Post & core/ dental implant courses by Indian dental academy

1

CONTENTS    

               

Introduction History Key words and definitions Consideration in restoring endodontically treated teeth.

Effects of endodontic treatment Anatomic and biologic considerations.

Indications and contraindications.

Ideal requirements of post core.

Classification of post core.

Treatment planning Stress analysis for post and cores Factors influencing retension and resistance.

Principles of preparation of endodontically treated teeth.

Custom made post core Prefabricated systems Provisional restorations Advances in post core system.

Removal of existing posts Success and failure of post cores.

Conclusion Review of literature References.

INTRODUCTION: “Teeth and artificial dentures, fastened with posts and gold wire, hold setter than all others. They sometimes last fifteen to twenty years and even more without displacement . . .”

Piree Fauchard – 1747.

Restorative dentistry and endodontics have reached a point where they enjoy a symbiotic relationship.

Endodontic treatment saves the tooth from extraction but only adequate restoration will reinstate it as a long-term functioning member of the mouth. The restoration of a tooth by root canal treatment is of limited value unless the crown of tooth is satisfactorily restored. The manner in which a root canal filled tooth is restored is therefore considerable importance.

The restoration of the endodontically treated tooth is a subject that has been evaluated and discussed widely in the dental literature. The restoration of endodontically treated tooth is complicated by the fact that much or all of the coronal tooth structure which normally would be used in the retention of the restoration has been destroyed by caries, previous restorations, trauma, and the endodontic access preparation itself.

The endodontically treated tooth is a unique subset of teeth requiring restoration because of several factors such as dehydrated dentin, decreased, decreased structural integrity and impaired neurosensory feed back mechanism when compared to a vital tooth. However, the treatment goal must be based upon a multitude of factors specific for each patient, so that the strategic architectural aspects that have/greatest impact on the ultimate strength of the pulpless tooth can be restored/reinforced.

Solution to this problem has challenged the inventiveness and ingenuity of dentists for centuries.

The endodontically treated tooth must be fortified in such a way that it will withstand both vertical and lateral forces and not be subject d to fracture. Amalgam as routinely used to restore a tooth is not considered the best choice, since the cusps are left unprotected and are subjected to vertical fracture. The use of a crown over an endodontically treated tooth, by itself is not recommended. Further reduction of already undermined walls may render the treated tooth subject to horizontal fracture at or near the gingival line. An inlay, in so far as it too is an intracoronal restoration, leads to same weakness as the amalgam.

This leaves the consideration an onlay, which covers the cusps and protects against vertical fracture. Still the potential for horizontal fracture remains, since the pulp chamber is usually undermined. For these

2

reasons vertical support must be added to all of the restorations mentioned so that they may be strong enough to protect the treated tooth from horizontal fracture.

Ro reinforce the treated tooth and protect against vertical fracture, some type of stabilization is required that will fasten the restoration to the remaining tooth structure. This is accomplished by using a post (also referred to a dowel), preferably with a core or coping and a crown or onlay as superstructure to give coronal-radicular stabilization. A post and core is a restoration consisting of a post that fills a prepared root canal and a core inserted into the pulp chamber that establishes the proper coronal tooth preparation.

The post and core is made with a rigid material which, when cemented into the root canal and pulp chamber provides a solid foundation restoration that is well retained in the tooth. So the primary function of a post is to aid in retaining a core to restore lost tooth structure for retention of a restoration and not to provide strength or resistance to fracture.

3

HISTORY:

Various methods of restoring pulpless teeth have been reported for more than 200 years. In 1747, Pierre Fauchard described the process by which roots of maxillary anterior teeth were used for the restoration of single teeth and the replacement of multiple teeth. Posts were fabricated of gold or silver and held in the root canal space with a heat softened adhesive called “mastic”.

In Fauchard’s day, replacement crowns were made from bone, ivory, animal teeth and sound natural tooth crowns. Gradually, the use of these natural substances declined to be slowly replaced by porcelain. A pivot (which is today termed a post) was used to retain the artificial porcelain crown into a root canal, and the crown post combination was termed a “pivot crown”. Porcelain pivot crowns were described in the early 1800s by a well-known dentist of Paris, Dubois de chemant. Pivoting (posting) of artificial crowns to natural roots became the most common method of replacing artificial teeth and was reported as the “best that can be employed” by Chapin Harris in the Dental Art in 1839.

Early pivot crowns in the United States used seasoned wood (white hickory) pivots. The pivot was adapted to the inside of an all-ceramic crown and also into the root canal space. Moisture would swell the wood and retain the pivot in place. Surprisingly, Prothero reported removing two central incisor crowns with wooden pivots that had been successfully used for 18 years. Subsequently, pivot crowns were fabricated using wood/metal combinations, and then more durable all-metal pivots were used. Metal pivot retention was achieved by various means such as threads, pins, surface roughening and split designs that provided mechanical spring retention.

Unfortunately, adequate cements were not available to these early practitioners – cements that would have enhanced post retention and decreased abrasion of the root caused by movement of metal posts within the canal. One of the best representations of a pivoted tooth appears in Dental Physiology and Surgery, written by Sir John Tomes in 1849. Tome’s post length and diameter conform closely to today’s principles in fabricating posts.

Endodontic therapies by these dental pioneers embraced only minimal efforts to clean, shape, and obturate the canal. Frequent use of the wood posts in empty canals led to repeated episodes of swelling and pain. Wood posts, however, did allow the escape of the so-called “morbid humors”. A groove in the post or root canal provided a pathway for continual suppuration from the periradicular tissues.

Although many of the restorative techniques used today had their inception in the 1800s and early 1900s, proper endodontic treatment was neglected until years later. Today, the endodontic and proshodontic aspects of treatment have advanced significantly, new material and techniques have been developed, and a substantial body of scientific knowledge is available on which to base clinical treatment decisions.

4

Key words and definitions:

Post or dowel: Refers to a cylindrical or tapered object that fits into the prepared root canal of a tooth and is synonymous with the term post or endodontic post.

Endodontic post or dowels usually cemented or threaded into a prepared channel, their purpose is to retain the core and equally distribute the forces of mastication along the long axis of the tooth.

The dowel is a post as other relatively rigid restorative material placed in the root of a non-viral tooth.

1.

Core: Refers to a build up restoration, usually amalgam/composite placed in a badly broken down tooth to restore the bulk of the coronal portion of the tooth to facilitate subsequent restoration by means of an indirect extracoronal restoration. It may serve as either final restoration or as a foundation or care for a crown.

Is defined as properly shaped and wall restored substructure which replaces missing coronal structure and retain the final restoration.

Core replaces coronal tooth structure that is lost and forms a bare that has sufficient bulk and retention for final restoration.

The core consists of restorative material placed in the coronal area of a tooth. This material replaces carious, fractured or otherwise missing coronal structure and retains the final crown.

2.

Ferrule: Is defined as a metal band that encircles the external dimension of the residual tooth.

Is defined as A 3600 metal collar of the crown surrounding the parallel walls of the dentin extending coronal to the shoulder of the preparation which resists stress exerted during post insertion.

3.

Pins: Used alone or in combination with posts to provide retention for core material.

4.

Final restoration: The form of crown given after post / core.

5

CONSIDERATIONS IN RESTORING ENDODONTICALLY TREATED TOOTH:

The restoration of endodontically treated teeth has been the focus of considerable controversy and empiricism. Time-tested methods have been highly successful in some respects, but failure is still apparent. Regardless of the system there should be a through understanding of the anatomy, and biology of dentin and root supporting the restoration on the part of the practitioner to support the contention that endodontically treated teeth have special needs that exceed the requirements of teeth with vital pulp. These unique aspects include, A) Effect of endodontic treatment on teeth and B) Anatomic and biologic considerations.

A) Effect of endodontic treatment on teeth: a) b) c) d) e)

The role of moisture loss on the nature of dentin Alterations of strength due to architectural changes in the morphology of the teeth.

Concepts of biomechanical behavior of tooth structure under stress.

Nature of dentin toughness in pulpless teeth.

Changes in the nature of the collagen alignment in pulpless teeth.

a) Role of moisture loss: The moisture content of the coronal dentin is approximately 13.2%. As the age increases the moisture content decreases due to increased deposition of peritubular dentin which contains more organic content and water.

Two major components of water content in any calcified tissues are, 1) Outside the calcified matrix, 2) Within the calcified matrix.

Water within the calcified matrix is divided in to, i) Free water to hydrate inorganic ions thus being involved in their movement – But this water can be removed at between 1000C and 1100C.

6

ii)

Firmly bound water, this doesn’t participate in the movement of ions. This firmly bound water is called the “water of hydroxyapatite crystal� and is not substantially reduced until temperature of 6000C is reached.

It is demonstrated that the pulpless tooth contains 9% less moisture than the vital tooth and this water loss is a irreversible damage and can not be recoverable even in saturated atmosphere and at body temperature. b) Architectural changes: The decreased strength seen in endodontically treated teeth is primarily because of the loss of coronal tooth structure. Endodontic procedures reduced tooth stiffness by a mere 5% attributed primarily by access opening. While a MOD cavity preparation reduces tooth stiffness by more than 60% with loss of marginal ridge contributing the greatest loss of tooth strength.

Substantial dentin can be removed during endodontic access preparation or canal cleaning and shaping, these procedures apparently do not significantly weaken the tooth.

With the reduction of the inner cuspal slopes that unite and support, or exposure of acute cuspal angles a greater chance of fracture exists.

Conversely the excessive removal of radicular dentin during cleaning and shaping or post space preparation compromises root strength. c) Biomechanical behavior: The behavior of teeth under load has been investigated and has provided information into the changes occurring in the pulpless tooth. Tidmarsh described an intact tooth as a hollow laminated structure that deforms under load. This laminated structure may shorten, its sides may bulge, and its cusps may be wedged apart by opposing cusps. Although under physiological loads, complete elastic recovery takes place, permanent deformation may follow very high / excessive on sustained loads. Therefore the tooth appears to respond like a prestressed laminate. It is characteristic of such a structure that it can withstand greater loads in the prestressed rather than in the unstressed state because in the prestressed state it can flex with the varying degree and angle of load.

How does this prestressed state come about in the tooth?

One hypothesis suggests that as the crown develops, the outward movement of the ameloblasts and the inward movement of the odontoblasts set up the stressed condition, which is then frozen or stabilized by mineralization of the matrix.

The significance of this phenomenon is that any cavity preparation, however small, destroys the prestressed state and releases the stresses.

This phenomenon is crucial if the cuspal inner slopes are removed during endodontic access preparation or cavity preparation thus destroying the prestressed state. Subsequently, stress is released, accompanied by a slight shift in cuspal structure. However, the tooth can deform to a greater extent under applied loads and thus be more susceptible to fracture. This concept would apply to teeth with endodontic cavity preparation and would be integrated in the nature of cuspal anatomy, its bucco-lingual width, and the angle of inclination.

Grimaldi et al illustrated that there is a direct relationship between the amount of central tooth structure lost in cavity preparation and the deformations under load.

To improve the retentive and mechanical properties as well as to decrease the percentage of root fractures some posts with combination of two or three basic types are introduced they are: 1) 2) 3) 4) 5)

Parallel sided posts with tapered apical ends Tapered flexi post Parallel V-lock drill and post system.

Parallel radix anchor system.

Parallel threaded posts with pre tapped channels.

d) Dentinal toughness: The toughness is measured by the total energy required to fracture a material- Another technique to determine the toughness of a material in micro indentation imprints made in a material with specific loads and the depth of indentation indicates a measure of hardness of material.

7

Dentin exhibits considerable plastic deformation beyond the yield point, it is a weak biologic ductile material in which strength and toughness may vary.

The shear strengths and toughness values of dentin from endodontically treated teeth is lower and significantly different from the values for dentin of vital teeth. It is demonstrated that 14% reduction in the strength and toughness is seen in endodontically treated teeth. e) Collagen alteration: Dentinal collagen consists of large fibrils characteristic of type I collagen. The intermolecular cross linking of collagen fibers achieve their characteristic physical properties of rigidity, resistance of strength and remarkably high tensile strength.

It is verified that there are more immature and fewer mature cross links in root filled teeth – Accounting for decrease in tensile strength and brittleness of pulpless teeth.

When all above five aspects of dentinal changes are integrated a reasonable explanation for the changes in the strength of the tooth structure are pulpless teeth can be formulated. These are fundamental, irreversible changes in the anatomy, biochemistry and biomechanical properties of dentin which makes up the bulk of remaining tooth structure after pulpal loss and endodontic treatment.

Dentin of pulpless teeth undergoes alteration in its inherent structure, reducing is tensile strength and flexibility. Because of the moisture loss and architectural changes of tooth structure – root filled teeth require unique restorative procedures related to their radicular anatomy and supporting bone.

B) Anatomic and Biologic considerations: Other than the alterations made by endodontic therapy some other important considerations during post endodontic restorations they are, a) The amount of remaining tooth structure b) The anatomic position of the tooth. c) The functional load on the tooth. d) The esthetic requirements for the tooth.

The various combinations of these factors will determine the selection of posts, cores, crowns and the technique of the treatment procedure. a) The amount of remaining tooth structure: The amount of tooth structure damage is one of the most important aspects in restoration of endodontically treated tooth. The amount of remaining dentin is far more significant to the long term prognosis of the restored tooth than in the selection of artificial post, core or crown materials.

Teeth with minimal remaining tooth structure present several clinical problems, these include. i) An increased root fracture risk. ii) A greater potential for recurrent caries. iii) Greater chance of restoration dislodgement or loss. iv) An increased incidence of biologic width invasion during preparation. b) The anatomic position of the tooth: Anterior teeth: A nonvital anterior tooth that has lost significant tooth structure requires a crown. The crown is supported by and retained by the post and core. Desired physical properties of Posts will determine the selection of materials for the crown, core, post, esthetic post and core materials are preferred here.

Posterior teeth: Posterior teeth carry greater occlusal loads than anterior teeth, and restorations must be planned to protect posterior teeth against fracture. The functional forces against molars required crown or onlay protection. c) Functional load of the tooth and prosthetic needs: The horizontal and torquing forces endured by abutments for fixed or removable partial dentures dictate more extensive protective and retentive features in the restoration. Abutment teeth for long span fixed bridges and distal extension, removable partial denture absorb greater transverse load and require more protection than do abutments of smaller bridges or tooth supported removable, partial dentures.

8

Similarly teeth that exhibit extensive wear from bruxism, heavy occlusion or heavy lateral function require the full complement of post, core and crown. d) Esthetic requirements of the tooth: Esthetic changes occur in endodontically treated teeth. Biomechanically altered dentin modifies light refraction through the tooth and modifies its appearance. Inadequate endodontic cleaning and shaping of coronal area also contribute to this discoloration.

Anterior teeth, premolars and often the maxillary first molar inhabit the esthetic zone of the mouth. These teeth are framed by the gingiva and lips to create an esthetically pleasing smile. Teeth in the esthetic zone require careful selection of restorative materials and careful handling of tissues.

2. Anatomic considerations: Radicular considerations: There remains a tremendous dependency on the radiograph as the essential diagnostic aid for determining the anatomy of the root to be restored. While routine periradicular radiographs provide only two-dimensional cross-sectional anatomy of the radicular tissues from mesial to distal, supplemental, views from proximal or occlusal angulation will supply additional information regarding the curvature or extra roots.

However, since the exact facio-lingual dimensions or the mesiodistal shape including the presence of invaginations or laminations of the roots between the facio-lingual dimensions of the root cannot be accurately ascertained, it is imperative to have a thorough knowledge of the root anatomy before reconstructing the tooth.

A brief review of the major concerns in radicular anatomy before the restoration of the endodontically treated tooth is indicated if a post is to be used.

It is not imperative that each endodontically treated tooth should receive a post as a part of the restoration. Sorensen and Martinoff indicated that treated tooth is unrealistic. Therefore, in those teeth that need a post to retain a core build up careful attention must be directed to the root anatomy for selecting the appropriate post design, including shape, length, and method of placement.

Maxillary central and lateral incisors – have sufficient bulk of root to accommodate most post systems.

Care must be exercised in using posts with excessive length if the root tapers rapidly to the apex – because the thinner the root walls at the depth of the post placement, the greater the chance for root fracture.

Maxillary canines – have wide faciolingual roots and root canal spaces that commonly necessitate a custom cast post for desired adaptation to the root walls and there is a possibility of proximal root invaginations.

Restoration of maxillary premolars – presents a variety of problems when one anticipates a postretained core. Root walls are commonly thin, and root tapers rapidly to the apex, especially when two distinct roots are present.

Proximal invaginations and canal splitting are common during preparation of the canal from the coronal to apical root structure.

Root curvatures to the distal are common-preclude using long posts.

The curvatures of the palatal root can be facial, results in root perforation during post space preparation or cementation.

Thinness of these roots – removal of dentin for the placement of a post results in a weakened root wall which in turn leads to fracture either cementation or during function.

Same observations are true for the second premolars, but these teeth generally have greater bulk of tooth structure.

Maxillary molar: Suitable root = Palatal root.

Even this root presents restorative problems. 85% of the palatal roots curve facially and when invaginations are present they are located on the palatal and facial surfaces. This combination of root curvature and radicular invaginations predisposes the root walls to weakening or perforation during placement of long or thick posts.

As a result palatal roots can be fractured, requiring root resection, tooth extraction or surgical endodontics to repair the perforation.

Placement of posts in the MB and DB roots is contraindicated.

Mandibular incisors: Difficult teeth to restore with a post and core – and success rates have been higher without a post. root walls are thin and proximal invaginations are common.

9

Placement of a post is commonly compromised by multiple canals with significant bone loss. precluding the placement of a post in an unsupported root. This problem was identified by Reinhardt et al – in teeth restored with a post and core having diminished bone support of 4-6mm, stress concentration occurs both at the post apex and on the adjacent root periphery in a relatively narrow band of remaining dentin-potential for fracture in greater.

Mandibular canines: similar as maxillary canines.

Mandibular premolars: Have sufficient bulk of root structure.

Care must be exercised to ensure that the entire root canal has been managed become there is a proclivity for multiple canals.

One area of concern: with first premolar is the angle of the crown to the root. Often the root will be lingual inclined and active drilling of a post space perpendicular to the occlusal surfaces will result in a perforation along the facial wall of the root.

Mandibular molars: Major problem due to mesiodistal thinness of the mesial and distal roots. Along the root curvatures, there are commonly invaginations and perforations that are invisible radiographically.

The roots may be substantially weakened if they are prepared for prefabricated circular posts – because the roots are externally wide facio-lingually and narrow mesiodistally. In these cases, fracture may occur during post cementation or patient function. These types of fractures have been termed “ODONTLATROGENIC” in origin and should be recognized by the dentist.

INDICATIONS AND CONTRAINDICATIONS: A) INDICATIONS : Anterior teeth: 1) Where the natural crown of root-filled teeth either has been lost or is extensively damaged.

2) Where the root-filled tooth is to be used as bridge abutment.

3) Where a change in axial position greater than 1mm is required.

4) In a crowned anterior endodontically involved tooth, to reinforce the crown covered tooth at cervical area susceptible to fracture.

5) Intact natural teeth crown grossly discolored and destined to receive a crown 6) Loss of two proximal surfaces with a lingual endodontic access opening which weakens the tooth.

Posterior teeth: Indications, 1) Indicated when the remaining coronal portion is insufficient to support the restoration and sufficient long thick root structure is present.

2) Indicated when the root-filled tooth is to be used an abutment for a bridge.

3) In case of malposed teeth, when preparation of tooth would cause exposure of the pulp- of choice for aligning coronal portion of the tooth.

4) Indicated in restored bicuspids that are endodontically involved.

5) A shortened tooth – due to the nature of destruction, or removal of undermined, undesirable tooth structure.

6) Where there is a vital tooth with insufficient retention for a conventional crown 7) Indicated in favorable periodontal and periapical conditions with good oral hygiene.

Contraindications : 1) Severe curvature of the root-eg: Dilacerations of the root.

2) Persistent periapical lesion 3) Poor periodontal health 4) Poor crown to root ratio 5) Weak / fragile roots 6) Teeth with heavy occlusal contacts 7) Patients with unusual and occupational habits 8) Economic factors 9) Inadequate skill.

10

IDEAL REQUIREMENTS OF POST CORE: Ideal properties of the post (post): Posts should have as many of the following clinical features as possible: 1) Maximum protection of the root 2) Adequate retention within the root 3) Maximum protection of the crown marginal cement seal 4) Pleasing esthetics, when indicated 5) Radiopacity 6) Be simple, safe, versatile, and reliable in clinical use.

7) Not create stresses in the remaining tooth tissues during preparation and cementation.

8) Allow an even distribution of all functional stress 9) Include provision to ensure appropriate support and retention of the core.

10) Include features of facilitate removal, if so required, even after prolonged periods of clinical service.

11) Be made of bioinert material (s) that resist corrosion and other forms of deterioration in the mouth 12) Have been the subject of relevant research, including clinical research sufficient to justify recommended applications, to support any claims made by manufacturers, and to demonstrate appropriate in service performance.

13) Be widely and readily available at reasonable cost.

14) Resist loosening and displacement due to occlusal and other functional stress.

Core materials: Requirements: 1.

Stability in wet environment 2.

Ease of manipulation 3.

