## 4 Discussion
In the enamel samples from Group 5 (Buccotherm), the enamel surface exhibited a diffuse, cloud-like structure. It has been reported that enamel samples exposed to a solution containing 500 ppm sodium fluoride showed a greater increase in microhardness than in the control group, which was confirmed by ESEM analysis [67]. The Splat, Logodent, Eyup Sabri Tuncer, and Buccotherm toothpastes contain hydrated silica as an abrasive agent, whereas Naturalive contains calcium carbonate. Carbonategroup abrasives act as a natural buffer due to their alkaline pH. Silica, mainly composed of silicon bonded to two oxygen molecules, is added to the toothpaste structure both as an abrasive and thickener [68]. Although the upper limit of RDA and REA, commonly used measures to evaluate the toothpaste abrasiveness, has been reported for adult toothpastes, no limit has been set specifically for children [26]. There was no information on the abrasiveness of the toothpastes used in our study. The lower surface roughness values after remineralization compared to those after demineralization, almost reaching the initial values, and the SEM analysis results, may indicate that the remineralization agents in the toothpastes made the tooth surface smoother through precipitation on the tooth surface. The correlation analysis revealed that the toothpastes increased or decreased the surface roughness according to their remineralization potentials. Despite the significant increase in the microhardness values created by Naturalive after the remineralization stage, the lack of a significant difference between other toothpastes and Naturalive in terms of surface roughness may have been due to the lower abrasiveness of calcium carbonate in the Naturalive toothpaste than hydrated silica or its remineralization efficiency. One study evaluated the abrasiveness of silica and calcium carbonate with similar particle sizes using the radiometric method, and it was reported that silica had a higher RDA value than calcium carbonate; it was emphasized that the abrasiveness value could increase with the agent's particle size [69]. It may be considered that the abrasive effect of the hydrated silica in Buccotherm is eliminated by the remineralization feature of its 500-ppm fluoride content. This study was conducted under in vitro conditions. The obtained results should be evaluated further by in vivo studies. Evaluations of the toothpastes included in the study using different methodologies and for longer durations may lead to changes in remineralization effects. The increases in microhardness values may also have been due to the effects of other products in toothpastes or their effects together with remineralization agents. To evaluate toothpastes' remineralization and abrasiveness activities, toothpaste manufacturers should provide more detailed information about toothpaste contents and concentrations, interactions, and the particle sizes of agents in toothpastes. Although providing quantitative information about the surface changes dependent on remineralization agents increases research costs, methods such as micro-CT and microradiography, which can measure lesion depth and mineral content, can be included in future studies when more detailed information is needed.