Bioactive oral gels containing Libidibia ferrea and Brazilian propolis preserve the mechanical and mineral properties of eroded human enamel

OBJECTIVES: To develop polyphenol-rich oral gels containing Libidibia ferrea or Brazilian brown propolis extracts and evaluate their effects on the mechanical and mineral properties of human enamel subjected to erosive-abrasive challenges. MATERIALS AND METHODS: Experimental gels containing L. ferrea (0.5% and 2.5%) or Brazilian brown propolis (0.5% and 2.5%) were formulated and evaluated for physicochemical properties, antioxidant activity, stability, and cytocompatibility. Seventy-two human enamel specimens were randomly assigned to six groups (n = 12): control gel, 0.5% and 2.5% L. ferrea gels, 0.5% and 2.5% propolis gels, and a commercial stannous fluoride toothpaste. Specimens underwent a 7-day erosive-abrasive cycling model. Surface microhardness, surface roughness, enamel crystallinity, phosphate-to-carbonate ratio, and color variation were assessed. Data were analyzed using ANOVA and Tukey's test (α = 0.05). RESULTS: All formulations exhibited near-neutral pH and satisfactory cytocompatibility. Stability was maintained under refrigeration, whereas color changes and precipitate formation occurred during storage at room and elevated temperatures. Following the erosive-abrasive challenge, the 2.5% L. ferrea and 2.5% propolis gel groups showed higher final surface microhardness, lower percentage surface microhardness loss, and lower final surface roughness than the other treatment groups (p < 0.05). Raman spectroscopy showed lower full width at half maximum values for the phosphate ν₁ band and higher phosphate-to-carbonate ratios in the 2.5% L. ferrea and 2.5% propolis gel groups than in the other groups (p < 0.05). CONCLUSIONS: Oral gels containing 2.5% L. ferrea or Brazilian brown propolis showed promising protective effects on human enamel under the in vitro erosive-abrasive conditions tested. CLINICAL RELEVANCE: These gels are promising candidates for erosive tooth wear prevention, pending in situ and clinical validation addressing color changes and concentration-dependent stability.