Mechanical properties of 3D printed denture base polymers

Studies on the mechanical properties of 3-dimensionally (3D) printed denture base polymers with appropriate test methods are lacking.

The purpose of this in vitro study was to determine the flexural strength (σ_f), elastic modulus (E), fracture toughness (K_IC), work of fracture (ω_e), and Martens hardness (HM) of 3D printed denture base polymers and to compare them with an injection molded material.

Three resins for additive (Lucitone Digital Print, LDP; Flexcera Base, FCB and an experimental material, EXP) and 1 for injection molding (IvoBase Hybrid, IBH) fabrication were analyzed. Standardized specimens were fabricated, polished, tempered, and thermal cycled (5 °C to 55 °C) before testing for σ_f, E, K_IC, ω_e, and HM. The results were explored by global analysis (α=.05). The Kolmogorov-Smirnov test was used to test for data distribution. Parametric and nonparametric tests followed by pairwise comparison were applied to test for differences between groups.

The σf, E, and HM of 3D printed polymers were significantly lower than those of the injection molded, both for the tempered and aged groups. The σf was lowest for FCB and highest for IBH in the tempered state. The K_IC and ω_e of the tempered EXP and IBH groups were lower compared with those of FCB and LDP. After aging, EXP, FCB, and IBH presented K_IC in the same range, but it was lower than for LDP. Compared with the printable polymers, the control group IBH was not affected by artificial aging.

The σ_f, E, and HM of printable polymers were lower than those of the control group, and specimens did not fracture in bend testing. In contrast, K_IC and ω_e were the highest for a printable polymer. Therefore, tension tests should be considered when testing ductile materials.