Antibacterial efficacy of chitosan-coated thermoplastic orthodontic aligners against oral pathogens: An <i>in vivo</i> study – a randomized controlled trial

Objectives: Clear aligners are becoming increasingly common in orthodontic treatment, yet they may operate as reservoirs for infectious bacteria. The polysaccharide chitosan has broad-spectrum antibacterial capabilities, although clinical evidence of its use on clear aligner surfaces is limited. The purpose of this study was to assess the antibacterial efficiency of a chitosan-coated thermoplastic aligner system in preventing microbial colonization. Material and Methods: In this randomized, double-blind clinical trial, 32 participants were divided into two groups: Chitosan-coated aligners (intervention) and uncoated aligners (controls) by random sampling. Coatings were applied through alternate immersion in chitosan and carboxymethylcellulose solutions, followed by crosslinking. Coating confirmation was done using Fourier transform infrared (FTIR) analysis. The plaque samples were collected at baseline, 7, 14, and 21 days and cultured on Tryptone Yeast Extract Cystine Sucrose Bacitracin Agar (TYCSB) agar to determine Streptococcus mutans colony-forming units (CFUs). Data were analyzed using repeated measures analysis of variance and Mann–Whitney U-test, with P &lt; 0.05 considered significant. Results: Baseline CFU counts did not differ significantly between groups. Over the study period, the chitosan-coated aligner group exhibited a statistically significant reduction in S. mutans CFUs compared with the control group ( P &lt; 0.001). The control group showed a progressive increase in bacterial colonization, whereas the intervention group maintained lower levels throughout. FTIR analysis confirmed successful deposition of chitosan nanoparticles on the thermoplastic surface. Conclusion: The application of a chitosan coating on thermoplastic orthodontic aligners significantly reduced bacterial colonization in vivo , suggesting that this surface modification may enhance aligner hygiene and contribute to improved oral health outcomes during orthodontic treatment.