Fracture strength of zirconia and alumina ceramic crowns supported by implants.

Abstract Abstract Due to the brittleness and limited tensile strength of the veneering glass-ceramic materials, the methods that combine strong core materials, as zirconia or alumina, is still under debate. The present study aims to evaluate the fracture strength and the mechanism of failure through fractographic analysis of single all-ceramic crowns supported by implants. Forty premolar cores were fabricated with CAD/CAM technology using alumina (n=20) and zirconia (n=20). The specimens were veneered with glass-ceramic, cemented on titanium abutments and subjected to loading test until fracture. SEM fractographic analysis was also performed. The fracture load was 1165 (±509) N for alumina and 1638 (±662) N for zirconia with a statistically significant difference between the two groups (p=0.026). Fractographic analysis of alumina-glass-ceramic crowns, showed the presence of catastrophic cracks of the entire thickness of the alumina core while, for the zirconia-glass-ceramic crowns, the cracks involved mainly the thickness of the ceramic veneering layer. The sandblast procedure of the zirconia core showed an influence on crack path deflection. Only few samples (n=3) showed limited micro-cracks of the zirconia core. Zirconia showed a significant higher fracture strength value in implant-supported restorations, indicating the role-played by the high resistant cores for premolar crowns.