Influence of sintering temperature and aging on the color and translucency of zirconia

Abstract

Statement of problem: Translucent zirconias are promising materials for monolithic prostheses. However, information on their optical behavior after sintering and aging protocols is scarce.

Purpose: The purpose of this in vitro study was to evaluate the color and translucency of zirconia subjected to different sintering temperatures and aging.

Material and methods: A total of 180 1.5-mm-thick disks were produced from translucent zirconia blocks: DD cubeX² white, DD cubeX² A2 shade, DD Bio ZX² white (Dental Direkt GmbH), and Lava Plus white (3M ESPE). White and A2 shade disks were made for each zirconia. DD Bio ZX² and Lava Plus were colored by immersion in dyeing liquids. All disks were divided according to the sintering temperature: 1400 ºC, 1450 ºC, and 1500 ºC (T₀). Subsequently, the disks were subjected to an aging protocol in an autoclave for 5 (T₁) and 20 hours (T₂). The L*a*b* coordinates were measured with a spectrophotometer. ∆E₀₀, ∆L', ∆C', ∆H', and TP were calculated using CIEDE2000, and CR was obtained using CIEXYZ. Repeated measures ANOVA and the Tukey HSD test were used for statistical analysis (α=.05).

Results: The 1400 ºC temperature produced the greatest ΔE₀₀ (5.25). A progressive increase in ΔE₀₀ was found after aging (especially in T₂), with a reduction in lightness and an increase in saturation in most groups (P<.001). The DD cubeX² white (DCW) and A2 (DCC) groups presented the highest TP₀₀ values, mainly at 1500 °C. The highest CR values were observed in the Lava Plus colored (LPC) group (1400 °C) (P<.001).

Conclusions: Sintering at a lower temperature than that recommended by the manufacturer can reduce lightness and increase saturation and opacity, especially after aging.