Effect of different materials on marginal accuracy of crown coping fabricated by a CAD-CAM system

Abstract

Objective: To compare the marginal gap of the crown coping fabricated from three different materials by the same CAD-CAM system.
Materials and Methods: Thirty crown copings were fabricated from three different types of materials, Zirconia (Ceramill ZI®, AmannGirrbach, Austria), PMMA (Ceramill PMMA®, AmannGirrbach, Austria) and Wax (Ceramill WAX®, AmannGirrbach, Austria) by the same CAD-CAM system (Ceramill, AmannGirrbach, Austria). The crown copings were milled without fully sintered shrinkage compensation. The crown copings were evaluated the marginal gap by the replica technique using low viscosity silicone. The replicas were cut in mesio-distal and bucco-palatal direction. The gap was measured using optical light microscope at 50X magnification. The marginal gap data from four positions of cutting were averaged as one datum and statistically analyzed by one-way ANOVA and Game-Howell post-hoc test (∝=0.05).
Results: The mean of marginal gap was 67.2±19.1 μm for zirconia, 514.3±55.1 μm for PMMA, and 44.9±14.1 μm for wax. The statistical analysis showed that the marginal gap of wax was significantly smaller than zirconia, while PMMA showed the largest gap (p<0.05).      
Conclusion: It is concluded that the crown copings that were fabricated from the three different materials milled by the same CAD-CAM system showed a significant statistical difference in their average marginal distance or gap. PMMA showed the worst in marginal gap.