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Results for “Shear Strength”

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PubMed2003

Techniques to improve the shear strength of impacted bone graft: the effect of particle size and washing of the graft.

BACKGROUND: When fresh morselized graft is compacted, as in impaction bone-grafting for revision hip surgery, fat and marrow fluid is either exuded or trapped in the voids between particles. We hypothesized that the presence of incompressible fluid damps and resists compressive forces during impaction and prevents the graft particles from moving into a closer formation, thus reducing the graft strength. In addition, viscous fluid such as fat may act as an interparticle lubricant, thus reducing the interlocking of the particles. METHODS: We performed mechanical shear testing in the laboratory with use of fresh-frozen human femoral-head allografts that had been passed through different orthopaedic bone mills to produce graft of differing particle-size distributions (grading). RESULTS: After compaction of fresh graft, fat and marrow fluid continued to escape on application of normal loads. Washed graft, however, had little lubricating fluid and better contact between the particles, increasing the shear resistance. On mechanical testing, washed graft was significantly (p < 0.001) more resistant to shearing forces than fresh graft was. This feature was consistent for different bone mills that produced graft of different particle-size distributions and shear strengths. CONCLUSIONS: Removal of fat and marrow fluid from milled human allograft by washing the graft allows the production of stronger compacted graft that is more resistant to shear, which is the usual mode of failure. Further research into the optimum grading of particle sizes from bone mills is required.

Bone Transplantation↗

PubMed2002

Ideal pure shear strength of aluminum and copper.

Although aluminum has a smaller modulus in [111]<112> shear than that of copper, we find by first-principles calculation that its ideal shear strength is larger because of a more extended deformation range before softening. This fundamental behavior, along with an abnormally high intrinsic stacking fault energy and a different orientation dependence on pressure hardening, are traced to the directional nature of its bonding. By a comparative analysis of ion relaxations and valence charge redistributions in aluminum and copper, we arrive at contrasting descriptions of bonding characteristics in these two metals that can explain their relative strength and deformation behavior.

Journal Article↗

PubMed1985

Effect of body size and cage profile on the shear strength of bones of caged layers.

The effects of body size and cage profile on the shear strength of bones from caged layers aged 72 weeks were studied. Bones tested included the radius, ulna, humerus, femur, and tibiotarsus. The ultimate shear force of the femur, tibia, and humerus all increased as body size increased (P less than 0.01). The wing bones of birds housed in high profile cages had higher shear breaking loads than birds housed in low profile cages. The ultimate shear stresses of the bones were not affected by body size or cage profile. The radius had the highest shear stress (29.2 MPa), followed in descending order by the ulna (19.1 MPa), tibiotarsus, humerus (11.4 MPa) and femur (11.3 MPa).

Animals↗

PubMed1987

Shear strength of the composite bond to etched porcelain.

The shear bond strength of composite resin to porcelain was investigated to optimize variables for bonding porcelain laminate veneers. Scanning electron microscopy was initially used to examine the surface configuration of porcelain prepared under various conditions. A factorial experiment was undertaken to determine the effects of three different bonding methods on both etched and non-etched porcelain. Composite resin was bonded to the porcelain groups using (a) unfilled resin, (b) silane, and (c) silane with dentin adhesive. The results indicated a significant difference in shear bond strength for the three bonding groups, depending on the porcelain surface condition. For the unetched samples, significant differences in bond strength were obtained for all three bonding conditions. However, for the etched group, there were no differences between the silane and silane-with-dentin-adhesive groups. Porcelain etching significantly increased bond strength across all three bonding methods and was the main contributor to the obtained values.

Acid Etching, Dental↗

PubMed2006

Evaluation of shear strength of oil treated laminated bamboo.

Studies were carried out on heat treatment of bamboo species Gigantochloa scortechinii Gamble using palm oil. The samples were laminated and glued. The adhesion results showed that the delamination of glue line increased as the temperature and duration of oil heat treatment increased. Maximum load and shear strength of the glue line reduced as the heat treatment become more severe. It was found that the palm oil used as the heating medium penetrated in some parts of the cell wall as well as in the cell lumen of the bamboo.

Adhesives↗

PubMed2001

Influence of loading types on the shear strength of the dentin-resin interface bonding.

