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.

Automated summary

The printing orientation has an effect on the fracture strength of 3-unit interim fixed dental prostheses, and specimens printed with 0 degrees and 30 degrees show similar fracture strength values with the milled specimens.