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The aim of this study was to compare the influence of heat treatment on fracture resistance (FR) of different ceramic materials used for CAD/CAM systems. METHODS: Eighty monolithic restorations were designed using the same parameters and milled with a CAD/CAM system (CEREC SW 5.0, PrimeMill, Dentsply-Sirona™, Bensheim, Germany), forming five study groups: Group 1 (n = 10), CEREC Tessera (Dentsply-Sirona™, Bensheim, Germany) crystallized (CCT), Group 2 (n = 10), CEREC Tessera uncrystallized (UCT), Group 3 (n = 20), Emax-CAD (Ivoclar Vivadent, Schaan, Liechtenstein) (CEC), Group 4 (n = 20), Vita Suprinity (Vita Zahnfabrik, Bad Säckingen, Germany) (CVS), and Group 5 (n = 20) Cameo (Aidite, Qinhuangdao, China) (CC). RESULTS: The average FR was similar for CCT, CC, and CEC at above 400 N, while CVS and UCT had the lowest values at 389,677 N and 343,212 N, respectively. CONCLUSION: Among the three ceramic materials that exhibited an FR above 400 N, CCT was considered the first recommended choice for CAD/CAM systems. This material not only demonstrated the highest FR but also exhibited outstanding consistency in the related measurements without the presence of outliers. Although the CC material showed high FR, its high dispersion revealed inconsistencies in the repetitions, suggesting caution in its use.
RESUMO
The development of digital technologies has allowed for the fabrication of new materials; however, it makes it difficult to choose the best methods to obtain occlusal splints with optimal properties, so it is essential to evaluate the effectiveness of these materials. The aim of the study is to compare the fracture resistance of occlusal splints made of different materials after thermo-mechanical aging. METHODS: A total of 32 samples were made from 4 materials (two 3D printed polymeric materials, a PMMA disc for CAD/CAM, and a conventional heat-cured acrylic resin); subsequently, the fracture test was performed using the load compression mode applied occlusally on the splint surface. STATISTICAL ANALYSIS: Four statistical tests were used (Shapiro-Wilk, Levene's test, ANOVA, and Tukey's HSD test). RESULTS: The following study showed that there are differences in fracture strength among the four materials investigated, where the highest strength was observed in the milled splint, with a mean of 3051.2 N (newton) compared to the strength of the flexible splint with 1943.4 N, the printed splint with 1489.9 N, and the conventional acrylic splint with 1303.9 N. CONCLUSIONS: The milled splints were the most resistant to fracture. Of the printed splints, the splint made with flexural rigid resin withstood the applied forces in acceptable ranges, so its clinical indication may be viable. Although the results of this research indicated differences in the mechanical properties between the CAD/CAM and conventional fabrication methods, the selection may also be influenced by processing time and cost, since with a CAD/CAM system there is a significant reduction in the production time of the splint material.
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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.
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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.
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The aim of this study was to evaluate and compare the fracture resistance of a single-unit fixed prosthesis, using a CAD/CAM PMMA material and two printed materials (3DPPa and 3DPPb). A typodont with a specific preparation for a full crown was used; a digital impression was made with a state-of-the-art scanner (PrimeScanTM, Dentsply-SironaTM, New York, NY, USA), and a full coverage restoration was designed using a biogeneric design proposal by means of specific software (InLAB 22.1, Dentsply-Sirona, NY, USA). Sixty crowns were prepared, divided into three groups according to the material: 3DPPa (n = 20), 3DPPb (n = 20), both 3D-printed from the .STL file with a resolution of 50 µm, and PMMA (n = 20) milled-derived, which were subjected to a thermocycling process. A universal testing machine (Universal/Tensile Testing Machine, Autograph AGS-X Series) with integrated software (TRAPEZIUM LITE X) equipped with a 20 kN load cell was used to determine the fracture resistance. Significant differences were found by Kruskal-Wallis test and multiple comparisons (p < 0.05) in fracture resistance between materials. The fracture resistance for the PMMA material was higher, and the standard deviation was lower (x = 1427.9; sd = 36.9 N) compared to the 3DPPa (x = 1231; sd = 380.1 N) and 3DPPb (x = 1029.9; sd = 166.46 N) prints. The restorations from the milled-derived group showed higher average fracture resistance than the provisional restorations obtained from the printed groups. However, the results demonstrated that all three materials analyzed in single-unit restorations are capable of withstanding the average masticatory forces.
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In this article, an experimental investigation was conducted to study the effects of 3D printed structured fabrics on the tensile strength of two additive manufacturing technologies: (i) fused deposition modeling (FDM); and (ii) stereolithography (SLA). Three types of structured fabrics were designed in a linked fabric structure, which resembled the main characteristics of a conventional textile. Through computer-aided design (CAD), the textile structures were sketched, which, in a STL format, were transferred to 3D printing software, and consequently, they were printed. The specimens were subjected to tensile tests to analyse the behaviour of the linked structures under tensile loads. The results obtained indicated that the elements structured in a linked fabric pattern showed a statistically significant effect between the design of the 3D printed structured fabric and its tensile strength. Some important properties in textiles, fabric areal density, fineness (tex) and fabric flexibility were also analysed. This study opens an important field of research on the mechanical resistance of textile structures manufactured by 3D printing, oriented for applications in wearables that have a promising future in the fields of medicine, aerospace, sports, fashion, etc.
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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.