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Biomedical subjects

R A Hesby

Publications and source records attributed to R A Hesby.

9 recordsLinked to original sources
PubMed1991

Adhesive properties of several impression material systems: Part II.

The effect of saliva contamination on the tensile adhesive bond strengths of four impression adhesive systems, (1) polysulfide, (2) polyether, (3) polyvinylsiloxane, and (4) condensation silicone impression adhesive, was studied. Standard acrylic resin tray samples of 1-inch square surface were made. Tray surfaces were contaminated with saliva either before or after the application of tray adhesives. Tensile tests were performed with a Universal Load testing machine. The tensile adhesive bond strengths of contaminated tray surface and contaminated adhesive were compared with a group of control. Contamination of all impression adhesives resulted in significantly lower bond strength. Except for the polyvinylsiloxane and polysulfide impression adhesive systems, saliva contamination of tray material significantly decreased adhesive bond strengths. Impression trays should be tried in the mouth, rinsed, and dried before adhesive is applied.

Adhesiveness↗
PubMed1991

Adhesive properties of several impression material systems: Part I.

The tensile adhesive bond strength of five impression adhesive systems was studied: polysulfide, polyether, polyvinylsiloxane, condensation silicone impression, and polyvinylsiloxane putty adhesive systems. Results showed no significant difference in adhesive bond strength to autopolymerizing acrylic resin between the former four impression materials studied. Polyether and medium-viscosity polyvinylsiloxane demonstrated significantly higher adhesive bond strength to polystyrene than either polysulfide or condensation silicone. The medium-viscosity polyvinylsiloxane impression material showed significantly higher adhesive bond strength to polystyrene than autopolymerizing acrylic resin whereas polysulfide and condensation silicone impression materials adhered significantly better to autopolymerizing acrylic resin than polystyrene. The polyvinylsiloxane putty did not adhere to its impression adhesive. Variation of the speed of tensile testing between 5 to 20 inches per minutes did not affect the adhesive bond strength of a polysulfide impression material.

Adhesiveness↗
PubMed1986

Dimensional stability of autopolymerizing acrylic resin impression trays.

A study was undertaken to determine the optimal interval between fabrication of an autopolymerizing acrylic resin custom impression tray and making a final impression. Twenty mandibular arch-shaped trays, 10 each of Fastray and Formatray resin, were evaluated for dimensional change. Both materials behaved similarly. Cross-arch contraction of the borders of buccal flanges and unilateral expansion of the borders of buccal-to-lingual flanges were observed. These changes indicate distortion. Linear dimensional changes occurred throughout 6 hours, which suggests that any impression made in a methyl methacrylate acrylic resin custom impression tray should be poured as soon as is conveniently possible. Significant linear dimensional changes were observed for only 40 minutes from the initiation of tray fabrication. This study concludes that while an aged tray is preferred, it is acceptable to make an impression in an autopolymerizing resin custom impression tray after 40 minutes.

Chemical Phenomena↗
PubMed1985

Marginal opening of single and twin platinum foil-bonded aluminous porcelain crowns.

The marginal openings of single and twin foil-bonded aluminous porcelain crowns were compared in crowns fabricated indirectly for extracted teeth and directly on typodont teeth. The crowns were cemented with zinc phosphate, embedded in plastic, and sectioned. Marginal opening was measured directly with a traveling microscope. There was no significant difference between the marginal openings of twin- and single-foil crowns fabricated indirectly for extracted teeth. When the crowns were constructed directly on typodont teeth to eliminate the variables of impression-making and die fabrication, the single-foil crowns possessed a significantly smaller marginal opening than the twin-foil crowns. Both the twin- and single-foil complete porcelain crowns resulted in clinically acceptable margins. The single-foil crowns were easier to make.

Aluminum Oxide↗
PubMed1985

Internal setting expansion of a dental casting investment measured with strain gauges.

A study was undertaken to investigate the feasibility of using strain gauges to evaluate the internal setting expansion of dental casting investments. A strain gauge was invested in the center of a casting ring to determine the linear setting expansion at the site of the wax pattern. The findings suggest that strain gauges can be used to measure setting expansion internally more accurately than volumetric or external surface measurement techniques. It was also found that winged strain gauges were more stable in the investment than wingless strain gauges.

Chemical Phenomena↗
PubMed1985

Effect of a two-step ringless investment technique on alloy castability.

An evaluation of the effects of a two-step ringless partial denture investment technique on the castability of a base metal crown and fixed partial denture alloy was made. Castability values were obtained for 60 test patterns cast on two different casting units at two different mold temperatures. No significant differences were found between the control technique and the experimental technique. However, significant differences were found between castings made by the two different casting units at a temperature of 1250 degrees F.

Dental Alloys↗