Enamel Remineralization Potential of Conventional and Biomimetic Toothpaste Formulations: A Comparative In Vitro Study

Background/Objectives: Dental caries remains one of the most prevalent chronic diseases worldwide, making enamel remineralization a key objective in minimally invasive dentistry. This in vitro study compared the remineralization efficacy of five therapeutic toothpastes containing fluoride, NovaMin, CPP-ACP, nano-hydroxyapatite, arginine, and xylitol. Methods: Sixty enamel specimens were prepared from extracted human posterior teeth and artificially demineralized. Samples were randomly allocated into six groups (n = 10): one negative control (C1) stored in artificial saliva and five treatment groups (P1–P5). A 28-day remineralization protocol with twice-daily applications was performed. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were used to assess surface morphology and elemental composition (Ca, P, F, Na, O, Ca/P ratio) at days 1, 14, and 28. Vickers microhardness testing was used to evaluate changes in mechanical properties. Statistical analysis included one-way ANOVA, repeated measures ANOVA, Tukey’s post hoc test, and Kruskal–Wallis where appropriate (α = 0.05). Results: All therapeutic toothpastes produced some increase in mineral content compared to the demineralized control. At day 28, significant intergroup differences were observed for calcium, phosphorus, and fluoride (p < 0.001). The arginine–fluoride formulation (P4) and the NovaMin-based formulation (P3) showed the most consistent increases in Ca and P, with SEM revealing the formation of a continuous, compact surface layer and marked reduction in prismatic porosities. Fluoride-containing toothpastes (P1, P3, P4) showed significant fluoride incorporation (p < 0.001 vs. control). The nano-hydroxyapatite/xylitol prototype (P5) produced a delayed but progressive increase in Ca and P, with partial filling of prismatic spaces. The CPP-ACP-based toothpaste (P2) led to limited changes, with only slight differences vs. control at day 28. Vickers microhardness values increased significantly in groups P1, P3, P4, and P5 (p < 0.05), in agreement with the higher mineral levels found in these samples. Conclusions: Under the present in vitro conditions, toothpastes containing fluoride in combination with NovaMin or arginine, as well as nano-hydroxyapatite/xylitol, demonstrated the highest remineralization potential under the present in vitro conditions, both chemically and mechanically. Xylitol-based formulations without a direct mineral supply showed limited effects. The pH and active composition of the toothpaste strongly influenced enamel remineralization outcomes.