Effect of angulation of 3D printed resin provisional bridges: an in vitro study on hardness and fracture loading

Objective: to evaluate the effect of printing angle of three-dimensional (3D) printed resin temporary bridges, through an in vitro study on hardness and fracture loading. Material and Methods: Specimens fixed bridges with three elements (N=5) and block specimens (N=1), were distributed among the experimental groups based on different printing angles: 0°, 45°, and 90°. Surface analysis using a scanning electron microscope (SEM) was conducted on one specimen from each experimental group. Hardness testing was then performed, with the specimens receiving five measurements on a Vickers microhardness tester and for fracture loading testing, force was applied using a piston attached to a testing machine. Finally, the bridge specimens were evaluated for fracture. Fracture loading and hardness data were subjected to a Anova 1 Factor statistical test (p<0.05), while the findings from surface analysis and fractures were analyzed qualitatively. Results: On the surfaces of the specimens, printing layers were mainly observed in the 90° group for block-type specimens. For hardness analysis, the 3D printing angle showed statistical significance between groups (P=0.000), while no significant difference was found for fracture loading (P=0.177). Finally, there was a prevalence of all failures for the 0° and 90° groups and retainer fracture for the 45° group. Conclusion: Different angles of provisional bridges manufactured by 3D printed resin affect hardness, but do not interfere with fracture loading. KEYWORDS Angulation; Dental prosthesis; Digital technology; Provisional bridges; Three-dimensional printing.