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Restoration of endodontically treated teeth

There have been many recent advances in the methods available for restoring endodontically treated teeth. This article provides a practical guide to the restoration of endodontically treated

teeth based on the amount of sound tooth structure remaining

Massimo Giovarruscio, Specialist Endodontic Clinical Teacher, Kings College London Dental Institute, London

Email: giovarruscio@me.com

The completion of root canal treatment does not signal the end of patient management. The endodontically treated tooth has to be restored to both form and function. In addition, there is now a greater appreciation that coronal leakage may cause failure. Therefore, the quality of the coronal restoration has an influence on treatment outcome. The availability of adhesive techniques has expanded treatment modalities. Amalgam cores and cast metal posts are being replaced by adhesive techniques and fibre posts; all-ceramic and composite resin crowns are chosen for better aesthetics.

Restoration choiceThe choice of restoration for an endodontically treated tooth is dependent on the amount of coronal tooth tissue left. In fact, this single most important factor will dictate the retention of the restoration and the fracture susceptibility of the tooth. The suggestion from existing literature is there is a relationship between the fracture resistance of endodontically treated teeth and the residual amount of tooth structure. Hence, the life expectancy of endodontically treated teeth may not necessarily be increased by the choice of

restoration but rather by the amount of tooth structure preserved. Anterior and posterior endodontically treated teeth present differing restorative demands. Anterior teeth may be less prone to fracture but compared with posterior teeth, aesthetic is a major consideration.

Anterior teethComposite resin restorationIn anterior teeth where there has been little previous restoration, a combination of composite resin placed over a base of glass ionomer cement may suffice. Composite resin is the most appropriate material for restoring the access cavity given its physical properties, high quality surface finish and the good seal achieved with bonding. If the tooth is discoloured, bleaching techniques may be used, particularly if the discolouration is mild (Figures 1a and b). Internal and external bleaching techniques may be applied.

Ceramic or composite resin veneersIf the coronal tooth tissue loss is less than one-third, the palatal aspect of the tooth is to be preserved but if it is impossible to obtain a good aesthetic result using a direct restoration, then a ceramic or composite resin veneer may be placed. Veneers normally cover the entire labial surface of the tooth, including the incisal edge and through to the proximal contacts (Figures 2af). Ceramic or composite resin veneers are seldom recommended for endodontically treated anterior teeth

as it is not easy to incorporate the access cavity within such restorations.

Metal-ceramic crownsAmong non-adhesive techniques, metal-ceramic crowns have become the most commonly prescribed indirect restoration for endodontically treated anterior teeth. A reduction of the labial surface of approximately 1.82 mm is necessary. The extent of tooth reduction may compromise the strength of the remaining tooth tissue, so caution should be exercised before prescribing such a restoration. Far from preserving residual tooth structure, it may actually promote its loss. In general, crowning of anterior teeth is indicated if the amount of tooth structure left is not sufficient for a direct restoration and for aesthetic reasons.

All-ceramic crownsAll-ceramic crowns are more fragile than metal-ceramic crowns. However, the advantages of all-ceramic crowns are:n Labial tooth reduction required is, again, less than that for metal-ceramic crowns

n Absence of a metallic substructure allows a better aesthetic result, especially in areas close to the soft tissues.After root canal the tooth could

become darker (discoloured) due to the endodontic procedures and for this sometimes an internal bleaching is required to match a better colour. As abutments for bridges, all-ceramic crowns are only indicated for three-unit bridges in cases of high aesthetic requirement; in

Jo Russell is Director of OraclePBS Ltd and Dentabyte QDOS Ltd. www.oracle-pbs.co.ukEmail: jorussell2@me.com

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such cases, a zirconium construction is indicated (Figure 3).

Resin crownsResin crowns require less tooth tissue reduction (typically 0.81 mm) and the aesthetics is good. However, they are just as expensive as metal-ceramic and all-ceramic crowns, and yet they are not as durable. They may be considered as interim rather than final restorations.

Posterior teethAmalgam restorationA conventional amalgam restoration, including interproximal extension but no cuspal coverage, is largely contraindicated because of the high risk of cuspal or root fracture (Hansen et al, 1990). Amalgam restorations providing a minimum of 2 mm of cuspal coverage was regarded as particularly suitable for mandibular molars but aesthetic concerns have diminished its popularity.

Composite resin restorationIn general, composite resin restorations cannot be regarded as definitive restorations in posterior teeth except in cases where there has been very limited loss of tooth structure; for example, small interproximal boxes and little or no cuspal overlay (Figure4). There is no consensus on the minimum thickness of composite resin required to protect cusps from fracture. Coverage of all cusps with less than 2.5 mm thickness of composite resin has been suggested. In most cases, the loss of tooth structure caused by proximal caries and the resultant large and deep access cavity makes the placement, shaping and finishing of a direct composite resin restoration difficult to perform. The problem may be compounded if cuspal coverage has to be provided. In such cases, a direct composite filling may result in a poor reconstruction of the coronal anatomy and deficient contact points will not be capable of preventing food impaction.

