Effect of cement film thickness on the fracture resistance of a machinable glass-ceramic

Abstract

Objectives. The aim of this study was to determine the fracture resistance of a machinable glass-ceramic plate cemented to a resin composite block as a function of the cement film thickness for two types of cement. Methods. Ceramic plates were cemented to resin composite blocks using either zinc phosphate cement or a resin composite cement. For the zinc phosphate cement, the film thickness was 33 ± 8 μm or 128 ± 8 μm; for the resin composite cement, the thickness ranged from 26 ± 11 μm to 297 ± 48 μm. The elastic modulus was determined for each of the cements. Fracture loads were obtained by using a spherical steel indenter in the center of the glass-ceramic plate. The Weibull distribution was used for the statistical analysis. Results. For glass-ceramic plates cemented with zinc phosphate cement, the fracture resistance was independent of the film thickness. When the resin composite cement was used, a gradual decrease of the fracture strength was observed that became statistically significant at a cement thickness of 300 μm or more. The characteristic fracture strength of glass-ceramic plates cemented with the resin comosite cement was about 75% higher than when using the zinc phosphate cement. This difference is attributed to the bonding of the resin cement to the ceramic plate and the supporting structure. Significance. The findings of this study suggest that the resistance to fracture due to indentation of the glass-ceramic may not be affected by the cement film thickness as much as previously thought.