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Antibodies specific to Gαq, PLCβ, Gαi 1-2, and PKA were immunohistochemically (IHC) localized in the pre-ameloblasts up to initial dentin matrix deposition and continued in the distal ends of the pre-secretory ameloblasts to the beginning of enamel matrix secretion. It was hypothesized that the endothelin B receptor (ETBR) and/or the extracellular Ca2-sensing receptor (CaR) would localize in the same locations as their known downstream signal transduction pathway (STP) effectors during events related to early amelogenesis. Localization was similar for the 4 signal transduction pathway elements and the CaR. The ETBR was not localized in any of the cells of the enamel organ. These findings indicate that the CaR and its related STPs are expressed in the pre-ameloblasts and pre-secretory ameloblasts in positions where they may be able to detect increases in extracellular Ca2+ concentrations observed in the pre-dentin matrix in a previous study. These observations are consistent with the hypothesis that increased levels of free Ca2+ in the pre-dentin matrix serve as a primary signal for modification of gene expression important to amelogenesis. [ABSTRACT FROM AUTHOR]

As the use of adhesive restorative materials has increased during the last several years, interest in adhesive materials that release fluoride has also grown. The purpose of this study was to measure fluoride release from several adhesive restorative materials and to evaluate its effect on dentin resistance to demineralization and on bacterial metabolism in a modified in vitro system. Standardized cavities (1.8 mm in diameter) were prepared in bovine teeth that had been ground to dentin. One cavity in each tooth was restored with one of the following restorative systems: (a) Single Bond and Z100; (b) Single Bond and Tetric Ceram; (c) Fuji Bond LC and Z100; (d) Fuji Bond LC and Tetric Ceram; (e) Fuji II LC; or (f) Fuji IX GP. The other cavity in each tooth was "restored" with wax as a control. For each restorative system, 12 specimens were evaluated for fluoride release during the first 24 hrs after restoration placement. Dentin adjacent to the restored sites was subjected to lactic acid challenge (pH 4.3) for 3 hrs, after which calcium release was measured. Another 12 specimens in each group were stored for 24 hrs in de-ionized water, and were exposed to an S. mutans suspension (1:1 THB/de-ionized water and 50 mM glucose, A660 = 0.2) for 6 hrs, followed by calcium release and pH measurement. Bulk specimens of each material were also made and stored in water. Fluoride released from Fuji Bond LC, Fuji IX GP, and Fuji II LC in bulk was significantly greater than from the other materials. In the restored dentin specimens, increased resistance to demineralization from a lactic acid challenge was directly related to fluoride release. The same effects were seen as a result of the S. mutans challenge. While fluoride release from restorative materials increased the resistance of dentin to demineralization in this system, the clinical relevance of the findings is not known. [ABSTRACT FROM AUTHOR]

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. The significance is that similar levels of F can be attained in developing enamel if the same total dose of F is delivered continuously or periodically once a day. Previous studies have shown that there is less chance of producing disturbances in enamel mineralization with continuous F delivery when compared with periodic F delivery at a lower daily dose. [ABSTRACT FROM AUTHOR]

This study measured the effects of variations in the maternal fluoride intake on changes in maternal plasma, fetal plasma, and fetal enamel fluoride levels of near-term guinea pig pups. Pregnant sows were divided randomly into one of three groups whose drinking water was either de-ionized or contained 5 ppm or 20 ppm fluoride supplied ad libitum. At approximately 55 days' gestation, maternal and fetal plasma and fetal enamel samples were collected and assayed for fluoride. Results showed an increase in mean fluoride concentration for maternal plasma from the de-ionized to the 20-ppm group. Mean fetal plasma fluoride concentrations were lower at base-line and increased much less than did maternal plasma levels. Mean fetal enamel concentrations increased in a fashion similar to that of the maternal plasma levels and exhibited significant differences among all groups. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The purpose of this study was to determine the F levels in plasma and molar enamel from rat pups whose mothers had received various levels of F during pregnancy and/or lactation. Rats were started on water containing 0 (Group I), 50 (Group II), or 100 (Group III) ppm F at the beginning of pregnancy or on the day of delivery. The mothers and pups were killed 13 days after delivery, and plasma F levels, milk F levels, and pup molar enamel F levels were determined. The mean maternal plasma F concentrations were 0.02 ± 0.005 ± ppm in Group I, 0.10 0.031 ppm in Group II, and 0.21 0.05 7 ppm in Group III. The milk F values were about twice as high as the respective plasma concentrations. The plasma F concentration in control pups was 0.003 ± 0.0002 ppm, and there was a rise to 0.006± 0.0002 ppm in Group III Enamel F concentrations were 0.62±0.13 ppm, 4.72 ±0.79 ppm, and 8.80±1.74 ppm, respectively. The plasma and enamel F values obtained from pups were not significantly different between the pre-natal/post-natal, and the post-natal-only groups. It was concluded that: (1) fluoride levels in the plasma and enamel of control rat pups were much lower than those found in adult rats, (2) such values could be increased only slightly when high doses of F were given to the mother, and(3) unlike values reported for other species, rat milk fluoride concentrations were higher than the respective plasma values. [ABSTRACT FROM AUTHOR]

