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PubMed1993

[Epicutaneous testing (patch testing)].

At present, patch testing is the only practical way of diagnosing allergic contact dermatitis, manifested as delayed hypersensitivity (type IV reaction). It can serve to confirm relevant allergens, but may also help to exclude suspected contact sensitivity. The test procedure varies somewhat from one clinic to another but has been standardized by the International Contact Dermatitis Research Group. Choice of test materials and their application may appear simple, but test readings and interpretation of results are most important. Positive reactions can be positive (allergic) or false positive (irritant), and relevant or not relevant to an existing or previous dermatitis. The dermatologist is the person best qualified to diagnose contact dermatitis by this test procedure.

Dermatitis, Allergic Contact↗

PubMed1989

[Usefulness of collagen gel matrix culture for biological evaluation of dental materials (in vitro)].

Cytotoxicity of zinc oxide-eugenol cement was investigated using collagen gel matrix culture. Diffusibility of the main components into the collagen gel was measured by either atomic absorption or ultraviolet spectroscopy. The agar overlay culture method was also carried out for comparison. Results from solution cultures containing diluted collagen were similar to those with diluted agar. Longer culture with either cement liquid, eugenol, or zinc chloride solution, resulted in more depressed cell growth. The lower the powder/liquid ratio for mixing, the higher the cytotoxicity for all the materials tested in gelled collagen. Also, cytotoxicity levels were always lower in cultures with collagen than in those with agar. Diffusibility of the materials into collagen gel was similar to that into agar, but the of diffused components in collagen gel was less. Thus, the usefulness of collagen gel matrix culture for biological evaluation of dental materials was equivalent to that of agar overlay culture. However, it is suggested that collagen as a tissue matrix might provide a favorable environment for cell culture, and hence allow biocompatibility testing of biomaterials under simulated conditions.

Agar↗

PubMed2006

Viscoelastic material model for the temporomandibular joint disc derived from dynamic shear tests or strain-relaxation tests.

Viscoelastic material models for the temporomandibular joint disc, based upon strain relaxation, were considered to underestimate energy absorption for loads with time constants beyond the relaxation time. Therefore, the applicability of a material model that takes the viscous behavior at a wide range of frequencies into account was assessed. To that purpose a non-linear multi-mode Maxwell model was tested in cyclic large-strain compression tests. Its material constants were approximated from dynamic small-strain shear deformation tests. The storage and loss moduli as obtained from a disc sample could be approximated with a four-mode Maxwell model. In simulated large-strain compression tests it behaved similarly as observed from the experimental tests. The underestimation of energy dissipation, as obtained from a single-mode Maxwell model was considerably reduced, especially for deformations with a higher strain rate. Furthermore, in contrast to the latter it was able to predict the increase of the stress amplitude with the compression frequency much better. In conclusion, the applied four-mode Maxwell model, based upon dynamic shear tests, was considered more suitable to predict higher frequency viscoelastic response, for instance during shock absorption, than a model based upon strain-relaxation.

Animals↗

PubMed1993

The performance of specialized collections of bisphenol A epoxy resin system components in the evaluation of workers in an occupational health clinic population.

Epoxy resin of the bisphenol A type (ERBA) is a common cause of occupational contact dermatitis. 167 patients with a history of potential exposure were patch tested with epoxy resin (molecular weight 340) (ERBAM) 1% in pet. and with a number of other ingredients in ERBA systems. 18% of the test patients exhibited a positive response to ERBAM. Phenyl glycidyl ether was the most frequent system component other than ERBAM itself to elicit a positive response (6.1%). Approximately 80% of those tested were unresponsive to ERBAM or any other of the system components, while 20% exhibited a positive response to one or more of the test materials. Only a small % were positive to system materials, but negative to ERBAM, in keeping with previous studies. The study suggests that there is a marginal benefit to testing with other than ERBAM 1%, except in instances where there is known exposure to another ERBA system ingredient, in which event, the patient should also be tested with the specific material to which they have been exposed if there is no response to ERBAM.

