Remineralization of Artificial Caries-like Lesions in Permanent Enamel by MI Paste One: Comparative Physicochemical Outcomes and In Vitro Resistance to Secondary Demineralization

Background: Patients with White spot lesions (WSLs) are seeking minimally invasive remineralizing treatment. While fluoride is the gold standard of non-invasive caries therapy, its remineralizing impact is predominantly superficial. MI Paste One (MIP-1) combines casein phosphopeptide–amorphous calcium phosphate (CPP–ACP) with 1100 ppm fluoride. This in vitro study aimed to assess the effect of MIP-1 compared with other agents. Methods: Enamel slabs were demineralized to create a caries-like lesion and randomized into five groups (n = 10): G1, WSL/artificial saliva (AS) (negative control); G2, deionized water brushing; G3, fluoridated toothpaste brushing; G4, MIP-1 brushing; G5, topical MI Paste application. Color change (ΔE), gloss (GU), microhardness (VHN), roughness (Ra), and surface topography (SEM) were assessed at four time points: baseline, first demineralization, treatment, and second demineralization. Results: All active agents improved microhardness after treatment. After secondary demineralization, G4 achieved the highest hardness, significantly superior to G3 (p = 0.016). G5 occupied a statistically intermediate position. CPP–ACP-containing agents (G4, G5) achieved color improvement that was significantly superior to controls. Conclusions: MIP-1 outperformed fluoride toothpaste in resisting secondary demineralization of permanent enamel WSLs. CPP–ACP made a measurable independent contribution to demineralization resistance in permanent enamel. These findings highlight the need for further clinical investigation of MIP-1.