Marginal fit consistency of copy-milled all-ceramic crowns during fabrication by light and scanning electron microscopic analysis in vitro

The aim of this study was to evaluate the marginal fit of copy-milled Celay In-Ceram crowns after different fabrication steps and to compare light-microscopic with scanning-electron-microscopic data. A master steel die of an upper middle incisor with a shoulder preparation and a rounded inner line angle was used. Impressions were taken to produce 10 working stone dies. One crown per working die was manufactured. The evaluation of the external marginal gap was performed on the master steel die by using a light microscope and a computerized video image analysis system after copy milling (A), glass infiltration (B), and veneering (C). Approximately 3900 readings were taken. In a final series the veneered crowns were measured by using a scanning electron microscope (Cs), yielding approximately 1000 readings. The results obtained were: A mean, 25.1 microm; s.d., 5.1 microm; range, 2.5-76.8 microm: B mean, 20.6 microm; s.d., 2.3 microm; range, 2.5-76.1 microm: C mean, 18.3 microm; s.d., 4.1 microm; range, 2.5-87.2 microm: Cs mean, 23.0 microm; s.d., 7.6 microm; range, 0.0-94.5 microm. The results were statistically evaluated using the t-test. The differences found between the series did not show practical relevance. Therefore, it is concluded that the manufacturing steps after copy milling have no obvious influence on the external marginal gap width. Scanning electron microscopic data seem to confirm the light-microscopic results. Hence, we expect that the Celay In-Ceram method yields a clinically acceptable marginal fit.