Fate and efficacy of polyacrylamide applied in furrow irrigation: full-advance and continuous treatments

Polyacrylamide (PAM) is applied to 400000 irrigated hectares annually in the USA to control irrigation-induced erosion, yet the fate of dissolved PAM applied in irrigation water is not well documented. We determined the fate of PAM added to furrow streams under two treatments: Initial-10, 10 mg L(-1) PAM product applied only during the initial hours of the irrigation, and Cont-1, 1.0 mg L(-1) PAM product applied continuously during the entire irrigation. The study measured PAM concentrations in 167-m-long PAM-treated furrow streams and along a 530-m tail ditch that received this runoff. Soil was Portneuf silt loam (coarse-silty, mixed, superactive, mesic Durinodic Xeric Haplocalcid) with 1.5% slope. Samples were taken at three times during the irrigations, both during and after PAM application. Polyacrylamide was adsorbed to soil and removed from solution as the streams traversed the soil-lined channels. The removal rate increased with stream sediment concentration. Stream sediment concentrations were higher when PAM concentrations were <2 mg L(-1) a.i., for early irrigations, and when untreated tributary flows combined with the stream. In these cases, PAM concentration decreased to undetectable levels over the flow lengths used in this study. When inflows contained >6 mg L(-1) PAM a.i., stream sediment concentrations were minimal and PAM concentrations did not change down the furrow, though they decreased to undetectable levels within 0.5 h after application ceased. One percent of applied PAM was lost in tail-ditch runoff. This loss could have been eliminated by treating only the furrow advance or not treating the last two irrigations.

Characterization of powder components of commercial bone cements

Acrylic bone cements have been used in orthopedic surgery without detailed information on their basic characteristics, especially on their powder components. In this study, the powder components of seven bone cements available on the market in Japan were characterized for morphology, polymer structure and molecular weight, content of residual monomer and benzoyl peroxide (BPO), and thermal properties using scanning electron microscopy, nuclear magnetic resonance spectroscopy, size exclusion chromatography, high performance liquid chromatography, and differential scanning calorimetry, respectively. Considerable differences between the seven bone cements were found in polymer structure and molecular weight, and especially in BPO content and in the morphology of the polymer particles such as shape, size and distribution. It was found that the BPO content was not always in agreement with the value given by the manufacturers on the package.

Spectrophotometric determination of polyacrylamide in waters containing dissolved organic matter

Using polyacrylamide (PAM) to reduce soil erosion in irrigated land has increased rapidly in recent years. A simple and reliable method to measure the PAM concentration in waters containing dissolved organic matter (DOM) is of great importance in assessing the fate and efficiency of PAM application. In this research, an analytical method to determine the PAM concentration of waters with correction for DOM interference was developed and tested. The method is based on a combination of determining the total concentration of amide groups by the N-bromination method (NBM) and determining the DOM content spectrophotometrically. The total concentration of amide groups of both PAM and DOM was determined by NBM at 570 nm. The DOM moiety, which is proportional to DOM concentration, was determined by spectrophotometry using a UV 254-nm wavelength. The actual PAM concentration of a water sample (soil extract containing PAM in this study) was obtained from NBM readings subtracted by the interferential DOM contribution using a correction curve. Analysis of PAM in two soil-water samples showed that the recoveries ranged from 94 to 100.3% for the 2 mg/L PAM sample and from 98.4 to 101.4% for the 10 mg/L PAM sample with various DOM concentrations. The coefficients of variation were <6% in all cases.

Noninvasive Raman spectroscopic identification of intraocular lens material in the living human eye

PURPOSE

To develop a safe noninvasive technique for identifying the material of intraocular lenses (IOLs) implanted in patients.

SETTING

Center for Biomedical Engineering and the Department of Ophthalmology and Visual Sciences, University of Texas Medical Branch, Galveston, Texas, USA.

METHODS

Raman spectroscopy was used to noninvasively identify the type of IOL implanted after previous cataract surgery in 9 eyes of 6 patients who were legally blind as a result of eye disease. Three IOLs were characterized: poly(methyl methacrylate) (PMMA) (n = 5), acrylic (n = 3), and silicone (n = 1). Confocal Raman spectroscopy was used with a laser power of 95 microW and exposure time of 1 second.