Composite resin and ceramic onlays/crownsSuch restorations are contraindicated in

divergent. Coverage of all the cusps with a thickness of no more than 2.53 mm is usually recommended. Glass ionomer cement or flowable composite resin may be placed over the root filling and in the pulp chamber in order to achieve the required thicknesses and internal form of the cavity preparation. Ceramic onlay/crowns are normally cemented with adhesive resins. All ceramic crowns are not really suitable in posterior teeth because of the risk of fracture, although they are sometimes used in premolars for aesthetic reasons.

There is no clear evidence to favour ceramic or composite resin onlays/crowns, but composite resin onlays/crowns are, in general, less expensive and easier to repair (Figure 5).

teeth that are meant as bridge abutments. An initial direct, self-curing composite resin core build-up is generally indicated; the colour should be a shade different from that of dentine, in order to differentiate the composite from the dentine. This core will serve as a guide in designing a cavity for optimal material thickness. Posts are not normally used for retention of the core. The onlay preparation is similar to that used for vital teeth. A minimum thickness of 1.52 mm is required for the composite resin or ceramic material.

The margins are normally a 90 shoulder finish, and the internal line angles of the cavity are rounded. Proximal boxes should only be extended above the contact points and internal walls should be

Figure 2. (a): Traumatised maxillary central incisors; (b and c): radiograph showing crown fracture involving the pulp and root canal treatment was needed; (d and e): ceramic veneer for UR1; and (f): direct composite restoration for UL1

Figure 1. (a): A discoloured maxillary left central incisor due to trauma following internal bleaching; (b): an aesthetically improved result was obtained without the need for a cosmetic restoration

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B C

D E

F

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Metal-ceramic crownsCuspal coverage is required where tooth structure loss is more than that associated with an access cavity. Metalceramic crowns are most extensively used for restoring posterior teeth and as bridge abutments. Unfortunately, a disadvantage is that heavy tooth reduction is necessary to create sufficient room for provision of metal-ceramic crowns.

PostsIndications for postsIn the restoration of endodontically treated teeth, the placement of a post is generally

suggested if the amount of residual tooth structure is not sufficient to support a core made of a plastic material (amalgam or composite). The idea that the placement of a post does not reinforce a tooth is indeed very popular and remains debatable. The placement of a fibre-reinforced composite post would seem to protect against failure, especially under conditions of extensive coronal destruction; the most common type of failure with fibre-reinforced composite posts is debonding (Cagidiaco et al, 2008).

The number of variables involved in designing clinical studies on the restoration

of endodontically treated teeth does not allow for its application to all teeth. The available evidences do not rule out the use of cast posts; however, since the use of cast posts may result in a significantly greater loss of tooth structure compared to fibre posts (Ikram et al, 2009), their use should be limited to those cases in which no additional dentine has to be removed to allow for their cementation.

Length of postsThe length of the post classically assumed to be ideal is when it reaches two-thirds the length of the root (Figure6). Unfortunately, most roots have curvatures that begin far more coronally; therefore, this rule cannot be applied in many cases. In conclusion, a post that is longer than the clinical crown of the tooth is advisable to limit the chance of decementation and root fracture.

Ideal properties of post/coresThe ideal properties of post/cores include:n Adequate compressive strengthn Strong enough to prevent flexion of the core during parafunctional movement

n Resistance to leakage of oral fluids at the core/tooth interface

n Ease of manipulationn Ability to bond to the remaining tooth structure.Although not ideal, composite resins

have the majority of these properties and are the material of choice as both post and core materials. As a core build-up material, composite resin may be bonded to the remaining tooth structure using dentine adhesives.

The ferrule effectA ferrule effect may be defined as the envelopment of the tooth structure by a crown. The ability to obtain a ferrule effect is regarded as pivotal to the success of any extracoronal restoration, irrelevant of the core that has been placed. The ideal extent of a ferrule remains contentious, with the complete envelopment of at least 2.0 mm of coronal tooth tissue regarded as optimal (Tan et al, 2005). This should provide adequate resistance to the lateral

Figure 3. A broken down mandibular first molar. Following root canal treatment, the tooth was restored using a fibre post and composite core followed by a zirconia crown

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forces imparted on the restored tooth. Ideally, this ferrule should be continuous around the entire circumference of the tooth (Figure7).

Properties of fibre postsStudies have shown that the mechanical properties of carbon, glass and quartz fibre posts are substantially similar; for this reason, the more aesthetic glass and quartz fibre posts have now replaced carbon fibre posts (Mannocci et al, 2001). The modulus of elasticity of fibre posts is generally lower than that of metal posts but, nonetheless, it is three to four times higher than that of dentine (Tan et al, 2001). The main difference, in terms of mechanical properties between fibre and metal posts, is the loss of flexural strength. As a result of this, the mode of failure of fibre post restored teeth is unlikely to be root fracture but normally, decementation that may or may not be associated with the development of caries at the interface between the tooth and the restoration. The adhesion of the fibre posts to the composite core is mainly micromechanical. The irregularities on the surface of the post provide the retention for the bonding resin.

