3-point Flexure Research Articles

Evaluation of 3-Point and 4-Point Bending Tests for Tensile Strength Assessment of GFRP Bars.

Glass Fiber Reinforced Polymer (GFRP) bars are used as reinforcement for structural concrete, especially in cases where corrosion of traditional steel reinforcement is a problem. The tensile strength of these reinforcing bars is the primary characteristic on which the design of concrete members reinforced with GFRP bars relies. Determination of the tensile strength of the bars using a direct tensile test is a time and resource-intensive task and therefore is not routinely conducted for quality control. The tensile strength can also be measured from flexure tests, which are much simpler than direct tensile tests, and use appropriate correlation formulations. In this paper, the applicability of flexure testing for the identification of bars' tensile strength is investigated by conducting and analyzing both 3-point and 4-point flexure testing. The correlation formulations are presented that allow the determination of tensile strength from the modulus of rupture. The Weibull weakest link model and the assumption of the same flaw distribution in tensile and flexure tests is adopted. The results of the 3-point and the 4-point bending are presented and compared. Comparisons are also conducted to select direct tensile test results. The work shows that 3-point and 4-point bending tests provide very similar results, with the difference between the results being 2% to 10%, suggesting both tests can be used for tensile strength determination of GFRP bars.

Effect of High Fiber Content on Properties and Performance of CFRTP Composites

Continuously reinforced thermoplastic composites are widely used in structural applications due to their toughness, light weight, and shorter process cycle. Moreover, they provide flexibility in design and material selection. Unlike thermoset composites, continuous fiber content to maximize mechanical properties in thermoplastic composites has not been well investigated. In this paper, three thermoplastic systems are investigated to study the optimum content of continuous fiber reinforcement. These systems include carbon fiber/polyphenylene sulfide (PPS), glass fiber/PPS, and glass fiber/high-density polyethylene (HDPE). Tapes were made at several fiber contents, and samples were compression molded and tested using thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), tensile, 3-point flexure, and short-beam shear tests. Results revealed that higher fiber content led to an increase in the glass transition and melt transition temperatures of the polymer. Some mechanical properties increased with fiber content and then began to decrease upon further addition of fibers, while other properties, such as ductility and interfacial bond strength, decreased with more reinforcement. Furthermore, the optimum fiber contents to maximize mechanical properties are different for different properties and different materials.

Determination of the KIC Fracture Toughness of the X210Cr12 High-Strength Material

Purpose: It is an important problem that the machines become unusable due to the deformation of the machine elements produced before the planned time. In this study, it was aimed to determine the KIC value of X210Cr12, which is a high strength material. In this way, more accurate load values can be used in the design.Methods: In the experimental study to determine the KIC value, the sample geometry, the crack depth, the load-dependent parameters and calculations and some conformity checks were carried out. Experimental system; KIC consists of 3-point flexure specimens, a press, an electronic circuit capable of detecting the change in load crack opening, and a logger.Findings: In the study, the loads were determined from experimental graphs. Subsequently, load-crack opening values were determined. With these data, the KIC values were calculated as 719,7 and 839,7 MPa.mm1/2 as the minumum and maximum values, respectively.Conclusion: The experimental graphs are in the form of curves that break abruptly with unstable crack propagation without showing plastic deformation. There is no study in the literature on the KIC value of X210Cr12 and it has been determined that it has a low KIC value compared to the high-strength steels studied. It is valuable to determine the KIC value, as fracture problems may occur in designs prepared with the material. The results of the study are data at room temperature.

Mesoscale DVC analyses and parameter calibration for pantographic block in 3-point flexure

In the present work, the mechanical response of a fiber network metamaterial was studied when subjected to 3-point flexure. To account for the initial deformation of the sample due to the fabrication process, backtracking (i.e., the nominal mesh was accurately repositioned in the reference configuration) was implemented in the Digital Volume Correlation (DVC) procedure. Kinematic fields were then measured via DVC at two different scales. Finite element based DVC was validated thanks to a series of initialization steps. The displacement fields were successfully measured and a peculiar deformation mechanism was observed. These measurements were employed to calibrate the constitutive parameters of a second gradient continuum model introduced for modeling this type of metamaterial. Numerical simulations are shown to be in good agreement with experimental measurements at the macroscopic scale.

