Maxillary sinus morphometry and root–sinus proximity in the posterior maxilla: a CBCT study

The aim of this study was to quantify maxillary sinus anteroposterior (AP), mediolateral (ML), and superior–inferior (SI) dimensions at 5 mm and 10 mm above the sinus floor on cone-beam computed tomography (CBCT) and compare them by sex; classify posterior molar root–sinus relationships using the Tian classification (IS/CO/OS); and also to assess whether sinus dimensions differ across Tian proximity categories in a tooth-, side-, and sex-stratified manner. This cross-sectional study analyzed 120 CBCT scans (62 males, 58 females; age 20–50 years) obtained from the College of Dentistry, between March to September 2025. Sinus dimensions were measured bilaterally at 5 and 10 mm from the sinus floor (reference levels) at axial and coronal views. Root length of the maxillary third, second, and first molars were recorded. Root–sinus proximity was categorized using the Tian classification. Sex comparisons were performed using independent-samples t-tests and Mann–Whitney U tests; associations between sinus dimensions and Tian categories were evaluated using one-way ANOVA with Tukey post hoc comparisons. Sinus dimensions were significantly larger in males on both sides at both reference levels (all p ≤ 0.022 on the right; all p ≤ 0.007 on the left). The right AP length at 5 mm was 33.3 ± 4.9 mm in males versus 29.7 ± 4.6 mm in females (p < 0.001). Root lengths did not differ significantly between sexes for most molars, with the exception of the right second molar, which was significantly longer in males (p = 0.019). Tian distributions were generally comparable between sexes except for the left first molar (p = 0.026), where Type CO was more prevalent in females (73.1%) and Type IS was observed only in males (10.4%). SI height at 5 mm showed the most consistent associations with Tian category, with Type OS demonstrating lower values than Type CO and Type IS. All 10 significant associations withstood Benjamini–Hochberg false discovery rate correction (adjusted p-values: 0.002–0.021). Maxillary sinus dimensions showed consistent sexual dimorphism at both reference levels, with males exhibiting larger AP, ML, and SI dimensions than females. Molar root lengths were largely comparable between sexes, with the exception of the right second molar. Root–sinus proximity patterns were generally similar between sexes, and associations between sinus morphometry and Tian proximity categories were selective rather than uniform, with SI height at 5 mm being the most consistently associated parameter. These findings highlight the importance of incorporating sex-specific anatomical considerations into CBCT assessments to optimize the predictability of sinus augmentations and implant surgeries in the posterior maxilla.