Q U I N T E S S E N C E I N T E R N AT I O N A L

ENDODONTICS

Richard D. Trushkowsky

Restoration of endodontically treated teeth: Criteria and technique considerations Richard D. Trushkowsky, DDS1 The restoration of endodontically treated teeth is often required and may represent a challenge as there is no consensus on ideal treatment. The failure of endodontically treated teeth is usually not a consequence of endodontic treatment, but inadequate restorative therapy or periodontal reasons. Prior to the initiation of endodontic treatment the restorability, occlusal function, periodontal health, biologic width, and crown-to-root ratio need to be assessed. If acceptable, the appropriate technique, material, and type of restoration to re-

store function need to be considered. Posts are used to provide retention for the core material and to replace missing tooth structure. The residual amount of tooth structure will determine its stability for restoration. The creation of adequate ferrule (approaching 2 mm circumferentially is ideal) minimizes the damaging effects of lateral and rotational forces on the restoration and post. (Quintessence Int 2014;45:557–567; doi: 10.3290/j.qi.a31964)

Key words: core, endodontically treated tooth, post

Caries and trauma are the most frequent causes of irreversible pulp damage resulting in root canal therapy. The restoration of these endodontically treated teeth is often required and may represent a challenge as there is no consensus on ideal treatment. However, endodontically treated teeth have been reported to have a reduced survival rate compared to vital teeth.1 The failure of endodontically treated teeth is usually not a consequence of endodontic treatment, but inadequate restorative therapy or periodontal reasons.2 Excessive removal of tooth structure during mechanical instrumentation of the root canal system, mechanical pressures during obturation, lack of cuspal protection, and large restorations can 1

Clinical Associate Professor, Associate Director, The Advanced Program for International Dentists in Esthetic Dentistry, New York University College of Dentistry, New York, USA.

Correspondence: Dr Richard D. Trushkowsky, The Advanced Program for International Dentists in Esthetic Dentistry, New York University College of Dentistry, 345 E 24th St, New York, NY 10010, USA. Email: rt587@ nyu.edu

VOLUME 45 • NUMBER 7 • JULY / AUGUST 2014

weaken the tooth. The prognosis of endodontically treated teeth is contingent not only on apical seal but also on the coronal sealing of the canal thereby reducing leakage of oral fluids and bacteria into the periradicular areas (Fig 1).3 The neurosensory response apparatus is impaired with the removal of the pulpal tissue, which may result in decreased protection of the endodontically

bacteria

Fig 1 The coronal seal is important to prevent microleakage. Decementation and micromovement produce microleakage. Where there is presumed shrinkage, the bacteria can infiltrate, causing secondary decay.

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treated tooth during mastication.4 Prior to the initiation of endodontic treatment the restorability, occlusal function, periodontal health, biologic width, and crown-toroot ratio need to be assessed. If acceptable, the appropriate technique, material, and type of restoration to restore function need to be considered.5 An ideal permanent restoration should restore esthetics and function, and protect the endodontically weakened tooth.6



Class V teeth have no remaining walls, and a post will be required to provide retention for core material. A ferrule, which is characterized by a 360-degree metal crown collar surrounding parallel walls of dentin and extending coronal to the shoulder of the preparation, would greatly increase the fracture resistance of the tooth.14 If a ferrule cannot be obtained, surgical crown lengthening or forced eruption may be required.

INDICATIONS FOR A POST The indications for a post have been modified in recent years based on the advantages of adhesive restorations, which may obviate the need for posts.7 Posts are used to provide retention for the core material and to replace missing tooth structure. The residual amount of tooth structure will determine its stability for restoration. Preparation for pulpal access diminishes mechanical strength by about 5%, but a mesio-occlusal-distal (MOD) cavity will result in a 63% reduction in strength.7 The importance of the marginal ridge was specified by Strand et al.8 The loss of tooth vitality does not result in a substantial change in moisture content compared to vital teeth.9 Unfortunately, the degree of remaining tooth structure left to require a post has not been delineated. Preoz et al7 established five classes depending on the number of axial cavity walls remaining: • Class 1 teeth have four remaining cavity walls, with a thickness greater than 1 mm. In this case, it was felt a post is not necessary and any final restoration can be utilized.10 • Class II and Class III have two or three remaining cavity walls. These teeth can possibly be restored without a post. The use of an adhesive core can provide adequate fracture resistance without the need for a post.11 • Class IV teeth have one remaining wall, and the core material will provide minimal or no effect on the fracture resistance of the endodontically treated tooth.12 The use of the tooth as an abutment for a fixed or removable partial denture will result in reduced fracture resistance as a consequence of crown preparation.13

