (Figs. 1 and 2) so that the distal end is inserted through the apex. The apical constriction was opened thus with #45 K-file to allow the optic fiber to penetrate through the canal.

Test Setup OCT pullback scans were performed by using a LightLab Imaging M2-CV system in combination with an ImageWire 2 catheter. This system is designed for intracoronary imaging in atherosclerotic plaque diagnosis. It is commercially available for clinical use in cardiac catheterization laboratories. The catheter consists of a 2-m long optical single-mode fiber inside a protective sheath, with a diameter of 0.5 mm.

The imaging depth in water is 3.3 mm. The axial and transverse image resolutions are 14 and 25 ␮m, respectively. The imaging guidewire is integrated into an imaging catheter, which is connected to a motor (Fig. 1). Both rotational and horizontal movements of the catheter could be performed, allowing the fiber to be pulled inside the imaged canal in an apical-coronal direction while rotating. This movement is also used in cardiovascular imaging and is commonly referred to as “pullback.”

The tooth was placed in a water bath to improve the optical match between the catheter and the tooth. Motorized “pullbacks” from the apex to the coronal opening were performed, with a speed of 1 mm/s and 10 rotations per second, using 312 lines per frame and 760 samples per line. The result is a stack of images with a spacing of 100 ␮m. These images were stored as “audio video interleave” files for visual inspection. All teeth were sectioned at 5 and 7 mm from the apical area with a saw microtome (Leica Microsystems SP1600, Wetzlar, Germany). Slices were then viewed through a stereomicroscope (Zeiss Stemi SV6; Carl Zeiss, Gottingen, Germany) by using a cold light source (KL 2500 LCD,

Figure 2. (A) The OCT catheter inside the root canal. (B) A rotating needle with a transparent tip is situated inside the catheter and serves both as a light source and as the receiver, transmitting the reflected beams to the imaging computer.

Carl Zeiss). Pictures were taken with a camera (Axio Cam, Carl Zeiss) at a magnification of ⫻12 and compared with the corresponding OCT images at the same level. Canal diameters were measured in crosssections and in the OCT images and were identified as oval when the ratio of long to short canal diameter was ⱖ1.5. “Risk zone” was defined as dentinal wall thinner than 1 mm.

Results Results are summarized in Table 1 and Figures 3 to 6. All oval canals, uncleaned fins, risk zones, and one perforation that was histologically detected were also visualized with OCT.

Discussion The results show excellent correlation between the histologic images and the OCT output. Risk zones were created in 30% of the teeth at 5 mm from the apex, and one root was perforated. The large master file (#50) and the anatomy of the roots that were used (lower incisors) could explain this large incident.

The use of novel imaging techniques is gaining a lot of attention in the field of endodontics. New computed tomography methods prove to be more accurate in the evaluation of bone lesions than conventional radiography (14). Similarly, canal morphology (15), root fractures (16), tooth anatomy (17), and the interface between the root canal and filling materials (18) were successfully shown with different computed tomography techniques. These methods use ionizing radiation, which could be harmful at higher doses when used in vivo. Furthermore, two major disadvantages are limiting the successful application of these methods for intracanal imaging: First, the resolution is usually not suitable for microscopic-level imaging. Digital dental radiography systems TABLE 1. Various Clinically Relevant Parameter Observed in Histology and OCT Images at 5 mm and 7 mm from the Apex Histology

Figure 1. (A) The OCT screen and machine. (B) The motor connected to the catheter. (C) The activated OCT catheter inside the root canal.

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Teeth with uncleaned fins Oval canals “Risk zones” (canal wall ⱕ1 mm thick) Perforation

OCT

5 mm

7 mm

5 mm

7 mm

2 7 3

1 8 2

2 7 3

2 8 2

1

0

1

0

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Figure 3. The OCT output at 7 mm from the apex shows a cross-section of a prepared canal. (A) The root canal, (B) cementum, and (C) dentinal tubules. (D) “Risk zone” (canal wall ⫽ 1-mm thick).

have a pixel size approaching 100 ␮m. Second, the probe size is usually much bigger than a root canal. These methods are also time consuming and often require the interpretation of thousands of images. In contrast, OCT combines a very narrow optical fiber measuring 0.5 mm in diameter, with high-resolution capacities, enabling imaging of objects measuring a few micrometers and does not involve ionizing radiation. The imaging wire can be deployed independently or integrated straightforwardly into existing therapeutic or imaging catheters. Furthermore, it can easily fit into a prepared root canal and is flexible, allowing penetration through curvatures. The optical probe rotates inside the imaged vessel so that adjacent lines in each rotation compose a frame showing a cross-section of the tissue architecture in the wall. The scan is quick and takes 15 seconds for a 15-mm long root.

The influence of a specific tissue’s microstructure on light propagation is an important factor when considering diagnostic applications of light. Dentin is a structure with anisotropic optical properties that is different from most other biological tissues (19) because the tubules are the primary cause of light scattering (20). In our experiments, the root dentin was semitransparent, allowing imaging of the outer root surface as well. However, a thicker dentine wall will not allow sufficient light penetration, and the outer outline of the root will not be seen.

However, some care has to be taken with interpreting measured distances in the OCT images of dentin. The OCT system assumes a refractive index of the imaging medium that is close to that of water (1.33), which is a reasonable approximation for soft tissues. Dental and bone-like

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materials have a higher index of refraction, closer to 1.5 (20). As a result, the distances inside the tooth are approximately 13% shorter than suggested by the images. Straightforward image processing can remove this ambiguity. The tooth was placed in a water bath to improve the refractive index match between imaging medium and dental material. A contrast in refractive index causes light to be reflected from the interface (21), reducing the signal from the tissue. A smaller refractive index step (achieved by imaging through water, instead of air) leads to a smaller reflection at the dentin interface and improves image quality.

Furthermore, because clinical application of the OCT system was also considered, placing the optical fibre in a wet canal is more clinically relevant. Indeed, one of the big disadvantages of the recently introduced “endoscope” to endodontic clinical practice (22) is that it requires a dry environment. The endoscope has a 0.7-mm probe that is inserted into a dry canal to image the inner anatomy. However, this system is based on a camera that produces a digital image and not on microscopic-level characterization or light propagation as observed by the OCT. Furthermore, no penetration of light through the dentinal tubuli is possible and, hence, no detection of the outer outline of the root. The smaller diameter and increased flexibility of the OCT probe allows deeper penetration and easier application in clinical situations.

It is noteworthy that the current experimental setting requires the catheter to penetrate through the apex, pulling it back through the canal.

Adaptation of the catheter to allow imaging from the fiber’s tip is possible, which will enable imaging without probing through the apex and thus allow

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Figure 4. Oval canals and uncleaned fins at 7 mm from the apex revealed by histology (H) and OCT (O): sample A and sample B.

Figure 5. Cleaned root canals at 7 mm from the apex revealed by histology (H) and OCT (O): sample A and sample B.

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Figure 6. Canal perforation during preparation at 5 mm from the apex revealed by histology (H) and OCT (O).

clinical imaging all the way to the apical part. Another disadvantage of the current setting is the cost of the OCT catheter. Because these wires are designed for disposable cardiac use, they are relatively expensive. Nonetheless, OCT imaging systems for clinical dental use are under development, and more affordable versions could be available soon.

In conclusion, this study shows a noninvasive and nondestructive technique for analyzing the anatomy and cleanliness of root canal walls.

OCT could generate intracanal microscopic images without applying ionizing radiation and could be used in vivo.

References 1. Wu MK, R’oris A, Barkis D, Wesselink PR. Prevalence and extent of long oval canals in the apical third. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2000;89:739 – 43.

2. Mauger MJ, Schindler WG, Walker WA 3rd. An evaluation of canal morphology at different levels of root resection in mandibular incisors. J Endod 1998;24:607–9.

3. Tamse A, Katz A, Pilo R. Furcation groove of buccal root of maxillary first premolars—a morphometric study. J Endod 2000;26:359 – 63.

4. Huang D, Swanson EA, Lin CP, et al. Optical coherence tomography. Science 1991;254:1178 – 81.

5. Regar E, van Beusekom HM, van der Giessen WJ, Serruys PW. Images in cardiovascular medicine. Optical coherence tomography findings at 5-year follow-up after coronary stent implantation. Circulation 2005;112:345– 6.

6. Pitris C, Jesser C, Boppart SA, et al. Feasibility of optical coherence tomography for high-resolution imaging of human gastrointestinal tract malignancies. J Gastroenterol 2000;35:87–92.

7. Gambichler T, Hyun J, Moussa G, et al. Optical coherence tomography of cutaneous lupus erythematosus correlates with histopathology. Lupus 2007;16:35– 8.

8. Low AF, Tearney GJ, Bouma BE, Jang IK. Technology insight: optical coherence tomography— current status and future development. Nat Clin Pract Cardiovasc Med 2006;3:154 – 62.

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9. Schmitt JM. Optical coherence tomography (OCT): a review. IEEE J Sel Top Quantum Electron 1999;5:1205–15.

10. Colston BW Jr, Everett MJ, Sathyam US, DaSilva LB, Otis LL. Imaging of the oral cavity using optical coherence tomography. Monogr Oral Sci 2000;17:32–55.

11. Otis LL, Everett MJ, Sathyam US, Colston BW Jr. Optical coherence tomography: a new imaging technology for dentistry. J Am Dent Assoc 2000;131:511– 4.

