Reflections on the reactivity of dental enamel.
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Animals↗
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An electrochemical study on the human dental enamel with special reference to isoelectric point.
In an attempt to make a dynamic study of the isoelectric point and the chargeability of human dental enamel, an electrochemical approach was utilized. Zeta potential of three kinds of the enamel was measured by a streaming potential method. As a result, these isoelectric points could be decided.
Dental Caries↗
Long term effects of primary molar pulpotomies on succedaneous bicuspids.
Forty-three bicuspids which replaced successfully pulpotomized vital or non-vital primary molars, and twenty bicuspids, which erupted following unsuccessful pulpotomies requiring extraction of the preceding teeth, were examined for defects of position and enamel. In comparison with contralateral control teeth, test teeth in both groups showed an increased prevalence of rotation and enamel surface defects.
Bicuspid↗
Sexual differences in dental development and prediction of emergence.
The dental development of a genetically homogeneous French-Canadian group of children ranging in age from 2.5 to 19 years was evaluated from 5,437 panoramic radiographs by the method of Demirjian et al. The maturity of each mandibular tooth was evaluated individually. For each stage of each tooth, the developmental curves of boys and girls were compared. A common pattern was found for each tooth, namely the chronological similarity between boys and girls in the early stages of development and the advancement of girls over boys for the later stages. Development scores were given to the seven mandibular teeth. Up to five to six years of age, no difference was found in the timing of dental development between boys and girls, in contrast to the older ages where girls were always more developed than boys. When the emergence curve was plotted with developmental curves, a close relation was established between the stage of formation of all teeth and their emergence, hence the predictive value of the use of dental maturity curves in clinics.
Adolescent↗
Developmental communalities in tooth emergence timing.
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Female↗
Intraoral mineralization of abraded dental enamel.
The iodide permeability (Ip) of abraded bovine enamel increased after short exposure to an acid buffer and decreased after short exposure to a mineralizing solution. Intraoral exposure gave a marked decrease in Ip after one h and a continued lesser decrease after two and three h. In vitro exposure to fresh and dialyzed saliva and various undersaturated solutions indicated that the intraoral decrease was due to mineralization rather than to pellicle formation. Analysis of the data also indicated that part of the mineral formed intraorally was more loosely bound to the enamel than that formed from an inorganic mineralizing solution. The rapid rate of the initial phase of intraoral mineralization shown in this study reveals a powerful mechanism for protecting the dentition against demineralization.
Acetates↗
The relationship among the permeability to iodide, pore volume, and intraoral mineralization of abraded enamel.
The results indicate that Ip measurements are fairly closely related to the pore volume of the enamel to a depth of about 13 micrometer. A previous finding - that intraoral exposure produced substantial mineralization of abraded enamel after one h, and a slower rate of mineralization during the next two h - was confirmed, and it was shown that the rate of mineralization decreased with a decrease in the pore volume of the enamel. The rapid rate of intraoral mineralization represents a powerful mechanism for maintaining a fully mineralized enamel surface. The sensitivity of the Ip method demonstrated in this study, and the finding that Ip measurements relate to the pore volume of the enamel, coupled with previous findings that the increase in Ip produced by mild acid etching of intact enamel is proportional with the amount of dissolved Ca, indicate that the method provides valid measurement of intraoral de- and remineralization.
Acid Etching, Dental↗
The effect of enamel de- and remineralization on permeability to iodide and urea.
Blocks of bovine enamel subjected to de- and remineralization were measured for changes in permeability to iodide and urea. Results were similar, indicating that the diffusion pathways for the two species were comparable, and that sites for iodide binding did not appear to exit.
Animals↗
Effect of inhibition of net calcium uptake on net fluoride uptake in developing rat molars.
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.
Animals↗
Correlated observations and analysis of maturation-ameloblast morphology and enamel mineralization.
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.
Ameloblasts↗
Ameloblast modulation and changes in the Ca, P, and S content of developing enamel matrix as revealed by SEM-EDX.
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.
Ameloblasts↗
Dental fluorosis in the primary and the permanent dentition in fluoridated areas with consumption of either powdered milk or natural cow's milk.
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.
Adolescent↗
Alkaline phosphatase induces the deposition of calcified layers in relation to dentin: an in vitro study to mimic the formation of afibrillar acellular cementum.
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.
Alkaline Phosphatase↗
Carbonate content in developing human and bovine enamel.
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.
Aging↗
Root development in mice lacking functional tissue non-specific alkaline phosphatase gene: inhibition of acellular cementum formation.
