Comparison of marginal fit of 3 different metal-ceramic systems: An in vitro study

Purpose: The aim of this study was to compare the marginal adaptation of me tal-ceramic crowns made with 3 different metal substructures. Materials and Methods: Seventy-five gypsum dies were fabricated from a master steel die. They were randomly divided into 3 groups of 25 dies each. A metal coping w as prepared on each die using a different technique for each group: composi te alloy, electroforming, and cast high-noble alloy. Ceramic was baked on a ll of the samples following the same protocol and simulating the shape and size of a maxillary central incisor. All specimens were evaluated under a s tereomicroscope at 200X magnification. The marginal gap was measured at 8 d ifferent points on each specimen before and after ceramic application and a lso on the master steel die. A total of 3,600 measurements was evaluated. T he results were statistically elaborated by means of a t test and one-way a nalysis of variance (ANOVA). Results: The ANOVA revealed a significant diff erence in mean marginal gap before and after ceramic application within eac h group. Electroforming (mean 32 mu m) and high-noble alloy (mean 31 mu m) showed better marginal fit after ceramic application and on the master stee l die compared to composite alloy (mean 68 mu m; P < 0.0001). Conclusion: M arginal gaps are influenced by the application of ceramic and by the alloy used for the substructure, and the values obtained were within the limits o f clinical acceptability (70 mu m).