In-vitro evaluation of marginal adaptation and porcelain bonding of galvano crowns and comparison with Ni-Cr alloys

In-vitro evaluation of marginal adaptation and porcelain bonding of galvano crowns and comparison with Ni-Cr alloysDt.Aycan SönmezFor long term success, dental prosthesis must have good mechanical properties and marginal fit. The purpose of this study was to evaluate marginal fit and bond strength of galvano-ceramic restorations and compare with conventional metal ceramic alloys.A total of 50 steinless steel dies representing prepared upper central teeth were fabricated and divided into 2 groups of 25 samples. Primarily, the vertical marginal discrepancies of gold copings and Ni-Cr copings evaluated, secondly vertical marginal discrepancies of porcelain fused to metal alloys and gold copings evaluated. The results in turns of gold group were 23.1±3.70 µm, 27.6±7.52 µm and of Ni-Cr group 65.2±12.30 µm, 72.5±13.77µm. Results indicated that, galvano-ceramic restorations exhibited significantly less marginal discrepancies than the conventional metal ceramic restorations. In mechanical failure test, force was applied to surfaces of the restorations with 135 degree to the horizontal axis and a crosshead speed of 0.5 mm/min until failure had occured.The fracture values (in Newton) and stress diagrams were saved. The mean fracture resistance for Ni-Cr group was 950.8±219.27 N and 555.1±126.36 N for galvano ceramic group. Significant differences were found for the resistance comparisions of two groups. While, conventional metal ceramic restorations resists to the stresses during masticatory forces, the use of galvano-ceramic restorations is limited where high masticatory forces occured.Key words: Galvanoceramic crowns, marginal adaptation, fracture strength, porcelain bonding.