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At least 109 records · Page 6Linked to original sources
PubMed2003

Effect of processing variables (different compression packing processes and investment material types) and time on the dimensional accuracy of polymethyl methacrylate denture bases.

In this study we determined the effect of different compression packing processes, investment materials (a hemihydrate and dental stone) and time on the dimensional accuracy of polymethyl metacrylate denture bases. Square stainless steel plates (15 mm x 15 mm x 5 mm) were prepared to make an acrylic resin specimen. The linear dimensional changes of acrylic resin were determined by measuring the distances of fix points. Measurements were made at 24 hours, 48 hours, 12 days and 30 days after setting with a digital compass. Dimensional changes of test specimens that were obtained with three different flasks and two press techniques were compared by univariate analysis. Measurements of the linear dimensions of specimens cured by different compression packing techniques suggested that differences existed. The time interval differences were not significant. According to the results; flask and investment material types affect the dimensional accuracy of test specimens (p < 0.05). The least dimensional change observed in the specimens was obtained with Type 1 flask-dental stone-manual press combinations.

Acrylic Resins↗
PubMed2006

Evidence on unusual way of cocaine smuggling: cocaine-polymethyl methacrylate (PMMA) solid solution--study of clandestine laboratory samples.

An abandoned clandestine laboratory was seized in Slovenia. All confiscated exhibits were analysed in a forensic laboratory, where the following analytical methods were applied: capillary gas chromatography coupled with mass spectrometry (GC-MS) combined also by solid-phase micro extraction (SPME) and pyrolysis (Py) technique, Fourier transform infrared spectrometry (FTIR) and scanning electron microscopy with energy dispersive X-ray detector (SEM-EDX). The most interesting analytical findings can be summarised as follows: at the crime scene some plastic pieces, which contained cocaine dissolved (as solid solution) in polymethyl methacrylate-plexiglass (PMMA), were found. The highest cocaine concentration measured in the plastic sample was about 15% by weight. Two larger lumps of material (12 and 3 kg) were composed mainly of PMMA and CaCO3 and contained only 0.4 and 0.5% of cocaine, respectively. As for the low cocaine concentration, we assume that those two lumps of material represent discarded waste product--residue after the isolation of cocaine from plastic. Higher quantities of pure solvents (41 l) and solvent mixtures (87 l) were seized. We identified three types of pure solvents (acetone, gasoline and benzine) and two different types of solvent mixtures (benzine/acetone and gasoline/acetone). The total seized volume (87 l) of solvent mixtures holds approximately 395 g of solid residue formed mainly of PMMA and cocaine. Obviously solvent mixtures were used for isolation of cocaine from the plastic. Small quantities of relatively pure cocaine base were identified on different objects. There were two cotton sheets, most probably used for filtration. One sheet had traces of cocaine base (76% purity) on the surface, while cocaine in hydrochloride form (96%) was identified on the other sheet. GC-MS analyses of micro traces isolated from analytical balances showed the presence of cocaine and some common adulterants: phenacetine, lidocaine and procaine. A cocaine sample compressed in the shape of block was also seized. The above analytical findings inferred us to the conclusion that the illicit laboratory was used for the isolation of cocaine from PMMA resin. Further more, analyses confirm that not only isolation but also further manipulation of cocaine, i.e. adulteration/dilution, as well as the formation of cocaine blocks took place in the house. The information obtained through analyses also allowed us to make some hypotheses about possible multistage isolation procedure.

Journal Article↗
PubMed1997

New uses for gentamicin-impregnated polymethyl methacrylate spacers in two-stage revision hip arthroplasty.

The use of antibiotic-impregnated cement as a bone spacer in two-stage revision hip surgery has been well described. Two additional placements for spacers are described: within the trochanteric osteotomy and overlying the greater trochanter. These spacers have been found to dramatically facilitate exposure at the second-stage procedure and are now being incorporated into all two-stage revision hip arthroplasties at The General Infirmary at Leeds.

Anti-Bacterial Agents↗
PubMed2006

Dynamic void behavior in polymerizing polymethyl methacrylate cement.

Cement mantle voids remain controversial with respect to survival of total hip arthroplasty. Void evolution is poorly understood, and attempts at void manipulation can only be empirical. We induced voids in a cement model simulating the constraints of the proximal femur. Intravoid pressure and temperature were recorded throughout polymerization, and the initial and final void volumes were measured. Temperature-dependent peak intravoid pressures and void volume increases were observed. After solidification, subatmospheric intravoid pressures were observed. The magnitude of these observations could not be explained by the ideal gas law. Partial pressures of the void gas at peak pressures demonstrated a dominant effect of gaseous monomer, thereby suggesting that void growth is a pressure-driven phenomenon resulting from temperature-dependent evaporation of monomer into existing trapped air voids.

Air↗
PubMed1983

A comparison of two techniques of refitting long-term polymethyl methacrylate contact lens wearers.

