X-ray diffraction characterization of dental gold alloy-ceramic interfaces

X-ray diffraction (XRD) was employed to study dental alloy-ceramic interfac es. A Au-Pd-In alloy, which requires oxidation before porcelain firing, and a Au-Pt-Pd-In alloy, which does not require oxidation before porcelain fir ing, were selected in this study. Alloy specimens were centrifugally cast. Specimen surfaces were metallographically polished through 0.05 mum Al2O3 s lurries. A thin layer (<50 <mu>m) of a dental opaque porcelain was fired on the alloy surfaces with and without initial oxidation. XRD was conducted a t room temperature on four types of alloy specimens: polished, oxidized, po rcelain fired after alloy oxidation, and porcelain fired without initial al loy oxidation. XRD was also performed on fired opaque porcelain without an alloy substrate. The detection of prominent gold solid solution peaks from alloy-ceramic specimens indicated that the incident X-ray beam reached the alloy-ceramic interface. In2O3 and beta -Ga-2 O-3 were identified on the ox idized Au-Pd-In alloy, while In2O3 and SnO2 were detected on the oxidized A u-Pt-Pd-In alloy. Preferred orientation was observed for all the oxides for med on the alloys. Minimum lattice parameter changes (<1%) for the gold sol id solutions were observed for both alloys before and after oxidation and p orcelain firing. Leucite (KAlSi2O6), TiO2, ZrO2 and SnO2 were detected on t he fired opaque porcelain. For both alloys, no additional oxides were ident ified at the metal-ceramic interfaces beyond those present in the oxidized alloys and the opaque porcelain. Similar results were obtained from alloy-c eramic interfaces where there was no prior alloy oxidation. The results ind icate the critical role of alloy surface oxides in metal-ceramic bonding an d support the chemical bonding mechanism for porcelain adherence. (C) 2001 Kluwer Academic Publishers.