12. Amaechi BT, Higham SM, Podoleanu AG, Rogers JA, Jackson DA. Use of optical coherence tomography for assessment of dental caries: quantitative procedure.

J Oral Rehabil 2001;28:1092–3.

13. Baumgartner A, Dichtl S, Hitzenberger CK, et al. Polarization-sensitive optical coherence tomography of dental tructures. Caries Res 2000;34:59 – 69.

14. Velvart P, Hecker H, Tillinger G. Detection of the apical lesion and the mandibular canal in conventional radiography and computed tomography. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2001;92:682– 8.

15. Eder A, Kantor M, Nell A, et al. Root canal system in the mesiobuccal root of the maxillary first molar: an in vitro comparison study of computed tomography and histology. Dentomaxillofac Radiol 2006;35:175–7.

16. Youssefzadeh S, Gahleitner A, Dorffner R, Bernhart T, Kainberger FM. Dental vertical root fractures: value of CT in detection. Radiology 1999;210:545–9.

17. Plotino G, Grande NM, Pecci R, Bedini R, Pameijer CH, Somma F. Three-dimensional imaging using microcomputed tomography for studying tooth macromorphology.

J Am Dent Assoc 2006;137:1555– 61.

18. Jung M, Lommel D, Klimek J. The imaging of root canal obturation using micro-CT. Int Endod J 2005;38:617–26.

19. Kienle A, Forster FK, Diebolder R, Hibst R. Light propagation in dentin: influence of microstructure on anisotropy. Phys Med Biol 2003;48:N7–14.

20. Zijp JR, ten Bosch JJ. Theoretical model for the scattering of light by dentin and comparison with measurements. Appl Opt 1993;32:411–36.

21. Born M, Wolf E. Principles of Optics. Ed 7. Cambridge, UK: Cambridge University Press; 2002:132– 4.

22. Bahcall JK, Barss JT. Fiberoptic endoscope usage for intracanal visualization. J Endod 2001;27:128 –9.

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Diagnosis of Vertical Root Fractures with Optical Coherence Tomography Hagay Shemesh, DMD,* Gijs van Soest, PhD,† Min-Kai Wu, PhD,* and Paul R. Wesselink, PhD* Abstract The purpose of this experiment was to evaluate the ability of optical coherence tomography (OCT) to image vertical root fractures (VRFs). Twenty-five mandibular premolars were prepared to size 50. Five teeth served as controls. Group 1 (n ⫽ 10) was treated with ethylenediaminetetraacetic acid and ultrasonic irrigation, whereas group 2 (n ⫽ 10) received no further treatments. Teeth from groups 1 and 2 were fractured, and the presence of a fracture line was demonstrated microscopically. Control group teeth were not subjected to any force. Teeth were pooled and scanned with an OCT fiber. The resulting video files were blindly interpreted by 2 observers .No fractures were detected in the control teeth. The overall sensitivity for detection of VRFs with OCT was 93% for group 1 and 84% group 2, whereas the specificity was 95% for group 1 and 96% for group 2. OCT is a promising nondestructive imaging method for the diagnosis of VRFs. (J Endod 2008;34: 739 –742)

Key Words Imaging, optical coherence tomography, sensitivity, specificity, vertical root fracture

From the *Department of Cariology Endodontology Pedodontology, Academic Center for Dentistry Amsterdam (ACTA), Amsterdam, The Netherlands; and the †Department of Biomedical Engineering, Thorax Center, Erasmus University Medical Center, Rotterdam, The Netherlands.

Address requests for reprints to Dr Hagay Shemesh, ACTA, CEP, Louwesweg 1, 1066 EA Amsterdam, The Netherlands.

E-mail address:hshemesh@acta.nl.

0099-2399/$0 - see front matter Copyright © 2008 by the American Association of Endodontists. doi:10.1016/j.joen.2008.03.013

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ertical root fracture (VRF) is a considerable threat to the tooth’s prognosis during and after root canal treatment (1). VRF presents a challenge to the clinician in that the diagnosis is often difficult and is based on subjective parameters. The current available methods to clinically diagnose VRF include illumination, x-ray, periodontal probing, staining, surgical exploration, bite test, direct visual examination, and operative-microscope examination. All of these have limited success (2– 4). Radiographic images could reveal VRF only if the x-ray beam is parallel to the fracture line (5), and thus in many cases radiographic diagnosis is based on other findings like the size and shape of the periradicular lesion and its location (6).

Lately, alternative diagnostic imaging systems with computed tomography were suggested (7, 8). Although these systems could visualize VRF, they all use harmful ionized radiation and present relatively low sensitivity in detection of VRF (7).

Bahcall and Barss (9) suggested a fiberoptic endoscope to image the canal internally, but images of a VRF were never shown by using this system. Furthermore, the minimal thickness of the imaging probe used, 0.7 mm, means that the canal should be enlarged to ISO size 70 – 80. Such a preparation is seldom performed in adult teeth.

Another requirement for the endoscope is a dry canal, which might prove difficult to achieve in teeth with VRF. Optical coherence tomography (OCT) is a high-resolution imaging technique that allows micrometer scale imaging of biologic tissues over small distances (10). It was introduced in 1991 (11) and uses infrared light waves that reflect off the internal microstructure within the biologic tissues. It achieves a depth resolution of the order of 10 ␮m and an in-plane resolution similar to the optical microscope. OCT has previously been shown to be a valuable tool in assessing intracanal anatomy, cleanliness of the canal after preparation, and even perforations (12).

The purpose of this experiment was to evaluate the ability of an OCT system to diagnose VRF under different conditions.

Materials and Methods Twenty-five lower premolars were chosen and accessed coronally with a diamond bur (FG 173; Horico, Berlin, Germany). The canal opening was enlarged with GatesGlidden drills #3 and #4, which were inserted 4 and 3 mm into the canal, respectively.

The canal was instrumented to a size 50 stainless steel K-file (Dentsply Maillefer, Ballaigues, Switzerland). Patency with file size 30 was verified. Irrigation with 2% sodium hypochlorite (NaOCl) by using a 26-gauge needle followed after every instrument, so that a total of 15 mL solution was used per tooth. The teeth were then divided into 3 groups: In the control group (n ⫽ 5) and group 2 (n ⫽ 10), teeth were flushed with 5 mL of water. In group 1 (n ⫽ 10), passive ultrasonic irrigation (PUI) was performed (13), and 10 mL of ethylenediaminetetraacetic acid (EDTA) 17% was used to flush the canals for 1 minute (14). A final flush of tap water followed. After preparation, the external root surface was inspected under a microscope (Zeiss Stemi SV6; Carl Zeiss, Gottingen, Germany) to exclude any external defects or cracks. During these procedures, roots were handled with a wet swab around them to keep them in 100% humidity and to avoid drying. VRF was artificially made immediately after in the 2 experimental groups; a size D stainless steel finger spreader (Hu-friedy, Leimen, Germany) was cut at the tip so its length was 12 mm, and it was inserted as far possible into the canal. Vertical pressure was applied to the spreader with a screw-table until a vertical line appeared on the outside surface of the root. No forces were applied on the control group teeth. A

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Figure 1. Appearance of VRF through an OCT scan. (A) VRF extends through the root 2.5 mm from the apex on 2 opposing sides of the canal; it appears as a bright line. The OCT catheter (C) is inside the canal. (B) VRF that has separated the dentin, 8 mm from the apex; the crack can be traced to the external root surface (S), and dentinal tubules can also be identified (T).

stereomicroscope (Zeiss Stemi SV6; Carl Zeiss) with a cold light source (KL 2500 LCD; Carl Zeiss) was used to inspect the roots. Pictures were taken with a camera (Axio cam; Carl Zeiss) at a magnification of ⫻12 to determine the location of the fracture line along the external surface of the root. All teeth were pooled and scanned with an M2-CV OCT system (LightLab Imaging Inc, Westford, MA) in combination with an ImageWire 2 catheter that has a diameter of 0.3 mm at its thinnest part, with a “pullback” technique (12) starting at the apex. The pullback speed was 1 mm/second, and video files were generated at a rate of 10 frames per second. Each frame consisted of 312 lines, with a scan depth of 3.3 mm in water. Distances were measured from the apex tip.

The presence of VRF in the OCT scan was noted at 3, 6, and 9 mm from the apex by 2 observers. The same observers reviewed the same scans again after an interval of 4 weeks. Interobserver and intraobserver agreement was assessed on the basis of the proportion of agreement and the values of the kappa coefficient. The sensitivity and specificity of the OCT scan in diagnosing VRF were calculated as well as the 95% confidence intervals for both groups.

Results Several features were observed and illustrated in Figs. 1–3. A bright line extending from the canal (Fig. 1A) and 2 bright lines with a void between them separating the dentin (Fig. 1B) were both considered a VRF. Fig. 2 compares a microscope photograph with registered OCT imagery, whereas Fig. 3 demonstrates how cracks can propagate inside the dentin.

The specificity and sensitivity are shown in Table 1 and demonstrate high to very high values of the OCT system in diagnosing VRF. For interobserver agreement, the mean kappa values were 0.9 for group 1 and 0.7 for group 2, showing very good to excellent reliability.

For intraobserver agreement, the mean kappa value of 0.9 for both observers shows very high reproducibility. Because the values of sensitivity and specificity of one group fell inside the 95% confidence interval of the other group, we concluded that the groups did not differ in regard to these parameters.

