Endodontic treatment outcome: effect of the permanent restoration.

Objective: To investigate the relationship between the presence of the coronal restoration and endodontic treatment success or failure.

Methods: This study comprised 200 endodontically treated teeth with 441 roots. Follow-up examination was conducted 4 +/- 0.5 years after completion of endodontic treatment. Outcome criteria were modified from Strindberg.

Results: Teeth/roots restored with permanent coronal restoration (casting or filling) had a higher success rate (80%) than teeth/roots not restored (60%; P < .01) in the analysis of aggregate data. However, the results of stratified analysis on key confounding factor (preoperative periapical diagnosis) showed that there is no significant association between the presence of permanent restoration and endodontic outcome. Teeth with preoperative apical periodontitis were less likely to be restored with a crown (23.9%) than teeth without apical periodontitis (76.1%; P < .01). Anterior teeth were more likely to be restored with a filling and sooner than the posterior teeth. These associations suggest a treatment selection bias.

Conclusions: Stratified analysis on the key confounding factor reveals that endodontic outcome is driven by the presence of preoperative root canal infection (apical periodontitis). Lack of stratification on key confounding factors inaccurately suggests that presence of permanent restoration contributes to the success of endodontic treatment in the aggregate analysis of grouped data. The choice to restore the tooth as well as the choice and timing of permanent restoration may be the result of a bias in treatment selection. Stratified analysis on key confounding factors is the key to valid analysis and accurate results.