Cytotoxicity of Aligners – A Comprehensive Review

Orthodontic clear aligners have gained widespread popularity due to their esthetic appeal and functional advantages over traditional braces. This review explores the material composition, biocompatibility, and potential health implications associated with long-term intraoral use of clear aligners. Most aligners are fabricated from thermoplastic polymers such as polyurethane, polyethylene terephthalate glycol, and polypropylene, which generally exhibit low cytotoxicity. However, exposure to oral conditions–including saliva, temperature fluctuations, and mechanical stress–can lead to material degradation and the release of residual monomers or additives, potentially causing mild to moderate cytotoxic effects. The postpolymerization process significantly influences material stability and clinical performance, with advanced protocols improving polymerization efficiency and reducing toxic potential. In addition, mechanical wear of aligners can result in the release of microplastics into the oral cavity, raising concerns about their systemic and local biological effects. These microplastics may interact with gut microbiota, contribute to inflammation, and potentially translocate to systemic circulation. This review also highlights the importance of standardized testing methods, including MTT assays and microscopic analysis, for evaluating cytotoxicity and material integrity. To ensure patient safety, continued development of biocompatible materials and adherence to regulatory standards are essential. Clinicians should remain informed about material properties and recommend proper usage and maintenance to minimize potential risks associated with aligner therapy.