The Influence of Three-Dimensional Impaction Depth on Surgical Difficulty During Mandibular Third Molar Surgery: A Cone-Beam Computed Tomography (CBCT)-Based Prospective Observational Study

Introduction Accurate preoperative prediction of the surgical difficulty associated with impacted mandibular third molars is essential for treatment planning and the minimization of operative complications. Conventional radiographic classifications have a limited ability to accurately represent the three-dimensional position of impacted teeth. This study aimed to evaluate the influence of a novel cone-beam CT (CBCT)-derived three-dimensional impaction depth index (3D-IDI) on the surgical difficulty of mandibular third molar removal. A novel 3D-IDI was developed to integrate the vertical, buccolingual, and anteroposterior dimensions into a single quantitative measure. Methods This study involved 90 patients with unilaterally impacted mandibular third molars who underwent standardized preoperative CBCT imaging. Vertical, buccolingual, and anteroposterior depths were measured to calculate 3D-IDI. Surgical difficulty was assessed using operative time and surgeon-assigned difficulty score. Receiver operating characteristic (ROC) curve, correlation, and multivariable linear regression analyses were performed. Results The mean participant age was 27.13 ± 4.56 years, and the mean 3D-IDI was 11.04 ± 2.68 mm. ROC analysis demonstrated excellent predictive performance of the 3D-IDI for identifying surgically difficult cases (area under the curve (AUC) = 0.938; 95% confidence interval (CI): 0.888-0.988; p < 0.001), with an optimal cut-off value of 9.67 mm, sensitivity of 88.2%, specificity of 89.7%, and overall accuracy of 88.9%. Deep impactions showed significantly longer operative time (42.45 ± 4.93 vs. 30.02 ± 4.02 minutes), higher surgical difficulty scores, and more frequent tooth sectioning than shallow impactions (all p ≤ 0.002). 3D-IDI demonstrated strong positive correlations with operative time (ρ = 0.901), and surgical difficulty score (ρ = 0.860) (all p < 0.001). Vertical and anteroposterior depths were identified as independent predictors of operative time. Conclusions The novel CBCT-derived 3D-IDI is a reliable predictor of surgical difficulty during mandibular third molar removal. Its incorporation into preoperative assessments may facilitate objective risk stratification, improve surgical planning, and optimize patient management. Further validation in larger samples is required.