Changes in fracture energy at FRP-concrete interfaces following indoor and outdoor exposure with sustained loading

Small-scale plain concrete precracked beams strengthened with carbon and glass fiber reinforced polymer (FRP) sheets were tested in 3-point flexure to evaluate changes in the FRP-concrete Mode II interfacial fracture energy following sustained loading for 6 and 13 years in indoor and outdoor environments. Mode II fracture energy of the interfacial region, GF, was calculated using strain profiles along the length of the FRP sheet, which were measured using digital image correlation and photoelastic techniques. In the post-conditioned experiments, larger GF values were measured as the debonded zone progressed from the sustained shear stress transfer region to the unstressed portion of the interfacial region far from the notch, particularly in beams with outdoor conditioning. In the interfacial region near the notch, the carbon FRP beams showed no reduction in GF in the indoor environment but reduction in the outdoor environment, while glass FRP showed reductions in both environments. In outdoor beams with glass FRP sheets, GF was not additionally degraded when the FRP was exposed to direct sunlight, in comparison to beams with the FRP exposed to indirect sunlight.

Deformation mode in 3-point flexure on pantographic block

Pantographic blocks are metamaterials made of a finite number of parallel pantographic sheets interconnected by cylindrical pivots. In this paper, a pantographic block subjected to 3-point flexure, where the prescribed displacements are parallel to the pantographic plane, shows essentially monoclastic deformation (i.e., one of the principal curvatures of the top surface is found to be negligible wrt. the other one). Pantographic blocks are modeled herein with a second gradient 3-dimensional continuum model that is valid at the length scale of pantographic cells. This reduced order model allows for predictive numerical simulations whose computational burden is relatively small. Second gradient effects (i.e., higher-order terms contributing to the strain energy) are limited to the second derivatives along the fibers of their transverse displacements. Digital Volume Correlation (DVC) techniques are employed to measure deformed shapes of pantographic blocks. A model-driven initialization procedure of DVC is followed to quantify the shape of such pantographic blocks in large displacements and strains.

Relationship between fracture toughness and fractal dimensional increment in two types of dental glass-ceramics with different fracture surface roughness.

Previous studies have reported the fractal dimensional increment of glass-ceramic fracture surfaces. The objective of this study was to determine the relationship between fracture toughness and fractal dimensional increment of two dental glass-ceramics with different volume fraction of crystals and different fracture surface roughness. Bar-shaped specimens were prepared from lithium disilicate (LDS) and nanofluorapatite (NFA) glass-ceramics. One face of each specimen was indented using a Knoop diamond at 25N (LDS) or 10N (NFA) followed by loading in 4-point, or 3-point flexure, respectively, until failure. Fracture toughness (Kc) was calculated using the surface crack in flexure (SCF) technique (ASTM C1421). Epoxy replicas of the fracture surfaces were scanned using the atomic force microscope (AFM) followed by noise filtering. The FRACTALS software was used to determine the fractal dimensional increment (D*) by the Minkowski cover algorithm. Median (25%, 75% quartiles) fracture toughness of LDS bars were 1.62 (1.59, 1.69)MPam1/2 and NFA bars were 0.68 (0.66, 0.74)MPam1/2, respectively. The median fractal dimension (D) value (25%, 75% quartiles) before noise filtering were 2.16 (2.15, 2.17) and after noise filtering were 2.14 (2.14, 2.15) for LDS and before noise filtering were 2.29 (2.21, 2.38) and after noise filtering were 2.17 (2.17, 2.18) for NFA. Median (25%, 75% quartiles) surface roughness (Ra) before noise filtering were 139 (119, 188)nm and after noise filtering were 137 (118, 187)nm for LDS and before noise filtering were 7 (6, 15)nm and after noise filtering were 7 (6, 15)nm for NFA. Noise filtering successfully eliminated noise from the material with smooth fracture surfaces (NFA), decreasing the measured fractal dimension. The NFA data fit a Kc vs. D*1/2 statistical model for fused silica previously tested using a similar technique. The equation relating fracture toughness to the fractal dimension was modified, accounting for the toughening mechanisms. Fractal analysis with noise filtering can be used to estimate the fracture toughness of dental glass-ceramics that do not exhibit crack bridging.

