[Effect of repeated sintering on the color and translucency of dental lithium disilicate-based glass ceramic]

To evaluate the effect of repeated sintering on the color and translucency of dental lithium disilicate-based glass ceramic.

Thirty disc specimens (10 mm in diameter, and 1.00 mm ± 0.01 mm in thickness) were fabricated using an IPS e.max Press HT A2 ingot and then randomly divided into six groups (SO, S1, S2, S3, S4, and S5) (n = 5). Each group was sintered 0, 1, 2, 3, 4, and 5 times individually according to the manufacturer's recommendation. After polishing, ultrasonic cleaning, and drying, the color parameters (L*, a*, and b* values) and transmittance (τ) of all the specimens were measured using a ShadeEye NCC dental colorimeter and a TM-2 spectrophotometer, respectively. Subsequently, C*ab and ΔE were calculated. The results were statistically analyzed using SPSS 17.0 software for ANOVA and LSD.

After repeated sintering, the L* value significantly decreased (P < 0.05), and the a*, b*, and C*ab values initially increased and then decreased (P < 0.05). The color parameters (L*, a*, and b*) and the C*ab values of group S3 were higher than those of the other groups. The τ values initially increased and then decreased (P < 0.05), and these values were optimal when sintered twice. In terms of transmittance (τ), statistical differences existed between the following groups: S0 and S2, S0 and S3,.S2 and S5, and S3 and S5 (P < 0.05). Compared with group S0, the color differences ΔE were 0.89 minimally and 2.01 maximally after different sintering times, which can be clinically acceptable.

Repeated sintering can affect the color and translucency of the IPS e.max Press lithium disilicate-based glass ceramic, but the color difference can be clinically acceptable.