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Recently, an injection system for use with microwaveable denture base resins was introduced. Preliminary evaluation of this system was performed a university-based dental laboratory. This article provides a description of the complete denture fabrication technique, as well as observations regarding its design and practicality.
Certain dental procedures require patients to be without their removable partial dentures. This can be a great inconvenience and psychologically difficult for some patients. This procedure permits duplicating existing removable partial dentures so that patients will not have to be without prostheses.
The causes of midline fracture of dentures are discussed in both clinical and materials science terms. Many midline fractures can be avoided by the application of established prosthodontic principles in constructing and maintaining dentures. Improvements in the resins and processing techniques can also reduce the incidence of midline fracture. The most promising approach to preventing or reducing the incidence of this problem appears to be reinforcement in the anterior part of the palate of the denture.
Samples were tested by following three processing methods: two processing cycles recommended by the manufacturer and quick violent boiling. Samples processed by following the recommended cycles showed statistically significant differences with regard to impact strength and Brinnel hardness, but without differences in the expected clinical behavior of the resin. Residual monomer ratio was higher when the boiling point was not reached, which seems to confirm the plasticizing effect of residual monomer. Samples were less brittle and less hard. Violent boiling increased porosity and lessened impact strength.
Nuclear magnetic resonance (NMR) 13C has been used to determine the tacticity of poly(methyl methacrylate) (PMMA) denture base materials. Curing cycle has no effect on tacticity. A tendency towards a mainly syndiotactic arrangement is shown. Industrially produced PMMA showed the same tacticity as the dental products.
The subgingival placement of any one of the three types of temporary crowns placed on 28 posterior teeth of seven subjects caused no detectable change in the gingiva over a 3 week period. There is a need for further study of the influence of temporary crowns on the different types of gingival tissue.
Pneumoconiosis in dental laboratory workers has been associated with exposure to metal alloys and silica used in the manufacturing of dental prosthetics. In this report, we describe a 27-yr-old dental student who was found to have bilateral basal pulmonary interstitial infiltrates and nodules on a chest roentgenogram after a brief episode of upper respiratory infection. An open lung biopsy revealed interstitial pneumonitis with an abundance of vacuolated macrophages in the alveolar spaces. Ultrastructural analysis showed in the alveolar and interstitial spaces the accumulation of macrophages laden with electron-lucent bodies resembling plastic beads. An inhalation exposure history, taken subsequent to these findings, revealed exposure to high levels of acrylic plastic in a dental school laboratory. Removal from the site of exposure has resulted in the gradual resolution of the roentgenographic abnormalities.
1. Pitting corrosion provides undercuts suitable for retaining a resin facing. 2. Using a cathode with a proper shape, pits were uniformly distributed on the surface of a metal casting. The size of pits varies, depending on the time of pitting treatment. 3. The retentive pits were excellent in both retentive strength and marginal sealing when compared with spherical powder and beads.
A specific testing system was used to determine the three-dimensional changes of interocclusal registration materials for a simulated patient and the derived stone casts. The results indicated that the deviations of the derived casts were more pronounced than the original models. There was great heterogeneity with all recording materials and the materials were not consistently accurate after limited storage of 30 minutes.
An external fixation frame for the leg is made up of Bonnel pins, strengthened by bands of autopolymerising resin. The experiment shows this apparatus to be solid, reliable and easy to use. The technique of application is extremely simple and the cost low. The indications are the same as those of proven classical fixation devices, which must be preferred for the moment, when possible. Its use is therefore limited, but justified under special circumstances (poorly equipped units far from major centres, war surgery).
Ethanolic solutions of various paracetamol (acetaminophen)/Eudragit E, S, and RS ratios were spray-dried to obtain solid particulates. The products were tableted and the dissolution test of the tablets in distilled water and test solution (pH 1.2 and 7.2) were evaluated. The quantities and types of polymer as well as the dissolution media influenced the drug release. Spray-drying technique provided by the different types of Eudragits was an effective method for prolonging the release rate of paracetamol.
A well adapted and structurally stable baseplate is very important to verify the accuracy of previous records in denture construction. Shellac baseplate is widely recognized for records base, it is inexpensive and readily available in uniform shapes, but it lacks adequate strength and dimensional stability. Reheating makes it brittle, thus limit its use. This paper discusses a technique used to stabilize and improve the strength of shellac baseplates. The technique was found simple, easy to adapt, produce and transfer accurate maximandibular jaw relations record during denture construction.
The effect of different metal and fibre strengtheners on the fracture resistance of polymethylmethacrylate was tested. Different types of commonly used metal wire and glass fibre, as well as carbon and aramid fibres, were used as strengtheners in test specimens. There were 21 groups, and each group contained 12 test specimens. Each metal strengthener had a beneficial effect on the fracture resistance of the polymethylmethacrylate (P less than 0.001-0.01). Some fibres, which were silanized for better adhesion, also had strengthening properties.
Denture hygiene is an important factor in the treatment of denture stomatitis. Sterilization of dentures by microwaves has been recommended, but using specialized equipment not available to the average person. This study tests the effect of microwaving on the dimensional stability of dentures (in an unmodified domestic microwave oven). After microwaving (10 mins at 604 W) some measurements showed significant contraction or expansion but reduced exposure (6 mins at 331 W) caused much smaller changes. The dimensional changes are inexplicable but at lower radiation are considered to be harmless.
Experiments have been carried out on the curing of poly(methyl methacrylate) denture base material in a microwave oven, using conventional dental flasks and flask clamps. It has been shown that it is important (a) to maintain sufficient pressure on the materials, (b) to avoid gaseous porosity by not heating too rapidly initially, and (c) to ensure that all metal is protected from exposure to microwaves. When the appropriate conditions of polymerisation were used, microwave-cured samples had satisfactory physical and mechanical properties according to American Dental Association specification number 12.
It has been shown previously that high levels of residual monomer have a deleterious effect on the properties of denture base polymers. Levels of residual monomer were determined on a homopolymer and a copolymer using gas-liquid chromatography. A wide range of recommended and 'short cut' curing cycles were then investigated which produced values ranging from 0.56 to 18.46%. From the ranges examined an optimum cycle of 7 h at 70 degrees C and 1 h at 100 degrees C was established which was used to polymerize 23 currently available synthetic denture base polymers. Only small differences were found between the materials tested with a range from 0.54 to 1.08% of residual monomer.
The aim of this study was to subjectively assess permanent denture base retention and stability in order to determine whether detrimental change occurred as a result of a second curing cycle. 100 complete upper denture bases were assessed by clinician and patient using visual analogue scales at try-in and insert. No statistically significant alteration in mean scores for retention and stability was seen. 5% of bases showed some deterioration, but none required rebasing or remaking as a result. The advantages of permanent bases during denture construction seem to outweigh the risk of loss of retention and/or stability as a result of distortion due to the second curing cycle.
A simple and reliable method has been developed for the in situ LR White embedding of cell monolayers grown on glass cover-slips. Combined with cytochemical or immunological procedures, this technique allows light and/or electron microscopy investigations of a large number of cells in the same horizontal plane within a relatively short period of time. It can be applied to cells grown on microgrid finder cover-slips which allows a distinct site of even an individual cell of a monolayer to be studied at first at the light microscope level and subsequently at the electron microscope level. Hence, it is also suitable for controlling manipulation of single cells, followed by their serial sectioning after relocation in the electron microscope.