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PubMed2003

Effect of high intensity vs. soft-start halogen irradiation on light-cured resin-based composites. Part I. Temperature rise and polymerization shrinkage.

PURPOSE: To determine polymerization shrinkage kinetics and temperature rise of light-cured resin-based composites after high intensity vs. soft-start quartz tungsten halogen irradiation. METHODS: Shrinkage kinetics was evaluated using the "deflecting disk technique", modified for simultaneous measurement of temperature within the resin-based composite using a thermocouple. Additional irradiations after 60 and 65 minutes allowed the determination of temperature rises caused by radiation or by reaction heat. Four hybrids (Filtek Z250, Herculite, Solitaire 2, Tetric Ceram), an inhomogeneously filled hybrid (InTen-S) and a microfill (Filtek A110, formerly Silux Plus) were cured using the quartz tungsten halogen units Astralis 10 and Optilux 501 in the high intensity (A10 HiPo: 10 seconds at 1300 mW/cm2; OL Boost: 10 seconds at 1140 mW/cm2) or soft-start modes (A10 Pulse: increase to 700 mW/cm2 within 10 seconds, three periods of 2 seconds at 1300 mW/cm2 alternating with two periods of 2 seconds at 700 mW/cm2; OL Ramp: exponential increase within 10 seconds, followed by 10 seconds at 1140 mW/cm2). RESULTS: The soft-start protocols produced less contraction, and polymerization shrinkage started later and progressed slower (or: more slowly), compared to high intensity irradiation [correction]. The lowest shrinkage was observed for InTen-S, followed by Filtek Z250 and A110, whereas Solitaire 2, Herculite and Tetric Ceram scored highest for this parameter. Temperature rise was caused more or less equally by radiation and by reaction heat and reached values of up to 28.9 degrees C relative to a baseline of 37 degrees C. For some combinations of curing modes and resin-based composites, less heat was generated by the soft-start protocols and by Optilux 501.

Analysis of Variance↗

PubMedDate not supplied

Post-gel shrinkage with different modes of LED and halogen light curing units.

This study compared the post-gel shrinkage of two LED (light-emitting diodes) lights (Elipar FreeLight [FL], 3M ESPE; GC e-Light [EL], GC), a high intensity (Elipar TriLight [TL], 3M ESPE) and a very high intensity (Astralis 10 [AS], Ivoclar Vivadent) halogen light to a conventional (Max [MX] (control), Dentsply-Caulk) halogen light. Ten light curing regimens were investigated. These included continuous (FL1, EL2, MX, TL1 and AS1), soft-start (FL2, EL4, TL2), pulse activation (EL1) and turbo (EL3) modes. A strain-monitoring device and test configuration was used to measure the linear polymerization shrinkage of a composite restorative (Z100, [3M ESPE]) during and post-light polymerization up to 60 minutes when cured with the different modes. Five specimens were made for each cure mode. Results were analyzed using ANOVA/Scheffe's post-hoc test and independent sample t-tests at significance level 0.05. Shrinkage associated with the various modes of EL was significantly lower than MX immediately after light polymerization and at one-minute post-light polymerization. No significant difference between MX and the various lights/cure modes was observed at 10, 30 and 60-minutes post-light polymerization. At all time intervals, post-gel shrinkage associated with continuous light curing mode was significantly higher than the soft-start light curing mode for FL and TL.

Analysis of Variance↗

PubMed2004

Effect of high intensity vs. soft-start halogen irradiation on light-cured resin-based composites. Part II: Hardness and solubility.

PURPOSE: To determine hardness and solubility of light-cured resin-based composites after high intensity vs. soft-start quartz tungsten halogen irradiation. METHODS: Knoop hardness of resin-based composite specimens was measured at 1.5 mm depth after dry storage for 24 hours at 37 degrees C so as to indirectly evaluate degree of cure. Solubility was determined gravimetrically by extraction of post-cured (24 hours, 37 degrees C) specimens in 50 wt% methanol for 72 hours. Four hybrid (Filtek Z250, Herculite, Solitaire 2, Tetric Ceram), an inhomogeneously filled hybrid (InTen-S) and a microfilled (Filtek A110, formerly Silux Plus) composite were cured using the quartz tungsten halogen units Astralis 10 and Optilux 501 in the high intensity (Astralis 10 High Power: 10 seconds @ 1300 mW/cm2; Optilux Boost: 10 seconds @ 1140 mW/cm2) or soft-start modes (Astralis 10 Pulse: increase to 700 mW/cm2 within 10 seconds, three periods of 2 seconds @ 1300 mW/cm2 alternating with two periods of 2 seconds @ 700 mW/cm2; Optilux Ramp: exponential increase within 10 seconds, followed by 10 seconds @ 1140mW/cm2). RESULTS: For the fast curing composites Z250, Tetric Ceram and InTen-S, equivalent hardness was observed after 10 seconds of high intensity and 20 seconds of soft-start irradiation. For the slower curing composites Herculite, Solitaire 2 and A110, the soft-start protocols produced higher hardness values. Regarding solubility however, the superiority of soft-start irradiation was also seen for Tetric Ceram and InTen-S. The lowest solubility was observed for InTen-S, followed by Z250, whereas Herculite and Solitaire 2 scored highest for this parameter.

