Objective <p>To evaluate 1-year bone resorption after lateral sinus lift and assess the influence of contributing factors (Schneiderian membrane perforation, sinus anatomy, and surgical variables).</p> Methods <p>This observational retrospective monocentric study compared CBCT-based volumetric outcomes in patients undergoing lateral sinus lift between 2020 and 2025. Scans were obtained immediately postoperatively and at 1-year follow-up, allowing precise three-dimensional assessment of grafted bone volume and evaluation of the impact of intraoperative membrane perforation. Bone volumes were measured using 3D Slicer^® with semi-automatic segmentation, a 3D imaging method enabling precise volumetric assessment of grafted bone. Multivariate analyses were performed to explore associations between anatomical features, graft characteristics, and bone resorption.</p> Results <p>Forty-one sinuses were analyzed (mean age 62.8 ± 11.4&#xa0;years). Bone loss was classified as &lt; 10% (n = 4), 10–25% (n = 12), 25–50% (n = 18), and ≥ 50% (n = 7). No significant differences in age, sex, initial bone height, volume, or membrane thickness were observed between perforation and control groups. Multivariate analysis suggested that initial graft volume and sinus morphology influenced cases with ≥ 50% resorption, while properly managed membrane perforations did not significantly affect graft stability.</p> Conclusions <p>One-year bone resorption after lateral sinus lift is multifactorial, and proper management of Schneiderian membrane perforations minimizes their impact on graft volume. The management of perforations and surgical technique appear to play a more significant role in graft stability than the simple occurrence of a perforation.</p>