RESULTS

Distinct spectral peaks associated with each type of IOL were obtained. These included spectra peaks at 2840 cm(-1), 2946 cm(-1), and 3000 cm(-1) for PMMA; 2917 cm(-1), 2939 cm(-1), and 3055 cm(-1) for acrylic; and 2900 cm(-1), 2961 cm(-1), and 3048 cm(-1) for silicone. The procedure was well accepted by patients, and there were no complications.

CONCLUSIONS

The specific Raman spectra of the IOLs allowed for noninvasive determination of IOL material with the use of a safe light dose and an exposure time of 1 second.

Relative influence of composition and viscosity of acrylic bone cement on its apparent fracture toughness

The composition and viscosity of an acrylic bone cement have both been identified in the literature as being parameters that affect the mechanical properties of the material and, by extension, the in vivo longevity of cemented arthroplasties. The objective of the present study was to determine the relative influence of these parameters on a key cement mechanical property; namely, its fracture toughness. Two sets of cements were selected purposefully to allow the study objective to be achieved. Thus, one set comprised two cements with very similar compositions but very different viscosities (Cemex RX, a medium-viscosity brand, and Cemex Isoplastic, a high-viscosity brand) while the other set comprised two cements with similar viscosities but with many differences in composition (Cemex Isoplastic and CMW 1). Values of the fracture toughness (as determined using chevron-notched short rod specimens) [K(ISR)] obtained for Cemex RX and Cemex Isoplastic were 1.83 +/- 0.12 and 1.85 +/- 0.12 MPa square root(m), respectively, with the difference not being statistically significant. The K(ISR) values obtained for Cemex Isoplastic and CMW 1 were 1.85 +/- 0.12 and 1.64 +/- 0.18 MPa square root(m), respectively, with the difference being statistically significant. Thus, the influence of cement composition on its K(ISR) is more marked relative to the influence of cement viscosity. Explanations of this finding are offered, together with comments on the implications of the results for the in vivo longevity of cemented arthroplasties.

Contribution to the biological assessment of orthodontic acrylic materials. Measurement of their residual monomer output and cytotoxicity

The acrylic materials used in orthodontics for the fabrication of removable appliances are subjected in the oral cavity to processes of change which influence their physical, mechanical and biological properties. It is therefore essential that every newly developed material must be judged in terms of its clinical value. In the present study, 2 orthodontic cold-cure acrylics, Orthocryl and Forestacryl, and 4 orthodontic photocure acrylics, Triad, Wil-O-Dont, Odontolux and Lux-A-Tech, were investigated and compared with 2 prosthetic acrylic materials: the cold-cure acrylic Palapress and the hot-cure acrylic Paladon. The quantity of residual monomers from methyl methacrylate (MAA) or urethane dimethacrylate (UDMA) eluted from the sample in a given time after the processing was estimated by high pressure liquid chromatography (HPLC). The cytotoxic properties of the materials were examined by Mosmann's proliferation-inhibition test with an established culture of fibroblasts (= MTT test). The hot-cure acrylic Paladon produced by far the smallest amount of eluted residual monomer and the least growth inhibition in the MTT test. The prosthetic cold-cure acrylic Palapress achieved significantly better results than the orthodontic cold-cure materials Orthocryl and Forestacryl. The photocure acrylics released less UDMA than did the cold-cure acrylics MMA. In the cell culture test, all the orthodontic materials examined were assessed as "slightly cytotoxic"; the prosthetic acrylics were graded under ISO-standard 10993-5 as "noncytotoxic". After soaking the plastic material in water for 3 days its cytotoxic properties, as exemplified by the cold-cure acrylic Forestacryl and the photocure acrylic Triad, were reduced, and during the following investigation no more inhibition of growth was observed. It was possible to confirm with the tests used that, for Triad, it is necessary to carefully remove the oxygen-inhibition layer of the photocure acrylic in order to improve the biological properties. The influence of the plastic material on fibroblast cultures was assessed, among other methods, by the quantity of residual monomers liberated. These were significantly reduced after soaking the manufactured substance in water for 3 days. Careful laboratory treatment of the photocure acrylics is necessary in order to improve their biological properties.