Rapid, hard set for immediate crown preparation 4.

Natural tooth color 5.

High compressive strength 6.

High tensile strength 7.

High MOE 8.

High fracture toughness 9.

Low plastic deformation 10.

Inert (no corrosion) 11.

Cariostatic properties 12.

Biocompatibility 13.

Inexpensiveness.

CLASSIFICATION OF POSTS AND CORES: 1.

2.

Depending upon the preparation : a. b.

Custom-made cost post and cores Prefabricated posts and cores

Prefabricated posts and cores are further classified into

Metallic 1.

Non-Threaded 2.

and wiptam wire.

3.

Non-Metallic

Non-threaded casts posts and cores. E.g. Para-post, master-post.

Threaded Ceramic Non-threaded wrought posts with cast on cores. E.g.(white Post, GT-post CM-post zirconium oxide) Non-thread wrought posts with direct build up cores. carbon fiber posts fiber-reinforced resin posts

11

E.g. Para-post, Master-post, GT-post, CM-post, Unimetric post, Dentatus anchor posts, and Ancorextra anchorage posts.

• •

A non-threaded post relies for its retention as well as equal stress distribution, on an intimate fit within the root canal and the use of a luting agent.

Threaded posts provide a distinct retentive advantage, but in the past their use has been controversial because of the potential risk of root fracture associated with the “active” cutting of the thread during placement.

Most modern threaded posts are now designed into canals that have been prethreaded or tapped and accordingly these posts are considered to be passive. There is an increase in stress within the root canal when luting cement is placed between the post and canal wall. However there is evidence that such fitting stress can be reduced, if not eliminated, in prethreaded canal – with a “split-shank post” – because of escape of excess luting cement occurs via the split shank.

1) 2)

Threaded integral wrought posts with solid core. E.g. Titronic –K-anchor post.

Threaded wrought posts with core super structure, E.g. RVS post, Exatec-post, vlock-komet post, Radix – Anker – Long Cytcopost.

3) Threaded wrought posts with direct build up cores. E.g. Vlock-Komet post, Tiflex pins, Titronic – KR post.

3.

Depending upon geometrical configuration a.

Tapered b.

Parallel 4.

Depending upon surface configuration a.

Smooth b.

Serrated c.

Threaded To improve the retentive and mechanical properties as well to decrease the percentage of root fractures some posts with combinations of two or more basic types are introduced they are  Parallel sided posts with tapered apical ends  Tapered flexi post  Parallel V lock drill and post system  Parallel radix anchor system  Parallel threaded posts with pre tapered channels, Parallel Sided Posts with Tapered Apical Ends: These posts, designed to provide the greater retention of parallel posts yet better conform to the tapered apical portion of the canal, come in 2 variations. One, the Degussa, is completely smooth-sided.

The straight and tapered portions are about equal in length. The second variation is the Unitek BCH system with lower frequency of serrations along the parallel sides and a smooth apical taper of about 2 mm. The BCH post also has a larger coronal portion to provide retention for core build-up materials.

Parallel posts with tapered ends have a lower retention potential. They produce little or no installation stress.These posts produce a definite wedging effect in the area of the apical taper.

Tapered Flexi-Post: Flexi-Post is a prefabricated, split-shank, parallel-sided, threaded post that reportedly absorbs the stresses of insertion, while providing maximum retention. As the apical half “collapses,” it becomes a tapered post.

The Flexi-Post gains its significant retention by its threads cutting into the dentin 0.1 mm to 0.2mm.

The channel to receive the post is prepared by a drill sized slightly larger than the diameter of the shaft of the post. The blades (threads) extend beyond the shaft by 0.2mm and engage into the dentin. Flexi-Post was found to be twice as retentive as Para-Post but not quite as retentive as the Boston Post system.

“Flexi-Posts provided the greatest resistance to torsion and tensile loading.

Because it is an active-type post, that is, self-threading into the dentin. Flexi-Post must exert some stress when it is installed. It is first “screwed” into the prepared canal with a tiny wrench, then removed counterclock wise, to be reinserted with cement into the same dentin threaded grooves. Because the apical half of the post is split, it collapses inwardly, thus reducing the strains that would otherwise be produced were it a solid screw post.

Parallel V-Lock Drill and Post System:

12

The widely separated “micro-threads” of the V-lock post extend 0.5 mm from the shaft and continue its full length. V-lock posts are supplied with precise drills that prepare a parallel-walled canal just slightly larger than the post shaft. They can be cemented with any cement or adhesive.

Burgess reported that V-lock posts were the most resistant to compressive loading – somewhat more than Flexi-post or Para-Post. In resistance to torsional loading tests, V-lock posts fell about midway between Para-Posts and Flexi-Posts.

Parallel Radix Anchor System : Radix anchor posts gain their primary retention by self-cutting counter-threads in the dentin. The Radix anchor post differs from the V-Lock post by the number of its threads, which are sharp low-frequency helical blades that extend only partly down the shaft. It is vertically vented. The Radix post is designed to fit snugly in a channel prepared for it in the root. It can be cemented with any cement, but preferably Composite resin.

Because of the limited number of threads, the Radix Anchor has less retention than other actively retained posts. Moreover, if the canal is ovoid or too flaring, the blades never contact dentin. In that case, it has hardly more retention in cement than a smooth post.

A fully seated Radix Anchor induces severe stress due to the surface irregularities of the root face and the nonperpendicular alignment of the post and coronal dentin.

Perhaps the most critical aspects of parallel-sided threaded design are the initial threading insertion and the later cementation. Following channel preparation, the post is carefully threaded into the dentin. It is then backed out to be returned, hopefully engaging the same counterthreads in the dentin, for final cementation.

The Radix anchor post generates greater stress under oblique compressive forces than the Kurer post. The main load transfer takes place between the threads and the dentin.

Parallel Threaded Posts with Pre-Tapped Channels : The Kurer Anchor posts are the only dowels on the market that fit into pretapped counterthreads in the dentin . Another unique feature of the Kurer Anchor is the Kurer Root Facer which prepares a flat seat in the root face into which the coronal portion is to fit perfectly.

“Parallel-sided, threaded posts, cemented into tapped channels, are superior in retention to all other post designs. Because of its high retentive capability, the Kurer post is favored when very high loads must be supported : partial denture and overdenture attachment abutments, long span bridges, etc. This post is also very useful when only short embedment depths are possible because of root length and shape.

Kurer posts produce severe apical stress levels if the apex of the post fully engages the bevel produced by the twist drill at the channel apex. This may be obviated by trimming the post length short of the apical bevel in the canal. When cemented, it should be fully seated with the end of the threaded shank just short of the tapered part of the channel. The coronal seat in the root-facer preparation should be just touching, not screwed down so tightly it produces strains. When Kurer posts are cemented into their tapped channels, their buffering effect is less pronounced. The main load transfer takes place between the threads and the dentin. The high-frequency threads of the Kurer design lower the localized stress concentrations under load because of the increased surface contact.

5.

New restorative classification of endodontically treated teeth :

By Paul R. Chalifoux The classification, which presents important considerations for restoration, is based on the number of canals, amount of coronal tooth structure, chamber space, canal quality, and orientation.

Classes 1,2 &3 refer to teeth with one, two or three canals. Each of these classifications is further subdivided into complete (c), partial (p) and no (n) coronal tooth structure. Complete coronal tooth structure comprises a range of 66-100%, partial, 33 to 65% and no. 0 to 32%. The percentage of remaining coronal tooth structure, after root canal and restoration preparation is defined as the least of the two percentages: The first percentage is a measurement of the coronal height – the second percentage of the smallest horizontal cross section in the gingival half, based on observation, experience and estimation.

Each of the above nine classifications is further subdivided/evaluated by: 1.

Chamber space 2.

Canal quality 3.

Canal orientation

Class 1 (one canal) 2 (two canals) 3 (three canals)

Tooth structure Complete (C), partial (P), No (N) Complete (C), partial (P), No (N) Complete (C), partial (P), No (N)

13

C = 66-100%, P = 33-65%, N = 0-32% Sub classification : Chamber space

Present

Canal quality

Absent Shape Size Taper

Canal orientation

Parallel interlocking

Interlocking; interlocking

limited

interlocking

non-

Segmented: straight, curved Uniform: straight, curved Diameter: uniform, segmented Length: straight, normal, long Uniform: parallel, tapered Segmented: parallel, tapered Canal-canal, canal-component

CORE classification: The core consists of restorative material placed in the coronal area of a tooth. This material replaces carious, fractured, or otherwise missing coronal structure and retains the final crown.

The core is anchored to the tooth by extending into the coronal aspect of the canal or through the endodontic post. The attachment between tooth, post and core is mechanical, chemical or both as the core and post are usually fabricated of different materials.

The remaining tooth structure can also be altered to enhance retention of the core. Although, pins, grooves and channels can be placed in the dentin, these modifications all increase the core retention and resistance to rotation at the expense of the tooth structure. In most cases the irregular nature of the residual, coronal tooth structure and the normal morphology of the pulp chamber and canal orifices eliminate the need for these tooth alterations. Using restorative materials that bond to tooth structure enhances retention and resistance without necessitating the removal of valuable dentin. Therefore, if additional retentive or antirotation form for the core is deemed necessary, dentin removal should be kept to a minimum.

Materials used: 1. Cast gold 2. Amalgam 3. Composite resin 4. Glass ionomer 5. RMGIC 1) Cast gold: Type III and Type IV cast gold alloys are used.

Advantages: 1. Offers good strength 2. Resistance to leakage derived from luting agent 3. Does not absorb water 4. COTE close to that of dentin.

5. Cast gold buildups require post for retention and substantial degree of coronal destruction to be used.

Disadvantages: 1. Time consuming 2. Expensive

2) Amalgam: Material of choice in high stress situations Advantages: 1. Simple to use 2. Radiopaque 3. High compressive strength and fracture toughness in both static and dynamic loading.

4. High contrasting color to the tooth 5. Dimensionally stable 6. Antimicrobial 7. Acceptable long-term performance as documented in the literature.

Disadvantages:

14

1.

2.

3.

4.

5.

High thermal conductivity High co-efficient of thermal expansion than the tooth Does not adhere to the tooth substance Low early strength –requires separate appointment for crown preparation Dark color of Amalgam – potential to lower the value of all – ceramic restorations causing a gray halo at the gingival margin.

3) Composite Resin: Possess satisfactory physical properties for use as core buildup material.

Advantages: 1. Reliable bond to tooth structure 2. Highly radiopaque 3. Command set nature – allows immediate crown preparation 4. Adequate fracture toughness and compressive strength in static and dynamic loading.

Disadvantages: 1. High coefficient of thermal expansion – potential for microleakage 2. Not dimensionally stable in wet environment 3. Water sorption – absorbs water = core expands, composite dries = core shrinks.

4) Glass ionomer cement: It should be used in posterior teeth with more than 50% of tooth structure remaining.

Advantages: 1. Adhesion 2. Fluoride release 3. Co-efficient of thermal expansion similar to tooth 4. Radiopaque 5. Contrasting color to tooth Disadvantages: 1. Low compressive strength and fracture toughness 2. Low flexural strengths.

5) Resin modified glass ionomer cement: Newest available core material.

Advantages: 1. Adhesion 2. Fluoride release 3. Easy to manipulate 4. Intermediate physical properties – lie between GIC and composite resin.

Disadvantages: 1. Low flexural strength and fracture toughness 2. Volume in stability – severe expansion during initial setting reaction.

3. Not a material of choice in high stress situations TREATMENT PLANNING: 1) Patient selection: As when embanking on any other restorative procedure, the health of the supporting tissues should be assessed, and any advice and treatment necessary to ensure the continuing health of these tissues carried out prior to definitive restoration of the teeth themselves. The patient’s ability and motivation of cooperate in treatment and after care must be assessed.

1. The age of the patient is also a relevant consideration. In anterior teeth – where the appearance is important, it is usual to place the crown margin, just within the gingival crevice. In young patients, where eruption either active or passive may not be complete, the margin may become exposed and aesthetically unacceptable. In such cases it may be necessary periodontally to replace the crown element of the restoration, until such time as the gingival margin reaches a stable position.

Since the crown margin, in such cases will require re-preparation, the post and core element cannot be designed to strengthen the root by means of a diaphragm.

2. Participation by the patient in contact sports is another factor to be considered. It is usually unrealistic to expect the patient to avoid such activities and so thought should be given to providing a mouth guard to minimize the possibility of damage to the tooth and crown by trauma.

2) The tooth crown: Factors to be considered include:

•

Extent of the tissue loss and whether this has resulted in over eruption of the tooth or its opponent.

15

• • •

Relationship to the adjacent teeth.

Any tilting of the tooth itself or if its’ neighbors.

Degree of occlusal wear (points to the magnitude of the forces to which the crown and post will be subjected during function).

•

Cosmetic considerations and exposure.

3) The root: a. b.

Tooth should have a sound root filling and a good prognosis.

Factors, which influence the retention of the post, should be considered.

E.g. i) Tapered posts are not suited to teeth with short roots. A threaded parallel-sided post may give a greater retention. ii) Fine, narrow canals / roots – require tapered posts to minimize the possibility of root perforation.

STRESS ANALYSIS FOR POST AND CORE:

Restoration of the pulpless tooth is critical for successful endodontic therapy. The nature of force existing in teeth and surrounding tissues has been a subject to investigation by dental researcher for a century or more. As technique has developed for increasingly radical restorations of damaged teeth, interest has naturally expanded to include stresses induced in reconstructed teeth in function.

Knowledge of the kinds of stress normal dental structures must withstand and therefore restored structures should withstand is of obvious value. The ability to perform stress analysis on reconstructed teeth is of substantial importance in optional prosthesis designs.

Stress analysis methods used: 1. Photoelastic stress analysis 2. Finite element stress analysis Clinical longevity of the post and core restoration can be function of : 1. The thickness of remaining dentin.

2. Magnitude and direction of the load.

3. Design of the post.

4. Fit of the post into the prepared root canal.

5. Quality of the cement layer.

16

Loading of cemented post and core in a root creates stresses in the root, and if the tensile stresses are high-fracture of the root may occur.

Frequent loading may cause strains and stresses in the cement film and consequent release of the post.

Physical principle: 1. Anterior teeth: In general,

Direction of the load ↓ Upper anterior teeth ↓ Upwards and outward, moving the crown of the tooth in a labial direction out of the arch, adjacent teeth giving no support.

In most cases : central dentinal core of the crown will be weakened by access cavity prep and possibly by caries as well. ↓ This means the main stress will be accepted by the remaining dentin at the labial gingival margins. Unless there is considerable bulk of dentin in that area – simple restoration of the coronal form may be insufficient to reinforce the tooth as the restoration materials are weak in tension. ↓ Generally necessary, to reinforce the crown by placing a post into the root canal. So moving the potential point of fracture from the gingival margin of the crown some distance up to the root towards the root apex. ↓ Load applied to lower anterior teeth ↓ Opposite downwards and inwards directions ↓ Tend to close the arch – and crown will gain support form adjacent teeth. ↓ Reinforcement by placement of the post is therefore not as important.

Tapered post: Increase stress concentration at coronal shoulder. It causes wedging effect – decreased stress concentration at the apex – due to absence of sharp angles and conservation of tooth structure.

Parallel post: Disperses the stresses uniformly along its length except at the apex. Because of definite seat of the post on the dentin, sharp angle at the apex of the post and reduced tooth structure.

FACTORS INFLUENCING RETENTION AND RESISTANCE: I. Retention features 1.

Post design : Regarding retention, the active threaded post is most retentive, followed by the passive parallel post: the passive tapered post is least retentive. The style of post selected should be based upon the amount of retention required for long-term success of the post.

For e.g. If the available post space is short, 5-6mm, a more retentive active post may be indicated.

If the available post space is 8-9mm and the canal is not funnel shaped – a tapered post may be a better choice. This is because the available post space is long enough to provide adequate axial retention and it does not require canal enlargement during post space preparation.

The design of the post head has a significant effect on the retention of the core material. A post should be selected that has a head designed appropriate for the chosen core material.

2.

Post length : It is evident that greater post length results in greater post retention. However it is important that 45 mm of gutta-percha remain at the apex to minimize leakage. When placing a passive post, it should generally be as long as possible while not encroaching on the necessary remaining gutta-percha.

3.

Post diameter and remaining dentin : Although post retention slightly increases with an increase in post diameter, the ultimate tooth-post combination is weakened because of the increased post diameter. The post diameter should be as small as possible while providing the necessary rigidity. It is always important to leave as much tooth structure as possible in all phases of treatment.

17

Each mm of increase (beyond 1/3rd the root diameter) causes a six fold increase in the potential for root fracture.

Three different philosophies regarding post diameter: • Conservative approach: Advocated by Mattison – to restrict the diameter of the post to conserve the remaining tooth structure.

Increase in post diameter-elevates stress in the radicular surface.

• Proportionist approach: Advocated by Stern and Hirschfeld – optimal diameter one-third the diameter of the root. It preserves sufficient tooth structure.

• Preservationist approach: advocated by Halle et al – proposed the preservation of at least 1.75 mm of sound dentin around the entire circumference of the post-sufficient to resist fracture of the tooth.

For selecting the post diameter – suggested that the proportionist and preservationist approach be applied.

4.

Surface preparation : Preparation of the both the surfaces of the post and the canal surface can significantly increase / improve post retention. Air abrasion and notching of the post have been shown to increases retention. Lab data indicate that placing notches or grooves in the surface of the canal also improves post retention.

5.

Canal preparation : There are three primary method of gutta-percha removal for post space preparation – including rotary instruments, heat, and solvents. All the three methods are effective – regardless of the method used, care must be taken to ensure that the PDL is not damaged. Injudicious use of rotary instruments, such as Peeso Reamers, may cause a significant temperature increase on the root surface. Similarly, a hot instrument may damage the PDL. Post space preparation may be accomplished at the same appointment in which the canal is obturated or can be delayed for 24 hrs or more. The in-vitro data do not indicate that one method is superior to the other.

Suchina and Ludington and Mattison et al found no difference between hot instrument removal and removal with gates glidden burs. However, Haddix et al measured significantly less leakage with a heated plugger than when either a GPX instrument or gates glidden drills were used.

6.

Cement placement : The method used to place cement into the canal before post placement has a significant effect on post retention. Spinning the cement into the canal with a Lentulo spiral has been shown to be the most effective method. The Lentulo spiral attached to a low speed handpiece smoothly spins the cement into the lateral walls of the canal and eliminates air pockets, hence absence of air voids, which may have significant effect on the retention of the post. Other methods used for placement of the cement are use of an endodontic explorer, paper point and direct application of the cement on the post. These methods produce voids in increasing numbers in the following order: The endodontic explorer < direct application < paper point < Lentulosprial: 7.

Luting cements : The importance of the type of cement used for Luting posts has been over emphasized in the dental literature.

Currently there are five types of cement available for post cementation. In recent years, there has been a greater deal of interest in the use of resin cement to bond a post into the prepared canal. Some lab studies have shown a significant increase in post retention with resin cement.

If zinc oxide eugenol is used as a sealer – it is not possible to bond a post into a prepared canal when Zinc oxide eugenol is used as the sealer. Composite luting cement provides no advantage over more traditional cements and it is significantly more expensive and technique sensitive.

Polycarboxylate cement has a lower compressive strength and therefore is not a first choice.

Glass ionomer has adequate physical properties – however it is a slow setting material that requires many hours of achieve adequate strength. Resin-modified glass ionomer cement – as originally formulated, had significant setting expansion.

The most traditional zinc phosphate – has adequate physical properties, is inexpensive, and easy to use – remains an excellent choice for post cementation.

18

Resin cement : 2 matrices a.

Calcium alunisoilicate glass polyacrylic acid b.

HEMA derivative The first matrix undergoes acid-base reaction to form an calcium aluminum polysalt hydrogel.

The 2 matrices cross-link to form hybrid materials.

Advantages : 1. Added advantages of GIC 2. Bond to enamel and dentin 3. Fluoride release 4. Light cured / dual cured 5. Better physical properties.

The ability of different cements to retain dental posts is related : • Mechanical properties of the cement • Bonding efficiency of the cement to the two surfaces being joined.

• Durability of the cement • The configuration of the post and the prepared canal, which influences the stress distribution within the cement, layer.  Zinc phosphate, polycarboxylate, GIC and resin cement – commonly used.  Cement layer provides a “buffer zone” that contributes to uniform stress distribution between the post and the canal  A thicken or variably thickened layer of cement could transfer stresses to the tooth in a different manner than a uniform layer of cement.  Inherent weakness / brittleness of the cement affect the fracture resistance of endodontically treated tooth.  Normal occlusal forces create micromovements of a crown and the cemented post.

These micromovements are considered to cause disintegration of the brittle cement in the most coronal surface of the post  Resulting in concentration of stresses at the apical end of the root and leading to root fracture because of an increased lever arm.

Newer resin cements bond effectively to dentin and to metal. they give additional resistance to fracture compared to brittle non-bonding zinc phosphate cement – as showed by Mendiza et al.

Cementation technique : has important effect upon the eventual retention and stress distribution of the post.  Essential to achieve a uniform, bubble free layer of cement that distributes the stress evenly throughout the entire root canal.  Use of a lentulosprial – considered to be superior to place the cement into the canal. It gives better spinning and spreading of the cement because of centrifugal dispersion of the cement.

