Journal of Osseointegration by Ariesdue srl

JOURNAL of OSSEOINTEGRATION

ARTHUR BELÉM NOVAES JR.1, RAQUEL REZENDE MARTINS DE BARROS2, VULA PAPALEXIOU3, ADRIANA LUISA GONÇALVES DE ALMEIDA4 1

2 3 4

Professor and Chairman of Periodontology, Department of Oral Surgery and Periodontology, School of Dentistry of Ribeirão Preto of the University of São Paulo, SP, Brazil Post-doctoral student, Department of Oral Surgery and Periodontology, School of Dentistry of Ribeirão Preto of the University of São Paulo, SP, Brazil Professor of Periodontology, Center of Biologic and Health Science, School of Dentistry, Catholic Pontifical University, PR, Brazil. Graduated in Biology and Microscopic and Image Analysis Laboratory Technician of the Department of Oral Surgery and Periodontology, School of Dentistry of Ribeirão Preto of the University of São Paulo, SP, Brazil

Buccal bone loss after immediate implantation can be reduced by the flapless approach ABSTRACT Aim The aim of this study was to evaluate the buccal bone remodeling after immediate implantation with flap or flapless approach. Material and Methods The mandibular bilateral premolars of 3 dogs were extracted and immediately three implants were placed in both hemi-arches of each dog. Randomly, one hemi-arch was treated with the flapless approach, while in the contra lateral hemi-arch tooth extractions and implant placement were done after mucoperiosteal flap elevation. Non-submerged healing of 12 weeks was provided for both groups. Histomorphometric analysis was done to compare buccal and lingual bone height loss, bone density and bone-to-implant contact in the groups. Fluorescence analysis was performed to investigate the dynamic of bone remodeling in the different groups. Results There was a significant association between the surgical flap and the extent of bone resorption around immediate implants. The loss of buccal bone height was significantly lower in the flapless group when compared to the flap group (0.98 mm x 2.14 mm, respectively, p<0.05). The coronal and apical buccal bone densities of the flap group were significantly higher when compared to the lingual components, showing anatomical differences between the bone plates. Fluorescence analysis showed no major differences in bone healing between the flap and flapless groups, supporting that the higher loss of buccal bone height is linked to the anatomic characteristics of this plate and to the negative influence of the detachment of the periosteum in immediate implant therapy. Conclusion The flapless approach for immediate post-extraction implants reduces the buccal bone height loss.

KEY WORDS Animal model; Bone resorption; Flapless surgery; Immediate implants.

October 2011; 3(3)

INTRODUCTION The immediate implant placement after tooth extraction has been reported to be as predictable as placing implants into healed sites (1); but with advantages such as reduced number of surgical procedures (2-8), reduction of the overall treatment time and also a possible preservation of the morphological contour of the ridges (3, 6). However, in regard to this last consideration, some studies in animals have shown contradictory results, describing pronounced resorption of the buccal, and to some extent, the lingual bone plates after implant placement in fresh extraction sockets (9, 10). Novaes Jr. (11) showed that the morphological and vascular characteristics of the bone crests may have an important impact on the bone remodeling process that occurs immediately after implantation. Through a histological analysis of specimens sectioned in buccal-lingual direction, they observed that the width of both bone plates increased from the coronal third to the most apical third, being the buccal plates always significantly thinner when compared to the lingual bone plates. More specifically, they described the coronal portion of the buccal bone plate as extremely delicate, which is in agreement with previous observations (10, 12), and this characteristic may explain almost in part why the buccal bone plates are more easily resorbed. They showed some slides where the buccal bone plates appeared without or with very few marrow spaces. In fact, the buccal bone plates were constituted, in a statistically significant way, by a higher cortical bone when compared to the lingual bone plates, in first and second coronal thirds; this bone density analysis was obtained by the subtraction of the bone marrow area from the total bone area. Interestingly, they also evidenced in some histological observations, marrow 45

JOURNAL of OSSEOINTEGRATION >

Belém Novaes A. Jr et al.

spaces in direct contact to the periosteum in the buccal bone plate, sustaining the hypothesis that one of the main functions of the periosteum and periodontal ligament blood vessels is to supply nutrients and cells to the alveolar bone (13). Conventionally, immediate implantation surgeries give emphasis to some important precautions such as less traumatic tooth extraction and implant primary stability, and are usually done with sulcular incisions and mucoperiosteal flap elevation. However, it is known that the displacement of the periosteum and alveolar bone denudement result in an acute inflammatory response and consequently in bone resorption (14-16). Osteoclasts were observed on surgical exposed alveolar bone areas during the first two weeks of wound healing (17). Besides, a relevant information to consider is that, although a pronounced loss of the buccal bone wall were frequently described after mucoperiosteal surgeries applied in periodontal treatment of dentate areas, the same was not observed on the thicker lingual wall (16, 18, 19). Kim et al. (20) compared the vascularity of periimplant mucosa between flap and flapless implant surgeries in a dog model and showed that the soft tissue around implants in flapless sites appeared to be free from signs of inflammation, while approximately half of the implants in the flap sites exhibited a surrounding edematous tissue that bled when gently probed. Additionally, the number of vessels observed was 51.4 ± 9.2 in the flapless group and 38.2 ± 8.1 in the flap group, and this difference was statistically significant. Based on these findings, they suggested that the more richly vascularized peri-implant mucosa provided by the flapless procedure is directly related to an increased blood supply around the implant, which may strengthen the resistance to inflammation. The purpose of the present study was to evaluate if the flapless approach can interfere in the buccal bone remodeling after immediate implantation in mongrel dogs, analyzing the histomorphometric parameters of bone height loss, bone density and bone-to-implant contact after 12 weeks of healing and also the dynamic of bone remodeling in four different times along this period through fluorescence analysis.

animals presented intact maxillas, no general occlusal trauma, and no oral viral or fungal lesions and were in good general health, with no systemic involvement as determined by a veterinarian following clinical examination. Food was withheld in the night preceding surgeries. The animals were pre-anaesthetized with acepromazine 0,2% - 0,05 mg/kg IM. After that an intravenous catheter was placed in the foreleg for induction with thiopental 2,5% - 5 a 8 mg/Kg IV. Animals were then moved to the operating room and maintained on gas anesthesia (1–2% isoflurane/O2 to effect). Conventional dental infiltration anesthesia was used at the surgical sites. The animals received a slow constant rate infusion of lactated Ringer’s solution (10–20 ml/kg/h IV) to maintain hydration during surgery. These procedures were made and accompanied by a veterinarian. The surgical procedures for the mandibular premolar extractions were done in each hemi-arch of each dog. Randomly, one of the sides was treated with the flapless approach (experimental group) (fig. 1A), while the contralateral side was treated with mucoperiosteal flaps (fig. 1B). The teeth were sectioned in a bucco-lingual direction at the bifurcation so that the roots could be individually extracted, without damaging the bony walls, using a periotome. After alveolar debridement, three Ankylos implants measuring 3.3 x 9.5 mm (diameter and length, respectively) were immediately inserted in the mesial socket of the correspondent three pre-molars in both hemi-arches of each dog, totaling 18 implants in the experiment. The implants were placed at the level of bone crest and a gap of 1mm from the buccal cortical wall to the implant was always left (fig. 2) without invading the lingual bone plate with

