Restoration of endodontically treated teeth / dental implant courses by Indian dental academy

RESTORATION OF ENDODONTICALLY TREATED TEETH CONTENTS:  INTRODUCTION

 ORIGIN AND DEVELOPMENTS

 TREATMENT PLANNING

 BASIC COMPONENTS OF POST AND CORE o POST o CORE

 CLINICAL TECHNIQUES

 FAILURE AND REMOVALOF POSTS

INTRODUCTION: Endodontic therapy has provided dentistry with the ability to retain teeth that just a few decades ago would have been extracted without hesitation. When the endodontic treatment has been completed, however, questions arise as how to restore and protect the tooth structure that remains. Here is where the role of pot endodontic restoration comes into play. The objective of post endodontic restoration is to restore the normal tooth structure, function and esthetics

ORIGIN AND DEVELOPMENTS; The questions that arise during the restoration of a tooth are not new ones. The replacement of missing tooth structure has been practiced by various cultures for thousands of years. There are numerous references to the importance of healthy teeth in the Old Testament, much of which deals with the period antedating 1000 BC. No wonder than that man has made every effort to restore lost tooth structure. Attempts to restore pulpless teeth using posts and crowns have been recorded for more than 200 years.

18th – 19th century: Posts become popular 1747 – Pierre Fauchard gave the first documented procedure. He used posts fabricated of gold or silver those were held in place with the heat-softened adhesive called “mastic Wooden vs. metal posts: There was much controversy over the type of post to be used.

Wooden posts, made of hickory or box tree, were popular as they were self-retentive because they swelled up after water absorption. They also caused less wear to the canal.

On the other hand, metal posts retained with cotton or silk thread or with wedges were detrimental to the root. Their intracanal movements caused abrasion of the canal walls.

Nevertheless, proponents of metal posts preferred fine gold or platinum that corroded less than copper, brass or silver.

Poor endodontic treatment – Poor prognosis: Sadly, endodontic therapy by these dental pioneers embraced only minimal efforts to clean, shape and obturate the canals. Frequent use of wooden posts in empty canals lead to repeated episodes of swelling and pain. A groove in the posts or root canal provided a pathway for continual suppuration from the periradicular tissues.

1839 – Chapin Harris in ‘The Dental Art’ reported ‘pivoting’ or ‘posting’ of artificial crowns to natural roots as the best method that can be employed for inserting artificial teeth and this became common practice1870s – Richmond Crown (integrated dowel crown) given by T.W. Richmond persisted for number of years. This originally consisted of a threaded tube in the canal that held the screw (dowel) placed through the porcelain crown. Later, with the advent of cements, this design was simplified to eliminate the tube and make the dowel, by then unthreaded, and integral part of the final gold-porcelain restoration.

Logan Crown was a variation of the Richmond crown and had an all porcelain crown instead.

Davis Crown (detached dowel crown) designed by W.C. Davis was an all porcelain crown with a post that could be detached (separated) and could be fixed into the prepared root end by cementation of the post to the root and crow

20th Century: The modern face 1910 – Focal Infection Theory given by William Hunter led to the belief that non-vital teeth were etiologic agents of many common diseases. The use of endodontic procedure declined rapidly during this period and it took about 30 years for dentistry to over come this bias.

In the next 50 years the standardization of instrument sizes, the biomechanical preparation of the canal and modern pharmacologic agents led to a high success rate of endodontic treatment in multi rooted, as well as, single rooted teeth. This resulted in its general acceptance by the profession and patients, and its common use in dental practice.

1960s – There was a changeover from the single porcelain crown cemented to the post to the separate, well-retained component, ‘the core’, which replaced the missing coronal tooth structure 1961 – Rosen described the extra coronal brace as “a subgingival collar of gold which extended as far as possible beyond the gingival seat of the core and completely surrounds the perimeter of the tooth, thus preventing tooth fracture”. This later came to be known as the ‘ferrule’. He also described the split casting technique for multi-rooted teeth with divergent canals 1967 – Kurer Post, by Peter Kurer, was a refinement of the previously used threaded posts.

1970 – The Parapost System described by Baraban went on to become the most popular prefabricated post and core system 1980 – Arun Nayyar describe the amalgam coronal – radicular dowel and core system.

Here, amalgam was condensed 2-4mm into canals, pulp chamber and coronal portion of tooth 1990 – Duret, Reynaud and Duret introduced the Composipost. This non-metallic post, based on carbon-fiber reinforcement principles, had high tensile strength and modulus of elasticity similar to dentin 1994 – Sandhaus and Pasche introduced the prefabricated zirconia post.

With advances in materials technology glass fiber and ceramic posts have been introduced. These non-metallic posts are tooth coloured and hence more esthetic than carbon fiber and metal posts. Also, improvements in resin luting cements have resulted in posts being chemically bonded to the dentin.

In summary, over 200 years of research by various clinicians and investigators has increased the longevity and serviceability of endodontically treated teeth. A variety of materials and techniques, based on sound biological principles, allow the contemporary dentist to treat different clinical situations with favourable results.

TREATMENT ASSESMENT: How are endodontically treated teeth different?

Biologic Concerns – Effects of Endodontics on Teeth (Gutmann) Endodontically treated teeth have special needs that exceed the requirements of teeth with viable pulps. The tooth structure that remains after endodontic treatment has been weakened and undermined by caries, fracture, tooth preparation and restoration.

Endodontic procedures further remove important intra-coronal and intra-radicular dentin.

Also, endodontic treatment changes the actual composition of dentin.

The combined result of these changes is increased fracture susceptibility and decreased translucency in non-vital teeth. The major changes in these teeth include: 1. Loss of tooth structure 2. Altered physical characteristics 3. Altered esthetic characteristics Loss of tooth structure Decreased tooth strength in endodontically treated teeth is primarily due to loss of coronal tooth structure. Endodontic procedures have been shown to reduce tooth stiffness by only 5%, whereas a mesio-occluso-distal (MOD) preparation reduces tooth stiffness by 60%, mainly because of loss of marginal ridge (Reeh et al, 1989).

Endodontic access into pulp chamber destroys structural integrity provided by the coronal dentin of the pulpal roof and allows greater flexing of the tooth under function. With reduction of the inner cuspal slopes, that unite and support the cusps during function by preventing excessive deformation, greater chances of fracture exist. In case of significantly reduced remaining tooth structure, normal functional forces may cause the tooth to fracture in the area of the smallest circumference, frequently the CEJ. In addition, excessive removal of radicular dentin during canal cleaning and shaping and post space preparation weakens the root.

Altered physical characteristics The tooth structure remaining after endodontic therapy exhibits irreversibly altered physical properties. Calcified tissues of pulpless teeth have 9% less moisture content than in vital teeth (Helfer et al, 1972). The collagen too has fewer mature and more immature crosslinks (Rivera et al, 1988).

Changes in collagen crosslinking and dehydration of the dentin result in 14% reduction in strength and toughness of endodontically treated molars, with maxillary teeth shown to be stronger than mandibular teeth and mandibular incisors to be the weakest (Carter et al, 1983).

The combined loss of structural integrity, loss of moisture and loss of dentin toughness compromises these teeth and necessitates special care in their restoration.

Altered esthetic characteristics A darkened endodontically treated tooth is a common clinical phenomenon.

Biochemically altered dentin modifies light refraction through the tooth and changes its appearance. Inadequate endodontic cleaning and shaping of the coronal area also contributes to this discoloration by staining the dentin from degradation of pulp tissue left in the pulp horns. Medicaments used in dental treatment and cements of root canal fillings can also affect the appearance of these teeth.

Endodontic treatment and restoration of teeth in the esthetic zone requires careful control of procedures and materials to retain a translucent, natural appearance.

Another major change that may make these teeth ore susceptible to fractures is loss of proprioception.

INDICATIONS: Why do we need posts?

Earlier concept stated the need for post and core restoration is mainly for resistance purpose. But now clinical studies and use have indicated that posts do not add significantly to the resistance of the teeth to fracture. Rather in certain cases they may even weaken the tooth by causing the wedging effect.

According to the new concept the main purpose of using the posts is mainly for retention of the core to the root.

Before initiation of restorative therapy the tooth must undergo thorough endodontic, periodontal, restorative and esthetic evaluations. The prognosis of the tooth, adjacent teeth, opposing teeth and patient desires for treatment should be considered.

1. Endodontic evaluation •

The quality of existing endodontic treatment should be evaluated.

•

New restorations, particularly complex restorations, should not be placed on abutment teeth with questionable prognosis. Endodontic re-treatment may be

indicated for teeth that exhibit radiographic pathology or clinical symptoms of inflammation.

•

Canals filled with silver cones or other inappropriate filling materials should be re-treated with gutta-percha, which is easily removed for canal space preparation and provides an adequate apical seal.

2. Periodontal evaluation Maintenance of periodontal health is critical to the long-term success of teeth that have been endodontically treated and restored. The periodontal condition of the tooth must be determined before initiation of endodontic therapy, and the effect of the planned restoration on the attachment apparatus must be considered.

•

Extensive caries, tooth fracture, previous restorations, perforations and external resorption can destroy tooth structure at the level of the periodontal attachment.

An attempt to place restorative margins on solid tooth structure beyond these defects further invades the biologic attachment zone.

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Violation of the biologic width can cause failure of the clinical results. A mutilated tooth in which restorative treatment would compromise the junctional epithelium or connective tissue attachment levels should be considered for periodontal crown lengthening surgery or orthodontic extrusion.

•

Teeth mutilated from caries or fracture often have excellent bone support, extraction of such teeth and replacement with implants should be considered.

3. Restorative evaluation •

It is essential to determine if the tooth is restorable before endodontic treatment is performed. Successful endodontic treatment is of no value if the tooth is extensively damaged to be reliably restored.

•

The strategic importance of the tooth should be determined, e.g. the distal most tooth in a quadrant can be critical to avoid a distal extension partial denture. Such teeth require predictable endodontic and restorative treatment. Conversely, extensively damaged teeth of no strategic importance, e.g. when adjacent healthy teeth are available or implants can be given, should be extracted.

•

The tooth to be restored should be able to withstand functional forces placed upon it after reconstruction. Risk of root fracture increases with the amount of missing coronal or internal radicular tooth structure. A critical amount of solid coronal dentin is required, which must be encased in the final restoration (the ferrule) for structural integrity of the restored tooth. If sufficient tooth structure is not available, the tooth should be periodontally or orthodontically extruded or extracted.

4. Esthetic evaluation Potential esthetic complications should be evaluated before initiation of endodontic therapy.

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Thin gingiva may transmit a shadow of dark root color through the tissue. Metal or dark, carbon-fiber posts or amalgam placed in the canal can result in unacceptable gingival discoloration from the underlying root.

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The translucency of all ceramic restorations must be considered in the selection of post and core materials. Tooth colored restorative materials should be selected.

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An esthetic tooth that will not need a crown after endodontic therapy requires critical control of endodontic filling materials in the coronal third of the canal and pulp chamber. Opaque substances will adversely affect the color and translucency of these teeth. Therefore, gutta-percha must be limited to a more apical level and pulp chamber should be thoroughly cleaned of remove gutta-percha and sealer.

