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 »  Home  »  Endodontic Articles 3  »  Relationship between number of proximal contacts and survival of root canal treated teeth
Relationship between number of proximal contacts and survival of root canal treated teeth
Discussion - References.



This hypothesis-testing study aimed to determine whether survival of RCT teeth was influenced by the number of PCs at access. Results are consistent with the previous investigation linking fewer PCs at access with loss of RCT teeth (Caplan & Weintraub 1997). Several explanations for this association are plausible. First, adjacent teeth help distribute occlusal forces over a wider span, potentially reducing the probability of tooth fracture. Secondly, RCT teeth adjacent to an edentulous space are more likely to serve as removable partial denture abutments, which may provide additional mechanical stress. Thirdly, patients with existing edentulous spaces may have a greater history of oral disease, place lesser value on keeping their teeth, or have more financial limitations than other patients, and thus may be less interested in saving a compromised RCT tooth. Previous tooth loss has been shown to predict future tooth loss (Burt et al. 1990, Eklund & Burt 1994), but these studies have not considered the endodontic status of the extracted teeth. One study that did consider endodontic status (Caplan & Weintraub 1997) reported a statistically significant relationship between previous tooth loss and loss of RCT teeth.
The goal of the present analysis was to ascertain the least biased estimate of the association between number of PCs at access and tooth survival. Thus, the enhanced survival of teeth with crowns should not imply that RCT teeth will have better survival if crowns are placed after obturation because the multivariate models did not necessarily include factors that might be related to crown placement. The decision not to crown an RCT tooth might depend on the tooth’s expected life span, e.g. providers may choose a less involved, less expensive restoration because of poor periodontal health. Nevertheless, better survival amongst teeth crowned after obturation is reasonable, since:

  1. the tooth’s endodontic landmarks would be preserved at access (reducing the probability of perforation);
  2. root canal treatment must have been considered ‘predictably successful enough’ to warrant crown placement;
  3. the RCT tooth would be protected from propagation of existing fractures;
  4. patients electing to crown a newly RCT tooth might be more dentally educated or financially secure, characteristics associated with tooth survival.

Also intuitive is poorer survival amongst second molars (Table 5), which generally are considered more difficult to treat endodontically due to anatomy and compromised visibility and access. They are more difficult to retreat and might be extracted more frequently, especially if non-functional or in a nonaesthetic area. Molars tend to be extracted more frequently than other teeth (Marcus et al. 1996, Hujoel et al. 1998); a 45-year study of Norwegian men found the mortality rate of second molars to be 1.9 times higher than that of first molars (Hujoel et al. 1998).
The increased mortality amongst RCT teeth with radiographic evidence of caries at access is not surprising. These teeth as a group might be expected to have less sound tooth structure than non-carious teeth, especially interproximally and toward the root surfaces. Further, their periodontal condition might well be worse due to carious extension. One would expect these features to be associated with subsequent tooth loss regardless of endodontic status.
Endodontic success has been addressed previously, and generally is determined using a combination of clinical and radiographic evaluation (Safavi et al. 1987, Sjögren et al. 1990, Smith et al. 1993, Ray & Trope 1995). However, endodontic success may or may not be correlated with tooth loss. RCT teeth can be lost for nonendodontic reasons such as periodontal disease and nonrestorable fracture, whilst many teeth considered to be endodontic failures are not extracted. Loss of RCT teeth, whilst not necessarily related to endodontic failure, may represent a more meaningful outcome to patients, especially if the decision to undergo endodontic therapy was based on expected tooth longevity.
As with all retrospective studies, data quality was dependent upon the accuracy and consistency of existing information. Certain variables likely related to tooth loss were unavailable, such as patients’ socio-economic status (SES). We chose not to estimate the degree of bone loss from periapical radiographs, since films were not standardized in terms of angulation. Also, most RCT teeth presumably had good periodontal support at access or they probably would have been extracted rather than endodontically treated.
The findings are generalizable to other patient populations, but with certain caveats. First, the sample included only patients with at least one dental visit every 2 years during an interval of 10–12 years. This restriction aimed to provide a sample whose dental services during followup were provided solely at the COD. In insured populations, continuous enrollment might serve this purpose (Caplan & Weintraub 1997), but regardless of the research setting, dental treatment might have been obtained elsewhere. Further, the study design did not permit direct assessment of patients’ motivation for maintaining a healthy dentition. However, restricting the sample to those patients with consistent utilization of dental services could be considered a proxy variable for ‘high level of dental education’. A relatively high level of motivation is assumed because the sample included only individuals who presumably elected to save their teeth via root canal treatment rather than opt for extraction.
The study population was treated at one university dental school. These patients might receive different procedures than they would in other settings due to varying philosophies of care and school requirements of students. Additionally, many patients undoubtedly seek treatment at the COD because of reduced fees, and thus may have a lower SES. This would affect our study’s primary conclusion only if the relationship between the number of PCs and tooth survival were influenced by SES, which is not likely; the observed adjusted HR of 3.1 is consistent with the odds ratio of 2.7 found in a group of dentally insured patients (Caplan & Weintraub 1997).
Finally, the sample was restricted to teeth undergoing initial root canal treatment because retreated teeth might have a systematically different survival experience. Survival of retreated teeth might be worse, considering that they already have failed or were destined to fail, which could be associated with future loss. In contrast, survival of retreated teeth might be better, since these patients probably represent a more motivated or higher SES group. The present bivariate analysis supports the latter concept. Of the 221 teeth undergoing initial root canal therapy, 13% subsequently underwent nonsurgical retreatment, root-end resection (apicoectomy), or root resection (root amputation) during the follow-up period; these teeth had better survival than those not subsequently retreated (Table 3).

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