Influence of postwashing process on the elution of residual monomers, degree of conversion, and mechanical properties of a 3D printed crown and bridge materials.

Abstract

This study aimed to determine the effects of the postwashing method and time on the mechanical properties and biocompatibility of three-dimensional (3D) printed crown and bridge resin. DLP (digital light processing)-printed specimens produced from Nextdent crown & bridge (C&B) resins were washed separately using an ultrasonic bath and rotary washer with TPM (tripropylene glycol monomethyl ether) for 3min, 6min, 10min, 20min, and 1h. Postcuring was applied for 30min to each specimen after the washing process. The flexural strength, Vickers hardness, water sorption and solubility, degree of conversion (DC), elution of residual monomers, and biocompatibility of the specimens were evaluated. The ultrasonic bath showed greater washing efficacy by reducing the residual HEMA (2-hydroxyethyl methacrylate) from 2.0634ppm to 0.1456ppm and reducing the residual TEGDMA (triethylene glycol dimethacrylate) from 1.4862ppm to 0.1484ppm. With prolonged washing, the flexural strength significantly decreased from 129.67±6.66MPa (mean±standard deviation) to 103.17±7.20MPa, while the Vickers hardness increased slightly for the first 6min and then decreased thereafter significantly. The DC was 87.78±1.34% after 3min and then gradually decreased with extended washing time. The cytotoxicity significantly decreases with the increment of the washing time. The washing effect on the elution of residual monomers was better for an ultrasonic bath than for a rotary washer. Extending the washing time reduces the mechanical properties and cytotoxicity of the Nextdent C&B resin.