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PubMed1987

A confirmatory study of the up-and-down method for acute oral toxicity testing.

Ten materials have been tested in parallel both by the "classical" method for acute oral toxicity (LD50) and by the up-and-down method. Materials tested included laundry and dishwashing detergents, a shampoo, a flavor, potassium hydroxide, and caffeine. All testing was done in Sprague-Dawley rats. Excellent agreement was seen between the two methods. The classical method typically used 40 to 50 animals while the up-and-down method required only six to nine animals per material.

Administration, Oral↗

PubMed1995

Special considerations for conducting genotoxicity tests with protein materials.

Standard genotoxicity tests are often inappropriate for testing new biological entities, in particular for recombinant proteins which are nature-identical. Arguments that these may contain mutagenic impurities are not substantiated; however, we have produced evidence that such impurities would be detected amidst a vast excess of protein. Concerns that human patients receiving therapy may be at risk from higher-than-physiological levels of proteins are also somewhat theoretical. However, it is apparent that genotoxicity testing will be required for these products for the time being, even if pragmatic approaches reduce the battery of in vitro tests to Ames and chromosomal aberrations only, and reduce the top dose in vivo to 1000x the human therapeutic dose. There is a number of physical and chemical properties of proteins that demand special approaches to methodology if the tests are to produce accurate results. The potential for adsorption to certain forms of glass and plastic means special care must be taken in dissolving and diluting test solutions; adherence to filters means special low protein binding, non-pyrogenic filters should be used for sterilisation of test solutions, where this is necessary; freeze-dried powders aliquotted in multiple vials should be dissolved in minimal solvent and cascaded from vial to vial rather than trying to empty the solid contents for bulk weighing. As proteins are often supplied in solution, in order to achieve sufficiently high test concentrations, it may be necessary to resuspend test bacteria/cells in the test solutions for short periods of time before centrifuging and resuspending in selective or growth media.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1979

Experimental fixation of bone cement and composite resins to bone.

The aim of this study was to ascertain whether the use of liquid acrylic resin or NeoCryl XK-53 acrylic emulsion or etching of the bone surface with phosphoric acid or the application of both these methods would improve the bonding of CMW bone cement or Concise and Silar composite resin to bone. The test materials were applied to fresh cortical bovine bone. Their bonding capacity was measured by the Instron Universal Testing Machine. The surfaces of the test materials and the bone surfaces were examined by means of optic microscope or scanning electron microscope. The bonding strength of the bone cement and composite resins as such were found to be of the same magnitude. A three- to five-fold improvement was obtained with liquid acrylic intermediary material. Acid etching impaired the bonding.

Acrylic Resins↗

PubMed2002

Microwave-assisted extraction of zearalenone from wheat and corn.

A microwave-assisted extraction (MAE) method has been developed for determination of zearalenone in wheat and corn by LC-MS with an atmospheric pressure chemical ionization interface (APCI). Matrix effects were minimized by use of matrix-matched standard curves for quantification of the analyte. The limit of quantification (LOQ) of the method was 30 ng g(-1) in wheat and 20 ng g(-1) in corn. The rapid LC-MS method enabled analysis of the extracts without clean-up, thereby reducing analyte losses, the time required for the analytical procedure, and costs. A factorial design approach was used to examine the effect on extraction efficiency of the main extraction conditions - time, temperature, and solvent. On the basis of results from statistical assessment extraction was performed with 1:1 (v/v) methanol-acetonitrile at 80 degrees C for 5 min. When these extraction conditions were applied to a wheat sample from a recently conducted international proficiency test, 92% (103 ng g(-1)) of the assigned zearalenone concentration (112 ng g(-1)) in the test material was obtained. This result was within the uncertainty (u) range of the assigned value of the test material (u=+/-15.8 ng g(-1), alpha=0.05) thereby demonstrating the accuracy of the method was sufficient. The precision of the whole method was also confirmed to be adequate, because the observed relative standard deviation (RSD) of 12% (n=10) also fulfils the quality criteria recommended by European guidelines for in-house method validation.

Chromatography, High Pressure Liquid↗

PubMed2002

Cochlear implants for children with significant residual hearing.