It also reduces voids and increases the contact of the cement with the walls.  During cementation – post space should be free of any residue, as it has been reported that even a small nodule on the post surface or temporary cement residue in the canal can generate enough force to cause root fracture during and after post cementation.

Other possible causes of root fracture are :  Development of hydrostatic pressure in the cement  Excessive seating pressure  Excessive torque exerted by the clinician on the post during cementation.

Before cementation of the post : 1. Post space should be cleaned by a chelating agent, 17% EDTA for 30 seconds.

2. Followed by rinsing with 5.2% NaOCI (30 sec) 3. Canals should be rinsed with water and dried with paper points.

This procedure will help the post space wall to be free of root canal sealant, debris and dentinal smear layer.

Film thickness Working time

Zinc phosphate ≤25

Poly carboxylate <25

GIC

Compomer

<25

Resin ionomer >25

1.5-5

1.75-2.5

2.3-5

2.4

3.10

Adhesive resin cement

>25 0.5-5

19

Setting time Comp.

Strength (MPA_ Elastic modulus Pulp irritation Solubility Microleakag e Removed of Retention

5-14 62-101

6-9 67-91

6-9 122-162

2 40-141

3-7 194-200

1-15 179-255

13.2

-

11.2

-

17

4.5-9.8

Moderate

Low

High

High

High

High

High High

High Very high

Very low Very low

Medium Low-moderate

Very low High-to very high Medium Moderate

Very low Very low to low

Easy Moderate

Low Lowhigh Medium Moderat e-high

GIC (Mpa)

ARC (Mpa)

RMGIC (Mpa)

14-21 7-19

44-50 70-100

17-27 50-53

Medium Moderatehigh

Difficult High

Li and white – Mechanical properties of luting cement : Zn phosphate (Mpa) Diametral T.S Flexural strength

10 4-7

Poly carboxylate (Mpa) 12 14.3-20

8. Venting : Because of the intraradicular hydrostatic pressure created during cementation of the post, a means for cement to escape must always be provided. Because virtually all prefabricated posts have a venting mechanism incorporated in their design, this factor is important with the custom cast post. A vent may be incorporated in the pattern before casting or into the with a bur prior to cementation.

II. THE RESISTANCE TRIAD: Second major consideration in the design of the post restoration is the resistance of the tooth – post-crown combination. If the resistance requirements are not met, the probability of failure is high, regardless of the retentiveness of the post.

Three parameters of resistance must be considered. The resistance triad consists of the 2. Ferrule effect 3. Vertical remaining coronal tooth structure 4. Anti rotation.

These features work in combination: therefore, if one of the features is minimal or non-existent, one are both of the remaining features must be increased.

2.

The first feature of the resistance triad is the ferrule : The Ferrule is a metal ring or cap intended for strengthening. The word probably originates from combining the Latin for iron (ferrum) and bracelets (viriola) (Brown, 1993).

Ferrul = ferrum + viriola (Latin term) A dental ferrule is an encircling band of cast metal around the coronal surface of the tooth. It has been proposed that the use of a ferrule as part of the core or artificial crown may be of benefit in reinforcing root-filed tooth.

A protective, or “ferrule effect” should occur owing to the ferrule resisting stresses such as functional lever forces, the wedging effect of tapered posts and the lateral forces exerted during the post insertion.

Rosen proposed the concept of an “extracoronal brace” subgingival collar or apron of gold which extends as far as possible beyond the gingival seat of the core and completely surrounds the perimeter of the cervical part of the tooth. It is an extension of the restoration crown, which by its hugging action prevents shattering of the root.

The collar significantly reduced the incidence of root fracture.

To be effective – it must encircle the tooth (360 0) and ideally extend at least 1.5mm onto tooth structure below the post and core margin.

20

3.

Vertical remaining tooth structure : Traditionally, it was thought that the face of the root should be flattened prior to the construction of the post and core. However, it has been shown that leaving as much natural remaining tooth structure as possible will significantly increase the resistance of the final restoration. Unfortunately, because of caries, trauma, or iatrogenic removal, vertical remaining tooth structure is not always available.

4.

Antirotation : Every post and core must have an antirotation feature incorporated in the preparation. â&#x20AC;˘ An elongated or oblong canal orifice can serve as an antirotation for post and core. â&#x20AC;˘ However, as the canal becomes more round, the need for incorporation of antirotation features becomes more important. This is especially true for anterior teeth. â&#x20AC;˘ Auxillary pins and keyways are prepared in the face of the root prior to construction of the post and are most common antirotation devices.

Instrumentation.

A wide variety of instruments can be used for enlarging the root canal for a post: Safe-ended reamers, hand file, standard burs with long shanks.

The preparation is begun by placing a hot endodontic plugger approximately half the length of the canal. This is followed by the actual post preparation. Peeso reamers or Gates Glidden drills are widely used for preparing the post space.

The Gates Glidden drill shares several common traits with the Peeso reamer: a non-cutting tip and a similar configuration in the cutting end. On the other hand, the Gates Glidden drill has much shorter cutting flutes (1.5-4.0mm) than those of the Peeso reamer (7.5-8.5mm). All sizes of both instruments measure 18 mm from the cutting end (base of the safety tip) to the end of the tapered shaft, which is flush with the head of the handpiece.

Because the Peeso reamers have a sharp, but noncutting tip, they will follow the path of least resistance, which is the cleared canal or the gutta percha in the canal. Peeso reamers will also conform more consistently to the original canal in the apical region than will other types of instruments.

Begin with the largest size that will fit easily into the canal. Prepare the canal to the complete predetermined length. Then switch to the next largest instrument in the graduated series and repeat the process. Do this until the desired diameter has been attained. Gates Glidden drills are easily used because the cutting portion is smaller and more maneuverable. They are often easier to use in starting very small canals. The Gates Glidden drills, distinguished by their shorter cutting flutes and more flexible shafts, use the same numbering system. The sizes range from 0.6 to 1.5mm. However, so that a no. 4 Peeso reamer (1.3mm) and a No.4 Gates Glidden drill (1.1mm) are not of the same diameter. The preparation should be completed with the series of Peeso reamers, however. The Peeso reamers numbered 1-6, range in diameter from 0.7 to 1.7 mm in graduated increments of 0.2 mm. The longer cutting segment in it will prepare a straighter canal wall with less likelihood of an undercut. The instrument is leaned over lightly as it is withdrawn from the mouth of the canal. This will result in an essential parallel-sided preparation with a tapered orifice.

Peeso Reamer Sizes: Reamer Number 1 2

Diameter

Teeth

0.7mm 0.9mm

3

1.1mm

4.

1.3 mm

5 6

1.5mm 1.7 mm

Mandibular incisor Maxillary first premolar Maxillary second molar (DF) Mandibular first molar (ML) Mandibular second molar (MF, ML) Maxillary second premolar Maxillary first molar (MF, DF) Maxillary second molar (MF) Mandibular first molar (MF, D) Mandibular second molar (D) Maxillary lateral incisor Mandibular premolar Maxillary molar (L) Canine Maxillary central incisor.

21

• • • •

Custom cast post has a long history of clinical success Developed in the 1930’s to replace the one-piece post crowns.

This procedure requires casting a post and core as a separate component from the crown This two-step procedure improves the marginal adaptation and allows for a variation in the path of insertion of the crown.

• The traditional custom cast post core provides a better geometric adaptation to excessively flared or elliptical canals.

• It almost always requires minimum tooth structure removal • Custom cast post and cores adapt well to extremely tapered canals or those with a non-circular cross-section or irregular shape, and roots with minimal remaining coronal tooth structure.

• This method requires two-appointment visits and a laboratory fee.

• As it is cast in an alloy with a modulus of elasticity as high as 10 times the natural dentin = this possible incompatibility can create stress concentration in the les rigid root, resulting in post separation or failure.

• The transmission of occlusal forces through the metal cores can focus stresses at specific regions of the root, causing root fracture.

• Upon esthetic considerations, case metallic post can result in discoloration and shadowing of the gingiva and the cervical aspect of the tooth.

The custom – cast post has a long history of clinical success. However, when it is compared to parallel pre-fabricated posts, both in vitro and in vivo, its superiority is questionable.

There are, however circumstances in which the custom-cast post is the restoration of choice, including, the following: 1. When multiple cores are being placed in the same arch. It is more cost effective to prepare multiple post spaces, make an impression and fabricate the posts in the laboratory.

2. When post and cores are being placed in small teeth, such as mandibular incisors. In these circumstances, it is often difficult to retain the core material on the head of the post.

3. When the angle of the core must be changed in relation to the post. Prefabricated posts should not be bent; therefore, the custom – cost best fulfills this requirement.

4. When an all-ceramic non-core restoration is placed it is necessary to have a core that approximately the color of natural tooth structure. If a large core is being placed in a high-stress situation, resin composite may not be the material of choice due to the fact that it tends to deform under a load. In this circumstance, the post and core can be cast in metal, and porcelain can be fixed to the core to simulate the color of natural tooth structure. The core porcelain can than be etched with hydrofluoric acid and the all-ceramic crown can be bonded to the core.

The traditional custom cast post core provides a better geometric adaptation to excessively flared or elliptical canals and almost always requires minimum tooth structure removal. Custom-cast post and cores adapt well to extremely tapered canals or those with a non-circular cross-section or irregular shape and roots with minimal remaining coronal tooth structure.

Patterns for custom cast posts can be formed either directly in the mouth or indirectly in the laboratory. Regardless, this method requires two appointment visits and a lab, fee. Also, because it is cast in an alloy with a modulus of elasticity that can be as high as 10 times greater than that of natural dentin, this possible incompatibility failure. Additionally, the transmission of occlusal forces through the metal core can focus stresses at specific regions of the root, causing root fracture.

Furthermore, upon esthetic consideration the cast metallic post can result in discoloration and shadowing of the gingiva and the cervical aspect of the tooth.

FUNDAMENTAL RULES FOR “POST” The post must be atleast as long as the crown it is to carry.

The post must have parallel sides or have a maximum convergence of 3.50.

The post must achieve a precision fit in the root canal.

Design principles to be considered…

The following design principles should be considered when using any post-retained crown system in the reconstruction of the tooth restorative complex.

1. Maximum post retention and core stability.

22

2.

Inherent antirotation of the post and core complex by accentuating the eccentric coronal shape of the root canal.

3. Minimal removal of the tooth structure 4. Morphologic intra-radicular adaptation.

5. Optimal esthetics 6. Inherent resistance to catastrophic failure of the root.

7. Lack of corrosiveness 8. Post with similar modulus of elasticity as root dentin to distribute applied forces evenly along the length of the post.

9. Restorative materials with flexural and tensile strength characteristics similar to root structure.

10. A system with uninterrupted bonding at all interfaces, resulting in increased resistance to fatigue and fracture, enhanced retention, and reduction in microleakage and bacterial infiltration.

Rational design principles for post and cores: No matter which cement or core material is used, there are certain design principles that need to be followed.

Prime objectives include: 1. A sealed interface between the restoration and the tooth structure, both down the post chamber and under the core. It is preferable that the luting material should bond to the tooth and prevent recurrent caries.

2. Adequate retention preferably not gained solely from the post but also from the core. Tooth structure can and should be retained, providing it has sufficient bulk and strength.

3. Inherent antirotation of the post and core complex 4. Minimal stressing of the residual tooth structure in preparation, post insertion, or postoperative function.

5. Negligible interference with preparation and restoration of the final crown complex.

6. Inherent resistance to catastrophic failure such as fracture of the tooth, caries down the post chamber, gross fracture of the core, or fracture of the post at the tooth level.

Prefabricated posts :

According to shape Parallel Tapered Parallel tapered

According to surface configuration Active Passive

But threaded post exhibit unfavorable patterns of stress distribution on placement and during faction.

Concentrate seen at the dentinal thread interface. To reduce stress induced by active posts.

1. Pretapping post channels 2. Limiting the number of post threads 3. Counter rotating the post by an ½ after its full engagement.

Custom Post-Core : Custom post-core can be fabricated in two techniques : • Direct • Indirect The procedures differ only in the means by which the post and core pattern is generated. Both utilize instrumentation and materials from the same system.

In the direct technique the custom post-core pattern is fabricated directly in the mouth on the prepared tooth.

The indirect technique utilizes an impression and stone die of the tooth for pattern fabrication. The pattern from either the direct or indirect technique is then invested and cast with gold or any other crown and bridge alloy.

Direct technique The direct custom post core is made by fabricating a resin or wax pattern in the prepared tooth in the patient’s mouth. Some form of plastic post or thin metal post is used as the central reinforcement around which the resin or wax pattern is formed. Relining the post, while it does take time provides for an accurate fit of the post in the canal, with faciolingual irregularities in the canal incorporated into the antirotational aspect of the post. When the canal is not ovoid enough to provide the needed anti-rotational stability, the canal preparation is modified with keyways to resist torque in the restoration.

The pattern can be made of wax reinforced with a plastic rod, a bur, a metal pin or a paper clip.

Acrylic resin can also be used for this purpose or wax and acrylic can be combined. The use of resin allows

23

the pattern to be formed into a well adapted solid post that can be manipulated easily in the mouth without becoming distorted or loose in the canal.

• After removing as much gutta-percha as possible with a hot endodontic plugger, begin the actual canal preparation with the largest reamer which will fit into the canal.

• Make a radiograph to check the accuracy of the preparation depth. Use the radiograph to make any necessary adjustments in the reamer length.

• A keyway is placed in the orifice of the canal to provide anti-rotational stability to the post. One or more vertical grooves are cut in the walls of the canals, extending 3-4 mm down the canal. The same effect can be achieved on a multi rooted tooth by placing a short post into a second canal.

• The keyway should be cut to the depth of the diameter of a No. 170 bur (nearly 1.0 mm) in the area of greatest bulk. A second opposing keyway is placed in larger teeth.

• Add a prominent contrabevel to provide a collar around the occlusal circumference of the preparation. It will aid in holding the tooth together and preventing fracture. This serves as a safeguard on a precision fitting post, which can exert lateral forces during cementation.

• The post-core pattern will be fabricated with a plastic screw and resin . Once the preparation is ready for the fabrication of direct pattern, wrap a cotton pellet tightly around a No.1 Peeso reamer and dip it into the duralay lubricant. The cotton should be completely coated with the lubricant.

• Insert the peeso reamer to the entire length of the post preparation. Then pump the reamer in and out to make sure that the entire canal is well coated. Some of the lubricant should be on the coronal part of the preparation as well.

• Use 14 gauge plastic sprues for the pattern. They are hard enough to reinforce the pattern and they will burnout cleanly. Plastic tooth picks are softened by the monomer and often are separated from the pattern during removal.

• Trim the sprue with a garnet disc so that it will fit into the canal easily. It must reach the apical end of the post preparation. Cut a small notch in the facial portion of the occlusal end of the plastic sprue to aid in orienting the pattern in subsequent steps. Coat the plastic sprue with monomer.

• Mix the duralay monomer and polymer to a thin, runny consistency in a dappen dish and fill the mouth of the lubricated canal as completely as possible with a plastic filling instrument.

• Coat the plastic sprue with the acrylic while it is still fluid.

• Seat the resin covered sprue in the canal until it has touched the apical end of the post preparation.

Make sure that all the external contrabevel is covered at this time.

• More resin is added to the coronal portion of the pattern to provide the bulk for the core. It can be added while the post is still polymerizing or it can be added as a fresh mix to the polymerized post.

• When the resin on the post itself becomes doughy, pump the pattern up and down to prevent its being locked into any undercuts in the canal.

• Remove the post from the canal and see if it extends the full length of the prepared canal . Fill any voids with soft utility wax and replace the pattern.

• Shape the coronal portion of the pattern to form it into a crown preparation for the final restoration.

• Remove the pattern from the mouth end roughly shape the axial surface with a garnet disc. Replace it in the tooth from time to time to ensure that the contours being shaped are consistent with the remaining coronal tooth structure. Be sure that the finish line of the final crown preparation is on tooth structure and not on the core.

• After complete finishing of core pattern, it is cast in gold or nickel –chrome alloy.

• The core portion of the casting should be smoothened to a satin or matte finish.

• Use a carbide no:34 bur to cut a V-shaped cement escape vent on the side of the post. This groove should help greatly to prevent damaging lateral stresses during cementation. While using the hard nickel-chrome alloys, this task can be made easier and faster by placing the groove in the acrylic pattern and retouching it in the finished casting.

• Prepare a thin mix of zinc phosphate cement and insert some into the mouth of the dried, isolated canal. Cover the blade of the instrument with cement a second time and hold it incisal to the mouth of the canal. Insert slowly rotating lentulo spiral paste filler through the mass of the liquid cement to carry the cement into the canal. Apply more cement to the mouth of the canal until no more will move into the canal.

• Liberally coat the post with the fluid cement and insert the post into the canal.

• Seat the post slowly with finger pressure, allowing the cement to escape ahead of the post. If the incisal edge of the core is uncomfortable against the finger, cushion it with a cotton roll. Never mallet the post to place. The close fitting hydraulic chamber formed by a custom post moving through a

24

â&#x20AC;˘

â&#x20AC;˘

viscous liquid in a parallel walled canal can produce considerable stress in the lateral walls of the tooth, and fracture could result.

When the cement has set , go over the axial surfaces of the core and tooth structure with a fine grit diamond as it is important to remove any minor undercuts in the axial surfaces near the margin of the post-core. If allowed to remain, any defects in the axial surface could present obstacles to the successful completion of the final restoration.

The tooth can now be restored with a crown. The portion of the coronal tooth form that has been built up with the core can be treated as though it were tooth structure when the final restoration is fabricated.

25

Indirect technique

A custom post-core can also be fabricated by making wax or resin pattern on a cast of the prepared tooth.

An impression can be made by injecting impression material into the canal and then using a lentulo spiral paste filler to ensure the elimination of entrapped air and voids in the impression of the canal.

The impression is reinforced with some type of rigid post. The items that have been used for this purpose are paper clips, short lengths of wire, plastic sprues, and a root canal instrument. These reinforcing devices not only strengthen the impression when it is made, but also when it is poured and separated.

A custom acrylic post can also be made in the tooth to serve as the impression of the canal in transferring it to a cast for fabrication of the core and restoration. When the indirect technique is used with one of the prefabricated precision plastic patterns, a post pattern is placed into the canal, and it is picked up in the impression. The post then creates its own space in the cast when the impression is poured.

• While any impression material with which the operator is familiar can be used, light body elastomeric materials which are more flexible is preferred.

• Once the cast is poured, a removable die should be fabricated. The cast is mounted in a Di-Lok tray. This permits the use of a removable die without any possible interference between a post pin on the bottom of the die and the post core preparation deep within the die.

• The wax pattern can now be fabricated on the die and working cast.

• Lubricate the die copiously with a die lubricant. Make sure the post preparation is well filled.

26

•

•

• • • •

• • • • • •

Dead soft,12 gauge round wax forms can be used to form the post. It is placed into the bottom of the canal in the lubricated die. Cut it off flush with the top of the coronal tooth structure with a sharp laboratory knife.

Grasp a piece of wire such as a straightened paper clip in cotton pliers and heat it in the flame of a Bunsen burner. Plunge the hot wire into the canal until it touches the bottom, melting all the wax in the canal. Hold it steady until the wire cools and the wax solidifies.

Gently pump the wire and soft wax post in and out a few times to make sure that it is easily removable from the die.

Use regular inlay wax to build up the core portion of the wax pattern.

Finish the margins of the core with a warm beaver tail burnisher to produce as well fitting a casting as possible.

The completed wax pattern will have the paper clip protruding from the incisal edge or lingual surface. The wire will serve as the main support of the sprue. Soft wax is added to the wire to thicken it to the diameter of a 10 or 12 gauge sprue.

Investing and casting can be done in the regular way. Place the completed post -core in the die, making sure that it is completely seated.

Relubricate the die and lubricate the core. Then wax a coping for the porcelain fused to metal crown.

Seat the cast coping back on the post core in the die. The marginal adaptation should be good and the fit of the coping over the post core and die should be passive, i.e., there should be no binding.

Porcelain fused to metal restoration is fabricated.

The post-core and crown are cemented sequentially, paying particular attention to the marginal fit of the porcelain fused to metal crown.

If there is any question about the ability of the technician to produce a well fitting crown with this non – stop technique, then the post-core should be cemented and an impression is made for fabrication of the porcelain fused to metal.

CUSTOM DOWEL-CORE (TWO PIECE) : Single piece post-core is an excellent restoration for anterior teeth and premolars, it is not often used for molars. If a molar has any bulk of coronal tooth structure remaining, it usually will be restored with an amalgam or a composite resin pin core. If there is no remaining coronal tooth structure, it is necessary to use at least one dowel to provide stability against horizontally directed forces. If a molar is to be restored with a single crown, a single-piece cast dowel-core or an amalgam or composite resin core with one or more prefabricated metal dowels can be used. A cast dowel core placed down one primary canal of a posterior tooth can be successful if the root is fairly long, straight, and bulky.

However, if a severely damaged tooth is to be subjected to the stresses of acting as an abutment for a fixed bridge or removable partial denture, more resistance and retention are required. Because of the root divergence found in most molars, using a dowel-core with two or three parallel dowels extended into multiple roots can be quite hazardous. Therefore a multi-piece dowel core with separate dowels should be employed.