Esthetic materials should be used to restore the access cavity.

Cases in which endodontic treatment may succeed but restorative or periodontal failure would occur should be identified and their replacement should be included in the overall treatment plan.

The main indications for this restoration can be grouped under the following headings:  Significant tooth structure loss o Anterior: full coverage o Posterior: cuspal coverage  High functional demands  Esthetic demands (anteriors)  Favorable anatomy of tooth Evaluation of the tooth is done on the following basis:  Amount of remaining tooth structure  Anatomical position of the tooth  Functional load on tooth

ďƒ˜ Esthetic requirements of tooth Considerations for restoring anterior teeth: a.

Anterior teeth do not always need complete coverage as studies have shown that intact root treated anterior teeth are stronger than those restored with post and core.

b.

Post and core is not required when there is minimal coronal damage, intact marginal ridges, intact cingulum, intact incisal edge and one or two small proximal lesions. Here, the treatment should be restoration of access opening with composite resin or GIC. If the tooth is discolored a non-vital bleaching technique is advised over complete crown. However all cases may not be successfully treated with bleaching, such teeth need full coverage.

c.

When a full coverage restoration is to be given in intact endodontically treated anteriors a post and core is recommended because after crown preparation for a metal ceramic or all ceramic crown, the amount of remaining tooth structure is decreased and the tooth would be susceptible to fracture as anterior teeth are subjected to shear (lateral) forces.

d.

A post and core followed by full crown is indicated when there is significant coronal damage and undermined marginal ridges, or coronal fractures involving all of incisal edge and major part of crown. It is important that atleast 2mm of tooth structure should be present apical to the resin core to provide resistance form.

e.

For small circular canals a prefabricated post and resin core is preferred. But when canal is elliptical or flared a custom cast post and core is indicated. In such cases intra-radicular rehabilitation i.e. buildup of the canal walls with composite and use of fiber-reinforced posts can also be done as an alternative to cast post and core.

Considerations for posterior teeth: a.

All endodontically treated posterior teeth require a full occlusal coverage restoration. This is because due to loss of the roof of the pulp chamber (which provides structural integrity) the occlusal forces tend to wedge the cusps apart, which may lead to tooth fracture.

b.

A gold or ceramic onlay is sufficient when there is minimal coronal damage, low risk of fracture (i.e. occlusion protects tooth from heavy lateral occlusal functioning contacts) or minimal occlusal forces (as when opposing teeth are artificial) and facial and lingual cusps are intact.

c.

A foundation (core) restoration with complete occlusal coverage is indicated when there is moderate coronal damage or extreme curvature of root.

Here one of the following foundations may be used:

1. Amalgam coronal-radicular core.

2. Pin-retained amalgam or resin composite. d.

In posterior teeth the pulp chamber and canals provide adequate retention for foundation buildup and hence generally do not require a post, unless coronal damage is extensive.

e.

Molars resist primarily vertical forces, whereas premolars are more likely to be subjected to lateral forces during mastication. Their cross sectional areas at the CEJ is smaller than that of molars and so are more prone to fracture. Though they are bulkier than anteriors, they are often single rooted with small pulp chambers that may not provide adequate retention and resistance. For these reasons, they require posts more often than molars. The remaining tooth structure and functional demands are the determining factors.

f.

The canal anatomy again dictates the choice of post. For circular canals a prefabricated post with composite or amalgam core is acceptable.

Extremely tapered or oval canals require custom cast post and core.

Anatomic Concerns (Gutmann) For restoring endodontically treated teeth with post and core restorations careful attention to root anatomy should be paid in order to select the appropriate post design in terms of length and shape and its method of placement. To achieve this end a thorough knowledge of root anatomy is important along with periapical radiographs at different angulations to determine the number of roots, their structure and curvatures. However, different teeth pose certain problems unique to their anatomy: Maxillary Teeth Central and lateral incisors – Normally, their bulky roots easily accommodate a post.

But excessive post lengths are to be avoided in roots that taper rapidly to the apex because the thinned out root walls at the apical extent of the post increase chances of root fracture.

Canines – Being wide faciolingually custom cast posts may be desired for better adaptation. Proximal invaginations may be present; hence thicker posts should not be used in order to avoid root perforation.

Premolars – The first premolar presents many challenging problems. It has thin root walls that are further weakened after removal of dentin. Roots taper rapidly to the apex, especially when two roots are present. Proximal invaginations and canal splitting are common. Facial curvature of palatal root and distal curvature of the roots may result in perforation during preparation or cementation.

The second premolar poses similar problems but due to greater bulk of the root shows fewer complications.

Molars – Only palatal root is suitable for post placement as it has the largest canal. In 85% of cases this root is facially curved. Invaginations may be present on palatal and

facial surfaces of this root, as a result of which, weakening or perforation of the root may occur during placement of long thick posts that, may not be disclosed on the radiograph.

First molars have deep concavities on the furcal surface of 94% of the mesiobuccal roots, 31% of distobuccal roots and 17% of palatal roots. Placement of post in the narrow mesiobuccal or distobuccal canal is generally contraindicated.

Mandibular Teeth Incisors and canines – These teeth are difficult to treat. In fact, success rate has been shown to be higher without a post. They have thin root walls, proximal invaginations and often multiple canals, which complicate post placement. Additionally, significant bone loss may be present which contraindicates post and core restoration.

Premolars – These teeth have sufficient root bulk for post placement, though occasionally multiple canals may be present. In the first premolar the angle of the crown to the root is an important consideration. Perforation may occur on the facial surface of the lingually inclined root if preparation is made perpendicular to the occlusal surface.

Molars – Proximal invaginations are common. First molars have root concavities on the furcal surface of 100% of mesial roots and 99% of distal roots. Perforations may not be seen on radiographs. Their canals are narrow mesiodistally and wide faciolingually and may become considerably weakened if prepared for large, circular prefabricated posts.

Distal canal is preferred for post placement as it is the largest.

Fractures may occur during cementation or patient function. These fractures are termed ‘odontiatrogenic’ in origin and may appear radiographically as furcal bone loss or proximal angular defects.

CLASSIFICATION: Ingle and Bakland I. Custom-cast Posts II. Prefabricated Posts 1. Tapered, smooth-sided 2. Parallel-sided 3. Tapered, self-threading screws 4. Parallel-sided, threaded 5. Parallel-sided, tapered apical end Weine I. Custom-cast Posts II. Prefabricated Posts 1. Tapered, smooth sided post systems 2. Parallel-sided, serrated and vented posts 3. Tapered, self-threading post systems

4. Parallel- sided, threaded post systems a. Self-threading b. Threaded with use of matched taps Parallel-sided, threaded, split-shank post systems

Cohen and Burns Classification according to desired physical properties: I. Retentive Qualities of Dowels- to anchor the dowel to the root and the core A. Dowel Design a. Dowel to root retention 1. Parallel 2. Tapered 3. Threaded 4. Chemically bonded b. Dowel to core retention 1. One-piece (integrated) dowel and core 2. Large dowel head with mechanical interlocking features 3. Small dowel head B. Dowel Composition a. Dowel to root retention 1. Metal dowels 2. Carbon fiber dowels 3. Fiber reinforced composite dowels 4. Ceramic and zirconia dowels b. Dowel to core retention 1. One-piece dowel and core i.

Custom-cast metal ii.

Zirconia iii.

Ceramic iv.

Fiber reinforced composite 2. Dissimilar dowel and core 3. Monobloc or Monocore (bonded, direct composite dowel and core combinations) C. Dowel Cementation 1. Mechanical retention (e.g. Zinc phosphate cement) 2. Cement bonding to tooth but not dowel (e.g. GIC) 3. Cement bonding to tooth and dowel (e.g. chemically adhesive cements)

II.

Protective Qualities of Dowels- against root fracture and microleakage A. Dowel Design a. Shape 1. Parallel 2. Tapered 3. Parallel with tapered apical end 4. Parallel, which increases in coronal diameter with series of parallel-sided steps b. Diameter 1. Metal dowels available in small diameters 2. Non-metallic dowels not available in small diameters.

Therefore, available as: i.

Tapered ii.

With two parallel steps containing a narrower, parallel apical portion c. Length- longer dowels give better retention B. Composition a. Stiffer than dentin i.

Metal- Stainless steel > Titanium alloy > Pure titanium ii.

Zirconia iii.

Ceramic b. Modulus of elasticity similar to dentin i.

Carbon fiber ii.

Carbon core iii.

Fiber reinforced composite iv.

Woven fiber, ribbon reinforced composite C. Dowel Design for Damaged Roots a. Light Transmitting dowel- to allow buildup of canal with composite and subsequent restoration with prefabricated dowel. b. Custom dowel and integrated core made of composite resin reinforced with a woven polyethylene fiber system.

III. Esthetic Qualities of Dowels1. Ceramic dowels 2. Zirconia dowels 3. Fiberglass reinforced composite dowels 4. Carbon core dowels Walton and Torabinejad I. According to shape

II.

III.

IV.

1. Parallel 2. Tapered According to construction 1. Custom made 2. Preformed According to nature of fit 1. Passive 2. Active According to surface configuration 1. Smooth 2. Serrated 3. Threaded

According to materials used Metals  Custom-cast posts o Gold alloys o Chrome-cobalt alloys o Nickel-chromium alloys  Prefabricated posts o Stainless Steel o Titanium o Brass

Non-metals  Carbon-fiber  Fiber-reinforced  Glass fiber  Quartz fiber

 Woven Polyethylene fiber  Ceramic and zirconia

BASIC COMPONENTS OF A POST AND CORE SYSTEM :

A: 4-5 mm apical seal B: Post C: Residual root attachment apparatus D: Core E: Final restoration Antirotational features : Pin Keyway

THE POST (it is the segment of the restoration inserted in the root canal of the endodontically treated tooth to aid in the retention of the core and the subsequent coronal restoration) The post is defined as the segment of the restoration inserted into the root canal to aid in retention of a core component. It is a rigid material placed in the root of a tooth. It can be fabricated from metal or from other non-metallic substances. The post is important in the restoration of non-vital teeth that have significant coronal damage and have insufficient sound tooth structure remaining above the periodontal attachment to secure a coronal restoration.

Functions: 1. Retention of restoration 2. Protection of remaining tooth structure The foremost purpose of the post is to provide retention for the core and coronal restoration. It also serves a protective function by dissipating the masticatory forces along the length of the root, thereby equally distributing the stresses and providing some relief at the margins. The post itself does not strengthen the root. On the contrary, the tooth is weakened if dentin is sacrificed to place a large diameter post.

Ideal properties of the post: • Maximum protection (or # resistance- Cohen-805 ) of the root.

• Adequate retention within the root.

• Maximum retention of the core and crown.

• Maximum protection of the crown marginal cement seal.

• Pleasing esthetics, when indicated.

• High radiographic visibility.

• Retrievability.

• Biocompatibility.

