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PubMedDate not supplied

A study of primary dental enamel from preterm and full-term children using light and scanning electron microscopy.

PURPOSE: The aim of this study was to examine the enamel thickness of the maxillary primary incisors of preterm children with very low birth weight (< 1,500 g) compared to full-term children with normal birth weight. METHODS: A total of 90 exfoliated maxillary primary central incisors were investigated using light microscopy and scanning electron microscopy (SEM). Three serial buccolingual ground sections of each tooth were examined under light microscopy, and maximum dimensions of the prenatally and postnatally formed enamel were measured. RESULTS: The enamel of preterm teeth was approximately 20% thinner than that for full-term teeth. Most of the reduction was observed in the prenatally formed enamel. This was 5 to 13 times thinner than that for full-term children (P<.001). The "catch-up" thickness of postnatally formed enamel did not compensate fully for the decrease in prenatal enamel (P<.001). Although none of the teeth used in this study had enamel defects visible to the naked eye, 52% of preterm teeth showed enamel hypoplasia under SEM, compared with only 16% found on full-term teeth (P<.001). These defects were present as pits or irregular, shallow areas of missing enamel. CONCLUSIONS: Preterm primary dental enamel is abnormal in surface quality, and is significantly thinner compared to full-term enamel. The thinner enamel is due mainly to reduced prenatal growth and results in smaller dimensions of the primary dentition.

Child, Preschool↗
PubMed1989

Characterization of human dental enamel by epithermal neutron activation analysis.

Dental enamel is considered to be a biological interface depending on two phenomena the surroundings and the individual's general metabolism. The analysis of its chemical composition is becoming more and more developed. A neutron activation method has been elaborated and applied to these analyses. The results obtained and their statistical interpretation emphasize the fundamental importance of trace elements as a result of their role in the main physiopathological phenomenon peculiar to dental enamel.

Dental Enamel↗
PubMed1999

Modeling the modification depth of carbon dioxide laser-treated dental enamel.

BACKGROUND AND OBJECTIVES: Many studies of laser-induced thermal decomposition of dental enamel have demonstrated a reduction in the rate of acid dissolution, size of artificial caries-like lesions, and acid reactivity. Additionally, studies have correlated the loss of carbonate from dental enamel with a reduction in acid dissolution. Dental mineral consists of hydroxyapatite with many substitutions, the major one being carbonate ( approximately 3-5% by weight), which markedly affects acid reactivity. The principle objective of the present work was to determine the precise depth of modification, i.e. , thermally induced decomposition of dental enamel (carbonate loss), at the predicted optimum laser irradiation parameters. STUDY DESIGN/ MATERIALS AND METHODS: Bovine enamel blocks were irradiated at lambda = 9.6 microm with 2-microsec and 100-microsec pulses and at lambda = 10.6 microm with 2-microsec pulses. Carbonate loss was calculated from infrared spectra as a function of depth and compared to numerical simulations of the maximum temperature rise. RESULTS: Carbonate loss was initiated at temperatures greater than 400 degrees C, but was complete only after repeated irradiation of the surface above the melting threshold. Carbonate loss of dental enamel irradiated at 9.6 microm with a 100-microsec pulse and at 10.6 microm with a 2-microsec pulse was greater than that of enamel irradiated at 9.6 microm with a 2-microsec pulse. The depth of carbonate loss in dental enamel irradiated with a 2-microsec pulse was greater for lambda = 10.6 microm than for lambda = 9.6 microm. CONCLUSION: The depth of modification is consistent with the presented model that incorporates the absorption depth and thermal relaxation time/pulse duration. However, repeated irradiation is required for complete removal of carbonate, depending on absorption depth and pulse duration.

Animals↗
PubMed1983

Molecular composition of the protein matrix of developing human dental enamel.

The protein matrix of fetal human dental enamel was isolated and fractionated by chromatographic and electrophoretic procedures. Nine principal protein fractions were isolated and characterized. Possible inter-relationships of these proteins and their comparison with data from other species were examined. Significant differences between human proteins and those described for cow or pig enamel were identified.