Effect of erosive media on microhardness and fracture toughness of CAD-CAM dental materials

BackgroundErosive acids might create surface flaws and deteriorate the mechanical properties of CAD-CAM materials. This invitro study aimed to investigate the effect of simulated gastric HCl and extrinsic erosive acids on surface microhardness and fracture toughness of CAD-CAM materials.Methods400 bar-shaped specimens (17×4×2 mm3) were prepared from 4 different CAD-CAM dental materials (n = 100/group); monolithic zirconia (Ceramill Zolid HT+, Amanngirbach, Austria), lithium disilicate ceramic (IPS e.max CAD, Ivoclar Vivadent, Liechtenstein), nanohybrid resin composite (Grandio Blocs, VOCO) and polymer-infiltrated glass network (Vita Enamic, VITA Zahnfabrik). Specimens from each material type were further subdivided into 5 groups (n = 20) according to the erosive media applied (simulated gastric HCl, white wine, Coca-Cola®, orange juice, and artificial saliva that served as a control). Specimens were immersed for 24 h in an incubator at 37 ℃, then ultrasonically cleaned in distilled water and air-dried. Half of the specimens were tested for Vickers microhardness (VHN) at parameters of 500 gf for 10 s, while the rest of the specimens underwent 3-point flexure till fracture. Fractured surfaces were examined under a scanning electron microscope (SEM) for fracture toughness (KIC) calculation using the quantitative fractographic analysis method. Data collected were statistically analyzed using two-way analysis of variance (α = 0.05) after verification of data normality and homogeneity of variances.ResultsErosive media created surface flaws that lowered the surface microhardness of the material and initiated the fracture pattern under different loads according to material type. The material type was a more predominant factor than erosive media that affected either the microhardness or the fracture toughness of CAD-CAM dental materials. The highest VHN and KIC values were found among Ceramill Zolid HT+ groups followed by IPS e.max CAD and Grandio Blocs regardless of the erosive media employed. Erosive media significantly reduced the VHN and KIC in Vita Enamic specimens compared to the rest of the material types.ConclusionAll CAD-CAM materials used, except Vita Enamic, showed high resistance against the erosive acids indicating higher longevity of the material in patients frequently exposed to either extrinsic or intrinsic acid.

M1 - Fracture Toughness and Fractal Dimension of Two Dental Glass-Ceramics

Studies have reported the fractal dimensional increment of glass and glass-ceramic fracture surfaces. The objective of this study was to determine the relationship between fracture toughness and fractal dimensional increment of two types of dental glass-ceramics with different volume fraction of crystals and different fracture surface roughness. Fifteen bar-shaped specimens were prepared from lithium disilicate (LDS) by sectioning the blocks (IPS e.max CAD, Ivoclar Vivadent). Ten beams were prepared by mixing and layering the nanofluorapatite (NFA) glass-ceramic powder (IPS e.max Ceram, Ivoclar Vivadent). One face of each of the specimens was indented using a Knoop diamond at 25 N (LDS) or 10 N (NFA) followed by loading in deionized water in 4-point, or 3-point flexure, respectively, until failure. Fracture surfaces were analyzed using scanning electron microscope (SEM). Fracture toughness (Kc) was calculated using the surface crack in flexure (SCF) technique (ASTM C1421). Epoxy replicas of the fracture surfaces were scanned using the atomic force microscope (AFM) followed by noise filtering. The FRACTALS software was used to determine the fractal dimensional increment (D*) by the Minkowski cover algorithm. In addition, surface roughness was computed from the AFM scans using the Gwyddion software. The median (25%, 75% quartiles) fracture toughness of LDS and NFA bars were 1.62 (1.59, 1.69) MPam1/2 and 0.68 (0.66, 0.74) MPam1/2, respectively. The median fractal dimension (D) value (25%, 75% quartiles) before and after noise filtering for LDS were 2.16 (2.15, 2.17) and 2.14 (2.14, 2.15), respectively, and for NFA were 2.29 (2.21, 2.38) and 2.17 (2.17, 2.18), respectively. The NFA follows the regression model (Y=1.99 X) between Kc and sqrt. D* for glasses as previous studies, but the LDS deviated from the model. The median (25%, 75% quartiles) surface roughness before and after noise filtering for LDS were 139 (119, 188) nm and 137 (118, 187) nm and for NFA were 7 (6, 15) nm and 7 (6, 15) nm, respectively. Noise filtering successfully eliminated noise from the AFM scans of the material with smooth fracture surfaces (NFA), resulting in a decrease in measured fractal dimension. The LDS data deviated from the model because of toughening due to crack bridging. Fractal analysis with noise filtering can be used to estimate the fracture toughness of dental glass-ceramics that do not exhibit crack bridging.

