Effect of convergence angle and luting agent on the fracture strength of In ceram crowns

This study compared the fracture strength of In ceram crown shapes fabricat ed with either 8 or 16 degrees total occlusal convergence; and attached wit h either a commercial zinc phosphate cement or a glass ionomer cement. Thir ty crown shapes (8 mm diameter and 8.5 mm high) were fabricated for each pr eparation design on a brass master die with approximately the same dimensio ns as a premolar. In ceram crown shapes were luted on to the die using zinc phosphate or glass ionomer. The crown shapes were fractured in a testing m achine (Instron) using a steel ball, 4 mm in diameter, that contacted the o cclusal surface and the resulting data were statistically analyzed using a Mann-Whitney test. The results indicate that there is no statistical differ ence in the fracture strength values between preparations with 8 degrees to tal convergence compared with 16 degrees using the same cement. However, cr own shapes luted with zinc phosphate on preparations with 8 and 16 degrees total occlusal convergence were significantly stronger than those luted usi ng glass ionomer cements (p < 0.05). (C) 1999 Kluwer Academic Publishers.