Objective To evaluate the accuracy of Cercon CAD/CAM system and the influence of different spacer thickness and spacer coverage area on the internal and marginal fit of the copings. Methods A stainless steel master model of first molar was replicated. After scanning, designs of copings were made with different spacer thickness and spacer coverage area. There were six groups: S10C70, S10C90, S30C70, S30C90, S60C70, S60C90. Measurements of the adaptation were performed with silicone impression material and an image analysis system. Results Univariate ANOVA showed that variation in the internal fit of copings was related to measuring location, spacer thickness and spacer coverage area. There was significant difference between different spacer coverage area groups, and significant difference between spacer thickness 10 μm and 30 μm groups, 10 μm and 60 μm groups, no significant difference between spacer thickness 30 μm and 60 μm groups. Mean marginal fit was （27.7 ±7.6）μm. There was statistically significant difference between both mesial, distal marginal gaps and both buccal, lingual marginal gaps. No difference between mesial and distal marginal gaps, and between buccal and lingual marginal gaps. Conclusion The accuracy by Cercon CAD/CAM system for the marginal and internal fit of zirconium dioxide copings is well within the range of clinical acceptability. Spacer thickness and spacer coverage area have statistically significant influence on the internal fit.
