Higher Flexural Strength Values Research Articles

Microstructure evolution of diboride and carbide phases in platelets-toughened (Zr, Ti)C-(Ti, Zr)B2 ceramics via reaction pressureless sintering

Fully dense (Zr, Ti)C-(Ti, Zr)B2 composites were sintered via reactive pressureless sintering of ZrB2 and TiC based on the in-situ reaction and solid solution coupling effects. The effects of TiC content and sintering temperature on microstructure evolution and mechanical properties were explored. Elongated (Ti, Zr)B2 platelets were observed, stemming from the in-situ reaction between ZrB2 and TiC, and exhibited a high aspect ratio with the increase of TiC content. Besides, phase decomposition structures featuring semi-coherent interfaces were identified in the ZrB2-70mol.% TiC system sintered at 2200 °C, attributed to the chemical miscibility gap. High values of hardness (27.0 GPa), flexural strength (533 MPa), and fracture toughness (4.6 MPa m1/2) are found in ZrB2-70 mol.% TiC composite sintered at 2200 °C. The low porosity, solid solution strengthening, grain refinement caused by carbide phase decomposition, and high dislocation densities and strain concentration at the semi-coherent interfaces of carbide phase decomposed structures play an important role on hardening and strengthening. Furthermore, the presence of in-situ synthesized (Ti, Zr)B2 platelets with a high aspect ratio significantly contributes to toughening.

Designing Hollow Brick Waste Based Alkali Activated Composites by Taguchi Method

The use of waste materials in alkali-activated material technologies is important in terms of sustainability. The production of alkali-activated composites (AAC) with hollow brick waste (HBW) as a binder may contribute to solving existing environmental problems related to the depletion of natural resources. In this study, mortars were produced using different concentrations (6 M, 8 M, and 10 M NaOH) and Alkaline Activator/Powder Material (AA/PM) ratios of 0.30, 0.35, and 0.40 through the alkali activation method. The hollow brick waste (HBW) powder was obtained by grinding inactive bricks in brick factories. The prepared mortars were cured separately for each mixture at 90°C for 24 hours. Compressive and flexural strength tests were performed on the prepared perforated hollow brick waste-based composites. The Taguchi method was used to determine the optimum mixing ratios by conducting compressive and flexural strength tests on the produced AAC. To optimize the parameters determined using the Taguchi method, the best mixing ratios were determined using the L9 (3^2) orthogonal index. The compressive and flexural strengths of the mixtures were evaluated considering the signal to noise ratio "larger the better" and the highest compressive strength value was 63.669 MPa and the highest flexural strength value was 6.629 MPa according to the optimum values. According to the obtained results, it was determined that the AAC produced at 6 M NaOH and 0.30 AA/PM ratio exhibited the highest compressive and flexural strength values.

Flexural Strength of Kenaf Fibers/Epoxy Bio-Composites: Content of Kenaf Fiber, Curing Times and Curing Temperatures

Kenaf fiber possesses the capability for application in bio-composite materials, owing to its appealing mechanical and physical properties. This research aimed to achieve the optimum flexural strength of kenaf fiber/epoxy bio-composites materials with variations in kenaf fiber content, curing time, and curing temperature using a casting process. This study found that kenaf fiber addition increased the flexural strength of kenaf fiber/epoxy bio-composite, by varying curing time (30, 45, and 60 minutes) and curing temperature (60, 90, and 150 °C). The results showed that the highest flexural strength was obtained at 90°C (72.5 MPa) at 20/80 kenaf fiber content, at various curing temperatures. Meanwhile, the same highest flexural strength value (72.5 MPa) was also obtained for 20/80 kenaf fiber content, 45 minutes at various curing times. SEM image shows that 20 Wt.% kenaf fiber content has a better dispersion compared with 10 Wt.% so that affects the flexural strength value.

Flexural strength of 3D-printed nanocomposite provisional resins: Impact of SiO2 and ZrO2 nanoparticles and printing orientations in vitro.

