Microplastic Release from Orthodontic Appliances

Abstract

Microplastics (MPs; mm) and nanoplastics (NPs; 1-1,000 nm) are pervasive environmental contaminants with growing implications for human health. MPs have been detected in multiple human biofluids and tissues, raising concerns about chronic exposure and potential downstream inflammatory and systemic effects. Orthodontic treatment relies heavily on polymer-based appliances (e.g., polyurethane, PETG, PMMA) worn for extended periods, yet the contribution of orthodontic appliances to microplastic exposure remains poorly characterized. This in vitro pilot study evaluated microplastic particles recovered after exposure of five commonly used maxillary orthodontic appliances to artificial saliva at 37°C under calibrated mechanical agitation intended to approximate clinically relevant wear patterns (nighttime wear-equivalent vs full-time wear-equivalent). Following exposure, a 1 ml aliquot of supernatant was analyzed using laser-directed infrared spectroscopy (LDIR) to quantify particle recovery, measure particle diameter and eccentricity, and assign polymer type. Because one appliance was tested per appliance type and control particle counts were very low, particle-count comparisons were interpreted descriptively and inferential statistics were limited to exploratory, polymer-stratified particle-characteristic comparisons between the two aligner systems at the full-time wear-equivalent condition. Controls contained few particles (Control_8: 1 PET particle; Control_20: 1 PET and 2 PTFE particles). In nighttime wear-equivalent conditions, particle recovery in the analyzed aliquot ranged from 11 to 16 particles across appliances (Essix PETG retainer: 16; Biocryl nightguard: 11; Hawley retainer: 16), with polymer composition varying by appliance. In full-time wear-equivalent conditions, the SmartTrack® and Zendura aligners yielded substantially higher particle recoveries and multiple polymer classifications. In polymer-stratified comparisons between SmartTrack® and Zendura at the full-time wear-equivalent condition, no differences in particle eccentricity or eccentricity-category distributions were detected after multiplicity correction; diameter differences were also not statistically significant after correction. These findings support that orthodontic appliances can contribute to microplastic particle recovery under simulated intraoral conditions while underscoring the need for replicated appliance-level studies and improved control characterization to estimate exposure and variability.