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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↗
PubMed1987

A comparison of the effects of continuous and periodic fluoride delivery on fluoride levels in plasma, enamel, and bones of nursing rats.

The purpose of this study was to determine and compare the F levels in plasma, enamel, and bones of nursing rat pups that received the same daily dose of F by continuous or periodic delivery during enamel development. The hypothesis was that F delivered continuously would result in enamel F levels higher than those attained when F was delivered periodically. For continuous delivery, copolymer devices (Southern Research Institute) that provide slow release of F were implanted in the backs of four-day-old rat pups. For periodic delivery, rat pups received F by intraperitoneal injection or gastric intubation. The doses were 0.01, 0.02, or 0.04 mg F/day. The rats were killed at 13 days of age, 24 hours after the last periodic delivery. Plasma was collected, femur and calvaria bones were removed, and enamel was scraped from developing first molars. Fluoride assay was by the microdiffusion method of Taves, with a F electrode. For the 0.02 mg F/day dose, plasma levels in control, implanted, injected, and gastric-intubated rats were 0.004, 0.020, 0.011, and 0.009 ppm, respectively. Enamel F levels were 1.1, 61.9, 54.0, and 42.3 ppm, respectively. Femur F levels were 2.2, 81.2, 84.8, and 68.1 ppm, respectively. Calvaria F levels were 2.5, 79.3, 80.1, and 67.9 ppm, respectively. The results showed that there was no significant difference in the enamel F levels or in the bone F levels in rat pups that received continuous or periodic, by injection, delivery of F at the same daily dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Amelogenesis↗
PubMed1987

Diffusion of fluoride through the rat enamel organ in vitro.

This study investigated the diffusion of fluoride through the enamel organ in vitro. The rat molar explants used were entirely in the secretory stage or predominantly in the maturation stage of enamel formation. The removal of the enamel organ or metabolic inhibition with iodoacetate caused significant increases in enamel fluoride uptake at both stages of enamel formation. Inhibition with dinitrophenol caused a significant increase only in the maturation phase. Uptake of fluoride in enamel was related to the fluoride concentration in the medium, except in the maturation stage explants, where increasing the medium fluoride concentration from 0.05 ppm to 0.08 ppm did not significantly increase fluoride uptake at any of the three observation times. The findings indicate that the enamel organ exists as a diffusion-limiting membrane to the movement of fluoride from the extracellular fluid compartment to the developing enamel.

Age Factors↗
PubMed1987

The short-term uptake and retention of fluoride in developing enamel and bone.

Eight- and 12-day-old rat pups were injected intraperitoneally with fluoride. Plasma, molar enamel, and bone samples were collected at observation times up to six hr after injection. In a second series, adult rats maintained for six weeks on water containing 5 ppm F were injected with fluoride. Plasma, incisor enamel, and bone samples were collected at the same observation times as those used in the first series. Fluoride assays were conducted by means of the microdiffusion, ion-selective-electrode method. In the suckling rats, plasma [F] levels peaked at 15 min and returned nearly to baseline in one hr. Significant increases in the [F] of developing enamel and bone were observed. No significant decline from the peak [F] seen in the hard tissues was observed over the six-hour period. Similar results were seen in the developing enamel of the adult rats. The data gave no evidence of a short-term reversible component of fluoride uptake in developing enamel. Apparent increases in F uptake in enamel and bone beyond peak plasma values suggest the presence of a diffusion-limiting membrane for fluoride from the extracellular fluids into the mineralizing matrix.

Age Factors↗
PubMed1987

Use of systemic fluoride supplements by North Carolina dentists.

This 1984 survey focuses on the use of systemic fluoride supplements by North Carolina dentists. Respondents included all the state's pediatric dentists and general practitioners who assay water supplies before prescribing fluoride supplements, and other randomly selected general practitioners who treat children. Whether practicing in fluoridated or nonfluoridated communities, most dentists prescribed systemic fluoride supplements but only a small number of practitioners assayed water supplies before doing so.

Child↗
PubMed1986

Fluoride uptake and retention at various stages of rat molar enamel development.

Suckling rat pups were given intraperitoneal fluoride injections at selected ages so that we could study fluoride uptake in the enamel of the maxillary first molar at various stages of enamel development. Plasma fluoride levels in six-day-old and 11-day-old pups were monitored following the intraperitoneal injection of fluoride. The findings indicate that: (1) fluoride was more easily taken up and retained during the early stages of enamel formation, but fluoride uptake can occur during all stages of enamel formation; (2) when injections were started early in enamel formation, more fluoride was contained in the enamel of the maxillary first molar at 13 days of age; and (3) the same dose of fluoride per gram body weight resulted in greater exposure to elevated plasma fluoride levels in six-day-old pups than in 11-day-old pups.

Amelogenesis↗
PubMed1986

Determinants of requests for water fluoride assay among North Carolina dentists.

Fluoride content of drinking water is an important criterion in prescribing fluoride supplements. The majority of practicing dentists and physicians prescribe fluoride supplements, yet many apparently are unaware of the fluoride levels in their patients' drinking water. Characteristics of North Carolina (NC) dentists, their practices, and their communities were investigated to determine factors associated with whether they requested fluoride assays of their patients' drinking water. Comparisons were made between dentists sampling (assaying) and those not sampling. Licensure renewal files provided characteristics of the 79 pedodontists and 1768 general practitioners (GP's) active in NC. Eighty-eight GP's (5%) and 26 pedodontists (33%) requested water fluoride analyses between December, 1982, and May, 1983. Significant predictors of fluoride assay request by GP's were the dentist's age, the geographic region of the state, the number of dentists in the practice, and an interaction between geographic region and the number of dentists in the practice. Younger GP's and those with fewer dentists in the practice were more likely to request fluoride assays of patients' water. For pedodontists, dentist's age and geographic region were significant predictors. Additional training concerning the need for water fluoride assay appears necessary, especially among older practitioners.

Age Factors↗