Evaluation of the flexural and repair bond strengths of 3D-printed temporary restorations

The aim of this study was to evaluate the early bending strength of 3D-printed temporary restorations and the repair bond strength after different surface treatments. Fifty samples of 25 mm × 2 mm × 2 mm in size were produced from methylmethacrylate-free photopolymer resin temporary material (GC TempPrint, GC, Japan) with a 3D printer (NextDent, 3D Systems, Netherlands). The samples were cleaned, polymerized, finished, and stored at 37 °C with 100% humidity for 24 h before testing. The initial flexural strength was evaluated via a 3-point bending test on a universal testing machine (AG-IS, Shimadzu, Japan). The broken samples were randomly divided into 5 groups for different surface treatments. In the control group, no surface treatment was applied to the fracture surfaces (Group C). In the other groups, sandblasting (Group G), sandblasting with a silane-containing agent (GS), sandblasting with 50 μm Al2O3 particles (S), sandblasting with 50 μm Al2O3 particles and a silane-containing agent (SS) were applied to the samples. The fractured surfaces were repaired with a high-filling flowable composite (G-Aenial Universal Flo, GC, Japan) and polymerized with an LED light device for 20 s. The bond strength was evaluated via a 3-point fracture test on a universal testing device. The data obtained were examined with one-way ANOVA and a paired sample t-test. The surface treatments applied to the fractured surfaces were examined via stereomicroscopy (Olympus microscope BX50, Japan). There was no significant difference in early-stage fracture strength among the groups (P > 0.05). There was a statistically significant difference in the repair bond strengths (P < 0.05). The highest repair bond strength was obtained in Group SS, and the lowest was obtained in Group C. Silane-containing agent application after sandblasting with Al₂O₃ was found to be the most effective method for repairing 3D-printed photopolymer resin temporary materials without methyl methacrylate.