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Biomedical subjects

N R Gjerdet

Publications and source records attributed to N R Gjerdet.

At least 73 records · Page 4Linked to original sources
PubMed1983

Metal release from cobalt-chromium partial dentures in the mouth.

The amounts of cobalt and chromium released to the saliva in individuals wearing cobalt-chromium partial dentures have been measured. Saliva was collected during a 5-min period, both with and without dentures in the mouth, and the two samples compared. More than 80% of the 30 cases showed increased amounts of metals with the denture in the mouth. Newer and larger dentures liberated more than did older and smaller ones. The median increase in chromium was approximately twice that of cobalt.

Chromium↗
PubMed1983

Dental casting alloys with a low content of noble metals: physical properties.

Several physical properties such as strength (UTS and fracture and proof stress), modulus of elasticity, strain (elastic and plastic elongation), hardness, and hardening ability were determined for five low-gold alloys and two conventional gold casting alloys (types III and IV). The composition and the structure (pores and defects) of the cast tensile test specimens were also studied. The results showed that alloys with a low content of noble metals could have properties comparable to those of the traditional types III and IV dental gold casting alloys. A marked difference was seen in the plastic elongation (ductility). A great number of defects (pores and oxide inclusions) were also observed, especially in the specimens with a high content of both palladium and silver.

Chemical Phenomena↗
PubMed1983

Liberation of copper, zinc, and cadmium from different amalgams.

Release of copper, zinc, and cadmium from six different amalgams in 0.9% NaCl solution has been registered during a 4-week period. The products showed widely different corrosion behavior. A dispersion-type amalgam released the smallest amounts of copper but the largest amounts of zinc. A product containing indium had a high rate of copper dissolution. Cadmium was liberated to a great extent from a copper amalgam. The rate of corrosion varied greatly for the different products during the time of the experiment. The liberation of copper and zinc was inversely correlated.

Cadmium↗
PubMed1983

Fracture healing after rigid intramedullary nailing in rats.

Rigid intramedullary nailing of the right tibia after osteotomy with resection of the fibula was performed on 48 male Wistar rats weighting 300-400 g. Nailing was performed with 1.4-mm nails after reaming. Nail stiffness was similar to that of intact tibias. The left leg remained unoperated as control. The animals were sacrificed after 4, 8, 12 or 16 weeks, and both tibiae were tested in a 3-point bending test. Of the 35 animals with the nail in situ, nine animals showed non-union at the time of testing. At 8 weeks stiffness had reached normal values, while strength and deflection showed about half of normal values. Poor strength and small deflectability combined with near normal stiffness may be taken as evidence that Wolf's law is valid also in newly formed tissues of fracture healing; the protection given by a rigid nail makes normal strength and pliability unnecessary.

Animals↗
PubMed1982

Corrosion of silver soldered orthodontic wires.

The amounts of metals liberated from silver soldered stainless steel and cobalt-chromium orthodontic wires were measured. Measurements were taken after 3 days and 24 days immersion in 0.9% sodium chloride solution. High amounts of copper and zinc and some cadmium from the silver solder were found. The silver soldered stainless steel wire corroded more than the cobalt-chromium type, and liberated more nickel and chromium than did the cobalt-chromium wires.

Chemical Phenomena↗
PubMed1982

Effect of instability of experimental fracture healing.

Bilateral tibial osteotomy with fracturing of the fibula was performed on ten Wistar rats weighing 300--350 g. Intramedullary nailing was performed with 1.4 mm nails after reaming. On the left side solid stainless rods were used, while on the right side the nails had a middle part made of titanium-nickel wire covered with polyvinylchloride (PVC), giving the nail a high degree of flexibility. After 8 weeks, nine of the ten flexible nails showed fracture of the central wire. The continuity was, however, maintained by the PVC tube. The bones with flexible nailing always showed hypertrophic callus while there was only scanty callus on the side with rigid nailing. Strength, deformation at fracture and stiffness were measured in a three-point bending test after removal of the solid nails and the fibulae. The strength of the tibiae was greatest on the side with flexible nailing, as was the deformation at fracture. The mean stiffness was higher in the bones with rigid nails, but the difference here was not statistically discernible.

Animals↗
PubMed1981

Fluoride release from a fluoride-containing amalgam, a glass ionomer cement and a silicate cement in artificial saliva.

This study aimed to compare the fluoride release from a fluoride-containing amalgam, a silicate cement and a glass ionomer cement in artificial saliva. After storing specimens in an artificial saliva for 7 weeks, the fluoride content in the solvent was measured by a spectrophotometric method. The fluoride release from silicate cement was about 5 times greater than from glass ionomer cement, which again showed a release 4 times greater than the fluoride-containing amalgam. The fluoride release relative to fluoride content in test specimens was greater from fluoride-containing amalgam and silicate cement than from glass ionomer cement.