Two methods were used to reduce net calcium uptake by the secretory stage enamel of developing rat molar explants. Neither method had a significant effect on fluoride uptake by the explants. These findings indicate that the mechanisms for uptake in the developing enamel are independent for calcium and fluoride. [ABSTRACT FROM AUTHOR]

The effects of parathyroid hormone (PTH), calcitonin (CT), 1,25(OH)2D3, and 24,25(OH)2D3 on calcium transport through the secretory stage enamel organ were studied on developing rat molars in vitro. 24,25(OH)2D3 increased 45Ca uptake by the explants. 24,25(OH)2D3 plus PTH further enhanced 45Ca uptake and resulted in an increase in net calcium uptake by the developing enamel. [ABSTRACT FROM AUTHOR]

Autoradiographs of molar teeth from 15-day-old rats that had been injected with 18F showed no tracer uptake in the late-mineralizing enamel. Autoradiographic and quantitative in vitro experiments indicated that the enamel organ limited fluoride uptake during the maturation phase of enamel formation. [ABSTRACT FROM AUTHOR]

The uptake patterns of 90Sr in developing rat molar enamel were studied in vivo and in vitro. Autoradiographic methods were used that preclude loss or translocation of tracers associated with water-soluble compounds in the sections. In eight-day-old rats injected with the tracer, 90Sr uptake in the enamel was significantly less than for dentin and bone, particularly at early sacrifice times. The uptake pattern of 90Sr was somewhat different from that pre piously observed for 45Ca. The in vitro experiments indicated that the viable intact enamel organ limits uptake of 90Sr by enamel in both the secretory and maturation phases of enamel formation. [ABSTRACT FROM AUTHOR]

The uptake of 48V in developing rat molar enamel was studied in vivo and in vitro using autoradiographic and quantitative methods. It was shown that the uptake of 48V in enamel is less than in bone and dentin, and that plasma protein binding of 48V is primarily responsible for the limited uptake in enamel. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

This study was undertaken to map signal transduction pathway (STP) components uniquely associated with the four major receptor groups and their related STPs in association with the events involved in amelogenesis in the rat. Whole-head, freeze-dried sagittal sections were obtained at the level of the maxillary first molars and picked up on transparent adhesive tape. The sections were not decalcified or fixed, providing optimum conditions for immunohistochemical (IHC) localization. Antibodies to pathway components Gsα, Giα, Gqα Sos-1, Grb-2, p125Fak, Jak2, and Vav were localized. The respective patterns of localization indicate that the Gqα-linked, the receptor tyrosine kinase-initiated, and the integrin receptor-initiated pathways are involved in the proliferating pre-ameloblast cells. In the differentiating and differentiated ameloblasts, the Gsα-linked cAMP pathway is involved, apparently reading a factor(s) released by the dentin matrix. The Gqα-linked, the receptor tyrosine kinase-initiated, the integrin receptor-initiated, and the cytokine receptor-initiated pathways are also up-regulated in the proximal ends of the ameloblasts. These observations indicate that all four of the major receptor groups are involved in amelogenesis and that the role of classes of ligands not previously implicated in enamel formation must now be considered. It seems that the cells of the enamel organ respond to the appearance and disappearance of autocrine and paracrine growth factors, but they also up-regulate specific STPs to enable them to respond to circulating hormones and growth factors whose concentrations in the extracellular fluids remain relatively constant. [ABSTRACT FROM AUTHOR]

