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Biomedical subjects

R L Cooley

Publications and source records attributed to R L Cooley.

At least 19 recordsLinked to original sources
PubMed1992

Laboratory evaluation of adhesive systems.

Adhesive bonding of resin materials to acid-conditioned enamel is a clinically proven technique in preventative, restorative, and orthodontic procedures. Laboratory evaluations of etched-enamel resin bonding have shown excellent bond strengths and the virtual elimination of marginal microleakage. Adhesion to dentin has been more of a challenge. Earlier-generation dentin bonding systems did not yield high bond strengths in the laboratory or prevent marginal microleakage. Newer-generation adhesive systems generally use a dentin conditioner to modify or remove the smear layer and a subsequent application of an adhesive resin bonding agent. Laboratory evaluations of newer systems have shown bond strengths that approach or actually exceed that of etched enamel resin bonding. Bond strengths have improved with the evolution of dentin bonding systems, and microleakage from the cementum/dentin margin has been significantly reduced or prevented with the newer systems. Although laboratory testing of adhesive systems provides a mechanism to screen and compare newly developed systems, clinical trials are essential to document long-term clinical performance.

Adhesives↗
PubMed1991

Comparison of manually and mechanically mixed glass ionomers.

Two mechanically mixed glass ionomer restorative materials (Ketac-Fil and Fuji Cap II) were compared with two manually mixed products (Chelon-Fil and Fuji Type II). One manually mixed material was substantially weaker than the others in bond strength tests. No significant differences in microleakage were found among the materials.

Analysis of Variance↗
PubMed1991

Comparison of wet and dry finishing of resin composites with aluminum oxide discs.

Samples of four composites (Herculite, Visio-Dispers, Silux, and Prisma-Fil) were finished with aluminum-oxide discs either wet or dry so that the effects of these two finishing procedures could be compared. The samples were evaluated for surface smoothness, color stability, and surface hardness. Surface smoothness was determined immediately after a sample was finished with a profilometer. Knoop hardness values were determined for each sample immediately after being finished and once a week for five weeks. Color stability was evaluated with a tristimulus colorimeter by the color of each sample being finished and once a week for five weeks. When surface smoothness was compared between the wet- and dry-finished samples, there was no significant difference between Prisma-Fil, Silux, or Herculite; however, the wet-finished Visio-Dispers was significantly rougher than the dry-finished. When surface hardness was compared, there was no significant difference in hardness values between the wet and dry samples when compared over time. When changes in color were evaluated, only Visio-Dispers had no significant change in color for both the wet- and dry-finished samples over the five-week evaluation period. Dry finishing of only one composite (Silux) produced a significant change in color. Dry finishing of composites was superior or equal to wet finishing in all tests except for the color change in Silux.

Aluminum Oxide↗
PubMed1991

Bond strength of light-cure fluoride-releasing base-liners as orthodontic bracket adhesives.

Fluoride-releasing bracket adhesives are desirable for their ability to minimize the potential for subsurface enamel demineralization adjacent to a bonded bracket. Self-applications with topical fluoride rinses, pastes, and gels have been documented to minimize and eliminate subsurface caries adjacent to bonded brackets. However, the success of these mediums are limited by patient compliance. A urethane with fluoride (TimeLine) and a glass ionomer with methyl methacrylate (Vitrabond), both of which are light cured and exhibit sustained fluoride ion release, were compared with a non-fluoride-releasing light-cured bracket adhesive (Transbond). Premolar brackets with mesh pads (A-Company) were positioned on the buccal surface of the premolars and placed in a PVC ring with polymethyl methacrylate. Two groups of 10 samples each of the tested material were prepared and immersed in distilled water immediately after in vitro bonding. Samples of each material were evaluated for enamel shear strength (Instron) at 24 hours and at 30 days. Bond strengths to enamel at 24 hours measured in megapascals (MPa) were 5.98 for TimeLine, 11.58 for Vitrabond, and 11.35 for Transbond. Bond strength to enamel at 30 days was found to be significantly less for TimeLine and Vitrabond: 3.05 for TimeLine, 5.39 for Vitrabond, and 10.80 for Transbond. The two fluoride-releasing, light-cured materials tested have low bond strengths after 30 days and are not acceptable as orthodontic bracket bonding agents. However, for patients with high caries risk, these materials may be placed around already bonded brackets.