The aim of this study was to investigate and compare the influence of zirconium dioxide nanoparticles (ZrO2 NPs) and silicon dioxide nanoparticles (SiO2 NPs) addition and printing orientation on the flexural strength (FS) of provisional three-dimensional (3D) printing resins undergoing thermal cycling (TC). Three dimensional-printed resin (NextDent C&B MFH) was used to fabricate 300bar-shaped specimens (25×2×2mm3 ). The ZrO2 NPs and SiO2 NPs specimens were divided into two groups, then subdivided into three groups, based on the nanoparticle concentration (i.e., 0 wt% (original group), 0.5 wt%, and 1 wt%). Each concentration was printed in three printing orientations (0°, 45°, and 90°). The printed specimens were exposed to 5000 cycles of TC, followed by a three-point bending test to assess the FS. Fracture surface analysis was conducted by using a scanning electron microscope (SEM). For data analysis, ANOVA and Tukey's post hoc were utilized (α = 0.05). Compared to the original material, the addition of ZrO2 NPs and SiO2 NPs had a significantly positive impact on the FS, (P > 0.001). After TC, the FS of the original group decreased significantly and had the lowest value. The highest FS value was observed in 1% ZrO2 NPs at 0°. Regardless of the nanoparticle concentration, the 0° orientation consistently showed a higher FS, compared to the 45° and 90° orientations. At all orientations (i.e., 0°, 45°, and 90°), the FS significantly increased with the addition of NPs, compared with that of the original material (P > 0.001). TC had a significantly negative effect on the FS of the unmodified groups. However, no significant differences existed in FS among the modified groups after TC. The addition of SiO2 NPs and ZrO2 NPs increased the FS of the 3D-printed provisional resin. Regardless of the nanoparticle concentration, the 0° orientation had the higher FS. TC had an effect on the original resin, whereas it had no significant effect on the nanoparticle-modified resins. In clinical practice, 3D-printed provisional nanocomposite resins printed at the 0° orientation could be recommended for long-term dental provisional restorations.

The influence of different fiber sizes on the flexural strength of natural fiber-reinforced polymer composites

This experiment aimed to investigate the impact of varying fiber lengths on the flexural strength of coconut fiber composites with epoxy resin. Coconut fiber composite panels were produced using rectangular molds. The effects of various fiber sizes, especially 2, 4, and 6 mm, respectively, were compared with fiberless and continuous fiber polymer composites on the flexural strength of Natural Fiber-reinforced Polymer Composites (NFPC). The lowest flexural strength is 10.04 MPa, was obtained for the NFPC sample with a fiber length of 2 mm, while the highest flexural strength value was 10.70 MPa with a fiber length of 6 mm. Generally, flexural strength is influenced by variations in fiber size but not significantly. The flexural modulus and flexural strength values exhibit the same trend. Fiber pullouts are visible on the fracture surface of the sample, and voids in the form of trapped gas are also apparent on the sample surface. Short fiber size is one of the causes of fiber pullout, which can reduce the flexural strength of short fiber polymers.

Relação entre a performance de placas de concreto permeável com escória de aciaria e as propriedades de forma de agregados graúdos

Abstract The growth of cities affects their permeable surface, which can unbalance hydrological cycles. The pervious concrete can be a viable solution to combat urban environmental impacts in this subject. This type of concrete can be told apart by the presence of interconnected pores and its drainage capacity. This paper aims to analyze the relationship between aggregate shape, mechanical resistance, and permeability of pervious concrete slabs containing steel slag. A Digital Image Processing (DIP) based method was used to measure aggregate shape properties. Three different mixes, using three types of coarse aggregate (gravel 12.5 mm, gravel 9.5 mm, and coarse steel slag), and a type of fine aggregate (fine slag) were tested, and flexural strength, flow, and permeability coefficients were obtained for the slabs. Results showed the potential of using steel slag, with higher flexural strength results (4.61 MPa). Indications of the relationship between aggregate shape parameters and slab properties were determined, with more polished, more angular, and more spherical material resulting in higher flexural strength values and lower permeability coefficient. The inverse relationship between the slabs’ permeability parameters and flexural strength was observed.

