An In-vitro Comparative Stereomicroscopic Analysis and Evaluation of Marginal Accuracy in Porcelain Fused to Metal Copings Fabricated in Two Different Finish Lines Using Variant Die Materials

Abstract

Limited published information is available about the influence of preparatory designs and die materials on marginal accuracy of porcelain fused to metal copings using recently developed die materials. To detect the influence of margin geometries and dimensional accuracy of contemporary die materials on vertical marginal gaps in Porcelain fused to metal coping using a Stereomicroscope (three dimensional analysis). Two chrome cobalt alloy models of mandibular first molars prepared to have shoulder and deep chamfer finish lines were CAD-CAM milled. Elastomeric impressions of these models were made in a custom tray, poured in Type IV Gypsum(n=10) and Resin modified Gypsum(n=10) and also packed with Epoxy resin (n=10) as a die material to form a total of 60 samples, 30 in each group (shoulder and deep chamfer). Wax patterns were fabricated, invested and castings in ceramic alloy were obtained in traditional manner. These copings were later analyzed on CAD/CAM models using stereomicroscope. Both the designs did not exhibit significant difference (p<0.05). Whereas, the three die materials exhibited significant difference (p<0.05) by Two way ANOVA test and Tukey's multiple Post Hoc test. Results from this study showed that vertical marginal gaps for copings fabricated on resin modified gypsum as a die material were within the clinically acceptable range. Margin geometries both shoulder and deep chamfer have equal influence on vertical marginal gaps in metal ceramic restorations. Copings fabricated on Epoxy resin dies exhibited highest value of vertical marginal discrepancy, where as least value was determined for copings constructed on dies fabricated from resin modified gypsum.