Biaxial Flexural Test Research Articles

Biaxial flexural strength and Weibull characteristics of a resin ceramic material after thermal-cycling.

The purpose of this in vitro study was to compare the flexural strength and Weibull characteristics of 3 different resin-ceramic materials with a zirconia-reinforced lithium silicate material after thermal-cycling. Four different computer-aided design and computer-aided manufacturing restorative materials (Vita Enamic, Lava Ultimate, Crystal Ultra, and Vita Suprinity) were tested. A total of 40 Ø12×1.2-mm disks were prepared and divided into 4 groups (n = 10). Their flexural strength was evaluated after 5000 thermal-cycles with a 4-point biaxial flexure test using a universal testing machine. The Weibull modulus and probability of failure were also determined from the biaxial flexural strength data. Data were analyzed with one-way ANOVA and the Tukey pairwise comparison test (α = 0.05). Significant differences were found among the materials in terms of biaxial flexural strength (p < 0.05). Vita Suprinity had the highest mean ±standard deviation flexural strength (289.1 ± 15.1MPa), and Vita Enamic had the lowest (100.0 ± 3.2MPa). The highest Weibull modulus was calculated for Crystal Ultra, followed by Vita Enamic, Lava Ultimate, and Vita Suprinity. Vita Suprinity had the highest flexural strength when compared with the other materials tested. Crystal Ultra had the highest flexural strength among the resin-ceramic materials. The highest Weibull modulus was calculated for Crystal Ultra and the lowest for Vita Suprinity.

Do preheated composite resin or adhesive resin layer strengthen the feldspar ceramic?

Statement of problemPreheated composite resin and adhesive coating have been recommended as luting agents for ceramic veneers; however, information about the mechanical behavior of feldspathic porcelain veneers after using these methods is still limited. PurposeThe purpose of this in vitro study was to evaluate the influence of the use of preheated composite resin or an adhesive resin layer on the strengthening of a feldspathic porcelain. Material and methodsFeldspathic porcelain disks were fabricated (N=210), etched (10% hydrofluoric acid for 90 seconds), and bonded according to resin-based luting agents (30 per group) for the biaxial flexural strength tests: photopolymerized resin cement, flowable composite resin, preheated composite resin, with or without previous adhesive coating. Characteristic strength and Weibull modulus were calculated. The viscosity of the luting agents was measured by using isothermal analyses. Finite element analysis simulated the flexural test. Fractographic and bonded interfaces were observed. ResultsThe use of preheated composite resin led to the lowest stress levels in the feldspathic porcelain veneers. However, it did not increase the ceramic strengthening compared with other luting agents, as higher values were observed with flowable composite resin (P<.05). The use of an adhesive resin layer had no significant effect on ceramic strengthening when associated with preheated composite resin or resin cement (P>.05). Preheated composite resin presented the highest viscosity and led to incomplete filling of the porcelain surface irregularities. Failures originated on the ceramic surface subjected to tensile stress and were typically associated with pores at the ceramic-luting agent interface. ConclusionsThe use of preheated composite resin or an adhesive resin layer did not have a positive effect on strengthening feldspathic porcelain.

Mechanochemical synthesis and cold sintering of mussel shell-derived hydroxyapatite nano-powders for bone tissue regeneration

According to the circular economy principles, processing routes aiming at reducing the natural resources consumption and the energy demand can be addressed as ‘green’. In this framework, mussel shells, a natural feedstock of calcium carbonate, were successfully transformed into nano-crystalline hydroxyapatite by mechanochemical synthesis at room temperature after mixing with a phosphoric acid solution. The as-synthesized powder was then consolidated up to 82 % relative density by cold sintering (600 MPa, 200 °C). The materials were fully investigated by physical, chemical and thermal characterization techniques. Cold-sintered samples were also subjected to biaxial flexural strength test, showing a flexural resistance of 23 MPa. Cell viability assessment revealed that cold sintered hydroxyapatite derived from mussel shells promotes faster adhesion and spreading of human bone marrow-derived mesenchymal stem cells, in comparison to a commercial hydroxyapatite sintered at 1050 °C. Therefore, cold-sintered mussel shells-derived hydroxyapatite can be a promising future candidate scaffold for bone tissue regeneration.

