Adhesion promotion of resin to zirconia by silicon nitride hydrolysis

Abstract

PURPOSE: To investigate the effect of surface treatment on zirconia by silicon nitride hydrolysis on resin zirconia bonding. METHODS AND MATERIALS: Yttria-stabilized zirconia samples (Upcera, Liaoning, China) were immersed in a 4M sodium hydroxide solution and heated to 90 ◦C. A 0.6wt% silicon nitride dispersion was prepared by adding silicon nitride nanopowder (US Research Nanomaterials, Houston, USA) into the solution. The zirconia samples were immersed into the dispersion for 6, 24, and 48 h. After the coating process, the zirconia samples underwent a thermal treatment at 1400 ◦C for 2 h. Another control test group was surface treated by sandblasting using a 100_msilica-coated alumina powder (3M ESPE, Seezle, Germany). Resin stubs were bonded to silicacoated zirconia samples. Four test groups (n = 8)were prepared. Each test group was divided into three subgroups and subjected to test in three storage conditions: dry, 30 d water aging at 37 ◦C, and thermo-cycled for 6000 cycles between 5.0±0.5 ◦C and 55.0±0.5 ◦C. Shear bond strength tests for all test groups were performed on a universal testing machine (ElectroPulsTM E3000, Instron, USA). Data were analyzed by two-way ANOVA and Tukey HSD (p < 0.05). The surface roughness was measured by an electro-mechanical profilometer (Surtronic 3+, Taylor Hobson, Leicester, England). Five readings were taken at different regions for each sample surface. The surface morphology and composition of silica-coated zirconia samples were examined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). RESULTS: Table 1 showed the results of mean shear bond strengths for all test groups. Two-way ANOVA analysis showed that there was a significant difference in mean shear bond strengths under various surface treatments (p < 0.001). There was no significant difference in storage conditions (p > 0.05). The average surface roughness, Ra (_m), measured were: polished (0.3±0.08), sandblasted (0.8±0.13), silica-coated (6 h): (0.4±0.07), silica-coated (24 h): (0.5±0.07), silica-coated (48 h) (0.5±0.1). The Ra of sandblasted zirconia surface was significantly higher than the other test groups of zirconia surfaces (p < 0.001). SEM micrographs showed that there were changes in the surface morphology of zirconia after various surface treatments. EDX analysis results showed that the highest silica content was obtained for 48h immersion. CONCLUSION: A new method of surface treatment of zirconia was developed. The results showed that durable resin zirconia bonding could be achieved.