Influence of thermo-mechanical cycling on porcelain bonding to cobalt-chromium and titanium dental alloys fabricated by casting, milling, and selective laser melting

Purpose: The aim has been to determine the effect of thermo-mechanical cycling on shear-bond-strength (SBS) of dental porcelain to Co-Cr and Ti-based alloys fabricated by casting, computer-numerical-controlled milling, and selective-laser-melting (SLM). Methods: Seven groups (n = 22/group) of metal cylinders were fabricated by casting (Co-Cr and commercially pure-cpTi), milling (Co-Cr, cpTi, Ti-6Al-4V) or by SLM (Co-Cr and Ti-6Al-4V) and abraded with airborne-particles. The average surface roughness (R-a) was determined for each group. Dental porcelain was applied and each metal-ceramic combination was divided into two subgroups - stored in deionized water (24-h, 37 degrees C), or subjected to both thermal (6000-cycles, between 5 and 60 degrees C) and mechanical cycling (10(5)-cycles, 60 N-load). SBS test-values and failure modes were recorded. Metal-ceramic interfaces were analyzed with a focused-ion-beam/scanning-electron-microscope (FIB/SEM) and energy-dispersive-spectroscopy (EDS). The elastic properties of the respective metal and ceramic materials were evaluated by instrumented-indentation-testing. The oxide thickness on intact Ti-based substrates was measured with Auger-electron-spectroscopy (AES). Data were analyzed using ANOVA, Tukey's HSD and t-tests (alpha = 0.05). Results: The SBS-means differed according to the metal-ceramic combination (p < 0.0005) and to the fatigue conditions (p < 0.0005). The failure modes and interface analyses suggest better porcelain adherence to Co-Cr than to Ti-based alloys. Values of R-a were dependent on the metal substrate (p < 0.0005). Ti-based substrates were not covered with thick oxide layers following digital fabrication. Conclusions: Ti-based alloys are more susceptible than Co-Cr to reduction of porcelain bond strength following thermo-mechanical cycling. The porcelain bond strength to Ti-based alloys is affected by the applied metal processing technology. (c) 2017 Japan Prosthodontic Society. Published by Elsevier Ltd. All rights reserved.