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At least 19 recordsLinked to original sources

[The compressive strength, tensile strength, flexural strength and micro-hardness of Plat-II Castable Ceramics].

In preparation for the clinical use of Plat-II Castable Ceramics (PCC-II), we tested its compressive strength, tensile strength, flexural strength and microhardness. The flexural strength was tested by the three-point bending test. The result showed that the compressive strength was 541.7 MPa; the tensile strength 42.5 MPa; the flexural strength 142.0 MPa; the modulus of elasticity 61.4 GPa; and the micro-hardness 499.6 kg/mm3. The strength anol micro-hardness of PCC-II materials were better than those of human enamel. So PCC-II is applicable to restorations in dentistry.

Ceramics↗

[Testing metal/acrylic bonds for shear strength, axial tensile strength and maximum bending stress].

The effects of thermocycling and water penetration on the bond strength of resin-metal-systems and improvements using bonding agents have been tested by shear, bending and tensile tests. After 10,000 cycles within 10 days in different water-baths with 5-37-55 degrees C, there is a decrease in bond strength by 40 to 60%. The use of bonding agents increases the adhesion of the resin to the metal by more than 100%. No significant differences were found between the three bonding agents Silicoater, Sebond MKV and OVS.

Acrylic Resins↗

Comparison of granule strength and tablet tensile strength.

The granule strength (crushing load) of lactose granulated with 1-9% povidone was measured initially and at intervals during a 1-year period. The granule strengths of dibasic calcium phosphate dihydrate granulated with various concentrations of starch and povidone were measured. The axial and radial tensile strengths of tablets compressed from these granules were determined and related to concentration of binder and granule strength. The effect of compressional force on the integrity of granules in a tablet matrix is shown in scanning electron photomicrographs of the fractured tablets which had undergone a diametral compression test. It appears that the compressional force and the concentration of binder contribute more than granule strength to tablet tensile strength.

Hardness↗

Physical properties of experimental vitreous membranes. I. Tensile strength.

The tensile strength of vitreous membranes, induced by silk sutures imbedded in the vitreous body and removed one to two weeks later, was investigated in rabbits. Three types of membranes were distinguished by their appearance under an operating microscope; dense, opaque, cylindrical membranes, (Type 1), broken with 2 to 16 Gm. of force and elongated from 127 to 200 per cent before breaking; thin, cylindrical membranes, (Type 2), broken with 200 mg. to 2 Gm. of force and elongated from 51 to 152 per cent before breaking; and thin film-like membranes imbedded in formed vitreous gel, (Type 3), broken with 200 mg. to 5.5 Gm. of force and elongated from 53 to 186 per cent before breaking. Vitreous membranes formed two to eight weeks after surgery resisted forces greater than those required to detach rabbit retina. The results of the experiment are relevant in the design of vitrectomy instruments.

Animals↗

A study on impact and tensile strength of acrylic resin filled with short ultra-high molecular weight polyethylene fibers.

In dentistry, acrylates have been used for preparing denture bases for 50 years. Although polymethylmethacrylates (PMMA) are known to be an ideal base material, they possess some undesirable mechanical properties, especially their impact strength and tensile strength, which appear to be unsatisfactory for some applications. Additives and fibers have therefore been used to enhance and improve these properties over the last two decades. The present article describes the mechanical properties, impact and tensile strength of PMMA reinforced with chopped ultra-high molecular weight polyethylene fiber (6 mm long). It was found that, although the processing involved for high loading of fibers into the PMMA was difficult, the resulting improvement of impact strength was substantial.

Acrylic Resins↗

A simple predictive model for the tensile strength of binary tablets.