MATERIALS AND METHODS Surgical procedure The study protocol was approved by the Institution’s Animal Research Committee of the School of Dentistry of Ribeirão Preto- University of São Paulo and was performed in three young adult male mongrel dogs that weighed approximately 16 kg. The 46

Fig. 1 One random hemi-arch was treated with the flapless approach (A) and the opposite hemi-arch was treated with a mucoperiosteal flap (B). October 2011; 3(3)

JOURNAL of OSSEOINTEGRATION Buccal bone loss after a flapless approach

the drill or the implant. Subsequently, healing caps of 1.5 mm of height were adjusted in order to provide a non-submerged healing in both groups. The flaps of the control group were repositioned and sutured with absorbable sutures (Vicryl, Ethicon, Inc., Johnson & Johnson Company, São José dos Campos-SP, Brasil), while the soft tissues were accommodated and then sutured in the experimental group. No grafting materials were used in the gaps between the buccal plates and the implants. The animals received painkillers and antiinflammatory agents. A broad spectrum antibiotic (penicillin and streptomycin 20,000 IU; 1.0 g/10 kg IM) was administered immediately post-surgery and re-dosed after 4 days. The animals were maintained on a soft diet for 14 days when the sutures were removed. The healing was evaluated weekly and plaque control was maintained by flushing the oral cavity with chlorhexidine gluconate. The remained teeth were cleaned monthly with ultrasonic points and all implants remained non-submerged during the experimental period. During the healing period fluorescence bone markers were administered (21) to observe the dynamics of bone formation. One week after implant placement,

calcein green (75 mg /Kg body weight-Sigma Chemical Co., St Louis, MO, USA) was intravenously administered; at the second week, it was administered 300 mg of red alizarin S/Kg body weight (Sigma); after 4 weeks it was administered 150 mg oxytetracyclin HCl/Kg body weight (Sigma); and finally after 12 weeks 75 mg calcein blue/Kg body weight (Sigma) were also administered. All dyes were prepared immediately before use with 2% sodium bicarbonate or saline. After preparation, pH was adjusted to 7.4 and the solution was filtered through a 0.45 Ìm filter (Schleider & Schuell GmbH, Dassel, Germany). Each dog received a total dose of 3 ml.

Histological processing The animals were sedated and then sacrificed with an overdose of thiopental twelve weeks after implant placement. The hemi-mandibles were removed, dissected and fixed in 4% phosphate-buffered formalin pH 7, for 10 days, and transferred to a solution of 70% ethanol until processing. The specimens were dehydrated in increasing concentrations of alcohol up to 100%, infiltrated and embedded in LR White resin (London Resin Company, Berkshire, England), and hard-sectioned in buccolingual direction using the technique described by Donath & Breuner (22). The most central sections were stained with Stevenel’s blue and Alizarin red S for histometric analysis using optic microscopy.

Histomorphometric analysis

Fig. 2 The implants were immediately inserted in the mesial alveolus of the correspondent extracted pre-molars in both hemi-arches of each dog. A jumping gap of 1mm from the buccal cortical wall to the implant was always left. (A) Image representative of the flapless group and (B) image representative of the flap group.. October 2011; 3(3)

Longitudinal buccal-lingual histological sections from each implant were captured through a video camera Leica DC 300F (Leica Microsystems GmbH, Nussloch, Germany) joined to a stereomicroscope Leica MZFL III (Leica Microsystems GmbH, Nussloch, Germany). The images were analyzed through the Image J program (National Institutes of Health, Bethesda,USA). The buccal bone wall resorption was determined in relation to the lingual bone wall as a linear measurement (relative measurement) (Fig. 3, 4). A horizontal imaginary line was drawn in order to evidence the height of the lingual bone plate, and then the measurement of the buccal bone wall resorption was obtained vertically from that line to the peak of the buccal bone plate. The buccal and lingual bone plates were also measured from the shoulder of the implant to the first bone-to-implant contact (absolute measurement). The percentages of bone-to-implant contact (BIC) were calculated throughout the implant perimeter, from the first coronal bone-to-implant contact, considering the mineralized bone in direct contact with the implant surface. The bone density was determined within two rectangles, one of them adjacent to the implant surface (BDA), and the other as mirror image of the first, but distant to the implant surface (BDD). This 47

JOURNAL of OSSEOINTEGRATION >

Belém Novaes A. Jr et al.

Fluorescence microscopic images were longitudinally captured from each implant through a video camera Leica DC 300F (Leica Microsystems GmbH, Nussloch, Germany) joined to a stereomicroscope Leica MZFL III (Leica Microsystems GmbH, Nussloch, Germany), using appropriated barrier filters. The filters of wavelengths used was I3 for calcein green that has

an excitation level between 450-490 nm, N2-1 for red alizarin S that has an excitation level between 515-560 nm, D for oxytetracyclin HCl that has an excitation level between 355-425 nm and A for calcein blue that has an excitation level between 340-380 nm. All the images were adjusted and analyzed through the Image J program (National Institutes of Health, Bethesda, USA) to determine the percentages of bone marked. The bone marked was determined in two different positions along the implants, at coronal and apical levels in both buccal and lingual sides, using the same pre-determined rectangle for all the specimens (fig. 5, 6). The quantity of bone marked represented the percentages of fluorescent bone in relation to the total area. A single examiner, with no knowledge of the experimental groups made the measurements.

Fig. 3 After 12 weeks of immediate implantation the specimens were sectioned in bucco-lingual direction to compare buccal and lingual bone plate’s dimensions. In (A) a representative image of the flapless group, while in (B) a representative image of the group treated with the elevation of a mucoperiosteal flap. Compare the heights of the buccal bone plates (arrows) between them. Note also the differences of bone density between the buccal bone plates (on the left) and lingual bone plates (on the right) of both images. Stevenel’s blue and Alizarin red S stain; magnification x 10.

Fig. 4 As in Figure 3, in (A) there is a representative image of the flapless group, while in (B) a representative image of the flap group. Note again the difference of vertical bone loss between them. In these images is more evident the higher bone density found in the buccal bone plates (on the left) when compared to the lingual bone plates (on the right), which is easily seen by the different number and dimension of marrow spaces found in them. Stevenel’s blue and Alizarin red S stain; magnification x 10.

analysis was done in two different positions of the implants, one coronal and other apical, permitting an intra-group evaluation. The bone density measurements evaluated the percentages of mineralized bone in relation to the percentages of marrow cavities. A single examiner, with no knowledge of the experimental groups made the measurements.

Fluorescence analysis

October 2011; 3(3)

JOURNAL of OSSEOINTEGRATION Buccal bone loss after a flapless approach

Fig. 5 Different bone markers at the coronal level of the implant. A: calcein green; B: red alizarin; C: oxytetracyclin; D: calcein blue

Fig. 6 Different bone markers at the apical level of the implant. A: calcein green; B: alizarin red; C: oxytetracyclin; D: calcein blue.

