Silica coatings formed on noble dental casting alloy by the sol-gel dipping process

The sol-gel dipping process, in which liquid silicon alkoxide is transforme d into the solid silicon-oxygen network, can produce a thin film coating of silica (SiO2). The features of this method are high homogeneity and purity of the thin SiO2 film and a low sinter temperature, which are important in preparation of coating films that can protect from metallic ion release fr om the metal substrate and prevent attachment of dental plaque. We evaluate d the surface characteristics of the dental casting silver-palladium-copper -gold (Ag-Pd-Cu-Au) alloy coated with a thin SiO2 film by the sol-gel dippi ng process. The SiO2 film bonded strongly (over 40 MPa) to Ti-implanted Ag- Pd-Cu-Au alloy substrate as demonstrated by a pull test. Hydrophobilization of Ti-implanted/SiO2-coated surfaces resulted in a significant increase of the contact angle of water (80.5 degrees) compared with that of the noncoa ted alloy specimens (59.3 degrees). Ti-implanted/ SiO2-coated specimens sho wed the release of many fewer metallic ions (192 ppb/cm(2)) from the substr ate than did noncoated specimens (2,089 ppb/cm(2)). The formation of a thin SiO2 film by the sol-gel dipping process on the surface of Ti-implanted Ag -Pd-Cu-Au alloy after casting clinically may be useful for minimizing the p ossibilities of the accumulation of dental plaque and metal allergies cause d by intraoral metal restorations. (C) 1999 John Wiley & Sons, Inc.