Anatomical Determinants of Lingual Nerve Safety During Impacted Mandibular Third Molar Surgery: A Cone-Beam Computed Tomography Study
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Published on: February 23, 2024
Bhanu Priya1, Srikanth Gadicherla2, Sruthi Menon Moothedath3
1Department of Oral Medicine and Radiology, Manipal College of Dental Sciences, Manipal Academy of Higher Education, Manipal, India.
Introduction:
Lingual nerve injury is a recognized complication of mandibular third molar extraction, with a reported incidence of 0.6-2.0%. The lingual nerve's superficial anatomical course adjacent to the lingual cortex makes it vulnerable to iatrogenic trauma, particularly in distoangular and vertical impactions. This study aimed to evaluate cone beam computed tomography (CBCT)-derived lingual cortical bone parameters and introduce the internal oblique ridge (IOR)-mylohyoid ridge (MR) interval as a radiographic safety corridor for the lingual nerve.
Materials And Methods:
This retrospective CBCT-based study included 48 subjects with vertical or distoangular mandibular third molar impactions. Buccal and lingual cortical thickness was measured at the cemento-enamel junction (CEJ), mid-root, and apical levels. Root morphology, lingual plate morphology, root-apex-to-lingual-cortex distance, buccolingual angulation, and the IOR-MR interval were also assessed. Independent samples t-tests compared parameters between impaction groups; statistical significance was set at p<0.05.
Results:
Distoangular impactions demonstrated significantly thinner lingual cortical bone at the apical level compared to vertical impactions (p=0.03). No significant differences were observed in buccal cortical thickness or lingual cortical thickness at the CEJ and mid-root levels between groups. Mean distal bone thickness in both groups was significantly below the cadaveric reference of 3.01 mm (p<0.001). The IOR-MR interval averaged 4.92 mm and 4.82 mm in vertical and distoangular groups respectively.
Conclusion:
Distoangular impactions demonstrate significantly thinner lingual cortical bone at the apical level, representing a measurable radiographic risk factor for lingual nerve injury during third molar extraction. The IOR-MR interval on preoperative CBCT provides a practical estimate of the lingual nerve's course, supporting its integration into routine presurgical planning for higher-risk impaction patterns.
