Relationship between framework thickness and fracture strength of Ce-TZP/Al crown

Objectives: The aim of this study was to investigate the effect of thickness of zirconia framework on the fracture strength of yttria- stabilized tetragonal zirconia polycrystals (Y-TZP) and Ceria-stabilized tetragonal zirconia polycrystals / alumina nanocomposite (Ce-TZP/Al) in the zirconia-ceramic crown restorations.
Methods: Artificial maxillary second premolars were prepared for metal-ceramic crown (1.0 mm shoulder finish line, 1.5-2.0 mm occlusal reduction) and all-ceramic crown restorations (1.0 mm buccal shoulder finish line and palatal light chamfer, 1.5-2.0 mm occlusal reduction) to serve as artificial tooth abutments. The Co-Cr tooth analogs were duplicated. Ce-TZP/Al (NANOZR, Panasonic Healthcare, Japan) and Y-TZP (Cercon base, DeguDent, Germany) were used. Two types of frameworks were fabricated corresponding to each Co-Cr tooth analogs as follows; overall wall thickness of 0.5 mm for all-ceramic preparation (Y-TZPs, Ce-TZP/Als), wall thickness of 0.3 mm with palatal supporting structure (Y-TZPm, Ce-TZP/Alm). A press ceramics (Vintage ZR Pressover, Shofu, Japan) were pressed with reproducing maxillary second premolar. After 10 crowns of each group were cemented to the Co-Cr tooth analogs using zinc phosphate cement, all specimens were loaded on the central groove along the long axis using universal testing machine (Autograph AGS-H, Shimadzu, Japan) until fracture and recorded as fracture load. The results were statistically analyzed with one-way ANOVA, at a significance level of 0.05. After ANOVA, multiple comparison was performed with the Dunnett T3 test at a significant difference probability level of 0.05.
Results: The fracture loads of Y-TZPs, Ce-TZP/Als, Y-TZPm and Ce-TZP/Alm were 1500.5 ± 525.8 N, 1401.8 ± 130.0 N, 1608.4 ± 464.6 N and 1711.3 ± 415.4 N. There were no significant differences between all groups.
Conclusions: Within the limitation of this study, it is suggested that Ce-TZP/Als, Y-TZPm and Ce-TZP/Alm provide comparable strength to Y-TZPs with its abutment tooth restored by metal post and core.