Mode II fracture behavior of parallel strand bamboo measured by 3-point end-notched flexure tests

Parallel strand bamboo (PSB) is a new type of bio-composite. In the present study, three-point bend end-notched flexure (3ENF) tests of PSB were conducted to analyze the fracture behavior including fracture process, resistant curves, and critical energy release rate in the longitudinal (L) system. The results show that transverse-longitudinal (TL) and thickness-longitudinal (ZL) specimens had the same fracture process including the stages of fracture process zone (FPZ) development and opening crack propagation but different mode II critical energy release rate (GIIc), and they indicate that the fiber bridging had a significant influence. The fracture processes suggest the PSB specimens of which the initial crack length was 0.5 times the half span had a stable crack propagating process, and the crack propagation length was wide enough to evaluate GIIc, which was 5.02 N∙mm-1 of TL specimens and 2.71 N∙mm-1 of ZL specimens. Besides, there was no obvious influence of span/depth ratio on the fracture resistance of both ZL and TL specimens when the ratio was larger than 15.

Electron Beam Cold Hearth Melted Titanium Alloys and the Possibility of Their Use as Anti-Ballistic Materials

Three commercial titanium alloys: two-phase α+β Ti-6Al-4V (low alloyed), and T110 (Ti-5.5Al-1.5V-1.5Mo-4Nb-0.5Fe, higher-alloyed), and β-metastable Ti-1.5Al-6.8Mo-4.5Fe were melted using EBCHM approach in the form of 100 mm in diameter ingots with the weight of about 20 kg each. After 3D hot pressing at single β-field temperatures ingots were rolled at temperatures below β-transus onto plates with thickness varying from 3 mm to 25 mm. Different heat treatments, including annealing at α+β or β-field temperatures, and special strengthening Surface Rapid Heat Treatment (SRHT) which after final aging provided special gradient microstructure with a hardened surface layer over ductile basic core, were employed. Mechanical properties were studied with tensile and 3-point flexure tests. It was established that the best combination of tensile strength and ductility in all alloys studied was obtained after SRHT, whereas at 3-point flexure better characteristics were obtained for the materials annealed at temperatures of (α+β)-field. At the same time, ballistic tests made at a certified laboratory with different kinds of ammunition showed essential superiority of plates having upper layers strengthened with SRHT. The effect of microstructure of the alloys, plate thickness and type of used ammunition on ballistic resistance is discussed.

Glycolic acid: Characterization of a new final irrigant and effects on flexural strength and structural integrity of dentin

The aim of this study was to characterize glycolic acid (GA) and examine its effects on powder and flexural strength of dentin. Particle size and energy-dispersive EDS in GA powder was performed for chemical analysis. Surface tension and pH levels of ethylenediaminetetraacetic acid (EDTA), citric acid (CA), and GA solutions were evaluated at different times and temperatures. Dentin powder and mineralized dentin beams were immersed for 1 min in EDTA, CA, or GA solutions and subjected to Fourier transform infrared spectroscopy for apatite/collagen ratio analysis and 3-point flexure test, respectively. GA showed the largest particle size (μm), and its surface tension was similar to that of EDTA and CA. Surface tension decreased in solutions of higher concentrations. GA showed pH stability at all times and temperatures evaluated. The apatite/collagen ratio reduced with increased GA concentrations, while flexural strength was not significantly affected by GA concentration. GA seems a good choice as a final irrigation solution after root canal preparation.

Are critical size bone notch defects possible in the rabbit mandible?

