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At least 19 recordsLinked to original sources
PubMedDate not supplied

Monitoring of acid-base status of workers at a methyl methacrylate and polymethyl methacrylate production plant in Bulgaria.

This study was carried out on 104 workers at three work operations and a control (nonproduction) area, within a methyl methacrylate (MMA)/polymethyl methacrylate (PMMA) production facility in Bulgaria. Airborne monitoring was conducted over a 10-year period for MMA and the reactant chemicals methanol and acetone cyanhydrine at the MMA operation, and MMA was monitored at the PMMA operation. Acid-base status of the workers was evaluated using traditional criteria (pH, pCO(2), pO(2), and HCO(3) in plasma). Data from retrospective monitoring of air levels of the chemicals were compared with the acid-base status of workers at the plant. In some cases air concentrations exceeded the threshold limit value, with the highest percentage of overexposure occurring with airborne MMA in the PMMA production operation. Acid-base disruption indicated by reductions in plasma pH and HCO(3) was found for all groups except the control population. The highest percentage reduction was associated with PMMA production workers. Additionally, respiratory acidosis, indicated by increased pCO(2), was noted in the MMA production and maintenance groups, implying that the response to MMA exposure may involve both the metabolic and respiratory acidosis component. This study was unique in that the combined exposure to MMA and the precursor chemical (methanol) were shown to produce the same effects in workers. It is suggested that when combined exposure occurs, disruption of acid-base status may occur. Enforcement of PPM requirements for coveralls and gloves should prevent skin contamination. Additionally, improvement of equipment in MMA and PMMA production areas is recommended: (1) automation of some manual operations; (2) use of respiratory protection during equipment cleaning; and (3) installation of local ventilation when applicable.

Acid-Base Imbalance↗
PubMed1997

Water sorption and solubility of glass fiber-reinforced denture polymethyl methacrylate resin.

Polymethyl methacrylate (PMMA) absorbs water slowly over a period of time, primarily because of the polar properties of the resin molecules. The aim of this study was to determine the water sorption and solubility of heat-cured and chemical-cured glass fiber (GF) PMMA composite used in dentures. The test specimens (n = 5) were fabricated from experimental, unidirectional, continuous GF reinforcement; the GF concentration of the test specimens was approximately 11% by weight. Water sorption and solubility were tested in accordance with International Standards Organization specification No. 1567. The results revealed that the type of acrylate had more of an effect on water sorption than did the presence of GF reinforcement in the test specimen (p = 0.001 and p = 0.049, respectively). In the GF-reinforced test specimens the type of PMMA also affected the water sorption values (p = 0.006). GF reinforcement affected the solubility values of the test specimen (p = 0.002), but the type of acrylate had no effect on solubility (p = 0.585). The results of this study suggest that the water sorption and solubility of unreinforced PMMA and PMMA reinforced with GF are in accordance with International Standards Organization specification No. 1567.

Absorption↗
PubMed2002

Snowflake degeneration of polymethyl methacrylate posterior chamber intraocular lens optic material: a newly described clinical condition caused by unexpected late opacification of polymethyl methacrylate.

OBJECTIVE: To report 25 cases of gradual, but sometimes progressive, late-postoperative degeneration of polymethyl methacrylate (PMMA) optics of posterior chamber (PC) intraocular lens (IOL) implants, often resulting in a clinically significant visual decrease long after the implantation, sometimes to a severity that required IOL explantation/exchange. DESIGN: Analysis of explanted PC IOLs, clinical histories, and photographs. PARTICIPANTS: We analyzed 25 case histories/photographs and/or explants from 18 patients implanted in the 1980s to mid-1990s with three-piece PC IOLs with PMMA optics and with polypropylene or PMMA haptics. The IOL optic from each case had characteristic snowflake or crystalline opacifications. This condition occurred with more than one manufacturer and in some cases was restricted to certain lot numbers. METHODS: The explanted IOLs (n = 10) were studied by gross inspection and by light and scanning electron microscopy, as well as confocal and energy dispersive spectroscopy. MAIN OUTCOME MEASURES: The snowflake lesions were noted within the IOL optics. The nature of these lesions was investigated. RESULTS: Assimilation of clinical information with pathologic and morphologic profiles of all cases suggested that the snowflake opacification was a small spherical lesion surrounded by an outer pseudocapsule composed of compressed, degenerated PMMA, with a central core containing convoluted fragments of PMMA. The lesions were classified into four clinical and pathologic grades according to their density and severity. CONCLUSIONS: This is the first clinicopathologic correlative report on this complication. We postulate that manufacturing variations in some IOL models fabricated in the 1980s and early 1990s are responsible. The snowflake lesions seem to represent a destruction of the PMMA material. The cluster of lesions in implanted lenses manufactured by Surgidev was less progressive than some other models, including lenses made by IOPTEX Research Corporation. This identification of a condition previously unreported is important to alert clinicians regarding these perplexing lesions that may otherwise be considered idiopathic, with no obvious clinical hint as to their origin. The prevalence noted thus far is still too low to in any way suggest that this condition would occur in 100% of PMMA IOLs from these manufacturers. However, these late-occurring lesions, present in lens models that were implanted in hundreds of thousands of patients in the last decade or so, could have constituted a true epidemic, except that many of the patients are now deceased.

