Effect of modeling liquid and glycerin application protocols on the surface roughness and microhardness of one shade resin composites

Abstract

To evaluate the effects of different modeling liquid and glycerin application protocols on surface roughness (R a ) and Vickers microhardness (VHN) of one-shade resin composites before and after coffee staining. Five resin composites (four one-shade and one conventional nanohybrid control) were tested using four surface protocols: modeling liquid with finishing/polishing (FP+), modeling liquid without polishing (FP−), glycerin over modeling liquid (GLY), and a control group. After 24-hour storage, baseline R a and VHN values were recorded. Specimens were then immersed in coffee for 7-days, followed by repeated measurements. Data normality was assessed using the Shapiro–Wilk test. Since the data were not normally distributed, Kruskal–Wallis, Mann–Whitney U with Bonferroni correction, and Wilcoxon signed-rank tests with Benjamini–Hochberg FDR correction were used. The significance level was set at p < 0.05. Surface protocol significantly affected all parameters ( p < 0.001), while composite type had no significant effect. The FP+ group showed the highest VHN and lowest R a values. In contrast, the GLY group exhibited clinically unacceptable roughness (R a >0.2 μm) and the lowest VHN across all materials. Coffee immersion increased R a and decreased VHN, yet the ranking of protocols remained stable. Application protocol plays a more critical role than material type. Modeling liquids are effective when followed by polishing, whereas their use with glycerin without mechanical finishing leads to significant surface deterioration and should be avoided.