Characterization of 3D printed provisional resins and evaluation of the effect of printing orientation on accuracy, mechanical and optical properties, accelerated fatigue strength and finite element analyses of these materials

Abstract

The choice of a certain orientation of three-dimensional (3D) printing of provisional restorations might interfere in important properties for their intra-oral longevity. The purpose of this research project is to characterize, through degree of conversion, composition and microstructure analyses, resins for 3D-printing (R3D) indicated for indirect provisional restorations, and evaluate the effect of printing orientation in accuracy, mechanical and optical properties, accelerated fatigue strength and tension distributions of occlusal loading with finite element analyses (FEA) of the R3D. One PMMA CAD/CAM resin (Vita CAD-Temp) will be used as a control (CT) and four R3Ds and their respective 3D printers will be evaluated: Freeprint Temp; C&B MFH; Dima Print Teeth; Cosmos Temp. The degree of conversion of R3Ds will be evaluated using the Fourier-transform infrared spectroscopy (FTS-40) and the composition, and microstructure of the R3Ds' particles will be evaluated by dissolving their organic matrix in sequential solutions of organic solvents for scanning electron microscope (JSM IT 300) and X-ray dispersive spectroscopy (X-Act) analysis. Samples from CT group will be obtained with a milling machine (Cerec InLab MCXL) and R3D samples will be obtained in their respective 3D-printing machines (Photon; NextDent 5100; Cara Print 4.0; Form 2) using three orientations: (A) 0o; (B) 45o; (C) 90o. To analyze accuracy and mechanical properties (flexural strength and modulus), samples (25 x 2 x 2mm) will be obtained for CT and R3Ds, which will be printed in different orientations (n = 20). The samples dimensions will be measured and compared to the reference values to analyze printing accuracy through mean percent error. The same samples will be submitted to three-point bending test in a universal testing machine (Instron 4411) after 24 h or 1 year of storage in distilled water at 37oC (n = 10). Disk-shaped samples (10-mm diam. X 1.5-mm height) from R3Ds at different orientations and from CT group will be obtained and polished to assess color and gloss. The luminosity and color coordinates will be assessed with a spectrophotometer (Easyshade) at the baseline, after 10,000 toothbrushing cycles (Toothbrushing Simulator), and after 120 h of accelerated ageing with ultraviolet-B light (C-UV), for color difference calculation (CIEDE:2000). Gloss will be evaluated at the baseline and after toothbrushing cycles with a glossmeter (Novo-cure). Finally, one hundred and eighty human third molars will be submitted to crown preparations, which will be scanned for the production of provisional restorations: CT group will be milled and R3D will be printed in the different orientations (n = 18). After manufacturing, the provisional restorations will be cemented to the tooth with a non-eugenol provisional cement (Temp Bond NE), and will be submitted to accelerated fatigue test in a fatigue machine (Acumen3). After failure, the maximum load-to-failure and the number of cycles-to-failure will be registered, and samples will be submitted to fractographic analyses in an optical microscope (Leica MZ 125). For FEA, an analyses software (ANSYS Workbench 14) will be used to simulate tension distribution among the printed layers of R3Ds with different printing orientations. 3D images will be obtained for qualitative analyses and for quantitative analyses, maximum main and von Mises values will be used. All data will be tested for their homogeneity and homocedascity, and submitted to analyses of variance and Tukey's test (± = 5%). Data of accelerated fatigue strength will be submitted to Kaplan-Meier survivor analyses (± = 5%). (AU)