Device Removal↗
PubMed1996

Dimensional accuracy of thermoformed polymethyl methacrylate.

Thermoforming of polymethyl methacrylate sheet is used to produce a number of different types of dental appliances. The purpose of this study was to determine the dimensional accuracy of thermoformed polymethyl methacrylate specimens. Five blanks of the acrylic resin were thermoformed on stone casts prepared from a silicone mold of a brass master die. The distances between index marks were measured both on the cast and on the thermoformed blanks with an optical comparator. Measurements on the blanks were made again 24 hours after processing and then 1 week, 1 month, and 3 months after immersion in water. Linear shrinkage of less than 1% (range 0.37% to 0.52%) was observed 24 hours after removal of the blanks from the cast. Immersion of the thermoformed specimens in water resulted in an increase in measured dimensions, but after 3 months' immersion these increases were still less than those of the cast (range 0.07% to 0.18%). It was concluded that it is possible to thermoform Perspex polymethyl methacrylate accurately.

Dental Materials↗
PubMed1998

In vivo cytogenetic studies of the genotoxic effects of polymethyl methacrylate employed in orthopaedics.

Polymethyl methacrylate (PMMA) is a material employed as a cement in prosthesis that has been found to induce cytogenetic damage in human lymphocytes in vitro. This effect is particularly achieved before the 5th day of the exposition, while after this period no significant variations appeared. In the present study, results of cytogenetic tests in humans are reported. Sister chromatid exchange analysis and micronucleus tests have been performed on lymphocytes of patients who had undergone prosthesization with cemented prosthesis (group A) or with biological anchorage prosthesis, as control (group B). DNA damage was investigated before implantation and 5 d after surgery in both groups. Cytogenetic tests did not show any significant increase in the number of micronuclei and sister chromatid exchanges with respect to control values in patients with PMMA cemented prosthesis.

Journal Article↗
PubMed1998

Flow characteristics of curing polymethyl methacrylate bone cement.

During polymerization, polymethyl methacrylate bone cements have complex viscoelastic characteristics. Within a short working time they transform from dough-like consistencies to solid cements. Therefore, the time at which a cement is introduced to cancellous bone surfaces and subjected to pressure is important, to achieve optimum flow and mechanical interdigitation. Achieving adequate mechanical interlock increases the area for load transfer and reduces localized bone-cement interface stresses. The aim of this study was to measure the flow characteristics for commercial bone cements as a function of time and calculate the apparent viscosities for the curing bone cements. The capillary extrusion method was used to measure the rate of flow of the curing cement, by means of a melt flow index apparatus, which was manufactured in-house. The tests were conducted using nozzles of different lengths and under two loads. This enabled the power index value, n, and the pressure at the die entry, P0, to be calculated for each material with respect to time. Once the flow characteristics were determined, a series of formulae were used to calculate the shear rates, gamma, the shear stresses, tau, and the apparent viscosities, eta a, of the curing bone cements. The results indicated that acrylic bone cements are non-Newtonian, pseudoplastic materials, since the power index values are less than 1.0 during the curing stage. The consistency indices, K, were calculated from the shear stress versus shear rate data. The apparent viscosities of the cements were found to increase with respect to increases in time. Clinically, it was considered desirable to inject and pressurize the cement into the medullary canal while its viscosity is relatively low in order to obtain maximum interdigitation into cancellous bone, provided adequate containment and a means of pressurization can be achieved. The pseudoplastic character of bone cements is responsible for their reduction in viscosity with increased shear rate, a property that may be exploited to enhance penetration with appropriate delivery.