Bond strength of brackets cemented with light-cured glass-ionomer cements to contaminated enamel

PURPOSE

To examine the effect of contamination on the bond strength of orthodontic brackets cemented with either a commercial (Fuji Ortho LC) or an experimental light-cured glass-ionomer cement to enamel, and the effect of etching times on the bond strength.

MATERIALS & METHODS

Simulated metal brackets were applied with the cements to bond polished and etched (37% phosphoric acid) bovine enamel with and without contamination by water, human saliva, and blood. After 1-day water immersion, the shear bond strengths were measured. The fractured surfaces were examined using SEM. Additional tests were conducted on: (1) the Knoop hardness of the contaminated cements, (2) the HEMA composition of the cements, (3) the viscosity of the cements, and (4) the intensity of transmitted visible light through the contaminants. The results were compared by ANOVA and Duncan's tests at P=0.05.

RESULTS

Water and saliva reduced the bond strength to polished and etched enamel, except for the bond strength of Fuji Ortho LC to polished enamel. The blood contamination produced poor bond strengths to polished and etched enamel. The experimental cement showed higher bond strengths to polished enamel with water and saliva contamination than Fuji Ortho LC. The bond strength of the experimental cement to etched enamel with and without contamination were comparable to those of Fuji Ortho LC. SEM micrographs revealed that the specimens exhibiting high bond strengths to polished and etched enamel mainly had cement-enamel interface failure and cement-metal mesh interface failure, respectively. Fuji Ortho LC had higher HEMA concentration than the experimental cement. The highest viscosity was measured with blood, followed by saliva and water. Blood contamination, showing the highest attenuation of the light intensity, reduced Knoop hardness of the experimental cement and Fuji Ortho LC.

Degree of conversion in denture base materials for varied polymerization techniques

New processing techniques for denture base acrylic resins have been introduced which have not comparatively quantified the residual monomer content. While proper processing keeps the residual monomer in a tolerable range for most patients, tissue irritation and reaction due to potentially higher residual monomer in these alternative techniques could be a clinical concern. Decreased degree of conversion may influence physical properties as well as biocompatibility. This investigation evaluated the residual monomer content of acrylic resins cured by three different polymerization modes. Materials (polymerization system) evaluated were: Lucitone 199 (conventional process), Accelar 20 (rapid boil-out), and Acron MC (microwave). Fourier transform infrared spectrometry (FTIR) was employed to determine the degree of conversion. All curing methods produced similar results (Lucitone 199 = 92.7% (0.21), Acron MC = 92.6% (0.57), Accelar 20 = 90.9% (0-73). Conversion for Accelar 20 (rapid boil-out technique), though statistically different (P < 0.05, ANOVA) from the other two materials and polymerization techniques, was only slightly less. It is unlikely that the rapid boil-out technique would induce more adverse tissue responses than the other techniques included in this study.

Determination of the compositional distribution of copolymers by frontal analysis continuous capillary electrophoresis

Frontal analysis continuous capillary electrophoresis (FACCE) was carried out for a series of random copolymers of an ionic monomer, sodium 2-(acrylamido)-2-methylpropanesulfonate (AMPS), and a nonionic monomer, acrylamide (AAM). The electropherograms appeared in order of anionic content and were generally sigmoidal, in contrast to that of hyaluronic acid (HA), which was abrupt and discontinuous. This difference could be related to the compositional heterogeneity of the copolymers, completely absent in the biopolymer. Through the range of copolymer composition (10-100% AMPS) the relationship between average mobility and nominal AMPS content could be described by a calibration curve, making it possible to deduce the compositional distribution of copolymer samples.

Effect of processing method on the dimensional accuracy and water sorption of acrylic resin dentures

STATEMENT OF PROBLEM

Acrylic resin complete dentures exhibit certain unavoidable dimensional changes. Processing shrinkage and expansion due to water uptake are 2 important aspects influencing dimensional accuracy.

PURPOSE

This study investigated linear dimensional changes and water sorption of dentures processed by dry and wet heat with different rates of cooling.

