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Results for “Compressive Strength”

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PubMed2000

[Material selection and structural design of simulated space module for field].

OBJECTIVE: To select the suitable material for the structure of simulated space cabin to meet the special requirements which the unitary metallic material cannot do. METHOD: The structural material was selected through comparison between the mechanical properties of fiber reinforced plastics (FRP) and a few conventional metallic materials. The content and arrangement of the fibers in the composite material were suitably designed according to load condition and structural shape of the cabin. RESULT: High strength and high stiffness, light weight, anti-fatigue and shock proof were achieved for the whole module structure. It meets the medical and hygienic standard for hazardous gases. CONCLUSION: The structural design of fiber glass reinforced plastics composite module was proved to be successful. It reduced the weight of the module body, and increased the strength and toughness of the whole module.

Compressive Strength↗

PubMed1997

Surface treatment effects on amalgam repair strength.

PURPOSE: To determine whether the use of microetching and bonding agents could improve the shear bond strength between aged and freshly added dental amalgam, simulating an amalgam repair. MATERIALS AND METHODS: Aged amalgam surfaces were treated with either a carbide bur or carbide bur + microetcher (Al2O3 abrasive). Five commercially-available adhesive systems were tested. Fresh amalgam was condensed through a split mold onto each prepared amalgam surface. Two control groups were included: a positive control consisting of non-repaired amalgam, and a negative control consisting of aged specimens which received neither carbide bur nor microetching preparation prior to the addition of fresh amalgam. In addition, one group received only carbide bur and another received only carbide bur and microetching treatments, without any adhesive. Following storage and thermocycling, each specimen was tested for shear bond strength. RESULTS: The mean shear bond strength of the repaired samples treated with carbide bur alone (25.8 MPa) was not exceeded by any of the other treatments. Neither microetching nor use of an adhesive agent significantly improved amalgam-to-amalgam shear bond strength. In some cases, use of an adhesive agent significantly decreased the shear bond strength of repaired amalgam samples.

Aluminum Oxide↗

PubMed1997

Fracture studies of selected dental restorative composites.

OBJECTIVES: The purpose of this study was to evaluate the flexure strength, elastic modulus, and fracture toughness (mode I, mode II, and mixed mode) of resin and four specially made dental restorative composite materials. METHODS: Testing was done on prismatic bars in flexure and disk specimens in diametral compression. Fracture strengths were analyzed using Weibull statistics. Statistical analysis consisted of a one-way analysis of variance followed by a Tukey multiple means analysis for each of the materials. In addition, the fracture strengths were analyzed using Weibull statistics due to the brittle behavior exhibited by these materials. RESULTS: The experimental results showed that the addition of fillers resulted in a significant three-fold increase in flexure modulus and a significant 30-50% increase in fracture toughness from the resin. As was indicated by the different Weibull modulus values, strength data obtained from four-point bending were not related with strength data from three-point bending. A straight notch vs. a relatively sharp V-notch gave higher fracture toughness values. Fracture toughness was dependent on the depth of a straight notch and was practically independent of the V-notch depth. Mode I and II fracture toughness in two composites (75Sr and 75Sr10) were carried out on precracked disk specimens in diametral compression. The results of mode I toughness were close to those obtained from the flexure testing. The mode II toughness values were greater than the mode I values by more than 30%. The data fit an equation of the form KI/KIC + (KII/KIIC)2 = 1(where KI, KII are the mode I and II stress intensity factors and KIC, KIIC are the respective critical values). SIGNIFICANCE: Notching technique, testing configuration (three-point vs. four-point loading), and method of testing (bar vs. disk) have significant effect on the fracture properties.

Analysis of Variance↗

PubMed1987

Osteoporosis: the structural and reparative consequences for the skeleton.

We have discussed the biomechanical and biomaterial properties of bone with emphasis on the microenvironment. The microdensity of bone tissues determines the resistance to compressive forces (strength = density2). The structural orientation of bone determines the ability of bone to withstand torsion and bending forces. Highly remodeled bone is brittle and fractures easily because of the multiple reversal planes within the bone plates. Conversely, augmentation of bone on the periphery by modeling leads to increased material microstrength and structural macrostrength. Consequently, appositional modeling augments whereas remodeling diminishes bone strength. Hip fractures, spinal fractures, Colles' fractures, and pelvic fractures have been discussed in terms of their pathophysiology and treatment. An algorithm (Fig. 4-7) has been presented for the differential diagnosis of patients with recently discovered spinal compression fractures. Lastly, a discussion of exercise demonstrated its beneficial role, especially in the retention of bone mass.