Materials Requirements: Selection of materials for posts is very important for clinical success. Functions of endodontic posts can be realized only when the following features are adequately incorporated into their design: • Stiffness • Strength • Fatigue characteristics and • Corrosion resistance Stiffness of the posts is an extremely important characteristic. Insufficient post stiffness permits excessive distortion of the restoration margins during function and, in the case of castings, leads to cement breakdown and recurrent decay. In addition to the modulus of elasticity, the dimension of the post also contributes to overall post stiffness. The smaller the diameter, the lower the stiffness. Consequently, a higher modulus of elasticity allows the use of smaller diameter posts. Therefore, a material with higher modulus is preferred for an endodontic post.

Yield strength indicates the onset of permanent deformation. A material with high yield strength will withstand a higher force before a permanent change in shape, and hence, the potential for permanent change of shape of the post and margins will be minimized during function.

Fatigue characteristics of the material used for post fabrication should be good because a post supporting a crown will be subjected to repeated cycles of loading and unloading during mastication. Stress concentrations, inclusions and corrosion pits will affect the fatigue behavior of posts.

The importance of corrosion resistance in metallic posts is not readily realized, as the post does not come into direct contact with oral fluids. The interaction between the posts and dentinal fluid produces corrosion products between the post and canal walls. This results in the application of lateral forces to the canal walls, which subsequently may fracture. Corrosion of posts has been implicated and amply documented in longitudinal and oblique fractures of the teeth. Corrosion, however, is not a concern with non-metallic and titanium posts.

Types of Posts I)

Metallic posts 1. Custom cast posts 2. Prefabricated posts. a. Passive. i) Tapered. ii) Parallel. b. Active.

II)

Non-metallic posts 1. Carbon fiber posts 2. Tooth colored posts • Fiber reinforced post • Ceramic and Zirconia posts.

Metal posts Custom-cast metal posts The custom cast post and core has a long history of success in restorative dentistry.

However, laboratory studies have consistently shown that the fracture resistance of teeth restored with custom cast posts is lower than that of teeth restored with many different prefabricated posts. In addition, retrospective clinical studies have shown prefabricated parallel posts to have greater clinical success than custom cast posts. Their tapered design exerts wedging forces on the root. This, coupled with the added expense, extra appointment and need for temporization, have made them fall out of favour.

Nonetheless, there are studies that report a high rate of success with cast post and cores and they offer advantage in certain clinical situations.

Indications: 1. When multiple posts and cores are being placed in the same arch. It is more time and cost effective to prepare multiple post spaces, make an impression and fabricate the posts in the laboratory.

2. When posts and cores are being placed in small teeth, such as mandibular incisors. In these instances, it is difficult to retain the core material on the head of a prefabricated post, as minimal space is available around 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 cast post best fulfills this requirement.

4. When an all-ceramic restoration is placed, it is necessary to have a core that approximates the color of natural tooth structure. If a large core is being placed on 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 fired to the core to simulate the colour of natural tooth structure. The core porcelain can then be etched with hydrofluoric acid, and the all-ceramic crown can be bonded to the core.

5. In excessively flared and elliptical canals where prefabricated posts may be difficult to use.

6. Cast post and cores are generally easy to retrieve when endodontic re-treatment is necessary.

Perhaps the biggest disadvantage for cast post and cores is in areas that require an esthetic temporary restoration. Temporary post/crowns are not effective in preventing contamination of the root canal system.

Materials used: The commonly used materials are Type III or IV gold alloys. The main constituents of these alloys are gold, copper and silver, with small amounts of palladium, platinum and

zinc. These alloys display excellent corrosion resistance, high modulus of elasticity and tensile strength. Strength of these alloys may be increased by appropriate heat treatment.

Non-precious nickel-chromium and cobalt-chromium alloys are also used. They are commonly used for endodontic post designs available in the form of plastic burnout patterns, which are invested and cast. These alloys are much stiffer than cast gold and exhibit higher yield and tensile strength.

Prefabricated Metal Posts Prefabricated posts are typically made of stainless steel, nickel-chromium alloy or titanium alloy. They are very rigid and with the exception of titanium alloys, are very strong. Because they are round, they offer little resistance to rotational forces. This is not a problem if adequate tooth structure remains, but if minimum tooth structure remains, anti-rotation features must be incorporated into the post preparation such as slots or pins.

A bonded material should be used for core.

Many of the prefabricated posts are made of titanium alloys and some are made of brass.

Titanium posts were introduced because of concerns about corrosion. Most of the titanium posts have a radiodensity similar to gutta-percha and sealer and are sometimes hard to detect on radiographs. Titanium posts have low fracture strength, which implies that they are not strong enough to be used in thin post channels. Removal of titanium posts can be a problem because they sometimes break when force is applied with a post removal instrument. Extended use of ultrasonic energy may be necessary to remove titanium posts which can be damaging to the tooth or surrounding tissues. For these reasons, titanium and brass posts should be avoided because they offer no real advantages over the stronger metal posts.

Posts or dowels can be generally classified as passive retention or active retention.

Passive retention posts depend upon their close proximity to the dentin walls, but by adherence of the cementing medium. Good examples are cast posts, smooth tapered posts, serrated parallel posts, and variations of these. E.g. Para-Post is a serrated, vented, prefabricated parallel post.

I) Passive Retention Posts As stated above, passive retention posts fit the canal or the channel in the canal specially prepared for them a) Tapered, Smooth-Sided Posts The oldest and most widely used design is the tapered, smooth-sided, cemented post.

Systems employing this configuration are the Kerr Endopost, and the Mooser post and all custom-cast posts. There is also a tapered - knurled post, the Ellman Nu-Bond. The wide usage of tapered posts may-be attributed to their ease of utilization since the tapered form is the natural shape of an endodontic canal Post Retention. The tapered, smooth-sided, cemented post is the least retentive of all post designs.

Stress from Installation. Because of their taper, these posts are self-venting and easily cemented. Hydrostatic pressures do not develop during cementation because a taper does not act as a piston

Stress from Mastication. Tapered-smooth posts are wedges and, as such, exert a wedging pressure upon roots during function. With other factors being equal, the propensity for root fracture from tapered posts is cause for concern b) Parallel-sided Posts Posts with parallel sides, when cemented into prepared parallel channels, provide much greater retention with less stress than tapered posts Examples are Whaledent-Posts, the Boston Post and the Parkell Parallel Post. The parallel and serrated Para-Post is the most widely used. (i) The Para-Post System Whaledent has introduced three post designs: the original Para-Post, Para-Post Plus, and the Unity System. All are passive, parallel, vented posts made of either stainless steel or titanium. Cement retention is gained by horizontal serrations on the Para-Post, spiral flutes and grooves on Para- Post Plus, and a raised diamond pattern on the Unity Post.

Any cementing medium is acceptable.

A. ParaPost, B. ParaPost Plus, C. Unity Post.

Post Retention. The parallel-sided, serrated, vented post provides substantially greater retention than the smooth tapered design. Consequently, these posts can be effectively employed in situations where higher applied forces are expected.

Stress from Installation. The Para-Post has a vertical groove cut the length of its serrations, allowing axial venting. This design allows cement to escape and thus avoids the stresses that may be induced in the dentin by other cemented parallel posts.

Stress from-Mastication. Overall, the parallel-sided, serrated Para-Post has been shown to provide the most equitable distribution of masticatory forces of all available post designs. Above all, it avoids the wedging effect of tapered posts.

All in all, though the Para-Post is not as retentive as active posts but is a good deal as less stressful in placement. It also withstands compressive and fatigue forces as well as the dentin-engaging (ii) The Boston Post System: In physical design, the Boston Post very much resembles a Para-Post without the vertical venting channel. It is a passive dowel, 99.6% titanium, with horizontal non-engaging serrations. It is almost wholly dependent on its special “cementing� medium for retention. In 1993, the Boston post configuration was redesigned with deeper grooves and an etched and roughened surface to allow greater retention.

Post Retention. Goldman and Nathanson developed the Boston Post at Tufts following their search for better dowel retention without the stress induced by dentin-engaging posts. They decided the best retention would be the dentin itself. Freed of the smear layer, the open dentinal tubules offered a labyrinth of interlocking space into which a cementing medium might flow. They finally settled on a dentinal wall bath of EDTA and NaOCl2.5ml of each irrigated into the canal. The first wash is with 17% EDTA (7.0 pH) to chelate away the inorganic dentin, followed by 5.25% NaOCl to remove the organic dentin. This totally removes the smear layer but leaves the peritubular dentin in place.

Nathanson one of the developers of the Boston Post system, found the tensile strength required removing a Boston Post was somewhat greater than a Flexi-Post cemented with EDSď›› composite resin, and twice as retentive as Para-Posts cemented with zinc phosphate cement. Removing the smear layer greatly enhances retention. Standlee and Caputo showed greater retention of passive posts, no matter the cementing medium, when the smear layer was removed.

Stress from Installation. As with the Para-Post, there is virtually no installation stress imposed by the Boston Post.

Stress from Mastication. No information is available about compressive or torsional forces applied to crowns restored with the Boston Post system. One questions the advisability or necessity, however, of producing the post from titanium, which has only half the stiffness of stainless steel. (iii) Parkell Parallel Post system: This is stainless steel passive, vented, serrated post with an anti-rotational lock that fits into a “seat� prepared in the root surface. There are no reports on the safety and efficacy of this system. Its popularity might be related to plastic core formers that come with the posts. These allow the dentist to build up an immediate composite resin crown core.

Cementing the post and core with 4-META adhesive, bonding both to the tooth surface, might allow for the lack of a ferrule. The Parkell Post also comes in a plastic burn-out pattern for a cast version. This model would encourage root preparation to receive a ferrule in the core casting. c)) 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 2mm. The BCH post also has a larger coronal portion to provide retention for core build-up materials.

Post Retention. Parallel posts with tapered ends have a lower retention potential than regular parallel posts of comparable length and diameter.

Stress from Installation. Parallel-sided posts with tapered ends, when cemented in place produce little or no installation stress.

Stress from Mastication. All the cemented, parallel-sided posts with tapered ends produce a definite wedging effect in the area of the apical taper. These posts will, therefore, be more apt to cause root fracture than parallel-sided posts of comparable length and diameter.

II) Active Retention Posts: As previously defined, active retention posts depend primarily on external threads that engage the dentin for retention. Cementation is necessary but secondary.

There are two types of these posts: (a)Those with self-threading screws that engage the dentin walls of a prepared post channel, cutting their own counter-threads, are best

epitomized by the Dentatus post, the Radix Anchor Post, and (b) the Flexi-Post. The type that “bolts” into counterthreads, pretapped in the dentin, is the Kurer Anchor post. a) Posts with Self-Threading Screws Tapered Dentatus: One of the earliest of the self-threading posts is the Dentatus. Although it is more retentive than passive/cemented posts, it is also more dangerous.

Post Retention. While it is true that the tapered Dentatus screw post is more retentive, it is also true that it gains its retention by spreading the dentin as it self-threads. Loss of the crown is often the first indication the root has split.

Stress from Installation. The self-threading tapered screw produces the greatest stress by far when installed in the root. Not only is it a wedge, but it sets up fracture lines as it “cuts” and spreads its way into the dentin. Stress is highest and most concentrated at lengths under 5mm when the Dentatus acts as a tapered wedge. Even when it is “backed off” one half turn, little reduction in stress concentration is seen.

