## 4 Discussion  
This study investigated the effect on color recovery and surface roughness of two toothpastes (SIR and SW) and their combination with another toothpaste (PP) with a polishing feature on composite samples. According to our results, using PP in combination with SW and SIR improved color recovery without increasing surface roughness in discolored composite resins. Therefore, the first hypothesis of the study was accepted. The International Organization for Standardization (ISO) does not recommend toothpaste exceeding the RDA value of 250 [13]. The toothpastes used in this study have different RDA values with different abrasiveness in safe limits between 30 and 105 (Table 2). Abrasion during brushing is caused not only by the abrasive particles in the toothpaste but also by the contact of the toothbrush with the tooth tissue. There are studies in the literature examining the abrasion properties of toothpaste by diluting it with artificial saliva at a ratio of 1:1 [24,25]. In the present study, toothpastes were diluted with artificial saliva at a ratio of 1:1 to better simulate the oral environment and examine the surface roughness and whitening effects of toothpastes. A coffee solution was preferred for the discoloration procedure since its increasing consumption by a large population causes the discoloration of both teeth and composite restorations. Coffee causes not only surface but also sub-surface staining due to its polar and delayed colorants being absorbed by the composite resin surface [26,27]. Moreover, it has been found that increasing temperature can accelerate the discoloration of the restorative materials [28]. Accordingly, in the present study, the composite samples were stored in a shaking incubator at a constant temperature of 37 \({}^{\circ}\)C to simulate the oral environment. The color changes were calculated by using the CIEDE2000 formula. It was preferred instead of the CIELab* system to avoid failures in evaluating minor to medium color disparities. The color changes were evaluated by comparisons with a 50:50% perceptibility threshold (PT) and a 50:50% acceptability threshold (AT). Clinical PT and AT were set at 0.8 and 1.8, respectively, regarding the CIEDE2000 formula [29,30]. \begin{table}
\begin{tabular}{l l l l l} \hline  & & & & & \\ \end{tabular}
\end{table} 
Table 8: Comparison of composites regarding the SRI scores. This study was conducted using a methodology including different types of composite resins, a new toothpaste formulation, and a contemporary brushing procedure, which makes it difficult to discuss the results with the previous studies. The effect of whitening toothpastes on the color change of composite resins has been examined in various previous studies. [PERSON] et al. stored composite samples in red wine and found clinically unacceptable \(\Delta\)E values for the R.O.C.S. Sensation Whitening toothpaste group after the brushing procedure [31]. [PERSON] et al. investigated different whitening toothpastes, including R.O.C.S. Sensation Whitening toothpaste, and found no differences among the toothpastes for the whitening effectiveness [32]. In a different study, [PERSON] et al. mentioned that the whitening toothpastes reduced \(\Delta\)E within the clinically acceptable limits [33]. In the present study, it was observed that the RDA value was not effective on \(\Delta\)E in the short-term (Table 3). When the long-term effect of the RDA value is evaluated, after one month of brushing procedure, color recovery for the SIR group was not within the clinically acceptable limits. After one month of brushing, the color change of SIR toothpaste compared to the initial time was higher among the other toothpastes. According to this result, the SIR toothpaste with a low RDA value (30 RDA) may provide less color recovery than the other toothpastes. However, after one month of brushing, the color recovery for the combination of SIR toothpaste and PP toothpaste was similar to the other toothpastes (Table 3).