Numerous high-strength ceramic materials are now available for dental CAD-CAM systems. It has been documented that marginal adaptation of a dental coping is one of the most important factors that affects the longevity of the restoration. Objectives: The purpose of this study was to evaluate the effect of various coping thicknesses and laboratory processes on marginal adaptation of alumina and zirconia crown copings utilizing CAD-CAM technology. Methods: A metal abutment was fabricated with a 1 mm marginal width, 4 mm abutment height, and 12° convergence angle. A Cerec inLab system (Sirona) was used to scan the abutment, design, and mill the test samples. Alumina and zirconia copings were fabricated with thicknesses of 0.6 and 0.8 mm, and cement space thicknesses of 20, 30, and 40 microns. Epoxy resin replicas of the abutment and copings were fabricated and the vertical interfacial gaps were measured with a Micro-Vu optical microscope at three stages: post milling (PM), post trimming (PT), and post infiltration with the glass phase (PI). Results: Mean interfacial gaps (? SD) in µm: Alumina (n=27-30): PM = 54.5 ? 12.6, PT = 55.6 ? 26.0, PI = 40.4 ? 35. Zirconia (n= 27-30): PM = 53.5 ? 12.0, PT = 47.5 ? 13.0, PI = 35.8 ? 13.9. Statistical analysis (ANOVA, p< 0.05) showed no significant difference among the 3 groups except for the zirconia PM and PI groups. The marginal gap was not affected by different coping thickness (n=156-180), 0.6 coping = 38.3 ? 22.9), 0.8 coping = 38.8 ? 21.6; and cement space thickness (n=56-120): 20µm = 36.5 ? 20.2, 30µm = 39.5 ? 21.4, 40µm = 39.9 ? 24.6. Conclusion: These results showed that glass infiltration improved marginal adaptation of CAD-CAM zirconia copings, thus allowing these restorations to meet clinical standards.

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