Of the 986 teeth, 128 were not examined but included in the data set, for they had been reviewed on at least one occasion more than 4 years postoperatively; 282 teeth were examined at the recall and 198 teeth had been documented to have failed from the records. Thus, the data set contained a total of 608 teeth. The median survival time of these treated teeth was 111months (Fig. 2). On closer examination of the overall survival curve (Fig. 2), an initial fast drop, which then slowed down after approximately18months, could be identified.
Of the teeth examined, none was associated with any clinical symptoms. One hundred and sixteen teeth were deemed to have failed, for a total number of failure of 314 teeth (52%) (Table 3). The majority of the failures occurred within the first 3 years after obturation, with a mean ‘life span’ of 39 months (SD = 39), median 26.5 months (Fig. 3). Teeth with no preoperative periapical lesion had a significantly better survival outcome after root canal treatment compared to those with a periapical lesion or widened periodontal ligament (Table 2; Fig. 4). Maxillary and mandibular molars and maxillary premolars had a significantly lower survival probability than maxillary and mandibular anteriors and mandibular premolars (Table 2; Fig. 5). Teeth restored with crowns survived significantly longer than those with intracoronal plastic restorations only (Table 2; Fig. 6). The use of an all-amalgam postcore or prefabricated post was associated with a significantly higher survival probability than no post or using a cast post (Table 2; Fig.7). Although the medicament used was found to be significant in the initial analysis (P = 0.047), it became an insignificant factor when all single-visit cases were excluded (Table 2).The preoperative periapical status, tooth type, type of post and the final restoration remained significant.

Figure 2. Overall cumulative survival probability, with 95% confidence interval, for all teeth included in the analysis (N = 608).



Table 3. Observed or documented reasons for failures up to the documented date of failure or the recall.



Figure 3. Incidence of failures (n = 314) with time.



Figure 4. Survival curve as a function of the preoperative periapical status (result after Cox Regression analysis and plotted at mean of other covariables).



Figure 5. Survival curve as a function of the tooth type (result after Cox Regression analysis and plotted at mean of other covariables).



Figure 6. Survival curve as a function of the type of coronal restoration (result after Cox Regression analysis and plotted at mean of other covariables).



Figure 7. Survival curve as a function of the type of post used (result after Cox Regression analysis and plotted at mean of other covariables).