Research on the prevention of tooth demineralization and the effects and mechanisms of different mineralization solutions on the metabolism of Streptococcus mutans.

Objective: To compare the preventive effects of various mineralization solutions on tooth demineralization and their influence on the metabolism of Streptococcus mutans (S. mutans).

Methods: Pure water, Ca/P mineralization solution, Ca/P mineralization solution with fluoride, Ca/P mineralization solution with zinc, Ca/P mineralization solution with magnesium, and Ca/P mineralization solution with strontium (Sr) were prepared. Tooth fragments were immersed in these solutions at 37°C for 24 h. Surface morphology was examined by scanning electron microscopy (SEM). The relative proportions of surface elements were analyzed, and new substances formed on the tooth surface were identified. Acid-etching was performed to evaluate changes in anti-demineralization ability and wear resistance. S. mutans was inoculated onto tooth surfaces, bacterial adhesion was observed using SEM, and water contact angles were measured. Changes in pH and metabolites of bacterial culture media were assessed. KEGG enrichment pathway analysis was conducted to explore metabolic pathways. Amino acids and organic acids in metabolites and bacterial proliferation were evaluated. RT-PCR was used to measure key glycolysis-related gene expression to verify the production of acidic metabolites.

Results: New substances were observed adhering to tooth surfaces by SEM; surfaces treated with zinc and Sr solutions were the roughest. Elemental proportion analysis indicated zinc had the highest adhesion potential, while Sr had the lowest. Newly formed substances included fluorapatite, magnesium hydroxide, and phosphate complexes. All experimental groups demonstrated improved acid resistance and good wear resistance. Sr treatment rendered tooth surfaces more hydrophilic and increased bacterial adhesion. All experimental groups inhibited acid production by S. mutans, particularly the fluoride group. Antibacterial tests indicated fluoride and zinc had the strongest antibacterial effects. KEGG pathway analysis suggested that the primary signaling pathways influenced by these substances were related to bacterial antibiotic formation and acid-salt metabolism. Metabolite analysis showed that experimental groups significantly inhibited the formation of acidic amino acids and organic acids, with fluoride exhibiting the most notable effect. RT-PCR results indicated experimental groups suppressed transcription of the glycolysis-related bacterial gene ldh, most notably fluoride. Additionally, transcription of bacterial adhesion genes decreased across experimental groups, with Sr markedly inhibiting spaP expression.