Biomechanical Phenomena↗

PubMed2007

Effects of human relaxin on orthodontic tooth movement and periodontal ligaments in rats.

INTRODUCTION: The rate-limiting step in orthodontic treatment is often the rapidity with which teeth move. Using biological agents to modify the rate of tooth movement has been shown to be effective in animals. Relaxin is a hormone present in both males and females. Its main action is to increase the turnover of fibrous connective tissues. Thus, relaxin might increase the amount and rate of tooth movement through its effect on the periodontal ligament (PDL). The purpose of this study was to measure the effect of relaxin on orthodontic tooth movement and PDL structures. METHODS: Bilateral orthodontic appliances designed to tip maxillary molars mesially with a force of 40 cN were placed in 96 rats. At day 0, the animals were randomized to either relaxin or vehicle treatment. Twelve rats in each group were killed at 2, 4, 7, and 9 days after appliance activation. Cephalograms were taken at appliance placement and when the rats were killed. Tooth movement was measured cephalometrically in relation to palatal implants. Fractal analysis and visual analog scale assessments were used to evaluate the effect of relaxin on PDL fiber organization at the tension sites in histologic sections. The in-vitro testing for PDL mechanical strength and tooth mobility was performed by using tissue from an additional 20 rats that had previously received the same relaxin or vehicle treatments for 1 or 3 days (n = 5). RESULTS: Both groups had statistically significant tooth movement as functions of time. However, relaxin did not stimulate significantly greater or more rapid tooth movement. Fractal and visual analog scale analyses implied that relaxin reduced PDL fiber organization. In-vitro mechanical testing and tooth mobility assessments indicated that the PDL of the mandibular incisors in the relaxin-treated rats had reduced yield load, strain, and stiffness. Moreover, the range of tooth mobility of the maxillary first molars increased to 130% to 170%, over vehicle-treated rats at day 1. CONCLUSIONS: Human relaxin does not accelerate orthodontic tooth movement in rats; it can reduce the level of PDL organization, reduce PDL mechanical strength, and increase tooth mobility at early time points.

Animals↗

PubMed2004

Effect of mixing method on the porosity of encapsulated glass ionomer cement.

OBJECTIVE: To observe cement specimens mixed by various methods non-destructively using microfocus computerized tomography (micro-CT) and to evaluate the effect of mixing method on porosity. METHOD: Five glass ionomer cements were used: two were hand-mixed and three were encapsulated. The latter were mixed either by shaking or rotating. Fifteen cylindrical specimens were prepared for each material by each mixing method and stored in distilled water at 37 degrees C until testing. The specimens were observed and analyzed using micro-CT. 201 sliced images were obtained horizontally along the length of the specimens. Three-dimensional reconstructions were made and the sizes, numbers and total volume ratio of bubbles in the specimens were calculated. RESULTS: Mixing method had a significant effect on porosity (P<0.05). For the luting/lining cement, mechanical mixing produced a significantly higher porosity (P<0.05). For the restorative cement, there were only small differences in porosity between specimens mixed by the two methods. More large bubbles were detected in specimens mixed mechanically than by hand for the fluid material. This suggested that for low-viscosity materials bubbles may combine until a certain viscosity is reached during setting. SIGNIFICANCE: The strength of glass ionomer cement is affected by incorporated porosity and this depends on the mixing method. For low-viscosity cements, hand-mixing is favored in order to reduce porosity and increase strength, but this is not generally applicable to high-viscosity cements.

Cementation↗

PubMed2006

The influence of water removal on the strength and toughness of cortical bone.

Although the effects of dehydration on the mechanical behavior of cortical bone are known, the underlying mechanisms for such effects are not clear. We hypothesize that the interactions of water with the collagen and mineral phases each have a unique influence on mechanical behavior. To study this, strength, toughness, and stiffness were measured with three-point bend specimens made from the mid-diaphysis of human cadaveric femurs and divided into six test groups: control (hydrated), drying in a vacuum oven at room temperature (21 degrees C) for 30 min and at 21, 50, 70, or 110 degrees C for 4 h. The experimental data indicated that water loss significantly increased with each increase in drying condition. Bone strength increased with a 5% loss of water by weight, which was caused by drying at 21 degrees C for 4 h. With water loss exceeding 9%, caused by higher drying temperatures (> or =70 degrees C), strength actually decreased. Drying at 21 degrees C (irrespective of time in vacuum) significantly decreased bone toughness through a loss of plasticity. However, drying at 70 degrees C and above caused toughness to decrease through decreases in strength and fracture strain. Stiffness linearly increased with an increase in water loss. From an energy perspective, the water-mineral interaction is removed at higher temperatures than the water-collagen interaction. Therefore, we speculate that loss of water in the collagen phase decreases the toughness of bone, whereas loss of water associated with the mineral phase decreases both bone strength and toughness.

