Biomedical subjects
Publications and source records attributed to P Cleaton-Jones.
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Movement of teeth during denture processing is an unsolved problem. This study investigates the amount of vertical tooth movement during controlled processing of acrylic, using 33 degrees and 0 degree teeth invested in specific mixes of plaster of Paris or dental stone. Forty sample set-ups each containing four posterior teeth were processed under strictly controlled laboratory conditions. Twenty of these samples carried 33 degrees teeth and the other twenty carried 0 degree teeth. Each group of twenty samples was randomly divided on a factorial design into batches of ten for investment in plaster of Paris or stone. The vertical movements were measured with a greater degree of accuracy than is required for clinical application. All results were analysed statistically. Significantly greater movement occurred with teeth invested in stone than those invested in plaster of Paris. Whereas, for teeth invested in stone, significantly greater movement occurred with 33 degrees than with 0 degree teeth, no such effect was found with teeth invested in plaster of Paris.
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The healing of standardized bony defects prepared in the mandibles of 24 vervet monkeys with a rotating bur uncooled, or cooled with saline or water, was studied. The experiment showed no difference in healing after 56 days irrespective of the coolant used or whether the bone was cut with or without a cooling agent.
Dental caries, debris (DI-S) and sugar intake were determined for 766 rural Black, urban Black, coloured, Indian and White children, using standardized techniques. In general sucrose intake, both quantity and frequency was low in rural Black children yet these children had relatively few caries-free individuals and higher than expected mean dmft scores. Comparison with earlier studies in the same localities has shown a worsening of dental caries in all groups except the White, in which the situation has improved. Sucrose consumption declined in rural Black, and White groups, remained steady in urban Black children and increased in coloured and Indian groups.
The pulpal response to Protemp (ESPE Gmbh) was compared to zinc oxide-eugenol, Super Syntrex (de Trey) and Protemp plus zinc oxide-eugenol liner in 144 vervet monkey (Cercopithecus pygerythus) incisor teeth, according to ADA Specification No. 41. Cellular displacement into dentinal tubules, superficial and deep inflammation were present only in the 3-day specimens in all materials. Mean scores for the test material were lower than both negative and positive controls. In the 30-day specimens the prevalence of reparative dentine under the test material was similar to the negative control, while at 90 days it was less than the negative control, although the severity in affected specimens was more than the positive control. Use of a zinc oxide-eugenol liner reduced the severity of reparative dentine formation.
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In the assessment of pulpal responses to dental materials there is no general agreement regarding which system should be used in the selection of histologic sections for assessment and which negative and positive control materials should be used. The present study is an evaluation, on 227 sections, of two pulpal assessment systems and three section-selection methods using a negative (zinc oxide and eugenol cement) and a positive (silicate) control material. The results indicate that, depending on which system is used, considerable variation in response can be noted. Better standardization of methods is necessary.
Five groups of 12 gravid female rats were exposed, during their entire gestation, intermittently for 6 h a day, 5 days per week, to 0.5% (5000 p.p.m.), 0.1% (1000 p.p.m.), 0.05% (500 p.p.m.) and 0.025% (250 p.p.m.) nitrous oxide-air mixtures (v/v), respectively. After killing the gravid rats on the 19th day of their pregnancies the numbers of corpora lutea of pregnancy were counted. Each uterus was examined for placentation sites and embryonic remnants and a detailed examination of the fetuses was undertaken. A significant reduction in mean litter size occurred only in the group exposed to 0.5% nitrous oxide in air (v/v). The mean litter sizes of the control and other exposed groups were comparable. No signs of fetal resorption or skeletal malformation were found in any group. The threshold of pollution for reduction in litter size has been shown in this study to lie between 0.1% and 0.5% nitrous oxide in air (v/v). A previous study on continuous exposure reported the threshold pollution to lie between 0.05% and 0.1% nitrous oxide in air (v/v). This investigation confirms that intermittent exposure to nitrous oxide-air mixtures increases the threshold for reproductive effects in rats.
In a study of male rat fertility male Wistar albino rats were exposed to 0.5% nitrous oxide/air mixtures (v/v) for 30 days and control rats were exposed to oil-free air for the same time period. Thereafter each male was mated with three nulliparous female rats and mated again with three more nulliparous rats after a 6-month recovery period. The offspring were weighed and measured for 8 weeks postnatally. There was a significant reduction in mean litter size of the female rats mated with the male rats directly after the nitrous oxide exposure period. The offspring from the female rats mated with the males directly after the exposure period were significantly smaller in size than the control group. These results show a reversible reduction in male Wistar rat fertility, after exposure to 0.5% nitrous oxide in air (v/v), as well as a postnatal growth depression.
This paper is a comparison of cross-sectional data on dental caries in the primary dentition undertaken between 1976 and 1981 in the Transvaal Province, South Africa, on 690 rural Black, 1463 urban Black, 870 Indian and 1622 White children aged 2-5 yr. There was a decrease in percentage dental caries prevalence in the urban White children and an increase in the other three groups, the fastest rate being seen among urban Indian children. Similar trends were noted for mean dmft. Dental caries in incisor and canine teeth remained fairly static but caries in molar teeth increased in the groups of Black and Indian children and decreased in the White children. Ratios d/dmft, m/dmft and f/dmft indicated that minimal treatment was received by all the children.
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