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Biomedical subjects

J W Bawden

Publications and source records attributed to J W Bawden.

At least 19 recordsLinked to original sources
PubMed1992

Calcium movement in vivo and in vitro in secretory-stage enamel of rat incisors.

The lower incisors of young rats were dissected, immersed in physiological saline containing 45Ca under various conditions, and processed for autoradiography. The data were compared with those from in vivo 45Ca autoradiography. In secretory-stage enamel, wiped free of the enamel organ and immediately immersed in radioactive saline, there was intense labelling in the surface layers. The labelled area expanded only gradually into the deeper layers at a rate similar to that observed in vivo. Labelling in the enamel was similar in pattern but much weaker in intensity when the incisor was identically treated in vitro with the enamel organ attached. Glutaraldehyde pretreatment of the exposed enamel abolished expansion of the labelled area, whereas a hypochlorite pretreatment allowed a rapid diffusion of the isotope into the deeper layers of the secretory-stage enamel. The findings confirm the role of the enamel organ as a diffusion barrier to the penetration of calcium from the extracellular fluid to the secretory-stage enamel, and suggest an intimate correlation between physicochemical properties of the organic enamel matrix and the rate of surface-to-interior diffusion of calcium within the secretory-stage enamel of rat incisors.

Animals↗
PubMed1992

Fluoride uptake in hard tissues of fetal guinea pigs in response to various dose regimens.

This study was designed to explore various aspects of maternal-fetal fluoride metabolism. In its first phase, 57 female guinea pigs were bred and randomly assigned to a control group (I) or one of three experimental groups: (II) 3 parts/10(6) fluoride in drinking water, (III) a single daily oral dose and (IV) 3 parts/10(6) fluoride in water and a single daily oral fluoride dose. The total mean doses received by groups II and III were similar. The total mean dose received by group IV was approximately double that for groups II and III. Samples of maternal plasma, and fetal bone and enamel were collected on the 57th day of gestation. In its second phase, 53 pregnant guinea pigs were given drinking water containing 0, 2, 4, 6 or 8 parts/10(6) fluoride during gestation. On the 57th day of gestation samples of maternal and fetal enamel were collected. All samples in both phases of the study were assayed for fluoride using the microdiffusion, ion-selective electrode method. In the first part of the study, mean fetal enamel fluoride by group was: I, 21.6 parts/10(6); II, 38.6 parts/10(6); III, 33.5 parts/10(6); IV, 54.9 parts/10(6). In the second phase, maternal enamel was linearly related to the fluoride dose. The same was true for fetal enamel except at the 8 parts/10(6) fluoride level in the water where there was no increase over the 6 parts/10(6) group. At all dose levels, fetal enamel fluoride uptake was approximately an order of magnitude less than maternal enamel fluoride uptake.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1992

Fluoride concentrations in human and rat bone.

The most recent report on fluoride concentrations ([F]) in human bone was published over a decade ago. Such data are of interest in the context of changing patterns in systemic fluoride exposure. In the study reported here, bone samples were collected from 24 human subjects who underwent orthopedic surgery. Medical histories and the best possible life-time systemic fluoride exposure information were obtained from each subject. Bone samples were assayed for fluoride concentration using the acid diffusion, ion selective electrode method. For ash from whole bone, the lowest value was 378 ppm in a 16-year-old subject, and the highest value was 3,708 ppm in a 79-year-old person. Fluoride concentrations in bone were significantly correlated with age (r = .62). The regression line intercept at birth was 442 ppm, and the slope was 22 ppm per year. When measured separately, trabecular bone ash fluoride concentrations were significantly higher than the corresponding cortical bone values. Trabecular and cortical bone samples from rats' drinking water containing 75 ppm F were assayed for F. The mean trabecular bone fluoride concentration was significantly higher than the mean cortical bone concentration. There was close agreement between F assay results using a modification of the acid diffusion method and the method originally reported by Singer and Armstrong. The human bone ash [F] values reported in this study are similar to those reported from other North American subjects over the last three decades. These findings are of interest in the context of evidence indicating increased systemic fluoride exposure in the United States population.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Fluoride and calcium content of enamel organ, muscle, liver and plasma in rats.