Adult↗

PubMed1997

Stress analysis of halo pin insertion by non-linear finite element modeling.

Halo fixation is associated with a high complication rate. The most common complications are loose pins and pin site infections believed to be exacerbated by loose pins. Although pin designs and the technique of pin insertion have changed little in over 30 years, the pin/skull mechanics are poorly understood. Halo pin insertion was modeled using nonlinear finite element analyses to determine the stress distribution in the human skull underlying and surrounding the point of pin fixation. Model validity was established by comparing pin insertion depth and the profile of the hole generated in the bone to the results of experimental mechanical tests. The region surrounding the pin tip within 1 mm was found to undergo plastic deformation and compressive loading in excess of the compressive yield strength of cortical bone. The implication is that damaged bone in this region is responsible for the high incidence of halo pin loosening. Resorption or migration of bone particles with periodic relief of compression in this region due to daily cyclic forces might result in an enlarged pin site and eventually, a loose pin.

Bone Nails↗

PubMed2003

Cobalt-based bulk glassy alloy with ultrahigh strength and soft magnetic properties.

Bulk metallic glasses--formed by supercooling the liquid state of certain metallic alloys--have potentially superior mechanical properties to crystalline materials. Here, we report a Co(43)Fe(20)Ta(5.5)B(31.5) glassy alloy exhibiting ultrahigh fracture strength of 5,185 MPa, high Young's modulus of 268 GPa, high specific strength of 6.0 x 10(5) Nm kg(-1) and high specific Young's modulus of 31 x 10(6) Nm kg(-1). The strength, specific strength and specific Young's modulus are higher than previous values reported for any bulk crystalline or glassy alloys. Excellent formability is manifested by large tensile elongation of 1,400% and large reduction ratio in thickness above 90% in the supercooled liquid region. The ultrahigh-strength alloy also exhibited soft magnetic properties with extremely high permeability of 550,000. This alloy is promising as a new ultrahigh-strength material with good deformability and soft magnetic properties.

Alloys↗

PubMed1996

Insertional torque and pull-out strengths of conical and cylindrical pedicle screws in cadaveric bone.

STUDY DESIGN: Insertion torque and pull-out strengths of conical and cylindrical pedicle screws were compared in human cadaveric vertebral bodies. OBJECTIVES: To compare the performance of the conical design with the cylindrical design, and to determine whether insertional torque correlates with pull-out strength. SUMMARY OF BACKGROUND DATA: A tapered pedicle screw design may lessen the likelihood of implant failure. Its effect on thread purchase is not known. Previous studies of cylindrical designs on the relation between insertion torque and pull-out strength have been conducted in bovine and synthetic bone. METHODS: Seventy-eight pedicles were assigned randomly to one of the following pedicle screw: Texas Scottish Rite Hospital (Sofamor-Danek, Memphis, TN), Steffee VSP (Acromed, Cleveland, OH), Diapason (Dimso, Paris, France), AO Schanz (Synthes, Paoli, PA), or Synthes USS (Synthes, Paoli, PA). Pedicle screws were inserted with a torque screwdriver. Each screw was extracted axially from the pedicle at a rate of 1.0 mm/sec until failure using an MTS machine (Bionix 858, Minneapolis, MN). Force data were recorded. RESULTS: The conical design had the highest insertion torque. There were no significant differences in pull-out between any of the screw types. Correlation between insertional torque and pull-out strength was statistically significant only with the Texas Scottish Rite Hospital and Steffee VSP in L4 and AO Schanz in L5. CONCLUSIONS: A conical screw profile increases insertion torque, although insertional torque is not a reliable predictor of pull-out strength in cadaveric bone. Screw profile (with similar dimensions) has little effect on straight axial pull-out strengths in cadaveric bone.

Aged↗

PubMedDate not supplied

Flexural strength of In-Ceram alumina and In-Ceram zirconia core materials.

