Fatigue Resistance and Fracture Strength of Zirconia -Machinable Ceramic Crowns

Objective: to determine the effect of framework design and veneering porcelain on the fatigue and fracture resistance of zirconium-oxide crowns. Methods: An ivorine molar was prepared to receive an all-ceramic crown. Using an epoxy resin (Viade), 40 replication dies were made of the prepared tooth. Forty zirconium-oxide cores (IPS e.max ZirCAD, Ivoclar-Vivadent) were fabricated (20 with even thickness and 20 anatomically shaped). Veneering layers were fabricated with two machinable ceramics using CEREC in-Lab (Sirona). Four groups were fabricated as shown in Table1. The VMII veneers were cemented on the copings using resin cement (PanaviaF 2.0, Kuraray), while the CAD veneers were fused to the copings using a fusion glass-ceramic (Crystall, Ivoclar-Vivadent). All crowns were cemented to their respective dies using resin cement (PanaviaF 2.0). After water storage (37 ¼C, 7d), all crowns in each group were subjected to cyclic loading in a universal testing machine (Instron 8501) , 50–600N for 500,000 cycles at 20Hz. After fatigue, crowns were loaded to fracture at crosshead speed of 1mm/min. The fractured samples were examined to determine fracture mode. Data were analyzed (Two-Way ANOVA, α=0.05). Results: All crowns survived the fatigue test without cracks or fractures. The fracture loads and modes are reported in Table1.  Two-way ANOVA revealed a statistically significant effect of the veneering material (P<0.001), but not for the core design or the interaction term. All the VMII crowns showed fractures involving the veneers only and lower fracture strength.70% of the CAD crowns had fractures involving both the core and veneer, and higher fracture strength. Conclusion: The veneering technique, but not the core design, had a significant effect on fracture strength and mode of zirconia-machinable ceramic crowns.

Acknowledgements: University of Toronto, Faculty of Dentistry Research Committee, Education and Research Foundation of Prosthodontics, Ivoclar-Vivadent, Kuraray, Select Dental Lab (Woodbridge, ON).

            Table 1