Nine-day-old rats were given oral fluoride doses (0.5 micrograms F/g body weight). Plasma, enamel organ, muscle and liver samples were collected from nondosed pups (baseline) and 15, 30, 60 and 120 min after the dose. Samples were assayed for fluoride and calcium concentrations. Adult rats were given 20 ppm F water for 6 weeks, and the same tissues were sampled and assayed for fluoride concentrations only. In the first phase of the study, enamel organ had significantly higher fluoride and calcium content than liver and muscle. In adult rats the fluoride content of enamel organ was again significantly higher than for liver and muscle.

Administration, Oral↗
PubMed1992

Fluoride intake from beverage consumption in a sample of North Carolina children.

Since the 1940's, the prevalence of dental fluorosis has increased in the US, concomitant with a reduction in dental decay. These changes have been attributed in part to the widespread use of systemic and topical fluorides. Various sources of increased systemic fluoride exposure have been investigated. However, little is known regarding fluoride intake from beverages in a sample of children of ages susceptible to dental fluorosis. The purpose of this study was to estimate the amount of fluoride ingested from beverages by a sample of North Carolina (NC) children of ages 2-10 years. Data on beverage consumption were collected by means of a diary format. A questionnaire was included so that demographic information and self-assessment on the accuracy of the diaries could be obtained. Beverages reported in the diaries were purchased, and their fluoride content was assayed. Daily total fluid intake ranged from 970 to 1240 mL, and daily beverage consumption ranged from 585 to 756 mL. The estimated mean daily fluoride intakes from beverages for children 2-3, 4-6, and 7-10 years of age were 0.36, 0.54, and 0.60 mg, respectively.

Age Factors↗
PubMed1989

Calcium transport during mineralization.

The translocation of calcium from the extracellular fluid compartment into the mineralizing matrix during hard tissue formation is not well understood. There are two general means by which such calcium movement may occur: 1) diffusion through the pericellular space, or 2) transcellular transport. Cementum and bone are difficult tissues in which to study the system and little is known about the mechanisms involved. Dentin offers certain advantages for study and it appears that calcium movement into the mineralizing matrix is by transcellular transport. Information concerning the transport mechanism is meager. Enamel is more easily explored. The apparent existence of intercellular junctions tight to calcium in the ameloblast layer at all stages of enamel formation indicates that calcium movement occurs by transcellular transport. Based on published findings, a hypothesis concerning mechanisms of transcellular transport may be advanced. It is proposed that the relatively low level of calcium transport through secretory ameloblasts occurs without direct involvement of a calcium binding protein. During the maturation stage, when calcium influx to the matrix is greatly increased, a calcium binding protein (9 kd) appears and facilitates transport while preventing unphysiologic increases in the cytosolic free calcium ion concentration. Differences in the calcium ion concentrations of extracellular fluid and enamel matrix fluid appear to be critical to the influx of calcium across the proximal cell membrane and the efflux of calcium across the distal cell membrane.

Animals↗
PubMed1989

Effect of an acute maternal fluoride dose on fetal plasma fluoride levels and enamel fluoride uptake in guinea pigs.

We conducted this study to measure maternal plasma, fetal plasma, and fetal enamel fluoride concentrations for four hours following an oral F dose to near-term pregnant guinea pigs. We placed female guinea pigs on de-ionized (Group I) or 3-ppm-F (Group II) drinking water prior to breeding and during gestation. On the 57th day of gestation, we administered a maternal dose of NaF solution (0.6 mg F/kg) by stomach tube. We collected samples of maternal plasma, fetal plasma, and fetal enamel at baseline, at 15 and 30 min, and at one, two, and four h after administration of the dose. We assayed samples for F using a modification of the micro-diffusion and ion-specific electrode method. Group I mean baseline F values were: maternal plasma, 0.016; fetal plasma, 0.002; and fetal enamel, 7.0 ppm. Group II mean values were: 0.055, 0.004, and 19.0 ppm. After the maternal fluoride dose, the mean maternal plasma [F] rose sharply for 30 to 60 min and declined to about 50% of peak values by four h. Fetal plasma [F] changed less in absolute values, but similarly to maternal changes relative to baseline. Fetal enamel mean [F] rose more in Group II than in Group I. Baseline F status had an important effect on F uptake in fetal enamel following an acute maternal fluoride dose.

