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PubMed1987

Osteogenic potential of nonvital tissues and synthetic implant materials.

Following the application of various techniques to restore or rebuild alveolar bone with different implants, results are generally unpredictable. In successful cases it is not clear whether the materials are capable of initiating osteogenesis by metaplastic induction, where endogenous bone formation had failed, or initiating osteogenesis by stimulating the regeneration of existing vital bone tissue by irritation. In order to discriminate between these two possibilities, 40 Sprague-Dawley descent rats were implanted with both devitalized tissues and synthetic materials in an area where bone is not usually formed: the anterior eye chamber. The test materials consisted of two devitalized tissues: boiled bone marrow and demineralized dentin, and six synthetic materials: formalin 10% and 40%, formic acid 10% and 88%, plaster of Paris, and ceramic tricalcium phosphate (Durapatite). Test materials were inserted into 59 chambers, but bone was not formed in any of these cases following a three-week experimental test period. Following implantation of 21 control chambers with viable mature marrow, bone was formed in 5 of 21 cases (24%), following the three-week test period. These findings appear to indicate that the reported cases where bone regeneration successfully occurred following implantation probably resulted from unpredictable irritational factors upon the existing vital bone tissue rather than by metaplastic induction.

Animals↗
PubMed1991

The Yucatan miniature swine as an in vivo model for screening skin depigmentation.

The usefulness of the Yucatan miniature pig as a screen for skin dipigmenting activity by topical application was evaluated with standard compounds. This is a naturally occurring breed of swine with light brown to dark brown skin that is relatively hairless. The skin morphology, including the pattern of pigment distribution, in this breed of swine closely resembles the human skin. Test compounds examined in this study included the three standard compounds with known clinical depigmenting activity, hydroquinone (HQ), 4-hydroxyanisole (4HA) and tert-butyl catechol (TBC), each at a 5% concentration. Test materials in 25 microliters of propylene glycol/ethanol (50:50) were applied topically twice daily, 7 days a week for 90 days to test sites on each side of the dorsal mid-line. Test sites were graded weekly for variation in pigmentation and local irritation. After 90 days of test material application, skin biopsies of the test sites were taken for histological evaluation. Topical application of HQ, 4HA and TBC promoted marked skin depigmentation which was substantiated by reductions of pigment and melanocytes observed on microscopic examination. While both HQ and TBC produced marked local irritation, 4HA was only mildly irritating. These results suggest that the Yucatan pig, could be a potentially useful model for screening compounds with skin depigmenting activity.

Animals↗
PubMed1998

Cytotoxicity testing of materials with limited in vivo exposure is affected by the duration of cell-material contact.

Silicones for dental impression largely are used to record the geometry of hard and soft dental tissues. They are considered to be medical devices, and the assessment of cytotoxicity is a necessary step in the evaluation of their biocompatibility. Extracts of six addition-type and six condensation-type silicones have been tested with L929 cells according to the ISO 10993-Part 5 standard. The cytotoxicity was evaluated by three different methods: neutral red uptake, propidium iodide (PI) staining, and amido black staining. According to the selected specific assay, contact between cells and material extracts was maintained for 24 h in the first series of experiments; then, considering that in vivo application of these materials is restricted to a few minutes, additional experiments were performed after 1 h of cell/extract contact. Analysis of the results showed that the addition-type silicones are nontoxic even when tested after prolonged exposure of the cells to the materials while the condensation-type silicones were cytotoxic at 24 h of incubation. Nevertheless, harm to the patient actually could be negligible, considering its very short time of exposure in vivo. This is supported by our finding that most are not toxic after 1 h. We suggest that the experimental conditions of cytotoxicity testing have to be relevant to the in vivo situation; accordingly, the time of exposure should be designed carefully.

Amido Black↗
PubMed2003

Determining the compression behaviour of pharmaceutical powders from the force-distance compression profile.