BACKGROUND: Previous research suggests that children with pure-tone averages of greater than 90 dB hearing level and/or open-set sentence perception of less than 30% may derive significant benefit from cochlear implantation. OBJECTIVE: To evaluate postoperative speech perception benefit and bilateral-bimodal benefit for 16 children whose preimplant speech perception scores exceeded conservative candidacy guidelines. STUDY DESIGN: Preimplant and postimplant repeated-measure design. METHODS: Sixteen child subjects who obtained 30% or greater on preimplant open-set sentence material, presented live voice audition alone, were selected for this study. Preimplant pure-tone averages ranged from 73 to 110 dB in the better aided ear. Preimplant and postimplant open-set word and sentence testing was completed in quiet and with competing background noise for separate ear and binaural conditions. RESULTS: Fourteen of 16 subjects had improved speech perception scores across all test materials after implantation. Group means were significantly higher for all test materials. Results in the bimodal-bilateral condition were significantly higher than implant alone for open-set word tests (scored for phonemes) and open-set sentences in quiet. CONCLUSION: The results of this study suggest that, with appropriate counseling and management, some children with significant residual hearing benefit from cochlear implantation, in particular improved speech understanding due to bimodal-bilateral hearing.

Adolescent↗

PubMedDate not supplied

Enhancing the predictive validity of Frog Embryo Teratogenesis Assay--Xenopus (FETAX).

Frog Embryo Teratogenesis Assay-Xenopus (FETAX) is a 4-day, alternative developmental toxicity assay designed to pre-screen chemicals and environmental mixtures. An approach used in the scoring of FETAX results, which focuses on the determination of characteristic abnormalities induced by a given test material, was used to evaluate results from previous validation efforts. Characteristic abnormalities are induced specifically by exposure to a given test material and are determined by the relationship between concentration and the response induced and the change in severity of response. Use of this approach eliminates non-specific effects that alter numerical endpoints, reduces intralaboratory variability, reduces the number of equivocal test results (gray area), helps to determine specific syndromes associated with teratogen exposure and, in some instances, increases the predictability of FETAX. In an effort to evaluate this approach, a 12-compound validation study that produced a relatively high degree of equivocal FETAX results was re-evaluated using the characteristic malformation criteria. Data were evaluated for repeatability, predictability and variability. Results from this study indicated that this scoring approach increased repeatability, test endpoint precision and predictability.

Abnormalities, Drug-Induced↗

PubMed1994

[Preliminary evaluation of biological-sanitary contamination of grass lawns and children's playgrounds in Warsaw in 1991].

This paper presents results of microbiological investigations of grass lawns and sand playgrounds in selected parks, Jordan gardens, squares, large inhabited complexes, creches and kindergartens on the territory of four parts of Warsaw (Zoliborz, Saska Kepa, Sródmieście and Mokotów). Following indexes were subjected to analysis: titer of bacteria from the coli group of general and fecal type, bacteria from the genus Clostridium and Salmonella and number of bacteria from Enterococcus species. In sanitary evaluation of tested material criteria proposed by National Institute of Hygiene (1970) and Institute of Rural Medicine (1990) were applied. Among tested materials, 50% of grass lawns and 40% of sand playgrounds were considered as unsanitary and dangerous (disqualified by all indexes). It was found that presence of Salmonella in all cases was connected with existence of large numbers of other members of Enterobacteriaceae family (10(3)-10(5) CFU/Ig.s soil) and of E. faecalis (10(2)-10(3) CFU/Ig. s. soil). Identified bacteria from genus Salmonella were most frequently represented by S. arizonae (90%) S. choleraesuis and other (10%). Comparison of own results with data obtained by Warsaw Sanitary-Epidemiological Station from previous years indicates worsening of sanitary status of green lawns and sand playgrounds in Warsaw City aglomeration. Continuously present high numbers of bacteria of sand playgrounds in kindergartens and creches is disturbing. In this situation there is an urgent need of systematic sanitary investigations of soil in natural conditions on territories a large agglomerations for determination of size of danger of contamination and preoparation of appropriate prevention.

Bacteria↗

PubMed1983

Dose selection as it pertains to testing a prodrug in carcinogenicity bioassays.

