Standard- versus low-dose CBCT in evaluating mandibular canal visibility and its impact on assessing the spatial relationship with mandibular third molars: a comparative analysis

Objectives To compare the visibility of the mandibular canal (MC) at three mesial-distal levels adjacent to the mandibular third molar (M3M) using standard-dose and four low-dose cone-beam computed tomography (CBCT) protocols, and evaluate their impact on assessing the spatial relationship between the MC and M3M. Methods A total of 100 CBCT scans were obtained from 20 dry mandibles with M3Ms, using one standard-dose, normal-resolution protocol (0.2 mm voxel; DAP: 322 mGy×cm 2 ) and four low-dose protocols with varying resolutions (0.15-0.4 mm voxel; DAP: 23-131 mGy×cm 2 ). For each scan, MC visibility at the distal, middle, and mesial thirds of the M3M was rated on a 4-point scale. The spatial relationship between the MC and M3M apex was evaluated both qualitatively (non-contact, contact, or penetration) and quantitatively (the MC-M3M distance). Pairwise comparisons between the standard-dose and each low-dose protocol were conducted using the Wilcoxon signed-rank test. Results The MC visibility at all levels was high (≥3.4/4) for all protocols except the low-dose, low-resolution protocol (voxel size: 0.4 mm; DAP: 23 mGy×cm 2 ). Significantly lower MC visibility was observed only with the low-dose, low-resolution protocol compared to the standard-dose protocol ( p = 0.006-0.026). No significant differences were found in the qualitative and quantitative assessments of the spatial relationship between the MC and M3M apex among any of the protocol pairs. Conclusions Although the lowest-dose, lowest-resolution CBCT reduced MC visibility, no significant differences were observed between standard-dose and low-dose protocols in assessing the MC-M3M apex relationship. Notably, the lack of significant difference should not be interpreted as evidence of equivalence, as the study used subjective image assessments without an independent reference standard. Low-dose CBCT may be considered in selected cases, but protocol selection should remain indication-oriented, patient-specific, and device-specific.