Effect of Speed Sintering on Low Temperature Degradation and Biaxial Flexural Strength of 5Y-TZP Zirconia.

Translucent zirconia is becoming the material of choice for the esthetic restorative material. We aimed to evaluate the surface structure, phase determination, translucency, and flexural strength of 5Y-TZP Zirconia (Katana STML Block and Disc) between the regular sintering and the speed sintering with and without low-temperature degradation (LTD). A total of 60 zirconia discs (30 per group; regular sintering and speed sintering) were used in this study. A CAM machine was used to mill cylinders out of the zirconia blanks and then cut into smaller discs. For the speed sintering, the zirconia blocks were milled into smaller discs. The zirconia discs were subjected to regular and speed sintering with and without LTD. Scanning electron microscopy was used to characterize the zirconia specimens and the zirconia grain size. Furthermore, the zirconia specimens were analyzed for elemental analysis using energy dispersive spectroscopy and phase identification using X-ray diffraction. The zirconia specimens were subjected to translucency measurements and biaxial flexural strength testing. The results of the zirconia specimens were compared among the groups. Statistical analysis was completed using SPSS version 20.0 to detect the statistically significant differences (p value = 0.05). A one-way ANOVA with multiple comparisons was performed using Scheffe analysis among the groups. The speed sintering presented smaller grain sizes. The zirconia specimens with and without LTD in regular and speed sintering presented a similar surface structure. Regular sintering showed more translucency compared to speed sintering. Multiple comparisons of the translucency parameter were a significant difference (p value < 0.05) between the various groups except for the comparison between speed sintering and speed sintering LTD. The regular sintering showed bigger gain sizes and slightly more translucency compared to speed sintering. The speed sintering showed higher biaxial flexural strengths compared to regular sintering. This shows that speed sintering can be considered a suitable method of sintering zirconia.

Effect of pigmentation techniques on the fatigue mechanical behavior of a translucent zirconia for monolithic restorations

This study aims to characterize the effect of pre- and/or post-sintering pigmentation techniques on the fatigue behavior of a 4YSZ ceramic (4 mol% yttrium stabilized zirconia). First, 4YSZ ceramic discs (IPS e.max ZirCAD, 15 mm diameter, and 1.2 mm thickness) were obtained and allocated according to the ‘pigmentation technique’ factor into 5 groups: Ctrl – unshaded ceramic disc (IPS e.max ZirCAD BL); Manuf – ceramic discs shaded by the manufacturer at block formation (IPS e.max ZirCAD MT A2); Brush – unshaded ceramic disc pigmented in the pre-sintered stage using a brush; Stain – unshaded ceramic disc pigmented in the post-sintering stage using a stain glaze (shade A2); Brush + Stain – combination of Brush and Stain techniques. The specimens were sintered and analyzed by a spectrophotometer (VITA Easyshade) for color differences (ΔE00 calculated according to CIEDE, 2000) to ensure that they present the same perceived color (ΔE00 ≤ 1.77, acceptability threshold). The specimens (n = 15) were submitted to biaxial flexural fatigue testing using a cyclic fatigue method (frequency of 20 Hz; 10,000 cycles per step; initial stress of 200 MPa; and step-size of 25 MPa) until specimen fracture. Fatigue strength (FS) and number of cycles until failure (CFF) were recorded with statistical purposes. Fractographic, complementary topography, elemental and roughness analyses were performed. The Ctrl shown the highest FS, CFF, and survival rates compared to the other conditions (p < 0.05), being only statistically similar to Brush. Stain showed the lowest FS, CFF and survival rates (p < 0.05). The Manuf and Brush + Stain shown intermediary performance. In regards of Weibull moduli, Brush shown the lowest values (lowest structural reliability), for both FS and CFF, being only statistically similar to Manuf. Topography analysis shown a uniform size of zirconia crystals in Ctrl, Manuf and Brush. In addition, a smooth glassy surface with some spots of impregnated pigment was observed in the groups where glaze was applied (Stain and Brush + Stain). This finding was corroborated by elemental analysis. Despite that, Stain and Brush + Stain presented the roughest surface (p < 0.05). In summary, the pigmentation techniques used to provide a Vita classical A2 color shade have a detrimental effect on the mechanical fatigue properties of a 4YSZ ceramic, except for the technique performed with the brush in the block pre-sintering stage. Despite this, the brush technique presents great variability in mechanical performance, resulting in lower structural reliability.

