OBJECTIVES: The aim of this study was to evaluate the effect of different types and design of zirconia frameworks as well as the effect of different veneering ceramics on the fracture strength of crowns. The importance of different abutment materials was also evaluated. MATERIALS AND METHODS: Eighty cores, 40 in a fully-sintered zirconia material and 40 in a pre-sintered zirconia material were made. Twenty cores of each material were made with a core of even thickness shape (ES) and 20 were made with a core with anatomical shape (AS). The cores were divided into subgroups and veneered with one of two different veneering ceramics: a porcelain and a glass-ceramic material. In total eight groups of 10 crowns were made. They were all cemented onto abutments made of resin. One extra group of 10 AS, pre-sintered zirconia cores veneered with glass-ceramic were made and cemented onto titanium abutments. All crowns underwent thermocycling and mechanical pre-load and were finally loaded until fracture. RESULTS: AS crowns withstood significantly higher loads than ES crowns (P-value <0.001), and crowns with titanium abutments withstood significantly higher loads than crowns supported by abutments made of inlay pattern resin (P-value <0.001). Three types of fracture were noted: minor and major fracture of the veneering ceramic, and complete fracture through core and veneer. ES crowns showed significantly more major fractures of the veneering ceramic than AS crowns. CONCLUSIONS: This in vitro study indicates that the design of the core, as well as the abutment support, significantly influences fracture load and fracture mode of yttria-stabilized tetragonal zirconia polycrystals crowns.
OBJECTIVES: The aim of this study was to evaluate the effect of different types and design of zirconia frameworks as well as the effect of different veneering ceramics on the fracture strength of crowns. The importance of different abutment materials was also evaluated. MATERIALS AND METHODS: Eighty cores, 40 in a fully-sintered zirconia material and 40 in a pre-sintered zirconia material were made. Twenty cores of each material were made with a core of even thickness shape (ES) and 20 were made with a core with anatomical shape (AS). The cores were divided into subgroups and veneered with one of two different veneering ceramics: a porcelain and a glass-ceramic material. In total eight groups of 10 crowns were made. They were all cemented onto abutments made of resin. One extra group of 10 AS, pre-sintered zirconia cores veneered with glass-ceramic were made and cemented onto titanium abutments. All crowns underwent thermocycling and mechanical pre-load and were finally loaded until fracture. RESULTS: AS crowns withstood significantly higher loads than ES crowns (P-value <0.001), and crowns with titanium abutments withstood significantly higher loads than crowns supported by abutments made of inlay pattern resin (P-value <0.001). Three types of fracture were noted: minor and major fracture of the veneering ceramic, and complete fracture through core and veneer. ES crowns showed significantly more major fractures of the veneering ceramic than AS crowns. CONCLUSIONS: This in vitro study indicates that the design of the core, as well as the abutment support, significantly influences fracture load and fracture mode of yttria-stabilized tetragonal zirconia polycrystals crowns.