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At least 1,099 records · Page 61Linked to original sources
PubMed1991

[An ultrastructural study of the fibrillary component of dental tissues].

The recent interest for highly sophisticated techniques of dental tissue preparation aiming to display very particular structures, moved the AA. to improve the literature suggestions. In particular they made TEM and SEM observations of transitional zones between healthy and normal pulp and dentin after decalcification and trypsin at different concentrations treatment. The images obtained draw in the attention the study facilities of a technique that really removes all the non collagenic material. The data obtained in the pericellular zones also allowed some interventions in the recent literature discussion about inter-odontoblastic fibres.

Decalcification Technique↗
PubMed1991

Scanning electron microscopy of the forming enamel of rat incisor: influence of fixative and treatments interacting with the organic matrix.

The forming enamel of rat incisor was either treated before fixation with one of these five treatments: ultrasonication, NaOCl, chloroform/methanol, NaOH or tween 20; or the incisors were first fixed and then submitted to one of these treatments. The structure of the forming enamel, compared with sections fixed with aldehyde and submitted to osmic maceration, depends on the way the samples were treated and on the fixative used. An amorphous material, removed by osmium tetroxide but not by aldehyde solution was seen to be located between fiber-like structures. In the region of inner enamel secretion the thickness of interrod septa was fairly constant, whereas in the region of outer enamel secretion, transverse septa of interrod enamel gradually became thinner and finally disappeared. The longitudinal septa did not display such changes. Longitudinal grooves and ridges were seen at the end of enamel completion. These longitudinal septa finally merged and formed a flat surface.

Animals↗
PubMed1977

[Calification of the dental system in dialized patients].

The authors present the case of an eight-years-old child, dialysed since the age of two following a bilateral nephrectomy. The chronological appearance of the teeth was not disturbed. By contrast, there was a delay in mineralisation of the dental organ, and in particular the root. There was lysis of the alveolar bone, resulting in a parodontopathy. The authors distinguish two ages in the effects of dialysis: the first period is that of the construction of the dental system and the second is the adult age at which the dental system is constituted.

Acute Kidney Injury↗
PubMed1990

[Study of dental maturity in children aged 3-16 years in Chengdu].

Dental maturity was studied in a group of 903 healthy children (boys: 465, girls: 438) born in Chengudu from 1972 through 1988. Dental maturity was estimated by the method of Demirjian and Goldstein, which is based on the development of seven left mandibular permanent teeth; teeth formation was studied. The standard and curves of dental maturity for Chengdu children (boys and girls) were constructed. At 3-5 years old, boys had their dental maturity slightly earlier than girls; there was no significant difference between boys and girls (P greater than 0.05). At the age of 7-14, girls were more advanced than boys (P less than 0.05). Developmental curves of seven left mandibular permanent teeth were plotted. The sexual difference was smaller at the crown developmental stage, and it increased during the root development. In all, girls were more advanced by 0.45 year than boys. The maximum average difference was 0.85 year for the canine. The time that each developmental stage has taken was shorter in 50% of girls as compared with that in boys, and it was longer in 28% of girls. There was no difference between boys and girls in the remaining 22% of cases.

Adolescent↗
PubMed1990

[Dependence of incisor dentin mineralization on plasma calcium levels in parathyroidectomized rats].

This experiment was performed to clarify whether mineralization of incisor dentin depends upon plasma calcium (Ca) levels. Male Wistar rats (7 weeks old) were parathyroidectomized (PTXed) and given vitamin D-deficient diets containing various amounts (0.3-2%) of Ca for 2 weeks in order to maintain the plasma Ca at various levels and to examine their relationship with the mineralization of incisor dentin. Plasma Ca levels, which were lowered to about 6 mg/dl by PTX, ranged from 5.1 to 10.1 mg/dl after feeding on diets containing various amounts of Ca; the plasma Ca level in the group given 2% Ca reached the same level as that in the sham-operated group. On the other hand, plasma phosphorus (P) levels, which were increased by PTX, reduced markedly with increases in dietary Ca, leading to hypophosphatemia in the group given 2.0% Ca. In this series of experiments, the plasma Ca levels in PTXed rats seemed to be kept constant by the dietary Ca without any involvement of hormones regulating the Ca metabolism because a high correlation was found between the plasma Ca and the dietary Ca (r = 0.987). Both dry and ash weights of the upper incisor also increased with the plasma Ca levels, but with the plasma P levels it was just the opposite. The content of ash in the incisor also increased with the plasma Ca levels. Transverse sections of the lower incisors stained with hematoxylin showed a zone of remineralization of the dentin on the lingual aspect in rats with plasma Ca levels of about 6.5-7.0 mg/dl; the width of the zone was greater in groups of rats with higher plasma Ca levels. Appositional rates of dentin (y, micron/3 days) as determined by a time marking method showed a high positive correlation with the plasma Ca levels (x, mg/dl). The regression equations were as follows: y = 4.8 + 5.7x (r = 0.915, p less than 0.001) on the lingual aspect and y = 6.0 + 5.8x (r = 0.959, p less than 0.001) on the labial aspect. There were a high positive correlation and a negative correlation between appositional rates of dentin and plasma Ca: P ratios (r = 0.928) and between appositional rates of dentin and plasma P levels (r = -0.927) or the products of plasma Ca x P (r = -0.834). These results suggest that the mineralization of incisor dentin depends upon the plasma Ca levels in PTXed rats.

