Influence of manufacturing technique on marginal fit of cobalt chromium restorations: An in-vitro Study.

Abstract

For porcelain fused to metal restorations, computer-aided designing (CAD) / computer-aided manufacturing (CAM) systems claim to provide improved marginal fit than conventional casting systems. The present in-vitro study was conducted to compare the marginal fit of cobalt-chromium alloy copings fabricated with milled wax/lost wax, CAD/CAM milling/sintering and direct metal laser sintering (DMLS) techniques. A metal die simulating a prepared tooth was fabricated and scanned using an optical scanner. A standardized coping design was used to manufacture 30 alloy copings divided into three groups of ten copings each i.e., milled wax/lost wax, milling/sintering and DMLS. A modified replica technique was used to measure the silicone film thickness at four pre-designated points on the margin under a digital stereo-microscope. The mean values for marginal gap were compared using one-way Analysis of Variance (ANOVA) followed by Tukey-Kramer test for all pair-wise comparisons. The mean marginal gap values obtained by using milled wax/lost wax technique, milling/sintering technique and DMLS technique were 88.44 μm, 61.135 μm and 55.39 μm, respectively. One-way ANOVA showed a significant difference for marginal fit between the lost wax group and the other two test groups (P < 0.05). The cobalt-chromium alloy copings fabricated using DMLS techniques displayed significantly better marginal fit than the milled wax/lost wax technique which may contribute to their improved clinical performance. DMLS technique produces restorations with an improved marginal fit and may be preferred by clinicians over milling and conventional casting techniques.