The anterior loop of the inferior alveolar nerve: prevalence, measurement of its length and a recommendation for interforaminal implant installation based on cone beam CT imaging

Abstract

Interforaminal implant surgery requires anatomical knowledge of the area and adequate information on the location of the various landmarks of significance such as the mental foramen, the anterior loop of the inferior alveolar nerve and the mandibular incisive canal. Cone beam computed tomography (CBCT) is a relatively new imaging modality that provides a multi-dimensional view of the facial skeleton with, in most instances, lower radiation dose to the patient compared to medical CT. The present study aims to use CBCT to identify and measure variation in the presence and extent of the anterior loop of the inferior alveolar nerve. This information may be used to provide recommendations to the surgeon without access to a 3D scan of the dento-alveolar region. Ninety-three patients scanned with a Newtom VG device for a variety of clinical indications were included in this retrospective study. Using the multiplanar capabilities of the device's software the prevalence and length of the anterior loop was assessed. The results show that an anterior loop could be identified in 48% of the cases with a mean length (range) of 0.89 mm (0-5.7). In almost half of the surveyed cases an anterior loop was present. Even though in 95% of the study cases the loop was <3 mm, a 100% safety margin in the placement of anterior mandibular implants, in the absence of a CBCT scan, would only be achieved with a distance of 6 mm between the anterior border of the mental foramen and the most distal interforaminal implant fixture.