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Discussion According to the current results, more information on the presence of VRF could become available with the use of OCT. No statistical significance for the difference between sensitivity and specificity was demonstrated between the 2 groups. The higher agreement between the observers after the ultrasonic cleaning and use of EDTA could be a result of better light propagation through dentin when the smear layer is absent or cleaner canal devoid of debris. The penetration of light through the dentin tubules allows imaging of structures beyond the canal walls and in some cases up to the cementum layer (12). If the tubules are blocked, less light could penetrate, giving rise to lowerquality imaging beyond the canal walls or in areas where the dentin is thicker.

Two factors might contribute to the development of VRF during the endodontic treatment: First, excessive canal shaping especially in teeth with curved roots or oval canals (15, 16) and excessive removal of tooth structure contribute to the overall weakening of the tooth, which promotes a higher incidence of VRF (17). Second, excessive hand pressure during lateral and vertical compaction of filling material can result in development of VRF (18).The detection of these fractures is usually not made during treatment and is diagnosed only years later (4, 19), leading to bone loss, malfunction of the involved tooth or area, and pain. The immediate identification of a fracture during treatment thus has great clinical value.

There is still confusion in the literature regarding the definition of various terms used to describe different fracture types. Split teeth, vertical fracture, complete, incomplete, primary, secondary fractures, crack, craze line, and other terms are sometimes used interchangeably.

Furthermore, a craze line might propagate into a fracture in certain conditions or along different levels of the same root (20, 21) (Fig.3).

Although some authors try to define the different terms (4, 22), many others avoid the definitions (16, 20, 23) or only refer to the clinical or diagnostic aspects (24). Still, a VRF is usually referred to as a “through and through” crack with a connection between the canal and the outer root surface or periodontal ligament (21, 25). Because the current study investigated teeth in which a clear fracture line was visible on the

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Figure 2. Root sample (A) where the fracture is marked by an arrow, and the corresponding OCT images at 9 mm (B), 6 mm (C), and 3 mm (D) from the apex. OCT visualization of the VRF is marked by arrows.

outer surface of the root and the force applied originated from within the canal, a “through and through” defect was assumed. Nevertheless, because OCT is an in situ imaging technique, cracks are always imaged at the site where they originate, and even if they do not propagate all the way to the exterior root wall, they could, in principle, still be imaged with OCT. Although this class of defects was not included in this study, they might be important for future in vitro work.

It is worth noting that there is not yet a commercially available OCT system for dental use. The OCT unit used in this study is designed for intra-

coronary imaging in atherosclerotic plaque diagnosis and is commercially available for clinical use in cardiac catheterization laboratories. Lantis Laser Inc (Denville, NJ) is currently developing an OCT dental system for lateral scanning, which will allow caries detection and periodontal examination (26). We believe that a specially designed endodontic probe will improve visualization for conventional endodontic treatment and could lead to better decision making and elevated standard of care.

In conclusion, OCT represents a powerful tool for evaluating VRF and has the potential to both identify VRF and detect its specific location

Figure 3. Sequence of video frames from a pullback, recorded approximately 4.5 mm from the apex, spaced 0.1 mm apart. A crack (white arrow) that originates in the canal (top left frame) can be followed as it propagates in the dentin.

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Group 1

Group 2

95 100

95 100

91 89

74 91

93 95

85 96

VRF, vertical root fracture; OCT, optical coherence tomography.

along the root. In vivo studies are needed to substantiate the clinical usage of OCT during endodontic treatment.

References 1. Tamse A, Fuss Z, Lustig J, Kaplavi J. An evaluation of endodontically treated vertically fractured teeth. J Endod 1999;25:506 – 8.

2. Morfis AS. Vertical root fractures. Oral Surg Oral Med Oral Pathol 1990;69:631–5.

3. Fuss Z, Lustig J, Tamse A. Prevalence of vertical root fractures in extracted endodontically treated teeth. Int Endod J 1999;32:283– 6.

4. Paul RA, Tamse A, Rosenberg E. Cracked and broken teeth-definitions, differential diagnosis and treatment. Refuat Hapeh Vehashinayim 2007;24:7–12.

5. Rud J, Omnell KA. Root fractures due to corrosion: diagnostic aspects. Scand J Dent Res 1970;78:397– 403.

6. Tamse A, Fuss Z, Lustig J, Ganor Y, Kaffe I. Radiographic features of vertically fractured, endodontically treated maxillary premolars. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1999;88:348 –52.

7. Nair MK, Nair UDP, Grondahl HG, Webber RL, Wallace JA. Detection of artificially induced vertical radicular fractures using tuned aperture computed tomography. Eur J Oral Sci 2001;109:375–9.

8. Hannig C, Dullin C, Hulsmann M, Heidrich G. Three-dimensional, non-destructive visualization of vertical root fractures using flat panel volume detector computer tomography: an ex vivo in vitro case report. Int Endod J 2005; 38:904 –13.

9. Bahcall J, Barss J. Orascopic visualization technique for conventional and surgical endodontics. Int Endod J 2003;36:441–7.

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10. Brezinski ME. Optical coherence tomography-principles and applications. Burlington, MA: Academy Press-Elsevier, 2006.

11. Huang D, Swanson EA, Lin CP, et al. Optical coherence tomography. Science 1991;254:1178 – 81.

12. Shemesh H, van Soest G, Wu MK, van der Sluis LW, Wesselink PR. The ability of optical coherence tomography to characterize the root canal walls. J Endod 2007;33:1369 –73.

13. van der Sluis LW, Wu MK, Wesselink PR. The efficacy of ultrasonic irrigation to remove artificially placed dentine debris from human root canals prepared using instruments of varying taper. Int Endod J. 2005;38:764 – 8.

14. Çalt S, Serper A. Time dependent effects of EDTA on dentin structures. J Endod 2002;28:17–9.

15. Frank RJ. Endodontic mishaps. In: Ingle, JI Backland, eds. LK Endodontics. 4th ed.

Hamilton, Ontario, Canada: BC Decker, 2002.

16. Wu MK, van der Sluis LW, Wesselink PR. Comparison of mandibular premolars and canines with respect to their resistance to vertical root fracture. J Dent 2004;32:265– 8.

17. Nissan J, Zukerman O, Rosenfelder S, Barnea E, Shifman A. Effect of endodontic access type on the resistance to fracture of maxillary incisors. Quintessence Int 2007;38:e364 –7.

18. Obermayr G, Walton RE, Leary JM, Krell KV. Vertical root fracture and relative deformation during obturation and post cementation. J Prosthet Dent 1991;66:181–7.

19. Fuss Z, Lustig J, Katz A, Tamse A. An evaluation of endodontically treated vertical root fractured teeth: impact of operative procedures. J Endod 2001;27:46 – 8.

20. Lertchirakarn V, Palamara JE, Messer HH. Load and strain during lateral condensation and vertical root fracture. J Endod 1999;25:99 –104.

21. Wilcox LR, Roskelley C, Sutton T. The relationship of root canal enlargement to finger-spreader induced vertical root fracture. J Endod 1997;23:533– 4.

22. Sutherland JK, Teplitsky PE, Moulding MB. Endodontic access of all-ceramic crowns.

J Prosthet Dent 1989;61:146 –9.

23. Nair MK, Grondahl HG, Webber RL, Nair UP, Wallace JA. Effect of iterative restoration on the detection of artificially induced vertical radicular fractures by Tuned Aperture Computed Tomography. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2003;96:118 –25.

24. Meister F Jr, Lommel TJ, Gerstein H. Diagnosis and possible causes of vertical root fractures. Oral Surg Oral Med Oral Pathol 1980;49:243–53.

25. Walton RE, Michelich RJ, Smith GN. The histopathogenesis of vertical root fractures.

J Endod 1984;10:48 –56.

26. Otis LL, Everett MJ, Sathyam US, Colston BW Jr. Optical coherence tomography: a new imaging technology for dentistry. J Am Dent Assoc. 2000;131:511– 4.

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Chapter IV Inspection of dentinal defects in the root canal wall

This chapter is enhanced by additional high-resolution images available on www.shemesh.nl

1. The effects of canal preparation and filling on the incidence of dentinal defects. Shemesh H, Bier CA. Wu MK, Tanomaru-Filho M, Wesselink PR. Int Endod J 2009 Mar;42(3);208-13.

2. The ability of different Ni-Ti rotary instruments to induce dentinal damage during canal preparation . Bier CA. Shemesh H, Tanomaru-Filho M, Wesselink PR, Wu MK, J Endod. 2009 Feb;35 (2):236-8.

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69 doi:10.1111/j.1365-2591.2008.01502.x

The effects of canal preparation and filling on the incidence of dentinal defects

H. Shemesh1, C. A. S. Bier2, M.-K. Wu1, M. Tanomaru-Filho2 & P. R. Wesselink1 1

Department of Cariology, Endodontology, Pedodontology, Academic Centre of Dentistry Amsterdam, Amsterdam, The Netherlands; and 2Department of Restorative Dentistry, Araraquara Dental School, Sa˜o Paulo State University, UNESP, Araraquara, SP, Brazil

Abstract Shemesh H, Bier CAS, Wu M-K, Tanomaru-Filho M, Wesselink PR. The effects of canal preparation and filling on the incidence of dentinal defects. International Endodontic Journal, 42, 208–213, 2009.

Aim To evaluate ex vivo the incidence of defects in root dentine before and after root canal preparation and filling.