Flexural Strength of Glass Fiber Post Following Conditioning with Various Chemical Solutions Running Title: Flexural Strength of Fiber Post with Different Chemical Treatments

The aim of this study was to assess various chemical solutions on the surfaces of glass fiber post could affect its flexural strength. A total of 80 Glass Fiber posts were divided into eight groups (n=10) based on surface treatment, untreated surface (control), 10% hydrofluoric acid (HF) for 1 minutes, 10% HF for 2 min, 24% hydrogen peroxide (H2O2) for 4 min, 24% H2O2 for 10 min, 35% H2O2 for 4 min, 35% H2O2 for 10 min, and chloroform solution for 1 hour. Fiber posts were immersed in the solutions for the required amount of time and then rinsed and dried. Fiber posts were loaded in three-point bending test using a mechanical testing machine, data recorded and Flexural strength (σ) was measured. Statistical analysis revealed that the highest value of flexural strength was shown in the group treated with 24% H2O2for 4minfollowed by Chloroform group, so they have no significant effect on flexural strength. While the least value was shown in group treated with10% HF for 2min.Treatment with HF significantly decrease flexural strength for both application times. Treatment with H2O2 showed significant decrease only in group treated with 35% H2O2 for 10 min. It was concluded that strong acid etching of HF and long application time of higher concentration of H2O2 had adverse effect on fiber post flexural strength.

Comparative evaluation of flexural strength of heat polymerized acrylic resin denture base material repaired with auto- polymerized acrylic resin using surface treated reinforcement materials – An in vitro study

: The purpose of this vitro study was to comparatively evaluate the flexural strength of repaired denture base resin using different surface treated reinforcement materials.According to ADA specification No. 12, typical heat polymerized acrylic resin specimens were created, and various repairs were made to them. Autopolymerizing resin was used for repair. The flexural strength was evaluated using the INSTRON universal testing equipment on a total of 90 samples (with 15 samples in each group). In this study the highest value of flexural strength was obtained for group in which the reinforcement was done with surface treated half round wires that were sandblasted, etched followed by application of alloy primer.: Specimens repaired with reinforcement increases flexural strength. Reinforcement with silanized woven roving e glass fibers showed significant increase in flexural strength compared to unreinforced specimens. There was no statistical difference between the samples repaired with sandblasted wires and etched wires group.

The effect of different concentration of emodin nanoparticles, as an antibacterial agent, on the flexural resistance of acrylic resin used in orthodontics: An in vitro study

The aim of this study was to investigate the impact of emodin nanoparticles (n-Emo) on the flexural strength of acrylic resin used in orthodontics. A total of 24 acrylic resin discs were prepared according to ISO:20795-1 and divided into four groups (n=6): 0% n-Emo, 0.5% n-Emo, 1% n-Emo, and 2% n-Emo. The flexural strength of each group was measured using the Universal Testing Machine. One-way analysis of variance (ANOVA) and Tukey tests were used to analyse the data. The highest flexural strength values were observed in the groups containing 0% and 0.5% concentrations of n-Emo, while the lowest mean flexural strength was recorded in the group containing 2% concentration of n-Emo. There were significant difference in flexural strength values between the groups containing 0% with those containing 1% and 2% concentrations (P=0.045, P=0.011, respectively), as well as between those containing 0.5% and 2% concentrations of n-Emo (P=0.041). The results of the study showed that the incorporation of n-Emo had a negative impact on the flexural strength of the acrylic resin utilized in orthodontics. Nonetheless, the mean flexural strength values of all groups fell within the normal range, implying that the addition of n-Emo did not jeopardize the mechanical properties of the acrylic resin. It is therefore conceivable that the use of n-Emo as an antimicrobial agent in acrylic resin could be a promising approach to reducing enamel demineralisation and dental caries, while preserving its mechanical properties. This study was approved by the ethics committee of the Tehran University of Medical Sciences (1401-2-398-54892).