Small differences in the shear bond test can make critical differences in the bonding strength values. The purpose of this study was to compare the influence of the orthodontic-looped wire, stainless steel tape and chisel systems used in shear bonding tests to verify the resistance in the dentin-resin interface. Forty-eight human teeth were used and divided in three groups. The teeth were ground until a flat smooth surface was achieved, that was delimited with an adhesive tape containing a hole of 4 mm diameter. After, the dentine surface was treated with Scotchbond Multi Purpose and the composite Z-100 was applied in layers, through a stainless steel mold. The samples were stored at 37 degrees C and 100% of relative humidity for 24 h and, then, submitted to 500 thermal cycles. After, they were taken to an universal test machine (Otto Wolpert) with crosshead speed of 6 mm/min. The results were statistically analyzed using a Tukey's test (p\lt 0.05). The orthodontic-looped wire determined the highest values of shear bond (13.33 MPa), following by chisel (7.81 MPa) and stainless steel tape (4.87 MPa). The debonding values depend on a complex stress combination produced during the loading of the samples. Small variations in test methodologies give statistically different values for shear bond strength. Different shear strength methods in vitro make the comparative clinical performance of the resin filling materials difficult.

Journal Article↗

PubMed2000

Influence of time and adhesive system on the extrusion shear strength between feldspathic porcelain and bovine dentin.

OBJECTIVES: The behavior of dual-cure cements over time remains unclear. This study evaluated the extrusion shear strength of the bond between feldsphatic porcelain and bovine dentin at different time intervals, using three adhesive systems based on dual-cure cements and one based on a self-cure cement. METHODS: The adhesive systems evaluated included: C&B/One-Step, Enforce/Prime&Bond NT Dual-Cure, RelyX ARC/Single Bond and Variolink II/Syntac SC. Discs of bovine root dentin, 2.5 mm thick, had the root canal prepared with a standardized taper. Porcelain truncated cones etched with 4% hydrofluoric acid and silanized were bonded into the perforations. The extrusion shear test was performed after 15 min, 4 h, 12 h, 24 h, and 7 days. Data were analyzed using the Weibull distribution. The failure mode was accessed by stereomicroscope and SEM. RESULTS: Statistical differences were found between 15 min and 7 days for Variolink II/Syntac SC and RelyX ARC/Single Bond, and between 15 min and 24 h for Enforce/Prime&Bond NT Dual-Cure. For C&B/One-Step, difference was found between 15 min and 4 h. Between 24 h and 7 days, only the system RelyX ARC/Single Bond showed a significant increase in the characteristic strength. SEM analysis revealed that the failure involved the hybrid layer/dentin or the hybrid layer/adhesive interfaces, regardless of the time interval and adhesive system. SIGNIFICANCE: High characteristic strengths were observed after 15 min when dual-cure cements were used. In general, the values found at 24 h or 7 days were higher than at 15 min. However, there was always a considerable probability of bonding failure at low stress levels for all the systems tested.

Acid Etching, Dental↗

PubMed1987

Regional variation in shear strength of the bone-polymethylmethacrylate interface.

Many investigators consider the polymethylmethacrylate-bone interface the weakest link in the bone-cement-implant system. Push-out tests, frequently used for in vitro evaluation of the bone-cement interface, produced inconsistent results of shear strength. Therefore, a more reliable model for testing the shear failure of the interface was developed. Better understanding of intrinsic variations in bone quality and geometry of endosteal bone at the interface may yield important insight into the patterns of clinical failure of cemented total joint prostheses.

Biomechanical Phenomena↗

PubMed1982

Tensile and shear strength measurements on brazed "T" joints used in construction of intra- and intermaxillary hooks.

Silver-brazed "T" joints, representing the first stage in the construction of intermaxillary hooks were fabricated under rigorously controlled conditions. Their tensile and shear strengths were then measured using specially developed test jigs. It was found that the braze joint itself was stronger than the component wires (under tensile load) while in shear mode, fracture occurred in one of a number of well-defined ways. The effect of prolonged heating was investigated using microhardness measurements and recommendations are made for the optimum brazing conditions.

Equipment Design↗

PubMed1997

The effects of density and test conditions on measured compression and shear strength of cancellous bone from the lumbar vertebrae of ewes.

