In vitro evaluation of the marginal adaptability of zirkonzahn & metal ceramic crowns before & after porcelain firing

Metal ceramic restorations are the most common type of full coverage restorations. Recently zirconium oxide ceramic has been introduced as a substitute for metal substructures. The aim of this study was to evaluate the marginal fit of zirconia & non-precious metal ceramic crowns before and after porcelain firing cycles. In this invitro study a master steel die of an upper central incisor with a chamfer finish line was used. Ten zirconia (Zirkonzahn) (Z group) and 10 base metal (NNB) copings (M group) with the same shape were fabricated on the die. After gap measurement, porcelain was applied on the copings with the same dimensions (ZP & MP groups). Marginal adaptation was evaluated on master die by stereomicroscope with 57x magnification. The data were statistically analyzed by One Sample kolmogorov-smirnov, Paired samples t-test, ANOVA and Post hoc scheffe tests. The results for the four groups were as follows:1)Z group: mean=37.07 µm, SD=18.92 µm and the range=0-78 µm.2) M group: mean=50.68 µm, SD=31.24 µm and the range=0-136 µm.3)ZP group; mean=36.96 µm, SD=21.735 µm and the range=0-87 µm.4) MP group: mean 63.7 µm, SD=37.961 µm and the range=0-171 µmSignificant differences were found between metal ceramic and Zirconia groups. Porcelain firing cycles decreased only the marginal adaptation of metal ceramic crowns significantly. Within limitations of this study, mean marginal discrepancies of the groups were all within the clinically acceptable standard level (up to 100 µm). However the mean marginal adaptability of the Zirkonzahn crowns were better than metal ceramic crown. The marginal adaptability of the metal ceramic crowns decreased statistically during porcelain firing cycles.