Spatial Discrepancies in CBCT-Based Localization of Impacted Mandibular Third Molars

Introduction and aims To quantitatively evaluate the accuracy of cone-beam computed tomography (CBCT) in localizing impacted mandibular third molar (IMTM), using surgical guides as an image transfer modality. Methods Patients requiring extraction of low-level horizontally impacted mandibular third molars underwent standardized CBCT. For 10 deeply impaction cases (Pell & Gregory Class C), personalized guides were designed and printed based on CBCT models to demarcate crown boundaries. Intraoperative mesiodistal and vertical discrepancies between guide-indicated and actual crown positions were measured. For an additional 60 cases without guides, only the horizontal discrepancy between the IMTM and the adjacent second molar was measured. Results Actual IMTM positions extended mesially beyond the second molar distal surface (mean: 4.51 ± 1.52 mm), with significantly greater deviations in Class C than Class B ( P < .05). Surgical guide-based measurements confirmed that actual crown positions were mesial and inferior to CBCT indications. Mean mesiodistal deviation was 4.94 ± 1.45 mm. Significant vertical discrepancies were also observed (mean superior: 5.21 ± 1.38 mm; mean inferior: 4.62 ± 0.95 mm). Conclusion In the mandibular retromolar region, CBCT-based localization may deviate from actual anatomy by several millimeters in mesiodistal and vertical dimensions, with deeper impactions showing greater discrepancies. Heightened vigilance is warranted when planning surgeries based solely on CBCT for deeply impacted IMTMs or retromolar foreign bodies. Clinical Relevance During mandibular retromolar region imaging, CBCT demonstrates mesiodistal and vertical deviations, with these error increasing as the target approaches the mandibular angle and inferior mandibular border.