Influence of Root Canal Filling and Coronal Restoration Quality on Periapical Health: A Retrospective Observational Study

Objective The aim of this study was to assess the association between the technical quality of root canal treatment and coronal restoration and periapical status in endodontically treated teeth and to explore their combined effects. Methods This retrospective cross‐sectional observational study included 257 patients and 798 endodontically treated teeth. Coronal restoration quality was assessed both clinically, using FDI criteria, and radiographically and categorized as good or poor restoration. Root canal fillings were classified as adequate or inadequate (good endodontic treatment [GE] vs. poor endodontic treatment [PE]) based on length, density, and taper. Periapical status was evaluated using the periapical index (PAI). Associations between treatment quality parameters and periapical status were analyzed using odds ratios (ORs) with 95% confidence intervals (CIs). Results Apical periodontitis (AP) was observed in 49.0% of root‐filled teeth. Inadequate coronal restoration, when clinical and radiographic criteria were combined, was significantly associated with AP (OR = 1.43; 95% CI [1.08–1.90]). Inadequate root canal treatment showed a stronger association with AP (OR = 2.30; 95% CI [1.64–3.21]), with all technical parameters (length, density, and taper) significantly influencing periapical status. Marginal adaptation alone, whether assessed clinically or radiographically, was not significantly associated with AP. When combined factors were analyzed, a gradient in risk was observed: teeth with inadequate root canal treatment (PE + GR and PE + PR) showed significantly higher odds of AP compared with the reference group (GE + GR), whereas adequate root canal treatment combined with poor restoration (GE + PR) was not significantly associated with AP. Conclusion Both root canal treatment and coronal restoration quality are associated with periapical health. However, their effects differ, with root canal treatment quality showing a stronger association with periapical status. Importantly, an adequate coronal restoration alone does not appear sufficient to compensate for an inadequate root canal filling.