ObjectivesSmall animal maxillofacial models, such as non-segmental critical size defects (CSDs) in the rabbit mandible, need to be standardized for use as preclinical models of bone regeneration to mimic clinical conditions such as maxillofacial trauma. The objective of this study is the establishment of a mechanically competent CSD model in the rabbit mandible to allow standardized evaluation of bone regeneration therapies.Materials and MethodsThree sizes of bony defect were generated in the mandibular body of rabbit hemi-mandibles: 12 mm×5 mm, 12 mm×8 mm, and 15 mm×10 mm. The hemi-mandibles were tested to failure in 3-point flexure. The 12 mm×5 mm defect was then chosen for the defect size created in the mandibles of 26 rabbits with or without cautery of the defect margins and bone regeneration was assessed after 6 and 12 weeks. Regenerated bone density and volume were evaluated using radiography, micro-computed tomography, and histology.ResultsFlexural strength of the 12 mm×5 mm defect was similar to its contralateral; whereas the 12 mm×8 mm and 15 mm×10 mm groups carried significantly less load than their respective contralaterals (P<0.05). This demonstrated that the 12 mm×5 mm defect did not significantly compromise mandibular mechanical integrity. Significantly less (P<0.05) bone was regenerated at 6 weeks in cauterized defect margins compared to controls without cautery. After 12 weeks, the bone volume of the group with cautery increased to that of the control without cautery after 6 weeks.ConclusionAn empty defect size of 12 mm×5 mm in the rabbit mandibular model maintains sufficient mechanical stability to not require additional stabilization. However, this defect size allows for bone regeneration across the defect. Cautery of the defect only delays regeneration by 6 weeks suggesting that the performance of bone graft materials in mandibular defects of this size should be considered with caution.

Mechanical Behavior of Titanium Alloys under Different Conditions of Loading

Taking three titanium commercial alloys: commercial purity titanium (c.p.Ti, single-phase α), Ti64 (Ti-6(wt.%)Al-4V, two-phase α+β) and TIMETAL-LCB (Ti-1.5Al-4.5Fe-6.8Mo, both two-phase α+β and single-phase β) as program materials, the influence of phase composition, microstructure and deformation rate (VD, varied from 10-4 to 101 s-1), and deformation mode (compression and 3-point flexure) on the mechanical behavior was studied and compared with data earlier obtained during tensile tests. The size of the matrix phase (alpha- or beta-grains) size and morphology of α+β intragranular mixture were varied using different treatments. Deformation Energy (UD) was used for analysis of the mechanical behavior of the materials tested. It was found that the UD dependencies on deformation rate are different for different methods of loading and are determined by a combination of the phase composition, dispersion, and morphology of the phase constituents. More ductile and less dependent on VD behavior showed c.p.Ti and Ti64 with globular microstructure on all three testing modes, while other materials had some negative features depending on the certain test conditions. Details of mechanical behavior, peculiarities of pores and cracks nucleation causing in final fracture are discussed basing on the results of detailed microstructure study of tested specimens.

Characterization of hybrid light-cured resin composites reinforced by microspherical silanized DCPA/nanorod HA via thermal fatigue

The mechanical and self-mineralized properties of nanohybrid composite resins used for the dental restoration of class V caries are investigated. The nanorod hydroxyapatite (Nr-HA) hybrid and the microspherical granular dicalcium phosphate anhydrate (DCPA) after silanization were mixed and used as fillers in different kinds of composite resins (abbreviated as DCPA, DCPA+5Nr-HA, and DCPA+10Nr-HA). Their composite strengths were measured via 3-point flexure. Their properties were characterized from environmental samples after water immersion for 24 h and exposure to thermal fatigue between 5 and 55 °C for 600 and 2400 cycles. The resin reinforced with high amounts of Nr-HA (DCPA+10Nr-HA) showed a significant increase in mineralization of the sample surfaces, which consequently enhanced microhardness. The presence of Nr-HA also increased the residual energy of samples during preparation and enhanced their capacity to reprecipitate after immersion and through thermal fatigue. However, the presence of Nr-HA also resulted in high ductility and early failure of the sample, especially in the reinforced group with the highest amount of Nr-HA (DCPA+10Nr-HA). The appropriate additive Nr-HA (DCPA+5Nr-HA) balanced the properties with less difference of strength and residual energy compared with the DCPA group. The additive showed superior capability in enhancing the release of ions and initiating mineralization after immersion with thermal fatigue in vitro. This newly developed composite resin may provide an excellent combination of stress bearing, improved residual energy before the sample fracture, enhanced mineralization capacity, and improved caries-inhibiting capabilities.

