Effect of printing orientation on the fracture strength of additively manufactured 3-unit interim fixed dental prostheses after aging

Objectives: To evaluate the effect of printing orientation on the fracture strength of 3-unit interim fixed dental prostheses fabricated by using additive manufacturing and to compare with those fabricated by subtractive manufacturing after thermomechanical aging. Materials and methods: A 3-unit fixed dental prosthesis was designed by using a dental design software (exocad DentalCAD 2.2 Valetta) in standard tessellation language (STL) format. This STL file was exported into a nesting software (PreForm) and 3-unit interim fixed dental prostheses with 5 different orientations (0°, 30°, 45°, 90°, and 150°) were printed by using a 3-dimensional (3D) printing interim resin (Temporary CB) (n = 10). The same STL file was also used to mill polymethymethacrylate (DuoCAD) 3-unit interim fixed dental prostheses as the control group (n = 10). All specimens were cemented onto cobalt-chromium test models representing a maxillary first premolar and first molar tooth with a long-term temporary cement (DentoTemp), and subjected to thermomechanical aging (120,000 cycles, 1.6 Hz, 50 N, 5–55 °C). Then, all specimens were loaded until fracture by using a universal tester. The data were analyzed with nonparametric 1-way analysis of variance (Kruskal-Wallis) and Dunn's tests (α = 0.05). Results: Additively manufactured specimens printed with 90° showed the lowest fracture strength values (P≤.048). However, the difference between specimens printed with 45° and 90° was nonsignificant (P>.05). Milled 3-unit interim fixed dental prostheses withstood significantly higher loads than 3-unit interim fixed dental prostheses printed with 45° and 150° (P≤.012). In addition, specimens printed with 0° showed higher fracture strength than the specimens printed with 45° (P=.01). Specimens printed with 0° and 30° presented similar fracture strength values with milled (P≥.057) and 150° printed (P>.05) specimens. Conclusions: Printing orientation had a significant effect on the fracture strength of 3-unit interim fixed dental prostheses. Among the additively manufactured samples, those printed with 0° showed similar fracture strength values with the subtractively manufactured samples. Clinical significance: Three-unit interim fixed dental prostheses fabricated with 0° and 30° using the 3D printing interim resin tested may be alternatives to milled PMMA in terms of fracture strength.