Toxicologists need more information than is usually available in the early stages of development of a drug in order to choose proper dose levels for testing in the bioassays. The approach most likely to result in successful bioassays involves an early multidisciplinary effort in which there is pharmacokinetic characterization of the test material in both rats and mice. Preliminary 3 month studies are desirable. Periodic sampling of plasma is essential to detect possible non-linear kinetics (as in the example we report herein) reflected as accumulation of the test material or metabolites. This is true regardless of the test substance. However, if one tests prodrugs it may be particularly helpful to know if chemical or enzymatic conversion of the prodrug is linear and if there is reversion to prodrug or other abberant metabolism. Failure to rule out these possibilities could result in subsequent clinically irrelevant organ damage or could compromise longevity or the interpretation of results in lifetime studies. Pharmacokinetic considerations are as valid as the more traditional biologic or morphologic end points used to estimate maximum tolerated or no-effect dose levels.

Animals↗

PubMed2006

Comparison of temperature increase in the pulp chamber during the polymerization of materials used for the direct fabrication of provisional restorations.

STATEMENT OF PROBLEM: Polymerization of resin materials used for the fabrication of provisional restorations is associated with an exothermic reaction. This temperature rise may present a serious biological problem, since it can cause iatrogenic thermal trauma to the pulp. PURPOSE: This in vitro study compared the temperature increase in the pulp chamber of a molar placed in contact with different resins used for the direct fabrication of provisional restorations. MATERIAL AND METHODS: Polymethyl methacrylate (Jet), polyethyl methacrylate (Snap), polyvinylethyl methacrylate (Trim), Bis-acrylic composite (Protemp II), and a VLP urethane dimethacrylate (Revotec LC) were compared with respect to their exothermic reaction properties during polymerization. A mandibular molar prepared for a complete coverage restoration was placed in an acrylic resin block. A thermal probe connected to a digital thermometer was placed into the pulp chamber. Specimens were submerged in a water bath to simulate intraoral conditions. The provisional resin materials tested were measured and mixed according to manufacturer's instructions. The resin mixture was placed into a vacuum-formed acetate template and was then positioned on the prepared molar tooth. The temperature was recorded during polymerization at 30-second intervals until it was evident that the peak temperature had been reached. Temperature increase was measured ( degrees C) for both the initial crown fabrication and the reline procedures. Data were analyzed with descriptive statistics, 1-way analysis of variance, and Tukey Honestly Significant Difference tests (alpha=.05). RESULTS: One-way ANOVA revealed significant differences (F=57.010, P<.0001) in temperature rise for different provisional resin materials. Mean temperature increase for the provisional crown fabrication ranged from 37.76 degrees C for the polyvinylethyl methacrylate to 39.40 degrees C for the polymethyl methacrylate. Mean temperature rise for the reline procedures ranged from 36.80 degrees C for the polyvinylethyl methacrylate to 37.69 degrees C for the polymethyl methacrylate. All of the tested materials produced an exothermic chemical reaction. CONCLUSIONS: Polymethyl methacrylate produced the higher exothermic reaction in both initial crown fabrication and reline procedures. Polyethyl methacrylate, polyvinylethyl methacrylate, and Bis-acrylic resins tested were not significantly different from each other.

Acrylic Resins↗

PubMed1992

Determination of doughing and manipulation times of acrylic resin denture base material and a proposal for a specification for a packing plasticity test.

The doughing and manipulation times of a range of acrylic resin denture base polymers are presented in this study. The methods evaluated were: (i) probing following American Society for testing materials specification, F451-76; (ii) hole penetration following British Standard, 2487: 1989 and International Standard Organisation, 1567: 1988; (iii) probing using a penetrometer employing a 20 g load and 1 mm diameter needle; (iv) oscillating rheometer apparatus used at a fixed frequency of 1 Hz by sweeping through a programmed linear increase in strain. The results indicate that each of the methods is capable of evaluating the doughing and manipulation times of the unprocessed polymers. It is concluded that the Bohlin VOR Oscillating Rheometer is excellent for investigating the flow properties of denture base polymers but it cannot be recommended for a standards specification test because of the high cost. The penetrometer method has been shown to be superior to the current standards specification test and would be ideal for a packing plasticity standards test.

Denture Bases↗

PubMed1979

Updated in vivo methods for evaluating topical antimicrobial agents on human skin.

Updated and expanded in vivo quantitative testing procedures to determine the efficacy of topical antimicrobial agents are presented. The occlusion test measures the ability of an agent to prevent the expansion of the resident microflora which occurs when an impermeable dressing is applied to the forearm. Measurements are made at 24 and 48 hr. The expanded flora test measures the ability of an agent to suppress a dense population of micro-organisms produced by expansion of the resident flora of the forearm by prior application of an impermeable occlusive dressing. Measurements are made at 6, 24 and 48 hr or after 10 min in the case for agents designed for immediate degerming. The persistence test measures the ability of an agent to establish a reservoir in skin and exert an antimicrobial effect up to 3 days after the last application of the test material. The ecological shift test determines any major alteration in cutaneous microbial ecology following several applications of the material under occlusive dressings. The serum inactivation test determines whether the presence of serum proteins interferes with antimicrobial activity.