Animals↗
PubMed1990

[Effects of 1,25-dihydroxyvitamin D3 on mineralization of incisor dentin in parathyroidectomized rats].

Male Wistar rats (8 weeks old) were parathyroidectomized (PTX) and given daily subcutaneous injections of different doses (0, 25, 50 or 100 ng/kg) of 1,25 (OH)2D3 for 13 days. Changes in plasma calcium and phosphorus levels were monitored at 3 day intervals. An appositional rate of dentin was estimated by a time marking method; that is, the distance of two lead lines deposited in a transverse section of the incisor dentin on the 9th and 12th days of the experimental period was measured. The plasma calcium levels that had been lowered by PTX were elevated dose-dependently following injections of the drug, but the plasma phosphorus levels that had been elevated by PTX were lowered. The body weight was not affected by the administration of the drug. However, the values for the dry weight and ash weight, and the calcium and phosphorus contents of the upper incisors increased dose-dependently. The mineralization of the dentin, that had been suppressed by PTX, also recovered dose-dependently. Apposition rates of the dentin in groups of rats given various doses of the drug (25, 50 and 100 ng/kg/day) averaged 46, 61 and 69 microns/3 days respectively. There was a significant correlation between the apposition rate of the dentin and the plasma calcium level. The correlation coefficients were estimated to be 0.956 (y = 17.2 + 4.6 chi, p less than 0.001) on the lingual aspect and 0.941 (y = 11.4 + 5.3 chi, p less than 0.001) on the labial aspect. However, the values for the mineralization of incisor dentin were inversely proportional to the plasma phosphorus levels. These results indicate that the stimulating effect of 1,25 (OH)2D3 on the mineralization of the dentin in PTX rats is primarily dependent upon the increase in plasma calcium levels by the hormone. The direct effect of 1,25 (OH)2D3 on the mineralization of dentin could not be demonstrated in this experiment.

Animals↗
PubMed1990

[The development of initial enamel caries--a phenomenon of interfacial reactions].

The investigation deals with earliest chemical changes in outermost enamel surfaces during initial caries development. After in vitro demineralization of enamel samples in acidulated hydroxyethylcellulose solution (pH = 5.1) for periods between 1 and 288 h the Ca/P molar ratios were determined in depths of 0.04 micron using the Rutherford Backscattering spectroscopy. The measured Ca/P ratios oscillate around the initial value. This behaviour is interpreted as a combined de/remineralization process.

Calcium↗
PubMed1990

[Current viewpoints and methods in caries diagnosis].

Results obtained in the caries pathogenesis in recent years as well as the successes in the field of remineralization opened the way to heal the initial stage of the caries by means of preventive methods. Increased attention should be paid to early diagnostics of the caries, and evolution of the new diagnostics methods should be followed by attention. Combined employment of the various diagnostics methods should be aimed at.

Dental Caries↗
PubMedDate not supplied

Clinical and histologic findings of the dentition in a hypopituitary patient: report of case.

Idiopathic hypopituitarism is associated with delayed dental eruption as well as delayed growth of the dentofacial complex. Both maxillary and (especially) mandibular growth can be affected. The clinical dental findings and histologic findings related to enamel maturation in the permanent dentition of a teenaged male with a hypopituitary condition are described.

Adolescent↗
PubMed1990

[Enamel mineralization in rats subjected to an excess fluoride diet: SEM study].

