Effects of heat-treatment methods on cytocompatibility and mechanical properties of dental products 3D-printed using photopolymerized resin

Purpose: The purpose of this study was to test heat-treatment methods for improving the cytocompatibility of dental 3D printable photopolymer resins. Methods: Nextdent C&B resin and a digital light processing 3D printer were used to print all specimens, which were divided into seven groups as follows: 1-month storage at controlled room temperature, 20 to 25 °C (RT), 24-hour storage at RT, 24-hour storage in RT water, 1-min immersion in 80 °C water, 1-min immersion in 100 °C water, 5-min immersion in 100 °C water, and autoclaving. Cell viability tests, cytotoxicity tests, and confocal laser scanning microscopy were performed to analyze the cytocompatibility of the 3D-printed resin. Fourier-transform infrared spectroscopy was performed after heat-treatment to determine the degree of conversion (DC). Results: Immersing printed resin samples in 100 °C water for 1 or 5 min after the curing process was an effective method for increasing cytocompatibility by inducing the preleaching of toxic substances such as unpolymerized monomers, photoinitiators, and additives. Moreover, the DC can be increased by additional polymerization without affecting the mechanical properties of the material. Conclusions: Immersing the printed photosensitive dental resins in 100 °C water for 5 min is a suitable method for increasing cytocompatibility and the DC.