Effect of time period on biaxial strength for different Y-TZP veneering porcelains

To assess the influence of time period on strength for different conventional Y-TZP porcelains.

Four types of porcelain were used. Porcelain powders were pressed in a steel die and fired in a furnace as recommended by the manufacturer. The blocks were sectioned into 2 mm-thick discs. Seventy specimens were fabricated from each type of porcelain. Of six jars, three contained 40 mL of dH₂ O and three were dry. Ten specimens were placed in each jar and stored in an incubator at 37°C. A biaxial flexural strength test was performed for all specimens at the baseline and each succeeding year for all groups, for 3 years, using an Instron with a crosshead speed of 0.5 mm/min.

The data were analyzed by ANOVA and Tukey at α = .05. At the baseline, the biaxial flexural strength of VitaVM9 was significantly higher than that of NobelRondo; however, there were no significant differences among Vita VM9 and Noritake CZR or NobelRondo, Lava Ceram, and Noritake CZR. There were significant reductions in the biaxial flexural strengths of all porcelains.

After 3 years, all porcelain groups showed a significant decrease in biaxial flexural strength. The medium used is found to have no significant effects on the mean biaxial flexural strength.

Certain commercially available Y-TZP porcelains are susceptible to decrease in strength over time, which might impact the integrity of veneered zirconia restorations. This reduction in strength is among the most common reasons for the failure of veneered zirconia as reported in several studies.