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 fabricated with either 8 or 16 degrees total occlusal convergence; and attached with either a commercial zinc phosphate cement or a glass ionomer cement. Thirty crown shapes (8 mm diameter and 8.5 mm high) were fabricated for each preparation design on a brass master die with approximately the same dimensions 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 machine (Instron) using a steel ball, 4 mm in diameter, that contacted the occlusal surface and the resulting data were statistically analyzed using a Mann-Whitney test. The results indicate that there is no statistical difference in the fracture strength values between preparations with 8 degrees total convergence compared with 16 degrees using the same cement. However, crown shapes luted with zinc phosphate on preparations with 8 and 16 degrees total occlusal convergence were significantly stronger than those luted using glass ionomer cements (p<0.05).