Biomodification of dentin collagen with hydroalcoholic propolis extract: Impact on resin–dentin adhesion

This in vitro study evaluated the effect of hydroalcoholic propolis extract (HPE) as a collagen cross-linking agent for preserving the dentin-adhesive interface. Dentin beams from human third molars were demineralized with 10% phosphoric acid and assigned to five treatments: distilled water (control), 6.5% grape seed extract (GSE), and HPE at 0.1%, 1%, or 10%. Elastic modulus (n = 10), dry mass variation (n = 10), and microtensile bond strength (µTBS, n = 8) were assessed after 24 h and after 6 months of storage. Collagen stability was analyzed using Fourier-transform infrared spectroscopy (n = 10). Elastic modulus was evaluated using Kruskal-Wallis and Friedman tests, dry mass variation, and µTBS with linear mixed-effects models. GSE produced the greatest increase in elastic modulus, followed by 1% and 0.1% HPE. After 6 months, all experimental groups maintained µTBS, except 0.1% HPE and the control, which showed reductions of approximately 30%. Spectroscopic analysis revealed increased Amide I and decreased Amide II bands in all treated groups, indicating enhanced collagen cross-linking. Overall, HPE-particularly at 1%-improved dentin collagen stability and contributed to the preservation of the adhesive interface over time.