The effect of whitening toothpaste on surface roughness ofresin-based restorative materials

The aim of this in-vitro study is to evaluate the effect of whitening toothpaste on surface roughness of resin-based restorative materials in different time periods. In this study, human tooth enamel (DM) as negative control group; a conventional nanohybrid composite resin, HXU (Herculite XRV Ultra, Kerr, Orange, CA, USA) as a positive control group; sonic activated nanohybrid direct bulk-fill composite resin, SF2 (SonicFill 2, Kerr, Orange, CA, USA) and reinforced microfilled indirect composite resin, TATL (Tescera, Bisco Dental Products, Seoul, Korea) as the experimental groups were used. All restorative materials were selected in A2 shade. In order to determine the surface roughness, composite resin samples were prepared by using 8 mm diameter and 4 mm high disc shaped metal molds. A total of 96 samples were prepared 24 samples for each composite resin material and the enamel surface of upper incisor human tooth (n= 12). In the polymerization of the samples, 1470 ± mW / cm2 LED light device (Elipar Deep Cure-S, 3M ESPE, St.Paul, MN, USA) was used. Each material is divided into two sub-groups depending on brushing procedure with distilled water or toothpaste (White Now CC, Signal, Unilever, Bulgaria). Two-dimensional brushing simulation was applied with a soft type toothbrush (Sensitive Expert, Signal, Unilever, Germany) for 5000, 15000 and 30000 cycles. Surface roughness was measured at all cycle times with mechanical profilometer. On the other hand, AFM device was used only in the initial phase and at the end of 30000 cycles. 2D and 3D images were taken in SEM and AFM. Statistical analysis was performed by using one-way ANOVA and then Post Hoc LSD test was used for multiple group comparisons, while two-way comparisons were analysed with independent sample t-test. The tests were performed at a statistical significance level of α=0.05. Surface roughness values which were obtained with mechanical profilometer (Surtronic S-128, Taylor Hobson, Leicester, England) found to be significantly higher than those measured by AFM. The composite resins samples brushed with toothpaste were showed higher roughness values compared to distilled water groups. However, surface roughness values were found to be lower in tooth enamel samples brushed with toothpaste. In the restorative material based comparison, AFM Line and AFM Surface measurements were consistent, while the roughness order of materials in mechanical profilometer measurements differed from AFM measurements. The additional polymerization methods and sonic activation did not have a positive contribution on reducing surface roughness values. Besides, whitening toothpaste, as expected, increased the surface roughness of resin-based composite resin materials.