Effect of printing temperature on the viscosity, photopolymerization, and mechanical properties of a highly filled 3D-printing dental resin composite.

OBJECTIVE: This study aimed to evaluate the effect of three printing temperatures on the viscosity; cure depth (Cd) and working-curve parameters (Dp, Ec); degree of conversion (DC) and polymerization kinetics; and post-cured flexural strength (FS), flexural modulus (FM), and the Weibull reliability of flexural strength of a highly filled dental resin composite. MATERIALS AND METHODS: Viscosity (n = 3) was characterized between 20 and 55 °C using a rheometer under steady-shear and shear-rate sweep protocols. Three 3D printing temperatures (25, 37, and 50 °C) were compared regarding photopolymerization and mechanical properties. Cure depth (Cd) (n = 10) was measured by polymerizing confined resin composite in a ring mold directly on the LCD printer and measuring the cured thickness. Penetration depth (Dp) and critical exposure (Ec) were calculated from Jacobs' working-curve analysis. Thin composite films were photopolymerized on the LCD printer at each temperature, and the degree of conversion (DC) (n = 5) was quantified by ATR-FTIR immediately after curing, after post-curing, and after 24 h; real-time polymerization kinetics (n = 5) were evaluated under matched irradiance using a temperature-controlled ATR setup. Flexural strength (FS) and flexural modulus (FM) (n = 30) were determined according to ISO 4049. Data were analyzed using one- and three-way ANOVA followed by Tukey's test (α = 0.05), and flexural strength reliability was assessed by Weibull analysis. RESULTS: Viscosity decreased exponentially with temperature, with the greatest drop between 25 and 35 °C. Cure depth increased at elevated temperatures due to improved early polymerization efficiency. DC was significantly affected by temperature, post-curing, and storage time, with no significant interactions, indicating independent effects among the tested variables. The maximum polymerization rate (Rp_max) increased at 50 °C. Flexural strength and Weibull parameters were not altered by temperature, whereas flexural modulus increased slightly but consistently from 25 to 50 °C. CONCLUSIONS: An increase in 3D-printing temperature reduced viscosity, increased cure depth, enhanced the degree of conversion, accelerated polymerization kinetics, and increased flexural modulus. However, these temperature-dependent changes in rheological and polymerization behavior did not translate into differences in flexural strength or Weibull modulus, and their influence on other aspects of printing performance remains to be established.