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Biomedical subjects

T E Donovan

Publications and source records attributed to T E Donovan.

At least 19 recordsLinked to original sources
PubMed1992

Polyvinyl siloxane impression materials: a review of properties and techniques.

Polyvinyl siloxane impression materials have been shown to have excellent properties as impression materials; however, they are sensitive to manipulative variables. Several methods of using very high viscosity (putty) materials to form "trays" to obtain uniform bulk of the wash impression are described, and the disadvantages of each of these techniques is pointed out. It is recommended that for best results acrylic resin custom trays should be used routinely. The interaction of polyvinyl siloxane materials with latex products is also discussed and problems that this inhibition can cause are stated. Suggestions to avoid this interaction are outlined. One of the disadvantages of the impression materials is that it has a relatively short working time. Refrigerating the material will increase working time without affecting accuracy.

Acrylic Resins↗
PubMed1991

Ceramic restorations: cast metal and cast glass.

Pertinent articles published between October 1989 and September 1990 related to metal-ceramic and all-ceramic crowns are reviewed. The main topic groupings are: 1) color and esthetics with metal-ceramics; 2) bond strength of metal and ceramic materials; 3) all-ceramic alternatives; and 4) the porcelain surface. Research published during this period advanced knowledge of photospectrophotometry and thermomechanical compatibility of porcelain-metal systems. Deficiencies in fit and strength for some all-ceramic systems are described. Further evidence was published supporting the efficacy of polishing porcelain. Additional documentation regarding the etching of ceramic materials, including Dicor (Caulk Company Ltd., Milford, DE) was produced. More research into use of titanium and titanium alloys as substructures for ceramic materials is required.

Color↗
PubMed1991

Indirect inhibition of polymerization of a polyvinyl siloxane impression material: a case report.

The inhibition of polymerization of polyvinyl siloxane impression materials by direct contact with latex gloves has been well documented. Indirect intraoral inhibition of polymerization that results from contact of oral tissues with latex gloves during tooth preparation and gingival retraction procedures has been reported. This case report illustrates the problems that can occur when the dentist used polyvinyl siloxane impression materials while wearing latex gloves. In the reported case, the inhibition is severe and obvious; in most situations the inhibition of polymerization is more subtle and is frequently undetected. Clinicians must be aware of this potential problem and the solution to it.

Dental Impression Materials↗
PubMed1990

An evaluation of impression techniques for osseointegrated implants.

A passive fit between osseointegrated implants and the prosthesis they will support has been advocated. An experimental model was developed to test the accuracy of three impression techniques and the components used to make the transfer records. Statistically, no significant difference was found between the three methods tested. From this initial study, it appears that further work is needed to isolate techniques that will predictably provide accurate registration of the position of endosseous implants.

Dental Abutments↗
PubMed1988

The effect of vacuum-mixed autopolymerizing acrylic resins on porosity and transverse strength.

Three brands of autopolymerizing acrylic resin were mixed and polymerized three different ways and tested for transverse strength and porosity. The procedures tested were bench-curing at ambient temperatures, vacuuming the mix before bench-curing, and curing in a pressure device. The data indicate that both vacuuming the mix and pressure-curing are successful in reducing porosity and increasing transverse strength. These improved properties would be valuable in the fabrication of provisional restorations and occlusal splints. The following conclusions can be drawn: 1. Use of a pressure device decreases porosity and increases the transverse strength in samples of autopolymerizing acrylic resin. 2. Use of a vacuum device on the mixed acrylic resin works as well as pressure polymerizing. 3. Use of either technique is indicated to improve the quality and longevity of autopolymerizing acrylic resin restorations, orthodontic appliances, and occlusal splints.

Chemical Phenomena↗
PubMed1988

Effect of chilled monomer on working time and transverse strength of three autopolymerizing acrylic resins.

Samples of three commercially available poly(methyl-methacrylate) autopolymerizing resins were made by using room temperature and chilled monomer. Working and setting times and transverse strengths were determined. The following conclusions can be drawn: 1. Working and setting times increased approximately 2 to 4 minutes when chilled monomer was used. This could be advantageous in certain situations. 2. Transverse strength decreased approximately 17% with the use of chilled monomer. The clinical significance of this decrease is not known.

Chemical Phenomena↗
PubMed1985

Evaluation of an improved centrifugal casting machine.

A Type III gold alloy, a silver-palladium alloy, and a base metal alloy were cast in two different centrifugal casting machines. With the number of complete cast mesh squares as an indicator of castability, the Airspin casting machine produced superior castings with all three alloys. The base metal alloy produced the greatest number of complete squares with both casting machines.

Centrifugation↗
PubMed1985

Review and survey of medicaments used with gingival retraction cords.

Data from a survey of 495 dentists indicate that most dentists used the mechanical-chemical method of gingival-deflection; 79.39% of those used cord containing epinephrine. It can be concluded that potentially significant amounts of epinephrine can be absorbed systemically from the local anesthetic solution, that secretion of endogenous epinephrine in response to stress occurs, often at levels sufficient to cause measurable changes in hemodynamic variables, and that absorption of epinephrine from impregnated strings occurs. The amount of absorption will vary with the exposure of the vascular bed, the length and concentration of the impregnated cord, and the length of time of application. It is possible that the actual total amount of circulating catecholamine would be cumulative, and the corresponding cardiovascular response would be related to the total amount of epinephrine in the bloodstream, regardless of the source. When the fact that we usually have inadequate data on the cardiovascular status of our patients is considered, as well as the tendency to make impressions of multiple prepared teeth, the continued use of epinephrine cord in dentistry must be viewed with alarm. Equally effective astringent gingival deflection agents such as alum, aluminum sulfate, and aluminum chloride exert no systemic effects. Therefore, there is little indication for use of epinephrine-containing retraction cords. Adequate medical evaluation, careful use of anesthetics that contain epinephrine, and sedative techniques when indicated will assure the safety of our patients.

Adult↗