Performance Of Pervious Concrete as A Replacement for Road Curb

Pervious concrete is a well-known type of concrete characterized by its high porosity and permeability. It finds extensive use in road infrastructure, particularly in pavement construction, and offers cost-saving benefits due to the absence of fine aggregates in its mixture. While road curbs are still commonly built today, the utilization of pervious concrete as a substitute for curbs is rarely observed. Therefore, this study focuses on evaluating the compressive strength, flexural strength, and suitability of pervious concrete as a curb replacement. In this investigation, different water cement ratios (0.30, 0.33, 0.35, 0.38, and 0.40) were employed during the mixing of pervious concrete to determine the most optimal ratio and achieve the highest compressive and flexural strength for the road curb. To obtain the results, compressive and flexural tests were conducted on ten curb samples after a curing period of 28 days. The study aimed to examine the diverse effects of the various water cement ratios. The findings indicate a decrease in compressive stress as the water cement ratio increased. Furthermore, the compressive strength of the concrete mix was significantly stronger at a water cement ratio of 0.30 but exhibited a decline with higher ratios. Similar results were obtained in the flexural test, where a water cement ratio of 0.30 recorded the highest value of flexural strength. However, a water cement ratio of 0.40 yielded the second-highest flexural strength. These results emphasize that a lower water cement ratio leads to higher concrete strength. To further enhance the strength of the concrete, several recommendations are proposed, including the use of coating reinforcement bars, adjustment of coarse aggregate size, and the addition of admixtures to the pervious concrete mixture.

Effect of Fibres on Physico-Mechanical Properties of Bulk-Fill Resin Composites.

To measure the flexural strength (FS) of bulk-fill resin composites and assess their long-term water absorption and solubility properties with and without the inclusion of short glass fibres. One resin composite, everX Flow with fibres, and four commercially available bulk-fill composites without fibres, namely, PALFIQUE, Activa, SDR Plus, and Filtek Bulk Fill One, were tested. Six specimens (2 × 2 × 25 mm) were fabricated for each material and stored in water for 1 day and 30 days to measure the flexural strength using a three-point bending test. To evaluate water absorption and solubility, circular disks measuring 15 × 2 mm (n = 5) were immersed in water for 60 days, and their weights were recorded periodically. After 60 days, the specimens were dried for an additional 21 days to determine solubility. Flexural strength values ranged from 101.7 to 149.1 MPa. Significant distinctions were observed among the resin composites at the onset of the study (p < 0.05). The highest FS value was identified in everX Flow, while ACT exhibited the lowest (p < 0.05). However, the flexural strength values exhibited a significant decrease with increased storage time (p < 0.05), except for ACT, which demonstrated a noteworthy increase. Concerning water absorption and solubility, ACT displayed the highest absorption, while the range of solubility varied from -0.88 to 5.8 μg/mm3. ACT also had the highest solubility, whereas everX Flow exhibited negative solubility. The addition of short fibres, along with potential differences in matrix composition, enhanced the flexural strength of everX Flow. However, the substantial reduction in flexural strength observed in everX Flow and SDR following exposure to water corroborates the manufacturers' recommendation to apply a conventional resin composite cap on these materials.

Development, characterization and antimicrobial activity of multilayer silica nanoparticles with chlorhexidine incorporated into dental composites.

In this study a dentistry nanocomposite with prolonged antibacterial activity using silica nanoparticles (SNPs) loaded with chlorhexidine (CHX) was developed. SNPs were coated with the Layer-by-Layer technique. Dental composites were prepared with organic matrix of BisGMA/TEGDMA and SNPs with or without CHX (0, 10, 20 or 30% w/w). The physicochemical properties of the developed material were evaluated and agar diffusion method was used to test the antibacterial. In addition, the biofilm inhibitory activity of the composites was evaluated against S. mutans. SNPs were rounded with diameters about 50nm, the organic load increased with increasing deposited layers. Material samples with SNPs loaded with CHX (CHX-SNPs) showed the highest values of post-gel volumetric shrinkage, that ranged from 0.3% to 0.81%. Samples containing CHX-SNPs 30% w/w showed the highest values of flexural strength and modulus of elasticity. Only samples containing SNPs-CHX showed growth inhibition against S. mutans, S. mitis and S. gordonii in a concentration-dependent manner. The composites with CHX-SNPs reduced the biofilm formation of S. mutans biofilm at 24h and 72h. The nanoparticle studied acted as fillers and did not interfere with the evaluated physicochemical properties while providing antimicrobial activity against streptococci. Therefore, this initial study is a step forward to the synthesis of experimental composites with improved performance using CHX-SNPs.

