Effect of solvents on mechanical properties of 3D-printed materials for definitive crowns

The aim of this study was to investigate the effect of solvents and storage time on the mechanical properties of 3D-printed resin composites for definitive crowns.

Three 3D-printed definitive crown resin composites: Permanent Crown (Formlab; PCR), VarseoSmile Crown plus (BEGO; VCP) and Crowntec (Saremco print; CT) and one milled resin composites: Grandio Blocs/ Disc (VOCO; Gr) were tested. A three-point bending test was used to measure flexural strength (FS) and flexural modulus (E_f) using a universal testing machine (Zwick/Roell Z020) (n = 10). Martens hardness (HM) and indentation modulus (E_IT) were measured using a Martens hardness instrument (Zwick/Roell Z2.5) (n = 18). Properties were evaluated on polished specimens 24 h after fabrication at room temperature in dry condition and then after 1 and 7 days of storage in either distilled water (DW D1/D7) or 75% ethanol/water (75% E/W D1/D7) at 37 °C. Data were analysed using two-way ANOVA and one-way repeated measure ANOVA (α = 0.05).

At dry condition, mechanical properties for PCR, VCP, CT and Gr were; for FS 135.6, 120.3, 132.3 and 231.0 MPa, respectively; for E_f 4318, 3963, 4109 and 13500 MPa, respectively; for HM 218.6, 213.6, 219.7 and 858.5 N/mm², respectively; and for E_IT 6.0, 5.7, 5.8 and 22.7 kN/mm², respectively. Findings revealed a differential response to solvent exposure among the tested materials. For 75% E/W D7, there was a significant reduction (≈ 20%) in the FS of all materials (p < 0.001). Storage time in 75% E/W significantly affected the HM of all tested materials: CT (p = 0.002), VCP (p = 0.026), PCR, and Gr (p < 0.001). At 75% E/W D7, HM for PCR, VCP, CT and Gr was 157.1, 178.4, 183.6 and 699.3 N/mm², respectively; E_f and E_IT had a lower reduction.

This study demonstrated that the mechanical properties of both 3D-printed and milled resin composites for definitive crowns are adversely affected by solvent exposure, particularly in 75% ethanol/water. After seven days of immersion in 75% E/W, all tested materials showed a substantial reduction in flexural strength and Martens hardness. However, the changes in flexural modulus and indentation modulus were less pronounced.