Two techniques for fitting long-term polymethyl methylcrylate (PMMA) lens wearers with a gas-permeable hard lens are compared. These are: complete cessation of all lens wear for the period necessary to achieve stability in the patient's refraction and corneal curvature, and immediate refitting with a Polycon lens. Eleven patients who had worn hard contact lenses for at least 3 years and had wearing times of at least 8 hr per day were refitted with each technique. Refitting with Polycon lenses slowed but did not otherwise inhibit the recuperative changes taking place in the cornea after PMMA lens removal; vision was better and more stable with this group.

Adult↗
PubMed1998

Effect of glass fiber reinforcement on some mechanical properties of autopolymerizing polymethyl methacrylate.

PURPOSE: This study investigated the different effects of quantitative percentages of glass fiber intensity on the transverse strength, maximum deformation, and the modulus of elasticity of acrylic resin. MATERIALS AND METHODS: Fifty-four specimens were formed in a specially designed mold to produce identical specimens in accordance with the manufacturer's recommendations. Six percentages of glass fiber reinforcement in loose random form were studied. Each glass fiber treatment percentage (0%, 1%, 2%, 5%, 10%, 15%) was related to the total powder/liquid mass. RESULTS: The results indicated that 1% glass fiber treatment enhanced the transverse strength of the tested specimen. Maximum deformation at failure in the tested treatment groups was found to be different. The interaction of glass fiber concentration on fracture strength and deformation was significant (p < 0.0001). CONCLUSION: The 1% glass fiber concentration was found to give the best fracture strength and deformation results. Significantly higher glass fiber percentages was found to weaken the resin.

Analysis of Variance↗
PubMed2002

Fabrication of a capillary immunosensor in polymethyl methacrylate.

A method for fabricating capillary-based immunosensors in a coupon milled from an inexpensive, commodity plastic (PMMA, plexiglass) is demonstrated. The key feature of the technique is the use of sol-gel technology to deposit a glass-like (Si [bond] OH) film on surfaces of the plastic capillary channels to facilitate antibody immobilization. The utility of this method was demonstrated in the context of continuous flow displacement immunosensors for the explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). These sensors exhibited sensitivity to low microg/l RDX concentrations and peak-to-peak signal variations that were generally less than 10% for multiple injections at a single RDX concentration. The useful lifetime of the coupons in these experiments was greater than 10 h even after multiple exposures to high (1000 microg/l) RDX levels. This sensor platform has the physical characteristics needed for a portable field instrument: small, light-weight, and rugged.

Biosensing Techniques↗
PubMed1997

Ultra-high-modulus polyethylene ribbon as reinforcement for denture polymethyl methacrylate: a short communication.

OBJECTIVE: The aim of this study was to determine the effect of polyethylene fiber ribbon on the transverse strength of denture base polymer. METHODS: One or two layers of ultra-high-modulus or ultra-high-molecular weight polyethylene (UHMP) ribbon were placed into rhombic test specimens of denture base polymer. The specimens were tested with three-point-loading, and the ribbons were positioned on the tension side of the specimen. Fractured test specimens were examined with SEM. RESULTS: The transverse strength of the specimens increased slightly from the incorporation of UHMP fiber ribbons (unreinforced polymer: 91 MPa; with one ribbon layer: 118 MPa; with two ribbon layers: 125 MPa). Adherence of the UHMP fibers to the denture base polymer was poor. SIGNIFICANCE: Improvement in transverse strength of the specimens was modest although the fibers were placed into an ideal position of the specimens. This lack of improvement was due to poor adhesion of the UHMP fibers to the polymer and inadequate impregnation of the fibers with denture base resin.

Analysis of Variance↗
PubMed2002

The dynamic volume changes of polymerising polymethyl methacrylate bone cement.

The Swedish hip register found an increased risk of early revision of vacuum-mixed cemented total hip replacements. The influence of cement mixing technique on the dynamic volume change in polymerising PMMA is not well understood and may be relevant to this observation. Applying Archimedes' principle, we have investigated the dynamic volume changes in polymerising cement and determined the influence of mixing technique. All specimens showed an overall volume reduction: hand-mixed 3.4% and vacuum-mixed 6.0%. Regression analysis of sectional porosity and volume reduction showed a highly significant relationship. Hand-mixed porous cement showed a transient volume increase before solidification. However, vacuum-mixed cement showed a progressive volume reduction throughout polymerisation. Transient expansion of porous cement occurs at the critical time of micro-interlock formation, possibly improving fixation. Conversely, progressive volume reduction of vacuum-mixed cement throughout the formation of interlock may damage fixation. Stable fixation of vacuum-mixed cement may depend on additional techniques to offset the altered volumetric behaviour of vacuum-mixed cement.

Bone Cements↗
PubMed1993

A comparison of bond strengths of soft denture liners to polymethyl methacrylate polymerized by conventional water bath and microwave curing techniques.

