Targeting mixed-species biofilms of Streptococcus mutans and Candida albicans on clear aligners: boron-based natural substance combinations for enhanced antibiofilm efficacy.

In orthodontic treatment, insufficiently cleaned clear-aligners can serve as reservoirs for biofilms. This study evaluates in-vitro biofilm models and investigates the antibiofilm efficacy of boron-based formulations with natural substances. Minimum inhibitory concentrations (MICs) were determined by microdilution, and Fractional inhibitory concentration by checkerboard methods. Biofilm inhibition was assessed at sub-MIC levels, and mature biofilm-eradication at supra-MICs. Time-kill assays were performed on mixed-biofilms of Streptococcus mutans and Candida albicans on clear-aligners. The MIC values of boric acid, sodium borate, and natural substances against S. mutans were 1,250-5,000, 4,000-8,000, and 2.5->10,000 μg/mL, respectively. Synergistic combinations included eucalyptol, epigallocatechin-gallate, resveratrol, and cinnamaldehyde. Biofilm inhibition rates ranged from 49%-58%, and eradication concentrations were 8-16xMIC. A formulation containing boric acid reduced viable cells by ≥5-log10 in time-kill assays. These findings indicate that boron-based formulations with natural substances suggest notable antibiofilm activity against mixed-species biofilms and may provide preliminary in vitro data for aligner-cleaning or oral-care products.