Stress from Mastication. The wedge configuration of the screw design is accentuated under load when occlusal forces are added to the installation forces described above.

Self-threading tapered screws possess the worst installation and occlusal stress-producing characteristics of all existing designs.

Tapered Flexi-Post: A variation of the self-threading screw is the Flexi-Post, which has become one of the most popular post systems. Flexi-Post is a prefabricated, split-shank, parallel-sided, threaded post that reportedly absorbs the stresses of insertion (by gradually closing during placement) while providing maximum retention. As the apical half “collapses”, it becomes a tapered post.

Post Retention. As a self-threading screw, the Flexi-Post gains its significant retention by its threads cutting into the dentin 0.1mm 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 Stress from Installation. 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 counterclockwise, to be reinserted with cement into the same dentin threaded grooves.

Stress from Mastication. Using a fatigue-testing apparatus that simulates the forces of mastication and swallowing, the Flexi-Post developers compared the cyclic-fatigue results from 6 endodontic post systems b) Self-Threading Parallel-Threaded Posts: Two principal self-threading parallel posts are currently popular, the V-Lock and the Radix Anchor System. Both have low frequency sharp threads, and both are vented to reduce hydraulic cementation stress. They differ in the length of the threads down the shaft.

Parallel V-Lock Drill and Post System: The widely separated “micro-threads” of the V-Lock post extend 0.5mm 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.

Post retention. An Oregon study found that V-Lock posts were less than half as retentive (112lbs) as Flexi-Posts (270lbs) and quite comparable to passive Para-Posts (106lbs) Stress from Installation. At Creighton, workers evaluated the possibility of cracks or fractures arising from the insertion of V-Lock posts and found none Stress from Mastication. At Texas, San Antonio, Burgess reported that V-Lock posts were the most resistant to compressive loading, somewhat more than Flexi-Post or ParaPost.

Parallel Radix Anchor System: Like the other active-retentive posts, Radix Anchor posts gain their primary retention by self-cutting counter threads in the dentin. As a parallel post, the Radix differs from the VLock 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 composite resin, also used to buildup the core, seems preferred.

Post Retention. 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.

Stress from Installation. If the post is fully seated (fully engages the bevel produced by the twist drill at the channel apex), severe stress levels will ensure. To obviate apical stress with Radix posts, they can be counter-rotated one half-turn after resistance is detected Perhaps the most critical aspect of parallel-sided threaded design is 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 for final cementation. In the initial threading operation, Ross, Nicholls, and Harrington noted that the Radix Anchor generated more apical root strains than any other post: 3428 micro-inches/inch of strain vs. 782 for the V-Lock, and 344 for the Flexi-Post. Apical strains during cementation were nearly as bad: 1743 for the Radix, 473 for the V-Lock, and 316 for the Flexi-Post. The authors felt that the sharpness of the threads and the difficulty of perfectly aligning the unthreaded apical end of the post with the prepared channel both played a significant role in strain production.

Stress from Mastication. The Radix Anchor post generates greater stress under oblique compressive forces than the Kurer post, for example. c) Parallel Threaded Posts with Pre-Tapped Channels: see BDJ 2005 also The Kurer Anchor posts are the only posts on the market that fit into pre-tapped counterthreads in the dentin. As such, they are the most retentive posts available, no matter what the cementing medium. Kurer anchor posts are parallel in design with no vertical vent. They have rounded high-frequency threads that fit into counterthreads “tapped� into the dentin with a manual thread cutter. They come in a number of configurations.

Another unique feature of the Kurer Anchor is the Kurer Root Facer that prepares a flat seat in the root face into which the coronal portion is to fit perfectly. This obviates the problem of Radix Anchor (fitting against an uneven root surface).

Kurer Root-Facer used to “mill” a flat foundation in root preparation for crown post head.

Post Retention. Parallel-sided, threaded posts, cemented into tapped channels, are superior in retention to all other post designs.

Stress from Installation. 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.

Stress from Mastication. When Kurer posts are cemented into their tapped channels, their buffering effect is less pronounced than it is for other designs. The main load transfer takes place between the threads and the dentin Non-metallic posts Fiber reinforced posts Carbon-fiber posts (Qualtrough and Mannocci) In 1990, Duret, Reynaud and Duret introduced a non-metallic material based on the carbon-fiber reinforced principle posts made of this material consisted of fibers of carbon surrounded by a matrix of polymer resin, usually an epoxy resin. A wide variety is available and includes parallel-sided, tapered, smooth and serrated forms.

Their main proposed advantage was that they were 1) more flexible than metal posts and 2) had approximately the same modulus of elasticity as dentin. This property allowed the post to stress under load, resulting in the better distribution of stresses between the post and the dentin, and minimizing risk of fracture.

The main disadvantages of the carbon fiber post are its dark colour and radiolucent appearance in a radiograph. More recent variations are zirconium coated (Aestheti Plus, Bisco) and hence, white in color. They are relatively easy to remove by boring through the middle of the post with an ultrasonic or rotary instrument. The orientation of the fibers help keep the instrument properly aligned.

Adhesive systems form weaker bonds to carbon-fiber posts than to stainless steel and titanium but stronger than to zirconium dioxide. The water sorption and solubility also vary with brand and homogeneity of polymer matrix and may affect the hydrolytic stability of the composite structure. In one study, water immersion was found to reduce the strength and stiffness to about 70-60% of the dry values. These posts also exhibited a significant decrease in strength after thermocycling. This has been attributed to degradation of the fibers or the matrix and to difference in thermal expansion coefficients between the two.

CONTENTS AND MECHANICAL PROPERTIES OF SOME FIBER-REINFORCED ROOT CANAL POSTS POST CONTENTS FLEXURAL FLEXURAL

Composipost (RTD) Light-Post (RTD) Luscent (Dentatus) ParaPostFiberWhite (Coltene/Whaledent) Postec (IvoclarVivadent)

Carbon fiber 64%,epoxy Quartz fiber 60%,epoxy Quartz fiber 70%.Polyester Glass fiber 42%,filler 29% methacrylate resin 29%

MODULUS (GPa) 145 46 40 29

STRENGTH (Mpa) 1,500 1,400 890 990

Glass fiber 61.6%,urethane 45 dimethacryalate 18.3% triethylene glycoldimethacrylate 7.6%

1,390

Other fiber-reinforced posts Carbon-fiber posts are black in color and do not lend themselves to esthetic restorations with all-ceramic units. This led to the introduction of silica-fiber posts (glass fiber and quartz fiber- both type of silica) that are translucent and tooth colored. These posts are glass-fiber (S glass) and quartz-fiber posts. Another type of fiber used in posts is bondable ribbon woven polyethylene (Ribbond), which can also be used with composite to create an entirely custom cast dowel and integrated core. This bondable ribbon post and core was shown to have significantly lower fracture resistance than CFPs, metal posts and custom cast posts.

Advantages: •

Greater flexure and fatigue strength than metal or zirconium posts.

•

Modulus of elasticity close to dentin.

•

Ability to form a single bonded complex within the root canal for a unified rootpost complex (monobloc).

•

Improved esthetics.

•

Their properties have the potential to reinforce a compromised root and to distribute stress more uniformly on loading to prevent root fracture.

•

Easy to remove by cutting through the post. The fibers keep the bur centered.

•

These posts will yield to stress, before root fracture occurs, better than cast or prefabricated metal posts.

Recent studies have shown that sandblasting these posts prior to cementation increases retention.

COMMON PASSIVE POST SYSTEMS BRAND NAME TYPE OF POST MANUFACTURER

C-Post Aestheti-Plus D.T.Light-Post Fiberkor Cosmopost Snow Post Lucent Anchor Parapost White

Carbon fiber Quartz fiber Quartz fiber Glass fiber Zirconium Zirconium Glass fiber Glass fiber

RTD/Bisco RTD/Bisco RTD/Bisco Jeneric/pentron Vivadent Danville Dentatus Coltene/Whaledent

Ceramic and Zirconium posts (Schwartz and Robbins) adv- esthetic & biocompatibility Another esthetic alternative to metal and carbon fiber posts are the ceramic posts. In 1994, Sandhaus and Pasche introduced the prefabricated zirconia endodontic post. These posts work clinically, but have several disadvantages: •

As a group, they tend to be weaker than metal posts, so a thicker post is necessary, which requires removal of additional radicular tooth structure.

•

Though the all-zirconium post is reported to have a modulus of elasticity higher than that of stainless steel, its fracture resistance is low.

•

Zirconium posts cannot be etched with hydrofluoric acid; therefore, it is not possible to bond a composite core material to the post, making core retention a problem. To overcome this, a technique has been described whereby a leucite-reinforced ceramic core material (Empress) is pressed onto the zirconium post.

•

Retrieval of zirconium and other ceramic posts is very difficult if endodontic retreatment is necessary or if the post fractures. Some ceramic materials can be removed by grinding away the remaining post material with a bur, but this is a tedious and dangerous procedure. It is impossible to grind away a zirconium post from a canal placement. For these reasons, ceramic and zirconium posts should be avoided.

All-Ceramic Post and Core (Koutayas and Kern) Almost simultaneously with the introduction of the current all-ceramic systems, the use of all-ceramic posts and cores was suggested as an alternative to solve the esthetic problems that metal posts and cores exhibit. In 1989, Kwiatowski and Geller described the clinical application of glass-ceramic posts and cores and in 1991, Kern and Knode introduced posts and cores made of glass infiltrated aluminium oxide ceramic. In 1995, Pissis proposed a technique for the fabrication of a post and core and a crown as a single component made out of glass-ceramic material. In 1994 and 1995, Sandhaus and Pasche and others introduced prefabricated zirconia ceramic endodontic posts to restorative dentistry. They also suggested use of zirconia ceramic for the fabrication of core buildup and post in one piece.

The major advantage of an all-ceramic post and core is its dentin like shade. The positive contribution of the dentin shade ceramic core is related to the deeper diffusion

and absorption of the transmitted light in the ceramic core mass. An all-ceramic restoration transmits a certain percentage of the incident light to the ceramic core and post on which it had been placed. Thus, with all ceramic posts and cores, the color of the final restoration will be derived from an internal shade similar to the optical behaviour of natural teeth. In addition, a ceramic post does not reflect intensively through thin gingival tissues, and it provides an essential depth of translucency in the cervical root areas.

They are also biocompatible and do not exhibit galvanic corrosion.

Relatively low fracture strength and toughness are the main obstacles for an extended use of conventional dental ceramics as post and core materials. High toughness ceramics, such as the glass-infiltrated alumina (In-ceram) and the dense-sintered alumina ceramic (Procera), show a 3-6 times higher flexural strength and fracture toughness than do conventional feldspathic and glass ceramics. Contemporary zirconia powder technology contributes to the fabrications of new biocompatible ceramic materials with improved mechanical properties, i.e. further increased flexural strength and fracture toughness.

Therefore, zirconium oxide ceramic seems to be a very promising material for the fabrication of all ceramic posts and cores.

