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Results for “Polymethyl Methacrylate”

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At least 289 records · Page 16Linked to original sources

PubMed1998

Repair of acrylic resin denture base reinforced with glass fiber.

STATEMENT OF PROBLEM: The ultimate goal of any denture repair is to restore the original strength of the denture and to avoid further fracture. PURPOSE: This study investigated the strength and deflection of repaired acrylic resin joints reinforced with various glass fiber concentrations. MATERIAL AND METHODS: Transverse strength, maximum deflection, and modulus of elasticity of glass fiber-reinforced polymethyl methacrylate acrylic resin were studied with a 3-point load test on 54 intact specimens. Six concentrations of type B glass fiber specimens were prepared (n = 9 per each fiber group). Fractured joint margins were rounded, a 2-mm gap was placed between them, and then they were repaired with autopolymerizing acrylic resin and retested. RESULTS: Transverse strength, maximum deflection, and the stiffness of all joints were significantly lower after the repair. Among the groups tested, the units treated with 1% glass fiber displayed the highest transverse strength before and after repair. Modulus of elasticity of the repaired 1% fiber concentration units was enhanced by approximately 25% over those repaired but untreated with glass fiber (0% fiber).

Analysis of Variance↗

PubMed1999

Temperature-dependence of the mechanical properties of FRP orthodontic wire.

The temperature-dependence of the mechanical properties of a new esthetic orthodontic wire with fiber-reinforced plastic (FRP) structure was investigated. The new FRP wire, fabricated by a hot drawing method, is 0.5 mm in diameter and has a multiple fiber structure composed of biocompatible CaO-P2O5-SiO2-Al2O3 glass fibers of 20 microns in diameter and a polymethyl methacrylate matrix. The flexural load at a deflection of 1 mm and Young's modulus at 24, 37, and 50 degrees C under wet conditions showed similar fiber fraction dependence to those under dry conditions for a fiber fraction of 40-51%. The flexural load and Young's modulus tended to decrease slightly with increases in temperature. This tendency was larger for the lower fiber fraction. However, the difference in flexural load for a temperature difference of between 24 degrees C and 50 degrees C was at most 10 gf. This is negligibly small, and a constant orthodontic force regarding temperature change would be advantageous from a clinical point of view.

Elasticity↗

PubMedDate not supplied

A statistical comparison of denture sanitation using a commercially available denture cleaner with and without microwaving.

Polymethyl-methacrylate dentures, worn by patients for periods ranging from 12 days to 48 years, were cultured and found to be heavily contaminated with a variety of microorganisms both externally and internally. A commercially available denture sanitizer, used as prescribed by the manufacturer, was ineffective at decontaminating the dentures. This study examined the effectiveness of this denture sanitizer when used in combination with a microwaving procedure. Statistical methods were used to compare the decontamination results of the denture sanitizer applied with and without microwaving. The statistical results indicated that the dentures were decontaminated most effectively when the denture sanitizer was used in conjunction with a two-minute microwave procedure.

Analysis of Variance↗

PubMed2004

Thermal degradation of PMMA in fluidised beds.

In recent years, the production and consumption of plastics have increased significantly and wastes are commonly incinerated or dumped in a landfill. Plastics pyrolysis, on the other hand, may provide an alternative means for disposal of plastic wastes with recovery of valuable gasoline-range hydrocarbons or the monomer. Pyrolysis of polymethyl methacrylate (PMMA) may result in very high recycling rates (90-98%) of the monomer methylmethacrylate (MMA) since the cracking of MMA to lighter molecules (CO2, CO and light hydrocarbons) is limited. The MMA-yield is mainly dependent on the residence time of the gas in the reactor and to a lesser extent on the operating temperature. The paper presents experimental work performed in a lead bath and in a fluidised bed. At low temperatures, the reaction is kinetically controlled, whereas at high temperatures, heat transfer restricts the overall reaction rate. It was demonstrated that the heat transfer in the fluid bed could be estimated by the equation of Kothari. A design procedure for a fluid bed PMMA-depolymerisation reactor is outlined and illustrated for a process of 1 tpd PMMA.