The tensile strength of tablets of single-component powders, such as microcrystalline cellulose (MCC), hydroxypropylmethyl cellulose (HPMC) and starch, and binary mixtures of these powder were measured at various relative densities. It was found that the tensile strength of tablets of powder blends was primarily dependent upon relative density but was independent of the tablet dimensions and compaction kinematics. It was found that the logarithm of tensile strength was proportional to the relative density. A simple model, based upon Ryshkewitch-Duckworth equation that was originally proposed for porous materials, has been developed in order to predict the relationship between the tensile strength and relative density of binary tablets based on the properties of the constituent single-component powders. The validity of the model has been verified with experimental results for various binary mixtures. It has demonstrated that the proposed model can well predict the tensile strength of binary mixtures based upon the properties of single-component powders, such as true density, and the concentrations.

Cellulose↗

[An experimental study of the strength in arterial prosthetic anastomoses: relationship between anastomotic tensile strength and its organization].

Five types of 6-mm diameter arterial prostheses, i.e.m woven Teflon, woven Dacron, velour woven Dacron, velour knitted Dacron and expanded polytetrafluoroethylene (E-PTFE), were studied in the dog to assess anastomotic tensile strength and its organization. Five types of composite grafts, about 3.0cm in length, were implanted in the abdominal aorta of fifty-two adult mongrel dogs using absorbable polyglycolic acid suture. At 16 weeks after the implantation, if the composite graft was patent, tensile strength of the bilateral anastomoses were measured and its organizations were examined microscopically. The mean forces required to disrupt the anastomoses of velour woven Dacron, velour knitted Dacron and E-PTFE were greater than those of woven Teflon and woven Dacron. At the disrupted sites of woven Teflon and woven Dacron, which were non-velour grafts, fibrous outer sheath were remarkably separated from the grafts. This results indicate that organization and fixation of fibrous outer sheath are the most important factors in the strength of arterial prosthetic anastomoses and velour grafts have superiority over non-velour grafts. The organization of E-PTFE was poor, but its tensile strength was equal to velour grafts. It is considered E-PTFE has an advantage due to non-crimped structure and requires further evaluation over longer period.

Anastomosis, Surgical↗

Functional loading augments the initial tensile strength and energy absorption capacity of regenerating rabbit Achilles tendons.

The biomechanical effect of functional loading was studied in surgically tenotomized, repaired and immobilized right Achilles tendons of 34 rabbits. Beginning from the 5th day after surgery, loading was initiated by removing the immobilization casts of the animals to permit unrestricted weight-bearing to tolerance. At each of 12, 18 and 21 days after surgery, functionally loaded tendons and their corresponding nonloaded controls were excised and compared for differences in tensile strength, tensile stress and energy absorption capacity. Functional loading induced a twofold increase in the tensile strength (P less than 0.05) and energy absorption capacity (P less than 0.05) of the tendons, at both 12 and 18 days after surgery. No statistically significant differences were observed in the tensile strength and energy absorption capacity of the tendons at 21 days after surgery. Statistically significant differences in tensile stress were not observed at any time period throughout the study. These findings demonstrate that functional loading augments the tensile strength and energy absorption capacity of experimentally tenotomized tendons without promoting re-rupture, but only during the very early stages of healing. Even though the healing process of rabbit tendons may differ from healing of human tendons, these results suggest that similar beneficial effects may be attained if repaired human Achilles tendon ruptures are carefully loaded during the very early rather than later stages of healing.

Achilles Tendon↗

Granulation tissue formation in oophorectomized rats treated with female sex hormones. II. Studies on the amount of collagen and on tensile strength.

The content of hydroxyproline and tensile strength of granulation tissue was studied in oophorectomized rats treated with female sex hormones. Estrogen alone caused a slight decrease of hydroxyproline, but had no effect on the tensile strength of the granulation tissue at one week. Progesterone alone or in combination with estrogen decreased the content of hydroxyproline and the tensile strength of the granulation tissue up to one week in the case of progesterone-treated animals and up to two weeks in the case of animals treated with the combination of the hormones. At one week no direct correlation was found between the amount of hydroxyproline and the tensile strength of granulation tissue in oophorectomized rats treated with estrogen and progesterone in combination.

