Bioactive flavonoid primers for stable and antibacterial bonding to caries-affected dentin.

Abstract

Objective: This study investigated the effects of experimental primers containing baicalein (BA), kaempferol (KA), or naringin (NA) when applied to caries-affected dentin (CAD) on the adhesion, collagen stability, and antibacterial potential.

Materials and methods: Extracted human molars with artificially created CAD were treated with experimental primers (20 mM BA, KA, or NA) or 3 controls: commercial adhesive only (CONT), 20% ethanol (SOL), or 0.2% chlorhexidine (CHX). Dentin bond strength (μTBS) was evaluated by microtensile test after 24 h, 12 months, and 24 months of aging. Collagen crosslinking was analyzed by micro-Raman spectroscopy, and mechanical properties of hybrid layer were assessed by nanohardness and Young's modulus at 24 h and 12 months. Antibacterial activity was evaluated using a microcosm biofilm model through colony-forming unit (CFU), confocal microscopy (live/dead), and biofilm morphology under SEM after 24 h of incubation. Data were analyzed by generalized linear models, ANOVA followed by Tukey's or Sidak's multiple comparison tests (α=0.05).

Results: Flavonoid primers significantly affected both bonding performance and bacterial viability (p < 0.05). After 24 months, BA and NA maintained μTBS values comparable to baseline and significantly higher than the CONT and CHX. Raman spectra revealed exclusive collagen crosslinking vibration with BA treatment. Nanohardness and modulus showed no changes over time. BA and NA exhibited strong antibacterial effects, reducing S. mutans and total lactobacilli counts and disrupting biofilm structure, with cell death proportions comparable to CHX.

Conclusion: Flavonoid-based primers, particularly those containing baicalein and naringin, demonstrated dual chemical-biological mechanism in CAD that enhanced the dentin bonding longevity with sustained antibacterial activity. They are multifunctional agents for minimally invasive and durable restorative strategies.

Clinical significance: Restoring cavities with caries-affected dentin is a challenge for restorative dentistry, which can be minimized by applying flavonoid-based primers that prevent early degradation of dentin adhesion and act as an antibacterial agent in contaminated tissue.