This study compared the tensile bond strengths of soft lining materials polymerized by using conventional water bath methods and microwave energy. The soft lining materials used in this investigation were heat temperature vulcanizing (H.T.V.) silicon material Molloplast-B, and room temperature vulcanizing (R.T.V) acrylic material Getz Soft Oryl. The H.T.V. specimens were prepared with retention, additional retention and without retention, and the R.T.V. specimens were prepared by using bonding agent and bonding agent plus retention. All were cured by both conventional water bath and microwave energy. Results showed that the mean bond strength of H.T.V. specimens ranged from 9.6 to 13.12 kg/cm2, while the mean bond strength of R.T.V. specimens ranged from 0.36 to 1.75 kg/cm2. In both conventional and microwave groups, the specimens prepared with retention, additional retention and without retention or using bonding agent and bonding agent plus retention did not show any significant difference when they were compared separately. But the difference between conventional and microwave groups was found significant in both H.T.V. and R.T.V. specimens. It showed that conventional water bath technique is better than microwave technique.

Acrylic Resins↗
PubMed2001

Flexural strength of heat-polymerized polymethyl methacrylate denture resin reinforced with glass, aramid, or nylon fibers.

STATEMENT OF PROBLEM: Despite the favorable properties of conventional PMMA used as a denture base material, its fracture resistance could be improved. PURPOSE: This in vitro study was performed to determine whether the flexural strength of a commercially available, heat-polymerized acrylic denture base material could be improved through reinforcement with 3 types of fibers. MATERIAL AND METHODS: Ten specimens of similar dimensions were prepared for each of the 4 experimental groups: conventional acrylic resin and the same resin reinforced with glass, aramid, or nylon fibers. Flexural strength was evaluated with a 3-point bending test. The results were analyzed with a 1-way analysis of variance. RESULTS: All reinforced specimens showed better flexural strength than the conventional acrylic resin. Specimens reinforced with glass fibers showed the highest flexural strength, followed by aramid and nylon. CONCLUSION: Within the limitations of this study, the flexural strength of heat-polymerized PMMA denture resin was improved after reinforcement with glass or aramid fibers. It may be possible to apply these results to distal extension partial denture bases and provisional fixed partial dentures.

Analysis of Variance↗
PubMed2006

Effects of porosity on the fatigue performance of polymethyl methacrylate bone cement: an analytical investigation.

Porosity has been shown to affect the fatigue life of bone cements, but, although vacuum mixing is widely used to reduce porosity in the clinical setting, results have been mixed and the effects of porosity are not well understood. The aim of this study was to investigate the effects of porosity using stress analysis and fracture mechanics techniques. The stress concentrations arising at voids in test specimens were found using analytical solutions and boundary element methods. The fatigue life of specimens containing voids of various sizes was predicted using fracture mechanics techniques. For spherical voids that do not occupy a significant proportion of the cross-section, the resulting stress concentration is independent of void size and too small to account for the observed crack initiation. Cracks must therefore initiate at additional stress raisers such as radiopacifier particles or additional voids. For large voids, the stress increases as the remaining cross-section of the specimen decreases, and this may account for much of the observed reduction in fatigue strength in hand-mixed cement. Although crack initiation may be largely independent of void size, there is an effect on crack growth rate. Cracks are predicted to grow faster around larger voids, since they remain in the stress concentration around the void for longer. This effect may account for the relationship between porosity and fatigue life that has been observed in samples without large voids. Since porosity appears to affect crack growth more than initiation, it may be less damaging in high-cycle clinical fatigue, which may be predominantly initiation controlled, than in short laboratory tests.

Bone Cements↗
PubMed2003

Histologic evaluation of human vertebral bodies after vertebral augmentation with polymethyl methacrylate.

STUDY DESIGN: Histologic documentation of vertebral bodies retrieved from human patients. OBJECTIVES: The purpose of this study is to illustrate the histologic findings of two cases in which vertebroplasty and/or kyphoplasty had been performed. SUMMARY OF BACKGROUND DATA: There are a number of controversies to vertebral augmentation, including the use of inflatable bone tamps, use of nonstandardized polymethylmethacrylate (PMMA) preparations, the extent and significance of thermal necrosis, any foreign body reaction, and cement extravasation. METHODS: Four vertebral bodies from two cases ranging from 1 month to 2 years after surgery were analyzed histologically. Microscope slides of retrieved vertebral bodies were reviewed with special reference for evidence of thermal necrosis, foreign body reaction, migration of cement, cement voids and fractures, and for the influence of the bone tamp on adjacent bone. RESULTS: The cancellous bone around the cement of the kyphoplasty specimen showed good density, suggesting that the tamping had displaced bone, essentially autografting the space around the cement. Bone immediately around the cement did not show extensive necrosis, but there were a few spicules of necrotic bone associated with creeping substitution, suggesting either thermal effect, the original fracture, or displacement of bone by the procedure. Foreign body giant cells and macrophages were identified in the fibrous membrane around the PMMA in all segments. These cells contained material consistent with cement particles and/or barium sulfate. Particles were also present within vascular spaces. CONCLUSIONS: To our knowledge, these cases are among the first published reports of human histology after vertebral cement augmentation and have implications concerning the nature of the surgical procedures as well as the material used for injection.

Adult↗