Objectives: The aim of this study was to investigate the characteristics of nitride film coatings and the effect of coating on the bond strength of dental porcelain fused to metal alloy. Methods: Two commercially available dental alloys (Olympia^® & Wiron88^®)were tested. Fifteen strip specimens (30 mm x 10 mm x 1.3 mm) were cast from each alloy and randomly divided into 3 groups. Five cast specimens were used as controls. In order to modify the surface properties of Au-Pd-based alloy (Olympia^®)and nickel-based alloy (Wiron88^®)a thin 10 mm x 10 mm layer of either titanium nitride (TiN) or titanium-aluminum nitride (Ti,Al)N film was deposited on dental alloys using a reactive radio-frequency sputtering method on the middle section of the specimen. An 8 mm x 8 mm porcelain veneer with uniform thicknesses of 0.2 mm opaque porcelain and 1.3 mm of body porcelain were baked on the center of nitride deposition. The specimens were then subjected to a four-point bending test on a testing machine. The failure loads were recorded and analyzed statistically with ANOVA and Scheffe' test. Results: The bond strengths ranged from 508.2 N ± 29.9 N to 627.2 N ± 15.8 N. The porcelain bond strength of the nitride film coating treatment groups were significantly higher than the controls (p<0.05). An electron probe microanalyzer with line profile mode was used to assess the characteristics of the interface between the nitride film and the porcelain layer. Conclusions: The results revealed that the nitride film coating (1) increased the bond strength of the tested metal substrates by elemental diffusion, (2) appeared to block some oxidation effect from the tested metal substrates, (3) maintained an appropriate oxide layer for porcelain bonding and (4) performed better masking effect on the compatibility of metal substrate. Supported by Taiwan Grant NSC 92-2314-B-010-034.

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