Analysis of Variance↗

PubMed1992

[Dermatologic risks of quartz-halogen lamps].

Halogene sources are used increasingly in general illumination. Their quartz envelop is technically necessary, but presents the disadvantage of to letting the emitted UVA, UVB and UVC go through. Originally used as in indirect lighting, they have been introduced as desk-top lamps, without filter. We have proceeded to the verification of their output with a spectrophotometer calibrated by actinometry and we have calculated their relative erythemal efficacy according to the Parrish's action spectrum for human erythema. We found that, at 10 cm from the human skin, the irradiance was able to induce a minimal erythema in about 10 minutes on clear back skin. At working distance (50 cm), a barely perceptible erythema could be observed on the back of the hands after 8 consecutive hours working. We also found that sunburn cells were present in the skin sensitized with a potent phototoxic agent (8-methoxypsoralen) applied 15 minutes before a 4-6 minutes irradiation with the halogen source (at 20 cm), thus, indicating a potential risk for local phototoxicity and photoallergy. The cumulative doses per year, for 4 hours exposure per day, five days a week, reaches 125 minimal erythemal doses, equivalent to the average yearly exposure of individuals for work and leisure. If one assumes that this regimen is maintained for 30 years, the risk for induction of skin cancers on the dorsal aspect of the hands and the forearms, may be increased by a 3.4 factor, according to the widely accepted previsional models.(ABSTRACT TRUNCATED AT 250 WORDS)

Erythema↗

PubMedDate not supplied

In vitro study of surface microhardness of a resin composite exposed to a quartz-halogen lamp.

OBJECTIVES: To determine the minimum exposure times consistent with optimized surface microhardness numbers (VHN) for the top and bottom surfaces, respectively, of a resin composite (1.5-mm depth) cured using a quartz-halogen activation lamp. Additionally, to determine the conditions appropriate to achieve optimized bottom/top hardness ratios. METHOD AND MATERIALS: Disk specimens of a commercial resin composite restorative (Spectrum TPH) were exposed to a quartz-halogen lamp, and VHNs were measured for the top and bottom surfaces at elapsed times of 1 hour and 24 hours. RESULTS: Data were dependent on exposure time, time elapsed after exposure, and the surface involved. Exposure time featured limiting values in excess of which no significant increase in microhardness took place. All microhardness data increased significantly over an elapsed time interval between 1 hour and 24 hours postexposure. Microhardness ratios (bottom/top) were dependent on exposure time only and were not influenced by time elapsed after exposure. CONCLUSION: Minimum exposure time may be considered as the greater of the times to achieve optimized top hardness and optimized hardness ratio, respectively.

Composite Resins↗

PubMed2005

Mechanical properties of two orthodontic adhesive materials polymerized with halogen and plasma curing.

OBJECTIVES: The aim of this study is to compare the efficiency of two polymerization techniques (halogen curing--Astralis 7 and plasma curing--Flipo), with two orthodontic adhesive materials (Enlight, a composite resin, and Fuji Ortho LC, a glass ionomer cement). METHODS: The efficiency of the polymerization techniques was shown by two mechanical tests. The hardness test was carried out on the exposed and non-exposed surfaces using 10 x 4 x 3-mm samples, polymerized either by halogen curing (40 seconds) or by plasma curing (5 seconds). The three-point bending tests were carried out on 2 x 2 x 25-mm samples polymerized as above. The samples were kept 1 hr at room temperature, then for 24 hrs in distilled water at 37 degrees C. RESULTS: Whatever the polymerization technique used, the results are similar for hardness and flexion, with the exception of the hardness tests carried out after polymerization with the Flipo light on the surface not directly exposed. CONCLUSION: In orthodontic practice, both polymerization techniques can be used. But a multi-bracket session can be long, and the reduction of time spent in the chair obtained by using plasma lamps seems to make this technique preferable.

