Comparison of bond strength of porcelain fused to core materials of metal and zirconia

Abstract

Advances in CAD/CAM systems have made it possible to process a homogeneous framework of zirconia which has excellent mechanical strength. Development of porcelain with a thermal expansion coefficient similar to zirconia has made it possible to fuse the two materials. I compared the shear bond strength of porcelain fused to zirconia with that of porcelain fused to metal frameworks. Zirconia cylinder specimens were milled 3mm in diameter and 10mm long. The upper portion of the specimens was airborne-particle abraded with 50μm or 100μm aluminum oxide particles to a circumference of less than 2mm. Opaque and dentin porcelain were applied to 1.5mm thickness using a mold. Porcelain was also bonded to a metal ceramic gold casting alloy, a Ni-Cr casting alloy, and milled pure titanium, respectively. Eight specimens were fabricated for each metal in the same manner as for the zirconia specimens. The specimens were subjected to shear bond testing in an apparatus mounted in a universal testing machine, with a cross-head speed of 0.5mm/min. The measurement data were analyzed by one-way ANOVA, and fracture surfaces were observed with Scanning electron microscopy and energy dispersive X-ray spectroscopy. The mean shear bond strengths were 31.5±5.3MPa for zirconia (50μm particles), 27.1±7.5MPa for zirconia (100μm particles), 32.1±2.3MPa for gold casting alloy, 28.2±4.2MPa for Ni-Cr alloy, and 24.5±6.2MPa for milled pure titanium. The bond strength of zirconia (50μm particles) was significantly greater than that of Ni-Cr alloy. There was no significant difference in the shear bond strength between zirconia ceramics and ceramics fused to casting gold alloys. The surface roughness of zirconia had little effect on bond strength. The reasons for failure of zirconia ceramic differed greatly from those of metal ceramic. There results suggest that zirconia ceramic restorations can be both biocompatibile and esthetic.