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Restoration of the Endodontically Treated Tooth This PEAK article is a special membership service from RCDSO. The goal of PEAK (Practice Enhancement and Knowledge) is to provide Ontario dentists with key articles on a wide range of clinical and non-clinical topics from dental literature around the world. PLEASE KEEP FOR FUTURE REFERENCE. Supplement to Dispatch February/March 2008 Dr. Dorothy McComb, BDS, MScD, FRCD(C) d e s k P D F S t u d i o T r i a l Endodontic treatment is largely perfo
  Restoration of theEndodontically Treated Tooth This PEAK article is a special membership service fromRCDSO. The goal of PEAK (Practice Enhancement and Knowledge) is to provide Ontario dentists with key articles on a wide range of clinical and non-clinical topics fromdental literature around the world. PLEASE KEEP FOR FUTURE REFERENCE. Supplement to Dispatch February/March 2008  Dr. Dorothy McComb, BDS, MScD, FRCD(C) deskP F Studio Trial  Endodontic treatment is largely performed on teethsignificantly affected by caries, multiple repeat restorations and/or fracture. Already structurally weakened, such teeth are often further weak ened by the endodontic procedures designed to prov ide optimal access and by the restorative proced ures necessary to rebuild the tooth. Loss of inhere nt dentinal fluid may also effect an alteration in toothproperties. It is therefore accepted that endodontically treated teeth are weaker and  tend tohave a lower lifetime prognosis. They requir e special considerations for the final restorati on,particularly where there has been extensive loss of tooth structure. The special needs involve ensuring both adequate retention for the final restorationand maximum resistance to tooth fracture.Together, and both equally important, retentionand resistance features for the final restorat ion are sometimes collectively termed anchorage. E nsuring optimal anchorage while maintaining adeq uate root strength for the particular clinical situationcan be challenging and the problems encountered have resulted in the development of many different materials and techniques. 2 Ensuring Continued Trust  ã  DISPATCH  ã FEBRUARY/MARCH 2008 Restoration of the Endodontically Treated Tooth Dr. Dorothy McComb, BDS, MScD, FRCD(C) Professor and Head, Restorative Dentistry Director of Compr ehensive Care ProgramFaculty of Dentistr  y, University of Toronto deskP F Studio Trial  Ensuring Continued Trust  ã  DISPATCH  ã FEBRUARY/MARCH 2008  3 Despite the abundance of literature on this topic, muchcontroversy and empiricism remains, particularly in thearea of post usage. Also, new concepts are being rapidly introduced that require further analysis before widespread acceptance can be recommended. Althoughdefinitive clinical research – particularly randomizedcontrolled clinical trials – is lacking in this area of dentistry, some sig nificant retrospective analyses of bothfailure and survival of endodontically treated teeth, as well as some key laboratory studies, have identified themajor factors that affect overall prognosis. Although thevast majority of in vitro studies have compared differenttypes of posts, core materials and luting cements, theseare considered of f ar less importance than the amountand quality of the remaining circumferential coronaltooth structure. 1,2 In a recent review, Morgano et al. havestated: “Although there are many new materials availablefor the restoration of pulpless teeth, the prognosis of these teeth relies primarily on the application of soundbiomechanical principles rather than on the materialsused for restorations.” 3 It is the purpose of this article to review currentprinciples for restoration of the endodontically treatedtooth, based on the best evidence available. MAINTAINING TOOTH VITALITY One of the major objectives of operative dentistry ismaintenance of tooth vitality. The concept of minimally invasive dentistry and the provision of well-sealed,quality restorations are necessary to reduce the negativeeffect of multiple repeat restorations leading to moreand more teeth receiving endodontic therapy.Recognition of the increased failure rate, susceptibility tofracture and reduced prognosis for the endodontically treated tooth leads to increased appreciation for thevalue of maintaining tooth vitality wherever possible.Localised pulp and tooth preservation techniques, as well as overall slowing down of the re-restoration cycle,cover a broad range of factors designed to maintaintooth vitality over a lifetime and include the following: ã Importance of caries risk assessment andmanagement of caries by patient-specificprevention. 4 ã Significance of the initial operative intervention,now reserved for active dentinal caries where noother more conservative management is possible. 5 ã Importance of operative and restoration quality  formaximum longevity and reduction in re-restorationfrequency. 6 ã Use of 2-stage deep caries management inappropriate cases to retain pulp vitality. 7 ã  Acceptance of effective repair techniques forisolated areas of disease, leakage or fracture in anotherwise sound restoration. 