## 4 Discussion  
In our study, a 7-day pH cycle, as used by [PERSON] et al. (2005), was implemented to evaluate the remineralization effects of five different toothpastes for children on artificially curious primary teeth [(28)]. The samples in our study were treated with a demineralization solution prepared using 2.2 mM CaCl\({}_{2}\), 2.2 mM KH\({}_{2}\)PO\({}_{4}\), 0.05 M CH\({}_{3}\)COOH, and 1.0 M KOH, and were kept in an incubator at 37 \({}^{\circ}\)C for 72 h, taking into account the study by [PERSON] and [PERSON] (2020) [(23)]. Lesion formation was monitored daily, and the demineralization of the enamel, observed as homogeneous chalky white areas without cavitation on the sample surfaces, was recorded. The preparation of the toothpastes in solution form simulated the dilution of toothpaste with saliva during brushing [(33)]. In our study, the toothpastes were diluted with distilled water at a 1:3 ratio (toothpaste: distilled water); the same ratio was used in other studies [(27; 34)]. The samples were immersed in the prepared toothpaste solutions for 1 min before the first demineralization cycle, before the second demineralization cycle, and after the second demineralization cycle during the 7-day pH cycle. This approach aimed to simulate brushing before and after dietary intake [(35)]. The abrasion on the tooth surface depends on factors such as the type, particle hardness, size, size distribution, and concentration of the abrasive in the toothpaste, as well as on the hardness, arrangement of the toothbrush bristles, the force applied during brushing, and the brushing technique [(36; 37)]. The toothpastes were prepared in solution form to eliminate these variables and isolate the effects of the toothpastes' abrasiveness. Applying the toothpastes in solution form enabled a standardized application across all samples. This study revealed that the Group 4 (Naturalive) and Group 5 (Buccothemr) toothpastes resulted in significantly higher microhardness values measured after remineralization than those measured after demineralization. Naturalive contains calcium carbonate, which is added to toothpastes as an abrasive. It has been reported that calcium carbonate has low solubility at a neutral pH, and dissolves at a low pH; that calcium mineral provides remineralization; and that carbonate neutralizes plaque acids due to an increase in local pH [(38)]. One study evaluated the plaque pH effects of two toothpastes, one with carbonate and the other with alumina trihydrate, which did not contain fluoride and had the same abrasiveness. It was found that the buffering effect was better and longer, and that the plaque's pH was significantly higher after using the toothpaste containing calcium carbonate [(39)]. Considering the SEM results of our study, it can be assumed that toothpastes with calcium carbonate may have remineralization efficiency. The Buccothemr toothpaste contains 500 ppm fluoride. One of the recommendations for reducing the potential risk of fluoridated toothpastes, as a risk factor for fluorosis in children under the age of six years, is using toothpastes with low fluoride concentrations. Studies on toothpastes containingfluoride at different concentrations have reported that 500 ppm fluoride in toothpaste may be sufficient to prevent dental caries [40; 41]. Similar to the results obtained in other studies, our microhardness and SEM analysis results showed the remineralization effect of the fluoride contained in this toothpaste and supported the argument that it is a standard in terms of its caries-preventive effect [42; 43]. The main action of mechanism of fluoride is its topical effect, which is caused by its continuous presence in oral fluids at low rates [44]. Fluoride, which exists in the plaque fluid through topical sources, is adsorbed onto the demineralized subsurface crystals, forms a fluorapatite-like structure with lower solubility than the original tooth mineral that is more resistant to acid attacks, inhibits demineralization, and provides remineralization [11].