Effect of Porcelain-to-Zirconia Ratio and Bonding Strategy on the Biaxial Flexural Strength and Weibull Characteristics of a Stress-Free Bilayer CAD/CAM Ceramic System.

To evaluate the biaxial flexural strength of different porcelain-to-zirconia thickness ratios and bonding strategies of a stress-free bilayer CAD/CAM ceramic system. A total of 60 zirconia discs (diameter: 15 mm; thickness: 0.3 or 0.5 mm; n = 30 for each thickness) were divided into six groups (n = 10 each) according to porcelain-to-zirconia ratio and bonding strategy: VM/Zr (control): zirconia discs veneered with a feldspathic ceramic (VM 9, Vita) in 0.9-mm and 0.7-mm thicknesses using a conventional hand-layering technique; VB/Zr-SBU: zirconia discs airborne particle-abraded with 50-μm Al2O3 particles followed by an MDP primer application (Single Bond Universal, 3M) and bonded to the porcelain with a resin cement (Panavia F 2.0, Kuraray); and VB/Zr-RC: zirconia discs airborne particle-abraded with 30-μm silica-coated Al2O3 particles and silanized and bonded to the porcelain with the same resin cement. Before cementation, the VB (Vitablocs II) discs were etched with 5% hydrofluoric acid (60 seconds), followed by silane application. The bilayers (thickness = 1.2 mm) were loaded with 750 g while light curing the resin cement. Two porcelain-to-zirconia thickness ratios were evaluated: 0.9: 0.3 mm and 0.7: 0.5 mm. All groups were subjected to 106 mechanical cycles, followed by a biaxial flexural test. Data (MPa) were subjected to two-way analysis of variance (ANOVA), Tukey test (5%), and Weibull analyses. Two-way ANOVA revealed that the factor porcelain-to-zirconia ratio (P = .0556) was not significant; however, the bonding strategy factor was statistically significant. Among the 0.5-mm zirconia groups, the VB/Zr-SBU group presented higher flexural strength (s) than the VM/Zr or VB/Zr-RC groups. Similar results were also found for the 0.3-mm zirconia groups, in which the VB/Zr-SBU group also presented higher strength than the others, which were similar in comparison (Tukey). The Weibull modulus was similar among the groups; however, the characteristic strength was significantly different (P = .000). The zirconia bonding strategy with 50-μm Al2O3 airborne-particle abrasion, followed by a primer application, increases the flexural strength of a stress-free bilayer CAD/CAM ceramic system.

Modeling of biaxial flexure tests of transport amphorae with the finite element method: Fracture strength, deformation and stress distribution

The measurement of mechanical behavior of ceramics provides essential information about the mechanical performance of ceramic vessels produced from these materials. In the present case study fragments of Hellenistic and Roman transport amphorae from the Southeast Aegean islands of Kos and Rhodes were investigated. In terms of material properties the flexural strength is of particular interest as it reflects the performance under typical mechanical loading emerging during use of these vessels. Flexural strength can be determined either in uniaxial tests, for example by three-point-bending, or more realistically, in a biaxial flexure test, for example loading with a sphere on a ring-supported ceramic disk. For the present case study ceramic disks, prepared from actual amphora wall fragments, were tested and load-displacement curves were recorded until final fracture. The flexural strength was calculated based on the maximum load at initial fracture. In order to further investigate the recorded curves in terms of elastic as well as plastic deformation and stress distribution, a three-dimensional numerical model of the biaxial flexure test was generated and evaluated using the finite element method (FEM). By adjusting the simulated behavior to the experimentally determined curves, an estimation of material properties was attempted. This approach is useful for the development of numerical models of contact loads in amphora assemblages, simulating for example storage in a cargo ship, in order to test different vessel shapes for their performance.