Acrylic Resins↗

PubMed2005

[A study on the ultraviolet spectra of halogenated benzoylferrocenes].

The ultraviolet spectra of all of the o, m, p-halogenated benzoylferrocenes have been studied the following rules obtained: 1. The lambdamax of the ultraviolet spectrum R band and K band for the isomers is lambdamax(m-X) > lambdamax(p-X) > lambdamax(o-X). 2. With the same substituted positions of the different halogen on the benzene ring, the lambdamax of the ultraviolet spectrum K band is lambdamax(C1) > lambdamax(Br) > lambdamax(I) > lambdamax(F), then, the lambdamax of ultraviolet spectrum R band is lambdamax(I) > lambdamax(Br) > lambdamax(Cl) > lambdamax(F).

Benzene↗

PubMedDate not supplied

Intensity of quartz-tungsten-halogen light polymerization units used in dental offices in Brazil.

PURPOSE: To determine the intensity of quartz-tungsten-halogen light polymerization units in dental offices in El Salvador, Brazil. MATERIALS AND METHODS: A team of researchers visited 100 offices in 2003. The team measured light intensity with a radiometer. The age and make of the units and the availability of light meters were recorded. RESULTS: One hundred twenty quartz-tungsten-halogen units were tested. Intensity ranged from 10 to 1,000 mW/cm2, with mean of 255.8 mW/cm2. Almost half (48%) of the units had values equal to or less than 200 mW/cm2. Their age ranged from 1 to 21 years. None of the offices had light meters. CONCLUSIONS: Clinicians should periodically monitor light intensity and carry out maintenance on their light polymerization units.

Composite Resins↗

PubMedDate not supplied

Binding of thiopental to human serum albumin in the presence of halogenated hydrocarbons and ethers.

Thiopental binding (substrate concentration 0.04.10(-3) M = 10 micrograms/ml) to 1% human serum albumin (HSA) studied by equilibrium dialysis in 1/15 M phosphate buffer solution (pH 7.4) was increased significantly from 40.2% (= control) to 55% in the presence of 4.71.10(-3) M halothane (= 11.36 vol%); 1.18.10(-3) M = 2.84 vol% halothane caused a lesser but still significant increase (vs. control) of thiopental binding. This halothane effect on the binding of thiopental to HSA was studied under several experimental conditions (variation of thiopental concentration, HSA concentration, pH of the buffer solution, temperature). Other halogenated hydrocarbons such as chloroform (6.2.10(-3) M) and carbon tetrachloride (5.2.10(-3) M) also markedly increased the binding of thiopental to HSA as compared to the control (percentage of fraction bound, 53 and 61%, respectively); the same effect, but to a lesser extent, was obtained under the influence of three halogenated ethers, i.e., enflurane (4.1.10(-3) M--greater than 45% thiopental bound), isoflurane (4.1.10(-3) M--greater than 50% bound) and methoxyflurane (4.3.10(-3) M--greater than 47% bound). Under the same experimental conditions, ethanol (up to 8.9.10(-2) M) and diethylether (up to 4.9.10(-2) M) did not increase the percentage of thiopental bound to HSA.

Carbon Tetrachloride↗

PubMed1990

[Distribution pattern of chemicals in surface waters as a reflexion of entry pattern--volatile halogenated hydrocarbons].

The part gives some data about various light volatile halogenated hydrocarbons in surface waters of the industrialized city and its surroundings--the halogenated forms, chloroform and bromoform and the most used solvents trichloroethylene, tetrachloroethylene, tetrachloromethane and 1,1,2,2-tetrachloroethane. 80% of the concentrations of chloroform, tri- and tetrachloroethylene were in the range of less than 1 microgram l-1, 90% of bromoform, tetrachloromethane and 1,1,2,2-tetrachloroethane were found to amount less than 0.1 microgram l-1. With the help of the differential-diagnostic assessment method described in the first part we tried to evaluate the data for tetrachloromethane. The highest values were obtained for almost all sampling points in April--a possible cause may be the use of this solvent for cleaning and repairing procedures with sport boats (although tetrachloromethane has been prohibited for such uses for some years there may be some remainders which were used for these purposes).

Hydrocarbons, Brominated↗

PubMed1989

Studies on heterocyclic compounds: 1,3-thiazolidin-4-one derivatives. III. Biological activity of halogenated 2,3-diaryl-1,3-thiazolidin-4-ones.

