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At least 19 recordsLinked to original sources
PubMed1988

Identification and characterization of enamel proteinases isolated from developing enamel. Amelogeninolytic serine proteinases are associated with enamel maturation in pig.

During tooth formation nearly all of the protein matrix of enamel is removed before final mineralization. To study this process, enamel proteins and proteinases were extracted from pig enamel at different stages of tooth development. In the enamel maturation zones, the major enamel matrix proteins, the amelogenins, were rapidly processed and removed. Possibly associated with this process in vivo are two groups of proteinases which were identified in the enamel extracts by enzymography using amelogenin-substrate and gelatin-substrate polyacrylamide gels and by the degradation in vitro of guanidinium chloride-extracted amelogenins. One group of proteinases with gelatinolytic activity consisted of several neutral metalloendoproteinases having Mr values from 62,000 to 130,000. These proteinases were inactive against amelogenins, casein and albumin, and were present in approximately equal proportions in enamel at all developmental stages. In the other group, two serine proteinases, with apparent non-reduced Mr of 31,000 and 36,000 exhibited amelogeninolytic activity. The substrate preference of the enamel serine proteinases was indicated by their limited degradation of casein and their inability to degrade gelatin and albumin. Contrasting with the distribution of the metalloendoproteinase enzymes, the serine proteinases were found only in the enamel scrapings taken from late-maturing enamel. The amelogenin degradation patterns in vivo, observed in the enamel scrapings, were similar to those produced in assays in vitro using partially purified fractions of enamel proteinases and amelogenin substrate. Together, these data strongly indicate an important role for the serine proteinases, and possibly the gelatinolytic proteinases, in the organized processing of the enamel protein matrix during enamel formation.

Amelogenin↗
PubMedDate not supplied

Inner enamel epithelia synthesize and secrete enamel proteins during mouse molar occlusal "enamel-free area" development.

Mesenchyme-derived instructions for odontogenic epithelial differentiation into ameloblasts and the production of enamel matrix has been well established. However, it is not known how position-specific differences within the enamel organ of rodent molar tooth organs regulate the enamel-forming vs. the enamel free areas in the developing cusp. Light microscopy, transmission electron microscopy, and immunocytochemistry using a rabbit anti-mouse amelogenin antibody, were used to map the position-specific patterns within the enamel organ. In the enamel-forming area, ameloblasts were associated with stratum intermedium. In the enamel-free area, another cell type was interposed between inner enamel epithelia (IEE) and stratum intermedium. IEE in the enamel-free area did not have Tomes' processes and secreted enamel matrix not only toward dentin but also between IEE cells. IEE became confluent with stellate reticulum; at this position stratum intermedium cells were no longer detected. The thickness and orientation of dentin matrix collagen fibers in the enamel-free area were different from the fibers in the enamel-forming area. These results suggest that the patterns of epithelial cell-cell and cell-matrix associations during position-specific enamel organ epithelial differentiation may regulate ameloblast matrix synthesis and/or the matrix secretion pathway.

Animals↗
PubMed1989

Ectopic tooth enamel. An SEM study of the structure of enamel in enamel pearls.

Eighteen human molars with enamel pearls ranging in diameter from 0.8 to 2.7 mm were sectioned, acid-etched, and processed for SEM observation. In addition to pearl enamel, the specimens contained crown enamel for comparison. All pearls were of the composite type. The enamel layer reached maximal thicknesses of between 0.3 and 0.7 mm opposite the tip of the dentinal cone. The enamel structure was normal, but more variable and irregular than crown enamel. The prism course was often irregular throughout the whole thickness of enamel. Distinct Hunter-Schreger bands were absent. Prisms and interprism were occasionally difficult to identify as separate entities. The packing of crystals seemed to be less tight in pearl enamel. The scarcity of Retzius lines was attributed to the method of preparation. Prism cross-striations with a periodicity ranging between 1.3 and 4.5 microns were frequently encountered. A superficial prism-free zone with a regular 1.7-2.5-microns striation was present in localized regions of many pearls. The formation time of a medium-sized pearl was calculated to be about 11.5 months. A variety of cross-cut prism configurations was observed. Occasional hypoplastic lesions and hypomineralized areas were encountered. In conclusion, pearl enamel possesses most of the structural attributes of crown enamel, but in general its organization seems to be less orderly. Enamel pearls represent developmental disturbances in position and timing more than in structure.