The dowel-core for a mandibular molar is usually divided into mesial and distal segments. The maxillary molar dowel –core is composed of facial and lingual components with the dowels in the two facial canals paralleling each other. When the mesiofacial and distofacial canals are too divergent to permit parallel dowels, a separate third dowel is required.

For a two piece dowel-core to achieve maximum strength and retention from the dowels in divergent canals, the pieces must be rigidly bound together after insertion. A number of ingenious methods have been proposed for accomplishing this. The core can be made in two halves, held together by interlocking lugs, which can be formed from a commercially available non-rigid connector pattern or by cutting a keyway or dovetail in one half of the core pattern.

A commonly used solution for the problem is the fabrication of the core with an integral dowel and a channel in the core through which an accessory dowel is cemented. The hole for the interlocking accessory dowel is aligned with a preparation in another diverging canal. The accessory dowel acts as a dowel-core within a dowel-core and its divergent direction helps to nail the core in place. The secondary dowel can be a prefabricated post or wire, or it can be a cast custom dowel. A variation on this theme uses a core with no attached dowel. It is pierced with channels for two or three diverging separate dowels which, when inserted and cemented, will hold the core firmly in position.

Finally the core be fabricated in two halves with pin holes in the first half and interlocking pins in the second half. The core is pinned together when both halves have been cemented in the tooth.

27

Any of these interlocking methods can be fabricated by the direct technique or by the indirect technique of which the latter technique seems to be far more expeditious and simple.

• In indirect technique, it is important to obtain an accurate impression of the canal preparation. A short segment of wire (paper clip) is placed in each canal to reinforce the impression dowel . Once the cast is ready, the wax pattern for the facial half of the dowel core will be fabricated first. On a mandibular tooth, it would be mesial half.

• Gauged, plastic sprues are tried into the two facial canals. Trim them with coarse garnet discs so they will fit easily to the bottom of their respective dowel preparation.

• After sufficient lubrication, place soft round wax forms into each of the two facial canals. Cut them off flush with the root face of the tooth.

• Plunge a hot PKT no.1 instrument to the bottom of each of the canals, melting the soft wax completely. While the wax in the facial canals is still soft, insert the trimmed solid plastic sprues into the wax and shove each of them to the bottom of its respective canal.

• To provide the locking mechanism for tying the two halves of the core together after cementation, pin holes are drilled in the facial half of the core.

• The facial half of a core is then produced. The external axial contours of the facial half will be consistent with the axial walls of a full crown preparation. The lingual surface will be flat smooth surface, which parallels the path of insertion of the palatal canal. Use an enamel hatchet for core and 1.5 mm wide ledge or shoulder in the occlusal third of the lingual surface.

• Carefully align a 0.7 mm drill with the path of insertion of the palatal canal.

• Drill the pin holes in the ledge, making them parallel with each other and the path of insertion of the palatal canal. For maximum effectiveness, they should extent the full length of the core.

• A short section of thin pencil lead is placed in each pinhole before investing. This will keep the holes patent during burnout and casting. About 2 mm of graphite should show at each end of the pin hole to ensure that the rods will be held securely by the investment.

• The pattern is invested, burned out, and cast .A gold alloy should be used because graphite rods are employed to maintain the pin holes. The contamination of a chromium containing alloy with carbon will increase brittleness and decrease corrosion resistance. Use the 0.7 mm drill to remove the graphite from the pin holes. Once the casting for the facial half of the dowel core has been fabricated, the lingual half can be made against it on the cast.

• Seat the completed facial of the dowel-core into the facial canals. Check to make sure that the lingual surface and the two pin holes are parallel with the dowel preparation in the palatal canal.

• Insert nylon bristles into each of the pin holes and lubricate the lingual surface of the facial core.

Relubricate the palatal canal profusely.

• Try a 14 gauge plastic sprue into the palatal canal. Trim the sides of the spring with a coarse garnet disc to allow the sprue to slip easily to the bottom of the canal.

• Wax or acrylic resin can be used to build the pattern. A fresh mix of resin is placed in the mouth of the canal, and the trimmed plastic sprue is seated to place.

• When the acrylic is near polymerization, pump the sprue in and out several times to ensure that it will not lock into any undercuts.

• Use a second mix of acrylic to build-up the required bulk for the lingual half of the core. The resin should surround the nylon bristles projecting from the facial core, and it should overlay the occlusal aspect of the facial core.

• Use garnet discs and carbide burs to shape the axial contours and occlusal planes of the lingual core. The core should now resemble a tooth preparation for a full crown.

• Use inlay wax to touch up any voids in the acrylic pattern. Margins should be well adapted and axial surfaces should be free from undercuts.

• After the lingual half is invested and cast, finishing is done with abrasive discs and rubber wheels.

• The two halves of the dowel core are assembled in the working cast to ensure that they will fit together in the tooth.

• The two piece dowel -core is now ready to be cemented in the tooth to rebuild it for placement of the final restoration. The facial half will be cemented first following immediately by the lingual half .On a mandibular tooth the mesial would be first, followed by the distal.

Cut a v-shaped cement vent down the length of each dowel to assist complete seating and the prevention of damaging stresses. The cemented dowel-core is now ready for completion. The finish line is touched up with a chamfer diamond to provide space for the bulk of metal adjacent to the acute

28

margin in the final crown. The margin of the final restoration will be placed on solid tooth structure to provide a marginal seal and to provide a band of reinforcing metal apical to the core Prefabricated post core systems;.

Dowel-Core under a crown: There are occasions when a tooth which has been restored with a crown will fracture causing the displacement of the crown. This is caused by weakened structural integrity of the crown as a result of previous restorations, caries, small diameter of coronal tooth structure, brittleness, trauma or a combination of some or all of these factors. Such a tooth may have been endodontically treated without placement of the dowel â&#x20AC;&#x201C; core or it may still have been vital.

Very often the fracture of the tooth will mean remaking the crown, or in the severe cases in which the fracture extends too far apically, it may even mean loss of the tooth. There are conditions which may permit less drastic treatment. Crowns that meet two criteria can be reused. First, the fracture must be restricted to coronal tooth structure without extending far enough apically to intersect the finish line. Second, the crown must exhibit adequate margins and have acceptable contours and esthetics.

The tooth is restored endodontically, if that has not already been done. A dowel preparation is then made in the canal and a dowel- core is fabricated using the inside of the crown as a matrix for the coronal portion of the dowel-core pattern.

Dowel-Inlay crown repair (Secondary intention post and core) : The teeth that have been restored with crown will sometimes require endodontic treatment later. It is a good idea to minimize these situations by never placing a cast restoration on a tooth with a pulp cap over an exposure. Nevertheless, not every pulpal complication can be foreseen, and endodontic treatment will occasionally be required after the tooth has been restored.

In most cases, the root canal treatment will be done through the cast restoration. While it is possible to remove a crown, the crown or the tooth preparation under it may be damaged in the process. If an otherwise sound restoration must be penetrated to provide an endodontic access, there arises a question of how will the tooth be restored after the endodontic procedure has been completed.

It is not enough to place an amalgam or composite resin restoration in the access opening for a single-rooted tooth. The tooth structure covered by a crown suffers from the same weakness that besets an endodontically treated tooth before placement of a crown. In fact, the problem is probably a little worse in this case. An endodontic access through a crown is often larger because the crown obscures the morphology of the tooth and makes it more difficult to locate the pulp chamber.

The solutions for these problems include 1.

Cast dowels with an attached inlay to close the access opening .

2.

Prefabricated dowel with a composite resin closure restoration.

3.

A prefabricated dowel with an amalgam seal.

This process of repair has been referred as a â&#x20AC;&#x153;secondary intentionâ&#x20AC;? dowel or post and core.

Core Fabrication with Precision Plastic Dowel The prefabricated precision dowel forms part of a system in which the dowel is designed to fit a canal space shaped by a specific instrument of matching size and configuration. This differs from the custom dowel-core because the canal is prepared to fit the dowel rather than a pattern being made as an impression of the internal aspect of the tooth. The resulting fit may not be as exact but it is usually clinically acceptable.

Precision plastic dowels are available in parallel and tapered configuration. Parallel dowels exhibit superior retention: studies have found them to be 1.9 times, 3.3 times and 4.5 times as retentive as prefabricated tapered dowels of equal length. If the surface is serrated, retention will be improved even more.

Core fabrication with Precision parallel plastic dowel: Prefabricated dowel patterns are available with a serrated surface and parallel -sided geometry (Para-Post). It is designed to be used with one or more parallel pins set in dentin peripheral to the canal.

The pins act primarily as anti-rotational features, although they may add some retention and resistance to dowel-cores which are lacking those qualities because of tooth size or morphology. The Para-Post is manufactured with a groove running its entire length to act as a cement vent.

Conditions which permit the use of a serrated parallel plastic dowel pattern include a fairly bulky root and a canal which is essentially straight. The dowel picked must be large enough in diameter to include the coronal portion of the canal, but small enough to leave an adequate thickness of dentin at the apical end. If the coronal portion of the canal has been enlarged excessively, a small dowel may fit too loosely, and a larger dowel may cause insufficient tooth structure to be left in the apical section.

29

It is also necessary to evaluate the tooth structure available for pin placement. If there is insufficient bulk to accommodate pins, key ways can be prepared in the walls of the canal. The most important factor in the retention of a precision parallel dowel, as with any dowel, is length. Since no part of the dowel preparation developed by the standard Para-Post drill is rounded over or tapered, the dowel space tends to come closer to the exterior of the root at its apical extension. An assessment of the length of the dowel space should take this into account. The dowel should be at least as long as possible without encroaching on the apical 4.0mm. of the endodontic filling.

Color coded plastic posts are available in diameters of 1.25 mm. (red), 1.50 mm. (black), and 1.75 mm. (green). Diameters of 0.9 mm and 1.0 mm can also be obtained. There is a paralleling jig for each of the diameters to be used in conjunction with a 0.7 mm Paramax twist drill. Plastic pins are used for an impression if the indirect technique is employed, and Iridioplatinum pins are used for the wax pattern and casting .

• A tooth being considered as a candidate for restoration with a Para-Post dowel-core should not be excessively tapered, and an adequate amount of tooth structure for pin placement should be present around the periphery of the canal.

• The canal preparation is done, using the appropriate size of drill form the Para-Post kit.

• The paralleling jig and a 0.7 mm Paramax drill are used to place pin holes parallel with the dowel space.

• After the plastic dowel pattern and iridioplatinum pins have been inserted, the core portion of the pattern is fabricated from autopolymerizing acrylic resin . Preparation of the core is accomplished ,producing in it the contour of a crown preparation for a porcelain fused to metal crown .

• The cast dowel-core is checked for complete seating and adequate fit. Any modifications needed on the core should be accomplished prior to cementation .

• The fabrication of the final crown is now accomplished. The dowel-core restoration is treated just as if it were a preparation in natural tooth structure.

Core fabrication with Precision tapered plastic dowel Most of the precision plastic dowel system which are marketed today are tapered with the taper ranging from 1.10 to 6.20. Ideally, the use of a tapered precision plastic dowel with a matched reamer of the same size obviates the need for relining the dowel in the canal when the dowel core is fabricated. The use of a taper is advocated by some authors because it more nearly approximates the tapered configuration of roots, thereby lessening the chance of a lateral perforation during dowel preparation. Tapered dowels exhibit the least stress during cementation, but they do tend to have a wedging effect.

To match the tapered plastic pattern to the dowel preparation with accuracy, it may be necessary to cut a little length form the small end of the pattern, or reinstrument the canal to enlarge it slightly, depending on whether the dowel is too loose or too tight. This must be done with great care, comparing the depth of the dowel preparation and the length of the dowel pattern. Otherwise, it is possible to wedge a tapered dowel into the canal making contact with the walls short of full seating of the dowel. The operator may misinterpret the slight tug-back that he feels as a manifestation of an accurate fit.

The use of a tapered precision plastic dowel with a matched- reamer of same size obviates the need for relining the dowel in the canal when the dowel core is fabricated. The most commonly used tapered plastic dowels are : 1. Calibrated Instrumentation kit 1. Colorama kit 2. P-D posts 3. The Endowel system The C.I (Calibrated instrumentation) Kit consists of three rotary instruments. The dowel preparation is begun with a bibevel twist drill. When the initial channel has been prepared, it is enlarged with a pointed reamer. The final diameter and taper is achieved with a tapered fissure bur whose size and taper match those of the dowel pattern. The smooth –sided patterns have a taper of 2.6 0, and they are available in two sizes: 1.0-1.3 mm and 1.2-1.6 mm. The two numbers in each set indicate the diameters at the tip and 10 mm from the tip. There is a separate set of instruments for each dowel size .

There are five sizes of patterns in the Colorama Kit: 0.8-1.3 mm., 0.9-1.4 mm., 1.0-1.6 mm., 1.01.8 mm., and 1.1-2.0 mm. The smooth sided dowel patterns are actually a combination of tapered and parallel – sided, with the tapered portion increasing in length from 5.0 mm on the smallest dowel to 9.0 mm on the largest. The tapered portion has a convergence angle of 6.2 0. The dowel preparation is accomplished with a color-coded engine reamer of a matching size, which is tapered near the tip and parallel-sided adjacent to the shank.

30

P-D Posts* are smooth sided plastic dowel patterns with a uniform convergence angle of 1.6 0. The dowel space is prepared with a reamer of like taper and diameter. Each reamer has an adjustable sliding metal stop which is held in place with a set screw. The patterns are available in sizes: 0.9-1.3 mm, 1.1-1.5 mm, 1.3-1.7 mm, 1.7-2.1 mm, and 1.9-2.3 mm .

The Endowel* system differs from the others in that its smooth tapered dowel patterns are matched to hand instruments, i.e., the standardized endodontic files and reamers. Therefore, they exhibit the 1.10 taper of standardized endodontic instruments. The dowels are available in eight sizes: 70 (0.7-0.9 mm.), 80 (0.8-1.0 mm.), 90(0.9-1.1mm.),100 (1.0-1.2mm.),110 (1.1-1.3 mm.), 120 (1.2-1.4 mm.), 130 (1.31.5 mm.), and 140 (1.4-1.6 mm.). In each pair of numbers, the first designates the diameter at the tip, while the second represents the diameter 10 mm. from the tip.

• The preparation for the dowel-core is begun by approximating the preparation for the final restoration, a porcelain fused to metal crown. This will facilitate fabrication of a properly contoured core pattern later.

• A series of hand files will be used to enlarge and lengthen the canal to the desired size. Because standardized endodontic hand files are used, this step could be nearly completed at the time of endodontic treatment and merely touched up at this point.

• A keyway should be placed at the mouth of the canal to provide anti-rotational resistance. Vertical grooves 3-4 mm. long are use on single rooted teeth, and a short dowel in a second canal is used on multi rooted teeth.

• The dowel –core pattern will be fabricated with the corresponding size of tapered plastic Endowel pattern. It can be used for making an impression for the indirect technique, or a direct core can be attached to the dowel in the tooth. Both wax and resin have been described for this purpose .

• Shape the coronal bulk of resin to form it into a crown preparation for the restoration which will ultimately be placed on the tooth.

• The tooth is ready to be restored with a crown, treating that portion of coronal tooth form, which has been built up with the core as though it were tooth structure.

Prefabricated Dowel / Cast Core : Another approach to the fabrication of dowel –core is one in which a precision made prefabricated dowel is matched in size to a bur or hand reamer. After the dowel preparation is completed, the prefabricated dowel is fit in the canal. The core is then made of resin or wax by either the direct or indirect technique. The metal dowel and its attached core pattern are invested and the core is burned out. Then the core is cast in metal.

Advantages : 1. Part of the dowel core is already completed before the procedure is even begun i.e., the dowel.

2. Superior strength of a wrought or drawn dowel when compared to a cast one especially when the dowel is less than 1.5 mm in diameter. The prefabricated dowels have been made of a variety of materials: gold, gold-platinum-palladium. iridoplatinum, platinized wire, nickel-cobalt-chromium and stainless steel. The core can be fabricated by the direct or indirect technique. Both parallel and tapered dowels are available.

A commonly used system has been the Endo-Post*, which has also been grouped under Precision Tapered Plastic Dowel and described earlier. The preparation for this type of dowel core is same as that of Precision Tapered Plastic Dowel.

Prefabricated Dowel / Composite Resin Core:

Perhaps the simplest and most efficient method for the fabrication of a dowel core restoration is the composite resin core in combination with a prefabricated stainless steel dowel. The entire procedure, from completion of endodontic obturation through the finished crown preparation, can be accomplished in a single appointment.

This system can be successfully used in a wide range of clinical situations. At one extreme, this type of dowel has been shown to significantly strengthen teeth with no coronal

31

destruction other than the endodontic access preparation.At the other end of the spectrum, the prefabricated dowel/composite resin core can be used to restore both anterior and posterior teeth than have little or no intact coronal tooth structure.

Composite resin is easily and quickly placed as a core material, and it has the added advantage of being completely polymerized within minutes, allowing work on the core preparation to progress immediately. Preparations on amalgam cores, on the other hand, often must be delayed until a subsequent appointment. The resin requires less bulk of core material, making it the material of choice for anterior teeth where there is often minimal space around the dowel.

The prefabricated dowel / composite resin core is adequate for restoration of single anterior teeth.

However most anterior bridge abutments should have cast dowel-cores. Many molars requiring crowns can also be restored with this system. Two or three dowels can usually be placed for resistance to obliquely directed forces, and there is typically room for a generous bulk of core material. On molars with excessive destructive of coronal tooth structure or with very deep finish lines, amalgam may be the material of choice rather than composite resin.

The dowel portion of the dowel/ composite resin core acts to resist any lateral forces placed on the crown. Care is taken to extend the finish lines for the final restoration well below the composite core. This gives the tooth a ferrule effect to resist any vertical forces. Auxillary pins should be used routinely to resist any rotational forces placed on the restoration. It is also proved that pins embedded in core material across a tooth may have a buttressing effect and resist splitting forces on the root.

The prefabricated dowel/composite resin core can also be used to restore a previously crowned tooth that has been endodontically treated. The head of the dowel is trimmed to fit within the confines of the access preparation and the dowel is trimmed to fit within the confines of the access preparation and the dowel is cemented. The space around the head is then restored with amalgam or composite.

There are several prefabricated stainless-steel dowels of both parallel- sided and tapered designs that are suitable for use with composite resin cores. The technique for all of these systems is virtually the same with only minor modifications in the method of canal instrumentation. They should all be used with auxiliary pins.

The prefabricated dowel systems used are 1. BCH system 2. C.I (calibrated instrument)kit 3. Colorama dowel 4. Ellman nubond Fast posts 5. P-D crown post 6. Para –post BCH system is comprised of two or three lengths in each of five diameters, for a total of 14 sizes.

They are meant to be used with Peeso reamers and they come in diameters of 0.8 mm., 1.0 mm., 1.2mm.,1.4mm.and 1.6 mm. The dowels are serrated and parallel – sided, with tapered tips and a round button on the occlusal end .

Ellman NuBond Fast Posts are serrated stainless steel dowels with a 1.6 0 taper. The canal is prepared with tapered reamers of matching sizes. There are six sizes; 0.9-1.2 mm., 1.1-1.4mm., 1.3-1.6 mm., 1.5-1.8 mm., 1.7- 2.1 mm., and 1.9 – 2.3 mm..

The C.I kit, Colorama dowel, P-D crown post has also been grouped under Precision Tapered Plastic Dowel and Para Post under Precision Parallel Plastic Dowel which has been described earlier.

The coronal preparation for prefabricated dowel/composite resin core is accomplished in much the same way as it is for a custom cast dowel-core.

• When the preparation of the canal space is initiated, some of the gutta percha in the coronal portion of the canal can be removed with a hot instrument. The length is established with a peeso reamer or a Gates Glidden drill.

• The shaping of the canal is now accomplished with the Para –Post drill.

• Pin holes are drilled around the canal space so that auxiliary pins can be placed.

• The pin holes are drilled to a depth of 2mm. with a self-limiting 0.5 mm. twist drill. It is not necessary for these pin holes to parallel the canal • The pins can now be placed. Cemented pins are preferred by some authors because self threading pins do produce stress, and they can cause dentinal crazing. If there is adequate bulk of tooth structure, and if the tooth has been nonvital for only a short period of time so that resilience is not impaired, small threaded pins should not represent too great a hazard.

• A hand wrench is used in an easily accessible area . When the pins are threaded into place, stop as soon as any resistance is encountered to prevent dentinal fracture. “Back off” slightly to reduce

32

•

• • •

• • • •

stress, but not enough to produce a loose fit. The pins are shortened, if needed to insure that they will be within the confines of the completed preparation and that they will not interfere with placement of the dowel. At least 2.0 mm. of pin should be left exposed.

The stainless steel dowel is now tried into the prepared space. Any reduction in length should be accomplished from the apical end, as the dowel head can provide added retention to the core material. The dowel should have a snug fit in the canal. If it does not, the canal has been overinstrumented.

A thin mix of cement is made of either zinc phosphate, polycar – boxylate or glass ionomer cements.

Cement is placed into the canal. An endodontic plugger, periodontal probe, or Lentulo spiral can be used for this purpose.