Statistical analysis Mean values and standard deviations were calculated. The data were grouped using the dogs as units for analysis. The mean differences between the groups for each histomorphometric parameter were analyzed through the Mann-Whitney nonparametric test with a confidence level of 95%. Besides for the fluorescence analysis, all measurements were statistically evaluated using the non-parametric analysis of variance, Kruskal-Wallis, and Dunn test October 2011; 3(3)

was used for multiple comparisons among the means. The confidence level was 95%.

RESULTS Clinical and histological observations Healing was uneventful for all animals and no implant was lost. All implants became osseointegrated after the 12-week postoperative 49

JOURNAL of OSSEOINTEGRATION >

Belém Novaes A. Jr et al.

FLAPLESS coronal

¨ : * coronal apical ? 93.42 ± 4.43 # 94.39 ± 5.29 & ? 97.08 ± 2.19 ? 95.91 ± 2.96 ¥ # ? 77.75 ± 12.58 ** » 84.55 ± 4.97 # / » 50.69 ± 9.90 & /» º 89.57 ± 5.83 ? / º 46.70 ± 9.00 ¥ / º & ¥ 66.00 ± 7.69 ** **

FLAP

apical

Buccal

BDA BDD BIC

90.37 ± 6.12 85.80 ± 13.87 * / ? 91.95 ± 8.84 95.52 ± 2.56 * / ? 77.39 ± 9.07

Lingual

BDA BDD BIC

87.13 ± 7.99 ¨ 59.88 ± 13.19 ? / ¨ 86.80 ± 7.01 : 56.82 ± 14.19 ? / : 70.50 ± 12.17

p=0.0023 p=0.0006 p=0.0262 p=0.0070 p=0.0006 p=0.0070 p= 0.0041 p=0.0006 p=0.0006 p=0.0006 p=0.0006 p=0.0262

Table 1 Percentages of bone density adjacent (BDA) and distant (BDD) and bone-to-implant contact (BIC) described as mean ± SD.

period. The marginal gaps between the buccal walls and the implants disappeared without the migration of connective tissue in both groups.

Histomorphometric analysis The loss of buccal bone height was statistically lower in the flapless group when compared to the flap group (0.98 ± 0.45 mm x 2.14 ± 0.34 mm) (p<0.0001). Additionally the comparisons of the absolute values of bone loss around the implants for the flapless and flap groups showed statistically significant differences between the buccal bone resorption of the experimental groups (2.46 ± 0.42 mm x 3.83 ± 0.21 mm, flapless and flap, respectively) (p<0.0001), but not between the lingual remaining bone heights (1.48 ± 0.27 mm x 1.70 ± 0.31 mm, flapless and flap, respectively). The comparisons within the groups showed statistically significant differences between the buccal and lingual bone resorption in the flapless (2.46 ± 0.42 mm x 1.48 ± 0.27 mm, buccal and lingual, respectively) (p<0.0001) and flap groups (3.83 ± 0.21 mm x 1.70 ± 0.31 mm, buccal and

lingual, respectively) (p<0.0001). The loss of the buccal bone in the flap group was more than 100% greater than the lingual bone. The buccal bone density was numerically higher in all the parameters evaluated when compared to the lingual bone density (Fig. 3. 4). These differences were statistically significant for all the comparisons tested, except for the flapless coronal buccal bone density (table 1). Although the buccal bone density was numerically higher for the flap group compared to the flapless group, these differences were not statistically significant for both coronal and apical parameters (table 1). The comparisons between coronal and apical bone density were statistically significant only for the lingual bone for both flapless and flap groups, with the apical bone having a lower density (table 1). There were no statistically significant differences between adjacent and distant bone densities for all the possible comparisons (table 1). All the implants presented considerable good

BUCCAL

LINGUAL

coronal

apical

Calcein green flap flapless p value

0 1.76 p>0.05

8.66 9.83 p>0.05

5.41 9.02 p>0.05

6.6 6.54 p>0.05

Alizarin red

flap flapless p value

1.05 9.83 p>0.05

21.1 26.07 p>0.05

21.71 13.36 p>0.05

15.83 12.76 p>0.05

Oxytetracyclin flap flapless p value

0 1.26 p>0.05

5.71 5.31 p>0.05

3.62 4.36 p>0.05

2.16 1.5 p>0.05

Calcein blue

0 1.49 p>0.05

2.4 2.89 p>0.05

1.12 1.79 p>0.05

2.27 1.45 p>0.05

flap flapless p value

coronal

apical

Table 2 Fluorescence analysis. Comparisons between flapless and flap groups considering the percentage of each bone marker administered during different time periods of bone healing. 50

October 2011; 3(3)

JOURNAL of OSSEOINTEGRATION Buccal bone loss after a flapless approach

GROUP

EVALUATED AREA

BONE MARKER

P VALUE

Calcein green Alizarin red Oxytetracyc Calcein blue

Flapless

Buccal Lingual

Flap

Buccal Lingual

Apical Coronal Apical Coronal

9.83 1.76 6.54 9.02

26.07* 5.31 9.83 1.26 12.76* / * 1.50* 13.35* 4.36

2.89* 1.49 1.45* 1.79*

*p<0.05 p>0.05 *p<0.01 *p<0.01

Apical Coronal Apical Coronal

8.66 0 6.6 5.41

21.1* 1.05 15.83 21.71*

2.40* 0 2.27 1.12*

*p<0.01 p>0.05 p>0.05 *p<0.01

5.71 0 2.16 3.62

*p<0.01

Table 3 Fluorescent analysis. Intra-group evaluation of the percentage of each different bone marker found in the apical and coronal areas of the experimental groups. GROUP

EVALUATED AREA

BONE MARKER Calcein green Alizarin red Oxytetracyc Calcein blue

Flapless

Flap

Buccal Lingual

Apical Apical

Buccal Lingual

p value Coronal Coronal p value

Buccal Lingual

Apical Apical

Buccal Lingual

p value Coronal Coronal p value

9.83 6.54 p>0.05 1.76 9.02 p>0.05

26.07 12.76 p>0.05 9.83 13.35 p>0.05

5.31 1.5 p>0.05 1.26 4.36 p>0.05

2.89 1.45 p>0.05 1.49 1.79 p>0.05

8.66 6.6 p>0.05 0.00* 5.41* *p<0.05

21.1 15.83 p>0.05 1.05* 21.71* *p<0.01

5.71 2.16 p>0.05 0 3.62 p>0.05

2.4 2.27 p>0.05 0 1.12 p>0.05

Table 4 Fluorescent analysis. Intra-group evaluation of the percentage of each different bone marker found in the buccal and lingual areas of the experimental groups.