Biocompatible Materials↗
PubMedDate not supplied

Long-term efficacy of biomodeled polymethyl methacrylate implants for orbitofacial defects.

OBJECTIVE: To report the long-term efficacy of custom polymethyl methacrylate implants using high-resolution computed tomographic modeling in the reconstruction of complex orbitofacial defects secondary to trauma. METHODS: Nine patients with complex orbitofacial bone defects after trauma were evaluated for this retrospective, nonrandomized, noncomparative study. All the patients underwent reconstruction using custom, heat-cured polymethyl methacrylate implants. Patients were followed up postoperatively and evaluated for complications. RESULTS: Nine consecutive patients (5 men and 4 women) aged 28 to 63 years who underwent surgical reconstruction using prefabricated, heat-cured polymethyl methacrylate implants were included in the study. The interval between injury and presentation ranged from 1 month to 40 years. There were no significant complications, including infection, extrusion, or displacement of the implant. In all of the patients, wound healing was uneventful, with antibiotic drugs administered perioperatively. Mean follow-up was 4.3 years from the first visit (range, 6 months to 10 years). CONCLUSIONS: Computed tomographic biomodeled, prefabricated, heat-cured polymethyl methacrylate implants are well tolerated in the long term. Their advantages include customized design, long-term biocompatibility, and excellent aesthetic results.

Adult↗
PubMed1997

Effect of methacrylic acid:methyl methacrylate monomer ratios on polymerization rates and properties of polymethyl methacrylates.

Five binary formulations were prepared from methyl methacrylate (MMA) and methacrylic acid (MAA) monomers, and six ternary formulations were prepared from polysols of 30% wt polymethyl methacrylate (PMMA)/MMA and MAA. Using thermal analyses (DSC and TGA) the polymerization kinetics, condition of postcuring, relative amount of residual monomers, and glass transition temperature (Tg) were determined. From bar-shaped samples, 25 x 5 x 0.9 mm in dimensions, mechanical properties [flexural moduli (E) and maximum strengths (sigma)] were measured in three-point bending. Polymerization kinetics of binary formulations improved over pure PMMA (from 15 to 4 min) as a result of over a 60-fold increase in propagation-to-termination constants (Kp/Kt) of MAA/MMA. The further addition of PMMA increased the viscosity, slowed down termination, and, consequently, improved the polymerization kinetics twofold. These enhancements occurred without a substantive change in the Tg of the ternary system (ca. 107 degrees C) over pure PMMA (ca. 112 degrees C). Moreover, the Es of the four ternary formulations averaged 2.94 GPa, which was comparable with many values reported in the literature. In contrast the sigma s of these same formulations averaged 97 MPa, which was about 25% better than earlier investigations of pure acrylic. When a thermoplastic material is required for pultruding profiles that cure fast and have good thermal-mechanical properties, ternaries of PMMA/MMA/MAA should be considered.

Biocompatible Materials↗
PubMed1997

Estimation of monomer content in polymethyl methacrylate contact lens materials by Raman spectroscopy.

Polymethyl methacrylate is the most commonly used contact lens material due to its excellent optical properties. However the presence of residual monomer in the structure alters its transparency as well as its biocompatibility, thus, there is a need to detect any remaining methyl methacrylate. Raman spectroscopy is a rapid, sensitive, and non destructive method as compared to other spectroscopic, chromatographic or polarographic methods. In this study, the spectra of some lens materials (prepared from methyl methacrylate, 2-hydroxy ethyl methacrylate, Hexamethyl disiloxane and polypropylene glycol with or without the addition of crosslinker ethylene glycol dimethylacrylate) were obtained by Raman spectroscopy. It was observed that an amount of crosslinker present in the structure proves effective for the unpolymerized monomer content. None of the samples, except those containing nexamethyl disiloxane, demonstrated any monomer residue.

Biocompatible Materials↗
PubMed1987

A polymethyl methacrylate method for large specimens of mineralized bone with implants.