Adult↗

PubMedDate not supplied

Effect of fluoride-releasing filling materials on underlying dentinal lesions in vitro.

Fluoride-releasing materials placed over carious tissue are assumed to enhance remineralisation of the underlying lesion. This remineralisation, however, also depends on the availability of calcium and phosphate, which may be supplied by the pulpal fluid. The aim of this study was to measure the fluoride release of glass ionomer cements (GICs) into underlying dentin and to measure the effect of the released fluoride on the remineralisation of the underlying dentinal lesions using transversal microradiography. Discs of fluoride-releasing GIC were placed on top of dentinal lesions in an in vitro model. The discs and the dentin slabs were covered completely by a protective layer of nail varnish, leaving only the pulpal side of the dentin slab open, and hence the dentinal tubules as the pathway for the incubation fluid to the GIC disc. Specimens were incubated in a remineralisation buffer. The materials tested were a conventional GIC, an experimental GIC that was designed to have a high fluoride release, and an inert material. Fluoride was found to penetrate through the dentin slab into the surrounding fluid. Fluoride uptake from the experimental GIC was higher than from the conventional GIC. Mineral content-depth profiles after 10 weeks' remineralisation revealed that in the outer 30 microm of the lesion a higher mineral deposition occurred for the experimental GIC than in both other groups. No differences in the overall change of integrated mineral loss were found for the tested materials. We conclude that high fluoride release from filling materials only results in superficially increased remineralisation of underlying demineralised dentin.

Analysis of Variance↗

PubMed2000

Tooth slice organ culture for cytotoxicity assessment of dental materials.

The purpose of this work was to develop a tooth slice organ culture method to assess the response of the cells of the dental pulp to commonly used dental materials and products. Wistar rat tooth slices were grown in culture for two and ten days in the presence of dental materials. After culture, the tooth tissues were processed and the responses of the pulpal cells were analysed histomorphometrically. Cytotoxic cell destruction was observed following the direct application of test materials to tooth slices (n = 298) after 10 days in culture (MANOVA, P = 0.0001), whilst the restoration of prepared deep dentine cavities (n = 30), with test products, did not result in a significant amount of pulpal injury (MANOVA, P = 0.287). In rank order of causing pulpal injury, the test materials from the most to the least cell destructive, was; Salicylic acid. Calcium hydroxide, Kalzinol zinc oxide eugenol, high-mercury Amalgam, Prime & Bond, Dycal, Barium sulphate, Hypocal, Scotchbond, Calasept, Life and One-step. Tooth slice organ culture, provided a cytotoxicity screening method for dental materials, bearing a closer physiological resemblance to the clinical situation than cell culture screening methods. Tooth slice culturing may have the potential to replace some types of in vivo animal experimentation, as there is a clear need to reduce this form of testing.

Animals↗

PubMed1986

Investigation of the potential carcinogenicity of a range of chromium containing materials on rat lung.

Twenty one chromium containing materials were examined for carcinogenic activity in a two year study using an intrabronchial pellet implantation system whereby pellets loaded with test material were surgically implanted into the lower left bronchus of rats. The principal aim of the study was to extend our knowledge of the carcinogenic potential of chromium compounds and, in particular, chromates (Cr6+). A statistically significant incidence of treatment related lung tumours was found with some sparingly soluble chromate materials. All tumours were large keratinizing squamous carcinomas of the left lung, except for a single left lung adenocarcinoma and two left lung anaplastic carcinomas. No bronchial carcinomas (0/100) were seen in the negative control group (blank pellet loaded with cholesterol), whereas bronchial carcinomas (22/48 and 25/100) occurred in the two positive control groups which received pellets loaded with 20-methylcholanthrene and calcium chromate respectively. Among the 20 test materials, only three groups gave statistically significant numbers of bronchial carcinomas. Two of these were groups receiving different samples of strontium chromate which gave 43/99 and 62/99 tumours. The third group, zinc chromate (low solubility), gave 5/100 bronchial carcinomas. A further zinc chromate group (Norge composition) produced 3/100 bronchial carcinomas which was not statistically significant. A few lung tumours were observed in other test groups.

