Surface analysis of etched enamel modified during the prenatal period.

Structural changes in the enamel surface subjected to induced demineralization and assessment of the influence of prenatal administration of ß-hydroxy ß-methylbutyrate (HMB) on enamel resistance were investigated. The examination was conducted on five sets of teeth from one-day-old spiny mice (Acomys cahirinus), one from the control and four from the experimental groups. Surface structure, molecular arrangement and crystalline organization of offspring's enamel both before and after etching were studied. Obtained results revealed that the physical and molecular arrangements of enamel were altered after the prenatal supplementation, and significantly affected its final structure and resistance against acid action. The enamel of incisors from the offspring which mothers were supplemented with HMB in a high dose (0.2 g/kgbw) and in the late period of gestation (26th-39th day) showed the highest endurance against acid treatment demonstrating only vestigial changes in their surface structure after acid action. Comparing to the remaining experimental groups, it was characterized by a reduced roughness and fractal dimension, significantly lower degree of demineralization and simultaneous lack of notable differences in the Raman spectra before and after acid etching. The results suggest that an increased enamel resiliency was the effect of a relatively high degree of mineralization and higher organization of the surface.

The morphology and mineralization of dental hard tissue in the offspring of passive smoking rats.

OBJECTIVE: To study the effects of maternal passive smoking on the morphology and mineralization of dental hard tissue in offspring rats. DESIGN: We have established a maternal passive smoking model. Offspring rats were sacrificed on the 20th day of gestation (E20) or the 3rd (D3) or 10th day (D10) after birth. We observed hard tissue morphology using Haematoxylin-Eosin (H&E) staining sections, used micro computer tomography (Micro-CT) to measure hard tissue thickness and volume on the mandibular first molars of the offspring rats, and used Micro-CT and energy dispersive X-ray spectroscopy with scanning electron microscopy (SEM/EDS) to determine the hard tissue mineral density and the ratio of calcium atom number/calcium atom+phosphorus atom number (Ca(2+)/P(3-)+Ca(2+)). RESULTS: Overall, the development of dental hard tissue was delayed in the offspring of passive smoking rats. The thickness and volume of hard tissue were lower in the offspring of the maternal passive smoking group than in the offspring of the control group. Mineral density of the hard tissue and the ratio of (Ca(2+)/P(3-)+Ca(2+)) were also reduced in the offspring of the maternal passive smoking group. CONCLUSION: Maternal passive smoking inhibits the morphological development and mineralization level of hard tissue on the mandibular first molars of offspring rats.

The amyloid protein APin is highly expressed during enamel mineralization and maturation in rat incisors.

This study investigated the expression and localization of APin (which was previously identified and cloned from a rat odontoblast cDNA library), during ameloblast differentiation in rat incisors, by using in situ hybridization and immunohistochemistry. The subcellular localization of APin varied during ameloblast differentiation, but was stage-specific. APin mRNA was not expressed in pre-ameloblasts, was weakly expressed in secretory ameloblasts, and was strongly expressed in maturation-stage ameloblasts as well as in the junctional epithelium attached to the enamel of erupted molars. In the maturation-stage ameloblasts, APin protein was conspicuous in the supranuclear area (Golgi complex) of smooth-ended ameloblasts as well as in both the supranuclear area and the ruffle end of ruffle-ended ameloblasts. During ameloblast-lineage cell culture, APin was expressed at a low level in the early stages of culture, but at a high level in the late stage of culture, which was equivalent to the maturation stage. APin protein was efficiently secreted from transfected cells in culture. Furthermore, its overexpression and inactivation caused an increase and decrease in matrix metalloproteinase-20 (MMP-20) and tuftelin expression, respectively. These findings indicate a functional role for APin in the mineralization and maturation of enamel that is mediated by the expression of MMP-20 and tuftelin.

Aspects of teeth from archaelogic sites in Sweden and Denmark.

