Strength Characteristic of Different Layers of Zirconia Discs Manufactured Using Various Multilayering Methods and Sintered at Variable Final Temperature

Background: Nowadays, yttria stabilized ZrO2 is the most commonly used esthetic material in fixed dental prosthodontics. The vast majority of full contour monolithic fixed dental restorations were made from multilayered translucent zirconia. The Aim of this Research: Was to study the flexural strength of three different layers of multilayered zirconia discs manufactured with two multilayering technologies (yttria graded and shade graded) and sintered at different temperatures. Method: Ninety bars were divided into 3 groups (n=30) made from three different zirconia discs manufactured with various multilayering techniques, Zircad PRime, Super Translucent Multilayered and Zolid FX, each main group subdivided into three subgroups (n=10) in accordance with the multilayered zirconia materials that were used and three different layers were utilized from each disc: Zircad PRime Cervical ZPRC, Zircad PRime Middle ZPRM, Zircad PRime Incisal ZPRI, STM Cervical STMC, STM Middle STMM, STM Incisal STMI, Zolid FX Cervical ZFXC, Zolid FX Middle ZFXM and Zolid FX Incisal ZFXI. After milling the specimens were separated from zirconia discs, then fully sintered conventionally for 2 hours according manufacturer instructions regarding final temperature and the strength evaluated with three point’s flexural strength bending test utilizing the universal testing equipment. Result: Non significant differences among layers of shade graded zirconia STM and Zolid FX while a difference was observed between layers of yttria graded zirconia Zircad PRime. Highest result was for ZPRC and lowest flexural strength result was for ZFXC. Conclusion: Neither all multilayered zirconia discs nor the variable layers are the same. Incisal layer of varying yttria concentrations multilayered zirconia demonstrates much lower flexural strength than cervical layer at the same disc, while shade graded multilayered disc variable layers have same strength, yttria content greatly influence strength of zirconia materials and sintering temperature has no effect on flexural strength of layers have the same yttria content.