Biomechanical Comparison of Inflatable Penile Implants: A Cadaveric Pilot Study

BackgroundThroughout the last decade there has been a growing interest in the biomechanical differences between inflatable penile prostheses (IPPs) and their significance with regard to the patient experience. AimTo present our findings assessing the biomechanical properties of IPPs with and without rear tip extenders (RTEs). MethodsThis is a biomechanical study of the 3 most commonly used IPPs (AMS CX, AMS LGX, and Coloplast Titan) as assessed by column compression, modified cantilever deflection, and 3-point bending methods. The IPPs were surgically placed into 3 fresh cadavers via an infrapubic technique by a single large-volume implanter. A biomechanical evaluation of the properties of each IPP inside the fibroelastic tunica albuginea was assessed in blinded testing, and analyses were based on industry standard methods for assessment. OutcomesMaximum axial load; kink formation; horizontal stiffness; and resistance to 3-point flexure testing were measured. ResultsAt maximum inflation, all 3 implants had similar performance. Differences appear to be most affected by fill pressures. In fact, only the AMS LGX at less than maximum inflation (LTMI) was unable to consistently withstand the roughly 0.9 kg (2 lbs) of pressure for column load testing mimicking vaginal intromission. The Coloplast Titan showed slightly better rigidity than the AMS LGX and CX devices in horizontal load testing, and, with 3-point flexure testing, the CX showed the best rigidity in the shortest phallus (A). Overall, the Titan showed slightly better rigidity in the longest phallus (C) and the phallus with mild Peyronie's disease (B). Clinical TranslationsPenile implants with circumferential expansion had higher rigidity on biomechanical testing and should be considered in a patient's decision during selection of a penile implant. Strengths and LimitationsStrengths include blinding of the biomechanical testing and analyses, surgical procedures performed by a highly experienced surgeon, and that this is the “closest to” in vivo evaluation (inside the tunica albuginea) of penile implant function and properties to date. Weaknesses are that this study was performed in cadavers and not in live patients. It also has a small sample size, including the use of only 3 cadavers, and there was no correlation of performance to patient satisfaction. ConclusionThe results of this study support the conclusion that all devices are capable of functionally restoring erectile capacity. However, we observed that, in general, the 2 circumferentially expanding penile prosthesis showed greater resistance in biomechanical testing when compared with longitudinal and circumferential expanding devices. This should be considered as a guide during device selection for a patient undergoing penile prosthesis.Wallen JJ, Barrera EV, Ge L, et al. Biomechanical Comparison of Inflatable Penile Implants: A Cadaveric Pilot Study. J Sex Med 2018;15:1034–1040.

Preparation and characterization of open-cell epoxy foams modified with carbon fibers and aluminum powder

Epoxy foams were prepared by the sacrificial template method. The porous template was prepared from carbamide granules and then impregnated with epoxy resin. The method ensured foams with low relative density of 0.334–0.358 and an open-cell structure consisting of regular spherical cells and round interconnecting windows. Epoxy resin was modified with short carbon fibers and aluminum powder. Both fillers ensured the increase in compressive strength by 12–15% as compared to the neat epoxy foam. The carbon fiber filler ensured much higher specific strength (up to 18.5–18.6 MPa·cm3·g−1) due to little effect on the foam density. Sandwich composite samples were prepared using CPRF facing and the epoxy foam core, and promising mechanical properties of the sandwiches were stated by the 3-point midspan flexure test.

Study on reinforced concrete beams with helical transverse reinforcement

In a Reinforced Concrete (R.C) structure, major reinforcement is used for taking up tensile stresses acting on the structure due to applied loading. The present paper reports the behavior of reinforced concrete beams with helical reinforcement (transverse reinforcement) subjected to monotonous loading by 3-point flexure test. The results were compared with identically similar reinforced concrete beams with rectangular stirrups. During the test crack evolution, load carrying capacity and deflection of the beams were monitored, analyzed and compared. Test results indicate that the use of helical reinforcement provides enhanced load carrying capacity and a lower deflection proving to be more ductile, clearly indicating the advantage in carrying horizontal loads. An analysis was also carried out using ANSYS software in order to compare the test results of both the beams.