Despite extensive investigation, the developmental mechanism or mechanisms resulting in dental fluorosis are unknown. Several hypotheses suggest abnormal matrix synthesis, secretion, and delayed and/or defective matrix degradation with retention of enamel protein. The purpose of this study was to characterize the protein composition of fluorosed human enamel. Nine permanent moderately fluorosed (developed in a 3.2 ppm H2O area) and ten permanent normal control teeth (from individuals with < 0.2 ppm F in their drinking water) were evaluated. The enamel fluoride concentration, protein content, and amino acid composition were determined for each tooth. The enamel proteins were further characterized by gel electrophoresis and by Western blot analysis by means of polyclonal antibodies raised against recombinant amelogenin protein. Fluorotic enamel had significantly elevated (p = 0.0001) F levels compared with normal enamel (mean [F-] fluorosed = 431 ppm; mean [F-] control = 62 ppm). While there was a significantly greater protein content by weight in fluorosed enamel compared with normal enamel (mean fluorosed = 0.27%; mean control = 0.11%), the amino acid profiles were similar for fluorosed and normal enamel. Gel electrophoresis showed fluorosed enamel to have a greater diversity of primarily low- molecular-weight proteins compared with normal enamel. Western blot analysis did not indicate retention of amelogenin in either fluorosed or normal enamel. This investigation showed that the protein content of fluorosed enamel was greater than that of normal enamel; however, the amino acid compositions were similar for fluorosed and normal enamel. Furthermore, there does not appear to be retention of significant amounts of amelogenin in fully mature, moderately fluorosed human enamel. Although delayed removal of the enamel matrix proteins may play a role in the hypomineralization defects seen in fluorosed enamel, the majority of these proteins are absent in the mature tissue of these moderately fluorosed teeth. [ABSTRACT FROM AUTHOR]

The article discusses biological mechanisms in the onset of fluorosis due to the use of fluoride. The authors suggest that increases in fluorosis could affect the use of fluorides to prevent dental caries. They discuss how studies indicate fluoride increases apatite nucleation and apatite crystal growth and inhibits the removal of amelogenin proteins during dental enamel growth. Research on how ameloblasts affect the mineralization of dental enamel is also noted. The reduction of zone refinement, in which apatite crystal formation is improved, due to fluoride dosage, resulting in problems regarding the growth of dental enamel, is considered.

Activation of the protein kinase C (PKC)-related signal transduction system has been associated with phenotypic expression in a wide variety of cell types. In in vitro studies, it has often been activated by relatively small increases in the Ca2+ concentration ([Ca22+]) in the medium. The studies reported here explored the hypothesis that localized increases in the extracellular [Ca2+] and activation of the PKC-related pathway may be involved in early dentin and enamel formation. Whole-head, freeze-dried sections through the developing molars of 5-day-old rats were evaluated by methods that localized non-crystalline Ca2+. Immunohistochemical methods were adapted for use with the freeze-dried sections, and two monoclonal antibodies were used to localize PKCα in the formative cells of the developing teeth. Low concentrations of extracellular Ca2+ were observed in the early, unmineralized dentin in the area of ameloblast differentiation. Increased concentrations occurred at the point of initial dentin mineralization, immediately before the beginning of enamel matrix deposition. PKCα was localized in the differentiating odontoblasts, at the beginning of dentin matrix deposition. It was intensely localized in the distal borders of the pre-ameloblasts, and appeared to redistribute in the cells during ameloblast differentiation. These observations suggest that local increases in the extracellular [Ca2+] and the PKC signal transduction pathway may be involved in key inductions in the early stages of dentin and enamel formation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 L Baseline F status had an important effect on F uptake in fetal enamel following an actue maternal fluoride dose. [ABSTRACT FROM AUTHOR]

The surface enamel of fetal bovine teeth was stained with GBIIA 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 secretary zone. The F level returned to secretary values in the succeeding unstained band. Thus, only changes in the F level of developing enamel appeared to be related to GBHA staining patterns. [ABSTRACT FROM AUTHOR]

