[Effect of polishing method and time on the fitness of CAD/CAM zirconia ceramic crown].

PURPOSE: To compare the effect of different polishing methods and time treatment on the fitness of CAD/CAM zirconia ceramic crowns. METHODS: Sixteen intact maxillary premolars were randomly divided into two groups, group A was treated with silicon carbide burs, while group B was treated with tungsten steel burs. At different polishing time points of the same tooth, digital impressions of each group were obtained, which were used to manufacture CAD/CAM zirconium ceramic crowns. After trial fitting, the gap impressions were obtained by using silicone rubber replication method, and the marginal and internal discrepancies were assessed. The data were statistically analyzed with SPSS 21.0 software package. RESULTS: The difference between the gap values of the marginal and internal markers of group A and group B was not statistically significant(P＞0.05). Compared with the no-polishing process, the differences of the marginal gap (39.67+/-8.35) mum and internal gap (45.18+/-7.16) mum of group A polished for 4 min, and the marginal gap (51.25+/-14.73) mum, and internal gap (48.56+/-6.45) mum of group B polished for 3 min, as well as the marginal gap (48.87+/-8.90) mum, and internal gap (45.99+/-7.12) mum of group B polished for 4 min, were all significant(P＜0.05). CONCLUSIONS: CAD/CAM zirconia ceramic crowns treated with silicon carbide bur for polishing 4 min and tungsten steel for 3 min has the best fitness.