Panoramic Radiographic Analysis of Mandibular Canal Morphology in Relation to Dental Implant Planning: A Cross-Sectional Radiological Analysis

Background: The identification of the canal of the mandible is important in the planning of dental implants in the posterior mandible where the inferior alveolar nerve is located. The use of panoramic radiography is popular because of low cost, ubiquity, and the ability to provide detailed 3D views, such as cone-beam computed tomography (CBCT) is cost effective. As a 2D technique, though, panoramic imaging is prone to magnification, distortion and superimposition of anatomical structures. The aim of this study was to assess the morphology of the mandibular canal as well as the available bone height (from alveolar crest to the channel) for implant planning in a cohort of Indian patients on panoramic radiographs. Material and Methods: The study was retrospective, cross sectional in nature and n = 200 digital panoramic radiograph of the adult Indian patients (age ≥20 years) were analysed. The inclusion criteria were clear visualization of the small angle of the mandibular canal, and the presence of at least one posterior tooth (premolar or molar) on both sides; cases were excluded which had pathology, artifacts or previous surgery in the mandible. Two calibrated examiners measured the vertical bone height (available bone height, ABH) – defined as the distance from the alveolar crest to the superior border of the mandibular canal – at the first premolar and first molar regions. The course of the mandibular canal was determined according to the Worthington system (progressive descent, catenary-like or linear). The repeat measurements showed inter-examiner reliability. The significance was set at p<0.05, and means±SD, t-tests (Male vs. Female) and chi-square tests (canal course frequencies by sex) were used for statistical analysis using SPSS v.25. Results: A total of 200 radiographs (95 males, 105 females) were analyzed (mean age 45.2±12.4 years; Table 1). The overall mean ABH at the premolar region was 14.0 ± 2.8 mm while at the molar region was 12.9 ± 2.5 mm (Table 2). Males had significantly greater bone height (premolar: 15.0±2.5 mm; molar: 14.1±2.3 mm) than females (premolar: 13.1±2.4 mm; molar: 12.0±2.4 mm; both p<0.001). Table 3 shows that the course of the mandibular canal was most often progressive, followed by catenary and linear courses. The distribution of canal courses was not significantly different between the sexes (p=0.20). Only TEM images showed clearly bifid canals, which agreed with the previously reported literature (<1%). Figure 1: Reference panoramic image with the outline of the mandibular canal. Figure 2: Measurement of the vertical dimensions using a calibration marker. Figure 3: Effects of beam angulation errors (foreshortening/elongation) on the resulting image distortion. Conclusion: In simple cases, panoramic radiography can be used for a reliable assessment of the height of available bone for implant planning and can allow accurate depiction of the mandibular canal. Clinicians should be mindful of its limitations (distortion, magnification) and when detailed 3D information is needed, should consider CBCT to prevent neurovascular injuries. These results highlight the need of a proper radiographic evaluation and a safety margin (of at least 2 mm) above the canal in implant surgery.

Keywords: Panoramic Radiograph, Mandibular Canal, Dental Implant Planning, Available Bone Height, Radiographic Analysis, CBCT.