A simple modified polymethyl methacrylate method is described for large mineralized bone specimens with implants and bioactive materials which produces consistently good histological preservation of the interface between bone and implant. Human femoral heads, whole rabbit condyles and canine tibias and femurs containing implants consisting of hydroxyapatite, smooth polyethylene, porous polyethylene and carbon were dehydrated in ascending grades of ethanol and cleared with xylene on an automated tissue processor which alternated vacuum and pressure for 22 hr. Infiltration was done with washed polymethyl methacrylate at 4 C under vacuum for 13 days. Polymerization was carried out in wide-mouth glass jars at 38 C for 36 hr so that the total processing time was less than 20 days. The only important modification was in the polymethyl methacrylate, which had less plasticizer than usual in order to give a harder block. This enabled production of 4 micron sections with good preservation of mineralized and cellular areas for the study of metabolic bone diseases, morphometry, fluorochrome labelling and interface analysis with the implant in situ.

Animals↗
PubMed1992

Histopathological evaluation of polymethyl methacrylate as an embolic agent.

Polymethyl methacrylate (PMMA) microspheres were used as an embolic agent to reduce the vascularity in eight patients with intracranial vascular tumours. Post embolization angiograms showed 30-60% reduction in the vascularity of the tumours. No patient developed any neurological complications in the immediate post-embolization period. These eight patients subsequently underwent surgery for the removal of their tumours. During surgery there was minimal blood loss and a good plane of cleavage was obtained between the tumour and the adjacent brain. The surgical specimens were examined histopathologically for the effects of PMMA. PMMA microspheres, in contrast to other cyanoacrylates--isobutyl-2-cyanoacrylate (IBCA)--did not elicit either inflammatory reaction or mural angionecrosis within the wall of the embolised vessels. The histopathological studies suggest that PMMA microspheres are an inert material and can be used as an adjunct in the management of intracranial vascular tumours.

Adult↗
PubMed2006

Biomechanical evaluation of vertebroplasty and kyphoplasty with polymethyl methacrylate or calcium phosphate cement under cyclic loading.

STUDY DESIGN: We developed a new method to simulating in vivo dynamic loading as closely as possible, which allows comparison of kyphoplasty and vertebroplasty, as well as augmentation materials. OBJECTIVE: Special interest was given to calcium phosphate cement, which might fail due to its brittleness. SUMMARY OF BACKGROUND DATA: Vertebroplasty and kyphoplasty are, with limitations, 2 promising alternative techniques to augment osteoporotic vertebrae with polymethyl methacrylate or calcium phosphate cements. However, little is known about the fatigue characteristics of the treated vertebrae under cyclic loading. METHODS: Twenty-four intact, osteoporotic bi-segmental human specimens were divided into 4 groups: (1) vertebroplasty with polymethyl methacrylate, (2) kyphoplasty with polymethyl methacrylate, (3) kyphoplasty with calcium phosphate cement, and (4) untreated control group. After augmentation of the middle vertebrae, all specimens underwent 100,000 cycles of eccentric loading during which the specimen revolved around its longitudinal axis. Pre-loading and post-loading radiographs, and subsidence measurements at different sites of the vertebrae were taken. The overall height was additionally determined every 20,000 cycles in the material testing machine. Finally, the specimens were cryosectioned to examine the cements. RESULTS: Loss of height progressed with strong individual differences in all groups, with an increasing number of load cycles up to median values of 2.8 mm for both augmented groups and 4.2 mm for the nonaugmented group. At the center of the upper endplate, subsidence in kyphoplasty was greater than in vertebroplasty, with little differences with respect to the kind of cement. The cryosections did not show any signs of fatigue in the polymethyl methacrylate, but small cracks were in the calcium phosphate. CONCLUSIONS: Vertebroplasty and kyphoplasty seem to be equivalent methods in strengthening osteoporotic vertebrae. However, these results cannot be transferred to the treatment of fractures with these methods. A "physiologic" loading situation was achieved by complex motion, including all combinations of flexion/extension with lateral bending during eccentric cyclic loading.

Aged↗
PubMed1995

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.

Acrylic Resins↗
PubMed1986

Evaluation of the burst mode of a neodymium: YAG laser in saline and polymethyl methacrylate.