Dental Enamel↗
PubMed1989

[Resin adhesion to the ground enamel. Influence of the ground depths of the enamel and etching times (1)].

The purpose of this study was to investigate the influence of the ground depths of the enamel and etching times on the adhesion of the resin on the ground enamel. Seventy-five extracted and frozen bovine mandibular young permanent incisors were used. The etchant used in this study was 40% phospholic acid gel and the etching times were 0, 10, 20, 30 and 60 seconds. All of the specimens were washed with an air water spray for 30 seconds after etching. The bonding agent and composite resin used in this study were Photo Bond and Photo Clearfil A (Kuraray Co.). Shear bond strengths to the outer enamel layers and inner enamel layers of the same teeth were measured. After the shear bond strength test, all the test surfaces of the enamel and resin specimens were observed using the SEM. The following conclusions were obtained. 1) The etching times which showed the highest bond strength were 20 seconds on the outer enamel layers (bond strength: 35.25 +/- 6.60 MPa) and 30 seconds on the inner enamel layers (bond strength: 40.15 +/- 6.59 MPa). 2) When the enamel was etched with all of the etching times, the bond strengths were significantly higher than those of the enamel without etching on the outer and inner enamel layers. 3) In the etched groups, significant differences between the bond strengths were not obtained among the different etching times on the outer and inner enamel layers. 4) In the comparison of the bond strengths between the outer enamel layers and the inner enamel layers, the bond strengths of the inner enamel layer were higher than those of the outer enamel layer with 0, 10, 30 and 60 seconds of etching times. However, a significant difference between the bond strengths was obtained only in the cases with 30 seconds of etching time. 5) In the etched groups, such a tendency toward a higher bond strength was observed in cases which showed poor enamel prism structures and poor resin tags, and resin widely adhered on the enamel surface. 6) Thirty seconds is a sufficient time for etching on the ground young permanent enamel using Photo Bond and Photo Clearfil A.

Acid Etching, Dental↗
PubMed1986

Penetration of various molecular-weight proteins into the enamel organ and enamel of the rat incisor.

During enamel maturation, most of the organic matrix is removed as the mineral content increases; it is postulated that proteolytic enzymes within enamel break down large proteins into more mobile fragments. To predict how such fragments might leave the enamel, the entry and penetration of various proteins into it was examined. Rats (100 g) were injected via the external jugular vein with 125I-iodinated calcitonin (3600), insulin (5700), epidermal growth factor (EGF; 6100) and albumin (68,000). They were killed after 10 min and radioautographs made to visualize these molecules in the incisor enamel organ and enamel. In addition, dissected incisors were wiped free of their enamel organs, dipped in the iodinated protein solutions for 10 min, and processed for radioautography. In all dipped teeth, except those exposed to albumin, there was a gradient of silver-grain density over the entire thickness of enamel in both the secretion and maturation zones. In all injected animals, enamel labelling in the secretion zone was only slightly above background. In the maturation zone of animals injected with calcitonin and insulin, many grains were over enamel adjacent to smooth-ended ameloblasts but not ruffle-ended ones. Animals injected with EGF and albumin had no labelled enamel in the maturation zone. Thus dipped rat incisor enamel was permeable to proteins with molecular weights as high as 6100. Localization of injected proteins indicates that the enamel organ restricts their passage into enamel, but proteins with molecular weights as high as 5700 may pass into enamel through or between smooth-ended ameloblasts. As exogenous proteins readily diffused into the enamel, it seems likely that enamel proteins of similar size can leave enamel by a similar route.

Animals↗
PubMed1989

Enamel proteases in secretory and maturation enamel of rats ingesting 0 and 100 PPM fluoride in drinking water.