An animal model (the ewe) was used to study mechanical parameters of cancellous bone specimens. Compression and shear tests were conducted on ewe vertebral trabecular bone (L1-L5) from old ewes (mean age: 9 years) under two different conditions: first, at room temperature in air ("standard" test conditions); and secondly, in a physiological saline bath regulated at 37 degrees C. The parameters obtained under "standard" test conditions with a uniaxial compression test were the mean value of the maximum strength (sigma max = 22.3 (7.06) MPa), Young's modulus (E = 1510 (784) MPa), the strain at maximum strength (epsilon sigma max = 3.21 (0.8) percent) and the energy absorbed during the test (W = 0.3 (0.12) MJ.m-3). No significant change was found when the test was carried out in a saline bath at 37 degrees C (p < 0.0005). An original shear test was performed to evaluate the shear strength which was found to vary from 7.5 (4.7) to 14.6 (8.53) MPa under "standard" test conditions depending on the method of calculation. Testing of the specimens in a 37 degrees C physiological saline bath induced a decrease in the shear strength from 32.5 percent (p < 0.0005) to 37.3 percent (p < 0.0001) of those measured under "standard" test conditions. The non-destructive measurement of the Bone Mineral Density (BMD) accounted for up to 73.3 percent of the maximum compressive strength sigma max and 61.5 percent of the maximum shear strength tau max determined in saline solution at 37 degrees C. These results showed that other parameters influencing the mechanical properties of trabecular bone and its structure appeared to be essential.

Absorptiometry, Photon↗

PubMed1988

Laser balloon angioplasty: effect of exposure duration on shear strength of welded layers of postmortem human aorta.

Laser Balloon Angioplasty (LBA) is a technique that may improve the results of balloon angioplasty by thermally sealing arterial dissections and reducing elastic recoil. To define the relationship between laser-exposure duration and the strength of thermal welds made between separated layers of arterial wall, 360 1-cm discs of human postmortem aorta were lased for six different exposure intervals at three different temperature ranges, comparing shear strength of thermal welds in the different groups. Twenty discs were lased to achieve plateau adventitial temperatures of 95 degrees C-104 degrees C (group A), 105 degrees C-114 degrees C (group B), or 115 degrees C-124 degrees C (group C) at each of the exposure periods (5, 10, 15, 20, 25, and 30 sec). A 400-micron fiberoptic coupled to a 1.06 micron continuous wave neodymium:YAG laser was placed perpendicularly 8 mm above the luminal surface of each disc, which had been split midway between the intimal and adventitial surface and reapposed. Mean laser energy ranged 78-378 J delivered in a decremental stepwise fashion to achieve quickly and maintain the target plateau tissue temperature. Mean weld strength increased in relation to both achieved tissue temperature and laser-exposure duration, with at least 10 sec necessary, at temperatures greater than 95 degrees C, for reliable thermal welding. Laser exposure for greater than 20 sec provided no statistical increment in weld strength. In the anticipated clinical performance of LBA, these data suggest that when thermal fusion of disrupted arterial tissues is desired, a laser-exposure duration of 10-20 sec is optimal.

Angioplasty, Balloon↗

PubMed1982

Shearing strengths of recycled direct-bonding brackets.

One hundred twenty freshly extracted human incisor teeth were bonded with several different brands of direct-bonding brackets and tested for retention prior to and after recycling of the brackets by two different commercially available methods. Measurements of shearing strengths were performed to observe any possible changes in the retentive properties of the brackets. The teeth were preconditioned by the application of adhesive material, followed by scaling and pumicing to remove any visible signs of composite. After bonding of the teeth and recording of retentive strengths, the brackets were recycled and the same teeth (after scaling and pumice) were rebonded and tested once more. A decrease in retentive strength was noted in all types of recycled brackets. One type of bracket showed a statistically significant change in strength, depending on the process used in recycling, while the other brackets did not show any difference between the two processes. A control consisting of twenty teeth bonded only once and twenty teeth bonded several times showed no statistically significant change in retention of brackets.

Chemical Phenomena↗

PubMed1981

The tensile and shear strength of a base metal weld joint used in dentistry.

Samples of a base mental alloy were cast and welded together using a conventional welding procedure. The joints were loaded and placed either in a corrosive environment or in air for varying time periods. The tensile and shear strength of the joints was unaffected by the corrosive environment, and the joints, despite some internal defects, appeared suitable for clinical use.

Chromium Alloys↗

PubMed1985

The shear strength between bone and porous ceramic root implants in the guinea pig incisor socket.

Porous alumina and apatite implants have been placed in 67 guinea pig incisor tooth sockets after tooth extraction under anaesthetic. Bone readily grew into the spaces of the implant, and reduced the fibrous connective tissue between implant and bone. 'Pushout' tests have monitored the shear strength of the interlock between bone and implant. Despite considerable variation in the interlock strength, apatite produced the strongest bone interlock. The interlock with alumina tended to be more fibrous. The relative merits of fibrous and bone interlocks in immediate root implants are considered for the augmentation of the alveolar ridge and prosthetic treatment.