Prediction of uniaxial and biaxial flexural strengths of resin-based composites using the Weibull model

The aim of the study was to assess the applicability of the Weibull model for resin-based composites (RBC) to predict the outcome of different flexural tests based on one another, while identifying the minimal sample number for a precise Weibull representation. Four RBCs underwent 3-point, 4-point and biaxial flexural testing (n=480). Fracture surfaces of all specimens were assessed under optical microscope, while fracture modes of the uniaxial specimens were documented. Representative specimens for each fracture mode were further analyzed under scanning electron microscope. Since fracture predominantly originated from a surface flaw, the effective surface was used in the Weibull model. The analysis was performed on 20, then 30 and finally 40 specimens per group to assess the effect of the specimen size. Further statistical analysis was performed through uni- and multivariate ANOVA, Tukey's post hoc test (α=0.05), and Pearson's correlation. The Weibull model could predict the results of uniaxial tests within the standard deviation, with the correlation between calculated and measured values reaching values of R2=0.985 and higher. Predictions for or based on the biaxial tests misestimated the measured values, with a weaker correlation (R2=0.875) between measured and calculated flexural strength (FS). The fit of the data to the Weibull distribution improved with rising sample size resulting in better predictions of the FS when n=40. The applicability of the Weibull model on RBCs allows accurate comparison between bending tests and their FS under consideration of the effective surface.

The effect of adjustment and finishing procedure on roughness, strength, and phase transformation of monolithic zirconia.

To evaluate the effect of adjustment and finishing procedures and thermal aging of monolithic zirconia on the surface roughness, phase transformation, and flexural strength. One hundred disk-shaped monolithic zirconia specimens were randomly divided into 5 groups: control, received only glazing; group Gr, was grinded; group GrP, was grinded and polished; group GrG, was grinded and re-glazed; group GrPG, was re-glazed after grinding and polishing. Half of the each group were stored in distilled water for 24h and the remaining were thermocycled for 5000 cycles. Topographic evaluations were done with profilometer and scanning electron microscope. Phase changes were assessed through X-ray diffractometer. The biaxial flexural strength test was calculated by universal test machine. Statistical analysis was performed by using two-way ANOVA and Tukey multiple comparison test (p < 0.05). Group Gr showed statistically higher surface roughness and flexural strength values than the other groups (p < 0.001). However, no significant differences were observed between finishing groups (p >0.05). Phase transformation was occurred in all groups but the differences were not statically significant (p >0.05). Artificial aging had no effect on surface roughness, flexural strength, and phase transformation (p >0.05). Surface roughness significantly increased after grinding, but finishing procedure approximated it to the control group. Glazing after grinding decreased the flexural strength, but polishing did not. Zirconia polishing system may be an alternative to re-glazing for monolithic zirconia. Polishing is one of the most effective finishing procedures that can improve the physical properties of the material without damaging its mechanical properties.

3D-printed resins for provisional dental restorations: Comparison of mechanical and biological properties.

To characterize the mechanical and biological properties of three commercially available resins, which are currently used for provisional restorations and to compare them to an experimental resin intended for definitive fixed dental prostheses. Three commercially available resins: Crowntec (CT, Saremco), Temporary C&B (FL, Formlabs), C&B MFH (ND, Nextdent), and the experimental resin: Permanent Bridge (PB, Saremco) were printed and subjected to biaxial flexural strength test, finite element analysis, Weibull analysis, scanning electron microscopy, cell proliferation, immunohistochemistry and cytotoxicity assays. Samples from CT, PB, and ND were provided directly from the manufacturers ensuring ideal workflow. FL was printed using the workflow as recommended by the manufacturer, using a Formlabs 2 printer and their post-processing units Form Wash and Form Cure. From the tested resins, PB yielded the best overall results in terms of mechanical properties. Cell proliferation and cytotoxicity did not show any significant differences among materials. PB showed higher values for probability of survival predictions (35%) when subjected to 250 MPa loads, whereas the other materials did not reach 10%. Despite mechanical differences between the evaluated materials, the outcomes suggest that 3D printed provisional resins may be used in clinical settings, following the manufacturers indications. New materials intended for long-term use, such as the PB resin, yielded higher mechanical properties compared to the other materials. Alternative printing and post-processing methods have not yet been evaluated and should be avoided until further literature is available. 3D printed resins for provisional restorations have become popular with the emergence of new technologies. In this study, we evaluated three different commercially available resins for provisional restorations and one new experimental resin. The results from this study indicate that commercially available resins could be used in clinical settings under certain conditions and limited periods of time. Following the manufacturers protocols is of paramount importance to not compromise these properties.

