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

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

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

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).

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).

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