A Novel Method for the Diagnosis of Transverse Maxillary Deficiencies Based on CBCT

Background/Objectives: To Develop a CBCT-based transverse diagnostic method that establishes normative buccolingual inclination values for permanent first molars and objectively distinguishes between dentoalveolar transverse deficiency and skeletal maxillary deficiency. Methods: A total of 1120 initial CBCT scans were reviewed, and 40 subjects with normal occlusion met the inclusion criteria. Volumes were reoriented using a standardized three-plane protocol, and molar angulations were measured relative to reference planes parallel to the occlusal plane. Intra- and inter-examiner reliability were assessed using ICC. Descriptive, comparative, and correlation analyses were performed bilaterally and between arches. Results: No significant right-left differences were observed for upper molar angulation (URM vs. ULM: 99.5° vs. 99.1°; t(19) = 1.560, p = 0.135) or lower molar angulation (LRM vs. LLM: 78.9° vs. 78.9°; t(19) = 0.301, p = 0.767). Non-parametric analysis confirmed these findings (ULM vs. URM: Z = -1.203, p = 0.229; LLM vs. LRM: Z = -0.427, p = 0.669). Significant positive bilateral correlations were observed in both arches (upper: r_S = 0.784, p < 0.001; lower: r_S = 0.837, p < 0.001). A significant negative correlation was found between upper and lower molar angulations (left side: r_S = -0.626, p = 0.003; right side: r_S = -0.858, p < 0.001), demonstrating dentoalveolar compensation. Conclusions: CBCT enables the precise assessment of molar buccolingual inclination and the establishment of normative patterns essential for transverse diagnosis. The proposed method allows the quantification of the maxillary "basal defect" after virtual dental decompensation, providing an objective tool to differentiate dentoalveolar from skeletal transverse discrepancies and guide targeted treatment planning.