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.