THE EFFECT OF CEMENT THICKNESS ON THE FRACTURE STRENGTH OF ALL-CERAMIC CROWNS

The effect of increasing cement thickness on the fracture strength of aluminous porcelain jacket crowns was investigated in this study. Thir ty-three aluminous porcelain jacket crowns were divided into three gro ups. In Group 1, only platinum foil was used to provide cement space. In Group 2 two layers and Group 3 four layers of die spacer were paint ed onto the metal die before impression taking. Each crown was cemente d onto a metal die with zinc phosphate cement and loaded until fractur e. The maximum force to break each crown was recorded. The average fra cture load was 408 N for Group 1, 365 N for Group 2 and 324 N for Grou p 3. ANOVA (SPSS) found a significant difference (p<0.05) between grou ps. A Scheffe Test revealed a significant difference between Groups 1 and 3. It was concluded that increasing the cement thickness above 70 mu m reduced the fracture strength of porcelain jacket crowns.