Pre-oxidation of selective-laser-melted titanium dental alloy: effects on surface characteristics and porcelain bonding
Maja Antanasova, Andraž Kocjan, Anže Abram, Janez Kovač, Peter Jevnikar
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 (Sa) 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 Ra and Sa 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.