Comparative Properties of Porous Phyllosilicate-Based Ceramics Shaped by Freeze-Tape Casting

Porous phyllosilicate-based ceramics were manufactured by freeze-tape casting from clays of different particle size and morphology in order to characterize their microstructure and stress to rupture changes before and after firing. Three raw clays were selected: HCR (77% Halloysite–10Å), KORS (29% kaolinite), and KCR kaolin (98% kaolinite). These clays exhibited a monomodal distribution and were used to prepare four slurries, three with each clay material and one consisting of a mixture of KCR and HCR labeled KHCR. After shaping by freeze-tape casting, the porosity and stress to rupture obtained by a biaxial flexural test were collected for disk-like samples after drying and sintering at 1200 °C. Results showed that KCR ceramic materials had the highest biaxial bending strength (70 ± 1.1 MPa) and those from KORS had the highest porosity value (80 ± 1%). SEM observation revealed a difference in microstructure and texture for the manufactured porous ceramic materials. In the KCR ceramic disks, the flattened pores appeared more textured, and the primary mullite crystallites formed a rigid skeleton within the amorphous phase. KORS ceramic materials showed a small quantity of secondary mullite needles which were randomly dispersed in a vitreous phase. The relatively important vitreous phase in the porous materials of HCR led to the bulk formation of small mullite particles. The biaxial flexural strength values were related to the presence of the mullite, as well as to the microstructure (volume, morphology, and size distribution of pores) after sintering.

5 - Effect of Roughness on Flexural Strength of Dental Lithium-Disilicate

A common process in dental clinics is to perform small fitting adjustments of dentures after testing in the patient's mouth using the micro-grinding tool. This procedure promotes a local roughness increase and can lead to the formation of microcracks on the prosthesis surface. The aim of this work was to investigate the benefits of a post-finishing heat treatment on the surface roughness smoothing and crack healing of lithium disilicate dental glass ceramics, and its effect on the flexural strength. Commercially available lithium metasilicate, Li 2 SiO 3 (IPS e-maxCAD), samples were heat treated at 840C-7min. The material was characterized by X-ray diffraction, Scanning Electron Microscopy, Vickers hardness, Youngs modulus and fracture toughness. One of the surfaces of the samples was machined, aiming to simulate the fitting procedure of dentures in the dentist's laboratory, generating a rough surface. Half of the samples were tested by biaxial flexural testing (3B-P) and the other half were submitted to a rapid heat treatment (840C-3min) and later tested by biaxial strength, with statistical analysis by Weibull. The Roughness parameters (Ra, PV and Rz) were measured using Zygo New View 7100 Optical Profiler. After the crystallization heat-treatment protocol suggested by the manufacturer, the formation of elongated lithium disilicate crystals, Li 2 Si 2 O 5 , with 36% residual amorphous phase was observed. In addition, the Vickers hardness of 6.1±0.3 GPa, fracture toughness of 1.90± 0.2 MPa.m1/2 and modulus of elasticity values of 91 ±2 GPa were obtained. The samples from the group without rapid heat-treatment showed bending strength of 203.5 ±33 MPa, with roughness values of Ra=0.6 ±0.2 μm, Rz=22 ±6 μm and PV=28 ±7 μm. After the rapid heat treatment, the roughness parameters Ra, Rz and PV were 0.3 ±0.2 μm, 9 ±6 μm and 5 ±4 μm, respectively. With this reduction in roughness, the flexural strength increased by 65%, with mean values of 336.6 ±32 MPa. Weibull modulus values were in the order of 5 for both groups. In the need for finishing machining of lithium disilicate-based glass-ceramic dental prostheses, the use of a rapid heat treatment at 840 C allows considerable gains in flexural strength. Increasing the service life of the prosthesis, due to a reduction on the surface roughness, promoted by the softening of the remaining amorphous phase in the glass-ceramic.

