Multi-peak Light-emitting Diode Curing Units and Polymerization of 3D-printed Crown and Bridge Resin

Purpose: This study aimed to evaluate the substitutive and additive efficacy of multi-peak light-emitting diode (LED) curing units for postcuring of a three-dimensional- (3D-) printed crown and bridge resin. Methods: A total of 792 disc- and 180 bar-shaped specimens were printed with a crown and bridge resin (NextDent C&B MFH) and post-cured using two LED curing units (VALO Cordless and Bluephase N G4) in fast and standard modes. Conventional post-curing (LC-3D Print Box, Group PC) was compared with LED-only curing (Groups V1, V2, B1, and B2) and LED-combined curing (Groups PV1, PV2, PB1, and PB2) in terms of microhardness, flexural strength, degree of conversion (DC), and CIE L*a*b* color and translucency parameters. Cytotoxicity of the resin eluates was evaluated using the WST-1 assay. Temperature increases on the resin surface were measured with infrared thermography. Data were statistically analyzed using ANOVA and KruskalWallis tests (alpha=0.05). Results: The microhardness and flexural strength in Groups V1, V2, B1, and DC in all LED-only groups were lower than in other groups (p<0.05). Larger color disparities existed between Group PC and all LED-only groups than between Group PC and the others (p<0.05). There was no significant difference in cytotoxicity among the groups. The temperature increase was lowest in Groups V1 and PV1 during light curing (p<0.05). Conclusions: Post -curing by multi -peak LED curing units was not as effective as the conventional post -curing device. Additional post -curing by LED curing units did not improve the material properties.