Others – root reinforcing post - coronal radicular post THE CORE The core is defined as a restorative material placed in the coronal area of a tooth to replace the missing coronal structure. The core is anchored to the tooth by extending into the coronal aspect of the canal, or through the endodontic post. This attachment between the core, tooth and post can be mechanical, chemical or both.

Although, the remaining tooth structure can be altered by placement of pins, grooves or channels in dentin, to retain a core and provide resistance to rotation, these modifications weaken the remaining 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 the need for removal of valuable dentin.

Ideal properties of the core material: • High compressive and tensile strength.

• High modulus of elasticity (rigidity).

• High fracture toughness.

• Dimensional stability.

• Ease of manipulation.

• Short setting time.

• The ability to bond to both tooth and post.

• Biocompatibility.

• Inert (no corrosion).

• Natural tooth color, when indicated.

• Low plastic deformation.

•

Low cost.

Core materials: 1. Cast core 2. Amalgam 3. Composite 4. Glass ionomer cement 5. Resin modified glass ionomer cement Cast Core A cast post and core is the traditional way to restore endodontically treated teeth. The core is an integral extension of the dowel and so does not depend on mechanical means for retention to the post. This construction avoids dislodgement of the core from the post and root when minimal tooth structure remains. Noble metals are non-corrosive. Ceramic cores can also be integrated with zirconia dowels in similar laboratory procedures.

Disadvantages: • Cast post and core are shown to have a higher rate of root fracture than prefabricated post and core.

• Expensive.

• Laboratory phase is technique sensitive. Casting a pattern with a large core and a small diameter post can result in porosity in the gold at the core-post interface.

Fracture may occur at this interface during function.

• Casting a core to a prefabricated stainless steel post degrades the physical properties of the post, resulting in a post and core not sufficiently strong or inert to withstand clinical forces.

Amalgam Core Amalgam is a traditional core buildup material with a long history of clinical success.

Advantages: • High compressive strength.

• High modulus of elasticity.

• Stable under thermal and functional stresses and therefore, transmits minimal stress to the tooth and cement and crown margins.

• Bonded amalgam improves the seal at the tooth and alloy junction.

• Amalgam is easily manipulated and has a rapid setting time.

Placement of a fast-setting high-copper alloy permits final crown preparation at the initial operative appointment, although early strength is low. Amalgam cores are highly retentive when used as coronal-radicular restorations or with prefabricated stainless steel dowels; they require more force to dislodge than cast post cores.

Disadvantages: • Potential for corrosion and subsequent discoloration of the gingiva or remaining dentin.

• Dark coloured, so cannot be used in anteriors.

• Its use is declining worldwide because of legislative, safety and environmental issues.

•

Low early strength – tooth preparation cannot be done on same apt.

•

Not bondable to tooth structure- exception being bonded amalgam

Composite Resin core Currently composite resin is the most popular core buildup material.

Advantages: • It can be bonded to many of the current posts and to the remaining tooth structure to increase retention.

• It has high compressive and tensile strength.

• Easy to manipulate and rapid set. The tooth can be prepared for a crown immediately often polymerization.

• Studies have shown that composite cores have fracture resistance comparable to amalgam and cast post and cores, with more favorable fractures when they fail.

• Tooth colored.

Disadvantages: • Composite shrinks during polymerization causing gap formation in the areas where adhesion is weakest.

• It absorbs water after polymerization causing it to swell. Water sorption also reduces its strength.

• Studies have shown that thermocycling reduces strength.

• Undergoes plastic deformation under repeated loads.

• Adhesion to dentin on the pulpal floor is generally not as strong or reliable as to coronal dentin.

• Strict isolation is an absolute requirement. If dentin surface is contaminated with blood or saliva during bonding procedures, the adhesion is greatly reduced.

• Composite is not a good choice with minimal remaining tooth structure particularly if isolation is a problem.

Recently, composite materials specifically for core buildup have been introduced in the market. These are: •

Self cure e.g. Clearfil Core, Core Paste, Rebilda, etc.

•

Light cure e.g. Clearfil Photocore, LC core, etc.

•

Dual cure e.g. Luxacore Automix Dual, DC Flow Core, etc.

Flowable composites are also available e.g. Flow Core. Some products have fluoride incorporated in them e.g. Core Paste with Fluoride. These composites have high compressive strength and many products are radiopaqe.

Glass Ionomer Core Advantages: • Their major benefit is an anticariogenic quality due to fluoride release.

• Useful for small buildups or to fill undercuts in prepared teeth, as they are adhesive materials.

Disadvantages: • Low strength and fracture toughness result in brittleness, which contraindicates their use in thin anterior teeth or to replace unsupported cusps.

• Exhibit low retention to prefabricated metal posts.

• Soluble and sensitive to moisture. Adhesive failure can occur from contamination of the tooth surface with debris, saliva, blood or protein.

• Not strong enough for a core for an FPD/RPD abutment tooth.

Indicated in posterior teeth in which: 1. Limited to small restorations in which core retention is not needed.

2. Bulk of core material is possible.

3. Significant sound dentin remains.

4. Additional retention is available with pins, grooves or channels.

5. Moisture control is assessed.

6. Caries control is indicated.

Resin modified glass ionomer core These materials have properties of both composites and glass-ionomer cements.

Advantages: • Fluoride release.

• Moderate strength. Greater than GIC, less than composite.

• Bond strength significantly higher than GIC. • Exhibit minimal microleakge.

• Solubility is in between that of GIC and composite.

Disadvantages: • Hygroscopic expansion of these materials can cause fracture of ceramic crowns.

As a core material, it is adequate for moderate size buildups.

BIOMECHANICAL PRINCIPLES OF POST AND CORE PREPARATION -

-

Conservation of tooth structure: o Preparation of the canal o conservation of coronal tissue Retention form o Anterior teeth:  Preparation geometry

-

 Post length  Post diameter  Post surface texture  Luting agent  Post material (cohen) o Posterior teeth: Resistance form: o Stress distribution o Rotational resistance

Conservation of tooth structure Root canal: When creating post space, the practitioner should use great care to remove only minimal tooth structure from the canal Thus it is recommended that the root canal be enlarged only the amount necessary to enable the post to fit snugly for strength and retention. Enlargement seldom needs to exceed one or two additional file sizes beyond the last file used for endodontic treatment.

Post width: Diameter of the post at tip: should not be more than one third the diameter of root 0.6mm: lower incisor 1mm : upper incisor, canine 0.8 mm : most teeth.

Post should not exceed 1mm at its tip. More bone should be left buccal to the post.

Coronal tissue: As much of the coronal tooth structure should be conserved as possible because this helps reduce stress concentration at the gingival margin It has been shown experimentally that if more than 2mm of coronal tooth structure remains, the post design plays little role in the fracture resistance of the restored tooth. Incorporation of this tooth structure within the final restoration provides the ferrule.

Retention form Post retention is defined as the ability of a post to resist vertical dislodging forces.

Retention of a post is affected by: 1. Preparation geometry and post design.

2. Post length.

3. Post diameter.

4. Surface texture.

5. Luting agent.

6. Number of posts.

7. post material (cohen) 1) Post design and preparation geometry: Circular canals can be prepared with drills or reamers to give parallel walls or minimum taper, allowing use of parallel-prefabricated post. Elliptical or excessively flared canals cannot be prepared to give parallel walls and require custom cast posts or tapered prefabricated posts.

2) Post length: Retention increases with increase in post length. One study shows that retention increases by more than 97% when post length equals or is greater than crown length (Sorensen and Martinoff). However, this length must be well within constraints of tooth length, canal morphology and root diameter in the apical area. Various criteria for post length are: 1. Minimum of 5mm of apical gutta-percha fill should be remaining.

2. Post length should be equal to 2/3rd of root length or greater.

3. Post length should be at least equal to the crown length.

4. When bone support is less, the post should extend at least half the length of root in the remaining bone.

3) Post diameter: Whether posts are cemented or threaded, diameter makes little difference in retentive ability. This is because posts are not placed in perfect cylindrical canals. In many cases the canal is ribbon or elliptical shaped, resulting in variable cement thickness or lack of total engagement. Thus, diameter variations are of little concern for providing retention.

4) Surface texture: A serrated or roughened post is more retentive than a smooth one. Roughening can be done with sandblasting.

5) Luting agent: Any of the current luting cements can be successfully used with a post if the proper principles are followed. The most commonly used luting agents are: zinc phosphate, resin, glass-ionomer and resin-modified glass ionomer. However, Resin-modified glass ionomer cements should be avoided as they expand on water absorption and may cause root fracture.

Generally, in the past, zinc phosphate was the cement of choice, but, recent trend has been toward resin cements because they: •

Increase retention.

•

Tend to leak less than other cements.

•

Provide at least short term strengthening of the root

6) Number of posts: It is possible to place more than one post in teeth with multiple roots. Additional posts may be used, where feasible, to increase retention and retain core material, especially in severely broken down teeth.

Considerations for posterior teeth: Relatively long or circular posts should be avoided in posterior teeth with curved ribbonshaped / elliptical canals. For these teeth, using short posts in divergent canals provides better retention.

If a cast core is used, it can be made in sections that have different paths of withdrawal.

Alternatively, the widest canal is selected for the major post and then short auxiliary post spaces are prepared in the other canals with the same path of withdrawal.

Resistance form Resistance is defined as the ability of the post and tooth to withstand lateral and rotational forces.

Stress distribution: One of the functions of a post and core restoration is to improve resistance to laterally directed forces by distributing them over as large an area as possible. However, excessive preparation of the root weakens it and increases the probability of failure.

The post design should distribute stresses as evenly as possible.

The influence of post design on stress distribution has been tested using photoelastic materials, strain gauges and finite element analysis. From these laboratory studies, the following conclusions have been drawn (Rosenstiel): 1. The greatest stress concentrations are found at the shoulder, particularly interproximally and at the apex. Dentin should be conserved in these areas.

2. Stress is reduced as post length increases. But excessive length reduces the thickness of dentin at the apical area and hence the fracture resistance decreases.

3. Parallel-sided posts distribute stresses more evenly than tapered posts, which can have a wedging effect. However, parallel posts generate high stresses at the apex.

4. Sharp angles should be avoided as they produce high stresses during loading.

5. High stress can be generated during insertions of smooth parallel-sided posts that have no vent for escape of cements. Therefore, these posts, longitudinal grooves (vents) running along the length of the post should be provided to allow escape of cement thus reducing the hydrostatic pressure and generation of stress. Tapered posts are self-venting and generally do not require vents.

6. Threaded posts can produce high stresses during insertion and loading, but they have been shown to distribute stress evenly if the posts are backed off a half-turn.

7. The cement layer results in a more even stress distribution to the root with less stress concentration.

In addition, fiber (carbon and glass) reinforced posts produce more even stress distribution along the lengths of the root than the metal posts.

Rotational Resistance: It is important that a post with a circular cross section not rotate during function. Where sufficient coronal tooth structure remains, this should not present a problem because the axial wall then prevents rotation. When coronal dentin has been completely lost: -

A small groove placed in the canal can serve as an anti-rotational element.

The groove is normally placed where the root is bulkiest, usually on the lingual aspect.