Animals↗

Wound healing. Tensile strength vs healing time for wounds closed under tension.

OBJECTIVES: To measure tensile strength of wounds closed with and without tension in rats, delineating the postoperative time interval when tensile strength is equal. To study patterns of growth in tensile strength. DESIGN: Transverse incisions on the backs of control rats were closed with minimal tension. In experimental animals, after excision of skin from the back, wounds were closed with closing tensions in excess of 70 g. Animals were killed at designated healing intervals for tensile-strength testing of wounds. SUBJECTS: One hundred Sprague-Dawley rats were divided into 5 groups days 5, 7, 10, 14, and 21, with equal numbers of control and experimental animals in each group. Wounds from 94 animals were available for breakload testing. INTERVENTION: Closing tensions were measured for transverse incisions on the backs of control animals before closure and after removal of 50 to 60 mm of skin from the backs of experimental animals. RESULTS: Tensile strength was not significantly different on day 5. However, wounds closed under tension showed significantly higher tensile strength on 7, 10, 14, 21. Polynomial regression suggests a cubic relationship between healing time and tensile strength. CONCLUSIONS: Results suggest that tensile strength of wounds closed under tension exceeds that of tensionless wounds as early as day 7 following surgery. This study also illustrates the 2 periods of rapid increase in wound tensile strength that probably coincide with specific stages of wound healing.

Animals↗

Moisture sorption profiles and tensile strength of tableted phenobarbitone formulations.

The tensile strength of tablets made from phenobarbitone and sodium phenobarbitone formulations after storage at increasing ambient relative humidity has been investigated. The moisture sorption and desorption profiles of the formulations were analysed for three locations of moisture: monolayer adsorbed moisture, normally condensed moisture and absorbed moisture. Maxima in tensile strength occur at moisture distributions determined by the disintegrant used. The changes in tensile strength have been explained in terms of changes produced in the interparticle separation, the range of the interparticle forces and changes in the ratio of the binding to diffusional forces, acting on the water molecules which are on the particles' surface.

Adsorption↗

Protease inhibitor reduces loss of tensile strength in rat anastomosis with peritonitis.

BACKGROUND: The tensile strength in intestinal anastomoses decreases postoperatively in association with degradation of the extracellular matrix, and these changes would be expected to be more intense in the presence of peritonitis. MATERIALS AND METHODS: In this study, we investigated extracellular matrix degradation and tensile strength in a rat model of intestinal anastomosis with peritonitis. In the chemical peritonitis model, peritonitis was induced 24 h earlier with intraperitoneal HCl. A serine protease inhibitor, nafamostat mesilate (NM), was given intraperitoneally to some animals every 12 h from immediately after the operation for 3 days. Immunostaining was performed by the standard streptavidin-biotin-peroxidase method after fibronectin (Fn) and factor XIII antigen retrieval on paraformaldehyde-fixed, paraffin-embedded tissue sections. RESULTS: In comparison with controls, administration of NM reduced the loss of tensile strength on Day 3 in a dose-dependent manner, and high-dose NM (20/mg/kg) significantly prevented the loss of tensile strength on Day 3 (P < 0. 05). In the control group, degradation of the collagen layer in the anastomosis was associated with disappearance of Fn and factor XIII staining on Day 3. The administration of NM attenuated these changes with intense immunostaining for Fn and factor XIII seen particularly between collagen fibers on both sides of the anastomosis on Day 3. In the chemical peritonitis model, administration of NM also significantly prevented the loss of tensile strength on Day 3 without disappearance of collagen fibers. CONCLUSION: These findings suggest that NM may be clinically useful for preventing intestinal leakage, particularly when anastomoses are performed under protease-activating conditions, such as intestinal edema and inflammation.

Anastomosis, Surgical↗

Adjustment of precompression force to reduce mixing-time dependence of tablet tensile strength.