Clinical and technical aspects of fibre post restorationsTooth isolationAs with all clinical procedures that involve adhesive dentistry, the use of the rubber dam is preferred.

Removal of the gutta-percha and canal enlargementThis is easily carried out using Gates-Glidden or Largo drills (Figure8a). Heated instruments may also be used to remove gutta-percha root filling.

Removing temporary cement and sealer remnantsThe removal of temporary cement and any sealer remnants is easily accomplished with

purpose. Once the required size of post has been selected, it is advisable to try the post in the root canal (Figure8d).

Bonding systemsBoth three-step bonding systems and self-etching primers can be used for the cementation of fibre posts as the bond strength to root dentine achieved with these two types of bonding agents is similar.

the use of ultrasonic tips and preferably aided by magnification with an operating microscope (Figure8b).

Drying of the root canalThe canal needs to be dried before the application of the bonding system. Paper points (Figure8c) or a controlled stream of air from a Stropko irrigator (Vista Dental, Racine, WI, USA) may be used for this

Figure 4. A mandibular first molar with occlusal root caries penetrating into the pulp chamber. The tooth was restored with two separate composite resin fillings after completion of the root canal treatment; this restoration will form an ideal coreshould a crown be needed in the future. Radiograph following completion of endodontic and restorative treatment is shown in the last image

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The primer is applied on both the root dentine and the post. It is advisable to use a self or dual-curing resin. Microbrushes are needed to ensure a uniform distribution of the bonding agent into the depth of the root canal (Figure8e).

Composite resin cementConventional core or dual-cured composite resins are also preferred for the

cementation of the post. These materials have mechanical properties closer to that of dentine. Light-cured composite resins are too thick to be inserted properly into the root canal whereas flowable composite and composite resin cements have a much lower modulus of elasticity and may, therefore, be the weakest part of the restoration.

Insertion of composite resinTo minimise void formation within the composite resin in the canal, it should be injected using a syringe with a special tip specifically designed for this purpose. The composite resin is injected into the canal starting from the bottom of the post space until it is completely filled.

Ultrasound transmitted via a tip placed in contact with the syringe may help ensure a more uniform distribution of the composite resin into the root canal (Figure8f).

Insertion of the postThe post is simply inserted into the root canal. There is no need to place composite resin onto the post itself.

Composite resin core build-upThe composite resin core is created immediately using the same self-curing material. A light-cured composite resin may also be used to complete the core build-up (Figure 8g), following which, crown preparation can be carried out at the same visit.

ConclusionA new approach to the restoration of endodontically treated teeth has been prompted by the introduction of fber-reinforced composite (FRC) posts. The survival of root-treated teeth has been

Figure 5. Maxillary second premolar and first molar requiring root canal treatment. Preoperative and postoperative radiographs. Since there is still a considerable amount of residual tooth structure left, both teeth were restored with composite onlays. Radiograph after completion of endodontic and restorative treatment; the composite resin onlays are radiolucent, hence not obvious radiologically

Key Pointsnthe choice of restoration for an endodontically treated tooth is dependent on the amount of coronal tooth tissue left.

nthe placement of a fibre-reinforced composite post would seem to protect against failure, especially under conditions of extensive coronal destruction.

n it is important to conserve a ferrule of sound dentine to increase the tooths resistance.

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assessed in several clinical studies.Variables such as tooth type and

position within the dental arch in relation to the occlusal forces, the presence of proximal contacts, and the type of the final restoration has been found to have an effect on the longevity of root-treated teeth. Additionally, the amount of coronal residual structure has been recognised as critical to the survival. In particular, the contribution to increase mechanical properties is to conserve a ferrule of sound dentine to increase the tooths resistance. The ferrule must be at least 2 mm in width. DN

Cagidiaco MC, Goracci C, Garcia-Godoy F, Ferrari M (2008) Clinical studies of fiber posts: a literature review. Int J Prosthodont 21: 32836

Hansen EK, Asmussen E, Christansen NC (1990)

Figure 6. The lenght of the post ideally when it reaches 2/3 the length of the root

Figure 7. The ideal ferrule should be continuous around the tooth at least 2.0 mm in width

Figures 8af. The ideal ferrule should be continuous around the tooth at least 2.0 mm in width

In vivo fractures of endodontically treated posterior teeth restored with amalgam. Endod Dent Traumatol 6(2): 4955

Ikram OH, Patel S, Sauro S, Mannocci F (2009) Micro-computed tomography of tooth tissue volume changes following endodontic procedures and post space preparation. Int Endod J 42(12): 10716

Mannocci F1, Sherriff M, Watson TF (2001) Three point bending test of fiber posts. J Endod 27(12): 75861

Tan PL1, Aquilino SA, Gratton DG et al (2005) In vitro fracture resistance of endodontically treated central incisors with varying ferrule heights and configurations. J Prosthet Dent 93(4): 3316

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