A Prospective Study on the Effect of Coronal Tooth Structure Loss on the Survival of Root Canal-Retreated Posterior Teeth Restored With Metal Ceramic Crowns With up to 10-Year Follow-Up.

AIM: The primary aim of this study was to evaluate whether the volume of residual coronal tooth structure influences the survival of root canal-retreated posterior teeth with up to 10-year follow-up. Secondary aims were to assess whether 12-month radiographic findings and the Dental Practicality Index (DPI) could predict long-term survival. METHODOLOGY: A total of 156 posterior teeth in 140 patients underwent clinical examination, baseline CBCT and PA prior to retreatment in a postgraduate endodontic unit under specialist supervision. Residual coronal tooth volume was quantified using intraoral scans following the completion of root canal retreatment and before core build-up and placement of metal-ceramic crowns. The metal-ceramic crowns were cemented using RelyX Luting Plus (3 M ESPE, St. Paul, MN, USA). Follow-up assessments were conducted at 12, 24, 36, 48, and 120 months (T12-T120). Periapical radiograph (PA) and cone beam computed tomography (CBCT) were obtained at T12, with additional periapical imaging at T48. Outcomes were categorized as 'survived' or 'extracted'. The optimal cut-off value for residual volume was identified using receiver operating characteristic (ROC) analysis and Youden's index. Associations between survival and clinical variables were analysed. RESULTS: The 10-year recall rate was 66.4%, with a Kaplan-Meier estimated 10-year cumulative survival of 85.4%. The optimal threshold for residual tooth volume was 41%, with 58 teeth (40.8%) below this threshold and 84 (59.2%) at or above it. Teeth with < 41% volume had an extraction rate more than three times higher than those with ≥ 41% (20.7% vs. 5.9%; p = 0.016). Teeth with an unfavourable 12-month CBCT result had a 4.5-fold increased risk of extraction compared to those with favourable outcomes (p = 0.004). DPI scores were not significantly associated with extraction risk (p = 0.67). CONCLUSION: Root canal-retreated posterior teeth demonstrated favourable long-term survival. A residual coronal tooth volume ≥ 41% was strongly associated with improved survival. In addition, favourable PA and CBCT findings at 12 months were associated with improved long-term outcomes. These findings support root canal retreatment as a reliable and biologically favourable treatment option for posterior teeth with persistent apical periodontitis.