Enhancing Silver Diamine Fluoride Treatment: The Role of Zinc in Reducing Discoloration and Maintaining Antimicrobial Efficacy

Background: Silver diammine fluoride (SDF; often incorrectly referred to as silver diamine fluoride in the literature) is an effective, minimally invasive treatment for dental caries; however, its widespread adoption is hindered by significant black discoloration of treated dentin. Zinc, known for its antimicrobial properties and potential interactions with silver compounds, may offer a novel approach to reducing SDF-induced staining while preserving its cariostatic effects. This laboratory study investigated the impact of a zinc pretreatment followed by SDF application on dentin discoloration, surface properties, and antimicrobial activity using an artificial caries model. Methods: Artificial caries lesion was induced in human dentin blocks using a Streptococcus mutans microbial biofilm model. After caries formation, the specimens were treated with 38% SDF alone or in combination with 15M or 20M zinc nitrate solution. Antimicrobial challenges were then further assessed using a duo-species (S. mutans and Candida albicans) biofilm model. Color changes over 14 days were assessed using grayscale image analysis. Surface roughness was measured using profilometry. Antimicrobial effects were evaluated through assessing culture media pH, viable S. mutans and C. albicans cell counts, biofilm biomass, and biofilm microstructure via multiphoton confocal imaging. Data were analyzed using simple linear regression, two-sample t-tests, and Wilcoxon rank-sum tests to evaluate differences among treatment groups. Results: Zinc incorporation significantly mitigated SDF-induced dentin discoloration. The application of 20M Zn with SDF significantly improved dentin whiteness compared to the SDF-only group (p = 0.0228). No significant differences in the surface roughness were observed between the zinc-treated and SDF-only groups. Both SDF alone and SDF+Zinc groups demonstrated significant reductions in S. mutans and C. albicans viability compared to the untreated controls (p ≤ 0.005). Zinc pretreatment preserved the antimicrobial effects of SDF and supported biofilm disruption and live-dead cell proportions. Conclusion: The study findings suggest that zinc-enhanced SDF regimen may offer an improved aesthetic profile while maintaining antimicrobial properties, potentially increasing clinical acceptability. Future studies should explore the long-term stability and clinical performance of zinc-enhanced SDF and assess various Zinc delivery regimens.