In previous communications from these laboratories, thiazolidinone derivatives of general formula (A) were synthesized and screened for antimicrobial activity. (formula; see text) where: X = H, CH3 Ar = phenyl Ar' = fluorinated or chlorinated phenyl The present communication is in part concerned with further extension of these studies to variously halogenated thiazolidinones of general formula (B). (formula; see text) where: X = H, CH3 R = H, 2-F, 3-F, 4-F, 3-Cl, 4-Cl R' = H, 4-F, 4-Cl These compounds were prepared by the general synthetic procedure previously reported for the 1,3-thiazolidin-4-one derivatives already prepared and screened in this SARs program. The general synthetic approach involves the cyclocondensation of the appropriate Schiff bases with alpha-mercaptoalkanoic acids such as thioglycolic and thiolactic acid. The prepared compounds were tested for their possible activity by a disk-diffusion assay (Kirby-Bauer modified). The organisms used were: S. aureus, S. beta-haemoliticus, B. subtilis, M. paratuberculosis 607, S. typhi, Kl. pneumoniae, E. coli Bb, Ps. aeruginosa, C. albicans, A. niger, S. cerevisiae. The results of this antimicrobial screening showed that the prepared compounds exhibited varying degrees of activity against Gram-positive, Gram-negative bacteria, and fungi. The second half of this report deals with the structure-activity relationships in all the compounds prepared and studied in this research program. For comparison of antimicrobial activity, the growth inhibitory activity of all the halogenated thiazolidinones of type (A) and (B), prepared and screened in this SARs study, were tabulated.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacteria↗

PubMed1989

[The mutagenicity of organic microcontaminants in the environment. IV. The mutagenicity of volatile organic halogens in the SOS-chromotest].

To determine the sensitivity and responsibility of microbial shortterm-tests for detection of the mutagenic potency of volatile halogenated hydrocarbons (OHC) 18 pure substances from the groups of halomethanes, -ethanes and ethylenes were examined with the SOS-Chromotest. The strain Escherichia coli PQ37 was used in the standard procedure (macro procedure) with and without metabolic activation by Aroclor 1254 induced rat-liver microsomes. Although the selected OHC were tested to high doses, none of the tested compounds showed mutagenic effects in Escherichia coli PQ37. Also those OHC's, which showed positive results in the Ames test or being suspected of carcinogenicity, showed no positive results in the SOS-Chromotest. Therefore, the standard procedure of SOS-Chromotest is not suitable to detect the mutagenicity of volatile organic and halogenated compounds. Supplementary investigations with modified methods are necessary to check the results, because there is a good correlation between Ames test and SOS-Chromotest by testing other groups of compounds.

Animals↗

PubMed1989

Oxidation of halogenated compounds by cytochrome P-450, peroxidases, and model metalloporphyrins.

Incubation of iodosylbenzene and [125I]iodobenzene with cytochrome P-450 (P-450) leads to the formation of [125I]iodosylbenzene (Burka, L.T., Thorsen, A., and Guengerich, F.P. (1980) J. Am. Chem. Soc. 102, 7615-7616), but to date it has not been possible to observe directly the oxidation of organic halides in NADPH-supported P-450 reactions because of the intrinsic instability of haloso compounds. 4-tert-Butyl-2,5-bis[1-hydroxy-1-(trifluoromethyl)- 2,2,2-trifluoroethyl]iodobenzene (RI) and the corresponding bromine analog (RBr) were utilized as model compounds because their oxidized derivatives (iodinane and brominane) are relatively stable. Several model metalloporphyrins efficiently oxidized RI to the iodinane in the presence of iodosylbenzene. Rates of reduction of Mn(V) = O tetraphenylporphin chloride by RI were considerably faster than for several other organic halides. NADPH-fortified rat liver microsomes oxidized RI to the iodinane, identified by its chromatographic retention time and characteristic UV spectrum. Purified P-450 enzymes also catalyzed the oxidation of RI to the iodinane; more selectivity among individual proteins was seen when the reaction was supported by NADPH and NADPH-P-450 reductase than by iodosylbenzene. Free thiol groups in P-450 and NADPH-P-450 reductase could be oxidized by iodosylbenzene, the iodinane or brominane, or by incubation with NADPH and RI or other organic halides. These results provide evidence that P-450 can oxidize organic halogen atoms. Iodo compounds are definitely oxidized, even though the apparent oxidation-reduction potential differences seem unfavorable. The halogen order seen for the reaction is a function of the oxidation potential. Organic bromine compounds are probably also oxidized by P-450, although the rates are much slower. Chloroperoxidase did not oxidize RI to the iodinane but horseradish peroxidase did so at a lower rate; in this case the iodinane is postulated to form via electron abstraction without oxygen transfer.