15 - Characterization and Thickness Effect on Fatigue Strength of Translucent Zirconias

To characterize the microstructure, hardness, and fracture toughness of yttria-partially stabilized zirconia ceramics and to evaluate the effect of thickness on their biaxial flexural strength (quasi-static and fatigue tests). Disc-shaped specimens (12 mm in diameter, 1.2 mm-thick) were obtained from 3Y-TZP (Vita YZ HT), 4Y-PSZ (Vita YZ ST), and 5Y-PSZ (Vita YZ XT) ceramics. The samples had their crystalline phases, microstructure and composition analyzed with X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy-dispersive X-ray spectroscopy (EDX). A microhardness tester was used to assess the Vickers hardness and fracture toughness of each material. Thinner discs were also prepared to evaluate the thickness effect (0.7 or 1.2 mm) on the biaxial flexural strength. The monotonic biaxial flexural strength tests were performed according to ISO 6872/2015. The same test set up was used to perform fatigue tests (incremental steps of 25 MPa for 10,000 cycles starting from 400 MPa). SEM images revealed surface defects on 4Y-PSZ and 5Y-PSZ samples, while 3Y-TZP exhibited greater grain uniformity. All ceramics showed similar chemical compositions. The main difference was the amount of yttria, which was higher in 5Y-PSZ, followed by 4Y-PSZ, and 3Y-TZP. The same trend was observed regarding the amount of cubic phase (5Y-PSZ > 4Y-PSZ > 3Y-TZP). 5Y-PSZ and 3Y-TZP presented the highest hardness values (1529.8 152.6 and 1421.5 109.7, respectively). The highest fracture toughness was observed in 3Y-TZP (5.66 0.56), while 4Y-PSZ (4.44 0.58) and 5Y-PSZ (4.29 0.38) showed similar values. The lowest flexural fatigue strength was observed in 5Y-PSZ (0.7 mm: 376.7 MPa and 60.3 ×103 cycles for failure, 1.2 mm: 440 MPa and 73 ×103 CFF), while 3Y-TZP and 4YSZ were statistically similar (3Y 0.7 mm: 520 MPa and 89 ×103 CFF, 1.2 mm: 516.7 MPa and 88.3 ×103 CFF, 4Y 0.7 mm: 603.3 MPa and 105.6 ×103 CFF, 1.2 mm: 546.6 MPa and 94.3 ×103 CFF). Comparing the monotonic and fatigue tests, 3Y-TZP suffered the highest (1.2 mm: 47.04%) and lowest (0.7 mm: 29.85%) percentage of degradation. 5Y-PSZ degraded more than 4Y-PSZ (5Y 0.7: 46.38%, 1.2: 41.38%, 4Y 0.7: 35.19%, 1.2: 38.52%). Despite the microstructural differences, 4Y-PSZ and 3Y-TZP had similar fatigue behavior regardless of thickness. 5Y-PSZ had the lowest mechanical performance.

64 - Ceramic Composites from Bovine Hydroxyapatite, ZrO2@SiO2, and Hydroxyapatite + 15%ZrO2@SiO2

This study aimed to synthetize and evaluate the biaxial flexural strength of dense polycrystalline experimental composites from bovine hydroxyapatite (HA); ZrO 2 @SiO 2 coreshell; and HA + 15%ZrO 2 @SiO 2 . HA was extracted from solid bovine bone residues and broken to submicrometric powder. ZrO 2 coreshell covered by SiO 2 was synthetized through Stober sol-gel method. Disc-shaped specimens (12 ×1.2 mm) were synthesized at 1300 C (HA), 1340 C (ZrO 2 @SiO 2 ), and 1300 C (HA + 15%ZrO 2 @SiO 2 ). The sintering temperatures followed the maximum temperature indicated for each material, according to the literature. Next, the specimens were submitted to biaxial flexural strength test. The results were analyzed regarding normality by Shapiro Wilk test. Comparisons were made by Kruskall-Wallis test (α = 0.05) followed by Tukey test. DRX analysis demonstrated the characteristic peaks of ZrO 2 and HA in HA +15%ZrO 2 @SiO 2 . It was also possible to observe HA crystallinity decreasing with the addition of the coreshell. ZrO 2 @SiO 2 biaxial flexural strength (140.2 16.05 MPa) was significantly greater (p<.001) than HA (99.2 8.66 MPa), and HA + 15%ZrO 2 @SiO 2 (107.5 5.44 MPa). HA and HA + 15%ZrO 2 @SiO 2 showed no statistically differences. ZrO 2 @SiO 2 sintering was a promising alternative to make crystalline materials and HA-ZrO 2 @SiO 2 composite can be a promising biomaterial, after the search for adjustments in the sintering process.

