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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.
A combined HCl-collagenase digestion technique and scanning electron microscopy were used to isolate the enamel organ and to confirm the presence of maturation ameloblasts of both ruffle-ended (RA) and smooth-ended (SA) types on maturing enamel in kitten permanent tooth germs. EDTA perfusion of animals fixed with aldehyde produced two or three belt-like shallow grooves (from 30 to 100 micron wide) running horizontally through the maturing enamel surface, coinciding closely with the SA distribution pattern. In animals that had been perfusion-fixed with unbuffered osmium tetroxide containing 2.5% potassium pyroantimonate, SEM-EDX analysis detected K in a superficial enamel layer overlaid by the SA layer. Potassium concentration decreased gradually toward the deeper layers. Very little K penetrated the enamel under the RA layer. Energy-dispersive x-ray analysis of Ca and P concentrations in the enamel revealed an even distribution of these elements throughout the superficial layer of maturing enamel. These results suggest that the SA layer forms an access route for K and EDTA and that, in spite of the obvious morphological and functional differences between RA and SA, the maturing enamel surfaces overlaid by these two cell types show similar degrees of mineralization.
Freeze-dried rat incisors were examined by high-resolution scanning electron microscopy (SEM) combined with energy-dispersive x-ray microanalysis (EDX) for determination of the correlation between the morphology of the enamel organ and the concentrations in the adjacent developing enamel matrix of calcium (Ca), phosphorus (P), and sulfur (S), as well as the Ca/P ratio. In SEM examination of the freeze-dried enamel organ, it was possible to identify the stages of enamel secretion, transition, and maturation, and furthermore to identify ruffle-ended and smooth-ended maturation ameloblasts. EDX analysis of the outer layer of forming and maturing enamel was carried out from the apical to the incisal end at interval points of approximately 50 micron. Ca and P concentrations increased gradually and continuously from the secretion zone to the end of the maturation zone, but never showed a steep rise in any of the zones examined. Maturing enamel overlaid by either ruffle-ended or smooth-ended maturation ameloblasts showed similar Ca and P concentrations. Throughout the outer enamel layer, the Ca/P molar ratio was fairly constant. Sulfur concentration began to decrease in the zone of enamel secretion, and was no longer detected in the middle of the maturation zone.
The aim of the present study was to describe the patterns of dental fluorosis in the primary and the permanent dentition of children born and reared in two different fluoridated areas, one in which powdered milk suspended in tap water was commonly used (Narssaq, Greenland: 1.1 ppm fluoride in the water) and one in which cow's milk was provided (Vordingborg, Denmark: 1.4-1.6 ppm fluoride in the water). Dental fluorosis was recorded by Thylstrup and Fejerskov's classification. In both locations, the prevalence of dental fluorosis increased the later in life the tooth type was formed. The prevalence of dental fluorosis in the earliest formed teeth was higher in the area where powdered milk was suspended in fluoride-containing tap water than where pasteurized cow's milk was used. In the first permanent molars, the maxillary incisors, and the canines, the prevalence was rather similar in the two areas. In the latest formed teeth, the premolars, the level of fluorosis was higher in Vordingborg. The pattern of dental fluorosis suggests that when powdered milk was used frequently, the children were exposed to a higher fluoride intake earlier in life than were those consuming cow's milk during infancy and childhood.
An attempt was made to test the hypothesis that alkaline phosphatase, an enzyme which is abundant in periodontal ligament, plays a role in the formation of acellular root cementum. Thin slices of bovine dentin were incubated in Iscove Modified Dulbecco's Medium supplemented with 10% normal rabbit serum and 10 mmol/L beta-glycerophosphate (beta-GP) or folded into pericardial explants. Intestinal bovine alkaline phosphatase (APase), covalently linked to agarose beads, was added to the cultures. In the presence of the enzyme, the dentin slices were covered with thin layers of mineralized material. Such layers were not observed in cultures not provided with APase-beads or beta-GP. They also did not form in relation to demineralized dentin. The layers of calcified material appeared to consist of crystallites embedded in a granular matrix of moderate electron density, which often exhibited the presence of incremental lines and resembled the matrix of afibrillar acellular cementum formed under in vivo conditions. When pericardial explants were interposed between the enzyme-containing beads and the dentin, mineral deposition in relation to the dentin was retarded. This finding lends support to the view that soft connective tissues interfere with the free diffusion of phosphate.
The present study describes the detailed changes in carbonate distribution throughout the different stages of development in human and bovine enamel, from early formation to maturation. Twenty-two human maxillary and mandibular deciduous anterior teeth and 46 bovine teeth were studied. The major mineral ions, calcium and phosphorus, were also analyzed to facilitate comparison of carbonate content with progressing mineralization. The results showed that as enamel matured and mineral concentration increased, carbonate concentration decreased. The observed decrease in percent carbonate per weight enamel mineral may be due to dilution by an influx of relatively carbonate-free mineral, and could, in part, explain the observed increase in crystallinity of enamel mineral as the tissue matures.
A study was completed in 1985/86 which examined the dental health of pre-school children from different ethnic groups and communities in South Africa: rural black, urban black, urban colored, urban Indian, and urban white. Enamel defects were recorded in primary teeth by use of the HHI, an index developed to measure hypocalcification and hypoplasia of enamel. The findings showed that colored children had the greatest number of enamel defects. The teeth most commonly affected were the maxillary anterior teeth and mandibular molar teeth. It is suggested that further epidemiological studies utilizing the HHI should be undertaken in pre-school children, especially from developing countries, to gain more information on the causes of enamel defects in the primary dentition and the possible use of such findings to predict nutritional health of individuals.
