Association Between Primary vs. Secondary Endodontic Infection and Maxillary Sinus Schneiderian Membrane Thickness on CBCT: A Cross-Sectional Study.

Background and Objective: Changes in the maxillary sinus mucosa and increased thickness of the Schneiderian membrane in the vicinity of endodontic lesions are common findings on CBCT. The aim of this study was to compare Schneiderian membrane thickness (SMT) in the maxillary sinus adjacent to primary and secondary endodontic infections and to investigate its relationship with selected radiographic variables. Materials and Methods: This retrospective cross-sectional study was performed on archival CBCT images. A total of 172 CBCT scans, including 86 cases with primary endodontic lesions and 86 cases with secondary endodontic lesions, were evaluated between September 2023 and March 2024. The study variables included SMT, bone thickness (BT) between the lesion and the sinus floor, lesion volume (LV), mucosal morphology, and alveolar bone perforation. Inter-rater reliability for quantitative measurements was assessed. Findings: In the total sample, the mean SMT was 3.72 ± 2.24 mm. Alveolar bone perforation was present in 62 cases. The mean SMT was 3.74 ± 2.01 mm in the primary group and 3.69 ± 2.46 mm in the secondary group. The mean difference was 0.06 mm (95% confidence interval [95% CI]: -0.63 to 0.71 mm), with no significant difference between the groups ( Conclusion: In this CBCT study, SMT was not significantly associated with primary versus secondary endodontic lesions. In addition, no significant associations were observed between SMT and age, LV, or BT between the lesion and the sinus floor. These findings should be interpreted as radiographic associations rather than causal relationships.