The purpose of this study was to examine ground sections of primary second molars and permanent first molars from the same jaws. Teeth from 11 individuals were collected from archaeologic sites in Sweden and Denmark. Longitudinal buccolingual sections were examined in a polarization light microscope and in a Philips scanning electron microscope (SEM). The seven teeth from Sweden appeared to have been subjected to environmental influences at their burial site, which had affected both the dentin and the enamel. The teeth from the Danish sites had a normal color, and no disintegration of the dentin was seen. The general morphologic appearance was normal in all primary and permanent teeth. The position of the neonatal line indicated a normal full-term gestational age. The observed accentuated incremental lines in both the primary and permanent enamel suggested periods of dietary changes, possibly related to periods of illness. SEM images of the surface area of the Swedish teeth showed an extremely porous enamel surface with severe changes in the prism structure as an effect of acid penetration. The Danish teeth did not show any marked changes in the enamel.

Prenatal fluoride for growth and development: Part X.

Examinations of prenatal fluoride supplemented (PNF) teeth in an animal model and in a five-month human fetus find these teeth to be more developed than the non-supplemented controls. The fact that PNF allows teeth to develop to their full potential suggests that PNF could be an essential nutrient for the entire human and this could be demonstrated most easily during rapid fetal growth. A review of the recent literature, including trials by NIH and The World Health Organization, provide evidence that fluoride (F) does allow the fetus to grow and develop to its full potential. The authors conclude that PNF must be supplied in at least a 2 mg/day pulse dose, and then F must be given from shortly after birth in a daily amount appropriate for the weight of the child with some consideration for the amount of F water utilized.

Chemical and X-ray analysis of fluoride, phosphorus, and calcium in human foetal blood and hard tissues.

To evaluate the beneficial effect of prenatal fluoride supplementation, the presence of fluoride in hard tissues in two populations of human foetuses coming from fluoridated (> or = 0.7 parts/10(6) F in drinking water) and non-fluoridated areas (< or = 0.1 parts/10(6) F in drinking water) were compared by chemical analysis and X-ray microanalysis. The fluoride concentrations measured in maternal and venous cord blood confirmed that placental transfer of fluoride was passive when fluoride intake was low. Total fluoride contents of tooth germs and mandibular bone appeared to increase with fluoride level in drinking water. However, these concentrations were too low to be detected by X-ray microanalysis. Phosphorus and calcium total contents were identical in mandibular and femoral bone of both populations. In incisor germs, phosphorus and calcium concentrations in enamel and dentine close to the amelodentinal junction did not differ significantly between the two populations. It is suggested that the low fluoride concentrations in enamel and dentine formed in utero would not have a significant effect on acid solubility.

Analysis of human enamel genes: insights into genetic disorders of enamel.

A number of inherited craniofacial diseases are known to be associated with gene mutations. Inherited genetic disorders of enamel formation called amelogenesis imperfecta (AI) affect the human population with a prevalence of 1 in 14,000 in the United States. Amelogenins, the major proteins in developing enamel matrix of mammalian teeth, have been suggested to participate in normal enamel matrix biomineralization, as well as with abnormal biomineralization such as seen in AI. The complementary DNA for mouse amelogenin gene (AMEL) has been cloned, characterized, and used as a probe to establish the chromosomal locations of AMEL for mouse and man. The human AMEL gene sequences have been located to the distal short arm p22.1----p22.3 region of the X chromosome, and the pericentromeric region of the Y chromosome. An assignment of human AMEL gene to the X chromosome p22 region together with a recent assignment of the X-linked AI disease locus to the Xp22.2 region support the association of the AMEL-X gene with AI. This also leads us to propose that a mutated AMEL-X gene produces altered amelogenin polypeptide, which is defective in its ability to participate in mineralization of enamel matrix, thus giving rise to the X-linked phenotypes of AI.

The carbohydrate moiety of mineral-bound proteins from fetal enamel: a basis for enamelins heterogeneity.