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INDICATIONS FOR A CROWN Baba and Goodacre15 suggest that most endodontically treated posterior teeth require a crown for longevity. However, although crowns improve the success of posterior teeth, this was not demonstrated for anterior teeth.16 Anterior teeth with minimal loss of tooth structure can be conservatively restored with composite in the lingual access opening and no post.17 A post provides minimal or no benefit for a structurally sound tooth.18 Many classical indications for the use of a crown have also been questioned.19 Unfortunately, the literature is equivocal as to the requirement for full coverage, although cuspal coverage is often recommended. Rocca and Krejci20 report that currently available adhesive techniques permit the use of direct composites and an endocrown (a circular butt-joint margin and a central retention cavity inside the pulp chamber, lacking intraradicular anchorage). The basis of this technique is to use the surface available in the pulpal chamber to assume the stability and retention of the restoration through adhesive procedures. The endocrowns provide full occlusal coverage and the use of the pulp chamber increases the available surfaces for adhesion. A variety of materials can be used including feldspathic porcelain, glass ceramic (eg, IPS e.max, Ivoclar Vivadent), or CAD/CAM blocks of either ceramic or composite or combinations of the two (Lava Ultimate Restorative, 3M ESPE). Molars can more readily be utilized in this fashion. Premolars are more in danger if canine guidance is absent as group function may permit a combination of both axial and shear forces on the premolar cusps.

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Q U I N T E S S E N C E I N T E R N AT I O N A L Trushkowsky

Fig 2

Fig 3

A wide variety of post shapes and materials is available.

An anatomic glass fiber post conforms to the root shape.

DESIGN AND TYPE OF POSTS Posts can be active (most retentive, eg, ParaPost XT, Coltène Whaledent; Flexipost, Essential Dental Systems), passive parallel or passive tapered (least retentive, eg, ParaPost Taper Lux, Coltène Whaledent), double tapered (DT Light-Post Illusion X-RO, Bisco), or parallel tapered (TENAX® Fiber White, Coltène Whaledent; ParaPostXP No-Ox, Coltène Whaledent). Regarding post shape, parallel-sided posts provide better retention, less stress formation, and increased fracture resistance than tapered posts.21 Regarding surface design, serrated posts provide better retention than smooth-sided posts, and threaded posts provide even better retention (Fig 2).22 An increase in post length has also been shown to be beneficial, but an apical seal of approximately 5 mm of gutta-percha is required.23 Excessive length can also become detrimental as the dentin in the apical third is very thin and perforation or increasing root fracture can become a possibility. The length of custom metal posts is usually recommended as two-thirds to three-quarters

VOLUME 45 • NUMBER 7 • JULY / AUGUST 2014

Fig 4 A glass fiber post provides a degree of light conduction into the canal and allows more complete polymerization. (Courtesy of Coltène Whaledent.)

of root length, and equal to or more than the length of the crown to be fabricated.24 Posts can be metallic (either custom cast posts or prefabricated) or fiber (custom [Fig 3] or prefabricated). Since their introduction in 1990,25 fiber posts have changed in shape and mechanical physical properties. Initially the posts were quartz or carbon fiber but now most are glass fibers, possessing a translucency that makes an esthetic restoration more easily obtainable. They also allow some degree of light transmission so that dual-cure cement can be used (Fig 4),26 as the translucency helps to provide adequate polymerization of dual-cure cements. However, the light intensity at the apical portion may be inadequate because of the distance from the light source and the light-scattering nature of the resin cement and the post. The quantity of light that is absorbed, reflected, and transmitted seems to be related to the resin matrix, the fiber composition of each post, and the intensity of the light source.27 Post shapes have been modified from a retentive shape to cylindrical or oval, which is more anatomical. Posts of this type provide better adaptation and remove less remaining root dentin.28

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Fractured Post and Crown

Fractured root

Fractured Post and Crown

Vector of Force

Fractured root

Vector of Force Vector of Force

a

Vector of Force b

Figs 5a and 5b Failure can be more catastrophic with a metal post than a glass fiber post. (a) Potential fracture location with glass fiber–reinforced composite posts. (b) Potential fracture location with metal posts.

parallel post space

1+ mm

1+ mm

Teeth restored with metal posts many times fail catastrophically with root fracture (Fig 5). The most frequent cause of failure in teeth reconstructed with fiber posts is not root fracture but debonding of the post, which can occur at the post-cement interface and/or between cement and root dentin.29 Boschian et al30 underscored the effect of elastic modulus of the post material on stresses transferred to tooth structures as an important factor. They reported that post materials that have a higher elastic modulus than dentin are capable of causing dangerous and nonhomogenous stresses in root dentin. The authors concluded that the arrangement that best preserves the integrity of the root, post, and core unit is when fiber posts are used for restoration. Unlike cast posts, post

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narrow walls

Restoration of endodontically treated teeth: criteria and technique considerations.

The restoration of endodontically treated teeth is often required and may represent a challenge as there is no consensus on ideal treatment. The failu...
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