Bone Cements↗

PubMed2005

A novel percutaneous system for bone graft delivery and containment for elevation and stabilization of vertebral compression fractures. Technical note.

OBJECT: Vertebroplasty and kyphoplasty are minimally invasive procedures used to treat persistently symptomatic vertebral compression fractures (VCFs). Both interventions usually involve injection of polymethyl methacrylate (PMMA). The purpose of this technical note was to review the theory and surgical technique for a novel percutaneous system for fracture reduction and stabilization of VCFs by using bone graft. METHODS: This technical note highlights the Optimesh system as an alternative method of minimally invasive VCF reduction and stabilization with the delivery of a bone graft containment device. Instead of using PMMA as in vertebroplasty or kyphoplasty, this system allows the delivery of allograft and/or autograft bone, with its osteoinductive, osteoconductive, and osteogenic properties. CONCLUSIONS: This system allows for restoration of sagittal alignment of the spine with direct control of bone graft delivery by using a mesh graft containment device that allows for ingrowth of new bone and vascular tissue.

Bone Cements↗

PubMed1997

Factors determining rigid contact lens flexure.

BACKGROUND: Many factors have been demonstrated to influence flexure of rigid contact lenses, but the contributions of surface tension and eyelid forces to flexure are not well understood. METHODS: We placed lenses on a model eye consisting of a polymethyl methacrylate (PMMA) base which could be flexed, and measured resultant flexure with a videokeratoscope. We varied the base toricity, sequence of measurement, and lens base curve. The effects of evaporation of the postlens fluid were also observed. RESULTS: Clinically significant flexure (> 0.50 D) occurred when two conditions were met: (1) the volume of the postlens space would increase if the lens unflexed, and (2) there was a paucity of fluid available to fill that space. Flexure was minimal (< or = 0.50 D) when ample fluid was present. CONCLUSION: Surface tension forces serve more to maintain rather than create rigid lens flexure. Our model helps to explain why steep-fitting lenses flex more and leads to several predictions for flexure, which appear generally to be obeyed.

Contact Lenses↗

PubMed2005

PMMA: an essential material in medicine and dentistry.

The first use of polymethyl methacrylate (PMMA) as a dental device was for the fabrication of complete denture bases. Its qualities of biocompatibility, reliability, relative ease of manipulation, and low toxicity were soon seized upon and incorporated by many different medical specialties. PMMA has been used for (a) bone cements; (b) contact and intraocular lens; (c) screw fixation in bone; (d) filler for bone cavities and skull defects; and (e) vertebrae stabilization in osteoporotic patients. The many uses of PMMA in the field of medicine will be the focus of this review, with particular attention paid to assessing its physical properties, advantages, disadvantages, and complications. Although numerous new alloplastic materials show promise, the versatility and reliability of PMMA cause it to remain a popular and frequently used material.

Biocompatible Materials↗

PubMed2003

Water sorption, solubility and dimensional changes of denture base polymers reinforced with short glass fibers.

The aim of this study was to determine water sorption, solubility and dimensional stability of injection and compression-molded polymethyl methacrylate based denture base polymer that was reinforced with various concentrations and lengths of E-glass fibers. For water sorption and solubility, 20 test groups with different fiber contents and lengths of fibers were prepared. Test specimens without fibers were used as a control. The water sorption and solubility was measured after 90 days water storage. For dimensional stability, rhombic test specimens were prepared and the dimensional changes were measured after processing, drying and storing in water for 4 days and 30 days and were compared with those on the brass model. The water sorption and solubility of injection-molded denture base polymer was lower compared to compression-molded specimens (p < 0.05). The dimensional accuracy of denture base polymer was not affected with fiber reinforcement (p > 0.05).

