The Effect of Digital Cement Space Thickness on the Marginal Discrepancy of Monolithic Zirconia Crowns: A CAD-CAM Study

PURPOSE: This in vitro study evaluated the influence of digital cement space thickness (80 μm, 100 μm, 120 μm) on the marginal discrepancy of monolithic zirconia crowns fabricated using CAD/CAM technology. MATERIALS AND METHODS: Seventy-five monolithic zirconia crowns were digitally designed and milled with cement space thicknesses of 80, 100, and 120 μm (n = 25 per group). Marginal discrepancies were assessed at eight predetermined points using scanning electron microscopy at ×100 magnification. The measurement points-mesial (M), mesiobuccal (MB), buccal (B), distobuccal (DB), distal (D), distolingual (DL), lingual (L), and mesiolingual (ML)-were precisely marked on each crown using a custom-made PMMA mold with pre-formed positioning holes to ensure consistent localization. Statistical analysis included one-way ANOVA and Tukey's post hoc tests. RESULTS: The mean marginal discrepancy at the 80 μm cement space was 33.35 μm, at the 100 μm cement space 31.36 μm, and 28.37 μm at 120 μm cement space. No statistically significant difference was found between groups. However, significant localized differences were found at the D and ML points between the 80 μm and 120 μm cement space groups (P = .035). All measured discrepancies were within the commonly accepted range (