-

An auxiliary pin on the root face can prevent rotation.

Rotation of a threaded post can be prevented by preparing a small cavityhalf in the post, half in the root and condensing amalgam into it after cementation of the post.

Additional cemented posts in multirooted teeth.

Oval or elliptical canals.

The Ferrule:

Rosen in 1961 described the extracoronal brace (ferrule) and defined it as “….a 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 restored crown which, by its hugging action, prevents vertical shattering of the root”.

More recently, Sorensen and Engelman (1990) defined Ferrule Effect as “…..a 360° metal collar of the crown surrounding the parallel walls of the dentin extending coronal to the shoulder of the preparation. The result is an elevation in resistance form of the crown from the extension of dentinal tooth structure”.

The walls and margins of the crown or cast telescopic coping encasing the gingival 2mm of the axial walls of the preparation form the ferrule. A properly executed ferrule significantly reduces the incidence of fracture in the non-vital tooth by reinforcing the root at its external surface and also by dissipating force that concentrates at the narrowest circumference of tooth.

As described by several authors, stress in the radicular dentin during function is concentrated to the circumference of the tooth, whereas the stress level is lowest within the root canal. The center of the root is a neutral area with regard to stress concentration, and thus no reinforcement is needed in this area. To reinforce the tooth, incorporating a ferrule into the design of the crown, embracing the circumference of the root, protects the

root where the maximum forces occur. The ferrule effect is a key factor in the failure of post treated teeth.

Fracture resistance is significantly increased with increasing ferrule length. The ferrule also resists lateral forces from posts and leverage from crown in function, and it increases the retention and resistance of the restoration (Cohen). As already stated, presence of a ferrule reduces influencedentin of post design on the Stressthe in radicular during function is fracture resistance of teeth. concentrated to circumference of tooth; stress is lowest within root canal.

To be successful, the ferrule must encircle a vertical wall of sound tooth structure above the margin and must not terminate on restorative material. Both the crown and crown preparation must meet five requirements: 1. At least 2mm of dentin axial wall height.

2. Parallel axial walls.

3. Metal must totally encircle the tooth.

4. Margins must be on sound tooth structure.

5. Crown and crown preparation must not invade the attachment apparatus.

This means that a 4-5 mm height and 1mm thickness of sound suprabony tooth structure should be available to accommodate the periodontal biologic width and the restorative ferrule. A tooth with remaining tooth structure that is insufficient to construct a ferrule should be evaluated for: -

periodontal crown lengthening surgery, or,

-

orthodontic extrusion.

to gain access to additional root surface. The lack of sufficient ferrule in the final restoration forces the core, the post and the root to accept high functional stresses, often resulting in fracture.

CLINICAL TECHNIQUES - Post selection - Removal of endodontic filling - Post space preparation - Preparation of coronal structure - Post fabrication - Core fabrication - Temporizaion - Try in and cemenation Post selection: The post system to be used depends on: 1) Root morphology.

2) Remaining coronal tooth structure.

3) Occlusal forces.

-

If the root narrows considerably in the apical one-third (e.g. maxillary first premolars and mandibular central and lateral incisors), the use of a parallel post may come dangerously close to perforating the lateral surface of the root.

Oval or ribbon-shaped canals cannot be prepared easily to receive circular, parallel post. In these situations a custom post formed to the shape of the canal conserves tooth structure and involves less preparation in the apical region of the root.

-

If it is possible to prepare a cylindrical channel equal to or longer than the clinical crown of the tooth, a parallel cemented post in combinations with coronal core will best fulfill requirements.

-

Where esthetics is a concern, tooth colored glass fiber or ceramic posts should be used.

Remaining Coronal Tooth Structure:As already discussed, the amount of

remaining tooth structure will determine the need for post and core restoration.

Occlusal forces: Occlusal forces on individual teeth are influenced by: •

Tooth type and position – Molars have high forces acting on them than for incisors and premolars.

•

Presence or absence of adjacent teeth – occlusal forces dissipated to adjacent teeth via proximal contacts. Absence of adjacent teeth increases the amount of forces acting on the individual teeth.

•

The functions the tooth must serve for e.g. RPD or FPD amount. Here the amount of forces acting on the individual tooth is increased.

•

Patient’s occlusal habits e.g. bruxism.

The higher the occlusal forces, the greater the retention needed. This can be achieved by using parallel-sided posts. In multirooted teeth, additional posts can be used to increase retention.

Removal of the Endodontic Filling Material It is recommended that the root canal system should first be completely obturated and then space made for a post. This will ensure that the lateral canals are sealed. A post cannot be placed if the canal is filled with a full length silver point, so these must be removed and the tooth re-treated with gutta-percha.

How? the two commonly used methods for gutta-percha removal are: 1. With a heated endodontic plugger.

2. With a rotary instrument.

Though previously it was thought that rotary instruments would disturb the apical seal, recent research has shown that both methods can be safely used to remove gutta-

percha without disturbing the apical seal when 5mm of gutta-percha is retained apically (Ingle).

When? Controversy also existed regarding the timing of removal of gutta-percha after endodontic treatment. It was believed that removal should be delayed by 1 week, as intermediate removal should disturb the apical seal. However now it has been shown that immediate preparation of the post space ( Fan et al, Solano et al) following obturation is the best technique. It minimizes the microleakage. Also preparation should be done by the same clinician as he is familiar with the root canal anatomy.

Removal with rotary instruments: Gutta-percha can be removed with GG drills, Pesso reamers, Parapost-drills and other commercially available burs. When rotary instruments like burs or drills (B & C) are used, it should be ensured that the instrument follows the gutta-percha and does not engage the dentin otherwise perforation will occur. For this reason GG drills and Peeso reamers (A) are preferred as their non-cutting tips keep them centered on the gutta-percha (the path of least resistance).

Technique: 1. Choose a Pesso reamer slightly narrower than the canal.

2. The depth of insertion is determined by superimposing the Peeso reamer over the radiograph of the tooth being restored. Set the stopper at the level of incisal edge of adjacent teeth.

3. Carefully remove the gutta-percha and avoid cutting the root dentin. Often only a part of the root canal fill need be removed with a rotary instrument, and the remainder can be removed with the heated condenser.

4. Once removal reaches the appropriate depth shape the canal as needed.

Removal with a heated endodontic condenser: In this method a heated endodontic plugger or an electronic device is used to remove the gutta-percha. This method is commonly used when gutta-percha is to be removed right after obturation as there are minimal chances of disturbing the apical seal.

Technique: 1. Before removing gutta-percha calculate the appropriate length of the post. As a guide, the post length should be equal to the height of the anatomic crown or twothirds the length of the root, whichever is greater, but 5mm of apical gutta-percha should be left. In short teeth, compromises must be made. An absolute minimum of 3mm of apical fill is needed. If this cannot be achieved without having a very short post, then prognosis of the tooth is impaired.

2. Avoid the apical 5mm if possible as curvatures and lateral canals are found in this segment. The instrument is gauged for length against a preoperative radiograph and the stopper is set at the level of incisal edge of adjacent teeth.

3. Apply rubber dam to prevent aspiration of instrument.

4. Select an endodontic condenser large enough to hold heat well but not so large that it binds against the canal walls.

5. The instrument is heated till it is red hot, inserted into the gutta-percha and is quickly withdrawn. This sears off the gutta-percha. If condenser it kept for a longer time or is not heated well the gutta-percha will stick to the instrument resulting in its being pulled out when the condenser is withdrawn, thus disturbing the endodontic seal.

6. If the gutta-percha is old and has lost its thermoplasticity, use a rotary instrument.

Enlargement of the Canal This is accomplished with instruments, Pesso reamers or a low speed drill. The purpose is to remove undercuts and prepare the canal to receive an appropriately sized post without excessively enlarging the canal. It has been recommended that the post be no more than one-third the diameter of the root with the root and walls at least 1mm thick. Thus, knowledge of average root dimensions is important in addition to root canal shapes.

Before starting canal preparation, remove any existing restorations, caries, bases and thin or unsupported walls of tooth structure. Preserving as much tooth structure as possible.

For Pre-fabricated Posts: 1. Set the stopper on the instrument to the predetermined length. Enlarge the canal one or two sizes with a drill, endodontic file or reamer that matches the configuration of the post. When Peeso reamers are used (A), the canal is enlarged to a diameter slightly smaller than that of the specific instrument (e.g. ParaPost Drill) required for the system being used. Final preparation is then done with that instrument (B). In case of a threaded post, a tap (to make threads in the dentin) follows the appropriate drill, unless self-threading screws are being used.

2. Enlarging the canal in 0.2mm increments diminishes the possibility of the instrument straying from the canal. Conventional drills used without any prior enlargement of the canal are more prone to stray from the original canal pathway than Peeso reamers.

3. Be careful not to remove more dentin at the apical extent of the post space.

Radiographs are not normally required, provided careful measurement techniques have been followed.

4. To provide anti-rotational resistance, a pin may be used. Drill one or two 0.6mm pin holes to a depth of 2mm, in the area of the greatest bulk between the canal and the periphery of the tooth (usually on lingual side).

For Custom-made Posts:

Often very little preparation will be needed for a custom-made post. However, undercuts within the canal should be removed and some additional spacing is usually necessary.

1. Set the stopper on the instrument to the predetermined length.

2. Gradually enlarge the canal (in 0.2mm increments) to the size that has been determined for that tooth. As already mentioned, it should not be greater than onethird the diameter of the root at the CEJ (A) and there should be a minimum thickness of 1.0mm of tooth structure around the post at mid-root and beyond (B).

3. If anti-rotational resistance is required use a no. 170 bur to make a key way or groove in the orifice of the canal. Place it in the area of greatest bulk. It should be cut to the depth of the bur (approx. 0.6mm) and up the canal to the length of the cutting blades of the bur (approx. 4mm). On a premolar and molar, the second canal serves the anti-rotational function.

Preparation of Coronal Tooth Structure After the post space has been prepared, the coronal tooth structure is reduced for the extracoronal restoration. Anterior teeth are restored with metal-ceramic crown or when esthetic posts and cores used, with an all-ceramic restoration. All-metal crowns are generally given for posteriors.

1. Ignore any missing tooth structure and prepare the remaining tooth as though it was undamaged.

2. The facial surface (in anteriors) should be adequately reduced for good esthetics.

3. Remove all undercuts that will prevent removal of pattern. This is not needed with direct core buildups.

4. Preserve as much tooth structure as possible.

5. Prepare the finish line at least 2mm gingival to the core. This establishes the ferrule. For custom-made post and core restorations, place a contra bevel (Fig.) with a flame-shaped diamond at the junction of the core and tooth structure. The bevel provides a metal collar around the occlusal circumference of the preparation (in addition to the ferrule) in bracing the tooth against fracture. It also provides a vertical stop to prevent over-seating and wedging effect of the post.

6. Complete the preparations by eliminating sharp angles and establishing a smooth finish line.

Post Fabrication Prefabricated posts: These have to be selected to match the dimensions of the canal. They must be seated till full depth. Any discrepancy between the coronal part of post and canal wall can be filled with core material during the build up of core.

To shorten the length of the post:

-

Do it at the apical end if the post has a special shape to the head (for retention of core).