Absorption↗

PubMed2003

Soft tissue augmentation with artecoll: 10-year history, indications, techniques, and complications.

Most of the biologic filler materials that increase the thickness of the corium in a wrinkle line are phagocytosed within a certain time. Therefore, a lasting effect can only be achieved with nonresorbable synthetic substances. Artefill consists of 20 volume percent microspheres of polymethyl-methacrylate and 80 volume percent of bovine collagen. Beneath the crease, the microspheres with their exceptional surface smoothness stimulate fibroblasts to encapsulate each individual one of the 6-million microspheres contained in 1 mL of Artefill. Collagen is merely a carrier substance that prevents the microspheres from agglomerating during tissue ingrowth. The 20 volume percent of microspheres in Artefill provides the scaffold for the 80% volume of connective tissue deposition, a complete replacement of the injected collagen. The filler material beneath a crease acts like a splint and prevents the possibility of its further folding, thereby allowing the diminished thickness of the corium in a crease to recover. This recovery process is well known even in older patients with facial paralysis or after a stroke, whose facial wrinkles and furrows on the paralyzed side disappear over time.

Biocompatible Materials↗

PubMed2006

Nanocomposite polymeric electrolytes to record electrophysiological brain signals in prolonged, unconventional or extreme conditions.

Chemically stable nanocomposite iono-conducting polymeric membranes (based on lithium salts and nanocrystalline oxide powders dispersed in a polymethyl methacrylate matrix) performed successfully in the recording of human brain responses to visual stimulation. Impedance was higher than that of conventional electrodes. However, the electrophysiological signals recorded by acid Al(2)O(3) and neutral Al(2)O(3) 5 wt.% and 10 wt.% nanocomposite gel electrolytes were comparable to those obtained with standard electrodes, even without preliminary skin cleaning and in the absence of gel electrolytes allowing better contact with and skin-electrode ionic conductance. The electrochemical and mechanical characteristics of these membranes make them fit for human and animal research, for clinical application (specifically in emergencies, prolonged electrophysiological recordings), or in unconventional or extreme conditions when fluid electrolytes are unsuitable (e.g., biomedical space research).

Animals↗

PubMed1999

Radiation exposure in spiral computed tomography. Dose distribution and dose reduction.

RATIONALE AND OBJECTIVES: The authors investigate the dose distribution of spiral and conventional computed tomography (CT) with film densitometry and to present a new method of evaluating the possibility of dose savings with spiral CT. METHODS: Films were exposed in a cuboid polymethyl-methacrylate phantom in conventional and spiral scan technique. Axial density profiles were obtained by digitizing the films using a fluorescent light scanner. The ratio of the number of rotations in spiral CT to the number of slices in conventional CT was calculated. RESULTS: In spiral CT with a pitch of 2, the densities in all points were lower than those in corresponding points in spiral CT with a pitch of 1 and in conventional CT with slice distance equal to slice thickness. A pitch of 1.5 in spiral CT led to a dose reduction of 14% to 30% compared with conventional CT. CONCLUSIONS: Increasing the pitch in spiral CT leads to a reduction of both integral dose and absorbed doses within the examined body region. The reduction of the integral dose can be significant, especially in cases where slice overlapping is diagnostically advantageous.

Humans↗

PubMed2002

Adsorption of proteins from infant and adult plasma to biomaterial surfaces.

