Radiographic evaluation of root apex to mandibular canal distance in the posterior mandible for assessing risk of inferior alveolar nerve injury during immediate implant placement.

BACKGROUND

Immediate implant placement in the posterior mandible is associated with a risk of inferior alveolar nerve (IAN) injury due to anatomical variations such as lingual concavities and variability in mandibular canal positioning. Accurate three-dimensional assessment of these structures is therefore essential.

OBJECTIVES

This study aimed to evaluate the root apex-mandibular canal distance (RAC), prevalence and morphology of lingual concavities, and cross-sectional ridge patterns in the posterior mandible to identify high-risk sites for IAN injury during immediate implant placement.

MATERIALS AND METHOD: Cone-beam computed tomography (CBCT) scans of 60 patients (600 posterior mandibular sites) were analyzed. Cross-sectional ridge morphology (C, P, and U types), lingual concavity dimensions (angle, depth, height), concavity zones (A, B, C), and RAC values for premolars and molars were assessed. Statistical analysis included normality testing followed by appropriate parametric or non-parametric tests, with significance set at p < 0.05.

RESULTS

U-type ridges were the most prevalent (58.3%), particularly in molar regions, while P-type ridges predominated in premolars (76.7%). The most concave point of the lingual surface was most frequently located in zone B (49.7%). The shortest RAC was observed at the distal roots of second molars (3.00 ± 2.13 mm), indicating the highest risk of IAN injury (p < 0.0001). Lingual concavity angle decreased and depth increased from premolars to second molars, whereas concavity height showed no significant variation.

CONCLUSIONS

The distal roots of second molars demonstrate the closest proximity to the mandibular canal and the deepest lingual concavities, representing the highest anatomical risk for IAN injury during immediate implant placement. Pre-surgical CBCT evaluation of RAC, ridge morphology, and lingual concavity characteristics is essential for safe and predictable implant therapy in the posterior mandible.