Amino Acids↗
PubMed1979

[Late development of human dental enamel].

Planes of longitudinal fractures of human dental enamel observed in scanning electron microscopy showed morphological variations related to age. This late maturation was observed along the enamel sheaths which disappeared in the subsurface and decreased in the rest of the structure. The destructions produced by demineralizing substances (phosphoric acid, citric acid, EDTA) were always more severe in enamel of older teeth when compared to younger samples. A pretreatment of the fragments with a urea solution increased the acid effects only in young enamel. It is suggested that the late maturation of enamel consists in a reduction of matrix components.

Acid Etching, Dental↗
PubMed1990

Effect of X-ray irradiation on the permeability of bovine dental enamel.

To estimate permeability properties of bovine dental enamel, complex impedance measurements and radioisotope diffusion experiments were carried out before and after X-ray irradiation (single dose, 72 Gy) of enamel specimens. Neither impedance measurements nor diffusion experiments showed significant changes in permeability.

Animals↗
PubMed1997

Amelogenin proteins of developing dental enamel.

The amelogenins of developing dental enamel are tissue-specific proteins, rich in proline, leucine, histidine and glutamyl residues, and synthesized by the ameloblast cells of the inner enamel epithelium. These proteins comprise the bulk of the extracellular matrix that becomes mineralized with a hydroxyapatite phase to become the mature enamel. Examination of the amino acid sequences of amelogenins from a range of mammals shows a high degree of evolutionary sequence conservation, suggestive of specialized function. Recently it has been shown that multiple amelogenin components, observed in the matrix, arise both by a sequence of post-secretory proteolytic processing and by the expression of alternatively spliced mRNAs generated from the amelogenin gene(s) that are located on the sex chromosomes. Although the function of these amelogenins in enamel biomineralization is unknown, physico-chemical studies of recombinant amelogenins have shown that they undergo a self-assembly process in vitro generating supra-molecular 'nanosphere' structures, and recent observations in vivo point to a functional role for the nanospheres in the ultrastructural organization of the secretory enamel matrix, conducive to the organized development of the earliest mineral crystallites.

Alternative Splicing↗
PubMed1989

Electron probe micro-analysis for subsurface demineralization and remineralization of dental enamel.

A quantitative study of fluoride distribution profile changes in dental enamel was conducted by means of electron probe micro-analysis (EPMA). Fluoride-deposited hydroxyapatite powders were chosen as fluoride standards, and analytical conditions were optimized. The lower limit of detection for fluoride was estimated to be 270 ppm, with an accelerating voltage of 5 kV, a specimen current of 40 nA, and a counting time of 40 seconds. Fluoride profiles in fluoride-treated dental enamel, which exhibited intact surface layers and subsurface demineralization, were determined. The results were also compared with those of an acid-abrasion method, and reasonable consistency was found between these two methods, although the acid-abrasion procedure yielded a slightly lower fluoride content in the initial layers, followed by a higher content of fluoride in the deeper layers. The precision of fluoride profile data obtained from EPMA permits further studies to be conducted on the kinetics of subsurface demineralization and intact surface layer formation ("white spot" formation) which is observed during the acid challenge of dental enamel.

Animals↗
PubMed1995

Hypoplastic area method for analyzing dental enamel hypoplasia.

Most analyses of dental enamel hypoplasia compare frequencies of disturbed tooth types, which do not account for variability in the area of affected enamel. An alternate methodology, hypoplastic area, is presented here that accounts for this variability by combining acute and continuous enamel hypoplasia into an interval-level variable. The method compares samples based on individuals, by multiple tooth type variables, or by a single value rather than by tooth types. Use of the hypoplastic area method is illustrated by analyzing human skeletal dentitions in three archaeological samples: Meroitic Nubians from Semna South, Sudan; Anasazi from Navajo Reservoir, New Mexico; and Mogollon from Grasshopper Pueblo, Arizona. Both univariate and multivariate statistical tests are employed to assess variation in defects between individuals and samples. By incorporating measurements of continuous defects, the hypoplastic area method provides information beyond that of frequency data in comparing levels of stress. Flexibility of the method is also discussed.

