Changes in the cytocompatibility, surface hardness, and surface topography of 3-dimensional-printed clear aligners after clinical use

Abstract

Introduction: This study evaluated how clinical use affects the surface properties and cytocompatibility of 3dimensional (3D)-printed clear aligners by comparing them against saliva-unexposed and artificial saliva-exposed groups. Methods: Eleven aligners were collected from 5 adult patients after 10 days of use (clinically used group). Two additional groups were established: the saliva-unexposed group (immediately after postprocessing) and the artificial saliva-exposed group (immersed in artificial saliva). All aligners underwent extraction for 1 day (day-1 extraction) and an additional 6 days (day-7 extraction). After 7 days of extraction, surface properties, including hardness (Shore D) and topography (scanning electron microscope imaging), were analyzed. Cytotoxicity to normal L929 cells was evaluated using 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assays. Proinflammatory responses in lipopolysaccharide (LPS)-induced presensitized L929 cells were assessed by quantitative polymerase chain reaction, measuring interleukin-6, tumor necrosis factor-a, and nitric oxide synthase 2 expression levels. Results: Shore D hardness did not differ among groups. Scanning electron microscope imaging revealed increased surface irregularities after salivary exposure. All groups exhibited no cytotoxicity (>70% viability) in both day-1 and day-7 extractions, with the clinically used group showing significantly higher cell viability than the saliva-unexposed group in both extractions (P <0.001). However, when LPS-induced presensitized cells were treated with day-7 extraction, only the clinically used group showed a significant increase in both interleukin-6 and tumor necrosis factor-a expression compared with LPS-only-treated cells (P <0.001). Conclusions: Saliva-exposed 3D-printed aligners exhibited increased surface irregularities and lower cytotoxicity compared with unexposed aligners. However, clinically used 3D-printed aligners may exacerbate proinflammatory responses in presensitized cells. Depending on the initial state of the cells, cytological responses to 3D-printed aligners may vary. (Am J Orthod Dentofacial Orthop 2026;169:370-8)