Effect of Variable Holding Time on Biaxial Strength of Conventional Sintering 4y and 5y Psz

Background: The biaxial strength of dental zirconia restorations is strongly influenced by sintering environments. Variations in sintering protocols could affect zirconia materials' flexural strength. Aim of the study: To examine the effects of varying sintering holding time settings on 4Y and 5Y PSZ translucent zirconia's biaxial flexural strength. Materials & Methods: A digitally designed 3D STL file of disc sample was made, then using CAD CAM, the disc specimens were milled out of 4Y PSZ super translucent multilayered STML and 5Y PSZ ultratranslucent multilayered UTML zirconia ceramics (Kurary Noritake). Specimens of both two main ceramic groups were distributed into 3 subgroups and subjected to 1, 2 and 3 hours holding sintering time at 15500 C. After sintering, samples were subjected to piston on 3-balls biaxial flexural strength tests, load was applied until failure occurred, strength results were statistically analyzed utilizing SPSS program and the findings were compared among groups through the use of 1-way ANOVA and T tests, level of significance was set at 0.05. Results: According to our study findings, the 4YSTML 2 hours holding revealed highest flexural strength for tested zirconia disc samples, whereas the lowest strength values was for 5YUTML 1 hour holding. Conclusions: At 15500 C sintering temperature, translucent 4Y and 5Y PSZ zirconia showed highest biaxial flexural strength when sintered conventionally for 2 hours, the strength was affected negatively by increased and decreased holding time.