Fracture Strength of Zirconia-frameworks Veneered with Pressed and Layered Ceramics

Objectives: The aim of this study was to test the fracture strength of zirconia frameworks for single crowns veneered with pressed or layered veneering ceramics. Materials and Methods: Standardized zirconia frameworks (N=120) were fabricated on metal tooth analogs using a CAD/CAM system (ZENO Tec, Wieland Dental). The frameworks were randomly divided into 8 groups (n=15 per group) and veneered to receive a standardized shape following the manufacturer`s instructions. Groups 1-4 were veneered with the following pressed veneering ceramics: PressX Zr (Wieland Dental; group 1), GC Initial LF (GC Europe; group 2), VITA PM9 (Vita Zahnfabrik; group 3), IPS e.max ZirPress (Ivoclar Vivadent; group 4). The remaining four groups (groups 5-8) were veneered with the following layered veneering ceramics: Zirox (Wieland Dental; group 5), GC Initial ZR (GC Europe; group 6), Vita VM9 (Vita Zahnfabrik; group 7) and IPS e.max Ceram (Ivoclar Vivadent; group 8). After the veneering procedures, the crowns were cemented to the tooth analog using a glass ionomer cement (KetacCem, 3M ESPE) and subjected to static loading. For this, the specimens were loaded at an angle of 45° to fracture in a universal testing machine (1 mm/min). Data were analyzed using one-way ANOVA, followed by a post-hoc Scheffé test (alpha=0.05). Results: With three brands of veneering ceramics (groups 1,2,3,5,6,7), mean fracture loads were not statistically significant (p>0.05) between pressed and layered veneering ceramic ranging between 965±164 N and 1109±359N. With one brand (groups 4 and 8), the crowns veneered with the pressed veneering ceramics demonstrated significantly higher (p<0.05) fracture strength than those with the layered veneer ceramic (1519±334 N and 894±160 N, respectively). Conclusions: Pressed veneering ceramics for zirconia single crown frameworks exhibited similar or better fracture strength than those of the layered ones.