METHODS

Fine crosses marked on tinfoil inserts were placed at the incisive papilla and tuberosity regions of edentulous maxillary casts and incorporated into the dentures during polymerization by 3 processing techniques. A traveling microscope was used to measure the distances between the reference points to determine dimensional changes. Water uptake and content were determined by the mass changes of the dentures with an electronic balance. Data of linear dimensional change and water sorption were analyzed by multivariate analysis of variance and analysis of variance, respectively. Bonferroni simultaneous confidence intervals (95%) were applied for multiple comparison.

RESULTS

Dry heat-processed and water bath-processed acrylic resin dentures did not exhibit significant differences in shrinkage (0.42% to 0.58%) at water saturation. Amounts of water sorption of dentures processed by dry and wet heat (0.50 and 0.48 mass%, respectively) were not significantly different, and their associated expansion did not entirely compensate for the processing shrinkage. The initial water content of dry heat-processed dentures (1.77 mass%) was unexpectedly slightly higher than that of wet heat-processed dentures (1.68 mass%). The rate at which the dentures cooled did not affect their initial water content and subsequent water uptake.

CONCLUSIONS

Water uptake of dry and wet heat-processed acrylic resin dentures after deflasking was in both cases low, and the dentures did not reveal significant differences in shrinkage at water saturation. Air oven-processed and water bath-processed acrylic resin dentures show similar dimensional shrinkage at water saturation.

Release of methyl methacrylate from heat-cured and autopolymerized resins: cytotoxicity testing related to residual monomer

Three heat-cured and three autopolymerized acrylic denture bases with different mixing proportions and/or processing methods were investigated for the amount of residual monomer content and methyl methacrylate (MMA) released into saliva after incubation during the first and second 24 hours after processing. A corresponding range of concentrations of MMA was also used to test for cell cytotoxicity using a culture of human oral fibroblasts. The results showed that the amount of residual monomer was dependent not only on the type of polymerization but also on the amount of liquid in the mixture ratio and the processing method. The acrylic resin that had the lowest residual monomer also released the smallest amount of MMA but resins which have higher residual monomer may not necessarily release higher amounts of MMA. MMA, tested in the same range of concentration as the MMA found leached from acrylic resin in this study, was found to be toxic in the cell culture. Therefore, it is recommended that dentists attempt to reduce the amount of leachable substances before insertion of new dentures. In addition, it is recommended that dentists advise their patients not to wear newly made dentures overnight, as this may cause mucosal irritation from the potential accumulation of leachable substances.

[The tissue reaction to acrylic plastics modified by supercritical extraction with carbon dioxide]

The process of extraction of admixtures from acryl plastic widely used in dentistry by means of supercritical carbon dioxide (sc-CO2) was studied and effects of extraction conditions on biocompatibility and toxicity of resultant materials assessed, sc-CO2 effectively purified the specimens from toxic compounds (monomers and low-molecular oligomers, methylmethacrylate, dichloroethane) and notably improved the biocompatability of polymer implants. Tissue reaction to ethacryl and protacryl depends on the degree of implant polymerization and duration of extraction of toxic substances from polymer.

NMR imaging application to the study of adsorption/precipitation of chemicals inside porous media

Chemical inhibitors are widely used to prevent undesired precipitation of salts (e.g., CaCO3 or CaSO4) inside formations. The phase behaviour of solutions of phosphine-polyacrylic acids, (PPAA) which belong to a widely used class of threshold inhibitor, investigated in presence of Ca2+ ions and placed in a column packed with quartz sand. Solutions were prepared using deuterated water (99.9%) as solvent. T1-weighted spin-echo images gave profiles of the distribution of phosphine-polyacrylic acids during flow of the solutions inside the sandpack, while spatially resolved T2 estimation (by nonlinear least-square fitting of several images acquired by varying the echo time) allowed precipitation phenomenon to be probed. In fact, spin-spin relaxation, which is particularly sensitive to slow motions, was affected by a precipitation process that caused a relevant T2 decrease in the area of interest. No adsorption occurred under the conditions adopted, whereas precipitation was visualized at the interface area between the different solutions. The phenomenon was very slow and was mainly governed by diffusion of the chemicals.