A generous layer of cement is placed on the dowel. The dowel is slowly pushed to the end of the canal space, allowing time for excess cement to escape. Hold the dowel in place with finger pressure until the initial cement set occurs.

After the cement has achieved its initial set, excess is removed from around the pins and the coronal portion of the dowel.

A matrix band or crown form is placed around the tooth to permit the placement of composite resin .

A preparation for a porcelain fused to metal crown is accomplished with diamond stones in a high speed hand piece, treating the composite resin as though it were tooth structure.

The porcelain fused to metal crown can now be fabricated over the composite resin core, which is retained and bolstered by a stainless steel dowel.

Core Fabrication with Parallel Threaded Dowel (Pretapped) This is another type of dowel which permits the completion of the tooth build-up in a single appointment. It employs threads on its parallel sides for retention, and it is inserted into a canal whose walls are pre threaded with a special tap. It differs from Other types of dowel because it is not passively inserted into the canal and held in place entirely by the cement Whether this threaded dowel is retained by mechanical interaction, or simply by increasing the surface area two or three fold, it demonstrates superior retention to other types of dowels.

Concern has been expressed over increasing the potential of root fracture by threading dowels into the canal. The stresses generated by threaded dowels certainly are greater than those generated by dowels retained by cement alone. However, mechanical testing has shown that when the tap is used profusely, fracture cannot be induced. As with any threaded retention device, there is some hazard for the tooth. The risk is minimal if the tooth in which it is to be placed is properly selected and the if the dowel is used correctly. The Kurer Anchor system should not be used on teeth with thin, fragile walls nor should it be used, by the heavy – handed operator. Kurer Crown Anchor is a system by parallel threaded pretapped dowel. The crown anchor consist of a stainless steel threaded shank (dowel) with a slotted machine brass head (core). The canal is enlarged with an elongated engine reamer, and its orifice is counter sunk with a root facer. A tap is then used to thread the canal for insertion of the anchor .

The Kurer Fin-Lock utilizes a threaded ”root face fin” or lock nut to snug against the countersunk root face. A narrow collar near the slotted end serves as additional retention for the composite resin core which will be added after cementation of the anchor .

The Kurer Crown Saver is a simple threaded dowel that has neither a head nor a lock nut and, therefore, does not require the use of a root facing instrument. It consists of a parallel threaded dowel which is cemented in the canal and serves as the retention for a composite resin build-up.

• Preparation of the dowel space will be accomplished with an engine reamer, which resembles the Peeso reamer, except for the greater length of the cutting flutes (15mm.,compared with 8.0mm for a no.6 Peeso reamer).

• A root facer is used to provide a flat countersink on the root surface around the mouth of the canal.

The counter sink allows the head, or core, of the anchor to be set completely within tooth structure, providing resistance to obliquely directed forces. It provides protection to the head and makes it less susceptible to fracture. Prepare the countersink to a minimum depth of 1.0mm.

•

Use the tap to thread the canals. Because this is the time of greatest stress build –up, it must be done carefully. Use only new, sharp taps. A tap should be discarded when the anchors in its kit have been used up.

33

• •

The anchor is tried in to establish its length and determine the adjustment necessary in the length of the dowel .

The head or core of the anchor must be shaped to resemble the contours of a crown preparation for the final restoration. Four adjustments are usually enquired 1. The incisor edge will probably need to be shortened.

2. The incisal portion of facial surface must be reduced to move the incisor-facial line angle to the lingual.

3. A concave area in the incisal 2/3 of the lingual surface must be created and 4. The axial walls should be slightly tapered.

• A slot is cut on the brass head at right angle to the incisal edge. This is made to screw the anchor into the tooth during cementation.

• A cement escape vent is extremely important in the seating of a threaded dowel. Cut a large v-shaped groove from the apical end of the dowel to the base of the core.

• Prepare a thin mix of zinc phosphate cement on the glass slab and apply a thin uniform coat over the dowel. Do not place any cement into the canal. Cement does not play a significant role in the retention of the threaded dowel, but is important as a sealer.

• Insert the dowel in the canal and thread it to position with the screw driver. Stop from time to time to allow excess cement to escape from the vent. If the dowel tends to overseat, that is turn past the position at which the facial and lingual features are in proper alignment, do not hesitate to reverse the anchor 1/8 or 1/4 turn to produce correct alignment.

• When the cement has set, the tooth which has been built up with the Kurer Crown Anchor is ready for fabrication of the final restoration.

Core Fabrication with Parallel Self Threading Dowel: This type of dowel offers a retention device which is intermediate between the stainless steel dowel / composite resin core and the pretapped parallel threaded crown anchor. The retention afforded by this type of dowel, whose threads are widely separated and shallow, is 94% greater than that for a serrated stainless steel post of the same size.

The self-threading anchor is 17-45% less retentive than similar size of pretapped threaded anchors. Because the radix anchor utilizes threads for much of its retention, it is capable of producing stress in the root. Continuing to thread the anchor after resistance is encountered could result in root fracture or stripping of the threads. If the dowel apex is allowed to engage the supporting tooth structure high apical stresses will be generated. High stress concentration will develop in the coronal portion of the root if the coronal flanges of the head come in contact with the root face. In order to avoid these problems, it is recommended that the dowel be reversed or backed off a half turn when slight resistance to threading is felt during cementation.

Radix Crown Anchors is a brand of parallel self-threading dowel. They are available in three diameters, 1.15 mm, 1.35 mm and 1.6 mm. The anchor consists of a low profile retentive spiral and a head with five rows of fins or lamellae which retain the composite resin core that is built around it. Maillefer reamers of appropriate matching sizes are used for canal enlargement.

The shallow threaded spiral on the coronal 60% of the dowel is interrupted by four cement vents which run the length of the dowel .

The anchor driver or wrench, used for threading the dowel into the canal, has four prongs which firmly engage four slots in the sides of the head. Anchor works best in teeth whose clinical crowns have some length and volume .

• Begin the tooth preparation for the parallel self-threading dowel by removing most of the coronal tooth structure with a diamond in a high speed hand-piece.

• Begin the preparation of the dowel space with Peeso reamers, which are smaller than matching size Maillefer reamer meant for the chosen size of anchor. The reamers are similar in configuration to the Peeso reamers, except for the greater length of the cutting flutes on the Maillefer reamer.

• The anchor driver provided with the kit is used initially for tapping the canal and then for reinsertion of the anchor into the tooth during cementation.

• As the cement sets around the dowel, remove the excess from the lamellae of the head and from under the bottom most fin near the root face. The tooth is then ready for fabrication of the composite resin core around the anchor head .

• The preparation for the final restoration will be made in the composite resin core with a diamond stone in a high speed handpiece.

34

• The final restoration is placed over the composite resin core which is retained with a Radix Anchor.

Core Fabrication with Tapered Self-Threading Dowel : This style of dowel has been in use for over 50 years. It is the simplest of all the threaded dowels.

The taper of the dowels is variable. Many of them have two tapers: one at the tip and another for the main body of the thread. The taper for the tip can be as little as 10 0 and as much as 30 0being less on long, thin dowels and greater on short, thick ones. The taper on the main body of the thread can range from 0-3 0. An amalgam or composite resin core is usually fabricated around the dowel after it is cemented.

Indications : Because of its dowel size and the bulky head, tapered self- threading dowels are generally restricted to use in molars. It is frequently used on teeth with a minimum of coronal tooth structure and multiple divergent canals.

The non-parallel relationship adds to the retentive qualities of the self-threaded dowel. Its use should be reserved primarily for single tooth restorations.

Advantages : The tapered self-threading dowel is simple and easy to use. The fact that it engages dentin with its threads unquestionably provides excellent retention. Dowel-core can be placed in a single appointment, often it can be done in the appointment during which the endodontic obturation is accomplished.

Disadvantages: This type of dowels also produce high stress concentration with its wedge- like action producing stress concentrations more severe than those seen in other types of threaded dowels. The danger of root fracture is most acute when excessive torque is applied or when the dowel is over twisted. Larger diameter dowel have been observed to cause root fracture especially in the teeth with ovoid canal.

It has been recommended that tapered, self threading dowels be passively cemented in slightly oversized canals. In a slight modification, a dowel with a snug sliding fit be cemented, engaging the threads no more than a single turn during seating.

This type of dowels have been marketed under different brand names, of which the Dentatus Screw post is the most commonly used. It is currently marked in a stainless steel and a gold- plated brass dowel, available in 6 diameters, 1.0, 1.2, 1.3, 1.5, 1.6, and 1.8 mm. There are four lengths of dowels, 7.8, 9.3, 11.8 and 14.2 mm. The head of each screw post is square, with two crossing slots on the end. There are two seating wrenches provided with the system.

One wrench is designed to fit internally into the head of the dowel to allow placement of the dowel in tight areas. It also permits insertion of a dowel whose head shape and size have been altered . A second wrench fits over the head of the dowel. It is useful on severely broken-down teeth in which the dowel head is unaltered. The Dentatus Screw Post should be considered for molar teeth in which the restoration of the coronal portion of the tooth is beyond the scope of the typical pin-retained core.

•

The dowel spaces are now prepared in the straightest and bulkiest roots. In most cases, it is possible to place two dowels. The distal canal of a mandibular molar and the palatal canal of a maxillary molar are usually the best suited to accommodate the primary dowel.

• The Dentatus Screw Posts are prepared for cementation by trying them in and making any necessary adjustments .

• An amalgam or composite resin core can now be placed. No auxiliary pins will be needed, unless only one dowel is used. In such cases, pins should be placed as anti-rotational retentive components .

• Preparation of the core is accomplished with burs and diamonds as though it were tooth structure.

On an amalgam core of this size, preparation is probably best delayed until a subsequent appointment. Use of a spherical high copper amalgam will achieve a hard enough set to do the preparation at the same appointment. Even its surface is more easily instrumented at a later appointment, however.

• The crown can be fabricated over the core in usual manner.

Amalgam Pin Core And Composite Resin Pin Core Not every endodontically treated tooth will require the use of a dowel in its canal to retain the core and assist the crown in withstanding occlusal forces. Most molars can be successfully restored without a dowel. Their greater circumference generally eliminates the necessity of a dowel to bolster the tooth.

Self threading pins are the most retentive of all pins. The retention of the amalgam core is subject to several variables. The depth of insertion of the pins into the dentin will play a role in their retention. The

35

optimum depth for self threading pins have been put at 2 mm, while for cemented pins it is 3-4 mm. The pin should also extend 2mm from the tooth into the amalgam.

It is generally consistent with the empirical recommendation of 1 pin for each missing line angle of tooth structure, 1 pin per missing cusp and 1 pin per missing wall. On the other hand, as the number of pins is increased to produce greater retention, the amalgam and the dentin are simultaneously weakened.

Crowns cemented to amalgam core are significantly more retentive initially than those cemented to composite resin core, although the latter gains strength with the passage of time.

Composite resin cores have been described for use with different types of dowel. They can also be used with pins in place of amalgam cores for the restoration of molars with some remaining coronal tooth structure. In addition to being easy to manipulate and strong, composite resin has the great advantage of allowing core insertion and crown preparation in one appointment.

On the negative side, composite resin cores exhibit greater micro leakage than do amalgam cores.

When this is coupled with the observation that crowns cemented to cores, amalgam or resin, leak more than crowns cemented to tooth structure., there is a strong potential for leakage into the canal. This finding is given credence by the clinical recommendation that the crown margin be on tooth structure, well removed form the margin of the core. Composite resin cores show less tensile bond strength for cast crowns than do amalgam cores at the time of cementation.

Composite resin cores should be employed only in the build-up of teeth to receive single crowns.

PROVISIONAL RESTORATIONS FOR ENDODONTICALLY TREATED TEETH A temporary restoration commonly plays an important role in the successful restoration of a tooth.

It is true that the normally essential role of pulpal protection is not of concern in dealing with an endodontically treated tooth. Nevertheless, the temporary restoration may be even more important to the patent receiving a dowel-core and a crown.

Functions:• Esthetic role • Protects the tooth from further damage • Prevents migration of adjacent contacting teeth • Provides occlusal function A number of different crown formers and dowels are used in various combinations. Polycarbonate crowns have been relined with acrylic, as have celluloid crown forms. Over impressions and plastic shells have used to form the outer contours of the crown. Other types of retentive devices have included plastic dowels relined with acrylic resin, a silicone dowel reinforced with a paper clip, metal dowels with no acrylic lining, and a wooden match stick. Some prefabricated dowel systems have steel dowels made specially for temporary crowns. However, they work best if the matching reamer was used in preparing the canal for the final dowel-core.

The polycarbonate crown is well suited for the routine single crown. If the temporary restoration involves a bridge, or unusual alignment or morphology in a single crown, a custom plastic shell will probably provide the best result in the shortest time.

Polycarbonate Crown The polycarbonate crown is used with a paper clip dowel to provide temporary coverage for the endodontically treated tooth. The coronal portion of the restoration is composed of a polycarbonate crown, relined with acrylic resin.

Initially, a crown is chosen that has dimensions compatible with the space it will occupy. In most cases, the crown will not adapt around the existing root without modification. Excess length is removed form the gingival margin of the crown, while the incisal area is left intact. This process is continued until the crown is adapted reasonably well to the gingival finish line, with the incisal edge in the proper position relative to the adjacent teeth.

A section of paper clip made of heavy gauge wire is placed into the canal to its full depth. A felt tip pen mark is placed 2-4 mm. above the remaining coronal tooth structure. The length of wire extending into the crown will be dictated by the length of the crown. The longer the exposed piece of paper clip, the better its retention in the acrylic resin in the crown.

36

Using a separating disc, cut the length of paper clip.. Some small notches can be placed in the wire at this time to assist in retention of the resin. Place a bend near the end of the wire. When embedded in the temporary crown, this bend will prevent the dowel from pulling out and rotating. Try the trimmed dowel in the canal and confirm that the polycarbonate crown will have room to seat without binding on the wire.

The root face is lightly lubricated with petrolatum to prevent any acrylic resin from sticking to the tooth during polymerization.

A thin mix of temporary acrylic resin is placed on the root face around the orifice of the canal.

Avoid placing any resin deep into the canal space itself, since this can make the crown difficult to remove.

Insert the paper clip dowel into the canal. Fill the polycarbonate crown with the same mix of acrylic resin.

Eliminate any voids in the material before placing it on the tooth. Seat the crown and confirm that it is in the proper position relative to the adjacent teeth. Excess acrylic can be removed with an explorer to make trimming easier. As the material reaches a doughy consistency, the crown should be pumped in and out of the tooth several times to avoid being locked in place during polymerization.

The pin-temporary crown can be placed in hot water to speed polymerization. Prior to trimming and contouring, it is helpful to mark the margin on the inside of the crown with a sharp pencil. The temporary crown is trimmed with sandpaper discs. The polycarbonate crown will frequently be overcontoured in the gingival one-third. Special attention should be given to properly shaping the restoration and making any needed adjustments in occlusion. Perforating the polycarbonate crown is not a problem because there is an underlying bulk of acrylic. The temporary crown is first polished with fine pumice and then with a high-lustre denture polish.

Temporary cement should be placed only in the coronal portion of the restoration. Avoid getting cement in the canal space. A zinc oxide-eugenol cement mixed with an equal part of petrolatum is acceptable. Seat the pin-temporary crown and hold it in place with firm finger pressure until the cement is set. Carefully clean the excess cement from around the margins.

Clear Plastic Shell Another method for constructing a pin-temporary crown involves the use of a clear plastic shell.

While the shell can be shaped by a vacuum forming machine, it is more easily and economically adapted by using silicone putty. Begin by placing the putty into an unperforated stock metal impression tray.

Cut a sheet of coping material in half and place it in a wire frame, shiny side down. The plastic material is slowly heated over a flame until it sags. If it is translucent, it should become clear as it softens. If the material is the clear variety, it should be heated until it begins to smoke slightly.

The heated coping material is quickly carried to the diagnostic cast. If the tooth to be restored is badly broken down, it should have been waxed to an acceptable contour and duplicated in plaster or stone.

A duplicate cast is necessary because the hot plastic would melt the wax if it were placed on the original cast.

The tray loaded with putty is placed over the plastic and firmly seated on the cast. Compressed air can be blown on the shell to speed cooling. After about 30 seconds, the tray and the silicone putty are removed. A well adapted plastic shell covers the cast. The coping material is removed from the cast and trimmed with scissors.

The finished shell should extend at least one tooth in either direction from the tooth being restored.

It should also be trimmed to extend no more than 2-3 mm, beyond the gingival sulcus. A paper clip is prepared in the same manner described previously. The end is bent to aid retention in the temporary crown.

The shell is filled with temporary acrylic resin. Before seating the shell, examine the acrylic from the outside to make sure there are no obvious voids or bubbles. They can be eliminated much more easily at this time than they can be filled in later. If the mold appears adequately filled, the shell can be seated. Make sure that it is in the proper position by firmly pressing on the incisal edges of the adjacent teeth. Avoid pushing on the tooth being restored because the coping material may over seat and distort the temporary crown.

When the material reaches a doughy consistency, remove the shell and separate it from the temporary crown. If it is left in place too long, it can be locked in place in the canal or between adjacent teeth.

Trim off as much flash as possible with scissors while the acrylic is still doughy. Reseat the crown on the tooth and remove it. Drop the temporary crown in a bowl of hot water to speed polymerization. The temporary crown is contoured with a sandpaper disc. Check the occlusion and adjust as necessary. Polish the crown first with pumice and then with high luster denture polish. Cementation procedure is same as that described for polycarbonate.

Success of failure of post core :

37

None of the clinical data provide definitive support of the concept that posts and cases strengthen endodontically treated teeth or improve their long term prognosis. Their purpose is for retention of a core that will provide appropriate support for the definitive crown or prosthesis. a. What is the clinical failure rate or post and cores?

Several studied provide clinical data regarding the number of posts and cores that failure over certain time periods. When this no is divided by the total no of posts and cores placed, the absolute failure rate is determined. A 9% overall average for absolute failure was calculated by over aging the absolute failure percentage from eight studies. In these studies the absolute percent of failure ranged from 7 to 14%. b. What are the most common types of post and core failures?

Seven studies indicate that post loosening is the most common cause of post and core failure.

Root fracture is the second most common failure cause, followed by post fracture. c. Is there a relationship between post form and the potential for root fracture?

Laboratory tests generally indicate that all types of threaded posts produce the greatest potential for root fracture. When comparing tapered and parallel cemented posts using photelastic stress analysis, the results generally favor the parallel cemented posts.

When evaluating the combined data from multiple clinical studies, threaded posts generally produced the highest root fracture incidence (7%) compared with tapered cemented posts (3%) and parallel cemented (1%). d. Does post diameter affect retention and the potential for tooth fracture ?

Studies relating post diameter to post retention have failure to establish a definitive relation ship.

Two studies determined that these was no increase in post retention as the diameter increased, where as three studies found no significant retention changes with diameter variations.

A more definitive relation ship has been established between post diameter and stress in the tooth.

As the post diameter increases, stress also increases in the tooth. Deutsch et al determined that there was a sinfold increase in the potential for root fracture with every millimeter the tooths diameter was decreased. e. What is the relationship between post diameter and potential for root perforations?

These are three distinct philosophies of post space preparation. One group advocated the narrowest diameter for fabrication of a certain post length (the conservationists). Another group proposed a space with a diameter that does not exceed one-third the root diameter (the praportionists) the third group advised leaving at least 1 mm of sound dentin surrounding the entire post (the preservationists).

The instruments used to prepared roots should be related in size to toot dimensions co avoid excessive post diameters that lead to root perforation. Safe instrument diameter to use are 0.6 to 0.7 m for small teeth such as mandibular incisors and 1 to 1.2 mm for large diameter roots such as the maxillary central incisor. Molar posts longer than 7 mm have on increased chance of perforations and therefore should be avoided even when using instruments of an appropriate diameter.

RECENT ADVANCES IN POST SYSTEMS : 1) FIBER-REINFORCED RESIN POST SYSTEMS

• • • • • • • • •

Carbon fiber post system Luscent anchor post system Twin luscent anchor post systems Double-taper post systems (D.T.Post system) Luminex post technology Bondable reinforcement fiber system Parapost fiber white system Anatomic post’n core.

2) CERAMIC POST AND CORE SYSTEM FIBER-REINFORCED COMPOSITE POST SYSTEM :

38

The addition of fibers to a polymer matrix results in a significant improvement in the mechanical properties of :

• • • •

Strength Fracture toughness Stiffness Fatigue resistance

FIBERS MAY BE COMPOSED OF WOVEN POLYETHYLENE, GLASS OR CARBON Advantages :

• • • • • • • •

One appointment technique No laboratory fees No corrosion Negligible root fracture No designated orifice size Increased retention resulting from surface irregularities Conserved tooth structure No negative effect on esthetics

Disadvantages :

• • •

Technique sensitivity Need for a careful adhesive protocol Need to maintain an inventory of the reinforcement materials.

CARBON FIBER POST SYSTEM INTRODUCED IN 1990 BY DURET, REYNAUD & DURET

• • •

These new posts are fabricated from continuous unidirectional carbon fibers, 8 µm in diameter, embedded in an epoxy matrix.

The fibers constitute 64% of the post by weight. Used in Europe and Canada (where it is known as COMPOSIPOST) since 1990, the C-POST is now available in the United States.