Methodology Eighty extracted mandibular premolars were divided equally in four groups. Group 1 was left unprepared. All other root canals were prepared using Gates Glidden drills and System GT files up to size40, 0.06 taper at the working length. Group 2 was not filled while the canals of the other groups were filled with gutta-percha and AH26, either with a master cone and passive insertion of secondary gutta percha points (group 3) or lateral compaction (group 4). Roots were then sectioned horizontally 3, 6, and 9 mm from the

Introduction Vertical root fracture (VRF) is a clinical complication that may be associated with root canal treatment and lead to extraction (Tamse et al. 1999). Endodontic procedures might contribute to the development of VRF as well as other localized defects such as craze lines or incomplete cracks in root dentine (Onnink et al. 1994, Sathorn et al. 2005). These localized defects may have the potential to develop into fractures (Wilcox et al.

Correspondence: H. Shemesh, Department of Cariology, Endodontology, Pedodontology, Academic Centre of Dentistry Amsterdam (ACTA), Louwesweg 1 1066 EA Amsterdam, The Netherlands (Tel.: +31 20 5188651; fax: +31 20 6692881; e-mail:hshemesh@acta.nl).

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apex and observed under a microscope. The presence of dentinal defects (fractures, craze lines or incomplete cracks) was noted and the differences between the groups were analysed with the Fisher’s exact test.

Results No defects were observed in the roots with unprepared canals. The overall difference between the groups was significant (P < 0.05). Canal preparation alone created significantly more defects than unprepared canals (P < 0.05). The total number of defects after lateral compaction was significantly larger than after noncompaction canal filling.

Conclusion Root canal preparation and filling of extracted teeth created dentine defects such as fractures, craze lines and incomplete cracks.

Keywords: craze lines, dentine, obturation, preparation, vertical root fracture.

Received 12 August 2008; accepted 14 October 2008

1997, Shemesh et al. 2008) and should therefore be prevented. Several factors may be responsible for the formation of dentinal defects: instrumentation and root filling (Onnink et al. 1994), high concentration of hypochlorite (Sim et al. 2001), tooth anatomy (Wu et al. 2004) and post-placement (Kishen 2006).

Lateral compaction of gutta-percha is widely used to fill the root canal system and was reported previously to be associated with an increased risk of VRF (Meister et al. 1980, Wilcox et al. 1997). Spreader design and applied forces were suggested as contributing factors to the appearance of VRF during lateral compaction (Pitts et al. 1983, Dang & Walton 1989). However, laboratory stress distribution studies consistently conclude that the pressure applied during lateral compaction is insufficient to cause VRF (Dalat & Spa˚ngberg 1994,

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70 Shemesh et al. Canal preparation and filling

Lertchirakarn et al. 1999). Thus, it remains unclear whether lateral compaction can cause VRF. As an alternative, several techniques where no compaction forces are used have been proposed and shown to produce an apical seal similar to that of lateral compaction when used in conjunction with dimensionally stable sealers (Dalat & Spa˚ngberg 1994, Tidswell et al. 1994, Ozok et al. 2008).

The purpose of this study was to compare the incidence of fractures and other dentinal defects before and after canal preparation and filling either with lateral compaction of gutta-percha or a technique where no compaction forces were used.

Materials and methods Eighty extracted mandibular premolar teeth were selected and stored in purified filtered water. Proximal radiographs were taken to verify the presence of a single canal. The clinical crowns of all teeth were removed using an Isomet 11-1180 low-speed saw (Buehler Ltd, Evanston, IL, USA), leaving roots approximately 16 mm in length. All roots were observed under 8· magnifications in a stereomicroscope (Zeiss Stemi SV6; Carl Zeiss, Jena, Germany) to exclude cracks. Twenty root canals were left unprepared (group 1) and the remaining 60 teeth (groups 2, 3 and 4) were subjected to the procedures described below. All roots were kept moist in purified filtered water throughout the experimental procedures in order to prevent dehydration.

Cleaning and shaping Canal patency was established with a size-20 K-Flexo File (Dentsply Maillefer, Ballaigues, Switzerland). The canal opening was enlarged with Gates Glidden drills 3 (size-90) and 4 (size-110) to a depth of 4 and 3 mm from the coronal orifice respectively. Canal preparation followed with System GT rotary files (Dentsply Maillefer) and a torque-control motor (Technika, Pistoia, Italy) at 300 rpm using the crown-down technique with series 40 and 30 files, ending with a size-40, 0.06 taper instrument to 1 mm short of the apical foramen.

Each canal was irrigated with a freshly prepared 2% solution of sodium hypochlorite (NaOCl) between each instrument, using a syringe and a 27-gauge needle.

Twelve millilitres of NaOCl solution was used for each root canal. After completion of instrumentation, passive ultrasonic irrigation was performed using an ultrasonic file size-15 (Satelec, Merignac Cedex, France)

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in order to activate the irrigation solution and clean the canals (van der Sluis et al. 2007). After completion of the procedure, canals were rinsed with 2 mL distilled water. The prepared roots were divided into three experimental groups of 20 roots each (groups 2, 3, and 4). Group 2 remained without root filling. Group 3 and 4 were filled with gutta-percha and AH26, using two different techniques according to the protocol described below.

Canal filling Canals were dried using paper point size-40. AH 26 (Dentsply De trey, Konstanz, Germany) was mixed according to the manufacturer’s instructions and introduced into the canal on two occasions, using a lentulo spiral, for 5 s each (Hall et al. 1996) rotating at 400 rpm to 1 mm short of the working length.

Standardized size-40 gutta-percha cones (Henry Schein, Mexico City, Mexico), with a 0.02 taper, were coated with sealer, and placed into the root canal to the working length. In group 3, two additional size-25 cones were placed to a depth where resistance was met without use of a spreader (Souza et al. 2008). Group 4 was sealed with the lateral compaction technique using a size C spreader (D1 diameter 0.3 mm, 0.04 taper) (Dentsply Maillefer) and size-25 standardized guttapercha cones. The force applied to the spreader was controlled using a digital scale and kept at a maximum of 2 kg. A polyether impression material (President, Coltene, Altsta¨tten, Switzerland) was used around the tooth during the filling procedures in order to mimic the mechanisms of stress distribution. The coronal gutta-percha was removed with a flame-heated plugger (0.5-mm diameter, Dentsply Maillefer), and the impression material was removed. Roots were stored for 1 week at 37 C and 100% humidity to allow the sealers to set.

Examination of roots All roots were sectioned horizontally at 3, 6 and 9 mm from the apex with a low-speed saw under water cooling (Leica SP1600, Wetzlar, Germany). Slices were then viewed through a stereomicroscope (Zeiss Stemi SV6; Carl Zeiss) using a cold light source (KL 2500 LCD; Carl Zeiss). Pictures were taken with a camera (Axio cam; Carl Zeiss) at a magnification of X12. The dentine was inspected and defects were noted. Defects were categorized as: ‘no defect’, ‘fracture’ and ‘all other defects’ (Fig. 1). ‘No defect’ was defined as root dentine

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(a)

(b)

(c1)

(c2)

Figure 1 Classification of the different dentinal defects. A – ‘no defects’, B – ‘VRF’, C – ‘other defects’ (C1 = ‘craze line’, C2 = ‘incomplete crack’).

devoid of any lines or cracks where both the external surface of the root and the internal root canal wall had no defects (Fig. 1a). ‘Fracture’ was defined as a line extending from the root canal space to the outer surface of the root (Wilcox et al. 1997) (Fig. 1b). ‘Other defects’ were defined as all other lines observed that did not extend from the root canal to the outer root surface. For example, a craze line – line extending from the outer surface into the dentine that did not reach the canal lumen (Wilcox et al. 1997) (Fig. 1.C1), or a partial crack extending from the canal wall into the dentine without reaching the outer surface of the root (Fig. 1.C2).

Statistical analysis Fisher’s exact test was performed to compare the incidence of fractures and other defects between the four groups using the SPSS/PC version 15 (SPSS Inc.,

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Chicago, IL, USA). The level of significance was set at a = 0.05.

Results Figures 2 and 3 summarize the results. The groups were significantly different from each other (P < 0.05).

The unprepared canals (group 1) had no defects. When considering the overall appearance of defects, the lateral compaction group (group 4) demonstrated significantly more defects than all other groups (P < 0.05), while roots with prepared canals (group 2) had significantly more defects than teeth with unprepared canals (group 1) (P < 0.05). When considering only fractures, the lateral compaction (group 4) had significantly more defects than the unprepared group (group 1) (P < 0.05) but not significantly more than the canal preparation-only group (group 2) (P > 0.05).

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72 Shemesh et al. Canal preparation and filling

Fracture present (with/without other defects) Other defect (fracture not present)

12

Number of teeth

10 8 6 4 2 0 No preparation

Only preparation

No compaction

Lateral compaction

Figure 2 Number of teeth presenting fractures or other defects. Groups with the same letter denote no statistical significance between them (P = 0.05).

All defects 18 16 No. of teeth

14 12 10 8 6 4 2 0 No preparation

Only preparation

No compaction

Lateral compaction

Figure 3 Number of teeth presenting a defect (either VRF or other defects or both). Letters denote statistical resemblance.

Groups with the same letter have no statistical difference between them (P = 0.05).

Discussion The sectioning method used in the current study allowed the evaluation of the effect of root canal treatment procedures on the root dentine by direct inspection of the root canal wall, observing not only VRF but also dentinal defects such as craze lines and incomplete cracks. When considering all the defects, the lateral compaction group had significantly more defects than all other groups (P < 0.05). Although no definitive conclusion can be made of the clinical consequences of the dentinal defects developed under these ex vivo experimental conditions, these findings may contribute to the understanding of long-term clinical observations (Meister et al. 1980, Tamse et al.

