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Biomedical subjects

W W Chee

Publications and source records attributed to W W Chee.

14 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

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↗
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↗
PubMedDate not supplied

Preliminary investigation of a disinfected gypsum die stone.

The setting time, comprehensive strength, diametral tensile strength, expansion, and fine detail reproduction of disinfectant-containing die stones (Steri-Die A and Steri-Die B) were compared to two commonly used die materials (Vel-Mix and Die-Keen). Six samples of each die material were formed from polysulfide rubber, condensation silicone, polyether, and poly(vinyl siloxane) impression materials. The disinfected die stones compared favorably to the controls in all tests with the following exceptions: Steri-Die B was weaker in both compressive and tensile strength and deficient in detail reproduction, especially with condensation polymerizing silicone.

Calcium Sulfate↗
PubMedDate not supplied

Interaction of gloves and rubber dam with a poly(vinyl siloxane) impression material: a screening test.

Polymerization inhibition of poly(vinyl siloxane) impression materials has been reported with the use of latex gloves. This study evaluated the effect on polymerization of a poly(vinyl siloxane) impression material in both direct and indirect contact with 25 brands of latex gloves, two brands of vinyl gloves, and two weights of rubber dam. Use of all but one of the latex products (96%) resulted in inhibition of polymerization with direct contact. Forty percent of the latex gloves tested inhibited polymerization with indirect contact. The vinyl gloves tested had no effect on polymerization. The implications of inhibited polymerization were discussed.

Dental Impression Materials↗
PubMedDate not supplied

Fine detail reproduction of very high viscosity poly(vinyl siloxane) impression materials.

Very high viscosity (putty) poly(vinyl siloxane) impression materials are used with both the conventional double-mix and single-mix putty/wash techniques. When the latter technique is used, portions of the impression of the prepared teeth may be made in the putty rather than the wash material. This study investigated the ability of ten different putty materials to reproduce fine detail. The American Dental Association stainless steel test die for Specification No. 19 was used. Two of the materials consistently reproduced the 20-microns groove. Three of the materials reproduced the 20-microns groove in one-half of the samples tested, while the remainder failed to do so.

Dental Impression Materials↗