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 microns or 128 +/- 8 microns; for the resin composite cement, the thickness ranged from 26 +/- 11 microns to 297 +/- 48 microns. 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 microns or more. The characteristic fracture strength of glass-ceramic plates cemented with the resin composite 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.