-

If the post has a specially shaped apical tip (e.g. tapered end in a parallel post like BCH post), do any needed shortening at the coronal end. At least 2-3mm of the post should be present supragingivally for retention and support of core material.

Custom-made posts: -

A custom-made post can be cast from a direct pattern or an indirect one. A direct pattern utilizing autopolymerizing resin is recommended for single canals whereas an indirect procedure is more appropriate for multiple canals.

Direct procedure: 1. Trim a 14-gauge solid plastic sprue so that it slides easily into the canal to the apical end of the post preparation without binding. Cut a small notch on the facial portion to aid in orientation during subsequent steps.

2. Mix acrylic resin monomer and polymer to a runny consistency.

3. Lubricate canal with petroleum or any other lubricating agent, on cotton wrapped on a Peeso reamer.

4. Fill the orifice of the canal as full as possible with acrylic resin applied with a plastic filling instrument. Alternatively: -

Use the bead-brush technique to add resin to the orifice, and to the sprue.

-

In the doughy stage, roll the resin into a thin cylinder, introduce it in the canal and push it to place with the monomer-softened sprue.

5. Seat the monomer coated sprue completely into the canal. Make sure the external bevel is completely covered with resin at this time. Trying to cover it later may disturb the fit of the post.

6. When acrylic resin becomes tough and doughy, pump the pattern in and out to insure that it will not lock into undercuts.

7. As the resin polymerizes, remove post from canal and make sure it extends till the apical end. If required, additional resin can be placed at the apical end and the post is reseated and removed. Any voids can be filled with soft dead wax e.g. utilizing wax Reinsert and remove to ensure smooth withdrawal.

8. A direct pattern can also be made using inlay wax in a similar manner.

9. Add more resin or wax to form the core. Shape it in the form of the final preparation.

Indirect Procedure: Any elastomeric material will make an accurate impression of the root canal if wire reinforcement is placed to prevent distortion.

1. Cut pieces of orthodontic wire to length and shape them like the letter J.

2. Verify the fit in each canal. It should fit loosely and extend to the full depth of the post space.

3. Coat the wire and tray with adhesive; gingival retraction would be needed for subgingival margins. Use a die lubricant to lubricate canals and facilitate removal.

4. Using a lentulospiral, fill the canals with elastic impression material.

5. Seat the wire to full depth, syringe in more impression material around the prepared teeth and insert the impression tray.

6. Remove the impression, evaluate it, and pour the final cast.

7. In the cast, trim a loose fitting plastic post or sprue to fit the preparation till the apical end without binding, make a notch for orientation. Use the impression as a guide to aid in orientation.

8. Apply a thin coat of sticky wax to the plastic post and add soft inlay wax in increments. It is best to start at the most apical end and make sure that the post is correctly oriented as it is seated to adapt the wax.

9. When post pattern is made, add wax to form the core.

10. Use the impressions as a guide to evaluate whether the wax pattern is completely adapted to the post space.

Core Fabrication Cast-metal core: These are shaped in resin or wax and added to the post pattern before the assembly is cast in metal. This prevents possible failure at the post-core interface. In addition to cast posts, they can also be cast directly onto most prefabricated post systems.

Advantages: 1. No failure at post-core interface.

2. Can be used with prefabricated posts.

3. Conventional high noble alloys can be used.

4. An indirect procedure can be employed, making restoration of posterior teeth easier.

Disadvantages: 1. An additional appointment is required.

2. More expensive than amalgam or composite cores.

3. Casting directly onto prefabricated posts may alter their physical properties, thus weakening them.

Direct procedure for single-rooted teeth: 1. Use a prefabricated metal or custom acrylic resin post.

2. Add resin by “bead� technique, dipping a small brush into monomer and then into polymer and applying it to the post. Light cured resin may be used.

3. Slightly overbuild the core and allow it to fully polymerize.

4. Shape the core with carbide finishing burs. Use water spray to avoid overheating of acrylic resin correct any small defects with wax.

5. Remove the pattern, sprue and invest immediately.

6. It can be similarly built with inlay wax and shaped with carvers when the direct pattern is made with wax.

Direct pattern for multi-rooted teeth: A direct pattern may be used for posterior teeth. A single piece core with auxiliary posts is used. The core is cast directly onto the post of one canal. The other canals already have prefabricated posts that pass through holes in the core. Smooth sided parallel or tapered posts are used as auxiliary posts.

1. Fit prefabricated posts into the prepared canals. One post is roughened (to which the core is cast onto); others are left smooth and lubricated. All posts should extend beyond the eventual preparation. Alternatively, the main post canal also be made by direct resin pattern and is then cast along with the core.

2. Build up the core with cold cure resin by the bead technique.

3. Shape the core to the final form with carbide burs.

4. Grip the smooth lubricated posts with force and remove them.

5. Remove, invest and cast, the core with the roughened post or resin pattern. When this is done, the holes for auxiliary posts can be refined with the appropriate twist drill.

6. After verifying the fit, cement the core and auxiliary posts to place.

Indirect pattern for multi-rooted teeth: When there is limited access, indirect approach is easier to use. A multi-piece post and core is made by this method (Split casting).

In the final cast: 1. Wax the custom-made posts as described previously.

2. Build part of the core around the first post.

3. Remove any undercuts adjacent to other post holes and cast the first section.

4. Wax the additional sections and cast them. Each section should be waxed to ensure that no undercuts are created.

5. Cast each section separately.

Alternatively, interlocking sections can be made by using dovetails to interlock the sections. But this makes the procedure more complicated and is of limited benefit, especially because the final buildup is held together by the fixed cast restoration.

Plastic Filling Materials: Amalgam, composite resin or GIC are used as core buildup materials with prefabricated posts. Due to its low strength GIC is generally not recommended unless minimal buildup is required.

Advantages:

1. Maximum tooth structure can be preserved, as undercuts need not be removed.

2. Treatment requires one less appointment.

3. Fewer laboratory steps, hence cheaper.

4. Good strength.

Disadvantages: 1. Long term success may be limited by: - Corrosion of amalgam.

- Low tensile strength of GIC. - High thermal expansion coefficients of composite resin cores.

2. Microleakage with thermocyling is found in composite and amalgam cores.

3. Certain procedures like rubber dam and matrix application may be difficult, especially with badly broken down teeth.

Amalgam cores: They are suitable for posterior teeth, particularly when some coronal structure remains. Their merits and demerits have already been discussed.

1. A matrix band is applied to the tooth and amalgam is condensed around the posts, and built up coronally.

2. Once it sets, the band is removed and core shaped with burs as needed. A fast setting high copper amalgam is used.

Amalgam Coronal-radicular Restoration Technique: Used for restoring posterior teeth that are largely intact. The procedure described by Nayyar et al (1980), with amalgam used for the posts as well is conservative of tooth structure. The restoration is placed at the same appointment as the root canal obturation for then the canals are still isolated, the canal anatomy is fresh in the practitioners mind and the core can serve as a support for the provisional restoration.

1. Remove the gutta-percha from the pulp chamber as well as 2-4mm into each root canal if less than 4mm of coronal height remains. Use a heated plugger.

2. Remove any existing restoration, undermined enamel, or carious or weakened dentin, establish cavity form. Even if cusps are missing, pins are not normally required because of extension into root canals.

3. If it is suspected that the floor of the pulp chamber is thin, then protect it from condensing pressures with a cement base.

4. Fit a matrix band for badly broken down teeth or an orthodontic band may be used.

5. Condense the first increments of amalgam into the root canals with a plugger.

6. Fill the pulp chamber and coronal cavity in the conventional manner.

7. Carve the alloy to shape: the impression can be made immediately. Alternatively, the amalgam can be built to anatomic contours and then shaped with burs.

Composite resin cores:

These are built up using crown forms. A clear crown form permits use of a light activated composite, while a polycarbonate form can be used with chemically activated composite.

1. If a polycarbonate crown form is used, place a separating medium.

2. Fill the crown form with resin and hold it in position over the protruding dowel until it polymerizes.

3. Remove the matrix and shape the core with burs to the form of a crown preparation.

4. The gingival finish line should be in tooth structure.

Alternatively, the core can be built with light activated composite in increments without using a crown form.

Investing and casting: The post-core pattern is sprued on the incisal or occlusal end. 1.0 to 2.0cc of extra water is added to the investment and a liner is omitted to increase the casting shrinkage (Shillingburg). This results in a slightly smaller post that does not bind in the canal, and it also provides space for the cement. A tight fit may cause root fracture. When resin is used, the pattern should remain for 30 minutes longer in the burnout oven to ensure complete elimination of the resin.

Provisional Restorations After endodontic treatment, if a cast post and core is planned, a provisional crown with attached temporary post can be fabricated for the teeth with limited supragingival structure. A provisional restoration is also needed while the post and core is being fabricated to prevent drift of adjacent and opposing teeth. Fitting a wire paper clip (e.g. or orthodontic wire) into the prepared canal or using a temporary post available with proprietary post systems can do this. Restoration is then conveniently fabricated with autopolymerizing resin with the direct technique.

Barrier technique: GIC cement 2-3 mm may be placed in the prepared post space over the remaining obturation.

The final post, core and crown should be fabricated as soon as possible, because microleakage can contaminate the post space and endodontic fill. Provisional restorations should be used with extreme caution because partial loss of the cement seal may go undetected for some time. This leakage can lead severe carious invasion and loss of tooth.

In addition to caries, leakage can jeopardize the success of endodontics.

Try-In and Cementation Any cement may be used if retention and resistance of the post are adequate. The choice of cement may become more important if the post has a poor fit in the canal. When resin cements are used, the post should be cemented with auto-cure or dual-cure resin cement because of limited light penetration into the root. Irrigation with 2.5cc of 17% EDTA to chelate calcium followed by 2.5cc of 5.25% NaOCl to flush away debris, has been recommended to remove smear layer and improve retention. Also, microbrushes can be used to deliver etchants and bonding agents deep into the canal.

Prefabricated posts: 1. Once the post has been selected, make a thin mix of cement and coat the post with it.

2. Introduce cement into the post space with a plastic instrument. Use a lentulospiral to ensure that the walls are coated with cement. According to Shillingburg, retention can be increased by as much as 90% if a lentulospiral is used.

3. Push the post slowly to place allowing excess cement to escape. Parallel-sided posts should have an escape vent to allow escape of excess cement.

4. Hold the post with finger pressure until initial set occurs. Then remove excess cement from around post head and pins.

5. Fabricate core, prepare it similar to a tooth preparation. Take impression for final restoration.

Custom-made posts: 1. Check the fit of the post-core in the tooth by seating it with light pressure.

2. If it binds in canal or will not seat completely, air abrade the post and reinsert it in the canal. Relieve any shiny spots.

3. The core portion of the casting should be polished. If required, a vertical groove, from apical end to contrabevel, can be cut in the post to provide an escape vent for the cement.

4. The canal should be cleaned with a cavity cleaner to remove lubricant / temporary cement which may inhibit set of resin cements and decrease retention.