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1999) that ex vivo methods often could not clarify. It may be hypothesized that craze lines and incomplete cracks might propagate and develop into fractures after completion of endodontic procedures, following additional treatments such as post-space preparation or retreatment (Wilcox et al. 1997), or simply by forces transferred to the root during masticatory function and occlusal loading (Assif et al. 2003).

Previous ex vivo experiments studying the influence of endodontic procedures on root dentine mainly used one or other of the following methodologies: resistance to fracture, stress distribution measurements or observations of the presence of defects in tooth sections (Obermayr et al. 1991, Onnink et al. 1994, Saw & Messer 1995, Wilcox et al. 1997, Lertchirakarn et al.

1999, Mayhew et al. 2000, Ribeiro et al. 2008).

Resistance to fracture is frequently measured to assess the weakening of the root after different procedures. This method differs from the one used in the current study in that it applies an external force until the root fractures (Ribeiro et al. 2008), while in the current experiment, the influence of various procedures on the root canal walls was directly observed and no external forces were applied. Furthermore, resistance to fracture provides no information on the incidence of dentinal defects other than VRF. Stress distribution studies record stress transmission to dentine during different procedures using strain gauges (Obermayr et al. 1991, Saw & Messer 1995, Lertchirakarn et al. 1999), or a photoelastic material (Mayhew et al. 2000). These studies have shown that the force needed to fracture a root is much higher than that formed during lateral compaction. The current study found relatively few VRF in all groups, confirming this conclusion.

The observation that many of the defects did not connect with the pulp space, and were located in places away from direct contact with intra-canal instruments is baffling. Wilcox et al. (1997) speculated that the stresses generated from inside the root canal are transmitted through the root to the surface where they overcome the bonds holding the dentine together. In the current study, craze lines were not seen in unprepared teeth proving that they were caused by the preparation and filling procedures. Onnink et al.

(1994) claimed that a fracture contained within the dentine in one section could communicate with the canal space in an adjacent section. This supposition was recently supported by nondestructive observations of VRF induced in extracted teeth and viewed with optical coherence tomography (Shemesh et al. 2008).

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In a series of scans depicting a dentinal defect in one root, an incomplete crack is shown to originate at the root canal wall but later propagates into dentine, demonstrating no communication with the root canal lumen at subsequent sections. In another recent publication, Soros et al. (2008) claimed that VRF is mainly a matter of crack propagation and should not be considered as an instant phenomenon.

In the current experiment, the roots were surrounded with an impression material during filling in an attempt to mimic the bony socket that may change the force distribution around the tooth when external forces are used, namely lateral compaction (Lertchirakarn et al. 1999). However, the clinical situation is more complex because of the presence of the periodontal ligament that could further influence the distribution of forces. While some studies did not attempt to imitate bone or periodontal ligament (Onnink et al.

1994, Ribeiro et al. 2008), others have made various attempts to do so. For example, Wilcox et al. (1997) used a single layer of aluminium foil and then embedded the teeth in acrylic resin, while Lertchirakarn et al. (1999) covered the roots with silicone paste.

However, it seems that these attempts are insufficient to mimic the anatomical and biological aspects of tooth structure (Saw & Messer 1995) and could contribute to the introduction of artificial changes in force distribution themselves. Soros et al. (2008) stated that elastomeric materials are incapable of withstanding compaction forces in the way that the natural ligament does and that they may collapse under pressure. In agreement with the current findings, they highlight the significance of crack initiation and propagation in the evaluation of VRF formation rather than the actual appearance of a VRF as a result of a specific stress application.

The forces of extraction may also contribute to the observation of incomplete fractures. However, since most of the premolars selected had calculus and staining but no deep carious lesions, an assumption could be made that they were extracted for periodontal reasons with minimal trauma (Onnink et al. 1994).

This is further confirmed by the finding that unprepared root canals had no defects. The Storage medium used to keep the teeth was purified filtered water. This medium was previously recommended for investigations of human dentine (Strawn et al. 1996) as it causes the smallest changes in dentine over time.

System GT instruments have lands, a U-shaped cross section and a noncutting tip. The lands make the instruments passive and prevent canal

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transportation (Schirrmeister et al. 2006). This design increases the contact area with the canal wall as compared to cutting instruments devoid of lands such as the ProTaper system, and might increase friction and torque and thereby fracture risk (Blum et al.

1999). This may explain the significantly larger number of defects in the preparation-only group (Fig. 2). It will be interesting to study whether similar defects will be present after preparation with instruments having different designs. Furthermore, Gates Glidden drills were used during the preparation procedure, as they were shown to improve workingsafety, avoiding apical transportation and reducing working time (Bergmans et al. 2002). They, too, might be a contributing factor to the formation of root defects during preparation, through the action of the burs on dentine, and the excess removal of root structure resulting in weakening of the root (Pilo et al. 1998, Kuttler et al. 2004).

Little is known on the effects of ultrasonic irrigation on the root canal walls. Further studies should be conducted on the effect of these instruments on root dentine.

Conclusion Under the conditions of this ex vivo study, the use of System GT rotary files and Gates Glidden drills to prepare canals resulted in dentinal defects. The use of a passive compaction technique to fill the canals of extracted teeth significantly reduced the incidence of defects compared to lateral compaction. Clinicians should be aware of the potential damage risks during canal enlargement, preparation and some root filling procedures.

Acknowledgements Carlos Alexandre Souza Bier was supported by the Brazilian Agency Capes, Grants No. 2094/07.

The authors wish to thank Irene H.A. Aartman from the Department of Social Dentistry and Behavioral Sciences, ACTA, Amsterdam, the Netherlands for her help with the statistical interpretation of the results.

References Assif D, Nissan J, Gafni Y, Gordon M (2003) Assessment of the resistance to fracture of endodontically treated molars restored with amalgam. Journal of Prosthetic Dentistry 89, 462â&#x20AC;&#x201C;5.

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Bergmans L, Van Cleynenbreugel J, Beullens M, Wevers M, Van Meerbeek B, Lambrechts P (2002) Smooth flexible versus active tapered shaft design using NiTi rotary instruments. International Endodontic Journal 35, 820–8.

Blum JY, Cohen A, Machtou P, Micallef JP (1999) Analysis of forces developed during mechanical preparation of extracted teeth using Profile NiTi rotary instruments. International Endodontic Journal 32, 24–31.

Dalat DM, Spa˚ngberg LS (1994) Comparison of apical leakage in root canals obturated with various gutta percha techniques using a dye vacuum tracing method. Journal of Endodontics 20, 315–9.

Dang DA, Walton RE (1989) Vertical root fracture and root distortion: effect of spreader design. Journal of Endodontics 15, 294–301.

Hall MC, Clement DJ, Brent D, Walker WA (1996) A comparison of sealer placement techniques in curved canals.

Journal of Endodontics 22, 638–42.

Kishen A (2006) Mechanisms and risk factors for fracture predilection in endodontically treated teeth. Endodontic Topics 13, 57–83.

Kuttler S, McLean A, Dorn S, Fischzang A (2004) The impact of post space preparation with Gates-Glidden drills on residual dentin thickness in distal roots of mandibular molars. Journal of the American Dental Association 135, 903– 9.

Lertchirakarn V, Palamara JE, Messer HH (1999) Load and strain during lateral condensation and vertical root fracture.

Journal of Endodontics 25, 99–104.

Mayhew JT, Eleazer PD, Hnat WP (2000) Stress analysis of human tooth root using various root canal instruments.

Journal of Endodontics 26, 523–4.

Meister F Jr, Lommel TJ, Gerstein H (1980) Diagnosis and possible causes of vertical root fractures. Oral Surgery, Oral Medicine, and Oral Pathology 49, 243–53.

Obermayr G, Walton RE, Leary JM, Krell KV (1991) Vertical root fracture and relative deformation during obturation and post cementation. Journal of Prosthetic Dentistry 66, 181–7.

Onnink PA, Davis RD, Wayman BE (1994) An in vitro comparison of incomplete root fractures associated with three obturation techniques. Journal of Endodontics 20, 32–7.

Ozok AR, van der Sluis LW, Wu MK, Wesselink PR (2008) Sealing ability of a new polydimethylsiloxane-based root canal filling material. Journal of Endodontics 34, 204–7.

Pilo R, Corcino G, Tamse A (1998) Residual dentin thickness in mandibular premolars prepared with hand and rotatory instruments. Journal of Endodontics 24, 401–4.

Pitts DL, Matheny HE, Nicholls JI (1983) An in vitro study of spreader loads required to cause vertical root fracture during lateral condensation. Journal of Endodontics 9, 544– 50.

Ribeiro FC, Souza-Gabriel AE, Marchesan MA, Alfredo E, SilvaSousa YT, Sousa-Neto MD (2008) Influence of different

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endodontic filling materials on root fracture susceptibility.

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Sathorn C, Palamara JE, Messer HH (2005) A comparison of the effects of two canal preparation techniques on root fracture susceptibility and fracture pattern. Journal of Endodontics 31, 283–7.

Saw LH, Messer HH (1995) Root strains associated with different obturation techniques. Journal of Endodontics 21, 314–20.

Schirrmeister JF, Strohl C, Altenburger MJ, Wrbas KT, Hellwig E (2006) Shaping ability and safety of five different rotary nickel-titanium instruments compared with stainless steel hand instrumentation in simulated curved root canals. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontology 101, 807–13.

