Flexural Strength of Two Multilayered and Monochromatic High Yttria Containing Zirconia Materials Following Different...

Sintering parameters influence the properties of zirconia. This study examined the effect of altering sintering temperature and time of monochrome and multilayer 5 mol% yttria-partially stabilized zirconia (5Y-PSZ) on flexural strength.

Three hundred specimens (width × length × thickness = 10 × 20 × 2 mm) were prepared from monolayer (Z_X) and multilayer (Z_M) 5Y-PSZ and randomly sintered at decreasing (T_D: 1,450°C), regular (T_R: 1,500°C), and increasing (T_I: 1,550°C) sintering temperature, with extremely short (H_E: 10 minutes), ultrashort (H_U: 15 minutes), short (H_S: 30 minutes), and regular (H_R: 135 minutes) sintering time (n = 15/group). The precrack was induced on the tension side before testing for flexural strength (σ).

Analysis of variance and Tukey's test were used for significant differences of σ at p < 0.05. The microstructure and crystalline (monoclinic; m, tetragonal; t, cubic; c) phase were evaluated by scanning electron microscope (SEM) and X-ray diffractometer (XRD).

Z_XT_IH_S indicated the highest σ for Z_X (315.81 ± 18.91 MPa), whereas Z_MT_IH_S indicated the highest σ for Z_M (335.21 ± 36.18 MPa). There was no significant difference for σ between Z_X and Z_M (p > 0.05). Sintering zirconia at T_I or H_R indicated significantly higher σ than sintering at T_D or T_R or with H_S, H_E, or H_U for both Z_X and Z_M (p < 0.05). There was no significant difference for σ between T_RH_R and T_IH_S, T_IH_U, and T_IH_E (p > 0.05). SEM indicated intergranular and transgranular fractures. XRD revealed predominately c- and t-phases and minor amounts of m-phase.

Increasing sintered temperature with decreasing time offers acceptable strength to regular sintering. Raising sintering temperature with decreasing time is suggested to facilitate chairside restorative reconstruction.