Biaxial Flexural Strength of a New Dental Zirconia Ceramic

Objectives: To determine and compare effects of storage conditions on biaxial flexural strength of a new type dental zirconia. Methods: Disc-shaped specimens (14.0±2 mm diameter, 1.2±0.2mm thick) of three types of zirconia were prepared according to ISO Specification test ISO 6872:2008(E): Noritake: NZ-HIP (fully sintered), NZ-No HIP; LAVA (3M ESPE). One side of each specimen was polished to a final finish of 6.7 microns (JIS #2000). Specimens were water-stored at room temperature at least 2 months, or were heated in an oven at 100°C for 8 hours to remove surface and inner water content, and then immersed in light mineral oil. Specimens were tested in a biaxial flexure jig in a universal testing machine (Model 8562, Instron, Norwood, MA) at a crosshead speed of 0.5 m/min. Peak load at failure was noted and biaxial flexural strength (FS) was determined using methods prescribed in the ISO specification (section 7.3.3.4). Twenty specimens per test condition were made and randomly tested. Statistical analysis consisted on a 2-way ANOVA among results, with Tukey's post-hoc test applied for pair-wise means differences at a pre-set alpha of 0.05. Results: Table presents mean biaxial flexure strength (MPa)(SD).

Within column (upper case) or row (lower case), values having similar letters are not significantly different.

ANOVA indicated significant effect of major factors (material p<0.001; storage p=0.005) as well as their interaction (p=0.014). Pooled storage effect among material indicated FS NZ-HIP>NZ-NO HIP>LAVA. Within each storage treatment, NZ-HIP>NZ-NO HIP>LAVA. FS of specimens stored in oil were significantly greater than those stored in water for all materials, except NZ-HIP, where there was no significant difference. Conclusions: Storage condition had no significant effect on HIP-treated specimens, while exposure to water significantly lowered FS of other zirconia groups. In all instances, FS NZ-HIP > NZ-NO HIP > LAVA.