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PubMed1975

The development of an abrasion testing machine for dental materials.

Wear testing should be an important part of the investigation into the physical and mechanical properties of some dental materials. It has, however, largely been ignored because of conflicting and unreproducible results. It was decided, therefore, to review the work done by other researchers and to examine the human masticatory cycle, and then present new parameters to design and construct a new dental abrasion testing machine. This new machine is described in detail and its capabilities briefly illustrated.

Dental Materials↗
PubMed2002

Shearing a glassy material: numerical tests of nonequilibrium mode-coupling approaches and experimental proposals.

The predictions of a nonequilibrium schematic mode-coupling theory developed to describe the nonlinear rheology of soft glassy materials have been numerically tested in a sheared binary Lennard-Jones mixture. In this Letter, we focus on the existence, behavior, and properties of an effective temperature T(eff) for the slow modes of the fluid, as defined from a generalized fluctuation-dissipation theorem. New, simple experimental protocols to access T(eff) are proposed, and one such experiment is numerically performed. Our results give strong support to the thermodynamic interpretation of T(eff) and make it experimentally accessible in a very direct way.

Journal Article↗
PubMed1996

Radiopacity of resin-modified glass-ionomer restorative cements.

This in vitro study compared the relative radiopacities of three commercially available resin-modified glass-ionomer cements (Vitremer, Fuji II LC, and Photac-Fil), an experimental resin-modified glass-ionomer (V-66), two conventional glass-ionomers (ChemFil and Fuji Cap II), and amalgam (as the control). Radiopacity was assessed densitometrically and expressed as equivalent thicknesses of aluminum. All the glass-ionomer cements were more radiopaque than enamel and dentin, with the exception of ChemFil and Photac-Fil. Apart from the control material, the experimental resin-modified glass-ionomer material, V-66, had the highest radiopacity of all the materials tested. Of the three resin-modified glass-ionomer materials tested, Fuji II LC was the most radiopaque and Photac-Fil the least. For the radiopacity of restorative glass-ionomer materials to exceed that of enamel, it should be greater than 1.5 mm of equivalent thickness of aluminum.

Absorptiometry, Photon↗
PubMed1985

Fourier transform infra-red spectroscopy applied to hazardous waste: I--Preliminary test of material analysis for improvement of personal protection strategies.

Many chemicals, when mixed, can produce potentially hazardous effects which are harmful to human health and to the environment such as heat, pressure, fire, explosion, violent reaction, and toxic dusts, mists, fumes, and/or gases. Waste chemicals handled on a remedial action site are analyzed by simple chemical methods for compatibility. Because it is difficult to base worker and community protection programs on this limited knowledge of material content, extreme precautions must be taken to ensure safety to all working on or living near hazardous waste remedial action sites. The approach used in this study involved the application of Fourier transform infra-red spectroscopy (FTIR) to the analysis of samples taken from the Chem-Dyne remedial action hazardous waste site. The data generated are compared to the results obtained using compatibility and GC-MS analysis procedures. Illustrations are given of improved personal protection strategies, based on drum material composition obtainable by FTIR. The requirements for further testing are defined.

Environmental Exposure↗
PubMedDate not supplied

Effects of age on human cumulative irritation responses.

A 10-day cumulative irritation test was conducted to evaluate whether or not test subjects 65 years of age and older would rank eleven test materials the same as subjects 18 to 45 years of age The test materials consisted of mild to moderately irritating chemicals. The test articles were ranked similarly for both groups of subjects. Statistical analysis indicated no significant difference between the groups of subjects. Thus older subjects should not necessarily be excluded in comparative studies of irritancy.

Adult↗
PubMed2004

A SEM evaluation of a 6% hydrogen peroxide tooth whitening gel on dental materials in vitro.

OBJECTIVES: The aim of this study was to evaluate the effects of a novel 6% hydrogen peroxide gel on the surface morphology of dental gold, amalgam, porcelain and composite. METHODS: Admixed high-copper amalgam and hybrid resin composite specimens were prepared in extracted teeth using standard clinical procedures. Feldspathic porcelain and type III gold specimens were prepared in a mould using standard laboratory procedures. One half of the specimens were covered with nail varnish to serve as the control side, leaving the other half exposed. The specimens were treated with pooled whole saliva (1 h), followed by the peroxide gel (20 min), rinsing with water and returning to saliva. This cycling protocol was continued until a total of 28 treatments with the peroxide gel were completed. The samples were prepared for SEM. RESULTS: There were no observable differences at 200x and 2000x magnifications between the control and peroxide gel treated sides on any of the materials tested. CONCLUSIONS: There were no significant effects of the 6% hydrogen peroxide gel on the surface morphology of any of the dental materials tested.

