Pre-oxidation of selective-laser-melted titanium dental alloy: effects on surface characteristics and porcelain bonding

Abstract

The heat treatment of dental alloys prior to porcelain application/veneering has been proposed as a way to ensure sufficient oxide scale and to promote the porcelain’s adherence in porcelain-fused-to-metal (PFM) fixed dental prostheses. The present study investigates the relationship between the bond strength of the dental porcelain to selective-laser-melted (SLM) titanium and the temperature of the titanium’s pre-oxidation. The SLM Ti-6Al-4V substrates were airborne-particle abraded and either left to passivate in air at room temperature (control) or pre-oxidized in a furnace under vacuum conditions (10 kPa) at temperatures of 300, 600, 750, or 800 °C. The surface characteristics were determined using contact profilometry to measure the profile roughness (Ra ), atomic force microscopy for the surface roughness (S a ) and Auger electron spectroscopy for the thickness of the oxide scale. Dental porcelain was applied to the metal substrates and the titanium-ceramic bond was assessed according to the ISO standard 9693-1:2012. The metal-ceramic interfaces were analyzed with scanning electron microscopy and energy-dispersive spectroscopy. The R a and S a values showed a strong positive correlation with the pre-oxidation temperature. The oxide scales covering the titanium surfaces thickened markedly at temperatures of 750 °C and above. However, the bond strength was negatively correlated with the pre-oxidation temperature. Room-temperature passivation in air following the airborne-particle abrasion of the SLM titanium resulted in a titanium-ceramic bond that is well above the ISO 9693-1:2012 recommended minimum value for metal-ceramic systems. Thus, no pre-oxidation of SLM titanium frameworks is necessary prior to the application/firing of porcelain.