The objectives of this study were to determine the specific surface area of secretory-stage and of maturation-stage enamel, to compare the fluoride uptake by isolated enamel at these two stages on a surface- area basis, and to examine the effect of the organic matrix on the fluoride uptake by whole enamel. Fetal bovine secretary and maturation stage enamel samples were collected, and a portion of the enamel at each developmental stage was treated with hydrazine for removal of the organic matrix. The specific surface areas of the enamel mineral, as determined by the multi-point BET method, were 59.3 m²/ g in the secretary stage and 37.9 m²/g in the maturation stage. Whole and deproteinated enamel samples were equilibrated in buffered solutions containing 10-5 to 10-3 mol/L fluoride, and the uptake was measured with a fluoride specific electrode. The results indicate that the in vitro fluoride uptake was controlled solely by the surface area of the apatitic mineral and that the organic matrix did not contribute to the fluoride uptake. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 up-take 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. [ABSTRACT FROM AUTHOR]

Eleven-day-old rat maxillary first molar explants were removed by microdissection and incubated in vitro to determine the direct effects of parathyroid hormone (PTH), calcitonin (CT), 1,25(OH)2D3, 24,25(OH) 2D3, and a combination of PTH and vitamin D3 metabolites on calcium uptake in the mineralizing enamel of the explants. None of the agents had a statistically significant effect. These results are in contrast to those observed on explants from six-day-old rats, where PTH + 24,25(OH) 2D3 caused a significant increase in net calcium transport. The findings are consistent with the hypothesis that the transcellular transport of calcium through the secretary stage and the maturation stage ameloblasts occurs by different mechanisms. [ABSTRACT FROM AUTHOR]

An extract of guinea pig thyroid gland produced a mild hypocalcemia indicative of the presence of thyrocalcitonin when administered intravenously to nongravid guinea pigs. Extract-induced hypocalcemia in gravid guinea pigs resulted in a rise in fetal plasma calcium values at the end of four hours. [ABSTRACT FROM AUTHOR]

Base line values were established for total and filterable maternal and fetal blood calcium in the guinea pig. It was also demonstrated that parathyroid extract and vitamin D raised the maternal total and filterable calcium levels but had no effect on fetal plasma calcium values. [ABSTRACT FROM AUTHOR]

Antibodies specific to Galphaq, PLCbeta, Galphai 1-2, and PKA were immunohistochemically (IHC) localized in the pre-ameloblasts up to initial dentin matrix deposition and continued in the distal ends of the pre-secretory ameloblasts to the beginning of enamel matrix secretion. It was hypothesized that the endothelin B receptor (ETBR) and/or the extracellular Ca2+-sensing receptor (CaR) would localize in the same locations as their known downstream signal transduction pathway (STP) effectors during events related to early amelogenesis. Localization was similar for the 4 signal transduction pathway elements and the CaR. The ETBR was not localized in any of the cells of the enamel organ. These findings indicate that the CaR and its related STPs are expressed in the pre-ameloblasts and pre-secretory ameloblasts in positions where they may be able to detect increases in extracellular Ca2+ concentrations observed in the pre-dentin matrix in a previous study. These observations are consistent with the hypothesis that increased levels of free Ca2+ in the pre-dentin matrix serve as a primary signal for modification of gene expression important to amelogenesis.

Findings on the localization and possible roles of the major growth factors, epidermal (EGF), platelet-derived (PDGF) and fibroblast (FGF) in early amelogenesis are contradictory and inconclusive. This study sought to localize immunohistochemically phospholipase (PLCgamma) and the EGF, PDGF and FGF receptors in the cells of the enamel organ during the events leading directly to early enamel formation in rat molars. PLCgamma is an immediate, downstream, signal-transduction pathway effector unique to the three receptors. A whole-head, freeze-dried sectioning method was used to reduce the possibilities of false-negative staining. A modification of the avidin/biotin complex method of immunohistochemical localization was used. Anti-PLCgamma and antibodies to each of EGF, PDGF and FGF receptors colocalized in the preameloblasts of the cervical loop, adjacent to the undifferentiated mesenchymal cells of the dental pulp. This staining disappeared shortly after the beginning of dentine mineralization. Staining for all four antibodies appeared on the proximal ends of the differentiating presecretory ameloblasts at the level of the beginning of predentine matrix deposition and continued in the secretory ameloblasts. It appears that EGF, PDGF and FGF have roles in the differentiation of ameloblasts and in control of cellular functions in presecretory and secretory ameloblasts. Their roles may represent redundancy of the kind seen in highly conserved tissues.

