An In Vitro Study to Investigate the Load at Fracture of Procera AllCeram Crowns with Various Thickness of Occlusal Veneer Porcelain

Purpose: The aim of this study was to investigate the effect of occlusal veneer porcelain thickness on the load at fracture of Procera AllCeram crowns. Materials and Methods: Fifty resin dies were manufactured to incorporate the features of an all-ceramic crown preparation on a premolar tooth. Fifty corresponding crowns were constructed and divided into five groups. Groups 1, 2, 3, and 4 were crowns with 0.6-mm-thick Procera cores and 0.4-mm-thick axial veneer porcelain and occlusal veneer porcelain thicknesses of 0.0 mm, 0.4 mm, 0.9 mm, and 1.4 mm, respectively. Group 5 specimens consisted of 0.6-mm-thick In-Ceram cores with 0.4 mm of axial porcelain and 0.4 mm of occlusal porcelain. The crowns were cemented onto their respective dies with a resin luting agent. Specimens were stored in distilled water at 37°C for 24 hours prior to placing them in a universal testing machine and applying a controlled compressive load at a cross-head speed of 0.1 mm/min until fracture occurred. Results: The mean loads at fracture were 419 N (group 1), 702 N (group 2), 1,142 N (group 3), 1,297 N (group 4), and 732 N (group 5). Statistical analysis revealed significant differences (P .05) in the load at fracture between the groups, except for between groups 2 and 5. Conclusion: Increasing the thickness of the occlusal veneer porcelain increased the load at fracture for Procera AllCeram crowns. There was no significant difference in load at fracture between the Procera and In-Ceram crowns.