Use Of Polymethylmethacrylate Research Articles

Hard Contact Lens???Induced Corneal Neovascularization Treated by Oxygenation

A 39-year-old man suffered from corneal neovascularization, through to result from hypoxia caused by improper use of polymethylmethacrylate (PMMA) hard contact lenses. The condition was successfully treated by oxygenation of the corneas under swimming goggles.

Possible Use of Polymethylmethacrylate Doped with Hg Dithizonate as a Dosimeter in the Mrad Range

It is the found that the 3 μ thin film polymethylmethacrylate (PMMA) doped with Hg dithizonate can be used for dosimetry in a range of adsorbed dose from about 1 … 4 Mrad from which the decrease of optical density of the main absorption band at 485 … 490 nm decreases exponentially by increasing absorbed dose. The effects of post storage irradiation and storage temperature on the radiation induced visible spectrum were investigated.

Thermally Induced Bone Necrosis in Rabbits

The exposure of bone to high temperatures has become quite common, especially with the increasing use of polymethylmethacrylate (PMMA) bone cement. With particular regard to total hip arthroplasty, many authors have commented on the temperature problem induced by the curing PMMA cement mass. Polymerization temperatures at the bone-cement interface have been measured and range between 40 degrees and 110 degrees, depending on the thickness of the cement line. Thermal bone damage is implicated as a significant cause of early loosening of implanted joint prostheses. The authors designed a fluid probe to deliver heated isotonic fluid directly over exposed cortical bone on a rabbit's proximal tibia. Scald temperatures ranged from 45 degrees-90 degrees for a standard exposure time of one minute. Bone tissue samples taken at intervals of one, two, and three weeks postoperatively were used to establish the thermal-damage threshold for living bone and assess regeneration potential. Controls were included to observe the reaction of bone to the surgical procedure. Bone necrosis was consistently seen in histologic sections at scald temperatures greater than or equal to 70 degrees. Although an inflammatory reaction replaced by a fibrous tissue scar was seen at the site of surgically damaged periosteum, no control animals showed evidence of either bone or marrow necrosis. These results led the authors to suggest that joint replacement systems in human bone, using PMMA bone cement, be designed to limit intraoperative temperature maximums to a level less than 70 degrees. By preventing excessive bone necrosis at the bone-cement interface, early loosening and subsequent implant failure may be significantly reduced.

The Use of Polymethylmethacrylate to Compare the Adsorption and Staining Reactions of Some Cationic Antiseptics

This study assessed the value of acrylic, in powder and optically clear forms, to measure the adsorption and staining properties of some cationic antiseptics. The uptake of chlorhexidine gluconate, chlorhexidine acetate, alexidine and cetyl pyridinium chloride onto acrylic powder was measured spectrophotometrically. Similarly, tea staining of perspex blocks exposed twice daily to the antiseptics and hexetidine, was measured over a 5 day period. The adsorption of chlorhexidine gluconate and acetate was similar and greater than alexidine but less than cetyl pyridinium chloride. Desorption of the adsorbed antiseptics was minimal after 48 hours soaking in water. Acid produced a variable desorption of antiseptics. Tea staining of blocks was significantly greater with antiseptic treated specimens compared to control specimens. However, staining resulting from alexidine was greater than cetyl pyridinium chloride which was greater than chlorhexidine. Hexetidine produced the least staining. Saliva treatment of specimens only increased the tea staining of control blocks. The results indicated that adsorption levels alone would not explain the differences in antiplaque and staining activity reported for the cationic antiseptics.

The use of polymethylmethacrylate to speed up the finishing of steel parts in rotating drums

The use of polymethylmethacrylate to speed up the finishing of steel parts in rotating drums

Use of polymethylmethacrylate to enhance screw fixation in bone

Pull-out testing of screws inserted into cement and bone under various conditions showed that the cement-screw complex was significantly stronger when the screw was placed in soft cement and the cement was allowed to polymerize without further manipulation. When screw fixation in osteoporotic bone was reinforced with cement, the bone was the weakest component in the system. Fixation under these conditions should be enhanced by increasing the area of contact between the cement and bone. By cooling the cement to prolong its working time, it could be injected with a syringe in such a way that maximum endosteal and periosteal contact was provided.

ESR investigations of the aromatic triplet state in polymethylmethacrylate

The use of polymethylmethacrylate (PMMA) as a host medium for the study of the aromatic triplet state by electron spin resonance spectroscopy (ESR) has been explored. The influence of photolytically induced host free radical formation on the triplet lifetimes and triplet spectral intensities is discussed. For naphthalene and phenanthrene the thermal dependence of the zero field splitting parameters D, E, and D* have been measured between 87 and 380 K. An unusual variation of D* with temperature at about 210 K is consistent with the presence of a second order phase transition of PMMA.

A Lower Transition Point for Polymethyl Methacrylate at 30°–32° C

IN view of the use of polymethyl methacrylate (PMMA) for the production of surgical and dental prostheses, its properties at body temperature and those encountered in the mouth are of particular importance. Furthermore, the necessity for the incorporation of metal inserts and porcelain teeth makes its thermal properties of unusual interest. The thermal expansion of both commercial PMMA (‘Perspex’) and samples prepared by dental techniques was examined by means of a specially constructed dilatometer. Increase in length was recorded by means of a dial gauge reading to 0.0005 mm, and temperatures were measured at three points along 70 mm specimens by means of a Leeds and Northrup potentiometer. Specimens were arranged in a silica vessel which in later experiments was filled with water to determine the effect of water absorption on the thermal properties of PMMA. Increase in length was plotted against rise in temperature between 20° and 40° C. The resulting graphs showed a change in upward slope between 30°–32° C. The thermal properties were studied daily for periods up to 35 days with the specimens immersed in water and for similar periods with the same specimen drying out. Graphs prepared as before showed no alteration in the position at which an upward change in slope occurred, although the thermal expansion was greater for saturated specimens than for dry ones. Several second-order phase transition points have been recorded1 for PMMA, but so far as we can ascertain, no reference to one in the temperature range of 30°–32° C has previously been reported.

ESR Studies of Triplet States in Plastics: Effect of Temperature on the Spectra

The use of polymethylmethacrylate (Lucite) as a host medium for the study of aromatic triplet states by ESR has been explored. The zero-field splitting parameter D* and the lifetime of the triplet state have been measured for a variety of aromatic molecules, and the effect of temperature on these parameters studied in the cases of coronene, triphenylene, and naphthalene.

Use of Polymethyl Methacrylate in preparing Thin Sections of Recent Sediments

IN the examination of Recent sediments it is necessary to identify accurately the mineral grains and lithic fragments which make up the deposit. Compositional properties such as the quantity and type of quartz, feldspar, calcite and the lithic, or rock, suite are keys to the proper interpretation of source and dispersal of a sediment. Such properties as diagenetic alteration of grains, mineral inclusions and specific rock types can be determined only by optical study of specially prepared petrographic thin-sections.