The aim of this study was to evaluate and compare the fracture resistance of temporary restorations made of polymethylmethacrylate (PMMA), graphene-modified PMMA (GRA), acetal resin (AR) and polysulfone (PS) obtained by a subtractive technique (milling) using a computer-aided design and manufacturing (CAD/CAM) system of a three-unit fixed dental prosthesis (FDP). Methods: Four groups of ten samples were fabricated for each material. Each specimen was characterized by a compression test on a universal testing machine, all specimens were loaded to fracture and the value in Newtons (N) was recorded by software connected to the testing machine. The fracture mode was evaluated on all samples using a stereomicroscope. Results: There were statistically significant differences (p value < 0.005) between PMMA and the other three materials (PMMA: 1302.71 N; GRA: 1990.02 N; RA: 1796.20 N; PS: 2234.97). PMMA presented a significantly lower value than the other materials, and PS showed the highest value. GRA and RA presented a similar range of values but they were still higher than those of PMMA. Conclusions: GRA, RA and PS are presented as valid options within the range of interim milled restorative materials and as alternatives to PMMA.
It is well known that the use of continuous reinforcing fibers can largely improve the typical low in-plane mechanical properties of 3D-printed parts. However, there is very limited research on the characterization of the interlaminar fracture toughness of 3D-printed composites. In this study, we investigated the feasibility of determining the mode I interlaminar fracture toughness of 3D-printed cFRP composites with multidirectional interfaces. First, elastic calculations and different FE simulations of Double Cantilever Beam (DCB) specimens (using cohesive elements for the delamination, in addition to an intralaminar ply failure criterion) were carried out to choose the best interface orientations and laminate configurations. The objective was to ensure a smooth and stable propagation of the interlaminar crack, while preventing asymmetrical delamination growth and plane migration, also known as crack jumping. Then, the best three specimen configurations were manufactured and tested experimentally to validate the simulation methodology. The experimental results confirmed that, with the appropriate stacking sequence for the specimen arms, it is possible to characterize the interlaminar fracture toughness in multidirectional 3D-printed composites under mode I. The experimental results also show that both initiation and propagation values of the mode I fracture toughness depend on the interface angles, although a clear tendency could not be established.
In this paper, the one-dimensional tensile behavior of Guadua angustifolia Kunth fibre/polypropylene (PP+GAKS) composites is modeled. The classical model of Kelly–Tyson and its Bowyer–Bader’s solution is not able to reproduce the entire stress—strain curve of the composite. An integral (In-Built) micromechanical model proposed by Isitman and Aykol, initially for synthetic fiber-reinforced composites, was applied to predict micromechanical parameters in short natural fiber composites. The proposed method integrates both the information of the experimental stress-strain curves and the morphology of the fiber bundles within the composite to estimate the interfacial shear strength (IFSS), fiber orientation efficiency factor ηFOD, fiber length efficiency factor ηFLD and critical fiber length lc. It was possible to reproduce the stress-strain curves of the PP+GAKS composite with low residual standard deviation. A methodology was applied using X-ray microtomography and digital image processing techniques for the precise extraction of the micromechanical parameters involved in the model. The results showed good agreement with the experimental data.
The aim of this study was to evaluate and compare the fracture resistance of definitive zirconia dioxide restorations obtained using a computer-aided design and manufacturing (CAD/CAM) system. Methods: Two groups of ten samples were analyzed for each material (n: 20); the first group was Zolid Gen X Amann Girrbach (ZGX) and the second group was Cercon HT Dentsply Sirona (CDS). The restorations were designed with identical parameters and milled with a CAD/CAM system. Each specimen was load tested at a speed of 0.5 mm/min, with a direction parallel to the major axis of the tooth and with an initial preload of 10 N until fracture using a universal testing machine (Universal/Tensile Testing Machine, Autograph AGS-X Series) equipped with a 20 kN load cell. The results obtained were recorded in Newtons (N), using software connected to the testing machine. Results: Statistically significant differences were found, and the fracture resistance of the monolithic zirconia crowns was lower in the CDS group (1744.84 ± 172.8 N) compared to the ZGX group (2387.41 ± 516 N). Conclusions: The monolithic zirconia CAD-CAM zirconia crowns showed sufficient fracture resistance when used in posterior molar and premolar zones with either material, as they withstood fracture loads greater than the maximum masticatory force.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.