The Influence of Recycling on the Properties of Interface between Ceramic and Dental Alloys

PURPOSE: The purpose of this study was to evaluate the effect of recycling on the properties of interface between 2 dental alloys and their corresponding porcelains. MATERIALS AND METHODS: Noble alloy (Pd-Cu-Ga) and high-noble alloy (Au-Pt) were used in this study. Metal matrices (cylinders Φ4 mm × 4 mm with pedestal Φ5 mm × 1 mm) were prepared by arc melting in argon after recasting 1-3 times. Corresponding porcelain with overall dimensions of Φ4 mm × 2 mm was veneered on each metal cylinder. There were 22 specimens in each alloy group. Specifically, two specimens of each group were chosen randomly for interfacial morphology and diffusion analyses by scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS). The remaining 20 specimens were divided into 2 groups with or without thermal cycling. The bond strength was evaluated by shear test, and the data were analyzed by two-way analysis of variance (ANOVA). The failure mode of shear test specimen was observed with a stereoscopic microscopy and subjected to the exact probability test (α = 0.05). RESULTS: According to the results from SEM, no obvious difference was observed in the interfacial morphology of both Pd-Cu-Ga and Au-Pt alloys among different recasting specimens. EDS analysis revealed that no significant difference was found in the width of elemental diffusion among 2 test alloys after recycling 1-3 times. Notably, in Pd-Cu-Ga alloy groups, the peak of Ga in thrice recasting was lower than those in first and second recastings. And there was no significant difference (P > 0.05) in the metal-ceramic shear bond strength of Pd-Cu-Ga and Au-Pt alloys after recycling 1-3 times, with or without thermal cycling. The results of failure modes observed on specimens were not affected by the recycling and thermal cycling in the 2 tested alloys. CONCLUSIONS: Within the limitations of this study, the Pd-Cu-Ga and Au-Pt alloys can be recycled 2 times without significant changes on the properties of metal-ceramic interface, with or without thermal cycling.