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Changes in the cytocompatibility, surface hardness, and surface topography of 3-dimensional-printed clear aligners
Eun-Hack Andrew Choi1, Utkarsh Mangal2, Jeong-Hyun Ryu1
1Department of Orthodontics, Institute of Craniofacial Deformity, Yonsei University College of Dentistry, Seoul, Republic of Korea.
Introduction:
This study evaluated how clinical use affects the surface properties and cytocompatibility of 3-dimensional (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-α, 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-α 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.
