Effect of head orientation on mandibular bone linear measurements in CBCT imaging

Cone Beam Computed Tomography (CBCT) is a widely used diagnostic tool for bone assessment. However, the impact of head orientation on linear bone measurements remains debated. This study aimed to evaluate whether the occlusal plane or the mandibular plane orientation provides more accurate measurements of mandibular height and width compared to a standard reference.

Five dry human mandibles were imaged at the Faculty of Dentistry, Islamic Azad University, Khorasgan, in 2024. CBCT scans were obtained using a NewTom VGi evo device. The scans were exported as DICOM and analyzed in ONDEMAND software. Measurements were taken in two head orientations: (1) occlusal plane parallel to the horizon and (2) mandibular plane parallel to the horizon. Mandibular height was measured from the alveolar crest to the inferior border at the incisor, canine, premolar, and molar sites. Bone width was measured from the buccal to the lingual cortical plate at the same sites. The measurement locations were pre-marked with gutta-percha to ensure consistency. The CBCT-derived measurements were then compared to caliper measurements.

Results indicated that measurements with the occlusal plane aligned to the horizon were generally closer to standard values compared to those with the mandibular plane aligned to the horizon. Statistically significant differences were observed in bone height at the canine site: mandibular plane (26.50 mm) vs. occlusal plane (26.99 mm) (p = 0.004), and both planes showed significant differences compared to the caliper measurement (27.78 mm) (p = 0.005 for mandibular plane, p = 0.018 for occlusal plane). At the premolar site, significant differences observed between the caliper measurement (28.57 mm) and both planes (mandibular plane: 27.36 mm, p < 0.001; occlusal plane: 27.62 mm, p = 0.01). In bone width at the canine site, both planes showed significant differences (p = 0.047). No significant differences were found at the molar site.

This study suggests that aligning the occlusal plane to the horizon results in more accurate CBCT-derived linear measurements of mandibular height and width compared to the mandibular plane orientation. Therefore, the occlusal plane may be the preferred reference for CBCT-based bone measurements.