Optimizing CAD/CAM ceramics: a comparative study of polishing and glazing effects on surface quality and aesthetic properties following coffee thermocycling

This in vitro study aims to evaluate the effects of two different surface finishing procedures-glazing and polishing-on the stability of colour, the translucency, and the roughness of surface with three CAD/CAM ceramic materials: lithium disilicate ceramic (LDC), zirconia-reinforced lithium silicate ceramic (ZLC), and translucent zirconia (TrZ). The process is evaluated before and after coffee thermocycling. A total of 120 samples (1.0 ± 0.1 mm) were prepared from LDC (IPS e.max CAD HT A2), ZLC (Celtra Duo HT A2), and TrZ (Cercon HT A2). All samples were subjected to standardized grinding for 20 s to simulate chairside adjustments and were then assigned to glaze (G) or polish (P) subgroups (n = 20). Surface roughness (Ra, Rz) was measured by using a contact profilometer, while colour coordinates (L*, a*, b*), colour difference (ΔE₀₀) (∆E00), and translucency parameter (TP) were recorded with a colorimeter. All samples underwent 10,000 coffee thermocycles (5–55 °C). Data were analysed by using one-way ANOVA, repeated-measures ANOVA, Kruskal–Wallis, and appropriate post-hoc tests (α = 0.05). It is seen that grinding produced the highest Ra and Rz values in ZLC, followed by LDC and TrZ. When surface treatments were completed, polished TrZ showed a significantly lower Ra compared with glazed TrZ, while ZLC and LDC exhibited lower roughness after glazing, although not significantly. Only the ZLC-P group demonstrated a perceptible colour change, yet all groups remained within the clinically acceptable threshold (< 2.23). Before and after thermocycling, LDC showed the highest TP values, followed by ZLC and TrZ. Thermocycling significantly increased Ra (except in TrZ-P and ZLC-P) and decreased TP values in all materials except LDC-P. Based on the results, it is concluded that surface finishing techniques and coffee thermocycling affect the optical and surface properties of CAD/CAM ceramics. Glazing generally provides smoother surfaces for glass-ceramics, whereas polishing has superior outcomes for translucent zirconia.