PURPOSE: The study compared the flexural strength of In-Ceram alumina and In-Ceram zirconia systems. The probability of failure of the two glass-infiltrated ceramic core materials was analyzed with and without lamination with Vitadur-alpha porcelain. MATERIALS AND METHODS: Ten uniform beams of core materials as well as 10 beams of laminated core materials were fabricated for In-Ceram alumina and In-Ceram zirconia. The samples were subjected to three-point bending tests. Flexural strength for both ceramic core materials was determined with and without their porcelain laminations. The strength data were analyzed using the Weibull method. Modes of failure for both systems were determined using scanning electron micrography. RESULTS: The strength of the In-Ceram zirconia system was significantly higher than In-Ceram alumina when comparing their core materials with and without porcelain lamination. The failure mode for both systems was predominantly transgranular fracture of alumina platelets. CONCLUSION: In-Ceram zirconia demonstrated higher flexural strength than In-Ceram alumina.

Aluminum Oxide↗

PubMed2004

Placement of solid screws with cannulated precision.

Cannulated screws can be inserted in a precise manner with minimal damage to surrounding structures but lack the mechanical strength of solid screws. Our method allows the insertion of a solid screw with the precision of the cannulated technique. With the use of equipment from a variety of operative sets from one manufacturer, a "custom" equipment set can be developed. This "custom" equipment set allows the surgeon to benefit from the strength of solid screws while preserving the precision of a cannulated system.

Arthrodesis↗

PubMed1997

Avulsion of the tibial tuberosity: muscles too strong for a growth plate.

PURPOSE: To ascertain whether there were significant knee extension strength differences between two adolescent male gymnasts (patient 1: age, 14.5 years; height, 159.3 cm; weight, 52.2 kg; patient 2: age, 15 years; height, 160.6 cm; weight, 54.8 kg) with avulsion of the tibial tuberosity associated with avulsion of the patellar tendon. CASE SUMMARY: Two adolescent male gymnasts underwent open reduction and internal fixation for avulsion of the tibial tuberosity associated with avulsion of the patellar tendon. Isometric extension strength of the contralateral uninjured knee and of the operated knee was significantly greater than for nonathletic adolescents of the same age (one-way analysis of variance [ANOVA], p = 0.001), and was at a higher part of normal strength than their gymnastic peers. DISCUSSION: A maximal contraction of the quadriceps is able to overcome the strength of the upper tibial epiphysis disrupting the extensor mechanism of the knee. RELEVANCE: Greater-than-usual strength, although normally of no undesired consequence, may play a role in avulsion injuries of major muscles.

Adolescent↗

PubMed1999

[Changes of biomechanical properties in goats at different times after ovariectomy].

This paper presents the changes of biomechanical properties in goats at different times after ovariectomy. 14 goats were randomly divided into three groups. These goats were ovariectomized and sacrificed at 180 days (n = 4), 360 days (n = 5) and 540 days (n = 5) after the operation. The right femur, tibia and metatarsus were taken out. The structure mechanical properties of femora were measured with the three-point bending method and those of metatarsus were measured with the compressing method. The material mechanical properties of flexure, compress and tensile strength in the compact bone specimens of femora and tibiae taken from broken ends were also measured. The results showed that the one-year group, compared with the half-year group, had all the bone geometric parameters decreased, but not statistically significant (P > 0.05); the elastic modulus of three-point bending of femora decreased by 23.27% and the others had no significant difference (P > 0.05); all the material parameters of flexurel, compress and tensile strength in compact bone specimens decreased, but only the ultimate strength of tibiae of flexure, compress and tensile strength decreased obviously (P < 0.05). The one and a half year group, compared with the one year group, had the bone density of femora and tibiae decreased, but not statistically significant (P > 0.05). All the bone geometric parameters of tibiae and the thickness of bone of femora increased (P < 0.05). The break load of three-point bending of femora increased (P < 0.05). Probably, it was related to the increase of the body weight in the one and a half year group. The elastic modulus and the ultimate strength decreased, but not statistically significant (P > 0.05). When compact bone specimens were used, the ultimate strength and elastic modulus of femora and tibiae in compress and the elastic module of tibiae in flexure decreased obviously (P < 0.05); and the others had no significant changes (P > 0.05). This study indicated that the degree of osteoporosis in ovariectomized goats increased at half a year, one year, and one and a half year postoperation, and hence suggested that the ovariectomized goat be a pretty useful big animal model of osteoporosis.

