Cytotoxicity evaluation of different clear aligner systems on human primary gingival fibroblasts: an in vitro study

Background: Clear aligners, widely adopted in modern orthodontics, are designed to stay in constant contact with the oral mucosa for extended durations. Persistent concerns exist about the possible leaching of cytotoxic agents like bisphenol-A from these materials, which have heightened the need for rigorous biocompatibility evaluation. Among various assays, the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide) assay is a reliable in vitro method, which assesses metabolic activity and cell viability, making it a gold standard for cytotoxicity screening. Objective: The objective was to assess and contrast the potential cell-damaging effects of three different clear aligner brands – Invisalign®, Smile® Aligners, and Illusion® Aligners using the MTT assay on human gingival fibroblasts (HGFs). Methods: Aligner pellets were immersed in normal saline for 30 days at 37°C. Eluents were diluted to 5, 10, and 20% concentrations. HGFs were exposed to these eluents for 48 hours, and cytotoxicity was assessed via MTT assay. To assess the survival rate of the cells, light absorbance was recorded at a wavelength of 570 nanometers. Results: Invisalign® showed the highest biocompatibility (97–98% viability across concentrations), followed by Smile® Aligners (94–99%). Illusion® Aligners exhibited significant cytotoxicity (80–92% viability), with a dose-dependent decline (p < 0.05). Conclusion: Material composition critically influences cytotoxicity. Invisalign® and Smile® Aligners are a safe options, while Illusion® Aligners require further refinement for clinical safety. These results highlight the need for transparency in material composition and standardization in manufacturing protocols for all aligner systems to ensure patient safety.