Experimental study on flexural strength of stitched foam composites

Sandwich composites and laminate composites are considered as major classes of lightweight structures in a wide range of engineering applications. Lightweight potential of fabric has demonstrated the specific mechanical properties of sandwich composites with or without core material. Many studies have shown that tension, compression, flexure, stress is improved or degraded up to 20% by a stitched process. The present paper focuses on the study of structural improvements of stitched foam composite and also to compare it with unstitched composite of the same glass fiber material. The use of vacuum bagging process to make the stitched foam composite structure and a simple hand lay-up technique for unstitched composite. These composites are made by using E Glass fiber 180GSM, aradur hy 951 hardener, Araldite ly 556 epoxy resin and glass fiber yarn. For stitched foam composite, laminates are stitched in transverse direction i.e., through thickness direction with high strength yarn. 3-point bending test is done to find flexural strength of both composites and compare their results stitched sample showed higher value of flexural strength and flexural rigidity after three-point bending test the strength of stitched composite is 40% more than unstitched composite material.

Evaluation of a biobased polycarbonate interpenetrated network in a dental resin composite

Silanization of filler particles in a dental resin composite is achieved by the formation of Si-O-Si bonds, however, these bonds are especially vulnerable to hydrolysis because this covalent bond has a significant ionic character due to the electronegativity differences between the atoms. The objective of this study was to evaluate the use of an interpenetrated network (IPN) as alternative of silanization reaction and to assess its effect in selected properties of experimental photopolymerizable resin composites. The interpenetrate network was obtained during the photopolymerization reaction of organic matrix (BisGMA/TEGDMA) with a biobased polycarbonate. Its characterization was performed via FTIR, flexural strength, flexural modulus, depth of cure, sorption water and solubility. A resin composite formulated with non-silanized filler particles was used as control. The IPN with a biobased polycarbonate was successfully synthesized. The results showed that the IPN based resin composite had higher values of flexural strength, flexural modulus, and degree of double bond conversion than the control (p < 0.05). Polymerization shrinkage, water sorption and solubility were statistically significantly lower than the control resin (p < 0.05). Finally, this study shows there were no statistically significant differences for the biocompatibility outcomes (p > 0.05). The biobased IPN replaces the silanization reaction in resin composites, improving physical and chemical properties. Therefore, IPN with a biobased polycarbonate could be potentially useful in the formulation of dental resin composites.

THE FLEXURAL STRENGTH OF BASALT CONCRETE MIX COMPARED WITH GRANITE CONCRETE MIX

This work aims at comparing the flexural strength of basalt concrete mix with granite concrete mix. A total of 24 concrete beam specimen of breadth 100mm, depth 100mm and length 500mm were made in the laboratory. The British standard mix design method was used to obtain four different mix designs for batching the ingredients comprising ordinary Portland cement, river sand, water, granite and basalt with two mix designs each corresponding to basalt and granite samples. The specimens were cured for 28 days and tested for flexural strength. The results show higher values of flexural strength for basalt mix compared to granite samples by five percent. The results show that basalt aggregates are suitable coarse aggregates for concrete mix.

Hyperbaric Pressure Effect on Dental Luting Cements

Background and Purpose: The aim of this study was to evaluate the flexural strength values of five luting cements that are commonly used in dental restorations after exposed to hyperbaric pressure.&#x0D; Methods: Five luting cements (polycarboxylate cement, glass ionomer luting cement, manual-mixed resin cement, and two auto-mixed resin cement) were prepared. (25 x 2 x 2 mm3) (n=16 for each) The specimens were divided into two subgroups (n=8) and were exposed to hyperbaric pressure (3 ATM) 20 times for 30 minutes. The control groups stored in ambient pressure. Universal testing machine was used for flexural strength measurement with a crosshead speed of 1 mm/min. &#x0D; Results: One-way ANOVA test was used for statistical analysis, the differences in flexural strength values were additionally evaluated by Weibull Analysis. Glass ionomer and polycarboxylate cement were the most effected resins from hyperbaric pressure changes. Regardless of the pressure changes, the highest flexural strength values were seen for the self-adhesive resin cements and polycarboxylate cement showed the lowest strength value.&#x0D; Conclusion: Resin cements can be used for cementation of the dental restorations in divers and individuals who are subjected to hyperbaric pressure.