Arizona↗
PubMed1997

[The study on chemical composition and crystalline structure of hypoplastic primary dental enamel].

The present study, firstly, analyzed chemical composition of hypoplastic primary teeth by electron probe analyzer and compared the hypoplastic part with the normal part in the same tooth; secondly, by X-ray diffraction analyzer, studied the hypoplastic dental enamel and the normal dental enamel, and compared the crystalline structure between different dental enamel and with that of the hydroxyapatite. The aim was to find out any change of crystalline structure. Two exfoliated hypoplastic deciduous anterior teeth were used for the electron probe study. The normal part of each tooth served as control. Determinations of weight percentage (wt%) were made for P, Al, Mg, Ca, Mn, Fe, Zn, Sr, Na, K and F. Four exfoliated hypoplastic deciduous anterior teeth and eight exfoliated normal deciduous anterior teeth were used for the X-ray diffraction study. We found by X-ray diffraction that the length of the alpha-axis of enamel crystallite and the distance of lattice plane (corresponding 300) were increased in defective enamel and could be associated with the increased content of magnesium detected by electron probe. Thus, the present study demonstrated that there were both quantity and quality changes in the enamel hypoplasia lesion, which may increase the susceptibility of the defective teeth to caries.

Calcium↗
PubMedDate not supplied

[Participation of protein-lipid complexes in the mineralization of dental enamel].

Insoluble complex protein-lipid-calcium phosphate was formed on neutralization of dental enamel solution. Nonpolar lipids were extracted by chloroform-methanol mixture; the phospholipids maintained their connection with the solid phase. After incubation of the enamel precipitate with an anionic detergent the enamel protein became solubilized and was studied by means of electrophoresis. The role of proteins and lipids in calcification of the dental enamel is discussed. Biological calcification appears to operate via a universal mechanism, as evidenced by similarity in molecular structures of organic mixtures of various mineralized tissues.

Amelogenesis↗
PubMed1996

Dental enamel defects and screening for coeliac disease.

Specific dental enamel defects (DEDs) in permanent teeth are frequently observed in coeliac patients. We examined the permanent teeth in 6949 secondary school children living in Trieste (78% of 8724 children born between 1978 and 1982). Children with DEDs were tested for serum antigliadin antibodies (AGAs) and antiendomysium antibodies (AEAs), and those positive for serum AGAs and/or AEAs underwent intestinal biopsy. Specific DEDs were observed in 52 children (0.59% of the total population examined). Serum AGAs and/or AEAs were positive in 10 cases. Nine patients underwent intestinal biopsy (one refused) and in four cases a flat mucosa was documented (one with short stature, three completely asymptomatic). The known incidence of CD in the study area was 1:1000 before the study programme and 1:670 (an increase of 44%) after it. Dental enamel inspection may be utilized for detecting undiagnosed coeliac disease in symptom-free schoolchildren. This clinical test is probably less sensitive than serum AGA screening test, but deserves some consideration because it is cheap, easy to perform and well accepted by the population.

Adolescent↗
PubMed1997

A quantitative backscattered electron imaging study of hypomineralization and hypoplasia in fluorosed dental enamel of deer.