Objective: To determine whether feeding sweetpotato cannery waste (SPCW) to cattle had adverse effects on dental wear, growth performance, or ruminal tissues., Design: Clinical trial., Animals: 36 Holstein steers., Procedure: Steers were assigned to 1 of 3 groups. All steers received ryegrass hay ad libitum. In addition, steers in group 1 were fed 3.2 kg of corn and soybean meal/steer/d, steers in group 2 were fed 0.45 kg of soybean meal/steer/d and SPCW ad libitum, and steers in group 3 were fed a mixture of SPCW and broiler litter ad libitum. Samples of rumen fluid were collected on day 56. Steers were slaughtered on day 84, and samples of rumen were submitted for histologic examination. Teeth from control steers were removed, and calcium ion loss in response to etching with 2.28% lactic acid solutions buffered to pH of 3.75, 4.0, 4.25, 4.5, and 4.75 was determined., Results: Average daily gain was lower for steers fed SPCW than for steers in the other 2 groups. Steers fed the SPCW-broiler litter mixture had only mild increases in tooth wear and tooth color scores, compared with control steers, whereas steers fed unbuffered SPCW had substantial increases in tooth wear and tooth color scores. Histologic abnormalities were detected in rumens from steers fed diets containing SPCW. Calcium ion loss decreased as pH of the etching solution increased., Clinical Implications: Results indicate that feeding cattle unbuffered SPCW can cause dental erosion, ruminal epithelial changes, and poor growth; however, SPCW buffered with broiler litter can be used as a cattle feed.

Purpose: Dental amalgam restorations provide a potential source for mercury (Hg) exposure in children. This study explored the possibility that Hg levels in dentin of exfoliated primary maxillary canines could detect cumulative Hg exposure from amalgam restorations in a sample of North Carolina children., Methods: Twenty-seven exfoliated maxillary canines from 3.3 children, without restorations or caries, were assayed for dentin Hg concentration ([Hg]). Urine samples were obtained from 21 subjects and assayed for [Hg] and diet surveys for seafood ingestion were completed for 26 subjects. A surface/month exposure index (SMEI) was compiled from dental records to quantify each child's cumulative exposure to amalgam restorations., Results: Results showed that dentin [Hg] ranged from undetectable levels to 15.7 ppm with a mean of 3.7 ppm. The SMEI scores ranged from 0-638 with a mean of 95. Ten subjects had low SMEI scores of 0-3, nine had scores 4-100, and eight had scores higher than 100. No statistical correlation was found for SMEI scores and dentin [Hg]. Urine Hg levels were found to be negligible and no relationship was found between urine [Hg] and reported ingestion of seafood or SMEI scores., Conclusions: Hg exposure in this sample of children was low and additional exposure from amalgam restorations could not be detected by the methods used in this study.

Purpose: In response to concerns about current and future demands for specialized pediatric dental care in North Carolina, a survey of private pediatric dental practices was conducted., Methods: Data were collected on the demographics and other practice variables. Information was also collected on the ages, caries activity, Medicaid status, estimated treatment needs, fluoridation status, and location of residence (urban/rural) of all new patients seen in each practice during three designated, consecutive days in November 1996., Results: The survey response rate was 76%. The data indicated that most pediatric dentists in North Carolina are quite busy. A total of 519 new patients were seen during the three-day survey period. The mean age was 4.7 years and 22% had advanced caries. Forty seven percent were caries free. Most of the disease was found in the primary dentitions of young children., Conclusions: The findings indicate that the specialized pediatric dental care system in North Carolina is operating close to its capacity and is overtaxed in many areas of the state.