Aim of our present work is to investigate with the SEM the process of enamel mineralization in the lower incisors of albino rats submitted for 21 days (a single amelogenetic cycle) to an hyperfluoric diet (five folds more than the normal). Our observations were performed on specimens fractured 8, 12 and 16 mm from the cervical loop transversally along the major axis of the incisor. It was demonstrated that the three different phases of enamel maturation were slower, so that, when the incisor erupted, mineralization was not completed and localized areas of demineralization were present. The authors are of the opinion that all morphological changes are dependent on the effect of fluoride on ameloblasts, either during their secretory or modulatory phases. On the basis of our results attention is pointed on the possible lesions of the enamel dependent from an unwary fluoride administration, particularly when decidual teeth are still present.

Animals↗
PubMed1990

Interaction of magnesium and fluoride in the rehardening and acid resistance of surface-softened bovine enamel in vitro.

Surface-softened bovine enamel was submitted in vitro to a treatment with calcifying solutions containing calcium and phosphate (Ca/P ratio = 1.67). Variation in treatment was created by the addition to the solutions of magnesium, fluoride or both. Subsequently, the enamel samples were submitted to two successive softening steps. Alterations of the enamel surface due to the different treatments were evaluated with a hardness tester. No significant difference in the rehardening was observed between samples treated with a magnesium- or a fluoride-containing solution. A 2 X 2 factorial analysis of variance showed that both additions had a highly significant main effect on the rehardening. A significant interaction effect was obtained between magnesium and fluoride. Subsequent acid treatments revealed that only fluoride adequately protected the enamel surfaces from further dissolution. The presence of magnesium seemed to weaken the acid-protective action of fluoride in vitro.

Animals↗
PubMedDate not supplied

[Homeostasis in the dental enamel-saliva system].

The formulae of micelles of salivary calcium phosphate are offered to explain the molecular mechanisms of functioning and breakdown of homeostasis in the saliva-enamel system, and the pathogenesis of dental caries and petrifaction formation. This ensured the possibility of controlling the oral mechanisms using goal-directed therapeutic and preventive means.

Calcium Phosphates↗
PubMedDate not supplied

[A mathematical model of the development of dental caries].

A mathematical model is suggested, simulating the development of carious process in a tooth, based on an analytical approach. The process of hydrogen ions diffusion into enamel microspaces is described via transport equation. A simplified model explaining the formation of the involvement of the body of the tooth under the enamel surface at the initial stages of caries development is described in detail. Analysis has shown that the theoretical model is in good correlation with experimental data on the rate of chemical reaction of Ca radionuclide accumulation in the enamel surface and deeper layers.

Dental Caries↗
PubMed1990

Tooth mineralization standards for blacks and whites from the middle southern United States.

Normative standards are provided for permanent tooth mineralization stages for blacks and whites of the middle southern United States. The data cover tooth development from 3.5 to 13 years of age. Females develop more rapidly than males, and blacks are nearly twice as sexually dimorphic (7.2%) as whites (3.7%). Within each sex, blacks achieve mineralization stages significantly earlier, by about 5%, than whites. This complements earlier findings that teeth erupt at appreciably earlier mean ages in blacks.

Adolescent↗
PubMedDate not supplied

Demineralization resistance and tensile bond strength of four luting agents after acid attack.

Resistance to acid demineralization provided by luting agents adjacent to enamel was evaluated for four different luting agents: composite resin, glass ionomer, polycarboxylate, and zinc phosphate cement. Cement solubility and enamel demineralization after acid attack at pH 3.0 were measured radiographically and calculated using computer-aided design. Tensile bond strength of a miniature crown seated on an accurately prepared preparation was evaluated after acid attack using an Instron instrument. Crown retention after 12 days was greater for the polycarboxylate (2,000 kg/m2) than the zinc phosphate cement (500 kg/m2). Crown retention for the glass ionomer (1,100 kg/m2) and composite resin luting agent (1,400 kg/m2) were similar statistically after 21 days of acid exposure. Cement washouts for zinc phosphate and polycarboxylate were similar, and were greater than either glass ionomer or composite resin luting agent. The amount of demineralization related to cements was, from greatest to least: zinc phosphate, polycarboxylate, composite resin, glass ionomer. Fluoride release was concluded to be initially effective in reducing enamel solubility in spite of cement solubility.

Composite Resins↗