Color stability and translucency of CAD-CAM lithium disilicate ceramic materials after repeated firings using...

The influence of repeated firings on the optical properties of recently introduced computer-aided design and computer-aided manufacturing (CAD-CAM) lithium disilicate ceramics remains unclear.

The purpose of this in vitro study was to evaluate the color stability and translucency of 3 CAD-CAM lithium disilicate ceramics after repeated firings, with and without glazing, using a conventional firing mode. For an advanced lithium disilicate ceramic, the effects of conventional and speed firing modes were compared.

Eighty specimens (12×14×1 mm) were fabricated from 3 CAD-CAM lithium disilicate ceramics: IPS e.max CAD (EM), Amber Mill (AM), and CEREC Tessera (CE). The specimens were assigned to 8 subgroups (n=10) based on material, glazing, and firing mode. For EM and AM, 20 specimens per material were equally divided into glazed and nonglazed groups. For the 40 CE specimens, a tiered allocation was used: the specimens were assigned to conventional or speed firing modes and subsequently subdivided into glazed or nonglazed status. Color change (ΔE₀₀) and translucency parameter (TP₀₀) were measured after normal firing and 1, 3, and 5 repeated firings. The effects of material type, glazing status, and repeated firing cycles on color change and translucency were evaluated using 3-way repeated-measures ANOVA with the least significant difference (LSD) post hoc test (α=.05).

Repeated firings significantly affected the color stability and translucency of CAD-CAM lithium disilicate ceramics (P<.001), with significant interactions between the number of firings and material type for ΔE₀₀ (P<.001) and TP₀₀ (P=.002). All specimens exhibited increased color change and reduced translucency after 5 firings. EM exhibited the lowest color change, AM maintained the highest translucency, while CE demonstrated both the highest color change and the lowest translucency. For CE, speed firing resulted in significantly lower ΔE₀₀ values (P<.001) and smaller reductions in TP₀₀ compared with the conventional firing mode.

Repeated firings significantly affected the color stability and translucency of all tested CAD-CAM lithium disilicate ceramics, with CE being most affected. Speed firing was more effective than conventional firing in maintaining color stability in advanced lithium disilicate ceramic.