## 4 Discussion
Therefore, using PP toothpaste in combination with conventional toothpaste may increase the whitening feature. The abrasive substances in the toothpaste provide effective and rapid biofilm removal while also protecting the tooth surface from extrinsic discoloration [34]. The cleaning effectiveness of the abrasives in toothpaste is affected by the size, sharpness, hardness, and concentration of these substances in the toothpaste [35]. A recent study found hydrated silica to be the most prevalent abrasive ingredient in toothpaste [36]. All toothpastes in the present study contain silica as an abrasive substance. The size (2-3 \(\upmu\)m), concentration, and distribution of silica particles in the PP toothpaste might have aided the cleaning effectiveness of the PP + SIR [33]. The organic components and the inorganic filler particle content of a composite resin may influence the level of discoloration [37,38]. Microhybrid composite resin is a glass-ceramic composite that includes filler particles of different sizes and distributions [39]. In the present study, the microhybrid composite Charisma Smart contains 78% by weight of microfillers with very fine (0.02-2 \(\upmu\)m) barium aluminum fluoride glass particles, and the other microhybrid, ELS, has microfillers between 50 and 3000 nm in size. On the other hand, nanofil composites contain agglomerated particles. Aggregated fillers and ceramic particle content cause nano-filled composite resin to be prone to porosity [38,40]. Therefore, nano-filled composites are considered vulnerable to water absorption and discoloration. The filler percentages of the nanofil composites tested in this study were 82% for G'aenial A'chord and 79% for Neo Spectra ST HV. Additionally, G'aenial A'chord has 300 nm barium glass particles, and Neo Spectra ST HV has prepolymerized fillers and non-agglomerated barium glass [41]. The other difference between nanohybrid and microhybrid composite resins is the filler particle size. Nanofil resins contain large amounts of atomic particles on the surfaces of the nanoparticles [19]. The quantum effect of nanoparticles causes the nanofil composites to be vulnerable to different surface interactions, including the adsorption of other substances [42]. [PERSON] and [PERSON] declared that the nanohybrid composite resin presented a lower color change than the microhybrid and nanoceramic composites after the discoloration procedure with the coffee solution [21]. On the other hand, [PERSON] and [PERSON] found that the lowest color change was in the microhybrid composite, and the highest was in the nanohybrid composite after immersion in the coffee solution [43]. In line with the literature, our study revealed that the microhybrid composite Charisma presented the lowest color change after the discoloration procedure (Table 4). The other microhybridcomposite group, ELS, presented a similar color change to the nanohybrid composites. A difference between ELS and Charisma composites is the filler content, and another chemical difference is the substitution of hydrophilic monomer TEGDMA in Charisma [43,44]. A possible explanation is that the polishing procedure could have lowered the surface reactivity of TEGDMA. TEGDMA may enhance surface hardness and elastic modulus compared to Bis-EMA, and this may provide better behavior against discoloration [44]. In the present study, after two weeks of brushing, ELS showed the highest color change compared to the beginning. With continued brushing, after one month, ELS presented a similar color change with the nanohybrid composites in the study. This may be explained by the fact that brushing may change the surface roughness and hardness of the composites [45]. It is stated in the literature that the addition of silica to toothpastes does not result in a linear increase in abrasiveness [46]. In the present study, there was no difference between toothpastes with different RDA values on composite surface roughness in the short-term or long-term.