Previous studies, in which the known janus kinase and signal transducer and activator of transcription (STAT) isoforms were immunohistochemically mapped in developing rat molars, implicated a sizeable list of cytokine superfamily receptor (CSR)/signal-transduction pathway (STP) linkages in the cells of the enamel organ involved in the events leading directly to early amelogenesis. Various combinations of upregulated janus kinases and STATs are known to be linked to single or small groups of CSRs. On the basis of the previous observations it was hypothesized that the interferon-gamma receptor (IFNgamma r) and the granulocyte colony-stimulating factor receptor (G-CSF receptor) would be localized in specific sites in the cells of the enamel organ during early amelogenesis. To verify this, whole-head, freeze-dried sections were here obtained at the level of the mandibular first and second molar from newborn and 5-day-old rats. These sections were not demineralized or fixed, reducing the possibility of false-negative results. Antibodies to the IFNgamma r and the G-CSF receptor were localized using a modification of the avidin-biotin complex method. In the newborn rats, IFNgamma r was localized in the preameloblasts in the cervical loop, the proximal and distal ends of presecretory ameloblasts, the outer enamel epithelium, the dental lamina, and in bone. In 5-day-old rats, it was confined to the proximal ends of the presecretory and secretory ameloblasts. The G-CSF receptor was observed in the molars of newborn rats in the preameloblasts, the proximal and distal ends of the presecretory ameloblasts, outer enamel epithelium, and in bone. In 5-day-old rats, G-CSF receptor was localized in the preameloblasts, the proximal ends of presecretory and secretory ameloblasts, the stellate reticulum, the outer enamel epithelium, and in bone. These findings indicate that the IFNgamma r and the G-CSF receptor, and their downstream STP linkages, are upregulated in the cells of the enamel organ and may be involved in the events leading directly to early enamel formation.

Since first shown to be effective by Bibby in 1942, professionally applied topical fluorides have been used successfully as a caries-preventive intervention. In the United States, the acidulated phosphate fluoride (APF) gels have been the most widely used agent for over two decades. While effective, APF has several practical disadvantages, including unpleasant taste and the risk of fluoride overingestion. The use of APF on infants and very young children is not practical or safe. Recently, fluoride varnish has become available in the United States. It has been used widely in Europe and Scandinavia for 25 years. Its effectiveness and safety are documented in over 50 clinical trials. Fluoride varnish is easy to apply, is well accepted by children, and eliminates the risk of overingestion of fluoride. Fluoride varnish is approved by the FDA as a "device" and must be used "off label" for the prevention of caries. Because of the large body of published data documenting its effectiveness and safety, there is no legal risk in using fluoride varnish off label. In fact, the American Dental Association has granted its seal of approval to Duraphat, one of the varnish products. Varnish offers considerable advantages in the dental public health setting. Of particular note, it is practical and safe to apply to the teeth of infants and very young children.

The expression of amelogenin mRNA in growing rat molars was studied. Northern blotting and the analysis of cDNA isolates revealed two predoninant variants. One group of cDNA inserts contained sequences of a long mRNA version and the other group contained mRNA sequences of the shorter leucin-rich amelogenin polypeptide (LRAP). The LRAP group was deficient in an internal stretch which coded for a peptide with a high potential for beta turns. Northern blot experiments showed that most amelogenin RNA in rat teeth was represented by two bands of 1.1 and 0.8 kb. Two oligonucleotide probes were designed that were specific for the long version and for the LRAP variant. The probes were used for in situ hybridization experiments on sections of developing maxillar teeth of rats between day 2 and day 15 after birth. Both RNA species were accumulated concomitantly and exclusively in cells of the inner enamel epithelium. Expression was first observed at the mesial cusp sides and finally involved the whole ameloblast layer except for the cells adjacent to the enamel-free region at the tip of the cusps. The early amelogenin RNA expression occurred adjacent to the initial deposition of the dentin matrix. Low amounts of amelogenin RNA persisted after the differentiation of ameloblasts into the maturative stage. The sequence of events was similar in all three molars.

45Ca uptake in mineralizing tissues may occur by net Ca uptake or by isotopic exchange. It is rarely possible to differentiate between these effects, making interpretation of the findings difficult. Unfortunately, this problem is not often considered, and 45Ca uptake is usually regarded as representative of only net calcium uptake. The study reported here was undertaken to estimate the extent to which 45Ca uptake in mineralizing enamel is due to net Ca deposition or to isotopic exchange, and to consider the implications. The enamel surfaces of the lower incisors of adult rats were notched at the gingival line, and the eruption distance over 16 hours was measured. This distance was used to establish the position of a 0.3-mm-wide increment of enamel at the beginning and end of the 16-hour period, during which it passed through the early-maturation stage of enamel formation. The rate of Ca uptake was determined by chemical assay. Other rats were injected with 45Ca, mean plasma specific activity values for the experimental period determined, and the rate of Ca uptake through the same area of enamel formation was estimated. The estimates were from two- to nearly ten-fold greater than those established by chemical assay, indicating that from 50 to 90% of the 45Ca uptake occurred by isotopic exchange. 45Ca uptake may indicate more about the labile state of Ca in mineralizing enamel than about the rate of mineral deposition.