Biomedical subjects
Publications and source records attributed to A Harrison.
The in vitro abrasion resistance of seven commercial composite resin restorative materials has been measured. Analysis of the composite microstructures shows that abrasion rates are dependent upon the size, hardness, and volume fraction of particles in the material. The most abrasion-resistant composites contain a high volume fraction of large, hard particles.
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Wear tests of various combinations of acrylic resin and porcelain were made using a machine which was designed to test materials under conditions similar to those of masticatory function by simulating the loads, sliding distances, and contact times encountered in the human masticatory cycle. The results showed that the amount of wear of the two materials worn in combination depended on the nature of the surrounding medium and on the surface roughness of the opposing material. Acrylic resin showed good wear resistance provided no third party abrasive or opposing hard, rough surface was present. When a mild abrasive was incorporated in the system, the acrylic resin vs acrylic resin combination wore almost seven times more than porcelain vs porcelain. Clinical experience would suggest that this is a reasonably sound order of wear.
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This survey has attempted to show some of the differences in techniques and materials used by three groups of dentists involved in prosthodontic work in the United States. Some contrasting features between dentistry performed by the NHS and that in the United States have been illustrated, but fair comparisons between the two systems could not be made because of the basic difference in the number of patients and completed treatments and the fee schedules.
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This study tried to determine whether a relationship exists between the degree of alveolar resorption of the edentulous mandible and the degree of osteoporosis, as expressed by the metacarpal index. Eighty patients were examined. Each had a radiograph of the left hand to show the second metacarpal, and a standard pan-oral radiograph. A morphological measurement of the metacarpal bone, which is a good indication of the mineral content of the skeleton, was made on each hand radiograph. Alveolar resorption was estimated on the pan-oral radiograph by taking the original height of the alveolar process as being three times the distance from the inferior border of the madible to the inferior edge of the mental foramen. The regression analysis revealed no relationship between osteoporosis, as measured by the metacarpal index, and the amount of alveolar bone resorption.
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Three dental amalgams were investigated to determine if their abrasion resistance was significantly affected by different packing pressures. Abrasive wear tests were performed on a machine designed to test materials under conditions similar to masticatory function. The results show that the abrasion resistance of the amalgams is unaffected by the packing pressure.
When 0-1 mM-S alpha-chlorohydrin was present in incubations, glycolysis by ram testicular spermatozoa was almost completely inhibited whereas 10 mM-R alpha-chlorohydrin had no effect. Male rats dosed orally with S alpha-chlorohydrin (3-25 mg/kg/day) became much less fertile than controls but those dosed with R alpha-chlorohydrin (13 mg/kg/day) did not. The loss of fertility was associated with a reduced ability of spermatozoa from the cauda epididymidis of these rats to oxidize glucose. It is concluded that the S enantiomer is responsible for both the inhibition of sperm glycolysis and the reduction in fertility caused by the racemic mixture of alpha-chlorohydrin.
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