Evaluation of Ultra-Low-Dose CBCT Protocols to Investigate Vestibular Bone Defects in the Context of Immediate Implant Planning: An Ex Vivo Study on Cadaver Skulls

Background/Objectives: This ex vivo study aimed to evaluate the diagnostic performance of ultra-low-dose (ULD) cone-beam computed tomography (CBCT) protocols in detecting vestibular bone defects for immediate implant planning, using intraoral scan (IOS) data as a reference. Methods: Four CBCT protocols (ENDO, A, B, C) were applied to four dried human skulls using a standardized setup and a single CBCT unit (Planmeca ProMax® 3D Mid, Planmeca Oy, Helsinki, Finland). All scans were taken at 90 kV, with varying parameters: (1) ENDO (40 × 50 mm, 75 µm, 12 mA, 80–120 µSv, 15 s), (2) A (50 × 50 mm, 75 µm, 9 mA, 20–40 µSv, 5 s), (3) B (100 × 60 mm, 150 µm, 7.1 mA, 22–32 µSv, 5 s), and (4) C (100 × 100 mm, 200 µm, 7.1 mA, 44 µSv, 4 s). Vestibular root surfaces of single-rooted teeth (FDI regions 15–25 and 35–45) were digitized via IOS and exported as STL files. CBCT datasets were superimposed using 3D software (Blender 2.79), and surface defects were measured and compared using one-sample t-tests and Bland–Altman analysis. The level of significance was set at p < 0.05. Results: A total of 330 vestibular surfaces from 66 teeth were analyzed. Compared to the IOS reference, protocols ENDO and A showed minimal differences (p > 0.05). In contrast, protocols B and C exhibited statistically significant deviations (p < 0.05). Protocol B demonstrated a mean difference of −0.477 mm2 with limits of agreement (LoA) from −2.04 to 1.09 mm2 and significant intra-rater variability (p < 0.05). Protocol C revealed a similar mean deviation (−0.455 mm2) but a wider LoA (−2.72 to 1.81 mm2), indicating greater measurement variability. Overall, larger voxel sizes were associated with increased random error, although deviations remained within clinically acceptable limits. Conclusions: Despite statistical significance, deviations for protocols B and C remained within clinically acceptable limits. ULD CBCT protocols are, thus, suitable for evaluating vestibular bone defects with reduced radiation exposure.