Tissue non-specific alkaline phosphatase (TNAP) is richly present in developing teeth including the cells of the periodontal ligament. Here, we investigated tooth and root development in mice lacking the TNAP gene. Heterozygous mutants were obtained from The Jackson Laboratory, Animal Resources (Bar Harbor, ME, USA) and bred. TNAP-deficient mice and their littermates were killed from 6 to 25 days after birth and their molar blocks processed for light and electron microscopy. It was observed that the eruption of the incisors into the oral cavity was delayed for 2 to 3 days. Also, the onset of mineralization of the mantle dentin in the roots of the developing molars was delayed for 2 to 3 days. Yet, dentin and enamel formation in the homozygous mutants showed a more or less normal pattern, with the exception of localized enamel hypoplasias. The most conspicuous finding was the defective formation of acellular cementum along the molar roots. Instead of a continuous layer, the cementum was deposited as very thin and irregularly shaped patches around the bases of the periodontal ligament fibers. Sharpey's fibers were short and poorly developed. In contrast, the development of the alveolar bone, the periodontal ligament, and the cellular cementum was seemingly unaffected. It is concluded that TNAP represents an essential factor in mantle dentin mineralization and in the formation of acellular cementum.
Alkaline Phosphatase↗
Molecular aspects of tooth pathogenesis and repair: in vivo and in vitro models.
Several growth factors and extracellular matrix molecules, which are expressed during embryonic tooth development, are re-expressed in dental tissues under pathological conditions. Pathological conditions such as caries lesions and dental injuries are often lethal to the odontoblasts, which are then replaced by other pulp cells. These cells are able to differentiate into odontoblast-like cells and produce a reparative dentin. Here we demonstrate the in vivo distribution of several molecules in human permanent teeth under normal and pathological conditions. The intermediate filament protein nestin, which is a marker of young odontoblasts, is absent from old permanent teeth. Similarly, the Notch protein, which is involved in cell fate specification and is localized in the sub-odontoblastic cell layer during odontogenesis, is not detected in adult dental tissues. In carious and injured teeth, nestin is expressed in a selective manner in odontoblasts surrounding the injury site, while Notch is expressed in the sub-odontoblastic layer of cells. We reproduced this physiological event in an in vitro culture system. Pulp cells cultured in the presence of beta-glycerophosphate formed mineralization nodules. As odontoblasts, pulp cells contributing to the nodule formation express type I collagen, osteonectin, dentin sialophosphoprotein, and nestin. In this in vitro assay system, nestin is up-regulated after local application of Bone Morphogenetic Protein 2 and 4. Fourier transform infrared microspectroscopy showed that both the organic and the mineral compositions of the nodules have the characteristics of human dentin and differ from those of enamel and bone. These findings show that both the molecular and the mineral characteristics of the human dentin matrix are respected in the in vitro culture conditions.
Adult↗
Hypocalcification and hypoplasia in primary teeth of pre-school children from different ethnic groups in South Africa.
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.
Child, Preschool↗
Disturbed enamel mineralization in a rat incisor model.
Possession of full-thickness hard enamel appears to be one of the indispensable life-saving characteristics of rats. Previous studies by Suga and his colleagues and by others demonstrated that various types of malformation are evoked in continuously erupting rat incisors. In the current report, we directed our effort to oversee various types of enamel malformation caused experimentally in rat incisors. We surveyed the specimens collected by Suga and his colleagues, as well as specimens we obtained. From the results, it is conceivable that perturbation of the programmed sequential events during enamel development is a major factor in the establishment of enamel malformation. Animal studies with either 1-hydroxyethylidene-1,1-bisphosphonate (HEBP) or a multidentate phosphonic acid (EDTPO) confirmed that dentin mineralization provides a certain inductive effect on the secretion of enamel matrix and subsequent enamel crystallization. Our recent studies using anti-microtubular agents led to the conclusion that the acceleration of mineralization in outer enamel is a type of enamel malformation, most likely due to disruption of the cellular regulation of calcium transport under severe toxic regimens. In future work, experimental approaches combining measurements of kinetic factors with static observation of enamel lesions are required before we can gain a comprehensive understanding of the pathogenesis of disturbed enamel mineralization. The kinetic factors to be considered include the rates of tissue apposition and tooth eruption which determine the total volume of tooth substance formed, and the rate of mineral accretion. Furthermore, information as to the composition, crystallinity, solubility, and mechanical properties of enamel defects is needed before we can assess the susceptibility of teeth having those lesions to caries and other physico-chemical attacks in the oral environment.
Ameloblasts↗