Mineral content and distribution of fluorosed and unfluorosed (control) dental enamel of roe deer and red deer cheek teeth were analyzed using digital backscattered electron (BSE) imaging of PMMA-embedded specimens. Compared to the controls, the fluorosed enamel exhibited various aberrations resulting from a fluoride-induced disturbance of the processes involved in enamel formation. Thus, the presence of surface hypoplasias and an enhancement of the incremental pattern in the fluorosed enamel are evidence of a fluoride impact on the secretory ameloblasts, whereas a (subsurface) hypomineralization of different depth and extent is indicative of a fluoride effect on the maturation stage of amelogenesis. The marked variation in the severity of enamel hypomineralization seen along the coronocervical axis of a specimen pointed to a fluoride impact of varying intensity during this period of tooth development. Our observations further indicated that, in some locations, ameloblasts severely affected by fluoride during enamel matrix formation were able to recover from this insult and to function quite normally during the maturation stage of amelogenesis. A major advantage of the BSE imaging technique used in the present study over other methods is that it allows for a combination of micromorphological information with quantitative data on the mineralization of the analyzed tissue, which proved to be very useful for the characterization of fluoride-induced changes in dental enamel.

Ameloblasts↗
PubMed1992

Initial dissolution rate studies on dental enamel after CO2 laser irradiation.

The influence of CO2 laser irradiation on the dissolution behavior of human dental enamel has been investigated. Human enamel was irradiated by a continuous-wave CO2 laser at 10.6 microns and initial dissolution rates (IDRs) were measured in 0.1 mol/L acetate buffer, pH = 4.5, both with and without calcium and/or phosphate common ion, by means of a rotating disk assembly. The effects of (1-hydroxyethylidene) bisphosphonic acid (EHDP), fluoride (F), and dodecylamine HCl (DAC) at various levels upon the IDR were also determined. All of the findings were consistent with the hypothesis that CO2 laser irradiation converts dental enamel to hydroxyapatite (HAP) possessing site #2 character (Yamamoto et al., 1986). The dissolution driving force function, KHAP = aCa10aPO4(6)aOH2, was found to have a value of 10(-129.9) after being lased, as compared with 10(-121.4) before being lased. The IDR values for EHDP (3 mmol/L) and DAC (3 mmol/L) were essentially zero as expected for site #2 HAP. For solution F, the deduced dissolution driving force function, KFAP = aCa10aPO4(6)aF2 was 10(-128.6) after being lased as compared with 10(-116.3) before being lased. These results all support the hypotheses (1) that laser irradiation may convert the surface of human dental enamel to an apatite of significantly lower effective solubility (i.e., site #2 HAP) than that of unlased enamel; and (2) that there is significant synergism between laser treatment and these chemical dissolution rate inhibitors (again consistent with site #2 HAP). Simple model calculations indicate that, in both the presence and absence of fluoride, these laser-induced changes in the driving force for dissolution should dramatically lessen the susceptibility of enamel to the types of acid challenge that might be encountered in the mouth.

Amines↗
PubMed1987

Effect of acid type on kinetics and mechanism of dental enamel demineralization.

The influence of acid type (pKa effects) of weak organic acid buffers on dissolution kinetics of dental enamel was critically examined for rigorous testing of the behavioral validity of the physical model of Patel et al. (1987). Quantitative evaluation of this model indicated that monitoring initial dissolution rates was a viable approach to critical testing of the model. Initial dissolution rates were determined in 0.1 mol/L acetate (pKa = 4.77), benzoate (pKa = 4.20), and salicylate (pKa = 2.98) buffers (pH = 4.50, mu = 0.50), with ground bovine enamel blocks of known surface area mounted in a rotating disk apparatus. The Levich theory was used to study dependence of dissolution rates on stirring rates in these buffers. The experimental data were analyzed by the physical model which includes pKa effects, complexation of the buffer anion with the other ions, surface kinetics, simultaneous diffusion and equilibrium of all species in enamel pores, diffusion layer thickness, and bulk solution composition. The KIAP (formula: see text) governing the dissolution reaction and the surface resistance factor were deduced from the model. Dissolution kinetics was also followed in these buffers in the presence of calcium or phosphate common ions. In effect, by conducting both the stirring rate studies and common ion experiments, we derived the driving force function independently by these two techniques. The results obtained in this study were consistent with the model, indicating that pKa effects on the dissolution of dental enamel can be accounted for quantitatively by the model, and it was found that weak acids do not influence either the apparent solubility or the surface reaction process of bovine dental enamel.

Acetates↗