indications of bone to implant contact and the results were remarkably similar between the groups. The buccal BIC in both groups is numerically higher when compared to the lingual BIC results, and statistically significant in the flap group (table 1). The analysis under fluorescent microscopy showed bone remodeling in the groups evaluated. The old bone always appeared darker and without labeling. Calcein green appeared in very well delineated green bands (fig. 5, 6A) as did in red the alizarin red marker, which in some specimens also showed a smeared diffuse pattern (fig. 5, 6B); oxytetracyclin showed thin yellow-green lines (fig. 5, 6C) and finally calcein blue was characterized by a soft blue color in a very diffuse pattern (fig. 5 and 6D). In many specimens the secondary osteons were demonstrated by the deposition of the labels in a concentric arrangement. The bone marker quantifications sequentially represented the healing pattern of each different group. The percentages of newly formed bone in the different parts are described in tables 2, 3 and 4. Table 2 represents the analysis between the flap and October 2011; 3(3)

flapless groups considering the different parts, while tables 3 and 4 show the results of the intra-group analysis, separately. A pattern of bone remodeling between the experimental groups (flap and flapless) and also between the different evaluated areas (buccal and lingual; apical and coronal) was detected (fig. 7, 8; tables 3, 4). No statistically significant differences were found between the flap and flapless groups (table 2), however numerically different values of bone formation were observed at the buccal coronal area of the groups, especially at the red alizarin period of application. Generally, the initial phases of bone remodeling that were represented by the calcein green and red alizarin, one week and two weeks after implant placement respectively, showed higher values of bone formation when compared to the other periods evaluated, after 4 and 12 weeks of implant placement. The alizarin red bone marker comprised the peak of bone formation for all groups. Administered after 2 weeks of implant placement, it exhibited the highest levels of marked bone (fig. 7, 8). 51

JOURNAL of OSSEOINTEGRATION >

Belém Novaes A. Jr et al.

buccal apical

buccal coronal

Calcein green

Alizarin red

Oxytetracyclin

Calcein blue

lingual apical

lingual coronal buccal apical

buccal coronal

lingual apical

lingual coronal

Fig. 7 Dynamic of bone formation at the different evaluated areas in the flapless group.

Fig. 8 Dynamic of bone formation at the different evaluated areas in the flap group.

Statistically significant differences were observed between red alizarin and calcein blue for bone remodeling evaluations at the flapless buccal apical areas and also at the flapless lingual apical and coronal areas (table 3). Still considering the intragroup analysis, the flap buccal apical and the flap lingual coronal areas also showed statistically significant differences between the alizarin red and calcein blue marked bone (table 3). When comparing the buccal and the lingual areas of the flap and flapless groups, statistically significant differences were found only between buccal coronal and lingual coronal areas of the flap group at the calcein green and red alizarin periods of application (table 4).

surgery in dogs confirmed that the elevation of the periosteum may cause circulatory insufficiency and then bone resorption (25). In general, the bone surface that is temporarily exposed usually undergoes a necrotic process that finishes in bone resorption, with exception of the broad bone plate that contains a significant number of marrow spaces and could have less bone height loss at the end of the healing period. Considering that one of the main functions of the periodontal ligament (PDL) blood vessels is to supply nutrients to the osteoblasts in the alveolar bone (13), it is easy to understand that after tooth extractions, only the vascularization provided by the periosteum remains. However, the elevation of mucoperiosteal flaps also compromises the blood supply from the periosteum. Fickl et al. (26) evaluated the hypothesis that tooth extraction without the elevation of a mucoperiosteal flap may decrease the post-surgery resorption level, and demonstrated that the act of leaving the periosteum in place decreased the resorption index of the extraction socket. They highlighted that the great impact of this finding might be when dealing with thin periodontal biotypes, where the osteoclastic activities of the internal and external sides could merge together and cause a more pronounced buccal bone plate loss. The results of the present study were consistent with these statements, especially for the flap approach group in which the loss of the buccal bone was more than 100% greater than the lingual bone as shown by the absolute measurements of bone loss around the implants. The statistically significant difference between flapless and flap groups when considering the buccal bone loss confirmed the importance of periosteum preservation in this type of implant therapy. On the other hand, there were no significant differences between the flap and flapless on the lingual bone plate resorption, indicating that the

DISCUSSION The flapless surgical approach significantly favored the preservation of the alveolar buccal plate height after immediate implant placement and a reasonable explanation could be the non-detachment of the periosteum and its vascular network. In this study the only difference between the groups was the flap elevation in the control group, which exhibited at least twice as more buccal bone loss when compared to the flapless group. Even better results were demonstrated by another study with a similar methodology, where the buccal bone loss of 2.11 mm for the flap sites was confronted by the 0.6 mm found at the test immediate implants treated with flapless surgery (23). Many years ago, Wilderman et al. (24) have primarily demonstrated that “although the exposure of bone by surgery allows its observation, some bone resorption is the penalty for this type of examination”. More recently, the evaluation of the microvascular responses after mucoperiosteal flap 52

October 2011; 3(3)

JOURNAL of OSSEOINTEGRATION Buccal bone loss after a flapless approach

morphology of the buccal and lingual plates might represent another crucial factor in determining the final bone resorption. Based on these facts it could be speculated that the immediate implant therapy was not the only factor that influenced the high level of buccal bone height loss of 2,5 mm in relation to the lingual bone plate described by Araujo et al. (9) after flap surgery. In our histological specimens the buccal bone crest appeared significantly thinner when compared to the lingual component. This pattern was also observed in different studies (10,12,17,19,27). Furthermore, the bone densities of buccal and lingual plates were very different in both groups. In general, while the buccal plates were constituted by a cortical bone type with sparse and decreased number of marrow areas, the lingual bone plates exhibited numerous and large marrow areas. This difference between the buccal and lingual bone densities was statistically significant in the apical portion of test and control groups, and was also statistically significant in the coronal portion of the flap group. This last finding could mean that this portion exhibited insufficient bone marrow spaces and source of blood vessels, and consequentially compromised angiogenesis that is usually related to bone loss (11, 25). There were no statistically significant differences between the bone densities adjacent and distant to the implants in both groups, but there was for the buccal bone densities of the apical portion of the flapless group. The significant lower density adjacent to the implant of the buccal bone observed in the intra-group evaluation (85.80% adjacent and 95.52% distant), and also the numerical difference between the groups considering this parameter (85.80% for flapless and 94.39% for flap) could be understood as another advantage of the non-detachment of the periosteum, providing vessels and consequently nutrients to the cortical bone plates. All the implants presented good BIC levels and the results were very similar between flapless and flap groups. The buccal BIC is numerically higher in both groups when compared to the lingual BIC and this could be related to the higher number of marrow areas found in the lingual bone plate. To sum up, the current study supports the existence of a close relationship between angiogenesis and bone resorption/formation (25), in which the remodeling process is strongly dependent on the interaction between new blood vessels and bone. Qahash et al. (28) demonstrated a significant association between the width of the buccal alveolar ridge and extent of bone resorption evaluated by incandescent and fluorescent light microscopy. They suggested that the width of the buccal alveolar ridge should be at least 2 mm to maintain the alveolar bone level. These observations have general October 2011; 3(3)