Animals↗

PubMed1976

Accuracy of six elastic impression materials used for complete-arch fixed partial dentures.

1. The accuracy of four types of impression materials used to make a complete-arch fixed partial denture was evaluated by visual comparison and indirect measurement methods. 2. None of the tested materials allows safe finishing of a complete-arch fixed partial denture on a cast poured from one single master impression. 3. All of the tested materials can be used for impressions for a complete-arch fixed partial denture provided it is not finished on one single cast. Errors can be avoided by making a new impression with the fitted castings in place. Assembly and soldering should be done on the second cast. 4. In making the master fixed partial denture for this study, inaccurate soldering was a problem that was overcome with the use of epoxy glue. Hence, soldering seems to be a major source of inaccuracy for every fixed partial denture.

Dental Impression Materials↗

PubMed2004

The performance-perceptual test and its relationship to unaided reported handicap.

OBJECTIVE: Measurement of hearing aid outcomes is necessary for demonstration of treatment efficacy, third-party payment, and cost-benefit analysis. Outcomes are usually measured with hearing-related questionnaires and/or tests of speech recognition. However, results from these two types of test often conflict. In this paper, we provide data from a new test measure, known as the Performance-Perceptual Test (PPT), in which subjective and performance aspects of hearing in noise are measured using the same test materials and procedures. A Performance Speech Reception Threshold (SRTN) and a Perceptual SRTN are measured using the Hearing In Noise Test materials and adaptive procedure. A third variable, the discrepancy between these two SRTNs, is also computed. It measures the accuracy with which subjects assess their own hearing ability and is referred to as the Performance-Perceptual Discrepancy (PPDIS). DESIGN: One hundred seven subjects between 24 and 83 yr of age took part. Thirty-three subjects had normal hearing, while the remaining seventy-four had symmetrical sensorineural hearing loss. Of the subjects with impaired hearing, 24 wore hearing aids and 50 did not. All subjects underwent routine audiological examination and completed the PPT and the Hearing Handicap Inventory for the Elderly/Adults on two occasions, between 1 and 2 wk apart. The PPT was conducted for unaided listening with the masker level set to 50, 65, and 80 dB SPL. RESULTS: PPT data show that the subjects with normal hearing have significantly better Performance and Perceptual SRTNs at each test level than the subjects with impaired hearing but that PPDIS values do not differ between the groups. Test-retest reliability for the PPT is excellent (r-values > 0.93 for all conditions). Stepwise multiple regression analysis showed that the Performance SRTN, the PPDIS, and age explain 40% of the variance in reported handicap (Hearing Handicap Inventory for the Elderly/Adults scores). More specifically, poorer performance, underestimation of hearing ability and younger age result in greater reported handicap, and vice versa. CONCLUSION: Reported handicap consists of a performance component and a (mis)perception component, as measured by the Performance SRTN and the PPDIS respectively. The PPT should thus prove to be a valuable tool for better understanding why some individuals complain of hearing difficulties but have only a mild hearing loss or conversely report few difficulties in the presence of substantial impairment. The measure would thus seem to provide both an explanation and a counseling tool for patients for whom there is a mismatch between reported and measured hearing difficulties.

Adult↗

PubMed1991

In vitro interaction between primary bone organ cultures, glass-ionomer cements and hydroxyapatite/tricalcium phosphate ceramics.

Primary organ cultures derived from neonate rat calvaria were maintained for 2 wk and used to study in vitro response of osteoblast and periosteal cells to the component and composite forms of three different glass-ionomer (polyalkenoic) cements, comparing them to densely sintered hydroxyapatite and tricalcium phosphate ceramics. Qualitative analysis by scanning and transmission electron microscopy revealed that osteoblasts colonized all the solid test materials, although there was a less favourable response to materials with a rough surface topography and to unset and fluoride-containing glasses. On solid materials migrated cells maintained their tessellated morphology and exhibited numerous micro-appendages anchoring them to the surface of the test materials. A collagen-containing extracellular matrix was elaborated on to the ceramics and set glass-ionomer cements, except for one (AquaCem). Mineralization of the extracellular matrix was seen adjacent to hydroxyapatite and tricalcium phosphate ceramics, that adjacent to the latter morphologically resembling bone.

Animals↗