Marginal and internal fit of pressed ceramic crowns made from conventional and computer-aided design and computer-aided manufacturing wax patterns: An in vitro comparison.

STATEMENT OF PROBLEM: To our knowledge, no studies have evaluated the influence of the wax fabrication technique on the internal adaptation and marginal accuracy of pressed ceramic single crowns. PURPOSE: The purpose of this in vitro study was to compare the marginal and internal fi t of a lithium disilicate crown fabricated either from conventional waxing or from a subtractive milled wax pattern. MATERIAL AND METHODS: Ten silicone impressions were made for a maxillary canine prepared to receive a complete crown. Two pressed lithium disilicate glass ceramic copings were made on the die poured from each impression. The first was from a conventional wax pattern and the second from milled wax blocks. The replica technique was used to measure the fit by scanning electron microscope at x80 magnification. Collected data were analyzed with the paired Student t test for the marginal and wall fit. For the occlusal fit, the difference in scores did not follow a normal distribution, and the Wilcoxon signed ranks test was used (alpha=.05). RESULTS: The mean values +SD were 170.3 +/-50.7 mum for the marginal fit and 130.3 +/-21.6 mum for the internal fit with the conventional technique. For the computer-aided design and computer-aided manufacturing (CAD-CAM) technique, they were 105.1 +/-39.6 mum and 98.1 +/-26.1 mum. Statistical significance was found for the marginal and internal fit (P<.05). The occlusal fit median and interval interquartile scores were 305.0 mum (269.9 to 334.4) for conventional fabrication and 199.0 mum (141.5 to 269.9) for subtractive manufacturing. The differences were not statistically significant (P>.05). CONCLUSIONS: The subtractive CAD-CAM waxing technique resulted in the improved fit of a pressed lithium disilicate crown by decreasing the marginal discrepancies and internal adaptation.