The force-displacement curves obtained from an eccentric tablet machine were examined in a new way. The tendency of the material for plastic deformation, fragmentation and elasticity is expressed as numerical values, which are comparable between different materials. The dependence of these numerical values on the compression pressure was modelled. The accuracy of the displacement measurement was improved by filtering out noise from the measurement data by a novel method. The plastic deformation of the material near the force maximum of the compression cycle could be seen accurately from this precise displacement data. The elastic deformation of the tablet machine was also defined very precisely from the running machine. Tablets were made with an eccentric tablet machine using fixed lower and upper punch adjustments. This ensured that the speed of the upper punch and the theoretical height of the tablets were the same for all compactions. Therefore, only the properties of the materials determined the differences in the shape of the compression curves. The test materials used were alpha-lactose monohydrate, two grades of microcrystalline cellulose, maize starch and dicalcium phosphate dihydrate. The results showed that the use of accurate displacement measurement is essential in order, to see the small variations in the shape of the force-displacement curve near the force maximum of the compression cycle, and it made it possible to dynamically calibrate the elastic deformation of the eccentric tablet machine during compression. It turned out that the numerical values obtained with the new method described the plastic, brittle and elastic properties of the tested materials satisfactorily in a wide compression pressure range.

Compressive Strength↗
PubMed2005

Bioelectrographic testing of mineral samples: a comparison of techniques.

OBJECTIVES: This study was initiated to determine the suitability of differing techniques to record optical properties of gemstones under electromagnetic stimulation. Such properties are of interest due to the historical use of gemstones in folkloric remedies, specifically as agents for concentrating, focusing, or otherwise conducting energy flows in the human body. DESIGN: The techniques researched produce a localized corona discharge around the tested material. The simplest technique, Tesla coil Kirlian photography (TCKP), uses a Tesla coil to introduce a strong electric current, and the circuit is completed by a glass electrode. The corona discharge is then photographed. The other technique used in the study is gas discharge visualization (GDV), which uses a pulsed current and a digital camera integral to the coil to produce digital images of the corona discharge. MATERIALS: Gemstones were tested both whole and in powdered form. The sample gemstones were amethyst, aquamarine, garnet, golden citrine, pink tourmaline, and yellow topaz. Powdered gemstones were ground to a particle size of 2-5 microns; whole gemstones were roundcut to a diameter of 5 mm. RESULTS: In our tests, TCKP showed divergent effects for differing types of gemstone. The most extreme effects were exhibited by tourmaline, both in powdered and whole form. In addition, TCKP appeared to indicate differing effects for gemstones of the identical type but mined from differing locations. The GDV technique showed differing data among the gemstones for the measured parameters, indicating that a high relative intensity did not correspond to the size of the corona discharge. CONCLUSIONS: While both techniques showed promise in distinguishing differences in corona discharge behavior in gemstone samples, further work is necessary to determine the significance of differences in geographical sources or between gemstones of similar crystalline structure. The techniques explored show promise in characterizing the properties of gem materials under electromagnetic stimulation.

Chromatography, Gas↗
PubMed1986

In vitro testing of dental materials by means of macrophage cultures. I: Methodological aspects.

Macrophages play a central role in the pathogenesis of inflammation. In addition, activated macrophages are the first cells to come in contact with foreign particles in tissue. In the present study the applicability of macrophages for in vitro biological screening of dental materials was tested. Monolayers of murine peritoneal macrophages were prepared. After three days culture the macrophages were inoculated with alloy particles prepared from silver and tin (Ag3Sn), the gamma-phase of dental silver-amalgam. After different inoculation periods the macrophages were fixed and examined with phase contrast microscopy, scanning electron microscopy, and energy dispersive x-ray analysis. Comparison with phagocytosis of particles injected intraperitoneally was also performed. Macrophage cultures inoculated with Latex particles served as controls. Ten minutes after inoculation with alloy particles, about 58% of the macrophages had ingested particles. EDAX-analysis indicated that the phagocytized alloy particles contained both silver and tin in the same proportions as in the original alloy. When the cultures had been inoculated for ten days, however, a marked reduction in phagocytosis was observed probably due to cytolysis of those macrophages which initially had phagocytized the alloy particles. The results indicate that, although the Ag3Sn alloy particles at all the time intervals studied were phagocytized more slowly and to a lesser extent than the Latex particles, the method could be of value in studying the biocompatibility of dental materials available in particulate form.

Animals↗
PubMed1983

In vitro thrombogenicity test of materials used in arterial prostheses. Comparison of fibrin deposition from blood on glass polystyrene and arterial prostheses.