Benzhydryl Compounds↗

PubMedDate not supplied

Inhibitory activity of glass-ionomer cements on cariogenic bacteria.

This study evaluated the antibacterial activity of the glass-ionomer cements Vitrebond (3M ESPE), Ketac Molar (3M ESPE) and Fuji IX (GC America) against S mutans, S sobrinus, L acidophilus and A viscosus, using the agar diffusion test. Inocula were obtained by the seed of indicators cultures in BHI broth incubated at 37 degrees C for 24 hours. Base layers containing 15 mL of BHI agar and 300 microL of each bacteria suspension were prepared in Petri dishes. Six wells measuring 4 mm in diameter were made in each plate and completely filled with one of the testing materials. A 0.2% chlorhexidine solution applied in round filter papers was used as control. Tests were performed 12 times for each material and bacteria strain. After incubation of the plates at 37 degrees C for 24 hours, the zones of bacterial growth inhibition around the wells were measured. Overall, the results showed the following sequence of antibacterial activity: Vitrebond (despite the activation mode) > 0.2% chlorhexidine > Ketac Molar > Fuji IX, according to Kruskal-Wallis and Mann-Whitney statistical tests. This study confirmed significant antibacterial activity for two conventional glass-ionomers and one resin-modified glass-ionomer material. The resin-modified glass-ionomer cement Vitrebond, regardless of the activation mode, presented the best antibacterial activity against S mutans and S sobrinus. The antibacterial activity against A viscosus for Vitrebond was similar to 0.2% chlorhexidine, while light activation reduced its antibacterial activity against L acidophilus.

Actinomyces viscosus↗

PubMed2004

Benefits of bilateral electrical stimulation with the nucleus cochlear implant in adults: 6-month postoperative results.

OBJECTIVE: To evaluate the benefits of bilateral electrical stimulation for hearing-impaired adult subjects using the Nucleus 24 cochlear implant in a multicenter study, and to compare and quantify performance on speech perception measures in quiet and in noise and localization ability for unilateral and bilateral cochlear implant use. DESIGN: : Repeated single subject measures were carried out for each subject, with each subject serving as their own control. Assessment of unilateral and bilateral listening conditions for performance on tests of speech comprehension and sound localization were performed. Speech comprehension measures were performed in quiet at 0 degree azimuth and in the presence of background noise simultaneously presented from the same speaker and spatially separated by 90 degrees, at S+45 degrees N45 degrees and at S-45 degrees N+45 degrees . Test materials included Freiburger monosyllabic words, Oldenburger sentences, and the Hochmair-Schulz-Moser sentences. Tests of localization were performed in the horizontal plane with 12 speaker locations 30 degrees apart using a shortened sentence stimulus from the Hochmair-Schulz-Moser sentences at two possible presentation levels of 55 and 70 dB sound pressure level for assessment of directionality. The binaural advantage provided by bilateral stimulation was calculated with respect to each ear separately, classified as either the better or poorer performing ear for each speech material in quiet and in noise test conditions. For localization of sound, the binaural advantage was compared with left and right ears separately. Paired comparisons for performance data in all conditions were carried out by considering measurements for each subject in different conditions as paired observations and applying the Student's t test to determine the statistical difference between the data sets. SETTING: Tertiary referral centers with a cochlear implant program. PATIENTS: Thirty-seven profoundly hearing-impaired adults were enrolled in the study, 22 simultaneously and 15 sequentially bilaterally implanted. All patients received the Nucleus 24 cochlear implant and used the Nucleus SPrint or ESPrit 3G speech processor, with the vast majority using the ACE speech coding strategy. RESULTS: For spatially separated speech in noise conditions, an interaural performance advantage for the ear closest to the speech source (i.e., with a superior signal to noise ratio) compared with that for the ear closest to the noise source (i.e., with an inferior signal to noise ratio) is consistently demonstrated regardless of whether it is the better or poorer performing ear closest to the speech signal. This is referred to as a significant binaural head-shadow benefit, resulting in a mean improvement between -10 dB and -11.4 dB in the critical signal to noise ratio required for 50% speech comprehension for the Olden-burger sentences and a mean improvement in the maximum score of 42% to 55% for the ear closest to the speech signal over the ear farthest away for the Hochmair-Schulz-Moser sentences. Bilateral stimulation is always observed to provide a performance advantage over the unilateral listening condition for either ear when ipsilateral to the noise source. In addition, as demonstrated by approximately half the subjects tested in noise with the Hochmair-Schulz-Moser sentences, a performance advantage of bilateral stimulation may be observed over the better ear alone when positioned ipsilateral to the speech signal, which is referred to as a binaural squelch effect. On average, for the group, this resulted in a statistically significant improvement in speech comprehension scores of 8% in the bilateral listening condition compared with the scores for the better ear alone. Through assessment of comprehension of coincidental speech in noise and speech in quiet, a significant benefit of binaural redundancy was noted for the group for Oldenburger sentence scores in noise and in quiet compared with unilateral scores for either ear and for the Freiburger monosyllabic words in quiet in comparison with the better ear alone scores. Binaural stimulation also led to a significant improvement in localization ability over either monaural condition, with the root mean square degrees of error reduced by 38 degrees compared with that observed for unilateral stimulation. CONCLUSION: Similar to what has been observed for bilateral acoustic stimulation in the past, bilateral electrical stimulation provides the foundation for the potential advantages of the head-shadow effect, providing a binaural head-shadow benefit and binaural auditory processing such as binaural redundancy and binaural squelch effects, all of which combine to lead to improved speech comprehension over unilateral listening conditions. The combination of improved speech comprehension and improved localization ability made available through bilateral electrical stimulation provides the necessary foundation to further assist the hearing-impaired listener to better cope with communication in the everyday listening situation both in noise and in quiet.