implications for implant placement with most surgical protocols, and even more for immediate implantation. Studies about the alveolar bone healing potential in peri-implant critical-size defects, showed that the thicker lingual bone plate provided a large wound space that was correlated with enhanced bone regeneration, while the implants placed closer to the buccal plate were associated with increased crestal bone loss (29,30). Another comparative study between flapless and flap surgeries for immediate post-extraction implants, also found a minor reduction of the buccal bone plate with the flapless approach, but emphasized the importance of the location of the implants in the confines of the alveolus (31). Based on this, it could be discussed that one reason for the higher buccal bone plate resorption of Araujo et al. (19) study could be due to the use of a 4.1 mm diameter implants in alveoli that are smaller (3.5 mm is the diameter of third premolars and of 3.9 mm of fourth premolars in dogs); in other words, the diameter of the implant was greater than the alveoli themselves. In the present study the implants were placed 1 mm away from the buccal marginal bone wall without invading the lingual bone plate with the drill or the implant. No residual defect was observed on the histological specimens after 12 weeks of healing and the formation of new bone could be a possible explanation as well as bone loss to some extent. This jumping gap distance has already been studied and it was shown that this defect may heal with new bone and a high degree of osseointegration without the use of barrier membranes (32). It was described that this kind of defect “allowed the formation of a coagulum that, even in the absence of a barrier membrane, it was properly protected by the periosteum of the soft tissue flap. In other words, during the healing of a ‘self-contained’ bone defect and in the presence of a proper periosteum, the use of a barrier membrane may not be required”, but this is dependent on the implant surface and time of healing allowed after implant installation and gap distance. From the fluorescence analysis of the present study no statistically significant differences were obtained between the flap and flapless groups, but the evaluation of the buccal coronal areas showed numerically higher new bone formation for the flapless group and the lack of statistical significance could be explained by the size of the sample. It was also observed that bone remodeling followed a pattern not only in the two experimental groups, but also in the different evaluated sections of the implants in an intra-group analysis – coronal and apical, buccal and lingual. It is well-known that the bone formative and resorptive phases are systematically intercalated (33). 53

JOURNAL of OSSEOINTEGRATION >

BelĂŠm Novaes A. Jr et al.

In the present study the peak of bone mineralization for the groups and subgroups studied comprised the period of 2 weeks after implant placement as marked by the red alizarin dye. This is in accordance to Abrahamsson et al. (33) that had already characterized this time period as a very active phase in the process of mineralization. The statistically significant differences found within the groups, for example between the red alizarin and calcein blue marked bone in the buccal apical area confirmed that bone remodeling is an ongoing process that also involves a decrease in the mineralization levels along time. This could explain the replacement of woven bone by lamellar bone as a physiological process. Finally, the evaluation within the experimental groups comparing buccal and lingual halves showed statistically significant differences for the flap coronal area at the first two periods of evaluation. This result could be explained by the very low values of bone thickness found for the buccal plate in this area, reinforcing the histomorphometric findings that described the lingual plates as thicker.

CONCLUSION In summary no major differences in the dynamics of bone healing, evidenced by the fluorescence analysis, has been detected between the flap and flapless groups that supports the hypothesis that the higher loss of buccal bone height is linked to the anatomic characteristics of the buccal bone, the negative influence of the detachment of the periosteum during the flap procedure in immediate implant therapy and the presence of a gap between the implant and the buccal bone plate. Within the limitations of this study, it can be concluded that the flapless approach for immediate post-extraction implants reduces the buccal bone plate resorption

REFERENCES 1. Chen ST, Darby IB, Reynolds EC, Clement JG. Immediate implant placement postextraction without flap elevation. J Periodontol 2009;80:163-172. 2. Knox R, Caudill R, Meffert R. Histologic evaluation of dental endosseous implants placed in surgically created extraction defects. Int J Periodontics Restorative Dent 1991;11:364-375. 3. Lazarra RJ. Immediate implant placement into extraction sites: surgical and restorante advantages. . Int J Periodontics Restorative Dent 1989;9:333-343 4. Lundgren D, Rylander H, Andersson M, Johansson C, Albrektsson T. Healing-in of root analogue titanium 54

implants placed in extraction sockets. An experimental study in the beagle dog. Clin Oral Implants Res 1992;3:136-143. 5. Nemcovsky CE, Artzi Z, Moses O, Gelernter I. Healing of marginal defects at implants placed in fresh extraction sockets or after 4-6 weeks of healing. A comparative study. Clin Oral Implants Res 2002;13:410-419. 6. Paolantonio M, Dolci M, Scarano A, d'Archivio D, di Placido G, Tumini V et al. Immediate implantation in fresh extraction sockets. A controlled clinical and histological study in man. J Periodontol 2001;72:1560-1571. 7. Rosenquist B, Ahmed M. The immediate replacement of teeth by dental implants using homologous bone membranes to seal the sockets: clinical and radiographic findings. Clin Oral Implants Res 2000;11:572-582. 8. Wilson TG, Jr., Schenk R, Buser D, Cochran D. Implants placed in immediate extraction sites: a report of histologic and histometric analyses of human biopsies. Int J Oral Maxillofac Implants 1998;13:333-341. 9. Araujo MG, Sukekava F, Wennstrom JL, Lindhe J. Tissue modeling following implant placement in fresh extraction sockets. Clin Oral Implants Res 2006;17:615624. 10. Araujo MG, Wennstrom JL, Lindhe J. Modeling of the buccal and lingual bone walls of fresh extraction sites following implant installation. Clin Oral Implants Res 2006;17:606-614. 11. Novaes AB, Jr., Macedo GO, Suaid FA, Barros RR, Souza SL, Silveira ESAM. Histologic evaluation of the buccal and lingual bone plates in anterior dog teeth: possible influence on implant dentistry. J Periodontol 2011;82:872-877. 12. Spray JR, Black CG, Morris HF, Ochi S. The influence of bone thickness on facial marginal bone response: stage 1 placement through stage 2 uncovering. Ann Periodontol 2000;5:119-128. 13. Matsuo M SC, Saito M, Kishi Y,Takahashi K. Vascularization an unsuccessful case following guided bone regeneration. . Jpn J Oral Biol 2000;42:573-579. 14. Bragger U, Pasquali L, Kornman KS. Remodelling of interdental alveolar bone after periodontal flap procedures assessed by means of computer-assisted densitometric image analysis (CADIA). J Clin Periodontol 1988;15:558-564. 15. Staffileno H, Levy S, Gargiulo A. Histologic study of cellular mobilization and repair following a periosteal retention operation via split thickness mucogingival flap surgery. J Periodontol 1966;37:117-131. 16. Wood DL, Hoag PM, Donnenfeld OW, Rosenberg DL. Alveolar crest reduction following full and partial thickness flaps. J of Periodontology 1972;43:141-144. 17. Araujo MG, Lindhe J. Dimensional ridge alterations following tooth extraction. An experimental study in the dog. J Clin Periodontol 2005;32:212-218. 18. Yaffe A, Fine N, Binderman I. Regional accelerated phenomenon in the mandible following mucoperiosteal flap surgery. J Periodontol 1994;65:79-83. 19. Araujo MG, Sukekava F, Wennstrom JL, Lindhe J. Ridge alterations following implant placement in fresh extraction sockets: an experimental study in the dog. J Clin Periodontol 2005;32:645-652. 20. Kim J-I, Choi BH, Li J, Xuan F, Jeong S-M. Blood vessels of October 2011; 3(3)

