Firing Protocols Effect on Optical Properties of Different Lithium Disilicates

Objectives: Different firing protocols are available for manufacturing restorations using IPS e.max lithium disilicate. To investigate the viability of using these procedures on a new generation, ‘advanced’ lithium disilicate, this study evaluated the Color difference (ΔE₀₀), Translucency parameter (TP₀₀) and Whiteness Index for Dentistry (WI_D) of both lithium disilicates differently fired and/or glazed.
Methods: Fifty disc-shaped (10 mm diameter x 1.2 mm thickness) specimens were fabricated from IPS e.max CAD – LD (Ivoclar) and CEREC Tessera – ALD (Sirona) and divided into five subgroups, according to glaze and firing protocol (Crystallized; One step crystallized and glazed; Crystallized and refired; Two step crystallized and glazed; or Long firing crystallization). ΔE₀₀, TP₀₀ and WI_D were accessed. Statistical analysis for color difference considering One step crystallized and glazed groups as reference, was performed using a 1-way ANOVA (α=0.05) followed by Tukey test. TP₀₀ and WI_D data were analyzed using 2-way ANOVA (α=0.05) and Tukey test.
Results: ANOVA showed no effect of firing procedures on ΔE₀₀, TP₀₀ and WI_D for LD. In addition, LD was more translucent and brighter than ALD. For ALD, all ΔE₀₀ in relation to the reference firing protocol were visible and not clinically acceptable (ΔE₀₀ > 1.77). ALD groups with one standard firing cycle presented higher TP₀₀ and WI_D.
Conclusions: The assessed firing protocols were found to have no significant impact on ΔE₀₀, TP₀₀, and WID of LD. Additionally, LD demonstrates higher translucency and whiteness compared to ALD. It was observed that ALD is less predictable when using different firing protocols, particularly when multiple firing cycles are involved. Consequently, alternative firing protocols result in clinically unacceptable color variations when compared to the manufacturer-recommended firing protocol for ALD.