Skeletal Class II malocclusion is associated with a more distant maxillary first molar-sinus adjacency: a retrospective CBCT study in adults

The relationship between maxillary posterior tooth roots and the maxillary sinus floor is a key risk factor in orthodontic treatment. This study systematically evaluated this relationship for the maxillary second premolar, first molar, and second molar in adults with different growing patterns. This retrospective cross-sectional study analyzed CBCT data from 502 adults (20–45 years). Patients were grouped by sagittal pattern (ANB angle: Class I, II, III) and vertical skeletal pattern (MP-SN angle: hyperdivergent, normodivergent, hypodivergent). A modified classification (scores 1–5) assessed the vertical relationship between each tooth apex and the sinus floor. The effects of age, sex, and skeletal pattern on scores were analyzed. After adjusting for age and sex, the vertical pattern showed no significant association with root-sinus scores (P > 0.05). Sagittally, Class II patients had significantly lower first molar scores than Class I patients ( P = 0.032), indicating roots positioned farther from the sinus floor. Age was significantly negatively correlated with scores (P < 0.001), and females had lower scores than males ( P < 0.001). While scores among tooth positions were correlated at the population level, high individual heterogeneity was observed, with 43.4% of patients showing irregular fluctuations. Vertical skeletal pattern is not significantly associated with the maxillary posterior root-sinus relationship in adults. Skeletal Class II patients exhibit a more distant maxillary first molar apex-to-sinus adjacency, indicating a static anatomical association. Increasing age is associated with more distant root-to-sinus adjacencies.