The C-POST has been shown to have a high fatigue resistance and high tensile strength among its advantages over other systems. The modulus of elasticity of the C-POST is similar to dentin, which allows it to flex slightly and not fracture roots as readily as a stainless steel post.

39

The C-POST is composed of carbon fibers in an epoxy matrix. It is cylindrically shaped with a twostepped shank and available in 3 diameters : 1.4mm, 1.8mm, and 2.1mm.

Flemming et al, Isidor & Brondum, and Purton and Payne have reported that this new type of post system has adequate rigidity and a high resistance to loading.

With proper bonding, the carbon post can restore the tooth to the same strength as stainless posts. Flemming postulated that this may be due to the more favorable stress distribution, which is a result of the passive bonding mechanism.

MECHANICAL PROPERTIES : The Composipost has the following mechanical properties :

• • •

COMPRESSION 440 MPA SHEARING 170 MPA TENSION 1,600 MPA

MODULUS OF ELASTICITY : Variable between 110 GPa and 8 GPa, According to the angle of the fibers. In the case of a 90 degree incidence Angle with the axis of the post, the modulus of elasticity will be 8 GPa, Which is identical to the radicular dentine DRAWBACKS OF C-POST SYSTEM

•

It is not esthetic

=

causes black / gray shadow due to carbon in the composition.

•

The post is radiolucent

LUSCENT ANCHOR POST SYSTEM :

The one-stop effective procedure for curing composites within the confines of canals providing anchorage and flawless aesthetics.

• •

Transmits polymerizing light within the confines of canals.

Provides the one-stop core anchor foundation with all restorative materials.

40

• • •

Reflects natural hues for flawless aesthetic restoration.

Visible radiolucency in canal and through the core materials.

Available in 3 diameters to fit very slim and large canals.

1)

Using the post space created, a Luscent anchor is tried into the canal. If there has been no moisture contamination, the oxygen-inhibited layer is still available for the next restorative layer.

2) Luxacore, an automixed, self-cured resin is injected directly into the canal. The Luscent post is inserted into the uncured composite resin, and the core build-up is commenced immediately. The luxacore will set within 4 minutes, at which point it can be shaped.

3) After preparation for a full crown, the Luscent anchor post-and-core is ready for the impression and provisionalization steps.

With the introduction of the Luscent Anchor (Dentatus USA, Ltd.) past technical compromises are eliminated. The anchors transilluminate light, are easy to use, and offer significant benefits in radiolucency, retention, and superb esthetics.

TWIN LUSCENT ANCHORS : Twice the Invention, Twice the Retention !

This innovative design is visible assurance against accidental debonding of adhesive and resincore materials. The slim mid-section creates a “physical choke”. The vent groove eliminates air resin entrapment and prevents rotational dislocation. It all adds upto a winning combination of light transmission, attractive esthetics and twice the retention.

•

Light transmitting : Effectively polymerizes composite within the deep confines of canals.

• • • •

• • • • • •

Esthetics : Eliminates shadows at the gingival, root and crown interface as well as through thin-laminate composite restorations. Reflects the surrounding colors and hues, compatible with natural esthetics.

Monobloc strength : Light or dual cure composites bonds to the fiberglass reinforced anchors creating a cohesive, very strong foundation for restorations.

Narrow radial midsection : Mechanical resistance seen in the anchor’s midsection provides double retention against accidental debonding of resins and restorative materials.

Double-end alternatives : The anchor cone shaped-end can be placed in deeper and narrower canals without excess removal of dentin or canal wall. The parallel end can be alternatively placed into long, wider canals of teeth. The parallel canals can be refined with drills, used in parallel canal post techniques.

Longitudinal vent-groove: Eliminates trapped air bubbles causing porosity, for completely filling the canal. Additionally, the vent-groove creates an antirotational resistance in the surrounding polymerized resin material.

Low modulus of elasticity (20.1 Gpa) : The Anchor’s elasticity in the range of healthy teeth, provides safety and cohesive resistance to impact.

Flexural Strength (579 Mpa): The Twin Anchors within the rang of healthy teeth are outperforming metal posts.l Convenient : Compatible for use with most off the shelf, brand-name light cured adhesives and resins. (Should be used in accordance with mnfr’s. specifications).

Fest : The one-stop procedure of simultaneously luting the anchor the building a monobloc core with dual-cure materials is economical and highly effective.

Versatile : Lucent Anchor and the Twin Lucent intro kits contain assorted small, medium and large anchors with matching reamers, and light transmitting forms-to-fit retainers for cores. The convenient refill kits contain 15 anchors in 1 size.

TWIN-LUSCENT STARTER KIT Available in 3 diameters to fit large and very slim canals.

15 twin luscent anchors (5 of each size, small, medium, large)

41

3 corresponding size reamers 1 pathfinder 1 probos II router 15 forms to fit DOUBLE TAPER POST SYSTEM (D.T POST)

The capacity of different types of post-and-core to protect the prosthetic restoration from biomechanical failures varies greatly. Post-to-canal adaptation represents an important element in the biomechanical performance of the prosthetic restoration.

The new DT- Post system was designed with the purpose of providing close canal adaptation wit minimal tooth structure removal.

The DT- Post system seem to offer a logical solution in restoring endodontically-treated teeth.

• •

D.T. Post provides bigger taper at the coronal level.

A better adaptation at the coronal level increases the amount of the fiber-epoxy high performance material, therefore, consequently decreases the thickness of the resin cement, a lower performance material, and reduces its polymerization total shrinkage.

•

D.T post combines the conservative aspect of Endo-composipost UM apically, and the greater size of the Composipost coronally.

The post is fabricated with a prestressed glass fiber system due to which it can resist more than 1,00,00,000 cycles in a fatigue resistance test, in which the closest competition could only take 1,73,000 cycles.

TRANSILLUMINATING LUMINEX POST SYSTEM :

• • • • • • • •

A user friendly, single office visit solution for restoring compromised thin-willed roots with strong adhesive materials.

All too often, fragile, thin-walled teeth present major restorative problems : cast posts or extractions were often the only alternative.

But today, there is a user friendly, single office visit solution to this problem.

The clear light transmitting posts polymerize light-cured composites within the entire root canal. After curing, the LUMINEX post is removed, leaving a ready canal for a corresponding classic post.

Reinfroced root strength : Light-cured composites internally reinforce the root structure providing maximum sheer load support and retention.

Improved control : Light-curing composites are easy to control, more adaptive, and safer than auto-cured composites that may prematurely harden.

Centered canal position : The luminex post technique centers the canal and forms a selected sized, full length parallel sided canal for corresponding dentatus classic metal posts.

Superior aesthetics : The light-cured composite inside the canal masks metal posts with a reflective tooth colored foundation for modern restorations.

42

•

Technique versatility : Luminex smooth and grooved posts may be also used as an impression and castable post pattern in the direct and indicrect fabrication of posts.

•

Superior delivery system : Selection of Luminex and metal posts in all sizes along with corresponding reamers and components are packaged in the refillable, easy to use dispenser.

PARAPOST FIBER WHITE SYSTEM :

•

The esthetic para post you’ve been waiting for…..

Material composition Glass Fiber 42% Resin 29% Filler 29%

• • • • • • • • •

Physical properties Tensile strength Fracture resistance (mean) Flexural Strength Flexural Modulus Compressive Strength

1200 Mpa 71.99 Kg 990 MPa 29.2 GPa 340 MPa

White, translucent color minimizes the possibility of shadowing in anterior restorations.

Metal-free for esthetics and for patients with metal allergies.

Flexural modulus measures closer to dentin than other post materials.

Filled resin/uni-directional fiber matrix strengthens the structure of the post without.

Compromising flexibility.

Passive, parallel-sided design mirrors the qualities of metal ParaPost®s.

Anti-rotational post hed of excellent adaptation of core material.

Specially fabricated to bond with most resin cements and core materials.

Readily removed if endodontic re-treatment becomes necessary.

The posts are color coded for use with existing ParaPost® drills.

BONDABLE REINFORCEMENT FIBER POST :

•

• •

• • • •

This method uses a bondable reinforcement fiber (e.g Ribbond, Seattle, Washington; Connect, Kerr), a fourth-generation bonding agent (e.g. Optibond, Kerr) a dual-cure hybrid composite (e.g., Veriolink II, Ivoclar Vivadent) as the luting agent, and a dual-cure hybrid composite as the core buildup.

The reinforcement material used for the post consists of polyethylene woven fibers that are treated with cold-gas plasma.

This plasma treatment converts the ultrahigh molecular weight fibers from hydrophobic material to hydrophilic. The effect of such treatment is to allow for complete wetting and infusion of the fibers by resin, creating a lower contact angle with the wetting resin and providing a greater bonded surface area to enhance the adhesion to any synthetic restorative material.

Spectroscopic analysis shows an increase in 0-C = 0 functional groups that allows chemical bonding between the polyethylene fibers and the resin.

Several types of weaves are used by various manufacturers, which can influence strength, stability and durability.

The leno weave of ribbond reportedly resists shifting and sliding under tension more than a plain weave, minimizing crack propagation by reducing the coalescence of micro cracks within the resin matrix into cracks that could lead to failure of the restorative complex.

This fiber network also provides an efficient transfer of stress within the internal fiber framework by absorbing the stresses that are applied to the restorative complex and redirecting those forces along the long axis of the remaining root structure.

ADVANTAGES : • Maximum post retention and core stability • Conservation of tooth structure • Internal adaptation

43

• Optimal esthetics • Resistant to catastrophic root failure • Lack of corrosiveness • Modulus of elasticity similar to root dentin • Flexural and tensile strengths similar to root structure • Uninterrupted bonding at all interface.

DISADVANTAGES • Technique sensitivity • Need for a careful adhesive protocol • Need to maintain an inventory of the reinforcement materials • Need to demonstrate long term effectiveness.

The ideal system of products for the endodontic-restorative continuum includes : • An esthetic resin fiber post • A composite core • Automixed resin luting cement • Current techniques that combine the automixed resin luting cement and composite core into the same component.

CERAMIC POST’S CORE

Composition : • Tetragonal Zirconia polycrystals (ZrO2-TZP) Stabilized by 3 mol % Y2O3 - 94.9% ZrO2 - 5.1% Y2O3 CERAMIC CORE MATERIAL In 1997 Ivoclar introduced a ceramic core materials that can be heat pressed directly onto Zirconia posts (IPS Empress Cosmo Ingot).

Glass Ceramic ingot developed for the heat pressing technique is composed of : • 58.5% SiO2 by weight • 15.5% ZrO2 by weight • 4.0% P2O5 by weight • 8.0% Li2O by weight, with 14 additives such as Na2O, K2O, Al2O3, and F. Advantages • Biocompatibility • High flexural strength = 1400 Mpa • Paralle! Sided post designed • High strength and resilience • Optimal esthetic appearance • Do not exhibit galvanic corrosion Disadvantages Low • Fracture Strength • Fracture Toughness

REMOVAL OF EXISTING POSTS

44

Occasionally the dentist is confronted with an endodontically treated tooth with a poor prognosis because of the fractured dowel. Retreatement with a post and core cannot be attempted unless the fractured post is removed. This can be dangerous, however, because the roots are brittle.

If sufficient length of post is exposed coronally, a post can be retrieved with thin- beaked forceps.

Vibrating the post first with an ultrasonic scaler will weaken brittle cement and facilitate removal. A thin scaler tip or special post removal tip is recommended. Ultrasonic removal is slower than other methods and may result in an increased number of canal intradentin cracks. Alternatively, a post puller can be used. This device consists of a vise to grip the post and legs that bear on the root face. A screw activates the vise and thus extracts the post.

A post that has fractured within the root canal cannot be removed with a post puller. The best means for handling an embedded fractured post was described by Masserann. He developed and designed an instrument for extracting posts or rigid instruments that are broken deeply within the roots with minimum damage. The method involves gripping the object through a tube or trephine which acts as a tubevice. This method is relatively harmless to the tooth and periodontium.

Masserann Procedure : From the Masserann kit, the appropriate size trepan bur is determined by a gauge supplied in the kit. Since the trepan burs are hollow end-cutting tubes, they fit over the end of the post and slide down its outside. The instrument is turned by hand cutting a small trench around the post. The fragment serves as the guide in the removal of the dentin or cement from around the post. After proceeding from one third to one half the way down the post, the trepan bur is replaced with the next smaller size, which will grip the end of the post to lift it out of the canal. If necessary, the trepans can be used to extend to the bottom of the post for easy removal.

After the post is removed, the root canal is enlarged with a Peeso reamer so that a conventional cast post and core can be made. Later an appropriate crown can be made for the tooth.

Advantages : 1) It is simple, 2) Little heat is generated, 3) There is no danger of pushing fragments further into the root, and 4) Excessive forces are eliminated with little chance of perforation or splitting the root.

This technique may make it possible to save strategic teeth that other wise might be lost.

Pierre Machtou, Philippe Sarfati and Anna Genevieve presented the Gonon post removing system for removing posts from the root canals prior to endodontic retreatment.

Gonon post removal technique : The principle of this instrument is comparable to a cork screw. The post and the tooth are separated by pitting the tooth against the post and creating enough force to overcome the bond.

1) The first step is to free the head of the post from the coronal tooth structure. All restorations including crowns must be removed.

Circumferential prereduction of the core may be achieved using a tapered diamond bur at high speed.

2) An ultrasound device is useful to vibrate the post and disintegrate the cement.

3) In order to facilitate the centering of the trephine, a special bur included in the Gonon kit is used to taper the protruding head of the post.

4) The high strength trephine is used to bore and gauge the protruding post to the exact size of a corresponding mandrel which is specially manufactured to thread the post.

5) Before the mandrel is screwed onto the post, three rings are positioned onto its shank. This acts to cushion the mandrel and to spread the forces onto the root surface as the post is being extracted.

6) The extracting pliers are fixed on the mandrel and the jaws of the pliers are expanded by tightening the knurled knob. This procedure will separate the post from the tooth quickly and safely facilitating endodontic retreatment.

Sometimes the space between the adjacent teeth is smaller than the width of the jaws. This problem may be resolved by slipping a hollow tube included in the package into the â&#x20AC;&#x153;longâ&#x20AC;? threaded mandrel.

CONCLUSION: Endodontic therapy is an essential component of the practice of restorative dentistry at the close of the 20th century. Dental practice and its success are inextricably tied to the quality of the restoration. Before

45

making a treatment decision, the restorative dentist must evaluate the quality of endodontic treatment, the periodontal support available, and the status of the remaining tooth structure. The subsequent restoration for the endodontically treated tooth is function of the remaining tooth structure, the shape and configuration of the canals, and the functional and esthetic demands on the tooth.

Arriving at the best solution is a complex process, affected by many different variables, including available post systems and restorative foundation materials. Although there are additional experimental laboratory data on which to base a restorative decision, long-term controlled clinical data are not yet available. Restoring the endodontically treated tooth remains one of the most challenging problems facing the restorative dentist. An uncomplicated and systematic decision making process, based on universally accepted philosophy and techniques, is necessary to maximize chances for a successful restorative outcome.

If certain basic principles are followed in the restorative of endodontically treated teeth, it is possible to achieve high levels of clinical success with most of the current restorative systems. These principles include:

      

Avoid bacterial contamination of the root-canal system.

Provide cuspal coverage for posterior teeth.

Preserve radicular and coronal tooth structure.

Use posts with adequate strength in thin diameters Provide adequate post length for retention Maximize resistance from including an adequate ferrule Use posts that are retrievable.

46

Review of literature Dominick C. Larato (1966) described the fabrication of the post and crown for pulpless teeth which can be cast as one unit by constructing a pattern with cold-cure acrylic resin and wax. A single unit cast post and crown saved valuable chair time and simplified an operation without sacrificing accuracy or esthetic requirements.

Morton L. Perel and Fredrick I. Muroff (1972) outlined the principles that are essential for any successful post and core restoration regardless of the method used based on both endodontic and fixed prosthodontic considerations.  The post must be long enough to prevent excessive internal stresses on the root.  The diameter of the post must be adequate to avoid bending the cast gold.  A positive occlusal seat for the core portion will prevent wedging action by the conical post.  Proper internal adaptation of the post will distribute the internal stresses as evenly as possible and will allow for only a thin, even layer of cement seal.  The core portion should be as close to the ideal as possible to receive the selected retainer. The core should replace only that missing tooth structure.  The post should lie in the direction of the long axis of the root.

Eugene C. Hanson and Angelo A. Caputo (1974) conducted a study to provide guidelines for the retention of dowels employing various dental cements such as polycarboxylate, zinc phosphate and ethyl cyanoacrylate with embedment periods of 1.5hrs, 7 to 12 days and 30 to 44 days (short, intermediate and long terms respectively).

Whaledent Para-Posts which are cylindrical, serrated, vented, stainless steel dowels with diameters 0.05 inch, 0.06 inch and 0.07 inch were used. The 0.06 inch diameter Para-Post exhibited the highest retention for all cements. Cyanoacrylate cements was the most retentive for all diameter dowels at 1.5hrs. With embedment terms of seven days or longer, there was no significant difference between cements according to retention values. Retention values increased with increasing time after installation for all cements and dowels. The teeth treated with camphorated monochlorophenol and having 0.06 inch dowels showed no significant differences in retention with any of the three cements.

Osvaldo Zmener (1980) conducted a preliminary study to evaluate the effect of dowel preparation on the apical seal of root canals obturated with sectional silver cones, or gutta-percha with lateral condensation and sealer cement.

The apical seal for the well-fitted silver point was most vulnerable when a section of the cone must be removed during the dowel preparation. However, the apical leakage appeared notably reduced when the silver point was not disturbed. In root canals sealed with lateral condensation of multiple gutta-percha points, leakage was reduced considerably when more than 4mm of gutta-percha filling remained in the apical portion of the canal. No significant difference was found when the coronal portion of the root canal filling was removed immediately after placement.

Edmund H. Kwan and Gerald W.Harrington(1981) evaluated the effect of two post preparation techniques – the warm pluggers and files and Gates Glidden drills on the apical seal immediately after filling

47

the root canal with filled teeth that have not had post preparations completed using India ink. They found that (a) The use of Gates-Glidden drills to remove gutta-percha for preparation of post space, immediately after filling the root, resulted in statistically less leakage compared with Guttapercha filled controls. (b) The use of warm pluggers and files to remove gutta-percha for preparation of post space immediately after filling the root canal when compared with gutta-percha filled controls, no statistical difference in leakage was found. (c) The degree of apical leakage was not related to the length of gutta-percha remaining after preparation of the post space.

E. Patrick Hoag and Thomas G. Dwyer (1982) conducted an invitro study to evaluate three clinical techniques for rebuilding posterior teeth a) An interlocking stock and cast-gold post and core. b) A standardized stainless steel post and composite resin core. c) An amalgam post and core technique.

The effect of a full gold crown on the three types of buildups was also evaluated.

The results indicated that the method of post and core technique may not be as significant as the placement of full coverage cast-gold crown restorations with sound design and placement of margins beyond the buildup restoration.

Allan S. Deutsch et al (1985) identified the key variable of root fracture like the design of prefabricated posts and determined their interrelationships. Three post types were tested a) The Radix no. 2 post b) The Medidenta medium long post and c) The Dentatus M-5 post.

They found that the conical threaded posts (Dentatus) fractured roots more often and at lower torque than parallel posts(Radix No.2 Post and Medidenta). The mean torque value for fractures for Dentatus was 29.5 inch-ounces, Medidenta-35.7 inch-ounces and Radix-36.4 inch-ounces.

R.A. Oliva and J.A. Lowe (1986) evaluated the effect of water sorption on composite cores as it relates to the marginal seating of cast restorations and its time of occurrence. They found out that Composite cores were not dimensionally stable when exposed to moisture. Composite core preparations exposed to moisture began to change dimensionally within 1 hr.The marginal seating of crowns constructed over these composite cores was affected by the instability of the core material.

R. Lewis and B.G. N. Smith (1988) identified the features of failed post retained crowns in order to point to further improvements in clinical technique. Five major causes of post crown failure were caries, root fracture, mechanical failure of the post including bending and fracture, and cementation failure or loosening of the post. Decementation accounted for the great majority of failures. Whenever possible, a more retentive design than the smooth tapered cast post should be used. The recommendation that the post length should be at least equal to the length of the crown remains a sound clinical guideline. Failure of the post crown within 3 years of cementation was more common than later failure.

Pierre Machtou, Philippe Sarfati and Anna Genevieve Cohen (1989) presented the Gonon post removing system for removing posts from root canals prior to endodontic retreatment which is safe and efficient and can be used for anterior, bicuspid and even molar teeth. The kit is also available with trephines which have counter clockwise threading. These trephines will facilitate the removal of screw and threaded posts.

Thomas Kvist,Eva Rydin and Claes Reit (1989) conducted a study to investigate the relationship between length and quality of root filling seal in teeth with posts and radiographic status of the periapical tissues. They found out that roots with posts in which the remaining root filling was shorter than 3 mm showed a statistically significant higher frequency of periapical radioluciences and an improper seal was more unfavourable in roots with posts. They finally concluded that the placement of a post will not per se

48

decrease the probability of periapical healing. They also suggested that the remaining root filling must not be shorter than 3mm.

John A. Sorensen and Michael J. Engelman (1990) evaluated the fracture resistance of endodontically treated anterior teeth with various ferrule designs and amount of coronal tooth structure.