Arithmetic Relationship between Fracture Load and Material Thickness of Resin-Based CAD-CAM Restorative Materials.

Data on the long-term behavior of computer-aided designed/computer-aided manufactured (CAD-CAM) resin-based composites are sparse. To achieve higher predictability on the mechanical behavior of these materials, the aim of the study was to establish a mathematical relationship between the material thickness of resin-based materials and their fracture load. The tested materials were Lava Ultimate (LU), Cerasmart (GC), Enamic (EN), and Telio CAD (TC). For this purpose, 60 specimens were prepared, each with five different material thicknesses between 0.4 mm and 1.6 mm (N = 60, n = 12). The fracture load of all specimens was determined using the biaxial flexural strength test (DIN EN ISO 6872). Regression curves were fitted to the results and their coefficient of determination (R2) was computed. Cubic regression curves showed the best R2 approximation (LU R2 = 0.947, GC R2 = 0.971, VE R2 = 0.981, TC R2 = 0.971) to the fracture load values. These findings imply that the fracture load of all tested resin-based materials has a cubic relationship to material thickness. By means of a cubic equation and material-specific fracture load coefficients, the fracture load can be calculated when material thickness is given. The approach enables a better predictability for resin-based restorations for the individual patient. Hence, the methodology might be reasonably applied to other restorative materials.

Effect of staining on the mechanical, surface and biological properties of lithium disilicate

PurposeTo simulate biodegradation and wear of stained and glazed CAD lithium disilicate ceramic, and evaluate their effects on the microbial adherence and mechanical and surface properties of lithium disilicate ceramic Materials and methods160 lithium disilicate ceramic discs were fabricated and divided in eight groups according to manual stain and glaze application with a fine paintbrush (without stain and glaze; with stain and glaze) and aging procedures (no aging; wear at 30 N load, 1.7 Hz, 3 × 105 cycles; biodegradation by exposure to microcosm biofilm; biodegradation + wear; biodegradation + wear). Profilometry was performed to determine the surface roughness and the wear consequences. Biaxial flexural strength test was performed, and a Streptococcus mutans adherence test was conducted to evaluate the number of colony forming units. ResultsUnaged samples with and without stain and glaze presented the lowest values of surface roughness (p < 0.001), but after aging (wear, biodegradation, or both), the samples in the stain and glaze groups were rougher than those in the no stain and glaze groups (p < 0.001). The stain and glaze groups showed the highest volume of wear after aging (p = 0.04), and had the lowest flexural strength values (p < 0.01), irrespective of the aging method. The aging method did not affect the flexural strength (p = 0.06). The number of colonies forming units was higher for biodegradation + no stain and glaze, biodegradation + wear + no stain and glaze, no aging + stain and glaze, biodegradation + stain and glaze, and biodegradation + wear + stain and glaze. The lowest values were observed for no aging + no stain and glaze. ConclusionThe staining and glazing of lithium disilicate increased the surface wear and bacterial adherence, and decreased biaxial flexural strength of the material. When exposed to S. mutans, surface roughness increased, and biodegradation favored bacterial adherence.

Strength and Toughness of Waste Fishing Net Fiber-Reinforced Concrete.

In this study, we estimate the potential efficiency of waste fishing net (WFN) fibers as concrete reinforcements. Three WFN fiber concentrations (1, 2, and 3% by volume) were mixed with concrete. Compressive strength, toughness, splitting tensile strength, and biaxial flexural tests were conducted. Compressive strength decreased but other properties increased as a function of fiber proportions. According to the mechanical strength observations and the ductility number, WFN fibers yielded benefits in crack arresting that improved the postcracking behavior and transformed concrete from a brittle into a quasi-brittle material. It is inferred that WFN fiber is a recycled and eco-friendly material that can be utilized as potential concrete reinforcement.