Aluminum Silicates↗
PubMed1982

Ocular irritancy responses to various pHs of acids and bases with and without irrigation.

Acids and alkalies were instilled into the eyes of 2 groups of rabbits; the eyes of one group were washed with tap water 30 s after exposure. Damage seen in washed and unwashed eyes was not always related to pH. Some strong acids with greater acidity than pH 2.5 produced opacities while 0.3% hydrochloric acid with a pH of 1.28 produced no ocular damage. Phenol (5%) and acetic acid (5%) with pHs greater than 2.5 produced damage equivalent to or greater than that produced by equal concentrations (w/v) of the mineral acids. All alkalies with pHs ranging from 11.5 to 13.5 produced opacities and other ocular damage of different degrees depending upon the alkali and its concentration. For example, low concentrations of some alkalies in the pH range from 11.3 to 12.8 produced no ocular changes. The duration of the corneal opacities produced by phenol, 1% sodium hydroxide, acetic acid and anhydrous sodium carbonate and the onset of corneal opacity produced by 5% sulfuric acid, the weak acids and 1% sodium hydroxide were reduced as a result of washing the test eyes 30 s after instillation of the test material. These data suggest that acidity and alkalinity of the test material are not the only factors to be considered in relation to a substances' capacity to produce severe ocular injury. The concentration of the test chemical and its period of contact with the eye prior to washing are also important.

Acids↗
PubMed1976

Cell-mediated immune response to products of Actinomyces viscosus cultures.

Hartley strain guinea pigs were sensitized with 0.5 ml of concentrated cell-free Actinomyces viscosus culture supernatant fluids mixed with Freund complete adjuvant. Fourteen to 16 days later the animals were challenged by intradermal injection with 0.1 ml of the culture supernatant, and the reactions were observed at 4, 8, 16, 24, and 48 h. Peritoneal exudate cells from sensitized animals were used for determination of migration inhibition factor, and guinea pig peripheral blood served as a source of cells for determining the induction of mitogenesis by antigenic material. Skin responses were consistently positive to challenge with the test material, whereas reactions to noninoculated culture medium were negative. Sensitized cells, challenged with antigen, resulted in 60% or greater inhibition of migration of indicator cells in migration inhibition factor experiments. Tests for mitogenesis showed a greater than fourfold increase in isotope uptake when sensitized cells were challenged with test material. The data are consistent with the suggestion that A. viscosus culture supernatants contain substances that induce cell-mediated immune responses in guinea pigs.

Actinomyces↗
PubMed1997

Flouride release from various restorative materials.

Fluoride release from six light-activated restorative materials, including two resinmodified glass-ionomers, two composites, and two compomers, was evaluated and compared with one conventional acid-based glass-ionomer cement. The amount and rate of release varied among the tested materials. Both resin-modified glass-ionomers and the conventional acid-base glass-ionomer cements released more fluoride then the composites and compomers (p < 0.05). Additionally, composite materials released less fluoride than compomer materials (p < 0.05). Release of fluoride by the tested materials showed a significant decrease after all the tested time intervals.

Acrylic Resins↗
PubMed2003

Effectiveness of dentine bonding agents against cariogenic bacteria in vitro: a comparison of two methods.

Data obtained from studies on the antimicrobial properties of bonding agents are the subject of controversy, probably because of methodological differences. This study compared two commonly used in vitro methods, the disc agar diffusion test and the well agar diffusion test. Agar plates were seeded with Streptococcus sobrinus, Lactobacillus gasseri, or Actinomyces naeslundii. For the well diffusion test, wells cut out of the agar were filled with the test material, and for the disc method, discs impregnated with the test material were applied to the agar; the discs and wells were both 9 mm in diameter. After incubation, measurements of the zones of inhibition showed little agreement between the two methods when bonding agents were tested; the mean differences (+/- sdiff) in the zones of inhibition between the methods were 0.7 +/- 3.4 mm (P = 0.40, one sample t-test against zero), 4.9 +/- 4.4 mm (P = 0.97), and 0.8 +/- 4.3 mm (P = 0.47) for S. sobrinus, L. gasseri, and A. naeslundii, respectively. Mean differences were less contrasting when chlorhexidine and pure components were tested (P < 0.05 for S. sobrinus and L. gasseri). These results indicate the need for a gold standard method to evaluate the antimicrobial properties of bonding agents.