Simultaneous promotion of mechanical and electrical properties of hot-pressing halloysite-based mullite ceramics through carbon incorporation

Halloysite (HAL) based mullite/carbon composites were fabricated by hot-pressing, using cheap HAL clay and chitosan as starting materials. The effects of sintering temperatures and carbon on the phase evolution, microstructure, bulk density, flexural strength and fracture toughness of composites were investigated. With increasing of temperature, the loading carbon on the surface of HAL further pyrolyzed and graphitized. The incorporation of carbon into matrix promoted the formation of silica-rich liquid phase and the process of mullitization due to the excellent thermal conductivity of carbon. The morphology of mullite crystal changed from sparse needle-like structure to interlocking columnar structure after the incorporation of carbon. The mechanical properties and electrical conductivity were greatly improved. The highest values of flexural strength and fracture toughness of mullite/carbon were 162.0 MPa and 3.1 MPa·m1/2, respectively. The best electrical conductivity reached 12.25 S/m in the case of mullite/carbon obtained at 1300°C.

Can postpolymerization for 3D-printed interim restorations be improved?

Statement of problemPostpolymerization methods influence the properties of 3-dimensionally (3D) printed materials. Nevertheless, it is a time-consuming step that could lead dentists to avoid the chairside use of 3D printing. Information assessing the impact of different postpolymerization workflows on flexural strength and color stability is sparse. PurposeThe purpose of this in vitro study was to analyze the impact of different postpolymerization methods on the flexural strength and color stability of 3D-printed resins used for interim restorations. Material and methodsThree resin materials: CT (Cosmos Temp; Yller Biomaterials), DT (Denture Teeth; Formlabs), and CB (C&B MFH; NextDent) were submitted to 4 methods of postpolymerization: a Form Cure polymerization chamber (FC) (Form Cure; Formlabs), a broadband LED device (Valo Grand; Ultradent Products, Inc) operating at 1000 mW/cm2 for 2 different polymerization times (40 seconds/V40 or 120 seconds/V120), and a custom-made polymerization chamber with a 24 W UV LED Strip (CC). The specimens were assessed for flexural strength using an universal testing machine immediately after polymerization or after 10 000 thermal cycles, and the color stability was evaluated using a spectrophotometer at baseline, after 7 days in dark, dry storage at 37 °C and after 24 hours of artificial aging in water at 60 °C. The data were evaluated using 3-way ANOVA (flexural strength) and 3-way repeated measurements ANOVA (color stability), followed by the Tukey HSD test (α=.05). ResultsFlexural strength showed significant differences for resin, postpolymerization method, time, and for the interaction between all effects. CT showed the highest overall flexural strength, while DT showed the lowest. In general, V120 produced specimens with higher flexural strength. Thermocycling did not reduce flexural strength except for CB polymerized with FC and V120, and DT polymerized with V40. For color stability, significant differences were found for resin, postpolymerized method, time, and for the interaction between all effects. The highest ΔE values were observed for DT polymerized using V40 after artificial aging. The lowest values were observed for the same resin but polymerized using V120 after 7 days in dark, dry storage at 37 °C. ConclusionsPostpolymerization with the broadband LED device for 120 seconds can produce specimens with higher flexural strength values and higher color stability when compared with the other postpolymerization workflows tested in this study.