Shemesh H, van Soest G, Wu MK, Wesselink PR (2008) Diagnosis of vertical root fractures with optical coherence tomography. Journal of Endodontics 34, 739–42.

Sim TP, Knowles JC, Ng YL, Shelton J, Gulabivala K (2001) Effect of sodium hypochlorite on mechanical properties of dentine and tooth surface strain. International Endodontic Journal 34, 120–32. van der Sluis LW, Versluis M, Wu MK, Wesselink PR (2007) Passive ultrasonic irrigation of the root canal: a review of the literature. International Endodontic Journal 40, 415–26.

Soros C, Zinelis S, Lambrianidis T, Palaghias G (2008) Spreader load required for vertical root fracture during lateral compaction ex vivo: evaluation of periodontal simulation and fracture load information. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontology 106, e64–70.

Souza EM, Wu MK, Shemesh H, Bonetti-Filho I, Wesselink PR (2008) Comparability of the results of two leakage models.

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Strawn SE, White JM, Marshall GW, Gee L, Goodis HE, Marshall SJ (1996) Spectroscopic changes in human dentine exposed to various storage solutions–short term. Journal of Dentistry 24, 417–23.

Tamse A, Fuss Z, Lustig J, Kaplavi J (1999) An evaluation of endodontically treated vertically fractured teeth. Journal of Endodontics 25, 506–8.

Tidswell HE, Saunders EM, Saunders WP (1994) Assessment of coronal leakage in teeth root filled with gutta-percha and a glass ionomer root canal sealer. International Endodontic Journal 27, 208–12.

Wilcox LR, Roskelley C, Sutton T (1997) The relationship of root canal enlargement to finger-spreader induced vertical root fracture. Journal of Endodontics 23, 533–4.

Wu MK, van der Sluis LW, Wesselink PR (2004) Comparison of mandibular premolars and canines with respect to their resistance to vertical root fracture. Journal of Dentistry 32, 265–8.

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Basic Research—Technology

The Ability of Different Nickel-Titanium Rotary Instruments To Induce Dentinal Damage During Canal Preparation Carlos Alexandre Souza Bier, DMD,* Hagay Shemesh, DMD,† Mário Tanomaru-Filho, DDS, MSc, PhD,* Paul R. Wesselink, DDS, PhD,† and Min-Kai Wu, MD, MSD, PhD† Abstract The purpose of this study was to compare the incidence of dentinal defects (fractures and craze lines) after canal preparation with different nickel-titanium rotary files. Two hundred sixty mandibular premolars were selected. Forty teeth were left unprepared (n ⫽ 40). The other teeth were prepared either with manual Flexofiles (n ⫽ 20) or with different rotary files systems: ProTaper (Dentsply-Maillefer, Ballaigues, Switzerland), ProFile (Dentsply-Maillefer), SystemGT (Dentsply-Maillefer), or S-ApeX (FKG Dentaire, La Chaux-de-Fonds, Switzerland) (n ⫽ 50 each). Roots were then sectioned 3, 6, and 9 mm from the apex and observed under a microscope. The presence of dentinal defects was noted.

There was a significant difference in the appearance of defects between the groups (p ⬍ 0.05). No defects were found in the unprepared roots and those prepared with hand files and S-ApeX. ProTaper, ProFile, and GT preparations resulted in dentinal defects in 16%, 8%, and 4% of teeth, respectively. Some endodontic preparation methods might damage the root and induce dentinal defects. (J Endod 2009;35:236 –238)

Key Words Craze lines, dentinal defects, nickel-titanium instruments, root canal preparation

From the *Department of Restorative Dentistry, Araraquara Dental School, São Paulo State University, UNESP, Araraquara, SP, Brazil; and †Department of Cariology, Endodontology, Pedodontology Academic Centre of Dentistry Amsterdam, the Netherlands.

Carlos Alexandre Souza Bier was supported by the Brazilian agency Capes, grant no. 2094/07.

Address requests for reprints to Dr Hagay Shemesh, ACTA, CEP, Louwesweg 1, 1066 EA Amsterdam, The Netherlands.

E-mail address: hshemesh@acta.nl.

0099-2399/$0 - see front matter Copyright © 2008 American Association of Endodontists. doi:10.1016/j.joen.2008.10.021

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T

he goals of endodontic instrumentation are to completely remove microorganisms, debris, and tissue by enlarging the canal diameter and create a canal form that allows a proper seal. Complications such as transportation, ledge formation, and perforation are well documented (1, 2). However, preparation procedures could also damage the root dentin resulting in fractures or craze lines (3). Wilcox et al. (3) examined teeth after hand preparation and lateral compaction of gutta-percha and sealer. Teeth not presenting vertical root fractures (VRFs) were retreated by removing the root canal filling and further enlarging the canal. No VRFs were observed after the initial preparation, whereas numerous fractures had occurred after further enlargement. All roots that eventually fractured had previously shown craze lines. They concluded that the more dentin removed the more chance for a fracture. The observation that all teeth presented craze lines led the authors to speculate that these could later propagate into VRF if the tooth is subjected to repeated stresses from endodontic or restorative procedures.

Indeed, evidence of recent years concentrate on the findings that VRFs are probably caused by a propagation of smaller, less pronounced defects and not by the force practiced during preparation or obturation (4, 5).

An increasing number of rotary nickel-titanium (NiTi) file systems have been marketed by various manufacturers. These systems differ from one another in the design of the cutting blades, body taper, and tip configuration. Despite the obvious clinical advantages of these techniques over hand instrumentation, the influence of the design of the cutting blades is still controversial (6, 7) and could generate increased friction and stresses within the root canal (8). Rotary instrumentation requires less time to prepare canals as compared with hand instrumentation but result in significantly more rotations of the instruments inside the canal (9). This may cause more friction between the files and the canal walls.

The goal of this ex vivo study was to compare the damage observed in the root dentin after endodontic preparations with different NiTi rotary files systems.

Materials and Methods Two hundred sixty extracted lower premolars were selected and stored in purified filtered water. This storage medium causes the smallest changes in dentin over time and was previously recommended for investigations of human dentin (10). The coronal portion of all teeth was removed by using an Isomet 11–1180 low-speed saw (Buehler Ltd, Evanston, IL) with water cooling, leaving roots approximately 16 mm in length. All roots were observed with a stereomicroscope under 12⫻ magnification (Zeiss Stemi SV6, Jena, Germany) to exclude cracks. Forty teeth were left unprepared and served as control group A. Twenty teeth were prepared with hand files (K-Flexofiles; DentsplyMaillefer, Ballaigues, Switzerland) using balance force crown down to file 40 and step-back 1-mm increments with Flexofiles #45 to 80 (Dentsply-Maillefer), resulting in a preparation with a taper of about 0.05. These teeth formed control group B. The remaining 200 teeth were randomly divided into four groups of 50 teeth each. Canal patency was established with a #20 K-Flexofile (Dentsply Maillefer). Thereafter, canal preparation followed with rotary files according to the relevant group (1– 4) using a torque-control motor (ATR; Technika, Pistoia, Italy) and at the torque and speed recommended by the manufacturer for the specific system used.

In group 1, the following sequence of ProTaper rotary files (Dentsply Maillefer) was used at 300 rpm to prepare the canals; an SX file was used to enlarge the coronal

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Basic Research—Technology portion of the canal, and then all files were used to working length: S1¡ S2¡ F1¡ F2¡ F3. The last file used was F4, which corresponds to file 40 with a taper 0.06 at the apical area.

In group 2, canal preparation with SystemGT files (Dentsply Maillefer) at 300 rpm using a crown-down technique. Files 50/0.12 and 35/0.12 were used to enlarge the canal opening, and GT series 30 and 40 taper 0.1, 0.08, 0.06, 0.04 were used consequently to prepare the canal till GT file 40/0.06 reached 1 mm short of the apical foramen.

In group 3, ProFile rotary NiTi files (Dentsply Maillefer) at 300 rpm were used in a crown-down sequence. ProFile Orifice shapers 2 and 3 were used to preflare the canal opening, and the preparation ended when a 40/0.06 file reached 1 mm short of the apex.

In group 4, S-ApeX rotary files (FKG Dentaire, La Chaux-de-Fonds, Switzerland) sizes 15 to 60 were used at a speed of 600 rpm. The manufacturer’s instructions were followed using the full sequence of 6 files available at the working length. This system has an inverted taper, and the preparation may result in a nontapered form.

In all experimental and control groups, each canal was irrigated with a freshly prepared 2% solution of sodium hypochlorite (NaOCl) between each instrument during the preparation procedure using a syringe and a 27-G needle. Twelve milliliters of NaOCl solution was used for each root. After the completion of instrumentation, passive ultrasonic irrigation was performed with an Irrisafe 20/21 file (Satelec, Merinac Cedex, France) in order to efficiently clean the canals and remove any debris still present (11). After completion of the procedure, canals were rinsed with 2 mL distilled water. All roots were kept moist in distilled water throughout the experimental procedures.

