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 degrees , 30 degrees , 45 degrees , 90 degrees , and 150 degrees ) 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 degrees 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 (alpha = 0.05). RESULTS: Additively manufactured specimens printed with 90 degrees showed the lowest fracture strength values (P</=.048). However, the difference between specimens printed with 45 degrees and 90 degrees 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 degrees and 150 degrees (P</=.012). In addition, specimens printed with 0 degrees showed higher fracture strength than the specimens printed with 45 degrees (P=.01). Specimens printed with 0 degrees and 30 degrees presented similar fracture strength values with milled (P>/=.057) and 150 degrees 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 degrees showed similar fracture strength values with the subtractively manufactured samples. CLINICAL SIGNIFICANCE: Three-unit interim fixed dental prostheses fabricated with 0 degrees and 30 degrees using the 3D printing interim resin tested may be alternatives to milled PMMA in terms of fracture strength.