Submandibular Fossa Concavity in the Posterior Mandible: A CBCT Evaluation for Implant Planning

Objectives: To evaluate the dimensions of submandibular fossa concavity and its spatial relationship to the inferior alveolar canal (IAC) in the mandibular first- and second-molar regions using cone-beam computed tomography (CBCT). Methods: This retrospective cross-sectional study included CBCT scans from 126 patients (252 hemimandibles), with four measurement points evaluated per side (1008 points). Concavity occurrence, maximum depth, the position of the deepest concavity point relative to the IAC, and the distances from the alveolar crest to the upper and lower limits of the concavity were assessed. Linear mixed-effects models and generalized estimating equations were used to account for repeated measurements within patients. Results: Concavity was identified at 636 of 1008 measurement points (63.1%), including 247 of 504 first-molar points (49.0%) and 389 of 504 second-molar points (77.2%). Maximum concavity depth was significantly greater in the second-molar region (β for first versus second molar = −0.386 mm; 95% CI: −0.559 to −0.213; p < 0.0001), whereas gender was not significantly associated with depth (p = 0.4281). The deepest concavity point was most frequently located parallel to the IAC (477/636; 75.0%). The crest-to-upper-limit distance varied significantly across measurement intervals (p < 0.0001) and was shorter in females (p = 0.0014). No statistically significant predictors were identified for the crest-to-lower-limit distance. Conclusions: Submandibular fossa concavity was frequently observed in the evaluated posterior mandibular measurement points, particularly in the second-molar region. Maximum concavity depth differed significantly by tooth region but not by gender. These anatomical findings highlight the relevance of evaluating the lingual mandibular contour and its relationship to the IAC during preoperative implant assessment.