Acid Etching, Dental↗
PubMed1991

Dentinal bond strengths and microleakage of a 4-META adhesive to amalgam and composite resin.

A 4-META-containing adhesive was evaluated for its ability to bond a composite resin and two types of amalgam to dentin. One group of composite resin was tested after 24 hours and another group after 24 hours of thermocycling. Shear bond strengths were: composite resin at 24 hours = 22.38 MPa; thermocycled composite resin = 20.86 MPa; spherical alloy = 3.38 MPa; admixed alloy = 3.84 MPa. Microleakage was evaluated after the 4-META adhesive was applied to cavity preparations and compared to that of a group treated with a cavity varnish. There was statistically significantly less microleakage in the 4-META group at both the occlusal and gingival margins.

Coloring Agents↗
PubMed1991

Effect of dentin adhesives on sealant bond strength.

This study evaluated the effect of four dentin adhesives on sealant shear bond strength. Five groups of 15 human extracted teeth (75 in total) were prepared to receive the following treatments: group 1, sealant only; group 2, sealant plus gluma primer; group 3, sealant plus gluma primer and sealer, group 4, sealant plus C & B Metabond. Each tooth had a bonding site prepared for each material by grinding a flat plane on the enamel with 600 grit. The enamel site was etched for 30 seconds, washed for 20 seconds and dried. Each material was mixed according to the instructions of the manufacturer. The sealant (Concise) was placed in a nylon cylinder, light-cured, stored in distilled water for 24 hours, thermocycled (100 cycles at 5 to 55 degrees C) and shear bond strength determined with a knife-edge blade in an Instron running at a crosshead speed of 0.5 mm/min. The results in MPa were: group 1, 11.8 +/- 4.5; group 2, 12.3 +/- 5.0; group 3, 10.3 +/- 1.9; group 4, 12.5 +/- 8.6; and group 5, 15.8 +/- 5.2. Statistically (ANOVA one way) there was no significant difference in the groups.

Acrylic Resins↗
PubMed1991

Evaluation of a phosphonate BIS-GMA resin as a bracket adhesive.

Panavia is a modified phosphate ester of dimethacrylate that purportedly forms a strong bond to tooth structure and to metals. The ability of this adhesive to bond orthodontic brackets to enamel was compared to the bond strengths of a no-mix bracket adhesive and a paste/paste autopolymerizing composite resin. Panavia did not form a bond as strong as that achieved by the bracket adhesive but was stronger than the composite resin.

Acrylic Resins↗
PubMed1991

Dentinal shear bond strength, microleakage, and contraction gap of visible light-polymerized liners/bases.

The bond strength and microleakage patterns of three light-curing glass-ionomer cement liners/bases (Vitrebond, XR Ionomer, and Zionomer) were evaluated and compared to a fluoride-releasing resin (TimeLine) designed for the same use. Bond strength tests were performed at 24 hours and 7 days. At 24 hours Vitrebond, Time-Line, and Zionomer had statistically significantly greater bond strengths than XR Ionomer. At 7 days, Vitrebond had a statistically significantly stronger bond than the others. Microleakage was evaluated after 24 hours of thermocycling. Vitrebond and XR Ionomer had statistically significantly less leakage than the others, while TimeLine had significantly more leakage than the others. Polymerization contraction gaps between the liners/bases and dentin were examined with scanning electron microscopy. Contraction gaps were approximately 10 microns with Vitrebond and XR Ionomer and 5 microns with TimeLine. A contraction gap generally was not observed with Zionomer.

Dental Bonding↗
PubMed1991

Current status of adhesive resin systems.

The advanced third-generation bonding agents have created excitement as they have the potential to develop effective dentin bonding. These materials have shown better bond strengths and less marginal microleakage than the previous generations of adhesives. Enamel acid etching and the new primer/adhesive systems can enhance the retention rates of resin restorations and reduce or eliminate marginal microleakage.

Adhesives↗
PubMed1991

Fluoride-releasing removable appliances.

A method was developed to give removable appliances a fluoride-releasing capability. Visible light-cured glass-ionomer cement inserts were made, placed in resins commonly used for removable appliances, and evaluated for fluoride release over a 2-month period. Fluoride release was measured daily for 7 days, weekly for 4 weeks, and monthly for 1 month. All specimens released fluoride at every time period. There was a "burst effect" in which more fluoride was released the first day, but the amount released decreased significantly on the second day. The amount of fluoride released decreased at each of the daily and weekly measurements, but became relatively stable after 7 days. All specimens were still releasing fluoride at the end of the 2-month test period.

