Evaluation of the Course of the Inferior Alveolar Nerve in the Mental Foramen by Cone Beam Computed Tomography

Purpose: Implant placement in the edentulous anterior mandible is frequently performed to stabilize prosthetic superstructures. The position of the inferior alveolar nerve (IAN), especially in an atrophic mandible, has to be considered to position implants properly. In this study, the prevalence of looping of the IAN was retrospectively determined to assess the need for imaging prior to implant placement in the anterior mandible. Materials and Methods: Cone beam computed tomography scans of consecutive patients were evaluated to assess the prevalence and size of IAN looping. The results were compared with respect to patient age and sex as well as degree of atrophy and bone height at the mental foramen. Results: Scans of 1,010 patients were obtained. IAN loops were found in 31% of the patients, with a significantly higher prevalence in male patients (33.1%) than in female patients (28.1%). The average size of loops was 1.4 ± 0.70 mm, with a maximum of 4.6 mm. For male patients, the average loop size was 1.6 ± 0.74 mm (maximum 4.6 mm), and for female patients an average dimension of 1.4 ± 0.63 mm (maximum 4.4 mm) was recorded. This difference was significant (t test). A significant difference with respect to the various classes of atrophy up to class 4 was not found. Conclusion: Loops of the IAN occur in about one third of patients and vary in size from 0.7 to 4.6 mm. Large anterior loops put the IAN at risk when interforaminal implants are placed. Either a sufficient safety distance or three-dimensional imaging procedures should be used to detect loops and locate the incisive canal, which could be harmed during the interforaminal implant placement. Keywords: anterior loop, cone beam computed tomography, dental implants, dental radiography, mental foramen, nerve alteration