The hemostatic mechanism of the newborn is immature. In general, the clotting times in screening tests are prolonged, the coagulation factors are low, and the coagulation inhibitors (with the exception of alpha-2-macroglobulin) are low. Recognizing that many of the proteins present in infant plasma are at low levels, it is of interest to determine if, following exposure to artificial surfaces, the profile of adsorbed proteins is different for infant versus adult plasma. The question of whether differences in protein profiles could lead to differences in thromboembolic episodes associated with the use of central venous catheters (or other blood-contacting devices) in infant versus adult subjects also is relevant. To address these issues, the adsorption of proteins from pooled infant plasma and pooled normal adult plasma to three different polymer surfaces (polyvinyl chloride, PVC; polymethyl methacrylate, PMMA; and polyethylene oxide-modified polyurethane, PEO-PU) was studied using SDS-PAGE and immunoblotting techniques. The total amount of protein adsorbed to each surface also was determined. It was found that the PMMA and PVC surfaces adsorbed considerably more protein than the PEO-PU surface. Furthermore, the amount of protein adsorbed to the PMMA and PVC surfaces from infant plasma was significantly less than that adsorbed from adult plasma. No such difference was seen for the protein-repellent PEO-PU surface. The immunoblot responses of proteins bound to the PMMA and PVC surfaces from infant plasma were, in general, weaker than those bound from adult plasma. It is likely that these differences were due to decreased protein levels in infant plasma.

Adsorption↗

PubMed2004

The effect of vessel material on granules produced in a high-shear mixer.

In this study the effect of different vessel wall materials on the granule size distributions obtained during high-shear granulation of different materials is investigated. The distributions obtained in glass and stainless steel vessels differ from those obtained in PMMA (polymethyl methacrylate) and PTFE (polytetrafluoroethylene) vessels. The high contact angle of PMMA forces all liquid immediately into the more easily wetted powder bed. In this vessel a fast liquid absorbing powder nucleates in the droplet controlled regime, leading to a narrow particle size distribution. In a vessel with a low contact angle (glass or stainless steel) a liquid layer can be formed on the wall surface. This liquid causes an inhomogeneous distribution of liquid over the powder bed; a broader granule size distribution is the result. With a powder that slowly absorbs liquid, local overwet areas can be created, resulting in large granules. This results in broader granule size distributions as well. In conclusion; the contact angle of the vessel material and the wetting rate of the powder used determine the granule growth process and the resulting granule size distribution.

Algorithms↗

PubMed1998

Fatigue model to characterize cement-metal interface in dynamic shear.

This study evaluated the interface shear strength between vacuum mixed polymethyl-methacrylate and two types of surface enhancements under static and dynamic shear loading. Cobalt chrome coupons with grit blasted or light plasma sprayed surfaces were tested. For each test, two coupons were mounted in a stainless steel chamber such that they were bonded with a 2-mm cement mantle for each test. Pullout and dynamic fatigue tests were performed on an Instron machine. The mean static pullout strength of the grit blasted surfaces was 13.78 (+/- 2.73) MPa, whereas that of the light plasma sprayed surfaces was 18.46 (+/- 1.98) MPa. The rate of degradation of interface strength caused by fatigue was almost identical for both surface treatments. Qualitative analysis showed that the failed light plasma sprayed surface generated more metal and cement particles. These data suggest that light plasma sprayed surfaces sustain higher loads but have a potential for increased debris generation.

Bone Cements↗

PubMed2003

Influence of fragment reaction of relativistic heavy charged particles on heavy-ion radiotherapy.

The production of projectile fragments is one of the most important, but not yet perfectly understood, problems to be considered when planning for the utilization of high-energy heavy charged particles for radiotherapy. This paper reports our investigation of the fragments' fluence and linear energy transfer (LET) spectra produced from various incident ions using an experimental approach to reveal these physical qualities of the beams. Polymethyl methacrylate, as a substitute for the human body, was used as a target. A deltaE-E counter telescope with a plastic scintillator and a BGO scintillator made it possible to identify the species of fragments based on differences of various elements. By combining a gas-flow proportional counter with a counter telescope system, LET spectra as well as fluence spectra of the fragments were derived for each element down from the primary particles to hydrogen. Among them, the information on hydrogen and helium fragments was derived for the first time. The result revealed that the number of light fragments, such as hydrogen and helium, became larger than the number of primaries in the vicinity of the range end. However, the greater part of the dose delivered to a cell was still governed by the primaries. The calculated result of a simulation used for heavy-ion radiotherapy indicated room for improving the reaction model.

