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(R) crowns after different fabrication steps and to comp are light-microscopic with scanning-electron-microscopic data. A maste r steel die of an upper middle incisor with a shoulder preparation and a rounded inner line angle was used. Impressions were taken to produc e 10 working stone dies. One crown per working die was manufactured. T he 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 ve neering (C). Approximately 3900 readings were taken. In a final series the veneered crowns were measured by using a scanning electron micros cope (Cs), yielding approximately 1000 readings. The results obtained were: A mean, 25.1 mu m; s.d., 5.1 mu m; range, 2.5-76.8 mu m: B mean, 20.6 mu m; s.d., 2.3 mu m; range, 2.5-76.1 mu m: C mean, 18.3 mu m; s .d., 4.1 mu m; range, 2.5-87.2 mu m: Cs mean, 23.0 mu m; s.d., 7.6 mu m; range, 0.0-94.5 mu m. The results were statistically evaluated usin g the t-test. The differences found between the series did not show pr actical relevance. Therefore, it is concluded that the manufacturing s teps after copy milling have no obvious influence on the external marg inal gap width. Scanning electron microscopic data seem to confirm the light-microscopic results. Hence, we expect that the Celay In-Ceram m ethod yields a clinically acceptable marginal fit.