JOURNAL of OSSEOINTEGRATION Buccal bone loss after a flapless approach

the peri-implant mucosa: a comparison between flap and flapless procedures. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2009;107:508-512. 21. Cho KS, Choi SH, Han KH, Chai JK, Wikesjo UM, Kim CK. Alveolar bone formation at dental implant dehiscence defects following guided bone regeneration and xenogeneic freeze-dried demineralized bone matrix. Clin Oral Implants Res 1998;9:419-428. 22. Donath K, Breuner G. A method for the study of undecalcified bones and teeth with attached soft tissues. The Sage-Schliff (sawing and grinding) technique. J Oral Pathol 1982;11:318-326. 23. Cardaropoli G MF, Osorio R, Toledano M, Pisani Proenca T, Thomsen P, Tarnow D. Healing following tooth extraction and immediate implant installation with flapless surgery. Clin Oral Impl Res 2007;18. 24. Wilderman MN, Wentz F, Orban BJ. Histogenesis of repair after mucogingival surgery. J Periodontol 1960;31: 283299. 25. Nobuto T, Suwa F, Kono T, Taguchi Y, Takahashi T, Kanemura N et al. Microvascular response in the periosteum following mucoperiosteal flap surgery in dogs: angiogenesis and bone resorption and formation. J Periodontol 2005;76:1346-1353. 26. Fickl S, Zuhr O, Wachtel H, Bolz W, Huerzeler M. Tissue alterations after tooth extraction with and without surgical trauma: a volumetric study in the beagle dog. J Clin Periodontol 2008;35:356-363.

October 2011; 3(3)

27. Adell R, Lekholm U, Rockler B, Branemark PI, Lindhe J, Eriksson B et al. Marginal tissue reactions at osseointegrated titanium fixtures (I). A 3-year longitudinal prospective study. Int J Oral Maxillofac Surg 1986;15:39-52. 28. Qahash M, Susin C, Polimeni G, Hall J, Wikesjo UM. Bone healing dynamics at buccal peri-implant sites. Clin Oral Implants Res 2008;19:166-172. 29. Polimeni G, Koo KT, Qahash M, Xiropaidis AV, Albandar JM, Wikesjo UM. Prognostic factors for alveolar regeneration: bone formation at teeth and titanium implants. J Clin Periodontol 2004;31:927-932. 30. Wikesjo UM, Susin C, Qahash M, Polimeni G, Leknes KN, Shanaman RH et al. The critical-size supraalveolar periimplant defect model: characteristics and use. J Clin Periodontol 2006;33:846-854. 31. Blanco J NV, Aracil L, Munoz F, Ramos I. Ridge alterations following immediate implant placement in the dog: flap versus flapless surgery. . J Clin Periodontol 2008;35:640648. 32. Botticelli D, Berglundh T, Buser D, Lindhe J. The jumping distance revisited: An experimental study in the dog. Clin Oral Implants Res 2003;14:35-42. 33. Abrahamsson I, Zitzmann NU, Berglundh T, Wennerberg A, Lindhe J. Bone and soft tissue integration to titanium implants with different surface topography: an experimental study in the dog. Int J Oral Maxillofac Implants 2001;16:323-332.

JOURNAL of OSSEOINTEGRATION

MARCO DEGIDI1, VITTORIA PERROTTI2, ADRIANO PIATTELLI2, JAMIL A. SHIBLI3, GIOVANNA IEZZI2 1 2 3

Private Practice, Bologna, Italy Dental School, University of Chieti-Pescara, Chieti, Italy Department of Periodontology, Dental Research Division, and Head of Oral Implantology Clinic, Guarulhos University, Guarulhos, SĂŁo Paulo, Brasil

Histology of a dental implant with a platform switched implant-abutment connection ABSTRACT Background Peri-implant crestal bone must be stable for aesthetic reasons. Aim of this study was a histologic analysis of an implant with a platform switched implant-abutment connection. A 32-year-old male patient participated in this study. The patient needed a bilateral mandibular restoration. Four implants were used, and were immediately restored and loaded the same day of insertion. After a 6 weeks healing period, one implant with platform-switched abutment was retrieved with trephine. Before retrieval the implant was osseointegrated and not mobile. On one side of the implant, a 1 mm resorption of the crestal bone was present. On the contrary, on the other side no bone resorption had occurred and about 1 mm of bone was present over the implant shoulder. The bone-implant contact percentage was 65.1 Âą 6.3 %. Platform-switching could help in maintaining the height of the peri-implant crestal bone.

KEY WORDS Crestal bone remodelling; Histology; Immediate loading; Microgap; Platform switching; Retrieved dental implants.

October 2011; 3(3)

INTRODUCTION The crestal bone level changes, frequently observed at dental implants, after exposure to the oral environment have become a topic of growing interest. The etiology of this peri-implant crestal bone resorption is still unknown, even if several causes have been proposed: surgical trauma, periimplantitis, occlusal overload, formation of a biological width, macroscopic and microscopic characteristics of the neck of the implant, implantabutment interface design, bacterial infiltration of the microgap, position of the microgap (1). Increasing esthetic demands require, frequently, a subgingival placement of restoration margins (2). The more apical positioning has, however, been associated with an increased crestal resorption of the alveolar bone (2). It has been shown that a crestal bone loss of about 2 mm occurs in the submerged 2piece approach, dependent on the location of the microgap in relation to the bone crest (3). This gap has been a matter of intense investigation and research in the past two decades (4-10). Less bone loss and inflammation were observed if the 2piece implants were placed with the microgap exactly at the bone crest level, and the least bone resorption/peri-implant inflammation occurred if the microgap was located 1 mm above the crest (3,4). The placement of an interface in a location apical to the alveolar crest would result in the greatest amount of bone loss (4,11). A bacterial colonization of the microgap has been described with the presence of an inflammatory cell infiltrate at the implant-abutment junction (IAJ) (410,12). The presence of infiltrated connective tissue (ICT) shows, probably, a response of the immune system to bacteria colonizing the IAJ (13). If the ICT is responsible for bone remodelling, shifting the 56

JOURNAL of OSSEOINTEGRATION >

Degidi M. et al.

microgap inward would, probably, shift the ICT further from the alveolar crest (13). Moving the IAJ away from the external edge of the implant shoulder and from crestal bone could help to reduce bone resorption by containing the inflammatory cell infiltrate within the angle formed at the interface, away from the adjacent crestal bone (14). Moreover, with a platform-switched abutment, a 90° step is created, compared to what happens to implants with a matching implant-abutment diameter, where a 180° step is present; the resulting confined area may produce a restriction of the ICT to this region (15). This can be obtained with the use of platformswitched implants (PLS), in which an abutment smaller than the implant shoulder is used (16). The aim of the present study was a histologic analysis of an implant with a platform switched implantabutment connection.

MATERIALS AND METHODS A 32-year-old male patient participated in this study. The study protocol was approved by the Ethical Committee of the UnG (University of Guarulhos, São Paulo, Brasil) and the patient signed a written informed consent form. The patient was partially edentulous and he needed a bilateral posterior mandibular restoration. Four implants were inserted: two implants in the right mandible (3i® implant with Nanotite surface; Implant Innovations, West Palm Beach, FL, USA), and 2 implants in the left mandible (Ankylos® plus implant; Dentsply-Friadent, Mannheim, Germany). All implants were loaded, without occlusal contact, with a fixed provisional prosthesis the same day of the implant surgery and immediately the same day of insertion. The implants had been splinted. One 3i® implant was retrieved, together with the abutment which was never removed, with a trephine bur after a 6 weeks healing period. Before retrieval the implant was osseointegrated and not mobile. The implant had been inserted 1 mm below the crest.