Comparison of chemical analysis of residual monomer in a chemical-cured dental acrylic material to an FTIR method

OBJECTIVE

The purpose of this work was to perform quantitative analysis of residual monomer in chemical-cured acrylic using an infrared spectroscopic method and to compare it to an accepted form of quantitative chemical analysis. Identical samples of acrylic were analyzed and compared using Fourier transform infrared (FTIR) spectroscopy with multiple standard additions vs. "wet" chemical analysis of bromination followed by titration.

METHODS

Two 6 g disks from a single mix of cold-cured acrylic (Lang Dental Mfg. Co., Inc.) were prepared and cured in room air for 1 hr using a ratio of 12 g of powder to 8 mL of liquid. One of the cold-cured acrylic disks was dissolved in glacial acetic acid and analyzed according to the "wet" technique described by Smith and Bains (Smith and Bains, 1956). The other disk was dissolved in methyl isobutyrate (MIBT). Five aliquots, zero plus four incremental additions of pure methyl methacrylate (MMA), were prepared from the MIBT solution. Absorption spectra were collected for all five aliquots. The data were plotted with the ratio of the mass of methyl methacrylate added to the mass of aliquot of MIBT solution as the independent variable, and the absorption, corrected for dilution, as the dependent variable. Least squares fit of the data yielded the slope and intercept. The ratio of intercept to slope divided by the weight fraction of the acrylic disk dissolved in MIBT yielded the concentration of methyl methacrylate in the disk.

RESULTS

The plot of absorbance as a function of mass ratio of MMA added to MIBT solution was linear over the concentration range covered (r = 0.999). Analysis of the spectroscopic data revealed a concentration of residual C = C double bonds of 0.32 +/- 0.01 mol/kg. "Wet" chemical analysis of the acrylic yielded a concentration of residual C = C double bonds of 0.288 +/- 0.003 mol/kg. There was significant difference (students t-test, 99% confidence level) between the two techniques with respect to the amount of residual monomer calculated.

SIGNIFICANCE

The multiple standard additions technique works well for the quantitative analysis of small amounts of residual double bonds in the poly(methyl methacrylate) chemical-cured acrylic polymer system, eliminating the need for an internal standard or external calibration.

Fluoride release of restorative materials exposed to a fluoridated dentifrice

The purpose of this study was to examine the effect that brushing with a fluoridated dentifrice (Crest--Procter and Gamble) has on the fluoride release of restorative materials. Thirty standardized discs were fabricated; 10 were P-50 (3M) nonfluoridated composite resin (control), ten were Heliomolar Radiopaque (Ivoclar/Vivadent) fluoride releasing composite resin, and ten were Ketac Fil (ESPE) glass ionomer cement. Specimens were placed into separate containers of 10 mL deionized water. Half the specimens from each group were brushed with fluoridated dentifrice for two minutes twice per day and rinsed. The fluoride level of each specimen was evaluated for thirty days, using a fluoride specific ion analyzer. An analysis of variance (ANOVA) and Duncan's test (p < 0.05) indicated significant differences in fluoride release. The brushed glass ionomer was significantly higher than all other groups and the glass ionomer not brushed was significantly higher than all composite groups. Glass Ionomer Cement-brushed > Glass Ionomer Cement > Fluoridated Composite Resin-brushed = Fluoridated Composite Resin = Composite Resin-brushed = Composite Resin. Brushed glass ionomer appears to release the highest fluoride level, acting as a fluoride reservoir from the dentifrice for subsequent fluoride release.

Laboratory evaluation of three visible light-cured resinous liners

OBJECTIVES

The aim of the present study was to evaluate the composition and the laboratory performance of three visible light-cured resinous liners (Cavalite, Ionoseal and Timeline).

METHODS

Monomers were separated from fillers and were analysed by HPLC. Set pastes were analysed by FTIR spectroscopy and diametral strengths and water solubility were measured.