Adolescent↗

PubMed1995

Cytotoxicity of four root end filling materials.

Leakage and scanning electron microscopic studies have shown that a mineral trioxide aggregate (MTA) used as root end filling material permits significantly less leakage and has better adaptation than other commonly used root end filling materials. Because these materials are in contact with the periradicular tissues, their cytotoxicity should be evaluated before in vivo tests. Using the agar overlay and radiochromium methods, the cytotoxicity of amalgam, Super EBA, IRM, and the MTA was evaluated. Statistical analysis of the data from the agar overlay technique shows that freshly mixed and set amalgam were significantly less toxic than the rest of tested materials (p< 0.00005). Fresh and set MTA ranked second when tested for cytotoxicity with this technique. Similar statistical tests revealed a significant statistical difference between the toxicity of freshly mixed and set materials after 24 h of incubation with radiochromium-labeled mouse L929 cells. The degree of cytotoxicity of fresh and set materials was MTA least toxic followed by amalgam, Super EBA, and IRM. Based on the results of the cell culture methods used in this study it appears that MTA is a potential root end filling material and warrants further in vivo evaluations.

Agar↗

PubMed1993

Matrix effects and the accuracy of cholesterol analysis.

We found evidence of bias due to matrix effect in 70% of 37 instrument/reagent-specific systems analyzing the total cholesterol content of a lyophilized proficiency testing material. We used a computational method to remove bias due to matrix effect from the proficiency testing database. After correction for matrix effect bias and when compared with the reference method, 92% to 93% of results for three lyophilized proficiency testing samples analyzed in 1989 and 1990 met the 1992 National Cholesterol Education Program total error goal of 8.9%, and 94% to 95% met the Clinical Laboratory Improvement Amendments of 1988 (CLIA '88) goal of 10%. However, compared with the definitive method for total cholesterol, the calibration bias of 41% of 37 peer groups exceeded the 1992 National Cholesterol Education Program goal for bias of 3%. Because the calibration bias of the method is incorporated into the peer group mean, use of peer group means as target values to assess result acceptability hinders advancement of the state of the art in interlaboratory comparability and the clinical effectiveness of laboratory testing. The prevalence of matrix effects has prevented successful application of accuracy-based evaluation of cholesterol test proficiency. The establishment of predictable recovery, preferably complete recovery, of cholesterol from reference materials is an important priority for cholesterol test methods. However, adjustment of proficiency testing results to remove the average bias due to matrix effects can help assess the actual state of the art in cholesterol test accuracy.

