Chitosan-Based Coatings for Orthodontic Appliances: Antimicrobial Properties, Potential Ion-Release Mitigation, and Clinical-Translation Perspectives

Fixed orthodontic appliances promote biofilm-mediated enamel demineralization and release metallic ions, motivating surface strategies that are intrinsic to the device rather than dependent on patient compliance. Chitosan, a biodegradable polycationic biopolymer, has been proposed as a multifunctional coating. This narrative review critically appraises the evidence for chitosan-based coatings on orthodontic appliances across three pillars—antimicrobial performance, ion-release/corrosion mitigation, and clinical translation—with explicit calibration of evidentiary strength. The evidence base is heterogeneous and of markedly uneven quality across the three pillars, and the conclusions below are weighted accordingly. Consistent with its narrative design, the literature was surveyed for critical synthesis rather than exhaustively, without formal eligibility screening, risk-of-bias appraisal, or quantitative pooling. Antimicrobial efficacy is the best-supported pillar, consistent in vitro and now extended by two short in vivo randomized trials, although all endpoints are microbiological surrogates rather than white spot lesion outcomes. Ion-release mitigation remains a plausible but insufficiently demonstrated effect: it is supported only indirectly, through electrochemical corrosion proxies on predominantly implant substrates, and no study quantifies ion-release reduction from a coated appliance. Coating durability under combined enzymatic and mechanical load—and its effect on friction—remains largely uncharacterized. Chitosan coatings are promising but translationally immature; durability, not antimicrobial potency, is the rate-limiting barrier. Defined clinical-endpoint and appliance-level ion-release studies are required.