Administration, Oral↗
PubMed1989

Fluoride gels.

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Fluorides↗
PubMed1988

The Ca, Pi, F, and proline content of developing bovine enamel under GBHA-stained and unstained bands.

The surface enamel of fetal bovine teeth was stained with GBHA to indicate the position of bands of smooth-ended and ruffle-ended ameloblasts relative to the developing enamel. The boundaries of the bands were scored, under a dissecting microscope, and the bulk enamel under each band was collected. The enamel samples were assayed for Ca, Pi, F, and proline. The amount of Ca and Pi in the enamel increased in successive bands and seemed unrelated to the overlying ameloblast cell type. The loss of proline seemed unrelated to cell type. The fluoride content of enamel increased by approximately 50% in the first stained band immediately adjacent to the secretory zone. The F level returned to secretory values in the succeeding unstained band. Thus, only changes in the F level of developing enamel appeared to be related to GBHA staining patterns.

Ameloblasts↗
PubMed1979

Estimation of actual caries prevalence and treatment needs from field survey caries information on a child population in U.S.A.

Caries scores (DT + Dt) were recorded under simulated field survey conditions on 270 children ranging in age from 3 to 12 years. The children were subsequently diagnosed under optimum clinical conditions. The findings from the field and clinical examinations were statistically analyzed to determine the relationships between "survey" and "true" caries scores. It is proposed that the true mean caries score can be estimated from the survey mean score by adding 1.5 teeth in the primary dentition and 2 teeth in the mixed dentition. Tables were devised to estimate treatment needs for children at various survey caries scores in each dentition category.

Child↗
PubMed1979

Ameloblasts--ion transport function.

Recent autoradiographic and in vitro studies have produced evidence that the cells of the enamel organ limit the movement of calcium into enamel during the matrix secretion phase, but have no effect on movement of calcium during the maturation phase. The cells of the enamel organ do not seem to control the flux of phosphorus into enamel at either phase of development. This concept is consistent with current theories on the control of ion fluxes into developing bone.

Ameloblasts↗
PubMed1978

Comparison of 33P with 45Ca distribution in developing rat molar enamel in vivo and in vitro.

The distribution of 45Ca and 33P in developing rat molar enamel has been studied using freeze sectioning and autoradiographic methods. The distribution patterns of the two tracers in vivo were dissimilar. The use of in vitro methods showed that flux of 33P into enamel is not influenced by the cells of the enamel organ. It is suggested that the factors controlling movement of calcium and phosphorus into mineralizing enamel may be similar to those proposed for bone.

Animals↗
PubMed1978

Influence of the pulpal route on uptake of 45Ca in enamel and dentin of developing rat molars.

45Ca uptake in developing enamel and dentin was studied by autoradiography. The findings indicate that the pulpal route does not supply significant amounts of calcium to the rapidly mineralizing enamel. Disruption of the odontoblastic layer did not seem to result in altered penetration of calcium into the dentin in a manner similar to that described for disruption of the matrix secreting cell layer of enamel and of bone.

Animals↗
PubMed1978

In vivo and in vitro study of 59Fe uptake in developing rat molars.

Autoradiographic methods were used to study 59Fe uptake in vivo in mineralizing tissues of young rats. Localization of 59Fe was observed in the ameloblastic layers of molars. In vitro studies were performed which demonstrated that 59Fe uptake in developing rat molar enamel was limited by the metabolic activity of the cells of the enamel organ.

Animals↗