Animals↗

PubMed2006

Effect of setting conditions on mineral trioxide aggregate flexural strength.

This study evaluated the effect of setting conditions (time and hydration) on mineral trioxide aggregate (MTA) flexural strength. MTA beam specimens were allowed to set for either 24 or 72 hours with specimens exposed to moisture on either one or two specimen surfaces. These moisture conditions were used to simulate MTA setting with only external tissue moisture (one-sided moisture) versus tissue moisture in combination with a moistened intracanal cotton pellet (two-sided moisture). Ten specimens were stored at 37 degrees C under each of the four experimental setting conditions (1) 24-hour/moist/2-sided; (2) 24-hour/moist/1-sided; (3) 72-hour/moist/2-sided; (4) 72-hour/moist/1-sided. After storage at respective setting conditions, MTA specimens were tested to failure with three-point bend test to measure flexural strength. Flexural strength of the 24h/moist/2-sided specimens, 14.27 +/- 1.96 MPa, was significantly higher (p < or = 0.05) than the flexural strength values associated with conditions two, three, and four, respectively, 10.77 +/- 1.44, 11.16 +/- 0.96, 11.18 +/- 0.99 MPa, which were not significantly different from each other (p > 0.05). Clinically, these results suggest that a moistened cotton pellet should be placed on the intracanal MTA surface under a temporary restoration; and if possible, to optimize flexural strength, the moistened pellet should only remain in place for 24 hours.

Aluminum Compounds↗

PubMed2001

The influence of fibre placement and position on the efficiency of reinforcement of fibre reinforced composite bridgework.

The effect of placement of ultra-high molecular weight polyethylene (UHMWPE) fibres on the flexural properties and fracture resistance of a direct dental composite was investigated. The UHMWPE fibres are increasingly being used for the reinforcement of laboratory fabricated resin composite crown and bridgework. The aim of this study was to assess the effect of a commonly used laboratory fabrication variable on the in vitro strength of beam shaped specimen simulating a three-unit fixed bridge. Four groups (10 specimens per group) of Herculite XRV were prepared for flexural modulus and strength testing after reinforcement with UHMWPE fibres. Two groups of control specimens were prepared without any fibre reinforcement. Half the specimen groups were stored in distilled water and the other groups were stored dry, both at 37 degrees C for 2 weeks before testing. The results of this study showed that placement of fibre at or slightly away from the tensile side improved the flexural properties of the composite in comparison with the unreinforced control specimen groups whilst the mode of failure differed according to fibre position. Scanning electron microscope (SEM) investigation revealed that placement of the fibre slightly away from the tensile side favoured crack development and propagation within the resin bridging the interfibre spaces in addition to debonding parallel to the direction of fibre placement. Laboratory fabrication variables may effect the strength of fibre reinforced bridgework significantly.

Analysis of Variance↗

PubMed2001

Strength and electron features of irradiated bone.

Radiation applied for therapy and diagnostics damages molecular/atomic couples of biotissues, bones being among them. As a result, electron peculiarities and mechanical behavior of the latter are altered. Correlation between strength of the irradiated bone and its electron features explored due to photo- and exoelectron emission measurements is reviewed.

Animals↗

PubMed2002

Effect of prolonged water storage and repeated thermocycling on the reinforcing ability of refrigerated Amalgambond Plus/High Performance Additive in third molars with large mesio-occlusodistal amalgam restorations.

OBJECTIVE: This in vitro investigation examined what effect prolonged water immersion and repeated thermocycling had on the fracture strength of extracted third molars restored with refrigerated Amalgambond Plus with High Performance Additive (AB+/HPA) and Tytin amalgam. MATERIALS AND METHODS: Mesio-occlusodistal (MOD) channels were prepared in one member from each of 19 contralateral pairs. After restoration, specimens were stored in water for 6 months, with thermocycling repeated every 2 months. Specimens were fractured in a universal testing machine, and the data were analyzed. Secondary effects of tooth location and tooth size were also examined. RESULTS: Fracture strengths of prepared/restored teeth were not statistically different from those of intact contralateral pairs (p > 0.05). Maxillary teeth had lower fracture strengths than mandibular teeth, and tooth size had no effect on fracture strength. CONCLUSIONS: Extracted molars with large MOD amalgam restorations bonded with refrigerated AB+/HPA had fracture strengths equivalent to those of intact contralateral pairs after 6 months of water storage and repeated thermocycling.

Compressive Strength↗