Acrylic Resins↗
PubMed1991

Retention of pins in amalgam.

The Max 021 titanium alloy self-threading retentive pin was evaluated for retention in amalgam and compared to the Link Plus titanium alloy self-threading pin. Fifteen specimens in which amalgam was condensed around the retentive pins were prepared. The specimens were mounted in a specially constructed test apparatus in an Instron Testing Machine and placed under a continuous tensile force (1 mm/min) until failure occurred. The mean force required to induce failure in the Max pin specimens was 87.6 (+/- 37.4) Newtons while the mean for the Link Plus pins was 180.4 (+/- 39.8) Newtons. The failure of the specimens using the Max pins was primarily a result of fracture of the amalgam with removal of the pin intact. The failure site of the Link Plus pin was primarily fracture of the pin itself. Statistically, a significantly greater force was required to induce failure in the Link Plus pins.

Dental Amalgam↗
PubMed1990

Dimensional stability of glass ionomer used as a core material.

This laboratory study evaluated the dimensional stability of two reinforced glass ionomers (Ketac-Silver and Fuji Miracle Mix) in comparison with amalgam. Ten core build-ups were prepared with each material on extracted human teeth. Four Minim pins were placed in each tooth for retention. A gold casting was made for each core build-up. The specimens were placed in a distilled water and the distance between the casting and the tooth was measured at 1 hour, 6 hours, and then every 24 hours for 7 days. After 7 days, the measured changes were small, ranging from 1 to 63 microns. The reinforced glass ionomers were found to be dimensionally stable in moisture over a period of 7 days.

Analysis of Variance↗
PubMed1990

Effect of sterilization on the strength and cutting efficiency of twist drills.

Retentive-pin twist drills were subjected to four methods of sterilization and then examined to determine possible effects on resistance to fracture, cutting efficiency, and surface condition. Sterilization methods included steam autoclave, chemical vapor autoclave, dry heat, and immersion in glutaraldehyde. Although the steam and chemical vapor groups had lower mean fracture strengths after sterilization, there was no statistically significant difference among the groups. Only the steam autoclave group showed a statistically significant loss of cutting efficiency. Scanning electron microscopic evaluation revealed that only drills sterilized by steam autoclave showed changes in the surface condition or cutting edges.

Dental Cavity Preparation↗
PubMed1990

Fluoride release from fluoride-containing liners/bases.

Five new visible light-curing cavity liners/bascs that contain fluoride were evaluated for fluoride release over a 17-week period. Fluoride was released from all the materials, but the level of fluoride release decreased significantly (P less than .01) over the test period. There was also a statistically significant (P less than .05) difference among the materials in the amount of fluoride released.

Dental Cavity Lining↗
PubMed1990

Evaluation of a fluoride-containing sealant by SEM, microleakage, and fluoride release.

A fluoride-containing sealant (FluroShield) was evaluated in vitro and compared to a sealant without fluoride (Helio-Seal). Both materials were applied to the occlusal surface of extracted teeth and microscopically evaluated for their ability to penetrate pits and fissures. Additional specimens were subjected to dye immersion and evaluated for resistance to microleakage. Disc-shaped samples of the fluoride-containing sealant were immersed in distilled water and analyzed daily for seven days for fluoride release. All specimens of FluroShield released fluoride during the evaluation period, but there were differences between the materials in resistance to microleakage.

Dental Leakage↗
PubMed1989

Evaluation of potassium oxalate as a cavity liner.

All dental restoratives exhibit some microleakage. Recent studies disclosed that oxalate salts were superior to Copalite varnish in reducing dentinal permeability, but inferior in reducing microleakage. This study compared the effectiveness of a potassium oxalate solution (DDS) with three other cavity liners (Copalite, Cavi-Line, Prisma Universal Bond) and a no-liner control in reducing microleakage under amalgam restorations. Under the conditions of this study, DDS solution was significantly effective in reducing microleakage under amalgam restorations.

Composite Resins↗
PubMed1989

Effect of glass-ionomer base on composite resin hardness.

The effect of the glass-mm, and 3 mm thicknesses were placed over glass-ionomer bases, and the microhardness of the external surface was compared with that of controls without a base. A significant reduction in surface hardness (p less than 0.05) was determined only for the 1-mm test specimens.

Composite Resins↗