Sectioning and Microscopic Observations All roots were cut horizontally at 3, 6, and 9 mm from the apex with a low-speed saw under water cooling (Leica SP1600, Wetzlar, Germany). Slices were then viewed through a stereomicroscope (Zeiss Stemi SV6, Carl Zeiss, Jena, Germany) using a cold light source (KL 2500 LCD, Carl Zeiss). The appearance of dentinal defects was registered by the author (CASB), after which pictures were taken with a camera (Axio Cam, Carl Zeiss) at a magnification of ⫻12. The pictures were then blindly inspected by the second author (HS). In four cases out of a total of 780 slices (0.5%), there was a discrepancy in the observations, and a consensus was reached after inspecting the slices again. In order to avoid confusing definitions of root fractures, three distinguished categories were made: “no defect,” “fracture,” and “other defects” (12). “No defect” was defined as root dentin devoid of any lines or cracks where both the external surface of the root and the internal root canal wall did not present any evident defects. “Fracture” was defined as a line extending from the root canal space all the way to the outer surface of the root (3). “Other defects” were defined as all other lines observed that did not seem to extend from the root canal to the outer root surface (eg, a craze line, a line extending from the outer surface into the dentin but does not reach the canal lumen (3), or a partial crack, a line extending from the canal walls into the dentin without reaching the outer surface).

Statistical Analysis Roots were classified as “defected” if at least one of three sections showed either a craze line, partial crack, or a fracture. Results were expressed as the number and percentage of defected roots in each group. A chi-square test was performed to compare the appearance of defected roots between the experimental groups by using the SPSS/PC version 15 (SPSS Inc, Chicago, IL).The level of significance was set at ␣ ⫽ 0.05.

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Figure 1. The number of teeth and percentage showing defect.

Results No complete fractures were observed in any of the samples. Control groups A (unprepared canals) and B (hand preparation) showed no defected roots. Craze lines and partial cracks (“other defects”) were found in the SystemGT, ProFile, and ProTaper groups, whereas no defects were observed in canals prepared with S-Apex files (Fig. 1). The difference between the experimental groups in the appearance of defects was significant (chi-square test, p ⫽ 0.001).

Discussion Recent ex vivo studies suggest that VRF is probably not an instant phenomenon but rather a result of gradual diminution of root structure (4, 5) .The current results could confirm that fractures did not occur immediately after canal preparation. However, craze lines occurred in 4% to 16%, and these may develop into fractures during retreatment or after long-term functional stresses like chewing (3). This is in agreement with Onnink et al. (13), who were the first to report dentinal defects as a consequence of canal preparation but only found small defects entirely within dentin that did not communicate with the canal wall. Less pronounced dentinal defects like craze lines were observed in the current study. Considering the crucial clinical importance of VRF and its determinant effect on tooth survival, even a small percentage of damaged teeth could be of clinical importance.

Ultrasonic irrigation was used in order to effectively clean the canal walls (11). However, ultrasonic action can also result in rough canal walls (14) and cause fractures after root-end preparations (15).

In the current experiment, ultrasonic irrigation was performed in all groups (11). Because all teeth were irrigated following the same protocol and roots prepared with hand files and S-ApeX files did not show any dentinal defects, the conclusion that the ultrasonic irrigation performed in this study did not contribute to the appearance of dentinal defects seems justified.

Sawing action could also result in dentinal defects. However, because both the controls and the S-ApeX groups did not show any defect, we may conclude that the defects seen were a result of preparation procedures.

The only rotary file system among those used in this study that did not show any dentin damage is S-ApeX. A literature search revealed no previous studies regarding this file system. It is the only system available with an inverted taper (Fig. 2) and may result in a parallel preparation similar to the previously described LightSpeed system (LightSpeed Technology, Inc, San Antonio, TX) (16).

The taper of the preparation and the files could be a contributing factor in the generation of dentinal defects. Wilcox et al. (3) concluded that the more root dentin that is removed the more likely a root is to fracture. However, in the present study, a uniformed tapered preparation (0.05– 0.06) was attempted in all groups except for the S-ApeX

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tistry Amsterdam, The Netherlands, for his clinical expertise with S-ApeX files.

References

Figure 2. The S-Apex file has an inverted taper.

preparation, which is not tapered at all. The observation that all groups prepared with rotary NiTi files showed various degrees of damage except for the nontapered group supports the idea that tapered files may generate an increased stress on the dentin wall. This observation is supported by Sathorn et al. (17) who concluded that by maintaining the canal size as small as practical, a reduction in fracture susceptibility could be expected.

The amount of material removed from the root canal depends on the shape of the rotary instrument and the penetration depth in the canal. Because the roots prepared with rotary files that had a taper of at least 0.06 in this study showed defects, it should be realized that these instruments remove more apical dentin as compared with hand files that have a taper of 0.02. It is noteworthy that ProTaper file F3 has a large apical taper of 0.09 (18), which could explain the higher incidence of damage observed in the ProTaper group as compared with the other tapered rotary files. Furthermore, significantly more rotations in the canal are necessary to complete a preparation with rotary NiTi files as compared with hand files (9). This, in itself, may contribute to the formation of dentinal defects.

Some of the defects seen did not connect with the pulp space. Wilcox et al. (3) speculated that the stresses generated from inside the root canal are transmitted through the root to the surface where they overcome the bonds holding the dentin together. Onnink et al. (13) speculated that a fracture contained within the dentin in one section could communicate with the canal space in an adjacent section. This was recently supported by nondestructive observations of dentinal defects induced in extracted teeth and viewed with optical coherence tomography (5).

Under the tested conditions and within the limitations of this ex vivo investigation, it may be concluded that the use of some rotary NiTi instruments could result in an increased chance for dentinal defects.

Acknowledgments The authors thank Wim van der Borden, DDS, Department of Cariology Endodontology Pedodontology, Academic Centre of Den-

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1. Schilder H. Cleaning and shaping the root canal. Dent Clin North Am 1974;18:269 –96.

2. Pettiette MT, Metzger Z, Phillips C, Trope M. Endodontic complications of root canal therapy performed by dental students with stainless-steel K-files and nickel-titanium hand files. J Endod 1999;25:230 – 4.

3. Wilcox LR, Roskelley C, Sutton T. The relationship of root canal enlargement to finger-spreader induced vertical root fracture. J Endod 1997;23:533– 4.

4. Soros C, Zinelis S, Lambrianidis T, Palaghias G. Spreader load required for vertical root fracture during lateral compaction ex vivo: evaluation of periodontal simulation and fracture load information. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2008;106:e64 –70.

5. Shemesh H, van Soest G, Wu MK, Wesselink PR. Diagnosis of vertical root fractures with optical coherence tomography. J Endod 2008;34:739 – 42.

6. Peters OA.Current challenges and concepts in the preparation of root canal systems: a review. J Endod 2004;30:559 – 67.

7. Bergmans L, Van Cleynenbreugel J, Beullens M, Wevers M, Van Meerbeek B, Lambrechts P. Smooth flexible versus active tapered shaft design using NiTi rotary instruments. Int Endod J 2002;35:820 – 8.

8. Blum JY, Machtou P, Ruddle C, Micallef JP.Analysis of mechanical preparations in extracted teeth using ProTaper rotary instruments: value of the safety quotient. J Endod 2003;29:567–75.

9. Pasqualini D, Scotti N, Tamagnone L, Ellena F, Berutti E. Hand-operated and rotary ProTaper instruments: a comparison of working time and number of rotations in simulated root canals. J Endod 2008;34:314 –7.

10. Strawn SE, White JM, Marshall GW, Gee L, Goodis HE, Marshall SJ. Spectroscopic changes in human dentine exposed to various storage solutions-short term. J Dent 1996;24:417–23.

11. van der Sluis LW, Versluis M, Wu MK, Wesselink PR. Passive ultrasonic irrigation of the root canal: a review of the literature. Int Endod J 2007;40:415–26.

12. Shemesh H, Bier CA, Wu MK, Tanomaru Filho M, Wesselink PR. The effects of root preparation and obturation on the incidence of dentinal defects. Int Endod J (in press).

13. Onnink PA, Davis RD, Wayman BE. An in vitro comparison of incomplete root fractures associated with three obturation techniques. J Endod 1994;20:32–7.

14. Stock CJ. Current status of the use of ultrasound in endodontics. Int Dent J 1991;41:175– 82.

15. Navarre SW, Steiman HR. Root-end fracture during retropreparation: a comparison between zirconium nitride-coated and stainless steel microsurgical ultrasonic instruments. J Endod 2002;28:330 –2.

16. Thompson SA, Dummer PM. Shaping ability of Lightspeed rotary nickel-titanium instruments in simulated root canals. Part 1. J Endod 1997;23:698 –702.

17. Sathorn C, Palamara, Messer HH. A comparison of the effects of two canal preparation techniques on root fracture susceptibility and fracture pattern. J Endod 2005;31:283–7.

18. West JD. Introduction of a new rotary endodontic system: progressively tapering files.

Dent Today 2001;20:50 –2, 54 –7.

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Chapter V Summary and conclusions Samenvatting en conclusies

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Summary and Conclusions New in vitro and ex vivo methodologies were presented in this thesis that measure, image and explore the root canal walls and related interfaces.

Numerous experiments were conducted and could lead to a better understanding of the influence of endodontic procedures on the root canal wall and vice versa. This will help to improve current practices that seem to fail in providing a reliable, predictable outcome.

In chapter II Different experiments were presented using the glucose penetration model. The ability of this model to detect leakage patterns through various materials, set ups and conditions was tested. The following could be concluded: - The glucose penetration model was more sensitive in detecting leakage along the root canal filling as compared to the fluid transport model.

- Removing the smear layer before filling did not improve the sealing of the apical 4 mm of filling.

- Resilon, a recently introduced resin type filling material, allowed more glucose penetration but the same amount of fluid transport as gutta percha root fillings in the apical 4 mm of the root, while no difference in leakage was detected with both models when the coronal 9 mm of the filling was tested.

