Effect of surface finishing, coffee thermal cycling, and repolishing on the optical properties of lithium disilicate-based CAD-CAM glass-ceramics.

STATEMENT OF PROBLEM

Despite the availability of lithium disilicate-based glass-ceramics with different compositions, the effects of aging, surface finishing, and repolishing on their color coordinates, color stainability, and translucency remain unclear.

PURPOSE

The purpose of this study was to evaluate the optical properties, including the Commission Internationale de l'Eclairage (CIE) color coordinates (L*, a*, b*, C*, and h°), color stainability (ΔE), relative translucency parameter (RTP), and translucency stability (ΔRTP) of polished and glazed lithium disilicate-based glass-ceramics after thermal cycling and repolishing.

MATERIAL AND METHODS

A total of 100 specimens from 5 lithium disilicate glass-ceramic materials (IPS e.max CAD [LDS], GC Initial LiSi Block [LD], Celtra Duo [ZLS], CEREC Tessera [ALD], and Amber Mill [NLD]) were prepared at 1.5 ±0.01 mm thicknesses. Each material was divided into 2 subgroups: mechanically polished and glazed (n=10). Color measurements were made initially, after 5000 coffee thermal cycles, and after repolishing. L*, a*, b*, C*, h°, ΔE, RTP, and ΔRTP values were recorded. Statistical analysis was conducted using robust ANOVA and Bonferroni multiple comparison tests (α=.05).

RESULTS

NLD had the lowest L*, a*, and b* values but the highest h°, while ALD showed the highest a*, b*, and C* values (P<.001). Polishing increased a*, b*, and C* but decreased h° compared with glazing (P<.001). After coffee thermocycling and repolishing, all materials showed color changes within clinically acceptable limits (ΔE <1.77). NLD had the highest RTP, while ZLS had the lowest (P<.001). Glazing increased RTP in most materials, though a significant decrease was observed in NLD (P=.002) and ZLS (P=.001). ΔRTP values remained clinically imperceptible (<0.62).

CONCLUSIONS

The optical properties of lithium disilicate-based glass-ceramics were affected to varying degrees by material type, surface finishing, coffee thermal cycling, and subsequent repolishing. All materials maintained clinically acceptable color stainability and translucency, though differences in color coordinates, stainability, and translucency were material dependent.