They found out that a) One millimeter of coronal dentin above the shoulder significantly increased the failure threshold. b) The preparations of the coronal walls should be parallel for maximum resistance form. c) The contrabevel design at either the tooth-core junction or the crown margin did not improve the failure threshold and d) The axial width of the tooth at the crown margin did not significantly increase the fracture resistance or alter the failure threshold.

Joe M. Goss, W. James Wright Jr., and William F. Bowles (1992) tested different dental luting materials for masking the radiographic image of cemented titanium alloy posts. They found out that Glass Ionomer luting materials obscured the outline of titanium alloy prefabricated posts more than composite resin, but less than zinc phosphate or polycarboxylate cements.

KcRolf, MW Parker and GB Pelleu (1992) evaluated the stress generated by five prefabricated endodontic dowels- Para post, Beta Post, Kurer Crown Anchor, Flexi-Post, Radix Anchor using a two dimensional photoelastic model. The cemented retained posts- Para Posts and Beta Posts were the least stressful of all the posts tested. Of the threaded posts â&#x20AC;&#x201C; Flexi Post and Radix Anchor produced the least stress and the Kurer Crown Anchor produced the most stress. The Flexi-Post and Kurer Crown Anchor were the most retentive, the Radix Anchor were one-half as retentive and the cement-retained Beta Post and Para-Post were the least retentive. So the Radix Anchor and Flexi-Post designs provided the best combination of high retention and low stress.

Patrice Milot and R. Sheldon Stein (1992) determined the role of post selection and bevel on the tooth preparation and subsequent crown restoration with respect to root fracture with simulated clinical forces. Three different post and core systems were used : a) Cast post and core b) Para Post Plus Post and c) Flexi-Post Post. The core build-up material was Ketac Silver material. They found out that when most of the tooth structure is preserved, the post selection has little or no effect on resistance to root fracture. A beveled preparation with the concomitant final restoration offers an increased resistance to root fracture. A non-beveled preparation with a concomitant final restoration is more prone to an incidence of vertical fracture.

Patrick M. Lloyd and Joyce F. Palik (1993) reviewed the literature regarding the diameter of dowels and identified three distinct philosophies of dowel space preparation. One group advocated the narrowest diameter for the fabrication of a dowel to the desired length. Another recommended a dowel space with an apical diameter equal to one third of the narrowest dimension of the root at the terminus of the dowel. A third group advised that at least 1mm of sound dentin should surround the entire surface of the dowel.

A combination of the one third and 1mm minimal philosophies yielded a practical guideline for dowel space preparation, particularly in aged teeth.

D.G. Purton and J.A. Payne (1996) investigated the flexural stiffness of the carbon fiber root canal posts and compared it with the stiffness of stainless steel post.They also compared the retention of a resin composite core material to the carbon fiber and the stainless steel posts.

The carbon fiber material was stiffer under transverse loading than was stainless steel because of its adequate rigidity. The resin composite core material was retained more strongly to the stainless steel posts than to the carbon fiber posts in tensile testing. The configuration of the posts significantly affected the retention of the resin composite cores and the mode of fracture on tensile loading.

49

Givanni E. Sidoli, Paul .A. King and Derrick .J. Setchell (1997) compared the invitro performance and the failure characteristics of the Composipost system which comprises of an epoxy-based carbon fiber post, a composite core material and a low viscosity Bis-GMA bonding resin against existing pore and core combinations ie. stainless steel post and composite core, gold alloy post and gold alloy core and an endodontically treated tooth only. The mean stress at failure was 8.89 for Composipost system, 2.40 for Stainless Steel post and Composite core, 15.25 for Cast gold alloy post / gold alloy core, 24.84 for endodontically treated tooth only. The Composipost system exhibited significantly inferior stress values at failure when compared with a cast gold alloy post and core combination when tested with a single angled compressive load. But the mode of failure of the Composipost system with angled compressive load testing was more favourable to the remaining tooth structure when compared with the cast gold alloy post and core system. Endodontically treated teeth only were significantly more resistant to angled compressive loading when compared with teeth restored with the various post and core systems.

Jon P. Dean, Billie Gail Jeansonne and Nikhil Sarkar (1998) conducted a study to evaluate the influence of endodontic and restorative procedures on fracture resistance of teeth and compare the incidence of root fracture among teeth restored with three different types of posts (Carbon fiber post,Tapered SS post,Parallel SS post) each supporting a composite core build -up.

The groups with post and composite build- ups failed at significantly lower force than the teeth in which the crowns had not been removed. There was no significant difference in the amount of force required to produce failure among the three groups with different posts and a composite build-up. The group restored with the carbon post had no root factures, whereas there were five fractures in each of the parallel and tapered post groups.

Buranadham S, Aquilino S. A and Stanford C.M (1999) 5 created a guideline in determining the dowel length in relation to the alveolar bone level. They said that the cast dowels should be extended more than 4mm below the bone level to minimize the stresses in the dowel and dentin regardless of the C:R ratio of the restored tooth.

Sonthi Sirimani, Douglas .N. Riis and Steven .M. Morgano (1999) compared the resistance to vertical root fracture of extracted teeth treated with post and core systems that were modified with polyethylene woven fibres (Ribbond) with those treated with conventional post and core systems. They found that cast posts and cores resulted in significantly higher failure thresholds than all others, except for prefabricated, comparably sized, parallel-sided posts with composite cores. The polyethylene woven fiber and composite resin without a prefabricated post resulted in significantly fewer vertical root fractures but mean failure was the lowest. Smaller diameter prefabricated posts combined with the polyethylene woven fiber and composite cores improved resistance to failure.

Spiros .O. Koutayas and Matthias Kern (1999) described the fabrication of all-ceramic posts and cores, using high-toughness ceramic materials such as alumina or zirconia ceramics, through 4 different techniques : a) The slip-casting technique-in which the core buildup and the post are made in 1 piece from the aluminium oxide ceramic material-In-ceram; b) The copy-milling technique which involves a manually guided copy-milling process in which a predesigned resin pattern is surface treated and copied in ceramic; c) The 2-piece technique which involves a prefabricated zirconia ceramic post and a copy-milled alumina or zirconia ceramic core and d) The heat press technique, which involves a prefabricated zirconia ceramic post and a heat pressed glass-ceramic core.

The 2-piece technique appeared to be the most promising method for post and core fabrication which in addition to improved esthetics provided a post and core with improved mechanical properties.

Brett I. Cohen et al (2000) compared the retention of 2 types of cores, Ti-core Titanium reinforced Composite and GC Miracle Mix silver reinforced Glass Ionomer, with 3 post designs namely, the Flexi-Post, and Access Post stainless steel dowels and a Cerapost Ceramic dowel. They found out that the post head designs of the stainless steel Access Post and Flexi-Post dowel provided greater retention than the smooth ceramic head design of the Cerapost dowel. Ti-core composite core material exhibited significantly higher strength and was more retentive than Miracle Mix glass Ionomer material.

50

Raphael Pilo and Aviad Tamse (2000) conducted a study to evaluate the residual dentin thickness of mandibular premolar after preparation of post space with Gates Glidden and Para Post drills with an innovative muffle device. The advantage of a muffle system is the ability to successively study several steps that allowed each root to serve as its own control.

Natural anatomy of mandibular premolars in the post space from Cementoenamel junction to 5mm apically comprised of constant residual dentin thickness in the FacioLingual axis and a decrease of 1mm in the MesioDistal axis. Rotary instrument, such as Gates Glidden and ParaPost drills, removed substantially more dentin in the MesioDistal axis. Minimal residual dentin thickness of 1mm was approximated by No. 5 ParaPost drill, 5mm below the Cementoenamel junction. Minimal or no reduction of residual dentin thickness during post space was recommended for mandibular premolars with oral /ribbon shaped cross sectional canal anatomy.

Alison J.E. Qualtrough,Nicholas.P.Chandler and David G.Purton (2003) compared the retention of five different esthetic post systems [Light post (tapered), Lightpost (parallel-sided), Parapost Fibrewhite, Snowpost and Dentatus Luscent] of similar dimensions in extracted teeth using titanium posts as controls. All posts were bonded using Panavia F.A 4-mm hollow, metal sleeve was luted over the free end of each post prior to mounting.

Parallel-sided Lightposts were significantly more retentive than all other posts. Parapost Fibrewhite posts were more retentive than tapered Lightposts and Snowposts. Serrated, parallel-sided stainless steel posts were no more retentive than either parallel-sided or tapered tooth-colored posts. Post dimension may influence the retention of tooth-colored posts, with parallel-sided posts being more retentive than tapered posts.

Chetan Arora et al (2003) highlighted some of the important biomechanical considerations that should be taken into account while restoring an endodontically treated tooth with post and core.

Some of the most important features of successful design for post and core are : 1) Adequate apical seal 2) Minimum canal enlargement 3) Adequate post length 4) Positive horizontal stop 5) Vertical wall to prevent rotation 6) Adequate margin placement Retention of a post within the root canal is dependent on 4 major factors a) Length b) Diameter c) Shape d) Surface configuration Length: The post should be as long as possible without jeopardizing the apical seal and integrity of remaining tooth structure. It is advised to maintain 3-5mm of apical seal with gutta-percha.

Diameter: Post should be as narrow as possible so that it is compatible with tooth strength to reduce incidence of perforation. But it should be wide enough to avoid bending or breaking.

Surface configuration: Serrated or Roughened post is more retentive than a smooth one. Threaded posts are the most retentive of all, but they also generate greatest stress Smooth posts develop least stress but they also provide least retention.

Shape: Parallel post is considered most retentive with least stress.

RESISTANCE : Ferrule is suggested to improve the integrity of endodontically treated tooth. Anti-rotational groove can be placed within the canal in the most bulkiest portion to prevent post rotation within the root canal when too much of tooth structure has been destroyed. A positive horizontal step approx 2 mm deep can be made within the root to minimize the splitting potential of a post by resisting apically directed forces and also by preventing wedging.

David G. Purton, Nicholas P. Chandler and Alison J.E. Qualtrough (2003) investigated the effects of thermocycling on the retention of 2 glass-fiber and resin â&#x20AC;&#x201C;Composite posts. The two brands of glass-fiber and resin-Composite posts investigated were

51

1)

Luscent Anchors (Dentatus) which are smooth-sided post, 1.6mm in diameter coronally, tapering to 1.0mm apically.

2) Lightposts (RTD) which are smooth-sided posts, with a 1.8mm diameter in the coronal one third, tapering to 1.0mm apically.

There was no significant difference in the forces required to cause post-retention failure between the control and thermocycled specimens. Lightposts were significantly more retentive than Luscent Anchor without thermocycling, but this distinction was not apparent in the thermocycled groups. Glass-fiber and resin posts cemented with resin cement offer acceptable levels of retention and are not susceptible to reduced retention from thermocycling. Thermocycling should be given less emphasis in tests for the retention of root canal posts cemented with resin cements.

Elio Mezzomo, Fernando Massa and Silmar Dalla Libera (2003) investigated the fracture resistance in teeth restored with cast post and cores with and without ferrule and using two different luting cements â&#x20AC;&#x201C; zinc phosphate and resin cements.

A 2.00mm cervical root ferrule showed higher fracture resistance regardless of the luting agent used. There was no statistical difference between the group of specimens cemented with resin cement and without ferrule and the ferruled groups. The non-ferruled group with zinc-phosphate cement showed the poorest results. The resin cement was better than zinc-phosphate cement in the no ferruled group.

Fahad Al-Harbi and Dan Nathanson (2003) evaluated the retentive strength of composite and ceramic endodontic dowel systems to the tooth and to the core foundation. The dowel systems tested were : Resin dowels (Fibrekor [FR]; Luscent [LU] ; Twin luscent Anchor [TLU]) ; Ceramic dowels (Cerapost [CR] ; Cosmopost [CO]) ; and a Titanium dowel (ParaPost XH [Ti]). In the Dowel to core retention, all esthetic dowels had significantly lower retentive values to core foundation than the Titanium ParaPost .

Among the esthetic dowels, the Fibrekor dowel system produced the highest core retentive value (337 N).

In the dowel to tooth retention, the fiber-reinforced resin dowels (Twin luscent and Fibrekor) had mean retention values to teeth similar to the Titanium Para-Posts cemented with resin and significantly higher than the Titanium Para-Posts cemented with zinc phosphate luting agent. Ceramic dowel systems had significantly lower retentive values than the other dowel systems tested.

Mian K. Iqbal et al (2003) explored the possible associations between prosthodontic, occlusal, endodontic, and periodontal factors and the endodontic status of endodontically treated teeth. Three factors were significantly associated with the presence of radiolucency : confirmed occlusal contact, by virtue of the tooth being involved in group function or the only contact in working- side and protrusive movements, endodontic filling and crown margins of poor quality.

R De Castro Albuquerque et al (2003) evaluated the effect of different anatomic shapes and materials of posts in the stress distribution on an endodontically treated incisor. Three post shapes (tapered, cylindrical and two-stage cylindrical) made of three different materials (stainless steel, titanium and carbon fibre on Bisphenol A-Glycidyl Methacrylate (Bis-GMA matrix) were compared in this study. The stress concentrations did not significantly affect the region adjacent to the alveolar bone crest at the palatine portion of the tooth, regardless of the post shape or material. However, stress concentration on the post / dentin interface on the palatine side of the tooth root presented signified variations for different post shapes and materials. Post shapes had relatively small impact on the stress concentrations while post materials introduced higher variations on them. Stainless steel posts presented the highest level of stress concentration, followed by Titanium and Carbon / Bis-GMA posts.

S.O. Hedlund, N.G. Johansson and G. Sjogren (2003) evaluated the retention of prefabricated root canal posts provided with a core of resin composite. The prefabricated root canal posts studied were Cosmopost, Composipost carbon fibres, Composipost / Estheti-Plus, Composipost Light-Post and Para Post Fiberwhite.

Only the Cosmopost system exhibited retention values lower than the conventionally cast gold alloy posts luted with zinc-phosphate cement due to an adhesive failure at the interface between the cement and the ceramic.

Newman MP, Yaman P, Dennison J, Rafter M, BillyE(2003)compared the effect of 3 fiber-reinforced composite post systems on the fracture resistance and mode of failure of endodontically treated teeth, and concluded that the load to failure of the stainless steel posts were significantly stronger than all the

52

composite posts studied. However, the mode of failure or deflection of the fiber-reinforced composite posts is protective to the remaining tooth structure.

Ferrari M, Mason PN, Goracci C, Pashley DH, Tay FR(2004) They hypothesized that demineralized collagen matrices (DCMs) created in dentin by acidic zinc phosphate cement within the dowel spaces degrade with time. Forty-two post-restored teeth were extracted after three periods of clinical service and were examined, SEM revealed a progressive degradation of the DCMs, becoming less dense after 3 to 5 years, losing structural integrity after 6 to 9 years, and partially disappearing after 10 to 12 years. TEM revealed evidence of collagenolytic activity within the DCMs, with loss of cross-banding and unraveling into microfibrils, and gelatinolytic activity that resulted in disintegration of the microfibrils.and concluded that Bacterial colonization and the release of bacterial enzymes and of host-derived matrix metalloproteinases may contribute to the degradation of collagen fibrils in root dentin after clinical function.

Sahafi A, Peutzfeldt A, Asmussen E, Gotfredsen K(2004) evaluated the effect of cement, post material, surface treatment, and shape (1) on the retention of posts luted in the root canals of extracted human teeth and (2) on the failure morphology, and concluded that Choice of luting cement was critical for all three types of posts. Parallel posts showed superior retention to tapered posts.

Chen XT, Li XN, Guan ZQ, Liu XG, Gu YX(2004) investigated stress distribution of different materials restored post-cores in dentine to provide a theoretical guidance for clinical use, and concluded that The materials with elastic modulus similar to that of dentin, such as polythene fiber reinforced composite, may be suitable for post restoration.

Usumez A, Cobankara FK, Ozturk N, Eskitascioglu G, Belli S(2004) compared microleakage of 3 esthetic, adhesively luted dowel systems with a conventional dowel system, and concluded that, Resin-supported polyethylene fiber dowels and glass fiber dowels tested exhibited less microleakage compared to zirconia dowel systems. The latter system should be further evaluated because of its unacceptable level of leakage.

Larson TD(2004). Reviewed the relevant literature from 1991-2003, a period of time when adhesive resin luting materials became available and luting crowns with zinc phosphate cements decreased.. Amalgam cores are regarded as the strongest material, best able to withstand adverse stress and restore teeth having the greatest loss of tooth structure. Composite resins, whether chemically cured or light cured, reinforced or not, appear best capable of core restoration for moderately broken down teeth. Glass ionomer materials are considered too weak to withstand stress as a core material, but are recommended as a base material to fill in undercuts and improve the accuracy of impression and fit of a crown.

Paul SJ, Werder P(2005) Retrospectively evaluated zirconium oxide posts with either direct resin composite cores or indirect glass-ceramic cores after several years of clinical service. And they concluded clinical success of zirconium oxide posts with direct composite cores suggests that this method of post-andcore reconstruction is clinically promising. Zirconium oxide posts with indirect glass-ceramic cores displayed a significantly higher failure rate and a high dropout.

Giachetti L, Scaminaci Russo D, Bertini F, Giuliani V(2005) Evaluated The performance of both light-curing and dual-cured adhesive/luting systems (as control), when used in combination with translucent fibre posts, which was evaluated by means of pull-out test and scanning electron microscopy (SEM ) observation. and they concluded that Dual curing of the All Bond 2+RelyX ARC system seems to be the most appropriate method since it allows to cure even those areas

53

which would not be otherwise reached by light. On the other hand, in apical areas, the incomplete curing of the Excite+Tetric Flow system could improve the post adaptation and allow the achievement of both an improved apical seal and a more even distribution of the stress along the canal walls.

Island G, White GE(2005) compared two different types of fibers and analyzed the fracture resistance between the two of them. Two groups were formed. Group I used non pre-impregnated resin fibers and group II used pre-impregnated resin fibers. Concluded that pre-impregnated fibers offer a better fracture resistance when used as post in endodontically treated primary anterior teeth.

Monticelli F, Goracci C, Grandini S, Garcia-Godoy F, Ferrari M(2005) evaluated the structural characteristics of post-and-core units made of a fiber post and of different types of resin-based composites used as core materials using Scanning electron microscope. And concluded Cores built up with flowable composites showed the highest integrity and the best adaptation onto the post.

da Silva RS, de Almeida Antunes RP, Ferraz CC, Orsi IA(2005) Evaluated The effect of the use of 2% chlorhexidine gel in post-space preparation on carbon fiber post retention and the bond strength of a resin cement used to lute carbon fiber posts, when drills and 4 different substances were used for the post-space preparation. And concluded that Xylene and chlorhexidine gel are good substances for the post-space preparation but the second has the advantage of antimicrobial activity and low toxicity.

Tan PL, Aquilino SA, Gratton DG, Stanford CM, Tan SC, Johnson WT, Dawson D(2005) investigated the resistance to static loading of endodontically treated teeth with uniform and nonuniform ferrule configurations, And they demonstrated that central incisors restored with cast dowel/core and crowns with a 2-mm uniform ferrule were more fracture resistant compared to central incisors with nonuniform (0.5 to 2 mm) ferrule heights. Both the 2-mm ferrule and nonuniform ferrule groups were more fracture resistant than the group that lacked a ferrule.

Aksoy G, Cotert HS, Korkut L(2005) evaluated the retention between a prefabricated dowel and 3 different core materials with or without a dual-polymerized adhesive resin luting agent. And concluded that adhesive resin luting agent tested appeared to have a significant strengthening effect on the dowel-head retention of the core materials.

Willershausen B, Tekyatan H, Krummenauer F, Briseno Marroquin B(2005) conducted a nonrandomized cohort study to evaluate the Survival rate of endodontically treated teeth in relation to conservative vs post insertion techniques, and concluded The results showed a high success rate for endodontically treated teeth when the final restoration was placed within a short period of time (two weeks).

A higher tooth loss was observed when metal post systems were employed suggesting that precaution is recommended when these types of posts are inserted.

Tait CM, Ricketts DN, Higgins AJ(2005) highlighted the fact that many anterior teeth requiring restoration are severely weakened having wide, flared canal spaces, and thin dentinal walls that are prone to fracture.

Traditionally these teeth have been restored using metal posts and are often unsuccessful because of lack of retention or root fracture. and they Described mineral trioxide aggregate (MTA) can be used to form an immediate apical seal rather than waiting months for apexification. Weakened roots can be reinforced using dentine bonding agents and composite resin and if insufficient coronal tooth structure is present a quartzfibre post can be placed to retain a composite core.

Yoldas O, Akova T, Uysal H(2005) evaluated the stress transfer of different post and core systems to the cervical part of the artificially created flared root canals, by using strain gauges. The post-core systems investigated were: (a) cast post-core system without resin reinforcement, (b) cast post-core system with resin reinforcement, (c) pre-fabricated post and resin core with resin reinforcement. It was concluded that the resin reinforcement of root canals before post-core applications reduces the stresses at the cervical part of the root surfaces.

54

Carvalho CA, Valera MC, Oliveira LD, Camargo CH(2005) evaluated in vitro the efficacy of root reinforcements by light-cured composite resin or zirconium fiber post in simulated immature non-vital teeth.and concluded that the use of root reinforcements with zirconium fiber post or composite resin can increase significantly the structural resistance of the weakened teeth, decreasing the risk of the fracture.