- When glucose penetration and fluid transport were used to measure the leakage through coronal root structures no leakage was detected. This confirms the assumption that root structures do not allow penetration of water or glucose through them.

- Root fillings with gutta percha and AH26 using the warm vertical compaction technique sealed the root canal better when passive ultrasonic irrigation had been used.

- Portland cement, MTA, Ca(OH)2 and Sealer 26 react with glucose solution. This may result in less detectable glucose in the penetration test.

Therefore, these materials should not be evaluated for sealing ability with the glucose leakage model.

In chapter III New endodontic applications for novel imaging techniques like ultrasound scan and optical coherence tomography were suggested.

- Ultrasound scan could generate three dimensional structural imaging of streptococcus mutans biofilms of various thicknesses and on different substrates without damaging the biofilm layer in a quick and easy manner and can therefore be used to evaluate biofilms longitudinally as a function of time.

- Optical coherence tomography proved to be a reliable method to image root canals and root dentin in a nondestructive way and without using ionized radiation. This technique holds promise for full in vivo endodontic imaging. Furthermore, it is a promising non destructive imaging method for the diagnosis of vertical root fractures. Both the sensitivity and specificity of this technique to diagnose vertical root fractures are high and a tendency for even higher specificity was demonstrated in canals where the smear layer was first removed.

In chapter IV the formation and incidence of dentinal defects in the root canal wall after different preparation and filling procedures was evaluated. It was concluded that some procedures cause more damage than others and that caution should be exercised with the use of rotary Ni-Ti files and lateral compaction of gutta percha.

- Root canal preparation and filling of extracted teeth created dentin defects such as fractures, craze lines and incomplete cracks. Canals filled with the lateral compaction technique showed more defects than those filled with non compaction methods.

- Some endodontic preparation methods might damage the root and induce dentinal defects.

Rotary Ni-Ti instruments damaged the teeth more than hand-filing. The new S-Apex system was the only rotary system that did not result in dentinal defects probably due to the inverted taper design.

The techniques described in this thesis could serve as a promising tool for future research: New knowledge on the different aspects of the root canal wall will hopefully help to improve the clinical outcomes and predictability of the endodontic treatment.

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Samenvatting en conclusies In dit proefschrift werden nieuwe in vitro en ex vivo onderzoekmethodes gepresenteerd die de wanden van het wortelkanaal en de eraan gerelateerde raakvlakken kunnen meten, visualiseren en verkennen. Talrijke experimenten werden verricht die zouden kunnen leiden naar een beter begrip van de invloed van endodontische behandelingen op de wortelkanaalwand en vice versa. Mogelijk kunnen hierdoor bestaande procedures die nog geen betrouwbaar en voorspelbaar resultaat bieden, verbeteren.

In hoofdstuk II werden verschillende experimenten gepresenteerd waarbij het glucose penetratie model werd gebruikt. De capaciteit van het model om lekkagepatronen te herkennen bij verschillende materialen en opstellingen onder verschillende omstandigheden, werd getest. De conclusies waren als volgt: - Het glucose penetratiemodel had een grotere sensitiviteit voor het opsporen van lekkage langs wortelkanaalvullingen dan het vloeistoftransport model.

- Het verwijderen van de smeerlaag voorafgaand aan het vullen, leidde niet tot verbetering van de afsluiting op 4 mm afstand van de wortelpunt.

- Resilon, een kunsthars dat recent geïntroduceerd is als vulmateriaal, vertoonde tussen 0 en 4 mm gemeten vanaf de apex, meer glucose penetratie dan Gutta Percha. Bij het vloeistoftransport model werd bij zowel Resilon als gutta percha een gelijke hoeveelheid lekkage waargenomen. Bij 0-9 mm gemeten vanaf coronaal werd er echter geen verschil waargenomen tussen beide testopstellingen.

- Bij het testen van lekkage door coronale wortelstructuren met zowel het glucose penetratie model als het vloeistoftransport model werd geen lekkage waargenomen. Dit bevestigt de aanname dat er geen water of glucose door wortelstructuren kan penetreren.

- Wortelkanaal vullingen van gutta percha met AH26, aangebracht door middel van warme verticale compactie, sluiten het kanaal beter af wanneer eerst passieve ultrasone irrigatie is toegepast.

- Portlandcement, MTA, Ca(OH)2 en Sealer 26 reageren met glucose oplossingen. Dit kan ertoe leiden dat er minder glucose wordt waargenomen in de penetratie test. Evaluatie van het afsluitend vermogen van deze materialen kan daarom niet worden onderzocht met het glucose lekkage model.

In hoofdstuk III werden nieuwe endodontische toepassingen geïntroduceerd voor moderne

beeldvormende technieken zoals ultrageluidscans en optical coherence tomografie.

- Met ultrageluidscans bleek het mogelijk om snel en gemakkelijk een driedimensionaal structureel beeld streptococcus mutans biofilms van verschillende diktes en op verschillende substraten te maken, zonder de driedimensionale structuur en vitaliteit van de biofilm te beschadigen. Dit maakt deze methode geschikt om biofilms longitudinaal te vervolgen.

- Optical coherence tomografie bleek een betrouwbare methode om wortelkanalen en worteldentine weer te geven zonder deze te beschadigen, en zonder ioniserende straling te gebruiken. De techniek heeft het vermogen in zich om een volledig endodontisch beeld te geven in vivo.

Ook kan deze vorm van tomografie gebruikt worden om verticale wortelfracturen te diagnosticeren zonder het element of omringende structuren te beschadigen.

De sensitiviteit en specificiteit hierbij is hoog, en als eerst de smeerlaag wordt verwijderd is er een tendens naar een nog grotere specificiteit.

In hoofdstuk IV werd het ontstaan en de incidentie van dentinedefecten op de wortelkanaal wand ten gevolge van verschillende preparatie en vultechnieken, geëvalueerd. Er werd geconcludeerd dat de ene techniek meer schade veroorzaakt dan de andere, zo is voorzichtigheid geboden bij het gebruik van roterende Ni-Ti vijlen en laterale compactie van gutta percha.

- Het prepareren en vullen van wortelkanalen bij geëxtraheerde elementen veroorzaakten dentine defecten zoals fracturen, crazelijnen en onvolledige barsten. Kanalen gevuld door middel de laterale compactie techniek vertoonden meer defecten dan kanalen die met de non-compactie techniek werden gevuld.

-Sommige endodontische preparatietechnieken kunnen mogelijk de wortel beschadigen en dentine defecten veroorzaken. Roterende Ni-Ti instrumenten beschadigen het element meer dan handvijlen. Het nieuwe S-apex systeem is het enige roterende systeem dat geen dentine defecten liet zien, waarschijnlijk ten gevolge van het omgekeerde taper ontwerp.

De beschreven onderzoektechnieken bieden een enorme kans voor de toekomst: Nieuwe kennis over de verschillende aspecten van de wand van het wortelkanaal kan er hopelijk toe bijdragen dat de klinische resultaten en de voorspelbaarheid van de endodontische behandeling zullen verbeteren.

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Acknowledgements Min Kai Wu, Paul Wesselink and Luc van der Sluis taught me a lot during the last years. They showed me how to read an article and how to write one, how to design an experiment and how to abandon one, how to present my ideas and how to conceal them, and especially, how to ask a question and how to try and answer one.

Rifat Ozok For his help with almost every question, dilemma or demand, and for his friendship and patience.

The laboratory staff and especially Marc Buijs, Rob Exterkate and Michel Hoogenkamp - what a professional, serious and reliable team you are.

Thanks for your instructions, remarks and criticism- I learned a lot from all of you.

Irene Aartman for helping me with the statistics.

Annemarie Verhoef for het advice on teaching, and for the Dutch translation…

Marijke Voorn - for helping me with my Dutch, from the very beginning, with the ordering of materials and instruments and for her wise (and often controversial) remarks during lunch…

To all the other members of the department, and especially Linda Peters for their advise and support.

David Goertz and Gijs van Soest from the Erasmus MC in Rotterdam (David is now back to his native Canada) and Paul Zaslansky from the Max Planck institute in Potsdam, Germany for

extending my horizons to unknown territories which will end up with a big breakthrough.

Erick Souza and Alexandre Bier from Brazil for their excellent work and enthusiasm.

Special thanks to the students I worked with and to the post-graduate students (TEO’s) for their critical questions and input.

The staff of the Verwijspraktijk in Amsterdam for being much more than my main source of income, and especially to Nicolien, Abe, Erwin, Rian, Jan, Tjebbe, Peter, Gordon. And Els and Andreas –also for agreeing to be my Paranymphs.

Tineke Looman: for the valuable advice, friendship and honest critic.

Anne Mieke Eggenkamp for the enthusiasm, professionalism and time. What a boost to my thesis!

Piet Dinkla- for the website and for your patience.

And Wijb- you already know I don't like to get sentimental, and you often heard what I think about these (too) long “thank-you” sections, so I am NOT going to thank you on these pages, but in a more personal way.

For more acknowledgements, links and contacts please go to www. shemesh.nl

HAGAY SHEMESH was born in Israel and immigrated to the Netherlands in 2002.

He lives in Amsterdam and works at the Academic Centre for Dentistry Amsterdam (ACTA) where he conducted this PhD thesis research. He also works as an endodontist in a private practice.

For more on this thesis, complete up-to-date list of publications, abstracts and presentations, curriculum vitae and additional information, please go to: www.shemesh.nl