Bias↗

PubMed1976

[Scanning electronmicroscopic study of 3 composite filling materials after 1 year's use].

This is an in-vivo comparative test of two test materials, composites Compo-Cap and Cosmic against Adaptic on a monkey (Macaca speciosa) over one year. No significant differences could be found and the defects on margins and in the surface was similar. Undubitable secondary caries could--unlike in a previous test with Epoxylite--not be found with these fillings.

Animals↗

PubMed2002

Polyetheretherketone--cytotoxicity and mutagenicity in vitro.

The results of the incubation of polyetheretherketone (PEEK) fibre material with seven different genotype variants of salmonella bacterium showed with and without an external metabolic activation system (S9) with no mutagenic or cytotoxic activity of the test material. In the so-called "plate incorporation test" in which the PEEK raw material is finely cut and applied direct to the agar plate without the addition of solvent there was, as expected, no evidence of cytotoxic or mutagenic effects. In the HPRT test there was a significant increase in the number of mutants per dish, both after addition of N-acetylaminofluorene and N-methyl-N'-nitro-N-nitrosoguanidine (with and without an external metabolic activation system = +S9), but not after treatment of the cells with PEEK-DMSO-eluate. This means that the PEEK material under study did not release any substances that cause V79 cells to mutate. The investigation of the toxic reaction on the material under study revealed that the number of surviving colonies per 10(5) surviving cells lay within the range of or below the solvent control even in the presence of high PEEK concentrations (5.0 microg/ml). Therefore, in summary, the study produced no evidence of cell damage caused by PEEK.

2-Acetylaminofluorene↗

PubMed1990

[The wear on enamel, amalgam and their enamel antagonists in a computer-controlled mastication simulator].

In a long-term in-vitro test the wear of enamel fossae, amalgam restorations and their opposing enamel cusps in the occlusal contact area was evaluated, qualitatively and quantitatively. The wear of enamel cusps differed from the wear of enamel fossae. The amalgam restorations wore down more rapidly than enamel fossae, but they were less destructive against their opposing enamel cusps. The wear of all tested materials was not linear. The results will serve as reference data for future long-term in-vitro tests of posterior restorative materials.

Computer Simulation↗

PubMed2005

Phosphorus removal in constructed wetlands: can suitable alternative media be identified?

Removal of phosphorous in constructed wetlands is limited by the capacity of the media to adsorb, bind or precipitate the incoming P. To enhance P removal and the life span of constructed wetlands the approach might be to use natural sands rich in calcium or iron, to use an alternative 'artificial' medium with high P-binding capacity, or to establish external P-binding filters after the wetland. Our studies focused on the evaluation of calcium-rich materials potentially useful as P-binding media. The materials tested included calcite products, natural sands and seashells. Tests included assessment of physical and chemical properties of the materials, extractions in P-spiked water at different P concentrations to determine P-binding equilibrium isotherms, and column experiments. In addition, full-scale tests were performed with calcite in an external filter. The result showed that equilibrium isotherm is an indicator of the potential P-sorption capacity of the media, although the value is of limited application for the determination of the binding capacity in full-scale systems. The columns showed that the materials do bind phosphorus. However, the binding capacities are still insufficient for the establishment of external P-removal filter; the volumes of the filters would be too large to be of practical use.

Adsorption↗

PubMed1998

Bond strength to dentin with artificial carious lesions: influence of caries detecting dye.

