Rick Carvalho

Introduction: Computer-aided design/computer-aided manufacturing in dentistry has lead to rapid expansion of new dental materials. A new product from Shofu (Shofu, Japan), TRINIA CAD/CAM blocks and pucks, offers an alternative to the existing resin composite CAD/CAM materials. The claimed mechanical properties of TRINA provide merit to further research and development of 3D fiber reinforced composites for CAD/CAM dentistry. Objective: To design and produce 3D braided fiber-reinforced composites for dental CAD/CAM applications. Materials and Methods: Experimental groups were designed and produced in conjunction with the Department of Materials Engineering, UBC. The proposed design parameters included: 50:50 volume fraction fibers, 45-degree braiding angle, and 14 mm*14 mm cross sectional area, the approximate size of currently available CAD/CAM blocks. Continuous S-2 glass fiber roving was used as the reinforcing agent. Three experimental 3D glass fiber preforms were produced with internal structural variations using a 4-step braiding technique. A 50:50 UDMA:TEGDMA resin matrix blend with a thermal curing agent was used for infiltration via submersion under vacuum, followed by thermal curing. An unreinforced resin blend and a unidirectional fiber-reinforced composite, with the same volume fraction and dimensions, served as control groups. Samples were prepared to 4 mm*4 mm*45 mm beams for three-point-bend testing. An Instron 5969 Dual Column Material Testing System was used to test the flexural properties of the samples. Scanning electron microscopy (SEM) was used to evaluate the fractured samples. Results: Results showed that incorporation of anisotropic unidirectional fibers had the most significant effect in reinforcing the resin blend. The unidirectional control group produced the greatest flexural strength and elastic modulus at 336.6 MPa and 37.3 GPa, respectively. The 2-ply+axial group followed at 236.52 MPa and 20.75 GPa. The 2-ply had values of 196.2 MPa and 11.83 GPa. The 4-ply had values of 96.48 MPa and 4.906 GPa. The 4-ply group failed to reinforce a resin control group, which had values of 102.65 MPa and 2.467 GPa.Conclusion: Incorporation of anisotropic reinforcing fibers has most significant influence on the experimental materials flexural properties.

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Electrospun nanofibers with and without nanoparticles are poorly explored in dental research. Nanocrystalline cellulose is a nanoparticle with distinguished properties that has already been associated with nanofibers, but yet not applied to any dental aspect.The objective of this work was to investigate the use of polyacrylonitrile (PAN) nanofibers containing nanocrystalline cellulose (NCC) in the light of the mechanical behavior of fibrous mat and experimental dental composites. Three experiments were performed to answer the following research questions: 1) Can nanocrystalline cellulose improve mechanical properties of polyacrylonitrile nanofiber meshes? 2) Does the method of dispersion (simple mixture vs. with solvent exchange) of NCC in PAN solution affect fiber formation and the respective properties of the meshes? and 3) Can NCC-containing PAN electrospun nanofibers affect flexural properties of experimental dental composites?Results showed that nanocrystalline cellulose, at low concentrations, significantly increases PAN nanofibers tensile properties (chapter 2). Dispersion methods affected both the morphology and mechanical properties of the fibers (chapter 3). Finally, when NCC-containing PAN nanofibers were used to produce experimental dental composites, there was a significant improvement in flexural strength and work of fracture (chapter 4). In conclusion, the findings indicated that the use of electrospun nanofibers and nanofibres containing nanoparticles is a promising approach to reinforce dental composites.

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