Evaluating the Role of Magnification in Minimising Tooth Substance Loss During Endodontic Access Cavity Preparation: An In Vitro Volumetric Analysis Using CBCT and IOS

Background and Objectives: The aim of this study was to evaluate the volume of dental tissue removed during conventional versus microscope-assisted coronal access cavity preparation by an undergraduate student in extracted mandibular incisors, and to compare the volumetric assessment capabilities of cone beam computed tomography (CBCT) and intraoral scanner (IOS) for this application. Materials and Methods: Thirty extracted mandibular incisors were randomly allocated to two equal groups: Group 1 (G1), access cavity preparation without magnification; and Group 2 (G2), access cavity preparation with the aid of an operating microscope. Volumetric analysis was performed using CBCT (RAYSCAN® Alpha Plus 130) and an intraoral scanner (3Shape TRIOS® 3) before and after access cavity preparation. Volume loss was calculated for each group. Differences in groups were assessed using the independent-samples Student’s t-test for CBCT data and the Mann–Whitney U test for IOS data. Reproducibility between methods was evaluated using the intraclass correlation coefficient (ICC). Results: The CBCT analysis revealed significantly greater tissue loss in G1 (mean 14.93 mm3, SD 4.42) than in G2 (mean 7.64 mm3, SD 2.72) (mean difference 7.29 mm3, 95% CI, 4.54–10.04; p < 0.001; Cohen’s d = 1.99, 95% CI, 1.10–2.88). The IOS analysis did not detect a statistically significant between-group difference (G1: mean 5.37 mm3 vs. G2: mean 4.55 mm3; p = 0.436). The ICC for volume loss between methods was 0.011 (95% CI: −0.150 to 0.237), below the threshold conventionally used to indicate acceptable reliability; because CBCT and IOS did not sample identical anatomical extents, this should be interpreted as limited agreement specific to the present protocols rather than general evidence of poor concordance between the two imaging methods. Conclusions: Within the limitations of this exploratory, single-operator in vitro study, microscope-assisted access cavity preparation resulted in significantly less CBCT-measured volumetric tissue loss than conventional access in mandibular incisors.