Processing of specimens The implant and the surrounding tissues were stored immediately in 10% buffered formalin and processed to obtain thin ground sections with the Precise 1 Automated System (Assing, Rome, Italy) (17). The specimen was dehydrated in an ascending series of alcohol rinses and embedded in a glycolmethacrylate resin (Technovit 7200 VLC, Kulzer, Wehrheim, Germany). After polymerization, the specimen was sectioned longitudinally along the major axis of the implant with a high-precision diamond disc at about 150 µm and ground down to about 30 µm. Three slides were obtained. The slides were stained with 57

acid fuchsin and toluidine blue and then washed under tap water, dried, immersed in basic fuchsin for 5 min, and then washed and mounted. Histomorphometry of bone-implant contact (BIC) percentage was carried out using a light microscope (Laborlux S, Leitz, Wetzlar, Germany) connected to a high resolution video camera (3CCD, JVC KY-F55B, JVC, Yokohama, Japan) and interfaced to a monitor and PC (Intel Pentium III 1200 MMX, Intel, Santa Clara, CA, USA). This optical system was associated with a digitizing pad (Matrix Vision GmbH, Oppenweiler, Germany) and a histometry software package with image capturing capabilities (ImagePro Plus 4.5, Media Cybernetics Inc., Immagini & Computer Snc Milano).

RESULTS A 1 mm resorption of the peri-implant crestal bone was present on one side with the bone located at the same height of the shoulder of the implant. A 0.6 mm gap was observed, on one side, between implant and bone, at the height of the shoulder of the implant. Inside this gap it was possible to observe newly formed bone trabeculae. The location of the first bone to implant contact (BIC) was found at about 0.7 mm from the implant shoulder (fig. 1). Inside this gap, there were no inflammatory cell infiltrate, osteoclasts or areas of bone resorption. Bone trabeculae were seen 1 mm above the level of the implant shoulder, about 1 mm from the implant. A 0.2 mm gap was present between the shoulder of the implant and the newly-formed bone, on the other side of the implant. Inside this gap, osteoblasts were depositing osteoid matrix in an apico-coronal and implantopetal direction. At the level of this portion of the interface, located near the shoulder of the implant, it was possible to observe only the presence of newly-formed bone. The BIC was located 0.3 mm from the implant shoulder (fig. 2). Also inside this gap no inflammatory cell infiltrate, osteoclasts, or areas of bone resorption were observed. At the interface with the abutment it was possible to observe the presence of connective tissue. A detachment of this connective tissue from the metal surface due, probably, to an artefact produced during retrieval or processing of the specimen, could be observed in some areas. This loose connective tissue presented only with a few, scattered inflammatory cells and a few small vessels (fig. 3). Newly-formed bone was found at the interface with the implant, and osteoblasts deposited osteoid matrix directly on the implant surface (fig. 4, 5). In some portions of the interface, newly-formed bone was located in tight contact with the metal surface October 2011; 3(3)

JOURNAL of OSSEOINTEGRATION <

Histologic analysis of a platform-switching implant

(fig. 6). No gaps, connective fibrous tissue was found at the interface, and no epithelial downgrowth was present. The BIC percentage was 65.1 Âą 6.3% (fig. 7).

Peri-implant bone level has been used as one of the criteria for assessing the success of dental implants (14). It is an important prerequisite in order to preserve the integrity of the gingival margins and

interdental papillae (14). The inward shift of the IAJ due to PLS, with a shift of the inflammatory cell infiltrate to the central axis of the implant, can be considered a desirable morphological feature that may prevent the horizontal saucerisation and preserve the vertical crestal bone levels (14,18,19). With PLS, the ICT is contained mainly above the implant platform and the peri-implant bone is shielded from the ICT (20). In a study in dogs it was found that PLS was not able to reduce crestal bone level changes to a significant

Fig. 1 On one side of the implant, a 1 mm resorption of the crestal bone was present and the bone was located at the same level of the implant shoulder. Acid fuchsin-toluidine blue 25X.

Fig. 2 Bone trabeculae were seen 1 mm above the level of the implant shoulder and about 1 mm from the implant. Acid fuchsin-toluidine blue 25X

Fig. 3 A detachment of the connective tissue from the metal surface of the implant caould be observed. This connective tissue presented loose with only a few, scattered inflammatory cells. Acid fuchsin-toluidine blue 40X

Fig. 4 Newly-formed trabecular bone was found along the concavities and convexities of the implant threads. Acid fuchsin-toluidine blue 40X

DISCUSSION AND CONCLUSION

October 2011; 3(3)

JOURNAL of OSSEOINTEGRATION >

Degidi M. et al.

Fig. 5 In the concavity of the implant threads osteoblasts depositing osteoid matrix directly on the implant surface could be observed. Acid fuchsin-toluidine blue 100X

Fig. 7 Trabecular bone with wide marrow spaces is present along the implant perimeter. Connective tissue, probably detached due to an artefact produced during retrieval or processing of the specimen, can be observed along the abutment. Acid fuchsin-toluidine blue 12X.

Fig. 6 Newly-formed bone in tight contact with the metal surface, with no gap at the interface could be seen. Acid fuchsin-toluidine blue 100X. found no infraosseous pockets, Howshipâ&#x20AC;&#x2122;s lacunae nor osteoclasts on the coronal segment of the implant (13). Moreover, PLS produced a reduction in the dimension of the ICT and its extension in an apical direction (13). It is likely that PLS was able to reduce the immune response of the organism to the presence of the microgap (13). The present study results showed that PLS could produce, around the implant shoulder, an area that could help to protect the peri-implant soft and mineralized tissues. This could, probably, determine the reduced bone resorption seen in the present histologic report. A very high BIC was found in the implant analyzed. This could be related to the fact that the implant had been immediately loaded and to the microstructured type of surface (26). In conclusion, the use of PLS could help to maintain the height of the peri-implant crestal bone, and to partially reduce crestal bone remodeling.

ACKNOWLEDGMENTS This work was partially supported by the Ministry of Education, University, Research (M.I.U.R.), Rome, Italy

level and it must be questioned if the concept of PLS may keep the adverse effects of microbial leakage away from the alveolar bone (12). On the other hand, several human radiographical and clinical studies have shown that PLS can determine a reduction of the vertical bone resorption vs conventional restorations with a matching abutment (18,20-25). In a histologic evaluation of a human dental implant, with a platform-switched abutment, Luongo et al. 59

REFERENCES 1. Vigolo P, Givani A. Platform-switched restorations on wide-diameter implants: a 5-year clinical perspective. Int J Oral Maxillofac Implants 2009;24:103-109. 2. Tan WC, Lang NP, Schmidlin K, Zwahlen M, Pjetursson BE. The effect of different implant neck configurations October 2011; 3(3)

