Comparison of the cytotoxicity of 3D-printed aligners using different post-curing procedures: an in vitro study

Objective: Three-dimensional (3D) printing technology represents a novel method for manufacturing aligners. The aim of the present study was to assess the in-vitro cytotoxicity of 3D-printed aligners using different post-polymerisation conditions.Materials: Aligners were printed using the same 3D-print resin (TC-85DAC, Graphy, Seoul, Korea) and printer (AccuFab-L4D, Shining 3D Tech. Co., Hangzhou, China), followed by different post-curing procedures. Six aligners were post- polymerised for 14 min using the Tera Harz Cure and a nitrogen generator curing machine (THC2, Graphy, Seoul, Korea) (P1). A further six aligners were post-cured for 30 min on each side using the Form Cure machine (FormLabs Inc, Somerville, USA) (P2). The aligners were cut into smaller specimens (2 mmx2 mm) and sterilised at 121 degrees C. The specimens were placed in 96-well plates containing Dulbecco's Modified Eagle's Medium (DMEM) at 37 degrees for 7 or 14 days. The viability of MC3T3E-1 pre-osteoblasts cultured with DMEM was evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The optical density of each cell culture was measured to assess cell viability, following which the data were statistically analysed using two-way and one- way ANOVA (alpha = 0.05).Results: The comparison of cytotoxicity revealed statistically significant differences between post-curing procedures and MTT timings (P < 0.001). After 7 and 14 days, the cell viability of P2 was significantly reduced compared to P1 and the control groups (P < 0.001), while P1 showed no significant differences compared to the controls. Overall, P2 post-curing exhibited moderate cytotoxicity, while P1 post-polymerisation was highly biocompatible.Conclusions: Different post- curing procedures may affect the in-vitro cytotoxicity of 3D-printed aligners. Clinicians should adhere to the manufacturer's recommendations when using 3D-print resin.