Search PubMed⌕ Search

Biomedical subjects

D B Boyer

Publications and source records attributed to D B Boyer.

At least 55 records · Page 3Linked to original sources
PubMed1987

Creep of amalgam at low stresses.

The creep and recovery of dental amalgam were studied with a torsional creep apparatus. The purpose was to investigate viscoelastic behavior in a low stress range that might result from normal chewing forces. The creep of specimens up to six months old was also studied. Four types of alloys for amalgam were used: two single-composition sphericals (SCS), an admixture-lathe-cut eutectic (ALE), and a conventional (CON). Constant torque was applied to dumbbell-shaped specimens for three hr and, after the stress was released, recovery was followed for 50 hr. All measurements were made in water at 37 degrees C after storage of the specimens for one week in 37 degrees C water. Creep was also measured at nine intervals on specimens aged from three hr to six months. The SCS amalgams exhibited the least amount of creep, followed by the ALE amalgam. The CON amalgam had the highest creep. The SCS amalgams approached linear viscoelastic behavior in the shear stress range of 0.78-4.10 MPa at 37 degrees C. They did not exhibit steady-state (viscous) creep at stresses less than 4.10 MPa. Recovery was complete but proceeded more slowly than creep. The ALE and CON amalgams exhibited viscous creep at 1.23 MPa and higher. The steady-state creep rate depended on stress, and the stress exponent ranged from 2.3-3.5. All except the ALE amalgam showed essentially constant creep compliance when aged up to six months, once the amalgamation reaction was completed after 24 to 48 hr. The compliance of the ALE amalgam gradually decreased over the six-month period.

Chemical Phenomena↗
PubMed1987

Fracture resistance of endodontically prepared teeth using various restorative materials.

This study compares the fracture resistance of endodontically treated premolars with modified types of cavity preparations and restoration with either amalgam or composite resin. The greatest influence on fracture resistance was the remaining tooth structure. The effect of adequate wall support on tooth strength was compared with intact unprepared teeth.

Acid Etching, Dental↗
PubMed1986

Effects of polymerization techniques on uniformity of cure of large-diameter, photo-initiated composite resin restorations.

The polymerization effectiveness of various methods of exposing large-diameter, light-activated composite resin samples is reported. Results of Knoop hardness testing showed that highest mean hardness was achieved by using a wide tip (13 mm) with either the spot cure or overlap method for 60 seconds. More uniform hardness resulted from the wide-tip with scanning methods and 60-second cure than resulted from the narrow-tip (8 mm) with the spot or overlap method and 20-second cure.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1985

Creep of posterior dental composites.

The creep of microspecimens of posterior dental composites was studied using a torsional creep apparatus. Shear stresses were maintained for 3 h and recovery was followed for 50 h. Creep curves were obtained at 21, 37, and 50 degrees C and four torque levels. The effect of conditioning the specimens in water up to 8 weeks was studied. The posterior composites exhibited linear viscoelastic behavior at low deformations. They had higher shear moduli and greater resistance to creep than conventional and microfilled composites. In aging experiments, maximum shear moduli occurred when specimens were 48 h to 1 week old. Subsequent softening was attributed to water absorption. Residual strain was highest when the composites were stressed within 24 h of initiating polymerization. Residual strain was very low in specimens 48 h to 8 weeks of age.

Aluminum Compounds↗
PubMed1985

Bond strength of cements to nickel-chromium and silver-palladium alloys.

The bonding of zinc phosphate, polycarboxylate, and reinforced ZOE cements to nickel-chromium and silver-palladium alloys was measured by cementing flat surfaces of the metals together. Polycarboxylate cement produced higher bond strengths than the other two cements to both metals. Polycarboxylate cement bonded better to nickel-chromium alloys than to a silver-palladium alloy. Zinc phosphate and reinforced ZOE cements had similar bond strengths except for Biobond, to which zinc phosphate cement provided higher bond strength. Polycarboxylate cement failed cohesively to both types of metals, and zinc phosphate and reinforced ZOE cements failed adhesively.

Chromium Alloys↗
PubMed1985

Composite resin compatibility and bond longevity of a dentin bonding agent.

The shear strength of a commercial dentin bonding agent was studied using human dentin in vitro. The agent was tested for compatibility with three proprietary composite resins. In addition, some samples were subjected to prolonged water immersion and thermocycling to determine effects on bond strength. There was no statistically significant difference in shear strengths when the three composite resins were used. In addition, there was no difference in shear strengths among those samples thermocycled or immersed for up to one year. The implications of this study are that the dentin bonding agent may be used with several composite resins with no significant difference in bond strengths, and that the bond seems stable when subjected to immersion or simulated intra-oral thermal stresses.

Adhesives↗
PubMed1984

Creep of conventional and microfilled dental composites.

The creep of microspecimens of two conventional and two microfilled composites was studied using a torsional creep apparatus. Small stresses below the materials' proportional limits were maintained for 3 h and recovery was monitored for 30 h. Creep curves were obtained at 21.5, 37, and 50 degrees C, and three torque levels. The composites exhibited linear viscoelastic behavior at low deformations. The magnitude of creep depended on the amount and type of resin in the composites. The materials did not recover their original shape after 30 h after the stress was removed. No transitions were observed in the temperature range employed. The shear moduli decreased with temperature and are in reasonable agreement with literature values obtained with other tests.

Acrylic Resins↗
PubMed1984

Bond strength and hardness of light-activated composite resins.

The bond strength of visible light-activated composites to etched enamel was measured as a function of exposure time. Studies have shown that the bottom surface may not be as hard as the top after customary cure times. Therefore this study also measured hardness and related it to enamel bonding. Plexiglas molds were used to simulate extracoronal applications where light is not attenuated by enamel. Bond strength and hardness of the bottom surfaces reached maximum values after the same exposure times with two of the three composites. More exposure time than normally recommended by manufacturers was needed to obtain maximum bond strength to enamel.

Chemical Phenomena↗
PubMed1984

Build-up and repair of light-cured composites: bond strength.

Interfacial bond strengths of light-activated composites were measured as a function of age using a transverse strength test. Bond strength between layers decreased with the age of the initial layer and reflected the setting curves of the composites. The highly-filled composites exhibited the greatest bond strengths. Uncut surfaces provided a better substrate for bonding than did ground surfaces. Use of a bonding agent on both uncut and ground surfaces improved bond strengths. Mean repair strengths of light-activated composites were similar to those of self-curing composites. Composites with ground surfaces aged for one wk had mean repair strengths 27% of the cohesive strength without bonding agent and 48% with bonding agent.

Chemical Phenomena↗
PubMed1984

Acid-etch retained cast metal prostheses: a seven-year retrospective study.

The results of this study showed: retention rate was good, caries on the retainer teeth was almost nonexistent, and the supporting tissue clinically did not appear to have a greater incidence of periodontal problems. We believe that these results indicate that the cast acid-etch retained anterior prosthesis should be considered a permanent restoration and a valuable aid for the dental patient.

Acid Etching, Dental↗