Mannocci F, Qualtrough AJ, Worthington HV, Watson TF, Pitt Ford TR(2005) compared the clinical success rate of endodontically treated premolars restored with fiber posts and direct composite to the restorations of premolars using amalgam. And concluded that restorations with fiber posts and composite were found to be more effective than amalgam in preventing root fractures but less effective in preventing secondary caries.

Creugers NH, Mentink AG, Fokkinga WA, Kreulen CM(2005). Tested whether: (1) the survival rate of cast post-and-core restorations is better than the survival of direct post-and-core restorations and post-free all-composite cores; and (2)the survival of these buildup restorations is influenced by the remaining dentin height after preparation, and concluded The type of post and core was not relevant with respect to survival.

The amount of remaining dentin height after preparation influenced the longevity of a post-and-core restoration.

Brunton PA, Christensen GJ, Cheung SW, Burke FJ, Wilson NH(2005) investigated, by questionnaire, the use and selection of materials and techniques for indirect restorations and fixed prosthodontics by dental practitioners in the North West of England and Scotland. And concluded the majority of the practitioners surveyed in this study used: amalgam for core build-ups; indirect posts; addition-cured silicone for impressions; and glass-ionomer cements for luting procedures.

Wu XH, Chen XM, Yang Y, Niu L, Yao W(2005) accessed the effects of post's diameter on the retention of post-core restorations And concluded that When the proportion of length and diameter was smaller than 4.372, the retention of post-core crown system increased with the decrease of the post's diameter. While the proportion was lager than a certain value, this rule did not exist.

Hu S, Osada T, Shimizu T, Warita K, Kawawa T(2005) evaluated the resistance to fracture of endodontically treated teeth with flared canals restored with different post and core The results of this study suggested that RCP prepared with 1-mm ferrule was the most desirable restoration for structurally compromised roots.

Bibliography : 1. Albuquerque RDC, Palleto LTDA, Fontana RHBTS, Cimini CA Jr. Stress analysis of an upper central incisor restored with different posts. J Oral Rehabil 2003; 30: 936-943.

2. Aksoy G, Cotert HS, Korkul L. Effect of an adhesive resin luting agent as the dowel head retention of three different core materials. J Posthet Dent. 2005 May;93(5):439-45.

3. Al-harbi F, Nathanson D. In Vitro assessment of four esthetic dowels to resin core foundation and teeth. J Prosthet Dent 2003; 90: 547-555.

4. Arora C, Singh RK, Chitre V, Aras M. Biomechanical considerations in the restoration of Endodontically treated teeth with post and core. J. Ind . Prosth. Soc 2003; 3: 41-45.

5.

Ayna E, Celenk S. Use of an alternative pontic foundation technique for a fibre reinforced composite fixed partial denture: a clinical report. J Prosthet Dent. 2005 May;93(5):412-5.

6. Brown PL, Hicks NL. Rehabilitation of Endodontically Treated Teeth using the Radiopaque Fiber Post. Compend Contin Edu Dent 2003; 24: 275-284.

7. Buranadham S, Aquilino SA, Stanford CM. Relation between Dowel Extension and Bone Level in Anterior Teeth. J Dent Res 1999; 78: 222 (abstract 930).

8. Caputo AA, Hokama SN. Stress and retention properties of a new threaded endodontic post.

Quintessence Int 1987; 18: 431-435.

9.

Cheung W. A review of management of endodontically treated teeth. Post, core and final restorations. J Am Dent Assoc 2005 May;136(5):611-9.

55

10. Carvalho CA, Valera MC, Oliveira LD, Camargo CH. Structural resistance in immature teeth using root reinforcement is vitro. Dent Traumatol. 2005 Jun;21(3):155-9.

11. Cohen BI, Pagnillo MK, Newman I, Musikant BL, Deutsch AS. Retention of a core material supported by three post head designs. J Prosthet Dent 2000; 83: 624-628.

12. Cohen S, Burns RC. Pathways of the Pulp. 8th Edn. St. Louis : Cv Mosby; 1994. p. 769-791.

13. Dean JP, Jeansonne BG, Sarkar N. In Vitro evaluation of a Carbon Fiber Post. J Endod 1998; 24: 807-810.

14. Deliperi s, Bradwell DN, Coiana G. Reconstruction and devital teeth using direct fiber reinforced composite resins: a care report. J Adhes Dent. 2005 summer,7(2):165-71.

15. Deutsch AS, Cavallari J, Musikant BL, Silverstein L, Lepley J, Petroni G. Root fracture and the design of prefabricated posts. J Prosthet Dent 1985; 53: 637-640.

16. Ertugrual HZ, Ismail YH. Anvitro comparison of cast metal dowel retention using various luting agent and tensile loading. J Prosthet Dent. 2005 May;93(5):446-52.

17. Fokkinga WA, Le Bell AM, Kreulen CM, Lassila LV, Vallittu PK, Creugers NH. Ex vivo fracture resistance of fracture resistance of direct resin composite complete crowns with and without posts on maxillary premolars. Int Endod J. 2005 Apr;38(4):320-7.

18. Freedman GA. Esthetic Post-And-Core Treatment. Dent Clin North Am 2001; 45: 103-116.

19. Galvan RI, Robertello FJ, Lynde TA. In vitro comparison of fluoride release of six direct core materials. J Prosthet Dent 2000; 83: 629-633.

20. Goldrich N. Construction of posts for teeth with existing restorations. J Prosthet Dent 1970; 23: 173-176.

21. Gardon MP. The removal of gutta-percha and root canal sealess from root canals. NZ Dent J. 2005;101(2):44-52.

22. Goracci G, Raffaelli O, Monticelli DF, Balleri B, Bestelli E, Ferrari M. The adhesion between prefabricated FRC. Posts and composite resin cores: Microtensile bond strength with and without post â&#x20AC;&#x201C; silanization. Dent Mater. 2005 May;21(5):437-44.

23. Goss JM, Wright WJ Jr, Bowles WF. Radiographic appearance of titanium alloy prefabricated posts cemented with different luting materials. J Prosthet Dent 1992; 67: 632-637.

24. Guzy GE, Nicholls JI. In Vitro Comparison of intact endodontically treated teeth with and without endo-post reinforcement. J Prosthet Dent 1979; 42: 39-43.

25. Hall DL, Williams VM. Crown repair with a cast post and core. J Prosthet Dent 1985; 53: 641-642.

26. Hanson EC, Caputo AA. Cementing mediums and retentive characteristics of dowels. J Prosthet Dent 1974; 32: 551-557.

27. Hedlund SO, Johansson NG, Sjogren G. Retention of Prefabricated and Individually cast root canal posts in Vitro. Br Dent J 2003; 195: 155-158.

28. Hoag EP, Dwyer TG. A Comparitive evaluation of three post and core technique. J Prosthet Dent 1982; 47: 177-181.

29. Ingle JI, Bakland LK. Endodontics. 4th ed. Baltimore : Williams and Wilkins; 1994: p. 880 â&#x20AC;&#x201C; 920.

30. Iqbal MK, Johansson AA, Akeel RF, Bergenholtz A, Omar R. A Retrospective Analysis of factors associated with the Periapical Status of Restored, Endodontically Treated Teeth. Int J Prosthodont 2003; 16: 31-38.

31. Jacoby WE Jr. Practical technique for the fabrication of a direct pattern for a post-core restoration.

J Prosthet Dent 1976; 35: 357-360.

32. Karapanou V, Vera J, Cabrera P, White RR and Goldman M. Effect of Immediate and Delayed Post Preparation on Apical Dye Leakage using Two different sealers. J Endod 1996; 22: 583-585.

33. King PA, Setchell DJ, Rees JS. Clinical evaluation of a carbon fibre reinforced carbon endodontic post. J Oral Rehabil 2003; 30: 785-789.

34. Koutayas SO, Kern M. All-ceramic posts and cores : The state of the art. Quintessence Int 1999; 30: 383-392.

35. Krupp JD, Caputo AA, Trabert KC, Standlee JP. Dowel retention with glass-ionomer cement. J Prosthet Dent 1979; 41: 163-166.

36. Kvist T, Rydin E, Reit C. The Relative Frequency of periapical lesions in teeth with Root Canal Retained Posts. J Endod 1989; 15: 578-580.

37. Kwan EH, Harrington GW. The effect of immediate post preparation on apical seal. J Endod 1981; 7: 325-329.

38. Larato DC. Single Unit cast post crown for pulpless anterior tooth roots. J Prosthet Dent 1966; 16: 145-149.

39. Lewis R, Smith BGN. A clinical survey of failed post retained crowns. Br Dent J 1988; 165: 95-97.

56

40. Lloyd PM, Palik JF. The philosophies of dowel diameter Preparation : A Literature review. J Prosthet Dent 1993; 69: 32-36.

41. Machtou P, Sarfati P, Cohen AG. Post Removal prior to Retreatment. J Endod 1989; 15: 552-554.

42. Malferrari S, Monaco C, Scotti R. Clinical Evaluation of Teeth Restored with Quartz FiberReinforced Epoxy Resin Posts. Int J Prosthodont 2003; 16: 39-44.

43. Mekayarajjananonth T, Kiat-amnuay S, Salinas TJ. A combined direct dowel and indirect core technique. Quintessence Int 2000; 31: 19-23.

44. Mezzomo E, Massa F, Libera SD. Fracture resistance of teeth restored with two different postand-core designs cemented with two different cements : An in vitro study. Quintessence Int 2003; 34: 301-306.

45. Milot P, Stein RS. Root fracture in endodontically treated teeth related to post selection and crown design. J Prosthet Dent 1992; 68: 428-435.

46. Monticelli F, Grandini S, Goracci C, Ferrari M. Clinical Behavior of Translucent-Fiber Posts: A 2year prospective study. Int J Prosthodont 2003; 16: 593-596.

47. Oliva RA, Lowe JA. Dimensional stability of composite used as a core material. J Prosthet Dent 1986; 56: 554-561.

48. Perel ML, Muroff FI. Clinical criteria for posts and cores. J Prosthet Dent 1972; 28: 405-411.

49. Pilo R, Tamse A. Residual dentin thickness in mandibular premolar prepared with Gates Glidden and Parapost Drills. J Prosthet Dent 2000; 83: 617-623.

50. Preiskel HW. Overdentures Made Easy â&#x20AC;&#x201C; A guide to Implant and Root supported prostheses.

Quintessence, Chicago 1996. p. 45-66.

51. Purton DG, Chandler NP, Qualtrough AJE. Effect of thermocycling on the retention of glass-fiber root canal posts. Quintessence Int 2003; 34: 366-369.

52. Purton DG, Payne JA. Comparison of Carbon fiber and stainless steel root canal posts.

Quintessence Int 1996; 27: 93-97.

53. Qualtrough AJE, Chandler NP, Purton DG. A comparison of the retention of tooth â&#x20AC;&#x201C; colored posts.

Quintessence Int 2003; 34: 199-201.

54. Rolf KC, Parker MW, Pelleu GB. Stress Analysis of five prefabricated Endodontic Dowel Designs : A Photoelastic study. Oper Dent 1992; 17: 86-92.

55. Rosenstiel SF, Land MF, Fugimoto J. Contemporary Fixed Prosthodontics, 3rd Edition. St Louis : Mosby, 2001. p. 272-312.

56. Saupe WA, Gluskin AH, Radke RA Jr : A comparative study of fracture resistance between morphologic dowel and cores and a resin-reinforced dowel system in the intraradicular restoration of structurally compromised roots. Quintessence Int 1996; 27: 483-491.

57. Sahafi A, Peutz Feldt A, Ravholt G, Asmussen E, Gotfredsen K. Resistance to cyclic loading of teeth restored with posts.

58. Seow LL, Ton CG, Wilson NH. Remaining tooth structure associated with various preparation designs for the endodontically treated maxillary second premolar. Eus J Prosthodont Restor Dent.

2005 Jun; 13(2):57-64.

59. Shillingburg HT, Kessler JC. Restoration of the Endodontically treated tooth. Chicago: Quintessence, 1982.

60. Sidoli GE, King PA, Setchell DJ. An in vitro evaluation of a carbon-fiber-based post and core system. J Prosthet Dent 1997; 78: 5-9.

61. Sirimani S, Riis DN, Morgano SM. An in vitro-study of the fracture resistance and the incidence of vertical root fracture of pulpless teeth restored with six post-and-core systems. J Prosthet Dent 1999; 81: 262-269.

62. Sorensen JA, Engelman MJ. Effect of post adaptation on fracture resistance of endodontically treated teeth. J Prosthet Dent 1990; 64: 419-424.

63. Sorensen JA, Engelman MJ. Ferrule design and fracture resistance of endodontically treated teeth. J Prosthet Dent 1990; 63: 529-536.

64. Sorensen JA, Martinoff JT. Endodontically treated teeth as abutments. J Prosthet Dent 1985; 53: 631-636.

65. Stern N, Hirshfeld Z. Principles of preparing endodontically treated teeth for dowel and core restorations. J Prosthet Dent 1973; 30: 162-165.

66. Strassler HE, Cloutier PC, A New Fiber Post for Esthetic Dentistry. Compend Contin Edu Dent 2003; 24: 742-753.

67. Tait CM, Richetts DN, Higgins AJ. Weakened anterior roots-intra radicular rehabilitation. Br Dent J. 2005 May 28;198(10):609-17.

57

68. Tidmarsh BG. Restoration of endodontically treated posterior teeth. J Endod 1976; 2: 374-375.

69. Toksavul S, Toman M, Uyolgan B, Schmage D, Nergiz I. Effect of luting agents and reconstruction techniques on the fracture resistance of pre-fabricated post systems. J Oral Rehabil. 2005 Jun:32(6):433-40.

70. Vermilyea SG, Gardner FM, Moergeli JR. Composite dowels and cores : Effect of moisture on the fit of cast restoration. J Prosthet Dent 1987; 58: 429-431.

71. Weins FS. Endodontic Therapy. 5th Edn. St Louis. Mo : Mosby Yearbook; 1976 p. 770-771.

72. Willershousen B, Tekyatan H, Krummenauer F, Briseno Marroquin B. Survival rate of endodontically treated teeth in relation to conservative v/s post insertion techniques a retrospective study. Eur J Med Res. 2005 May 20;10(5):204-8.

73. Williams VD, Bjorndal AM. The Masserann technique for the removal of fractured posts in endodontically treated teeth. J Prosthet Dent 1983; 49: 46-48.

74. Yolds O, Akova, Uysal H. An experimental analysis of stress in simulated flared root canals subjected to various post core applications. J Oral Rehabit. 2005 Jun;32(6):427-32.

75. Zmener O. Effect of dowel preparation on the apical seal of endodontically treated teeth. J Endod 1980; 6:687-690.

Products: Pins & Posts

>> Fiber Glass Posts

Sort

GlassixÂŽ

Exatec Pilot Drill

Whaledent Fiber Glass Post System

Cytec Blanco Post System

Morita Glass Fiber Posts

Cytec Blanco Calibration Drill

Luscent Anchors

Cytec Enlarging Drill

Twin Luscent Anchors

FibreKleer Postâ&#x201E;˘

Snow Posts

SybronEndo Fiber Post

Mirafit Black & White

Hahnenkratt Fiber Glass Posts

Core-Post

Ice Post

Fibrekor Post

DMG Dental Fiber Glass Post

58

Achromat™ Esthetic Fiber Post System

Cure-Thru IntegraPost

PD Fiberglass Posts

Parkell Fiber Glass Posts

FRC Postec®

Polydentia Posts

Exatec Blanco Post System

EDS Post System

Exatec Calibration Drill

GC Fiber Post

Glassix

The glass fibre will prevent from breaking and makes it very resilient and will not like a hard and numb metal post transmit stress and shock to the dentine. it will work together with the dentine to absorb any stress or shock as it has about the same elasticity as the dentine itself.

Quality made in Swizerland

Whaledent Fiber Glass Post System

Esthetic Post System The newest addition to the Para-Post family of endodontic posts fills the growing need in esthetic dentistry for a high retentive ,metal-free ,parallel sided ,passive post system

Morita Glass Fiber Posts

Carbon fiber is the latest & most advanced material in dental posts. Glass fiber is the perfect material when you want to obtain the advantages of carbon fiber combined with superior esthetic results.

Luscent Anchors

·Tranmits polymerzing light within the confines of canals ·Provides the one-stop core anchor foundation with all restorative material. ·Reflects natural hues. visible radiolucency.

Snow Posts

The white, radiopaque fiber reinforced post ·A higher percentage of fiber fill allows use of smaller post diameters ·Unidirectional fibers and flexular modulus close to that of dentin assures equal distribution of stress ·White translucent system offers enhanced radiopacit MIRAFIT BLACK & WHITE (Hager) Black for Posteriors & White for Anteriors CORE-POST (Denmat) It is designed to flex with teeth under normal conditions, thus eliminating tooth stress and fractures that can occur with standard metal posts.

FIBREKOR POST (Pentron) FibreKore Post System allows an integrated bond between tooth structure, bonding agent, resin cement and composite core material ACHROMAT™ ESTHETIC FIBER POST SYSTEM (Axis) This radiopaque post is available in two styles, one with an "arrowhead" design for more core retention and an "non-arrowhead" design. Both designs are parallel-sided, serrated and have a machined surface to provide maximum surface atea fro increased bonding strength.

PD FIBERGLASS TAPERED CROWN POSTS (PD) Braided Glass Fiber: in a multi-axial arrangement and in a composite bonding, providing high resistance to bending and torsion forces.

Matrix: Epoxy resin with apx. 65% glass fiber content Features: ·Physico-chemical compatibility and high bonding between post, cement and dentine ·Prevents root fracture, oxidation and corrosion ·Flexibility and high resistance ·Aesthetic thanks its white color Swiss Made FRC POSTEC® (Ivoclar Vivadent) Fiber reinforced, esthetic, endodontic post. ·Reinforced glass fibers in a composite matrix creating excellent light transmittance & translucency. ·Strength properties comparable to dentin allows for the gentle introduction & even distribution of forces on the remaining tooth structure.

59

·Tapered design reduces the amount of tooth structure that needs to be removed when placing the post. ·Two sizes with matching reamers to meet all clinical indications. ·Excellent radiopacity when paired with Variolink II esthetic resin cement. ·Composite base material allows for retrieval with rotary instruments if further endodontic treatment is required.

EXATEC BLANCO POST SYSTEM (Hahnenkratt) High quality carbon fiber and glass fiber posts with rounded retention grooves for better bonding. The Exatec Posts comes with a bigger head for core build-up. Post is tapered from 1.5mm down to .98mm.

Made in Germany.

CYTEC BLANCO POST SYSTEM (Hahnenkratt) High quality carbon fiber and glass fiber posts with rounded retention grooves for better bonding. Made in Germany.

FIBREKLEER POST™ (Pentron) The ideal post for esthetic restorations superior strength. Unbeatable esthetics and effective light transmission.

Parallel body design with retentive head, ideal for core build up, offers increased mechanical core retention.

Tapered design requires less tooth removal, offers option for conservative dentistry.

PEERLESS POST (SybronEndo) A fully customizable fiber posts. Adjustable on both ends, PeerlessPost provides a custom fit that is both esthetic and radiopaque · Has a unique "keystone" links that are proven more retentive than other popular posts · Exhibits a low elastic modulus similar to that of dentin, there by decreasing the risk of root fracture CONTEC BLANCO (Hahnenkratt) Radiopaque Fiber Glass Post (White)

ICE POST The white, radiopaque fiber reinforced post  A higher percentage of fiber fill allows use of smaller post diameters

LUXAPOST Transparent glass-fiber-reinforcement composite post with a flexural modulus that reacts to pressure and stress, much like natural dentin.

The endodontic post combines high quality with ease of use.

Luxaposttappered form corresponds extremely to the tooth root, providing a preperation that is gentle. comfortable, and beautifully conformed to the tooth surface.

CURE-THRU INTEGRA POST (Premier) Light-transmitting Zirconia Glass Fiber Post      

Safe and Simple to Use Esthetic Strong and Flexible Factory Silanated for Secure Adhesion Light Transmitting Tapered Tip Design C-I WHITE™ POSTS (Parkell) Glass Fiber posts for maximum cosmetics. Fiber reinforced epoxyresin post with best combination of cost, radiopacity and strength.

Post is opaque white.

POLYDENTIA GF POSTS (Polydentia) White opaque posts with 80% glass fibers strength, reliability and highest aesthetics. GF Posts provide an excellent al metal posts, and are the ideal solution for aesthetic restorations on both anterior and posterior teeth. The white opaq Polydentia GF Posts ensures excellent aesthetic results without undesirable coloring in the cervical area of the tooth.

FLEXI-FLANGE FIBER Tooth colored for the perfect aesthetic restoration. The patened split tap used prior to post placement provides retentive grooves without stress

60

Item No.

P

GC FIBER POST (GC America) The excellent fatigue resistance is attributable to the unique chemistry and high filler content of GC Fiber Posts, reducing risk of restoration failure. The taper design of GC Fiber Posts maximizes adaptation and minimizes dentin removal, preserving root structure and strength. Its radiopacity enables easy checking of the post length at try-in.