The Fracture Load of Three CAD-CAM Veneering Systems over Zirconia

Objective: To compare the fracture loads of three CAD/CAM veneering systems on zirconia crowns: LavaDVS(3M-ESPE); Rapid Layering Technology(Vita); and a CAD-on technique(Ivoclar Vivadent). Methods: Three groups were used in this study: (Group1) LavaDVS-feldspathic glass-ceramic compact sintered to zirconia framework using fusion porcelain; (Group2) Rapid Layering Technology-feldspathic glass-ceramic veneer cemented to zirconia framework using dental cement; (Group3) Cad-on -a lithium-disilicate glass-ceramic veneer sintered to zirconia framework using fusion ceramic. Fifteen specimens were produced for each group. Group 1 was produced initially on a standardized #3 crown preparation. Group 1 zirconia copings and CAD veneers were produced in an authorized LavaDVS center and then fired/fused and glazed according to the manufacturer's instructions. From these zirconia copings and final restorations, a digital model was developed using the Cerec InLab (Sirona) to produce Groups 2 and 3 which were then fired/joined and glazed according to the respective manufacturer's instructions. The occlusal morphology and layer thicknesses were the same for all crowns in the study. All crowns were formed to composite preparations (TetricEvoCeram, Ivoclar Vivadent) and stored in water for a week at 37C before cementation (Multilink Automix, Ivoclar Vivadent) then stored again after cementation in water for another week at 37C. The crowns were loaded using a 15-mm diameter steel ball at a crosshead speed of 0.5mm/min with an Instron Universal Testing machine. Crack initiations were monitored acoustically, and failure load was recorded. Results: The failure load values (N) were Group 1: 1688±602, Group 2: 1833±460, and Group 3: 3534±602. Using ANOVA (p≤0.05), a statistically difference was found between Group 3 and Groups 1 and 2. No statistical significance was found between Group 1 and Group 2. Conclusion: Within this study, the lithium disilicate CAD/CAM layering technique produced higher failure loads in comparison to feldspathic CAD/CAM layering techniques.