JOURNAL of OSSEOINTEGRATION Bone resorption and platform-switched connection

on soft and hard tissue healing: a randomizedcontrolled clinical trial. Clin Oral Impl Res 2011;22:1419. 3. Hermann JS, Schofield JD, Schenk RK, Buser D, Cochran DL. Influence of the size of the microgap on crestal bone changes around titanium implants. A histometric evaluation of unloaded non-submerged implants in the canine mandible. J Periodontol 2001;72:1372-1383. 4. Piattelli A, Vrespa G, Petrone G, Iezzi G, Annibali S, Scarano A. Role of the microgap between implant and abutment: a retrospective histologic evaluation in monkeys. J Periodontol 2003;74:346-352. 5. Broggini N, McManus CM, Hermann JS, Medina R, Schenk RK, Buser D, Cochral DL. Peri-implant inflammation defined by the implant-abutment interface. J Dent Res 2006;85:473-478. 6. Persson LG, Lekholm U, Leonhardt¬ A, Dahlen G, Lindhe J. Bacterial colonization on internal surfaces of Branemark system implant components. Clin Oral Impl Res 1996;7:90-95. 7. Quirynen M, Bollen CM, Eyssen H, van Steenberghe D. Microbial penetration along the implant components of the Branemark system. An in vitro study. Clin Oral Impl Res 1994;5:239-44. 8. Jansen VK, Conrads G, Richter EJ. Microbial leakage and marginal fit of the implant-abutment interface. Int J Oral Maxillofac Implants 1997;12:527-40. 9. Piattelli A, Scarano A, Paolantonio M, Assenza B, Leghissa GC, Di Bonaventura G, Catamo G, Piccolomini R. Fluids and microbial penetration in the internal part of cement-retained versus screw-retained implantabutment connections. J Periodontol 2001;72:11461150. 10. Quirynen M, van Steenberghe D. Bacterial colonization of the internal part of two-stage implants. An in vivo study. Clin Oral Impl Res 1993;4:158-161. 11. Hermann JS, Buser D, Schenk RK, Cochran DL. Crestal bone changes around titanium implants. A histometric evaluation of unloaded non-submerged and submerged implants in the canine mandible. J Periodontol 2000;71:1412-1424. 12. Becker J, Ferrari D, Mihatovic I, Sahmn, Schaer A, Schwarz F. Stability of crestal bone levet at platformswitched non-submerged titanium implants: a histomorfphometrical study in dogs. J Clin Periodontol 2009;36:532-539. 13. Luongo R, Traini T, Guidone PC, Bianco, Cocchetto R, Celletti R. Hard and soft tissue responses to the platform-switching technique. Int Periodontics Restorative Dent 2008;28:551-557. 14. Atieh MA, Ibrahim HM, Atieh AH. Platform switching for marginal bone preservation around dental implants: a systematic review and meta-analysis. J Periodontol 2010;81:1350-1366. 15. Hurzeler M, Fickl S, Zuhr O, Wachtel HC. Peri-implant

October 2011; 3(3)

bone level around implants with platform-switched abutments: preliminary data from a prospective study. J Oral Maxillofac Surg 2007;65 (Suppl.):33-39. 16. Lazzara RJ, Porter SS. Platform switching: a new concept in implant dentistry for controlling postrestorative crestal bone levels. Int J Periodontics Restorative Dent 2006;26:9-17. 17. Piattelli A, Scarano A, Quaranta M. High-precision, cost-effective system for producing thin sections of oral tissues containing dental implants. Biomaterials 1997;18:577-579. 18. Fickl S, Zuhr O, Stein JM, Hurzeler MB. Peri-implant bone bone level around implants with platformswitched abutments. Int J Oral Maxillofac Implants 2010;25:577-581. 19. Canullo L, Pellegrini G, Allievi C, Trombelli L, Annibali S, Dellavia C. Soft tissues around long-term platform switching implant restorations: a histological human evaluation. Preliminary results. J Clin Periodontol 2011;38:86-94. 20. Cappiello M, Luongo R, Di Iorio D, Bugea C, Cocchetto R, Celletti R. Evaluation of peri-implant bone loss around platform-switched implants. Int J Periodontics restorative Dent 2008;28:347-355. 21. Trammel K, Geurs NC, O’Neal SJ, Liu PR, Haigh SJ, McNeal S, Keneally JN, Reddy MS. A prospective, randomized, controlled comparison of platformswitched and matched-abutment implants in shortspan partial denture situations. Int J Periodontics Restorative Dent 2009;29:599-605. 22. Rodriguez-Ciurana X, Vela-Nebot X,Segalà-Torres M, Calvo-Guirado JL, Cambra J, Mendez-BlancoV, Tarnow DP. The effect of inter-implant distance on the height of the inter-implant bone crest when using platformswitched implants. Int J Periodontics Restorative Dent 2009;29:141-151. 23. Veis A, Parissis N, Tsirlis A, Papadeli C, Marini G, Zogakis A. Evaluation of peri-implant marginal bone loss using modified abutment connections at various crestal level placements. Int J Periodontics Restorative Dent 2010;30:609-617. 24. Vela-Nebot X, Rodriguez-Ciurana X, Rodado-Alonso C, Segalà-Torres M. Benefits of an implant platform modification technique to reduce crestal bone resorption. Implant Dent 2006;15:313-320. 25. Cocchetto R, Traini T, Caddeo F, Celletti R. Evaluation of hard tissue response around wider platform-switched implants. Int J Periodontics Restorative Dent 2010;30:163-171 26. Orsini G, Piattelli M, Scarano A, Petrone G, Kenealy J, Piattelli A, Caputi S. Randomized-controlled histological and histomorphometric evaluation of implants with nanometer-scale calcium phosphate added to the dual acid-etched surface in the human posterior maxilla. J Periodontol 2007,78:209-218.

JOURNAL of OSSEOINTEGRATION

MARCO DEGIDI1, VITTORIA PERROTTI2, ADRIANO PIATTELLI2, JAMIL A. SHIBLI3, GIOVANNA IEZZI2 1 2 3

KEY WORDS Crestal bone remodelling; Histology; Immediate loading; Microgap; Platform switching; Retrieved dental implants.

October 2011; 3(3)

JOURNAL of OSSEOINTEGRATION >

Degidi M. et al.

JOURNAL of OSSEOINTEGRATION <

Histologic analysis of a platform-switching implant

(fig. 6). No gaps, connective fibrous tissue was found at the interface, and no epithelial downgrowth was present. The BIC percentage was 65.1 Âą 6.3% (fig. 7).

Fig. 1 On one side of the implant, a 1 mm resorption of the crestal bone was present and the bone was located at the same level of the implant shoulder. Acid fuchsin-toluidine blue 25X.

Fig. 2 Bone trabeculae were seen 1 mm above the level of the implant shoulder and about 1 mm from the implant. Acid fuchsin-toluidine blue 25X

Fig. 4 Newly-formed trabecular bone was found along the concavities and convexities of the implant threads. Acid fuchsin-toluidine blue 40X

DISCUSSION AND CONCLUSION

October 2011; 3(3)

JOURNAL of OSSEOINTEGRATION >

Degidi M. et al.

Fig. 5 In the concavity of the implant threads osteoblasts depositing osteoid matrix directly on the implant surface could be observed. Acid fuchsin-toluidine blue 100X

ACKNOWLEDGMENTS This work was partially supported by the Ministry of Education, University, Research (M.I.U.R.), Rome, Italy

JOURNAL of OSSEOINTEGRATION Bone resorption and platform-switched connection

October 2011; 3(3)