The dependence of tablet tensile strength on lubricant mixing time, pre- and main compression pressure was measured with microcrystalline cellulose, dicalcium phosphate dihydrate and starch 1500 on a rotary tablet machine. Loss of tablet tensile strength arising from lubricant overmixing can be substantially reduced in the case of microcrystalline cellulose by adjustment of pre- and main compression. This facility may be used in addition to or instead of reducing mixing time, or displacing lubricant by adding extra formulation components.

Excipients↗

Effect of the association of nystatin with a tissue conditioner on its ultimate tensile strength.

PURPOSE: This study evaluated the ultimate tensile strength of a tissue conditioner without nystatin incorporation (GI-control group) and the same tissue conditioner modified by the addition of nystatin in two concentrations: GII-500,000 International Units (U) and GIII-1,000,000 U, in which each milligram of the medicament corresponded to 6079 U. MATERIALS AND METHODS: Dumbbell-shaped specimens (N= 7) with a central cross-sectional area of 33 x 6 x 3 mm were produced for the three experimental groups. After polymerization following manufacturer's instructions, specimens were immersed in distilled water at 37 degrees C for either 24 hours or 7 days and then tested in tension in the MTS 810 at 40 mm/minute. Data were analyzed by two-way ANOVA followed by Tukey's test, at 95% level of confidence. RESULTS: The means (force-grams (gf) +/- standard deviation) of the ultimate tensile strength were: GI-634.29 +/- 122.80; GII-561.92 +/- 133.56; and GIII-547.30 +/- 73.47 for 24-hour storage, and GI-536.68 +/- 54.71; GII-467.50 +/- 143.51; and GIII-500.62 +/- 159.76 for 7-day storage. There were no statistically significant differences among the three experimental groups (p > 0.05). The ultimate tensile strength means of all experimental groups after 7 days were significantly lower than those observed after 24 hours (p= 0.04). CONCLUSIONS: The results of this study suggest that the addition of nystatin into the tissue conditioner investigated in concentrations below 1,000,000 U did not affect its ultimate tensile strength.

Analysis of Variance↗

[Tensile strength properties of lower limb nerves in the mature age].

Tensile strength and deformation properties of tibeal and common fibular nerves were analysed in 78 cadavers of both sexes people aged from 21 to 60. It was established that in mature age nerve tensile strength and elasticity increases with low extent of elongation. At the age from 21 to 50 tensile strength and rigidity decrease with significant deformations due to nerve fibre degeneration. After 50 ys tensile strength and rigidity grow higher due to the developing sclerosis of nerve trunks. The nerves studied posses equal tensile strength that decreases synchronously during the period of maturity. Changes of deformation and tensile strength properties of the nerves within the period of maturity is connected with age-related reorganization of their intratruncal structure. Diversities in mechanical properties of different nerves is determined by qualitative and quantitative peculiarities of their morphological structure.

Adult↗

Powder flow studies III: tensile strength, consolidation ratio, flow rate, and capsule-filling-weight variation relationships.

The tensile strength of consolidated powder beds was studied by applying a series of loads to the surface of the powder beds in a tensile tester. The results were plotted as tensile strength versus consolidation pressure. The linearity of these plots suggests a direct relationship between tensile strength and consolidation pressure. The following plots gave linear relationships: (1) tensile strength versus consolidation ratio, (b) tensile strength versus coefficient of variation of the filled weight of the capsules, and (c) logarithm of the tensile strength versus logarithm of the flow rate. These results suggest a direct relationship between tensile strength and consolidation ratio and their usefulness in studying powder flow. The physical significance of the empirical equation used in consolidation studies was explored. A comparison of the empirical equation with a theoretically derived equation, under certain assumptions, suggests that the consolidation ratio is a function of the ratio of the initial volume to the net volume and a function of the coefficient of Rankine. The coefficient of Rankine is a function of the angle of internal friction in the static powder bed.

Capsules↗