RESULTS

The monomers identified in the liners were BisEMA/2-HEMA (Cavalite), BisDMA/BisGMA (Ionoseal) and UEDMA (Timeline). Significant variations were found in the filler content but the mechanical response as assessed by the diametral tensile strength showed no statistical differences. The curing efficiency ranged from 24.2 to 31.0% (top surfaces) to 26.0-54.0% (bottom surfaces) of remaining C = C bonds. No positive correlations were found between curing efficiency and optical properties. The bond strength of the liners to dentine was negligible compared with that to composite. All the liners demonstrated extensive gap formation and debonding at the liner-dentine interfaces in marginal adaptation testing. Statistical differences were noticed in the water absorption and water solubility values of the products. Ionoseal showed extensive hydrolytic degradation compared with the other liners. No evidence of acid-base reaction was found in the set products.

Thermoforming polymethyl methacrylate

This study characterized a range of commercially available polymethyl methacrylate sheets with respect to molecular weight, residual monomer content, and glass transition temperature and then developed a thermoforming procedure that produced visually satisfactory thermoformed polymethyl methacrylate specimens. Molecular weight values of Perspex material were considerably greater than those of the other materials. All materials but Diakon had residual monomer concentrations of less than 1% and glass transition temperature values greater than 100 degrees C. Perspex material was selected for further investigation. It was necessary to preheat Perspex sheets in an oven at 160 degrees C for at least 30 minutes before heating and forming on the thermoforming apparatus to obtain acceptable specimens.

The effect of preparation conditions of acrylic denture base materials on the level of residual monomer, mechanical properties and water absorption

OBJECTIVES AND METHODS

The curing of several commercial powder/liquid mixtures of acrylic denture base materials was carried out at different temperatures and curing times. The levels of residual monomer, tensile strength, percentage elongation before break and water absorption were measured.

RESULTS AND CONCLUSION

It was found that the level of residual monomer determined by gas-liquid chromatography decreased with curing time and temperature increase. At the same time, the tensile strength was improved and water absorption decreased.

A new light-cured glass ionomer cement that bonds brackets to teeth without etching in the presence of saliva

Previous studies stress certain advantages of glass ionomer cements, for use in bonding orthodontic brackets to teeth. Failure rate, however, had been higher than with conventional procedures. A new light-cured glass ionomer cement exhibited all the necessary qualities needed to bond brackets, without any etching and in the presence of saliva. The tensile strength of this cement exhibited enough resistance to forces needed to move teeth. The debonding procedures were also completely undamaging to the underlying enamel surfaces. On removal of the appliances, no decalcification was observed on any teeth, because the cement releases fluoride. Both the time saved during a routine strap-up, plus the ease to both the operator and the patient, could make light-cured glass ionomer cement the ultimate choice for bonding techniques after many trials, this cement is now being routinely and successfully used on all patients.

Modified polyalkenoate (glass-ionomer) cement--a study

Conventional glass-ionomer cements with varying amounts (5-15%) of borax (Na2B4O7.10H2O) as modifier were prepared. These mixtures were spatulated with an aqueous solution of polyacrylic acid with a powder to liquid (P/L) ratio of 1.5:1. Properties such as working time, setting time, compressive strength, diametral tensile strength, solubility and fluoride release of these cements were determined. It was observed that the working time and setting time of the resultant cements shortened with the addition of borax. Certain physical properties such as compressive and diametral tensile strength, solubility and disintegration of these glass-ionomer cements deteriorated with borax addition but fluoride release from them was unaffected.

A clinical evaluation of posterior composite resin restorations

There is a trend towards manufacturers seeking to provide dentists with a single, all-purpose composite resin, usually of the small particle hybrid type. This three-year clinical study compared the clinical performance of three different types of composite resin used in posterior teeth and identified several modes of failure. Of the 330 restorations (three composite resins and one amalgam control) initially placed in 72 patients, 223 restorations in 48 patients were available for evaluation at three years. Modified clinical criteria for assessing the restorations were able to discriminate among the composite resins. A microfilled composite and a small particle hybrid exhibited increasing evidence of marginal fracture (crevice) with time. In addition, the small particle hybrid showed evidence of wear at the margins more frequently than the other materials. Of the restorations available for assessment, four restorations of each of these two types of composite resin required replacement during the study. Coarse particle hybrid restorations showed evidence of wear but little evidence of marginal fracture.