We evaluated effect of burst mode on the plasma length of a Q-switched Neodymium: YAG laser in saline and polymethyl methacrylate with or without UV-absorbing pigment. In a saline solution, the plasma length was independent from the number of pulses used. In polymethyl methacrylate the plasma length increased proportional to the number of pulses in a burst mode. This effect was more pronounced in polymethyl methacrylate with UV absorber than without UV-absorbing pigment.

Cataract Extraction↗
PubMed2005

Management of intra-abdominal hypertension in patients with severe acute pancreatitis with continuous hemodiafiltration using a polymethyl methacrylate membrane hemofilter.

To evaluate, with a prospective observational study, whether continuous hemodiafiltration using a polymethyl methacrylate membrane hemofilter (PMMA-CHDF) is effective for prevention and treatment of intra-abdominal hypertension (IAH) and abdominal compartment syndrome (ACS) on patients with severe acute pancreatitis (SAP). The study was carried out in the general intensive care unit (ICU) of a university hospital. Seventeen consecutive patients with SAP were treated in the intensive care unit and underwent PMMA-CHDF whether or not they had renal failure. Blood level of interleukin (IL)-6, as an indicator of cytokine network activation, and intra-abdominal pressure (IAP) were measured daily to investigate their time-course of changes and the correlation between the two. The blood level of IL-6 was high at 1350+/-1540 pg/mL on admission to the ICU. However, it significantly decreased to 679+/-594 pg/mL 24 h after initiation of PMMA-CHDF (P<0.05), and thereafter decreased rapidly. Mean intra-abdominal pressure (IAP) on admission was high, at 14.6+/-5.3 mm Hg, with an IAP of 20 mm Hg or over in 2 of 17 patients, showing that they had already developed IAH. The IAP was significantly lower (P<0.05) 24 h after initiation of PMMA-CHDF, and subsequently decreased. There was a significant positive correlation between blood level of IL-6 and IAP, suggesting that PMMA-CHDF improved vascular permeability through elimination of cytokines, and that it thereby decreased interstitial edema to lower IAP. Sixteen of the 17 patients were discharged from the hospital in remission from SAP without development of complications. Continuous hemodiafiltration using a polymethyl methacrylate membrane hemofilter appears to be effective for prevention and treatment of IAH in patients with SAP through the removal of causative cytokines of hyperpermeability.

Abdomen↗
PubMed1994

Tinting effect of ultraviolet radiation on intraocular lenses of polymethyl methacrylate.

Intraocular lenses (IOL) made of polymethyl methacrylate (PMMA) lack an important yellowish pigment useful as a filter in the visual process and in the protection of the retina from short wavelength light. It was found that the PMMA used for IOL manufacturing can be tinted by dry exposure to mercury near-UV emitting lamp (emission maximum, 365 nm, light bandwidth +/- 140 nm; irradiance of 50-100 W/sq m as measured at the PMMA surface; time of exposure 70-100 h, room temperature). The UV irradiated samples were stored in the atmosphere of N2 under the heating-protected and clean conditions. The IOL sample holder allowed to remove IOL loops and their fixation areas from the zone of the passing light. The absorptive properties of IOLs treated with UV light were similar to those of young human lenses. Raman vibration and fluorescence spectral analyses of IOLs have shown that the yellow colour and its intensity in the irradiated samples depends on the presence of conjugated C = C and C = O groups (pi-pi conjugation) in the chemical composition of PMMA. When the PMMA samples were exposed for 70 h to a high level of UV radiation (50-100 W/sq m) no damage was seen with scanning electron microscopy at both side surfaces of the IOLs. The PMMA water exhaustive extracts made by 70 h of UV radiation exposure did not show any cytological damage when injected into the cell cultures of fibroblasts. The threshold for optical breakdown in PMMA was detected by 100 h of UV radiation at the level of exposure equivalent to at least 20,000 times levels for expected ambient UV exposure to PMMA within the eye. A rigorous quality index defined as the ratio of the line C = C/C = O stretching mode intensities was introduced for the UV-absorbing PMMA photostability. The findings suggest an applicability of the photochemical tinting and further research to test the efficacy and safety of UV-absorbing chromophore induction in the PMMA IOLs.

Absorption↗