Context: In maxillary first molars, the complex root anatomy increases the risk of technical errors that can contribute to the development of periapical pathology. Cone-beam computed tomography (CBCT) allows for a three-dimensional evaluation of technical errors and periapical lesions.

Aims: To evaluate the presence of periapical pathology resulting from technical errors in endodontic treatments performed on maxillary first molars using CBCT.

Settings and Design: A retrospective cross-sectional observational study was conducted using CBCT scans obtained at a radiographic center in Quito, Ecuador, between 2020 and 2025.

Methods and Material: 748 endodontically treated maxillary first molars were evaluated. The images were analyzed to identify technical errors, including untreated canals, omission of the MV2 canal, underfilling, overfilling, instrument fracture, and root perforation.

Statistical analysis used: Descriptive statistics were used, including absolute frequencies and percentages. To determine the association between endodontic procedure errors and the presence of apical lesions, Pearson's chi-squared test was used, considering a significance level of p < 0.05. Additionally, the odds ratio (OR) with 95% confidence intervals (95% CI) was calculated to assess the strength of the association.

Results: Periapical lesions were present in 551 teeth (73.66%). The most frequent technical error was underfilling (42.4%). Root perforation showed the greatest risk of periapical lesions.