Aluminum Oxide↗

PubMed2001

Shear strength after ethylenediaminetetraacetic acid conditioning of dentin.

On the basis of previous studies, it was hypothesized that a chelating agent such as ethylenediamine-tetraacetic acid (EDTA) in a saturated aqueous solution (24%) can function as a dentin conditioning agent with exposure times comparable to that of phosphoric acid without compromising shear bond strength. Thirty caries-free human third molars, divided equally between two groups, were used. In group one, four experimental surfaces were prepared on each tooth, and cylindrical copper matrixes with a diameter of 5 mm were attached to the prepared surfaces. The experimental surfaces were then treated with a 24% EDTA gel for 30, 60, 120, or 240 sec, respectively. Dentin was bonded with All Bond 2, after which a flowable composite was added and light-cured. In group two, which served as control, two surfaces were prepared on each tooth. One surface was left unetched, whereas the other side was treated with 24% EDTA-gel for 30 sec. A shear bond strength test was performed at a crosshead speed of 1 mm/min until the composite debonded. There was no statistically significant difference (P< 0.89) between results of the shear bond strength test for the different EDTA conditioning times. The control group showed a significant difference in shear bond strength between untreated surfaces and surfaces conditioned for 30 sec with EDTA. Thus, the results indicate that the duration of EDTA gel conditioning of dentin surfaces need not exceed that of phosphoric acid in clinical practice to obtain an acceptable level of bond strength.

Acid Etching, Dental↗

PubMed1996

Interfacial shear strength and histology of plasma sprayed and sintered hydroxyapatite implants in vivo.

The interfaces of bone with sintered hydroxyapatite (SHA) and plasma sprayed hydroxyapatite-coated (HAC) implants in the femora of six dogs were examined by light microscopy, scanning electron microscopy, energy dispersive X-ray analysis, and push-out tests. The results demonstrated that there was no significant difference at 12 and 24 weeks after insertion between the interfacial shear strengths with bone for the two types of implants, however, the histological characteristics of the bone around the plasma sprayed HA could be distinguished from that of the sintered HA. The HAC implants showed an early surface biodegradation as compared with the SHA implants. The observed differences in the interfacial zones may be attributed to different bone cell activities and variations in the dynamics of bone formation, possibly resulting from a higher level of dissolution/reprecipitation along the plasma sprayed HA surface.

Animals↗

PubMed1999

The relation between surface roughness and interfacial shear strength for bone-anchored implants. A mathematical model.

A rough bone implant surface was conceptualized as being built up of pits of different sizes and of different shapes. Hypotheses were formulated regarding the mechanical strength of the interfacial bone based upon the present knowledge of the character of the tissues adjacent to endosseous implants and the mechanical characteristics of different bone constituents. A surface roughness parameter was derived, the pit effectivity factor (fpe), which describes how effective the individual pits of the rough surface are as retention elements with regard to shear. Another surface roughness parameter was defined, the pit density factor (fpd), the value of which depends upon how densely packed the pits are. The interfacial shear strength of a rough implant surface with known microgeometry can be estimated by means of these two surface roughness parameters. The effectiveness of pits of different sizes and of different shapes was investigated using this model.

Algorithms↗

PubMed2003

Relationship between surface characteristics and interlaminar shear strength of oxyfluorinated carbon fibers in a composite system.

In this work, a direct oxyfluorination method was used to study the effect of oxygen content on surface and mechanical interfacial characteristics of oxyfluorinated carbon fibers in an epoxy matrix system. The changes of surface functional groups, chemical compositions, and structures of the carbon fibers were characterized by Fourier transform infrared spectrometer, X-ray photoelectron spectroscopy, and X-ray diffraction measurements. Also, the mechanical interfacial properties of the composites were evaluated by means of interlaminar shear strength tests. The results indicated that graphitic carbon was the major carbon functional component on the carbon fiber surfaces and other functional groups were also present, such as Cz.sbnd;O, Cz.dbnd;O, HOz.sbnd;Cz.dbnd;O, Cz.sbnd;F(x), after oxyfluorination of carbon fibers. No large changes of structure were found with the content of oxygen. Consequently, these introductions of oxygen functional groups onto the carbon fiber surfaces led to an improvement of the ILSS of the composites.

Journal Article↗