Actinomyces↗
PubMed2001

Color stability of provisional restorative materials after accelerated aging.

PURPOSE: Color of 11 provisional restorative materials (4 acrylic resins and 7 resin composites) was evaluated by reflection spectrophotometry immediately after fabrication, after aging for 15 kJ/m(2), and after aging for 60 kJ/m(2) to determine relative color stability under experimental aging conditions. MATERIALS AND METHODS: Specimens of provisional restorative materials were polymerized according to manufacturers' instructions and aged in an artificial aging chamber with exposure to a total ultraviolet irradiation of 60 kJ/m(2) in increments of 15 kJ/m(2). Color was measured by CIE L*a*b* on a reflection spectrophotometer before and after aging. Color change (Delta E*) was calculated and analyzed statistically by analysis of variance with repeated measures after 15 and 60 kJ/m(2) intervals of aging. RESULTS: Statistically significant changes in color were observed after accelerated aging at both the initial and final aging intervals. Five of the 11 provisional materials tested showed perceptible color change (Delta E* from 3.6 to 9.3) after accelerated aging of 15 kJ/m(2). Seven of the 11 provisional materials tested showed perceptible color change (Delta E* from 3.4 to 9.4) after accelerated aging of 60 kJ/m(2). CONCLUSIONS: Clinically perceptible color changes (Delta E* Delta 3.3) can be expected in some acrylic resin and composite resin provisional materials after accelerated aging.

Acrylic Resins↗
PubMed1987

Microbiological evaluation of drinking water construction materials--comparison of two test procedures.

Materials used in contact with drinking water can impair water quality by supporting the growth of aquatic microorganisms. In order to prevent this problem several different test procedures have been developed but to date no comparative study of the performance of these methods has been published. During collaborative studies between the regional laboratories of the Thames Water Authority, London, and the Institute of Hygiene, University Bonn, duplicate samples of 11 PVC materials were exchanged and evaluated by the standard methods used in the United Kingdom (UK) and the Federal Republic of Germany (FRG). There was a good agreement between the results as assessed by the published criteria. When a stricter criterion for interpreting the results of the UK method was applied to the findings, a complete agreement between the methods was observed.

Bacteria↗
PubMed1993

Effect of salivary films on the surface properties of elastomeric impression materials.

Impression materials exposed to the oral cavity are subjected to spontaneous adsorption of salivary films. The aim of this study was to evaluate the effect of adsorbed salivary films on some surface properties of one condensation, four addition silicone and one polyether impression materials. The results showed that adsorbed salivary films caused an increase in the critical surface tension and in the polarity ratios for all materials tested. A reduction in the number of voids in die stone casts was also noticed, along with an improvement in the gypsum compatibility with the impression materials tested. It can be concluded that the presence and effect of salivary films should be taken into consideration when studying the surface properties of elastomeric impression materials.

Calcium Sulfate↗
PubMedDate not supplied

Results of the L5178Y mouse lymphoma assay and the Balb/3t3 cell in vitro transformation assay for eight phthalate esters.

Eight phthalate esters, with alcohol chain lengths of 1-11 carbon atoms and with various degrees of branching, were tested in vitro in the L5178Y mouse lymphoma mammalian cell mutation assay and in the Balb/3T3 cell transformation assay. The tests were performed as part of a voluntary testing agreement between the Chemical Manufacturers Association's Phthalate Esters Panel and the United States Environmental Protection Agency (US EPA). The esters tested were: dimethyl phthalate (DMP), di-n-butyl phthalate (DBP), butyl benzyl phthalate (BBP), di-¿n-hexyl, n-octyl, n-decyl¿ phthalate (610P), di-isononyl phthalate (DINP), di-¿heptyl, nonyl, undecyl¿ phthalate (711P), di-isodecyl phthalate (DIDP) and di-undecyl phthalate (DUP). Both DMP and DBP were found to produce significant increases in the mutant frequency in the mouse lymphoma assay in the presence but not in the absence of an Aroclor-induced rat liver activation system (S-9). Ester 610P gave equivocal results in the mouse lymphoma assay in the presence and absence of rat liver S-9. There was no indication of mutagenic potential for any of the other test materials in the mouse lymphoma assay, and none of the test materials increased transformation frequency in the Balb/3T3 cell transformation assay. Aldehyde metabolites of the de-esterified alcohols are postulated to play a role in the positive results for DMP and DBP.

