Effect of different polishing systems and acidic media on surface properties of bulk-fill composites

Objectives: The aim of this study was to evaluate the changes in color and surface roughness characteristics of four different bulk fill and one universal composite resin, polished with two different polishing systems, after immersion in two drinks and artificial saliva. Methods: In this study, a total of 360 disc-shaped samples of 8 mm diameter and 2 mm thickness were prepared for 3 different polishing methods [Mylar strip, Sof-Lex Discs, (3M ESPE, St. Paul, MN, USA), Clearfil Twist Dia, (Kuraray Dental, Tokyo, Japan)] and 3 different solution [artificial saliva, cola (The Coca-Cola Company, Atlanta, USA; pH 2.53) and energy drink (Red Bull GmbH, Am Brunnen, Austria; pH 3.54)] groups from 5 different composites [Filtek Z250 (3M / ESPE, USA), Tetric EvoCeram Bulk Fill (Ivoclar Vivadent, Schaan, Liechtenstein), Filtek One Bulk Fill (3M ESPE, St Paul, MN, USA), Beautifil-Bulk Restorative (Shofu, Kyoto, Japan), Estelite Bulk Fill Flow (Tokuyama Dental Corporation, Tokyo, Japan)] (n = 8). The composite resin was placed in a metal mold and polymerized with a standard light source according to the manufacturer's recommendations. The samples were divided into subgroups according to the polishing method and polishing was done in line with the manufacturer's suggestions. The color value and surface roughness measurements of the samples were made before and after holding them in different solutions for 7 days. Color change (ΔE) was recorded in CIELAB color system, roughness values as average Ra. Statistical analysis of the data obtained as a result of the study was performed using the Three-Way-ANOVA test. Results: Among the composite resins, Z250 (0,104 ±0,095 μm) showed the highest roughness change and the Estelite Bulk (0,027 ±0,023 μm) group showed the lowest change in roughness (p<0,01). The highest color change was observed in group Beautifil Bulk (ΔE=4,839 ±3,415), while the least color change was seen in group Z250 (ΔE=1,501 ±0,415) (p<0,01). Among the polishing groups, the highest roughness change was observed in group Mylar Strip (0,104 ±0,102 μm), the lowest change in roughness was seen in group Twist Dia (0,431 ±0,352 μm), while the highest color change was seen in group Soflex (ΔE=3,383 ±2,653) and the lowest change in group Twist Dia (ΔE=1,975 ±0,992) (p<0,01). When the beverage groups were evaluated, the change in roughness was caused by cola (0,088 ±0,083 μm) the most, artificial saliva (0,036 ±0,042 μm) the least, while the color change was caused by energy drink (ΔE=3,123 ±2,477) the most and the least artificial saliva (ΔE=1,787 ±0,640) (p<0,01). Conclusions: According to the results of this study, the color and surface roughness, which are the physical properties of the restorations, may affect the type of composite material, the polishing methods and acidic drinks. Keywords: Bulk fill composite, composite resin, polishing method, acidic drink, surface roughness, color stability.