5. Cement the post as for prefabricated posts.

6. Modify the core if necessary. Make an impression for the final restoration.

ESTHETIC POSTS TECHNIQUE: With increasing self-awareness the demand for superior esthetics has increased.

Thus, use of esthetic, tooth-colored posts are now most commonly used in the anterior region. Three main techniques are utilized: 1. Fiber posts with composite cores.

2. Ceramic (zirconia) posts with composite/ceramic cores.

3. All-ceramic posts and cores.

Techniques for fiber posts Two categories of fiber reinforced posts are available: 1. Prefabricated posts.

2. Chairside-fabricated posts.

PREFABRICATED SYSTEMS (Freedman)

Several prefabricated post systems are available to the practitioner for the restoration of the endodontically treated tooth.

Intraradicular Rehabilitation Occasionally, the post-endodontic presentation of the canal may be too wide for routine direct restoration. This may have occurred as a result of extensive decay or aggressive instrumentation of the canal or the patient may be young with large canals. Simply placing a post in this canal would leave a very thick layer of cement. It is also difficult to position the post in an ideal location for the subsequent restoration. The Luminex Light Transmitting System (Dentatus, New York, NY) is used to rehabilitate this canal to an ideal size and shape.

1. The canal is reamed to the desired depth with a size-matched reamer. The reamer is correlated in size and shape to a corresponding light transmitting post and a Luscent Anchor.

2. The Luminex Light Transmitting Post (LTP) is tried in and adjusted for length. The canal is then dried, etched and rinsed.

3. A dual-cured fifth-generation bonding agent, Prime & Bond NT Dual Cure (CaulkDentsply, Milford, DE) is then applied to the internal surface of the canal, air blown to eliminate pooling, and light cured.

4. A microhybrid, EsthetX (Caulk-Dentsply) is injected into the bonded canal and the Light Transmitting Post is pushed into the uncured composite resin to its full depth.

5. The LTP and the composite resin are light cured together for 60 seconds. The Light Transmitting post allows the passage of light through its body but does not bond to the composite material.

6. A hemostat is used to rotate and remove the LTP, leaving an ideally shaped and sized post space for the size-matched Luscent anchor (Dentatus), which can be placed immediately.

At this stage the post space can be treated routinely. The post-and-core procedure will be predictable, and the prognosis for the tooth much improved.

Alternatively, as the Luscent Anchor also transmits light, intraradicular rehabilitation can be done directly with this post without using the Luminex Post.

Luscent Anchor Post Technique The Luscent anchor post (Dentatus) is a fiber-glass, clear resin post that is designed to refract and transmit natural tooth colors for esthetic post-and-core foundations. The Luscent anchor is radiolucent and identified on radiographs by the surrounding resin cement. Designed to be placed passively in prepared canals, it is available in three diameters, and is size integrated with the Light Transmitting Posts. The Luscent anchor is easily removed, if required, for endodontic re-treatment.

1. Using the post space created by the LTP, 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 (Zenith, Englewood Cliffs, NJ), 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.

ParaPost Fiber White Technique The ParaPost Fiber White Post (Coltene/Whaledent, Mahwah, NJ) is a filled resin, mono-directional fiber matrix with a flexural modulus that very closely approximates that of the natural dentin. The color of the post is white translucent, designed to minimize shadowing under all-ceramic restorations. The parallel-sided posts are intended for passive seating in the canal, and the antirotational post head stabilizes the core materials.

The ParaPost fiber white is available in four diameters, color-coded to matching drills.

These posts are readily removed should endodontic re-treatment be necessary.

1. The post-endodontic canal is refined with a familiar, color-coded ParaPost drill.

2. The ParaPost Fiber White post is tried into the canal and the canal is then dried, etched, rinsed, and left slightly moist.

3. One Coat Bond (Coltene/Whaledent) is applied into the canal, air thinned and then light cured.

4. Luxacore is injected into the bonded canal and the Fiber White post is seated into the uncured composite to its full depth. The core can be built up immediately and it sets within 4 minutes.

5. With the judicious application of build-up materials, the ideal crown foundation is closely approximated. It is now ready for the final crown preparation.

Chair side fabricated post (Freilich et al) This technique utilizes polyethylene woven ribbon (Ribbond) fibres along with a composite resin.

Technique: 1. The tooth is isolated and using heat or Peeso reamers, gutta-percha is removed from the canal to the desired length.

2. The existing canal is not enlarged or shaped any further.

3. Strips of Ribbond is cut in excess of twice the post space.

4. The canal space is etched, rinsed and a forth generation dentin bonding system is applied to the canal, pulp chamber and remaining tooth structure.

5. A dual-cure or chemical-cure composite resin luting cement is applied into the canal.

6. The Ribbond fiber is saturated with resin, forming it into a V-shape and is placed into the canal leaving the excess as an “ear� out into the chamber / remaining tooth structure. As many pieces of Ribbond are placed as will fit into the canal.

7. Composite resin core material is applied to the coronal extension (ear) of Ribbond to create a core. The core is shaped as the crown preparation.

Ceramic posts - These posts, mainly zirconia posts, can be used with either composite cores or ceramic cores can be fabricated over them. The ceramic core provides the advantage of greater strength at the post-core interface.

All-ceramic posts and cores (Koutayas and Kern) These are fabricated, using high-toughness ceramic materials such as alumina and zirconia ceramics, through four different techniques: 1. The Slip-casting Technique 2. The Copy-milling Technique 3. The Two-piece Technique, which involves a prefabricated zirconia post and a copymilled alumina or zirconia ceramic core.

4. The Heat-pressed Technique, which involves a prefabricated zirconia ceramic post and a heat-pressed glass-ceramic core.

Laboratory studies have shown ceramic posts to have lower fracture strength than fiber posts. However, they provide superior esthetics, as their optical properties are similar to natural teeth.

FAILURE AND REMOVAL OF POST AND CORES: Vire classified failure of endodontically treated teeth are: 1. Prosthetic failures.

2. Periodontic failures.

3. Endodontic failures.

Of these, prosthetic failures occurred 59.4% of the times, thus emphasizing the need to properly restore endodontically treated teeth to increase their longevity.

For post and core restorations, failure rates between 7% and 15% have been reported in the literature (Torbjorner). The main factors that make endodontically treated teeth more disposed to technical failure are: 1. Thin-walled, weakened roots unable to withstand high stress.

2. Reduced retentive surfaces resulting in high stress levels in the cement.

The main causes of post and core restoration failure are:

1. Dislodgement of post (loss of retention).

2. Root fracture.

3. Fracture of post.

4. Caries.

5. Periodontal disease.

Careful, case selection, adherence to biomechanical principles of post and core restoration, appropriate post selection and meticulous maintenance of oral hygiene on the part of the patient can prevent this.

Failure mode An important factor related to resistance is failure mode. All post systems have some percentage of clinical failure. However, some posts cause a higher percentage of failures that result in teeth that are non-restorable (unfavorable fractures). For example, teeth restored with less rigid posts, e.g. fiber posts, tend to have failures that are more likely to be restorable. These posts tend to fracture rather than causing root fractures.

Even if root fractures occur, they are generally favorable, i.e. can be restored.

Even zirconia posts fracture more commonly than metal posts.

On the other hand, stiffer metal and zirconia posts fail unfavorably, causing nonrestorable root fractures (oblique or vertical). In fact, parallel-sided metal posts classically cause oblique root fractures with apical part of the fracture corresponding to the apical part of the post The tapered post design tends to cause vertical root fracture due to its wedging effect. A positive coronal seat lessens this to some extent.

Failure between post and core is also seen. This is most common in case of zirconia posts and composite cores as zirconia posts are not easily etched.

Teeth prepared with a ferrule also tends to fail in a more favorable mode. Recent research has shown that use of bonded posts and cores without ferrule, results in comparable fracture resistance to preparations with a ferrule.

The type of core material also can affect failure mode. It has been shown that composite cores tended to fail more favorably than amalgam or gold.

Removal of existing posts Occassionally an existing post-and-core must be removed (e.g. for retreatment of a failed root canal filling). If sufficient length of post is exposed coronally, the post can be retrieved with thin-beaked forceps. Vibrating the post first with an ultrasonic scaler will weaken the cement and facilitate removal. A thin scaler tip is recommended.

Post removal by ultrasonic device. A, Preoperative radiograph of the left maxillary first premolar with a parallel-sided threaded post that had to be removed for endodontic retreatment. B, After the coronal portion of the post has been well isolated, the tip of the ultrasonic device is placed against it and energy is applied to disrupt the cement interface.

Note the suction tip, which removes water from the water spray used with the ultrasonic

handpiece. C, After a time, the post becomes loose within the canal and can be retrieved by forceps. D, Radiograph of the premolar after post removal.

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 extracts the post.

Post removal by extractor. A, The Thomas (Gonon) post-removing system. It includes pliers, trephine burs, mandrels, and washers. B, Preoperative radiograph of the left maxillary lateral incisor with a post. C, Note the flared shape of the post in this preoperative view and the height of the surrounding tooth structure. D, A high-speed bur is used to free the post from coronal tooth structure and parallel its sides. (NOTE: An ultrasonic device may be used at this point to disturb the cement interface.) E, A trephine bur machines the post to the correct diameter and places threads for the mandrel. F, The mandrel is threaded onto the post with special washers, which distribute the forces from the extractor evenly over the tooth. G, The beaks of the pliers are fitted onto the mandrel; the knob of the pliers is then rotated, which separates the beaks, and the post is extruded from the tooth. H, The removed post still attached to the mandrel and pliers. 1, Radiograph of the lateral incisor after post removal.

A post that has fractured within the root canal can not be removed with a post puller or forceps. The post can be drilled out, but great care is needed to avoid deviation. The technique is best limited to relatively short fractured posts.

Post removal by high-speed bur. A, Preoperative radiograph of the right maxillary lateral incisor, in which both the crown and part of a post have been fractured off. A portion of the Kurer-type, parallel-sided, threaded post remains within the canal. B, Because of the large diameter of the post and its position within the canal, a high-speed handpiece was chosen to drill it out. C, Radiograph to verify the correct orientation of the bur's progress inside the canal. With this method of post removal, the operator must be extremely careful not to let the high-speed bur contact the canal wall, which would gravely compromise tooth structure. D, Radiograph of the incisor after post removal and retreatment.

Another means of handling an embedded fractured post (described by Masserann in 1966) uses special hollow end-cutting tubes (or trephines) to prepare a thin trench around the post. The technique has proved to be quite successful. Retrieval can be facilitated by using an adhesive to attach a hollow tube extractor.

Masserann technique for the removal of fractured posts. A and 8, Maxillary incisor with a post that has fractured inside the canal. C, The diameter of the post is gauged with a sizing tool, and D, the selected trephine is carefully rotated counterclockwise to create a narrow channel around the post. E, When the instrument has removed sufficient material, the post is recovered. F,The fractured crown and post after removal.

Biological width- it is the dimension of space that healthy gingival tissues occupy coronal to alveolar bone. It is a combination of 1.07mm alveolar bone to JE and 0.97mm JE to base of sulcus i.e. 2mm (avg). Restoration should not be placed 2mm from JE else inflammation results. (glikman 9th edi - 950)