Color Characteristics of High Yttrium Oxide-Doped Monochrome and Multilayer Partially Stabilized Zirconia upon Different Sintering Parameters.

OBJECTIVES

Sintering influences the optical properties of zirconia. This study examined the effect of altering sintering temperature and time of monochrome (Mo) and multilayer (Mu) 5 mol% yttria-partially stabilized zirconia (5Y-PSZ) on color characteristics.

MATERIALS AND METHODS

Three hundred specimens (width × length × thickness = 10 × 20 × 2 mm) were prepared from Mo and Mu (with cervical [C], middle [M], and incisal [I] region) 5Y-PSZ and randomly sintered at decreasing (Td: 1,450°C), regular (Tr: 1,500°C), and increasing (TI: 1,550°C) sintering temperature, with extremely short (He: 10 minutes), ultrashort (Hu: 15 minutes), short (Hs: 30 minutes), and regular (Hr: 135 minutes) sintering time ( = 15/group). Color appearance ( ), translucency parameter (TP), contrast ratio (CR), opalescence parameter (OP), and color appearance difference (∆ ) were evaluated in the CIE Lab* system. Microstructures were evaluated by scanning electron microscope (SEM) and X-ray diffractometer (XRD).

STATISTICAL ANALYSIS

Analysis of variance (ANOVA) and Bonferroni comparisons were determined for significant differences ( < 0.05).

RESULTS

Significant differences in color parameters upon zirconia type, sintering temperature, and sintering time, and their interactions were indicated ( < 0.05). Increasing sintering temperature and extended sintered time resulted in larger grain, reduced tetragonal-to-monoclinic phase transformation, and significantly increased the TP and OP, but decreased the CR and ∆ ( < 0.05). Decreasing sintering temperature and time led to clinically unacceptable color appearance.

CONCLUSION

Mo was found to be more translucent than Mu. To achieve the most favorable optical properties, increasing sintering temperature and extending sintering time are recommended. Decreasing sintering temperature is not suggested. However, shortened sintering time is feasible, but it needs sintering with increasing sintering temperature to achieve a promising color appearance.