PURPOSE: To evaluate the influence of dyes for caries detection on tensile bond strength of adhesive materials to artificial carious dentin. MATERIALS AND METHODS: Buccal and lingual enamel of human molars were removed leaving intact dentin surfaces. The entire surface of each specimen was covered with nail varnish, keeping a window area of 4 x 4 mm. Artificial carious lesions were induced with acidified gel. Three dyes (0.5% basic fuchsin; Caries Finder and Cari-D-Tect) were used according to manufacturers' recommendations. Specimens were etched with 35% phosphoric acid for 20 s, washed and dried, leaving a wet dentin surface. The adhesive system (Prime & Bond 2.0) was applied in two layers and light-cured. Restorative materials (TPH Spectrum, Dyract, Advance) were bonded using a 3-mm diameter inverted-cone mold. Control groups were made without dye. Eight samples were tested for each group. After 24 hrs of storage in distilled water, the samples were debonded using a testing machine at 0.5 mm/min crosshead speed. RESULTS: ANOVA and Tukey-Kramer test showed that TPH Spectrum (0.73 MPa) and Dyract (0.74 MPa) had similar bond strengths, and both were higher than Advance (0.0 MPa), which was statistically different (P < 0.01). The use of the dyes did not cause any changes in tensile bond strength for any tested materials.

Analysis of Variance↗

PubMed1985

Dental pulp response to bacterial cell wall material.

Lipopolysaccharides (LPS) from Bacteroides oralis and Veillonella parvula and cell wall material from Lactobacillus casei were studied for their capacity to induce leukocyte migration in the dental pulp and in an implanted wound chamber. Three adult monkeys were challenged using lyophilized material sealed into buccal Class V cavities prepared in dentin. Pulp tissue responses were observed histologically eight and 72 hours after initiation of the experiment. Subjacent to cut dentinal tubules, bacterial materials induced polymorphonuclear leukocyte (PMN's) infiltration in the pulp tissue of the majority of test teeth examined. Responses were similar for the three bacterial test materials at both time periods. Topical applications of bovine serum albumin (BSA), used as a control, induced significantly less accumulation of PMN's. Assessments of induced exudate volumes and leukocyte densities in chambers implanted in rats showed comparable rankings with pulpal experiment between test (i.e., bacterial) and control (BSA) materials. Analysis of the data indicates that high-molecular-weight complexes of bacterial cell walls may adversely affect pulpal tissue across freshly exposed dentin.

Animals↗

PubMed2006

Film thickness and rheological properties of luting agents for crown cementation.

The film thickness and rheological properties [viscosity and tan sigma], of different resin based crown and bridge luting agents, including Panavia 21, Superbond, All Bond C&B Cement, Variolink were compared with zinc phosphate cement. A modification of the method in ISO 9917 (1991) and a controlled stress rheometer were used to monitor the changes in the film thickness and rheological properties respectively. For each material, the film thickness and rheological characteristics were determined at 60s after start of mixing and then made at regular intervals until immediately before the material was set. For the initial film thickness, the difference among the values for Varionk, Superbond and zinc phosphate cement was not significant (P>0.05), and less than 25microm. The values for All Bond C&B Cement and Panavia 21 were at least twice that of the other materials tested. All Bond C&B Cement produced the highest film thickness value at both the initial period and at 240s. Regarding viscosity, Superbond had the lowest initial value but the highest value at 240s. Variolink gave the highest initial value of viscosity, but the differences in the initial values among the other materials were small. During the whole period of testing, zinc phosphate cement gave the highest values of tan sigma, and Panavia 21 showed no significant change in any of the measured properties. The methods were able to distinguish the behaviour of different cement materials. Some resin cements produce larger than optimal values of film thickness and in some cases this is related to a rapid increase in viscosity after mixing. It is expected that differences in the ability of cements to form thin films will affect the seating of cemented restorations.