Mechanical characterization of a multi-layered zirconia: Flexural strength, hardness, and fracture toughness of the different layers

This study compared the flexural strength under monotonic (static - sσ) and cyclic load application (fatigue - fσ), hardness (H) and fracture toughness (KIC) of different layers of a multi-layered zirconia (IPS e.max ZirCAD MT Multi, Ivoclar). Each layer was sectioned, classified into three groups according to yttria content (4-YSZ, 4/5-YSZ and 5-YSZ), and shaped on samples for flexural strength and fracture toughness tests (bars: 1.0 × 1.0 × 11 mm); and Vickers hardness test (plates: 1.5 × 4.0 × 5.0 mm). Flexural strength under monotonic load application (sσ; n = 10) was obtained through two different devices (three-point-bending and ball-in-hole device) and fatigue flexural strength (fσ; n = 15; initial load: 10 N; step-size: 5 N; 10,000 cycles/step) was assessed using a ball-in-hole device under cyclic load application. Vickers hardness test (n = 5), fracture toughness test (n = 10), and additional analyzes (Finite Element Analysis - FEA, Energy-dispersive X-ray spectroscopy - EDS and Scanning Electron Microscopy - SEM) were also performed. No differences were found between the different devices in the monotonic flexural strength test, and FEA showed similar tensile stress distribution for the two devices. 4-YSZ showed higher values of flexural strength under monotonic and cyclic load application modes (sσ = 1114.73 MPa; fσ = 798.84 MPa), and fracture toughness (KIC = 3.90 MPa√m). 4/5-YSZ had an intermediate sσ; however, fσ was similar to 5-YSZ (404.00–429.36 MPa) and KIC similar to 4-YSZ (KIC = 3.66 MPa√m). No statistical differences were found for hardness and Weibull modulus for fatigue flexural strength data. The amount of yttria in the layer compositions increased from 4-YSZ to 5-YSZ, and larger zirconia crystals were observed in the topographic images of 5-YSZ. Failures in the flexural strength and toughness tests started from the face subjected to tensile stress. Different layers of the multi-layered zirconia blank presented distinct mechanical properties. 4-YSZ (cervical layer) presented the highest flexural strength under monotonic and cyclic loads (fatigue), and higher fracture toughness even similar to the transition layer (4/5-YSZ). Hardness was similar between the layers. The ball-in-hole device performed similarly to the three-point bending device and can be used as an alternative to the traditional method.

The Effect of Salivary pH on the Flexural Strength and Surface Properties of CAD/CAM Denture Base Materials.

This study aimed to evaluate the influence of different salivary pH on flexural strength, hardness, and surface roughness of computer-aided design and computer-aided manufacturing (CAD/CAM) milled and three-dimensional (3D)-printed denture base resins. One heat-polymerized, two CAD/CAM milled (IvoCad, AvaDent), and two 3D-printed (FormLabs, NextDent) denture base resins were fabricated and divided into five groups (n = 10) according to the solutions: three groups were immersed in different salivary pH (5.7, 7.0, or 8.3), one group was immersed in distilled water (DW) as a positive control, and one group had no immersion (negative control). All immersions were performed at 37°C for 90 days. Flexural strength, hardness, and surface roughness were measured before and after immersion. Data was analyzed with analysis of variance and post hoc Tukey's test (α = 0.05). After immersion, all specimens had lower flexural strength values when compared with those with no immersion. Comparing the immersion groups, the highest flexural strength value (93.96 ± 3.18 MPa) was recorded with IvoCad after immersion in DW while the lowest value (60.43 ± 2.66 MPa) was recorded with NextDent after being immersed in 7.0 pH saliva. All specimens had significant decrease in hardness except IvoCad and AvaDent specimens where both presented the highest surface hardness (53.76 ± 1.60 Vickers hardness number [VHN]) after immersion in DW while NextDent showed the lowest hardness value (24.91 ± 2.13 VHN) after being immersed in 8.3 pH saliva. There was statistically significant difference between the baseline and different artificial salivary pH solutions in terms of surfaces roughness, with the highest surface roughness were found in 3D-printed resin materials. After exposure to artificial saliva with different salivary pH, the milled CAD/CAM denture base resins showed higher flexural strength, hardness, and lesser surface roughness than conventional and 3D-printed denture base resins.