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Biomedical subjects

B K Norling

Publications and source records attributed to B K Norling.

36 records · Page 2Linked to original sources
PubMed1984

Lifelong food restriction prevents senile osteopenia and hyperparathyroidism in F344 rats.

Studies were carried out on male F344 rats to examine the influence of aging and life-prolonging food restriction on bone and circulating parathyroid hormone levels. In ad libitum fed animals, the weight, density and calcium content of the femur increased with age and achieved their peak levels by 12 months of age. These levels remained stable until about 24 months and by 27 months of age the ad libitum fed animals had lost appreciable amounts of bone. The maturation of the femurs of the animals maintained on 60% of the ad libitum food intake was delayed and their bones were lighter, less dense and contained less calcium than bones from ad libitum fed rats of corresponding ages. But at 6, 12 and 24 months of age, the femur strength to body weight ratios were very highly significantly greater (P less than 0.0001) for the restricted animals compared to the ad libitum fed controls. Circulating immunoreactive parathyroid hormone increased progressively with aging in the animals fed ad libitum and the animals that experienced bone loss at advanced age also had the highest level of the hormone. In contrast, in the food restricted animals aging was not associated with a marked increase in serum parathyroid hormone or with senile bone loss. The data are discussed in relation to the mechanism of the observed changes.

Aging↗
PubMed1983

Relationship between creep, gamma 2, and marginal fracture of dental amalgams.

The effect of gamma 1 and gamma 2 on the creep deformation of dental amalgams has been investigated. It has been shown that the creep of a conventional amalgam is not dependent on gamma 1 as was previously reported. Rather it is strongly influenced by gamma 2 and its volume fraction. It has been speculated that Sn-rich grain boundaries also enhance creep by facilitating grain boundary sliding. The reported correlation between creep and marginal fracture has been explained in terms of this dependence of creep on corrosion-prone Sn-rich microstructural constituents of amalgams.

Chemical Phenomena↗
PubMed1983

Effect of mandibular molar anatomy on the buccal Class I cavity preparation.

In mandibular molars, enamel dramatically increases in thickness at the buccal pit area and progresses occlusally due to an extensive concavity in the buccal dentinal core. In order to comply with the principles of operative dentistry, this anatomic variance dictates that, if the ultimate restoration is to be placed in dentin, the axial wall of a Class I buccal pit preparation should incline medially rather than follow the external contour of the tooth. The occlusal cavosurface angle of the preparation should be obtuse to coincide with enamel rod direction. Retention, when needed, should be placed at the mesio-axial and disto-axial line angles to avoid undermining occlusal intercuspal enamel, especially as the preparation approaches 2 mm occlusal to the buccal pit.

Dental Bonding↗
PubMed1981

Evaluation of the bonding of three porcelain repair systems.

1. Fractured porcelain bars repaired with Fusion/Concise displayed significantly greater repair strength (p less than .05) than bars repaired with Den-Mat and Cervident. 2. Comparing mean strengths of all samples before and after repair with Fusion/Concise indicated that only 18% of the original strength was regained following repair. 3. The low repair strengths of the tested materials indicate that their use is a temporary clinical procedure.

Composite Resins↗
PubMed1981

Fracturing molars with axial forces.

Extracted human molars were prepared with different sized occlusal cavities and restored with a high-copper amalgam. Loads were applied along the long axis of the teeth, and forces required to fracture the teeth were recorded. More force was required to break samples with the larger restorations than was required to break samples with the smaller restorations.

Copper↗
PubMed1981

Fracture resistance of mandibular molars with occlusal class I amalgam preparations.

The finding that large occlusal Class I restorations weaken premolars is not confirmed for natural mandibular molars because no statistically significant difference was found in the mean loads needed to fracture mandibular molars that were unprepared, minimally prepared, or prepared with a large occlusal amalgam restorations. Similarly, there was no statistically significant change in the amount of force necessary to fracture natural mandibular molars prepared with sharp vs round internal line angles (a no. 56 vs a no. 330 bur). Duplication of the experiment in acrylic resin mandibular molars confirmed the results of a previous experiment by Re and Norling as well as the results relating to sharp vs round internal line angles found in this experiment on natural mandibular molars. Acrylic resin teeth of homogeneous shape and substance overcome some of the sampling problems inherent in obtaining suitable human teeth for testing purposes; however, further testing of this material is indicated.

Dental Amalgam↗
PubMed1980

A new prophylaxis instrument: effect on enamel alterations.

A study was made to determine the efficacy of a new jet abrasive tooth-polishing device and its effect on enamel surfaces. Extracted teeth with extrinsic stain were polished with the jet abrasive. Smoothed enamel surfaces were polished with the jet abrasive, a rubber cup with paste, and an ultrasonic instrument. The surface alterations were then compared.

Dental Enamel↗
PubMed1979

The effect of nonionic surfactants on bubble entrapment in elastomeric impression materials.

The incorporation of certain nonionic surfactants into silicone and polysulfide elastomers increases their wettability by gypsum products and consequently results in less bubble entrapment in poured casts. The choice of the most effective surfactant is critical and differs not only between types of elastomer, but also between brands of a single type. The beneficial effect of the optimal surfactant is not reduced by rinsing the impression prior to pouring. While the working time of silicone is increased by surfactant additions, that of polysulfide is essentially unaffected, as are the dimensional accuracies and permanent deformations of both materials.

Air↗
PubMedDate not supplied

X-radiation spectra.

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Computers↗