8 The high incidence of teeth currently receiving endodontic therapy has been recently noted in aprovocative article by Christenson 9 entitled “How to kill atooth.” While acknowledging that more patients areliving longer with heavily restored teeth, it was sugg estedthat some of the newer techniques and materialscommonly used today are a factor. Included wereposterior composites, resin bonded indirect restorations,and aggressively cut veneers or all-ceramic crowns.Optimal bonding procedures are critical for suchrestorations to prevent leakage leading to pulpalpathology and the technique-sensitivity of bonding materials and resin luting cements was also discussed.For practitioners experiencing patient post-operativesensitivity with total-etch bonding, the authorrecommended changing to the use of a 2-step self-etching primer and adhesive. Similarly, the use of self-etching resin cements was recommended for pulpalproblems associated with resin cements. A major priority is prevention of post-operative problems andmaintenance of pulpal health. Endodontically treated teeth are weakened due todecreased or altered tooth structure attributed to: ◆ caries and/or previous restorations ◆ fracture or trauma ◆ endodontic access and instrumentation ◆ decreased moisture The weakness is directly correlated to the quantityof lost dentine. deskP F Studio Trial  CUSP FRACTURE OF ENDODONTICALLYTREATED TEETH Cusp fracture is a common occurrence in the heavily restored dentition, but endodontically treated teeth withintra-coronal restorations are at higher risk and theoccurrence of unrestorable sub-gingival cusp fractures ismore common. 10-12 Using data from over 46,000 patientsfrom 28 dental practices, Fennis et al. found only 20.5cusp fractures per 1000 person years of risk. 13 However,there was a positiv e correlation between endodontically treated teeth and subgingival fracture location. Whereasrestoration of a fractured cusp on a posterior vital toothis relatively straightforward, cusp fracture of a non-vitaltooth is likely to be more catastrophic. Loss of strategicinternal architecture of the tooth leads to increased cuspdeflection during occlusal function. This is mostpronounced in endodontically treated bicuspids withMOD cavities and doubling the cavity depth increasesthe deflection by a factor of 8. 14 Cuspal deflection inmolars increases w ith increasing cavity size and isgreatest following endodontic access. 15  Anendodontically treated posterior tooth may have a cavity depth 3-4 times greater than a vital tooth – hence thesignificantly greater risk of fracture. (Figure 1) In a 20-year retrospective analysis of 1638endodontically treated posterior teeth restored withamalgam without cusp coverage, fracture was asignificant problem. 11 Maxillary bicuspids with MODrestorations showed the lowest survival rate overall (28%fractured within 3 years, 57% after 10 years and 73% after20 years). The most serious fractures were found for themaxillary second molar and accounted for the majority of the extractions due to vertical fracture. It wasconcluded that silver amalgam without cusp coverage was unsuitable for restoration of multiple surfaces of theendodontically treated tooth.Enamel-bonded MOD composite restorations inbicuspids have shown greater resistance to fracture thanamalgam restorations – but only up to 3 years 10 . After thistime period, the failure of resin-restored and amalg am-restored endodontically treated teeth was similar. Thelong-term effect of current-day bonded intra-coronalrestorations is largely unknown due to a lack of clinicalstudies on non-vital teeth. It is accepted that effectiv ecomposite bonding can restore some of the strength lostthrough cavity preparation, but the prognosis is guardedfor the endodontically treated tooth due to the higherstresses and expected progressive fatigue of the bonding mechanism. Short-term use of direct posteriorcomposites may be justified in selected situations.Bonded CAD/CAM ceramic inlays for endodonticall y treated teeth performed poorly in vitro, with a highnumber of severe tooth fractures, and should beavoided. 16 It is evident therefore that endodontically treatedposterior teeth with intra-coronal restorations show  ahigh risk of unrestorable cusp fracture. The use of crowns can significantly improve the success forposterior teeth. 12 FAILURE OF ENDODONTICALLY TREATED TEETH  Analysis of the reason for all extractions of endodontically treated teeth over a period of 1 year in abusy military clinic revealed that almost 60% of these were unrestorable tooth fractures, 32% involvedperiodontal problems and only 7% were endodonticfailures. 17 Failure can be due to less than optimalendodontic therapy but inadequate or unsuccessfulrestorative treatment is the major issue. Close to half of  4 Ensuring Continued Trust  ã  DISPATCH  ã FEBRUARY/MARCH 2008 Both sound and restored teeth may fracture butendodontically-treated teeth are at greater riskand require special considerations. Figure 1 Vertical tooth fracture of an endodontically treated maxillary molar restored with a bonded composite restoration. Restoration of the Endodontically Treated Tooth deskP F Studio Trial
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