Ions↗

PubMed2006

How much sterile saline should be used for efficient lavage during total knee arthroplasty? Effects of pulse lavage irrigation on removal of bone and cement debris.

Bone and polymethyl methacrylate (PMMA) debris particles generated during total knee arthroplasty (TKA) reportedly cause third-body wear. The present study investigated the volume of pulse lavage sufficient for removal of intraoperative PMMA and bone particles. Subjects comprised 8 patients who underwent cemented TKA. Pulse lavage with 8 L of sterile saline was performed using a pulsatile irrigator. During pulse lavage, aspirated fluid was collected in a 1-L aliquot, and the number and size of bone and PMMA particles in each fluid were measured. Image analysis revealed that the number of particles peaked at first lavage and gradually decreased until eighth lavage. Significant differences were found between the first vs second, second vs third, and third vs fourth lavage. However, no significant differences were found beyond the fourth lavage. This study indicated that 4 L of pulse lavage is effective for removing the particles during cemented TKA.

Aged↗

PubMed2003

Visual performance of acrylic and PMMA intraocular lenses.

AIM: To evaluate the quality of visual functions after cataract surgery and intraocular lens (IOL) implantation with different lens materials and compare the results with age-matched subjects with clear phakic eyes. METHODS: Control and pseudophakic groups involved individuals aged between 50 and 75 years, without any accompanying ocular or systemic disease. In all, 50 eyes implanted with foldable acrylic IOLs, and 41 eyes implanted with polymethyl-methacrylate (PMMA) IOLs were compared with 45 phakic eyes as controls. Visual functions were evaluated for contrast sensitivity function and glare disability. The results were compared statistically using one-way analysis of variance (ANOVA). RESULTS: At high luminance levels, the difference among groups for contrast sensitivity was statistically significant for all spatial frequencies (P<0.05). Although the acrylic IOL-implanted eyes had better results at all three spatial frequencies, no significant difference existed between the two study groups for these spatial frequencies (P>0.05). Glare disability scores were significantly higher in the PMMA-IOL group compared to the control and acrylic-IOL groups. CONCLUSION: The visual quality achieved in pseudophakic eyes was not as good as in clear phakic eyes in regard to contrast sensitivity and glare. However, acrylic IOLs fared better than PMMA IOLs.

Acrylic Resins↗

PubMed2000

Optical cylinder designs to increase the field of vision in the osteo-odonto-keratoprosthesis.

BACKGROUND: The single optical cylinders used in the osteo-odonto-keratoprosthesis (OOKP) are known to produce very small visual fields. Values of 40 degrees are typically quoted. The purpose of this paper is to present designs for new optical cylinders that significantly increase the field of view and therefore improve the visual rehabilitation of patients having an OOKP. METHODS: Computer ray-tracing techniques were used to design and analyse improved one- and two-piece optical cylinders made from polymethyl methacrylate. All designs were required to have a potential visual acuity of 6/6 before consideration was given to the visual field and optimising off-axis image quality. Aspheric surfaces were used where this significantly improved off-axis image quality. RESULTS: Single optical cylinders, with increased posterior cylinder (intraocular) diameters, gave an increase in the theoretical visual field of 18% (from 76 degrees to 90 degrees) over current designs. Two-piece designs based on an inverted telephoto principle gave theoretical field angles over 120 degrees. Aspheric surfaces were shown to improve the off-axis image quality while maintaining a potential visual acuity of at least 6/6. This may well increase the measured visual field by improving the retinal illuminance off-axis. CONCLUSIONS: Results demonstrate that it is possible to significantly increase the theoretical maximum visual field through OOKP optical cylinders. Such designs will improve the visual rehabilitation of patients undergoing this procedure.

Computer-Aided Design↗