Wear behavior of silica-infiltrated monolithic zirconia: Effects on the mechanical properties and surface characterization

The objective of this study was to assess the wear behavior and its effects on the flexural strength of silica-infiltrated zirconia compared to glaze and polishing finishing treatments. To do so, disc-shaped samples of a second-generation zirconia were prepared and divided into three groups: silica infiltration, glazing, or polishing. Half of the samples of each finishing were subjected to sliding wear testing using a steatite antagonist. The discs and antagonists had their volume loss measured. The wear-tested and the other half of samples were subjected to biaxial flexural strength testing and the following characterization analyses were also performed: roughness, hardness, X-ray diffraction, profilometry, and scanning electron microscopy (SEM). Data were evaluated with ANOVA and Weibull analyses. Glazing caused greater antagonist volume loss, followed by silica infiltration, and polishing. Silica-infiltrated zirconia surface was similarly worn to polished, which was lower than that for glazed zirconia. Polished zirconia presented the highest flexural strength. However,the strength decreased and became similar in all worn groups. Silica infiltration showed slightly lower characteristic strength after sliding wear. The highest roughness and hardness values were observed on glazed zirconia. These values decreased after wear testing and became similar to the other groups. SEM evidenced an irregular surface for glazing. No phase transformation occurred after sliding wear. Despite producing some volume loss on zirconia and antagonist surfaces, silica infiltration is a promising alternative for finishing monolithic restorations. Moreover, the damage caused by sliding wear leads to decreasing the strength of zirconia regardless of the surface finishing.

The breakdown of the Weibull behavior in dental zirconias

AbstractHere we attend to the controversy of the use of Weibull statistics for describing the strength distribution of dental brittle materials. Our approach is purely experimental by means of testing for the strength size effect, a requirement for Weibull materials. Zirconia materials of five important dental manufacturers were selected, each represented by two compositions, being one a 3 mol% Y2O3‐stabilized zirconia, and the other being a “translucent” zirconia with 4 or 5 mol% stabilizer content. Specimens of increasing sizes were fractured, whether by using a biaxial flexure test in plates or a uniaxial bending test in beams, thereby sampling different ranges of effective surfaces and volumes. A systematic deviation from the Weibull behavior over the range of 1–40 mm2 effective surface was demonstrated, regardless of manufacturer and Y2O3 content in the powder. Extensive testing using a wider range of specimen sizes narrowed down the threshold for the breakdown of the defect size distribution from the parent population to be located between 10 and 20 mm2 effective surface. A comparable behavior was confirmed for the partly sintered white‐bodies, with similar defect morphology to the fully sintered analogs, indicating a defect size distribution stemming from the pressing steps of manufacture. The defect shape related to open particle aggregate junctions, pointing to an association of their size distribution to that of the distribution of aggregate sizes in the source powders.

Surface treatments and its effects on the fatigue behavior of a 5% mol yttria partially stabilized zirconia material

This study evaluated the effect of distinct surface treatments on the fatigue behavior (biaxial flexural fatigue testing) and surface characteristics (topography and roughness) of a 5% mol yttria partially stabilized zirconia ceramic (5Y-PSZ). Disc-shaped specimens of 5Y-PSZ (IPS e.max ZirCAD MT Multi) were manufactured (ISO 6872–2015) and allocated into six groups (n = 15) considering the following surface treatments: Ctrl – no-treatment; GLZ – low-fusing porcelain glaze application; SNF – 5 nm SiO2 nanofilm; AlOx – aluminum oxide particle air-abrasion; SiC – silica-coated aluminum oxide particles (silica-coating); and 7%Si – 7% silica-coated aluminum oxide particles (silica-coating). The biaxial flexural fatigue tests were performed by the step-stress method (20Hz for 10,000 cycles) with a step increment of 50N starting at 100N and proceeding until failure detection. The samples were tested with the treated surface facing down (tensile stress side). Topography, fractography, roughness, and phase content assessments of treated specimens were performed. GLZ group presented the highest fatigue behavior, while AlOx presented the lowest performance, and was only similar to SiC and 7%Si. Ctrl and SNF presented intermediary fatigue behavior, and were also similar to SiC and 7%Si. GLZ promoted a rougher surface, Ctrl and SNF had the lowest roughness, while the air-abrasion groups presented intermediary roughness. No m-phase content was detected (only t and c phases were detected). In conclusion, the application of a thin-layer of low-fusing porcelain glaze, the deposition of silica nanofilms and the air-abrasion with silica-coated alumina particles had no detrimental effect on the fatigue behavior of the 5Y-PSZ, while the air-abrasion with alumina particles damaged the fatigue outcomes.