Contemporary Restoration of Endodontically Treated Teeth. Nadim Z. Baba
laboratory research, provide an interpretation of those research results, and then offer clinical guidelines to aid development of the best possible treatment plan for endodontically treated teeth (ETT). Varying levels of clinical and laboratory data are available in support of clinical guidelines. Therefore, a number of these key variables will be presented and discussed in this chapter to aid clinicians in arriving at the best treatment plan for each endodontic situation.
Tooth Fracture and Survival
For decades, practitioners have recognized a difference between vital teeth and ETT. In fact, more than half a century ago, Healey wrote that, “the remaining coronal portion of the treated pulpless tooth quite apparently is more brittle or fragile than when it contained a vital pulp.”2 Healey’s perception was accompanied by another observation. ETT have a greater tendency to fracture during extraction and, therefore, are more likely to be removed in pieces than as intact teeth.2
Another clinical perception about ETT is that they do not have the same longevity as vital teeth. Case in point, fixed partial dentures are more likely to fail if the abutment teeth are nonvital.3–7 Moreover, when posterior ETT are not restored with a crown, they have been found to fracture more often than vital teeth.8 These perceptions have emerged from reports based on both clinical and laboratory research and now are sufficiently well recognized to guide clinical decisions.
Tooth fracture
A 1999 study by Chan et al9 involving 315 teeth with vertical root fractures over a 13-year period determined that 60% of those fractures occurred in ETT while 40% occurred in vital teeth. Furthermore, the incidence of fracture in both nonvital teeth and vital teeth was 1.4 times higher in male than in female patients. Vertical fractures occurred more frequently in first molars for both vital and nonvital teeth.
Among ETT, the fracture rate of mandibular first molars was more than twice that of maxillary first molars, maxillary second molars, and maxillary first and second premolars. In molars that received endodontic treatment, the roots most likely to fracture were the mesiobuccal roots of maxillary molars and the mesial roots of mandibular molars.9 Interestingly, nonvital canines were the teeth least susceptible to fracture. A subsequent survey of cusp fractures in general dental practices found that teeth with a history of endodontic treatment were susceptible to subgingival fracture in unfavorable locations.10
Tooth survival
Clinical evidence also is available to support the perception that ETT have a lower survival rate than their vital counterparts. According to a 1992 Swedish study assessing the reasons for tooth extraction among 200 patients, ETT were lost more often than vital teeth.11
A subsequent retrospective study of 202 nonvital teeth by Caplan et al12 compared the survival of ETT with their contralateral counterparts after a median time of 6.7 years. Of the 202 matched pairs, 16% were anterior teeth, 41% were premolars, and 44% were molars. For all types of teeth, those that were endodontically treated were three times more likely to be extracted then their vital, contralateral counterparts. Of particular note, molars that received endodontic therapy were seven times more likely to be extracted than endodontically treated premolars and anterior teeth.12
Presence or absence of proximal contact
The survival of ETT has even been correlated to the presence or absence of proximal contact. Analysis of data from multiple studies determined that ETT with two proximal contacts had significantly longer survival rates than teeth with one or no proximal contacts.8, 13 In a review of charts, radiographs, and computer databases of 400 teeth from 280 patients, it was determined that ETT with two proximal contacts had substantially better survival than teeth with fewer than two proximal contacts.13
A meta-analysis of 14 clinical studies also identified ETT with both mesial and distal proximal contacts as having an increased rate of survival.14 In addition, a 4-year, cumulative tooth survival analysis of 759 teeth with primary root canal treatment and 858 teeth with secondary root canal treatment (retreatment) determined that teeth with two proximal contacts had a 50% lower risk of being lost than teeth with one or no proximal contact. Terminal teeth in the arch were associated with almost a 96% higher risk of loss than teeth that were not the distalmost tooth in the arch.15 Furthermore, second molars had an appreciably poorer 10-year survival rate than all other types of teeth.8
Fixed partial denture survival rates
As mentioned previously, multiple clinical studies, some dating back more than a quarter of a century, have shown that fixed partial dentures fail more often when supported by endodontically treated abutment teeth than when they are supported by vital abutment teeth.3–7 One clinical study compared single crowns and fixed partial dentures over a 16- to 20-year period. It was reported that the long-term survival rates of three-unit fixed partial dentures on vital teeth were comparable to those of fixed partial dentures with at least one endodontically treated retainer. However, fixed partial dentures with more than three units and those with cantilevered units had significantly more failures.16
Restoration Selection for Pulpless Posterior Teeth
There is a substantial body of evidence to indicate that endodontically treated posterior teeth are likely to fracture unless they are restored with a complete-coverage crown. In some instances, the resulting fractures are so significant as to result in tooth loss. According to a 20-year, retrospective study of 1,639 posterior teeth restored with amalgam but without cuspal coverage, maxillary premolars (with mesio-occlusodistal [MOD] amalgam restorations) had the highest fracture rates. In fact, 28% of the maxillary premolars fractured within 3 years of endodontic therapy, 57% fractured after 10 years, and 73% fractured after 20 years, in the absence of some type of complete crown.17
Tooth fracture rates
Of all the teeth that fractured in the 20-year study cited above,17 4% experienced catastrophic vertical fractures. Within that 4% of fractured teeth, the maxillary second molars accounted for 34.5% (10 of 29 fractures) of the teeth requiring extraction. In another study involving 220 molars followed for as few as 6 months and as long as 10 years, there were a total of 101 failures due to caries, cracks in the tooth or the restoration, loss of the restoration, or root fracture. Of these 101 teeth, 14 (13.9%) were judged to be nonrestorable. However, teeth with maximal tooth structure, mirroring that of a Class I restoration with at least 2.0 mm of surrounding axial wall thickness, had the highest 5-year survival rate (78%).18
An even larger study of 837 endodontically treated posterior teeth, with and without coronal-coverage restorations, reported a significant increase in clinical longevity when cuspal-coverage crowns were provided on maxillary and mandibular premolars and molars. The maxillary premolars experienced only a 6% failure rate when crowns were present, while the failure rate for premolars that did not receive a cuspal-coverage cast restoration was 44%. Similarly, maxillary molars restored with crowns had a 2% failure rate, while molars that were not restored with a crown had a 50% failure rate.
Similar outcomes were noted in mandibular premolars. One study reported a 6% failure rate when crowns were present but a 38% failure rate for ETT without crowns. For mandibular molars, the failure rate was only 3% for ETT with crowns but 42% for ETT without crowns.19
Large-scale data analysis
When examining the results of initial endodontic treatment in 1,462,936 teeth, researchers found that 97% of teeth were retained in the oral cavity 8 years after the initial nonsurgical endodontic treatment.20 Although the percentage of tooth loss was small, 41,973 teeth were actually extracted during this observation period, of which 85%, or 35,697 teeth, did not have complete-coverage crowns. There was a statistically significant difference (P < .001) between teeth with crowns and those without crowns for all types of teeth. In fact, the number of nonvital premolars without crowns that required extraction was 5.8 times higher than that of premolars restored with crowns. In the case of nonvital molars, the number of teeth without crowns that required extraction was 6.2 times higher than the number extracted when molars were protected by complete crowns.20
An analysis