Coagulation rates in fresh, normal, venous blood was investigated when a given volume of blood was allowed to contact various materials of equivalent surface area, at 22 degrees C, without disturbance. The coagulation rate was determined indirectly by measuring residual thrombin-clottable fibrinogen in cell-free supernatants after arresting coagulation at fixed time intervals with a Ca++-chelating type of anticoagulant and comparing the thrombin-clottable fibrinogen content of the test samples with control samples of blood anticoagulated immediately after venipuncture. In glass containers, after initial formation of the clot, progressive fibrin formation, measured by the rate of disappearance of thrombin-clottable fibrinogen, was found to take place as a gradual and linear progressive process not complete at 30 min after venipuncture with blood stored undisturbed at 22 degrees C. Various graft materials in tubular form were prepared to ensure equivalent blood surface contact. These were investigated for their influence on fibrinogen to fibrin conversion of fresh venous blood in a 15-min period at 22 degrees C. Fibrin formation was greatest in microvel pre-treated with clotting blood and decreased in the following order: microvel, woven Dacron, knitted dacron and Gore-tex. Gore-tex showed by far the least thrombogenicity of all the tested graft materials. We discuss our reasons for making our measurements under non-flow conditions and the reason for measuring fibrinogen to fibrin conversion rather than measuring platelet deposition on the various surfaces.

Arteries↗
PubMed2001

Feasibility of the use of eye movement data in the analysis of neurobehavioral test performance.

Better understanding of the functions and abilities underlying some neurobehavioral tests would assist the assessment of the consequences to the health or well-being of exposed populations for which decrements in such tests have been found. Eye movements, which can be useful in evaluating specific theories of visual and cognitive processes, were measured while a single participant completed the NES Symbol-Digit Substitution test. Relationships between the durations and the frequencies of eye fixations within different parts of the test material and overall test performance were examined. The overall pattern of eye-movement behavior observed was as predicted: fixations within three regions of visual interest were made, usually in the order lower matrix, upper matrix, keyboard. Both the upper matrix fixation latency and the number of regional fixations made per item were found to be strongly associated with overall item response latency. This suggests that speed and efficiency of searching and the ability to maintain concentration appeared to be key attributes related to test performance for this participant. For suitable tests, eye-movement data may be useful for assessing and measuring the latencies of subtask components in a real test situation. Monitoring eye movement represents an alternative methodology to using sub test composites, or factor analysis, as a means of tapping into the functions underlying neurobehavioral test performance.

Eye Movements↗
PubMed1994

Clinical testing of dental materials--histological considerations.

In order to assess the biocompatibility of dental materials, clinical studies, as well as in vitro studies, are needed. Although no bacteria were detected inside tubules, pulp reactions were observed when either adhesives of the last generation aiming to create an hybrid layer were used or restorative materials controlling the interface between the biomaterial and dental tissues. However, the reactions were feeble to moderate. Reparative dentine seldom appeared after such treatments. Differences between odontoblast and pulp cells, the nature of the lesion (necrosis or apoptosis), and differences between sound experimental and carious teeth seen in the real clinical situation are discussed in the context of in vivo human studies.

Adolescent↗
PubMedDate not supplied

Effect of long-term ovariectomy on bone mechanical properties in young female cynomolgus monkeys.

Feral adult female cynomolgus monkeys were divided into two groups: normal controls and ovariectomized. Tibiae and trabecular bones from the femoral head, from each group, were tested using a materials testing machine. The bending stiffness of the tibiae was measured by nondestructive three-point bending tests and their maximum torque capacity by destructive torsion tests. The compressive strength of the trabecular bones was measured by compression tests. Ovariectomy caused significant decreases in elastic modulus of the tibiae (p < 0.008), measured by three-point bending tests, and in shear modulus (p < 0.015), failure shear stress (p < 0.01), and failure torque (p < 0.001) of the tibiae, measured by torsion tests. It caused a significant decrease in cortical bone density (p < 0.005), but no significant changes in tibial cross-sectional area and in cortical shaft external and internal diameters. The differences in elastic modulus, maximum compressive strength, and density of femoral trabecular bone samples between the two groups were not significant.

Animals↗
PubMed2003

Biomechanical comparison between conventional and rapid expansion of skin.

