Contemporary Restoration of Endodontically Treated Teeth. Nadim Z. Baba
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from multiple studies has demonstrated that ETT without crowns were lost at six times the rate of teeth with crowns.7 In a systematic review of single crowns on endodontically treated teeth, the 10-year survival of teeth with crowns was 81%, whereas the 10-year survival of ETT restored with a direct restoration (composite resin, amalgam, or cement) was 63%.21 A meta-analysis involving 14 clinical studies determined that crown placement on ETT increased tooth survival.9 The results of a recent 4-year cumulative tooth survival analysis, after primary and secondary root canal treatments, indicated a reduction in tooth loss by approximately 60% when ETT were restored with a cast restoration.10 Maxillary premolars and mandibular molars had the highest frequency of extraction due to tooth fracture.10
Time until failure
The time interval until failure and tooth loss also has been assessed for ETT with and without complete crowns. Those teeth without crowns failed after an average period of 50 months while pulpless teeth restored with a complete crown were lost after an average of 87 months following placement of a complete cast restoration.22
In contrast, a shorter, 3-year investigation found comparable success rates between endodontically treated premolars restored with only a post and direct Class II composite resin restoration and premolars restored with complete-coverage crowns.23 Similarly, a retrospective cohort study18 indicated that endodontically treated molars, intact except for the endodontic access opening, were successfully restored using composite resin restorations. Interestingly, composite resin restorations had better clinical performance than dental amalgam restorations. The 2-year probability of survival of molars restored with composite resin restorations was 90% versus 77% for amalgam restorations. At the 5-year point, the survival probability declined markedly for both restorative materials, to 38% for composite resin and 17% for dental amalgam restorations.18
Interestingly, clinical studies and other laboratory investigations mentioned previously reported positive results when composite resin restorations were used to restore ETT. In fact, these results support the use of composite resin rather than a cuspal-coverage crown when the tooth is intact except for the endodontic access opening or is minimally restored. Unfortunately, there are no long-term clinical data comparing the survival of pulpless posterior teeth with composite resin restorations to that of teeth restored with complete crowns that vary in terms of the amount of the remaining tooth structure. It would be helpful if there were studies comparing the survival rates of premolar and molar teeth restored without crowns with the following conditions: (1) intact except for a conservative endodontic access opening; (2) a Class I restoration and an access opening; (3) a small Class II restoration and an access opening; (4) a large Class II restoration; and (5) a large MOD restoration.
Additionally, normal occlusal forces place substantial stresses on teeth.24 These same stresses can cause vertical fractures in both nonvital and vital teeth.3 It also has been reported that parafunctional habits produce higher failure rates for fiber posts restored with composite resin.25 Therefore, the effects of heavier-than-normal occlusal forces, as well as parafunctional habits, on ETT restored without crowns should be examined more extensively to determine their impact on tooth survivability.
Complex amalgam restorations versus complete crowns
Aside from complete crowns, complex amalgam restorations also have been used to restore both vital and nonvital teeth. In these cases, an evaluation of the remaining tooth structure should be made to determine whether to replace or cover (“cap”) weakened cusps with dental amalgam restorative material.
In one randomized, controlled clinical trial, vital teeth were carefully evaluated for cusp strength. Weak cusps were reduced, and an 88% survival rate was reported for the 268 teeth receiving extensive amalgam restorations after a 100-month period. Forty of the 268 restorations (14.9%) required some form of clinical treatment during the study to secure or increase their clinical lifetime, resulting in a 72% survival rate.26 A retrospective study of 128 vital teeth with complex amalgam restorations, described by the authors as posterior restorations replacing one or more cusps, included a time-life survival analysis. In that report, the percentage of restorations surviving for 10 years was 54%, but that amount declined to 36% after 15 years and only 19% after 20 years.27 In another study of 124 cusp-covered Class II amalgam restorations, the cumulative survival rate was 72% after 15 years.28
When amalgam restorations were placed in nonvital teeth, positive results also were reported in both laboratory and clinical studies, provided that a sufficient thickness of amalgam covered the cusps. In one laboratory study, 48 teeth were restored with mesio-occlusal (MO) restorations with a 4.0-mm thickness protecting the buccal cusps and 3.0 mm of amalgam over the lingual cusps.29 When an angular load was applied to the restored cusps, the authors concluded that amalgam was a suitable material for cuspal restoration of pulpless teeth.29 In another laboratory study of 36 extracted, intact mandibular molars, endodontic access openings were placed in the teeth, and the root canals were instrumented as they would be clinically to initiate endodontic therapy. The teeth were then prepared and restored with either MO or MOD amalgam restorations, with and without cuspal coverage. Specimens receiving amalgam coverage of the entire occlusal surface, with at least 2.0 mm of the cuspal coverage, retained their cuspal stiffness.30 However, without cuspal coverage, teeth with conventional Class II MO and MOD amalgam restorations were not considered adequately protected.30
One clinical study of 100 pulpless teeth, restored with amalgam overlying the cusps, found that the amalgam restorations were successful after 3 years of service.31 The results of another investigation included a recommendation that all cusps adjacent to teeth with missing marginal ridges be covered (“capped”) with a sufficient thickness of amalgam.32
Restoration Selection for Pulpless Anterior Teeth
One of the most misunderstood and perhaps challenging clinical decisions has to do with how to manage anterior teeth following root canal therapy. There is a clinical perception that endodontically treated anterior teeth without crowns are less prone to fracture than posterior teeth.19 A study of 1,273 ETT conducted more than 25 years ago found that crowns significantly increased the survival rate for posterior teeth, but the same outcome was not valid for anterior teeth.19
In this study, the maxillary premolar success rate for ETT increased from 56.0% when no coronal coverage was provided to 93.9% with coronal coverage. Maxillary molars exhibited similar results with the success rate increasing from 50.0% (no crown) to 97.8% (with coronal coverage). For maxillary anterior teeth, the success rate was 85.4% with no crown and 87.5% with a crown. For mandibular anterior teeth, the success rate was 94.4% with no crown and 97.5% with a crown. From these results it was concluded that intact pulpless anterior teeth, except for a conservative endodontic access opening, do not require complete crowns. The authors of this chapter suggest that the results of this study make it reasonable to restore pulpless anterior teeth with composite resin when they are intact except for the access opening; when they are weakened by large and/or multiple restorations; and when they require significant color or form changes that cannot be managed by some type of more conservative treatment.
Despite the findings of Sorenson and Martinoff,19 anterior teeth without crowns can indeed fail and require extraction, as was reported in the previously cited study of more than 1.4 million teeth.20 In that extensive investigation, 83% of the anterior teeth that were extracted had not received a crown, while 9.7% of the extracted teeth had crowns and posts and 7.3% of the extracted teeth had crowns but no posts.20 Thus, stronger evidence confirms that the longevity of endodontically treated anterior teeth is increased when they are restored with crowns, in contrast to the findings reported by Sorensen and Martinoff in 1984.19
Clinicians must carefully evaluate the amount of remaining coronal tooth structure in anterior teeth before deciding not to recommend complete coronal coverage. Additionally, as with posterior teeth, there are no tooth survival data comparing intact pulpless anterior teeth with similar teeth having small restorations and those with large restorations where substantial amounts of tooth structure are missing. Likewise, data regarding the impact of heavy occlusal