Enamelins were prepared from the soft enamel of bovine fetuses. They were purified on synthetic hydroxyapatite and separated in two fractions by affinity chromatography on a ConA-ultrogel column. The two fractions were different with respect to their electrophoretic behavior, stainability, amino acid composition, phosphorylation, and glycosylation. The ConA-binding fraction, consisting of three molecular species with apparent molecular weights of 33, 37, and 45 kD, contained organic phosphorus and high levels of sugars. The Gal/Man ratio suggested a biantennary structure. The ConA-unbound fraction contained two major molecular species with molecular weights of 70 and 56 kD, and represented 70% of the total enamelin preparation. The amino acid composition of this fraction showed a higher level of alanine and a lower level of proline when compared with that of total enamelins. Its sugar composition was unusual, being principally constituted of N-acetyl galactosamine and N-acetyl glucosamine.

Single bovine enamel particles examined by electron optics.

Whole enamel scrapings from teeth of embryonic calves have been separated by density gradient centrifugation in organic solvents into fractions (1.6 less than p less than 2.4 g/cm3) representing progressive stages of mineral phase maturation. Single enamel particles or their small aggregates from such fractions were examined by transmission electron microscopy, electron diffraction, and high-spatial-resolution electron probe micro-analysis. The electron optical methods demonstrated the presence of poorly crystalline hydroxyapatite as the only detectable solid phase in all fractions. Octacalcium phosphate and brushite were not identified in the fractions. Changes in electron diffraction patterns were indicative of a progressive increase in apatite crystallinity with enamel maturation. Molar Ca/P ratios were found to range from 1.48 to 1.70, with a higher mean value obtained for lower-density fractions (p less than 2.0 g/cm3). Lower-density fractions contained some particles with high ratios (approximately equal to 2.0-4.0) and a non-uniform distribution of Ca and P, as revealed by electron probe mapping. These characteristics are suggested as possibly being related to carbonate phases in early enamel.

Distribution and uptake of magnesium by developing deciduous bovine incisor enamel.

Magnesium concentrations determined in deciduous bovine enamel at different stages of development were similar to those previously published for human and rat enamel ranging from 0.1 to 0.4 per cent. Highest concentrations, i.e. greatest uptake, occurred after secretion, in the transitional and maturing enamel. Uptake had occurred throughout the tissue thickness and was not confined to the surface. Magnesium probably enters enamel in the tissue fluid which replaces the organic matrix. Some magnesium is lost as fluid is replaced by calcium and phosphate but part is retained probably on or near crystal surfaces.

Development of enamel in human fetal teeth.

The present study concerns enamel development in human fetal teeth. Chemical analysis and the appearance of developing enamel from maxillary and mandibular central and lateral incisors of human fetuses aged from five to nine mo distinguished two main stages during this period of development. The first stage corresponded to the production of forming enamel, which was soft, translucent, and partially mineralized, and the second to the maturation or secondary mineralization of enamel. The enamel at this stage appeared opaque when dried. The transition of forming enamel to maturing enamel was accompanied by a decrease in protein concentration, a distinct change in amino-acid composition, and a rise in the concentration of calcium and phosphate. Ultraviolet and chloronaphthalene inhibition studies revealed that the third and final stage in enamel development, the mature hard enamel, was generally absent, but was found in a very small percentage of maxillary and mandibular central incisors from nine- and ten-month-old fetuses, at the incisal tip. In both maxillary and mandibular canine teeth, only the forming stage in enamel development was observed during the fetal period. Further studies relating the length of each zone in enamel to fetal age provided information relative to the timing and rate of enamel development in each tooth.

Differentiation of odontogenic tissues in organ culture.

Molar tooth germs from 17-d-old mouse embryos were cultivated in a Trowell-type culture, and different culture media were tested for their ability to support enamel formation. The medium which allowed secretion of considerable amounts of enamel matrix by ameloblasts consisted of BGJb medium supplemented with 20% horse serum, 10% chick embryo extract and 0.9 mM ascorbic acid. At the onset of culture the teeth were in the early bell stage. After 2 weeks of cultivation both odontoblasts and ameloblasts had differentiated, and considerable amounts of predentin and enamel matrix had been secreted. Similar development was also seen in teeth which had been enzymatically separated into the mesenchymal dental papilla and epithelial enamal organ and subsequently recombined in vitro. This method allows good differentiation of odontogenic tissues, and is considered suitable for further studies of tissue interactions in the tooth rudiment.