This study was designed to investigate the effects of different surgical expansion regimens on the biomechanical features of expanded skin. Two hundred and forty millilitres expanders were implanted on the backs of six adult dogs. Six flaps were designed on the dorsum of each dog. After serial expansion, the expander was left beneath the skin for a certain period of time, which is called the maintaining period. Rapid expansion and conventional expansion with various maintaining periods were compared. The experimental result shows that the area gain of expanded skin surface had no significant difference between the rapid and conventional expansion. Both the tension in vivo and the instant stretch-back ratio increased during the expansion, but fell almost to control values after four weeks' maintaining period. Biomechanical properties in vitro, such as tensile strength, stress-strain, stress-relaxation, and creep were tested by INSTRON material testing machine. Results show that the biomechanical properties of expanded specimens differ significantly from those of their controls immediately after expansion. However, the difference reduces with prolongation of maintaining time. With the same maintaining period, the biomechanical properties of rapidly expanded skin are similar to conventionally expanded skin. We conclude that rapid skin expansion did not demonstrate any deleterious effect when compared with the conventional expansion. Extension of the maintaining period can improve the biomechanical properties of expanded skin and effectively reduce the stretch-back ratio. Therefore, rapid expansion with an extended maintaining period is acceptable in clinical practice.

Animals↗
PubMed1983

Differences in reaction characteristics between human and bovine-based control materials for iron determination.

Reaction rate studies were carried out on various quality control specimens using a ferrozine iron determination kit. The time required for complete color formation differed among the various materials tested. Quality control materials of bovine origin required a much longer incubation time for full color formation. Using a fixed incubation procedure, the bovine controls would give a falsely low result. The present study suggests that caution is indicated when quality control data using bovine materials are interpreted.

Animals↗
PubMed1995

Prediction of thoracic and lumbar vertebral body compressive strength: correlations with bone mineral density and vertebral region.

The bone density of thoracolumbar vertebral columns (T1 to L5) from 18 individuals was measured using quantitative computed tomography and dual energy x-ray absorptiometry. Three hundred six isolated vertebral bodies were tested in a materials test device to determine their compressive strength. Between T1 and L5 the mean segmental increase in bone mineral content was 0.3 g, while the corresponding mean decrease in trabecular density was 4.7 HU. Midvertebral body cross-sectional area increased by an average of 46 mm2 per segment and the mean segmental increase in compressive strength was 0.17 kN. Compressive strength was significantly correlated with bone mineral density measured with dual energy x-ray absorptiometry (r = 0.86). Vertebral trabecular density samples measured with quantitative computed tomography were poorly correlated with compressive strength (r = 0.28); however, this was improved when the trabecular density was multiplied by the midvertebral body cross-sectional area (r = 0.83). This study provides information concerning the relationships between density and mechanical properties of all thoracic and lumbar vertebral bodies across a wide age range. While the load-bearing capacity of the vertebral bodies is largely dependent on their geometry and bone density, this relationship has been only extensively tested for the lumbar spine. This study extends these observations over the lumbar and thoracic regions to provide a comprehensive analysis of the strength characteristics of each vertebral body. This is particularly important given the paucity of data on the thoracic spine where age-related vertebral fractures predominate. These data provide a basis for the development of models to predict the potential for thoracolumbar fractures in the elderly vertebral column.

Absorptiometry, Photon↗
PubMed1989

Toward phonetic intelligibility testing in dysarthria.

The measurement of intelligibility in dysarthric individuals is a major concern in clinical assessment and management and in research on dysarthria. The measurement objective is complicated by the fact that intelligibility is not an absolute quantity but rather a relative quantity that depends on variables such as test material, personnel, training, test procedures, and state of the speaker. This paper reviews scaling procedures and item identification tests as they have been applied to dysarthric speech. Based in part on previous studies of speech of the hearing impaired, a profile has been designed to direct research on the acoustic or physiologic correlates of dysarthric intelligibility impairment. In addition, a word intelligibility test is proposed for use with dysarthric speakers. This test is designed to examine 19 acoustic-phonetic contrasts that are likely to (a) be sensitive to dysarthric impairment and (b) contribute significantly to speech intelligibility. Preliminary data from a sample of subjects with amyotrophic lateral sclerosis are presented to illustrate the use of this test in the phonetic interpretation of intelligibility impairment.

Adult↗