3T3 Cells↗
PubMed1993

Hardness and Young's modulus determined by nanoindentation technique of filler particles of dental restorative materials compared with human enamel.

The recently developed nanoindentation technique was used to measure hardness and Young's modulus of small filler particles in resin composites and other dental restoratives. This technique eliminates the need to visualize indentations. Load and displacement are continuously monitored during a loading-unloading sequence, and hardness as well as Young's modulus are then calculated from the load-displacement curves taking into account the geometry of the indenter. Thirteen posterior composites, 3 dental ceramics for CAD/CAM restorations, 1 sintered porcelain, and 1 amalgam were investigated in this study. The results were compared to the hardness and Young's modulus determined by nanoindentation of human enamel. Of the dental materials tested, only five materials contain inorganic filler particles with a nanohardness not statistically different from that of enamel. The predominant fillers in all other materials, except amalgam and the prepolymerized resin fillers in Bell Firm PX, were found to be significantly harder. The dental restorative materials, except the alloy phase in amalgam, were composed of particles with a Young's modulus significantly lower than that of human enamel. The alloy phase in amalgam had a Young's modulus value comparable to that of enamel.

Dental Amalgam↗
PubMed1993

Use of ophthalmic topical anaesthetics.

Pretreatment of the eyes of rabbits with a topical anaesthetic can be viewed as a refinement of the test for eye irritation. It reduces pain at the time of test-material administration, decreases animal distress and permits easier application of the test agent to the eye. In some cases, however, use of an anaesthetic either alone or in combination with the test substance may alter ocular responses or provide little benefit. Although anaesthetic pretreatment may result in decreased pain at the time of test-compound administration, it does not affect possible pain after the effects of the anaesthetic have dissipated. Some anaesthetics are themselves irritating to eyes. In addition, anaesthetics reduce blinking and tearing, thereby maintaining the test-material concentration at the surface of the eye longer. Corneal permeability may also be increased with pretreatment use of an anaesthetic, and may bring the test agent into contact with more structures of the eye. Some anaesthetics delay healing after ocular injury. All of these varied effects may result in increased irritation to the eye. Overall, pretreatment with anaesthetics has usually resulted in a tendency for slightly higher irritation scores; eye irritancy classification is usually unaffected.

Anesthetics, Local↗
PubMed1983

Comparative effects of chitosan and cholestyramine on lymphatic absorption of lipids in the rat.

The effects of chitosan and cholestyramine on intestinal absorption of oleic acid and cholesterol were assessed in adult male rats with cannulae in the thoracic duct lymphatic channel. In acute studies, 50 mg of either cholestyramine or chitosan were included in the test emulsion for intragastric administration. Over a 24-h lymph collection period, cholestyramine caused a 47% depression of cholesterol absorption and a 32% interference with oleic acid absorption. Chitosan had a similar effect on the absorption of both lipids under these conditions (51 and 41% depression, respectively). Studies were also conducted in animals fed for 4 wk on defined diets containing 1 and 5% levels of the test materials. Absorption of lipids from the standard aqueous emulsion was tested in lymph duct cannulated rats which had been fasted overnight. In these animals, prefeeding either cholestyramine or chitosan at the 1% level caused an 18 to 28% reduction in absorption of both lipids with greater variability in the chitosan-fed group. When either test material was fed at the 5% level, absorption of cholesterol was reduced by 63 to 69% and absorption of oleic acid by 58 to 62%. Although these agents may act by different mechanisms, the data suggest that chitosan is as effective as cholestyramine in its acute effects on lipid absorption and that, with chronic feeding, both materials cause equivalent adaptive changes in intestinal transport of administered fatty acid and cholesterol.

Animals↗