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In this study, we introduce a cultivation method for mandibular first molars from mouse embryos. We also investigate the in vitro effects of several drugs on tooth formation. Histological observations demonstrated that the tooth germ dissected from 17-day-old embryonic mice and cultivated for 7 days under the conditions described here showed clear mineralization in the dentin and enamel. Alkaline phosphatase (ALP) activity and calcium content in the tooth germ increased developmentally during 7-day cultivation. The increase of calcium was preceded by that of ALP in the germ. The removal of ALP attached covalently to the external surface of plasma membranes by phosphatidylinositol specific phospholipase C disturbed in vitro mineralization in the tooth germ, suggesting that ALP functioning as an ectoenzyme is involved in the physiological process of tooth formation. To elucidate the effects of calcium regulating hormones and several drugs on tooth mineralization, ALP and calcium content were measured and also the tooth germ was observed histologically. The results obtained from the present study suggest that this in vitro system provides a useful tool for investigating both the direct action of drugs on tooth formation and the mechanisms of drug action.
Effects of chlorpromazine on the mineralization and alkaline phosphatase activity (ALP) in the tooth germ were examined and compared with those of retinoic acid and HEBP (1-hydroxyethylidene-1, 1-bisphosphonate). Mandibular first molars from 17-day-old mouse embryos were cultured with or without drugs. Calcium content and ALP in the tooth germ increased gradually from 0 to 7 days in culture, the increase of calcium being preceded by that of ALP. Retinoic acid suppressed increases of calcium and ALP in the tooth germ but not in the specimens precultured for 2 days, suggesting that retinoic acid inhibits the mineralization at an early developmental stage of the tooth. HEBP, a physiochemical inhibitor of mineralization, suppressed the increase of calcium, but significantly enhanced the increased of ALP in the tooth germ. Chlorpromazine, which has an antagonistic action towards calmodulin, also suppressed the increases of calcium and ALP in the tooth germ. Calmodulin antagonists W-7 and W-5 similarly suppressed the increases of calcium and ALP; W-5 had less effects on both calcium and ALP. These results indicate that calmodulin may be involved in the regulation of the mineralization in the tooth germ. These drugs are shown to possess different modes of inhibitory action on the mineralization.
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Root surfaces which have lost their attachment due to chronic inflammatory periodontal disease present significant increases in calcium, magnesium, phosphorus, and fluoride. The clinical significance of this effect is not known in regards to wound healing, but it may be helpful in control of cervical sensitivity.
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According to clinical studies, infants of diabetic mothers (IDM) seem to run a higher risk of mineralization disturbances in the enamel than normal healthy infants. In order to evaluate this observation at the histologic level, exfoliated primary incisors were collected from 74 IDM, representing two types of care during gestation and the perinatal period, and from 52 healthy children. The width of the neonatal line was evaluated in the enamel and the dentin by study of bucco-lingual undemineralized sections. Pre- and postnatal enamel was classified according to discolorations, deviations of prisms and hypoplasia. Microradiographic studies included measurements of the neonatal lines and classification of the degree of mineralization in the pre- and postnatal dental hard tissues. Irrespective of treatment, the IDM showed a significantly higher incidence of widened neonatal lines and also an increased frequency of postnatal disturbances compared to the controls. The observations are discussed against the background of the neonatal hypocalcemia reported in IDM.
Ground sections of deciduous teeth from 64 infants with birth weights below 2000 g and from 43 healthy full-term infants were examined in polarized light and by microradiography. The deciduous enamel displayed various changes, which were more frequent and pronounced in the low-birth-weight group. The main findings were diffuse areas of increased porosity and distinct subsurface lesions in the postnatal enamel. Five teeth with enamel hypoplasia from the low-birth-weight group were also examined. The hypoplasias were all located along the neonatal line. The postnatal enamel seemed to be more susceptible to disturbances in the mineralization than the prenatal enamel. The subsurface lesions showed an arrest in the very late stages of enamel maturation, which frequently occurred in the cervical deciduous enamel. Enamel hypoplasia is considered to be a result of severe neonatal hypocalcemia.
Amelogenins are the predominant proteins found in the developing enamel matrix and are believed to play a crucial role in normal mineralization. Although the amelogenin gene is found as a single copy in all species in which it has been examined, multiple amelogenin polypeptides ranging in size from 5 to 25 kDa are obtained upon extraction of developing enamel matrix, making identification and characterization of individual components difficult. This heterogeneity may be ascribed to transcription of divergent genes located on the X and Y chromosomes, alternative splicing of the primary transcripts, physiologic degradative processing, and artefactual degradation. In order to characterize individual components, antibodies were produced to the following peptides: (1) QPLQPMQPMQPLQPLQPL (corresponding to the repeat sequence encoded only in the bovine X chromosome gene), (2) IRHPPLPP (corresponding to a unique sequence generated by alternative splicing found in leucine-rich amelogenin peptide (LRAP), (3) LPDLPLEAWPATDKTKREEVD corresponding to the amelogenin carboxy-terminus. Amelogenin proteins obtained from fetal bovine molars were subjected to SDS PAGE and Western electrotransfer, and immuno-ultrastructural analysis. These analyses demonstrated that: (1) the distribution of amelogenin polypeptides isolated from male fetuses differed appreciably from that of females, (2) the LRAP junctional peptide sequence can be specifically identified, and (3) the LRAP peptide can be immunolocalized in the enamel matrix of both males and females.