Analysis of Variance↗

PubMed1990

Special considerations for conducting permeation testing of protective clothing materials with gases and chemical vapors.

Testing the permeation resistance of protective clothing materials against chemical gases and vapors requires attention to additional factors over conventional material permeation testing with liquids. Permeation testing factors relevant to gas and vapor challenges are described, and results for testing various material-gas combinations are reported. Challenging protective clothing materials with gases presents a series of special problems including gas delivery, cell integrity, sufficient analytical detection, and disposal. The concentration and other properties of gases and vapors are very sensitive to small changes in temperature and pressure. The method of delivering gases or vapors to the test cell must provide for careful regulation of these variables and maintain homogeneous contact of the chemical with the material over the test period. While many organic vapors are easily and directly detectable by gas chromatographic methods, several gases require special collection media and analytical procedures to achieve detection limits below 1 ppm. Handling of exhaust gas from the challenge chamber of the test cell must reflect safe laboratory practices without creating unnecessary chemical waste. Recommended procedures and results are presented for the six new gases added to ASTM Standard Guide F1001, Selection of Chemical Liquids and Gases to Evaluate Protective Clothing Materials, as well as for other difficult test gases used in evaluating protective clothing materials.

Air Pollutants↗

PubMedDate not supplied

Initial interlaboratory validation study of FETAX: phase I testing.

An interlaboratory validation study was undertaken to evaluate the repeatability and reliability of the Frog Embryo Teratogenesis Assay-Xenopus (FETAX), which is a whole embryo developmental toxicity screening assay. A three-phase experimental program with seven participants was carried out. Phase I was a training and protocol evaluation phase where the identity of the three test materials was known. Hydroxyurea, isoniazid and 6-aminonicotinamide were tested in Phase I. Because the chemicals has been tested previously in FETAX, the same concentrations needed to establish the 96-h median lethal concentration (LC50) and the concentration inducing malformations in 50% of the surviving embryos (EC50) were used by all laboratories. The results of Phase I are presented in this report, and FETAX has proved to be as repeatable and reliable as many other bioassays. Some excess variation was observed in individual laboratories. Some of this variation may have been due to training difficulties. One change in protocol design necessitated by this study was the use of 6-aminonicotinamide as a reference toxicant. While 6-aminonicotinamide provided excellent concentration-response data in most laboratories, the protocol was written too strictly based on historical FETAX data. Phases II and III are currently in progress.

6-Aminonicotinamide↗

PubMed2004

Optimal screw diameter for interference fixation in a bone tunnel: a porcine model.

The study investigates the optimal interference screw dimensions required to secure a tendon graft in a bone tunnel. A standard 8 mm pig flexor-tendon graft was inserted into a standard open-ended 8 mm bone tunnel of a porcine distal femur and secured using either 7 mm, 8 mm or 9 mm diameter metal interference screws (Arthrex Inc, Naples, FL). The construct was tested to failure using a Shimadzu ASG 10KN Universal Material Testing Machine (Shimadzu, Tokyo, Japan). Load and mode of construct failure were recorded for 37 individual constructs. There was no significant difference in the load at failure between the 7 mm screw (192 N; range 151-232) and 8 mm screw (181 N; range 150-212) (p>0.05). There was a significant difference between the 7 mm screw and the 9 mm screw (109 N; range 67-151) (p=0.006) and between the 8 mm screw and the 9 mm screw (p=0.015). When using a 9 mm screw, 100% of the constructs failed by cut out of the graft at the tunnel opening. The 7 mm constructs failed by slippage of the tendon from the bone tunnel in 83% of cases, with only 17% failing by cut out at the tunnel opening. The 8 mm constructs demonstrated a mixture of failure modes, with slippage occurring in 58% of cases, cut out in 38% and failure of the graft substance in one case (4%). In this model, screw diameters equal to or 1 mm less than the tunnel/tendon diameter provides better fixation than using a screw 1 mm larger. The mode of failure differs for each of these screws.

Animals↗