Amino Acids↗

PubMedDate not supplied

Halogenated hydrocarbon epoxides: some predictive methods for carcinogenic activity based on electronic mechanisms.

We summarize some of our computational studies (involving an ab initio self-consistent-field molecular orbital procedure) of the reactive properties of halogenated hydrocarbon epoxides. Two of the factors that are believed to determine the carcinogenicities of halogenated olefins and their metabolically produced epoxides are discussed in detail. These are the epoxide's tendency toward oxygen protonation, and its subsequent reactivity. The first of these provides a means for identifying suspect carcinogens, on the basis of our earlier observation that epoxide carcinogenicities are associated with relatively strong negative electrostatic potentials near the oxygens (the protonation sites). With regard to the epoxide's reactivity, optimum carcinogenicity appears to require that this be at an intermediate level. We have investigated the feasibility of using calculated C-O bond orders as measures of reactivity, with encouraging initial results, which suggest that this reactivity requirement may provide a means for ranking the activities of carcinogens.

Calorimetry↗

PubMed1985

Biotransformation of halogenated solvents.

The toxicity of most halogenated solvents is associated with their biotransformation. The bioactivation can be due to the formation of stable, toxic metabolites or the formation of reactive, electrophilic intermediates. The paper summarizes present knowledge on the biotransformation of several halogenated compounds, ie, methyl halides, methylene halides, haloforms, carbon tetrachloride, chlorinated ethanes, and chlorinated alkenes. Some of the relevant enzymatic metabolic reactions are also discussed.

Animals↗

PubMed1979

Leak detection and low level monitoring of halogenated anesthetics.

Halogenated compounds used in anesthetics are generally detected and monitored by gas chromatography or infrared analysis. For a quick, reliable, and economical method of detecting these compounds, the HLD-440 leak detector proved to be effective. The instrument is simple to calibrate and operate. It is safe and is capable of detecting halogenated anesthetics in concentrations at least as low as 2 parts per million.

Air Pollutants↗

PubMed1984

Metabolism of genotoxic agents: halogenated compounds.

Most halogenated compounds showing genotoxicity do not themselves react with macromolecules but are transformed to reactive metabolites. In order to explain the widely different genotoxicities of halogenated ethylenes, the 'optimum stability' theory of epoxides has been developed recently. An epoxide must be reactive to alkylate DNA, but stable enough to reach the target from the place of its formation. Also, pharmacokinetic aspects are important in accounting for differences in genotoxicities of closely related compounds; examples are provided. Reactive metabolites may bind to proteins, to lipids and coenzymes, and to DNA, but binding to targets other than DNA is far more common than DNA alkylation. An example is provided by investigations on 2,2'-dichlorodiethyl ether from which chloroacetaldehyde is formed. In contrast to vinyl chloride, which generates chloroethylene oxide (chlorooxirane) as well as chloroacetaldehyde, this compound leads to extensive covalent protein binding of metabolites, but not to DNA binding.

Alkylating Agents↗

PubMed1981

Nephrotoxicity of halogenated vinyl cysteine compounds.

S-(1,2-dichlorovinyl) cysteine (DCVC), is a potent nephrotoxin. In order to determine if other vinyl cysteine conjugates were nephrotoxic, halogenated vinyl cysteines, HVC-1 and HVC-2, were prepared from chlorotrifluoroethylene (CTFE), a fluorocarbon monomer, or chlorotifluoroethylene, a metabolite of halothane, respectively. Three days after receiving DCVC (5-10 mg/kg), CD-1 mice developed focal renal tubular necrosis. Mice treated with HVC-1 or HVC-2 (5-10 mg/kg) also developed renal necrosis by 3 days post exposure. HVC-1 was not as potent as DCVC with the necrosis limited to the pars recta. At equivalent doses HVC-2 caused less necrosis of the pars recta than HVC-1. The degree of nephrotoxicity by all three compounds exhibited a dose-response from 1-25 mg/kg. Doses greater than 25 mg/kg were often lethal within 3 days and the mice had a complete zonal necrosis of the renal cortex and a two-fold increase in kidney weight. Structural analogues, S-(chlorethyl) or S-(hydroxyethyl) cysteine, did not cause renal necrosis in mice at doses up to 200 mg/kg. These studies indicate that the enzymes reportedly responsible for converting DCVC to a nephrotoxic intermediate will also bioactivate other halogenated vinyl cysteines.

Animals↗