Chemical Phenomena↗
PubMed1981

Flowing of light-bodied elastic impression materials.

The ability of light-bodied elastomeric and reversible hydrocolloid impression materials to spread on a surface was studied in vitro. The material which most readily coated the surface was a polysulfide, followed by silicone, hydrocolloid, and polyether materials. The influence of surface energy was studied by comparing the spreading of impression materials on high energy (glass) and low energy (PTFE) surfaces. Only for polysulfide and hydrocolloid materials was any effect observed: The glass was more readily coated than PTFE. As a result of an increase in temperature of the elastomeric materials a reduction in the materials' ability to wet the surface was found for silicones and polysulfide, but not for polyether. An addition-polymerized silicone product showed the strongest temperature dependence. A strong negative correlation was found between spreading ability and viscosity of elastomeric materials.

Colloids↗
PubMed1981

The use of periodical literature in a Norwegian dental library.

Periodical loans, photocopy requests, and reading room use of back volumes of periodicals at the University of Bergen Dental School library were registered during a twelve-month period. Loans were sorted by title and year, and titles were grouped by specialty and language. Total borrowing was 2.242, and the annual aging factor was 0.89 (half-life 5.8 years). Twelve periodicals accounted for 50% of total borrowing. While most specialized dental journals had a lower aging factor than dental journals as a whole, orthodontic journals had an aging factor of 0.92 (half-life 8.7 years). Non-English-language journals accounted for 22% of borrowing. Scandinavian-language titles (16% of borrowing) had a lower aging factor (0.87, half-life 5.1 years) and seemed to be used more as news journals. The languages of other journals used were German (4.7% of borrowing), French, and Russian.

Libraries, Dental↗
PubMed1980

Galvanic cells including cobalt-chromium alloys.

Galvanic cells may be created when dentures made of cobalt-chromium alloys are placed on teeth with metallic restorations. The power of such cells was evaluated in an in vitro galvanic using amalgams, gold alloy, and nickel-chromium alloys. The amalgams and one of the nickel-chromium alloys revealed high corrosion currents when placed in contact with cobalt-chromium alloy, the conventional amalgam showing the highest values. The gold alloy and another nickel-chromium alloy exhibited low corrosion currents and they were noble with respect to cobalt-chromium.

Chromium↗
PubMed1978

Corrosion and creep of dental amalgam.

The influence of stress on corrosion was investigated by a potentiostatic technique. Amalgrams with low creep, both with and without gamma2-phase, revealed small increases in current with stress application while alloys with high creep exhibited large increases in current. Rupture of protective oxide due to increased strain for high creep alloys may explain the phenomenon.

Corrosion↗
PubMed1978

Porosity of resin filling materials.

Four paste-paste types of resin filling materials and three capsulated products were tested with respect to porosity content and size distribution of the pores. The data were obtained by using an automatic image analyzer. The paste-paste products were inserted into the test cavities by a bulk-packing technique and an injection technique. The results showed that the use of a syringe reduced the porosity content, mainly by the elimination of big pores. The capsulated products were not less porous than the paste-paste materials.

Dental Materials↗
PubMed1977

Dimensional changes of periodontal dressings.

The linear dimensional changes of three commercial periodontal dressings were measured during 24 hours. The dressings revealed different degrees of dimensional changes, which may indicate that exhibit variations in adaptation to wound surfaces.

Periodontal Dressings↗
PubMed1977

Contraction stresses of composite resin filling materials.

The polymerization shrinkage of composite resin filling materials and the tensile stresses developed when the shrinkage is restrained were measured in an in vitro experiment. This allows an estimation to be made of the forces exerted upon the enamel walls of cavities filled with the resin in the acid etch technique. The results indicate that the stresses acting on the enamel are low compared to the tensile strength of the enamel.

Composite Resins↗
PubMed1976

Elastic properties of resin-based filling materials.

Some aspects of the viscoelastic behavior of resin-based filling materials have been studied by the use of a bending test. The specimens, designed as cantilever beams were loaded for 30 sec and then unloaded. The tests were performed at 1/2 h, 1 h, 3h, 24 h, and 1 week after mixing of the materials. The strains were measured by electric strain gauges cemented to the tensile side of the beam. Six products were tested, five of them composites. Different brands of materials showed considerable variation in degree of viscoelastic behavior. The value for elastic after-effect decreased markedly with time, reaching a fairly constant value at 24 h. Elastic moduli showed a similar increase and the stiffest materials exhibited the least elastic after-effect.

Composite Resins↗