Colorless Quaternary Tannic Acid Coatings With Antimicrobial Properties For Aligners

Surface degradation of clear aligners promotes bacterial adhesion and biofilm formation, increasing the risk of enamel demineralization and compromising aesthetics. This study aimed to enhance the antimicrobial performance of clear aligners by introducing a hydrophobic quaternized tannic acid (QTA) coating, without affecting their mechanical strength or optical clarity. QTA coatings were applied to clear aligner substrates via dip-coating and characterized using SEM-EDS, XPS, Raman spectroscopy, and FTIR. Water sorption in artificial saliva and mechanical properties were evaluated, along with optical transmittance and color stability. Antimicrobial performance was assessed using mono- and polymicrobial biofilm models of Streptococcus mutans, Candida albicans, and human saliva-derived microbiota. Biofilm formation and viability were analyzed by CFU counting, crystal violet staining, MTT assays, SEM imaging, and live/dead fluorescence staining. Biocompatibility was assessed via CCK-8 cytotoxicity assay, hemolysis testing, and an oral mucosal irritation model in golden hamsters. QTA was effectively grafted onto aligner surfaces without compromising mechanical or optical properties. The QTA coating exhibited strong antimicrobial activity, reducing microbial viability by over 99% for S. mutans and 82.9% for C. albicans (p < 0.05), and significantly inhibiting biofilm formation in both mono- and polymicrobial models. Antimicrobial efficacy remained stable after prolonged exposure to artificial saliva and three months of storage, with biocompatibility confirmed by low cytotoxicity, minimal hemolysis, and no mucosal irritation in vivo. Quaternary tannic acid-based coatings on aligners demonstrate potent and sustained antimicrobial activity, favorable biocompatibility, and preserved functional properties, indicating strong potential for clinical orthodontic application.