THE EFFECT OF SHORT TERM WATER STORAGE ON FRACTURE TOUGHNESS AND MICRO HARDNESS OF A LOW-SHRINKAGE SILORANE AND DIMETHACRYLATE BASED NANOHYBRID COMPOSITES

Objectives: The purpose of this study was to assess the effect of water storage on the fracture toughness (K1C), and micro-hardness of a low shrinkage silorane based and a nanohybrid dimethacrylate composite resin materials.Materials and Methods: Two types of composite resins were selected: nano hybrid methacrylate based (Grandio) and microhybrid silorane based (Filtek P90). For fracture toughness test, a total of 40 single edge notched bar-shaped specimens were prepared and stored in distilled water for 24hrs and 6 weeks. The effect of water uptake on fracture toughness following each storage regimen was determined by loading the specimens to failure in a 3-point flexure strength test setup using a universal testing machine. For Vickers hardness test, 40 disc shaped specimens (height 2 mm, diameter 5 mm) were prepared from each composite material and subjected to testing after 24 hours and six weeks of water storage. The fractured surface was examined using scanning electron microscopy (SEM) to determine the failure pattern following both storage periods.Results: Statistical analysis (T=8, p<0.0001) revealed that the 24hrs fracture toughness of Silorane was singnificantly higher (1.65±0.12 MP a.m1/2) than Grandio (1.11±0.12 MP a.m1/2). After six weeks storage in water the two materials showed a significant decrease (T=13.5, P<0.001) in fracture toughness with Silorane still exhibiting a higher fracture toughness (1.22±0.07 MPa.m1/2) compared to Grandio (0.56 ± 0.08 MPa.m1/2). Silorane showed a highly significant difference in VHN (67.18±1.33) compared to Grandio (42.37±0.73) at the 24 hrs period. After 6 weeks storage in water, a significant decrease was observed in VNH of Grandio (30.55±0.71) while Silorane did not show any decrease in VHN (67.44±1.16). SEM imaging findings were consistent with the results Conclusions: Within the limitations of this study, Silorane P90 exhibited higher fracture toughness and microhardness compared to Grandio nanohybrid composite in both storage periods. Although water storage decreased fracture toughness of Silorane it still remained significantly higher than Grandio. VHN of Silorane was not significantly affected by water storage after six weeks, while, Grandio showed a highly significant decrease in VHN following water storage.

Cross-linked dry bonding: A new etch-and-rinse technique

ObjectiveTo determine if acid-etched, cross-linked dentin can be dehydrated without lowering bond strength below that of cross-linked wet-bonded dentin in vitro. MethodsUsing extracted human third molars, control acid-etched dentin was bonded with Single Bond Plus, using either the wet- or dry-bonding technique. Experimental acid-etched dentin was treated with 5mass% grape seed extract (GSE) in different solvents for 1min before undergoing wet vs dry resin-dentin bonding with Single Bond Plus. Completely demineralized dentin beams were treated with 5% GSE for 0, 1 or 10min, before measuring stiffness by 3-point flexure. Other completely demineralized beams were treated similarly and then incubated in buffer for 1 week to measure the collagen solubilization by endogenous dentin proteases. Results24h microtensile bond strengths (μTBS) in wet and dry controls were 53.5±3.6 and 9.4±1.8MPa, respectively (p<0.05). 5% GSE in water gave μTBS of 53.7±3.4 and 39.1±9.7MPa (p<0.05), respectively, while 5% GSE in ethanol gave μTBS of 51.2±2.3 and 35.3±2.0MPa (p<0.05). 5% GSE in 5% EtOH/95% water gave wet and dry μTBS of 53.0±2.3 and 55.7±5.1MPa (p>0.05). Cross-linking demineralized dentin with 5% GSE increased stiffness of dentin and decreased collagen degradation (p<0.05). Significance5% GSE pretreatment of acid-etched dentin for 1min permits the dentin to be completely air-dried without lowering bond strength.