Dental enamel formed during ingestion of high levels of fluoride in drinking water has an increased organic content in the maturation stage, which may be due to a delay in the breakdown of amelogenins during the early-maturation stage of enamel formation. This delay in the breakdown of amelogenins in fluorosed enamel suggests an effect of fluoride on enamel proteases which hydrolyze the early secreted enamel proteins. In this study, we compared the proteases present in fluorosed and control secretory-stage and maturation-stage enamel. Enamel was demineralized and separated in SDS gels containing 0.1% gelatin. After incubation in 100 mmol/L Tris-HCl, pH 8, with 10 mmol/L CaCl2, the gels were stained with Coomassie Blue, and proteases were seen as clear zones of degraded gelatin. Similar bands of proteolytic activity were seen in fluorosed and in control enamel. In the maturation stage, more proteases were present than in the secretory stage of enamel formation. Less digestion of gelatin substrate occurred in several proteases found in the fluorosed maturation-stage enamel as compared with the control maturation-stage enamel. This suggests that the amount of protease secreted or the activity of the proteases may be altered in fluorosed maturation-stage enamel.

Animals↗
PubMed1991

In vitro penetration of 125I-amelogenin into the enamel and enamel organ of rat incisors.

This work attempted to introduce pre-labelled intact amelogenins into developing rat enamel in vitro. The intention was ultimately to trace the fate of such proteins in the developing enamel matrix and to examine the effect of these and other molecules on ameloblast behavior. The penetration of 125I-amelogenin (25 KDa) directly into the young enamel of rat incisors, in vitro, keeping the enamel organ intact is described. The enamel (an extension approximately 8 mm from the apical end of the tooth) together with the enamel organ, was separated from the underlying dentine and placed over a strip of filter paper covering a well of micro-culture slide filled with Eagle's medium containing 125I labelled amelogenin and incubated at 37 degrees C. The enamel faced the strip of filter paper and so was adjacent to the medium. After 1 h pieces were either washed in cold medium, fixed and embedded in Epoxy-resin, or incubated in cold medium for another 1 to 10 h at 37 degrees C before embedding. One-micron thick sections were processed for autoradiography and the results showed a decreasing gradient of silver grain concentration from the dentino-enamel junction towards the enamel organ. It is expected that by determining the nature of the labelled material incorporated into the enamel and enamel organ the fate of amelogenins could be better understood.

Ameloblasts↗
PubMed1991

The development of enamel tubules during the formation of enamel in the marsupial Monodelphis domestica.

In Monodelphis domestica, although both processes from odontoblasts and projections from ameloblasts were found in developing enamel, the majority of the contents of enamel tubules were probably processes that originated from odontoblasts. Processes from odontoblasts penetrating into enamel touched part of the ameloblasts in the stage of enamel formation. No specialised cell junctions were seen at the adherence between the two. There were no enamel tubules in the aprismatic and pseudoprismatic enamel layer. It is likely that enamel tubules exist only in prismatic enamel. The majority of enamel tubules seemed to contain no cell processes in the stage of enamel maturation, indicating that the cell processes in the tubules probably degenerate after the stage of enamel formation.

Amelogenesis↗
PubMed1988

The macroscopic and scanning electron-microscopic appearance and microhardness of the enamel, and the related histological changes in the enamel organ of erupting sheep incisors resulting from a prolonged low daily dose of fluoride.

The hypothesis that diffuse opacities in enamel result from a chronic, mild disturbance to ameloblast activities was tested using fluoride. Three sheep (HF) were dosed orally with 0.5, and 3 (LF) with 0.2 mg fluoride/kg body weight daily for 6 months. A control sheep (C) received no additional fluoride. The 7 sheep were killed at or close to the time of emergence of their permanent central incisors. One tooth from each sheep was sectioned longitudinally. The enamel related to the secretory (S) and maturation (M) phases of ameloblast activity at the start of fluoride dosing was determined from a tetracycline marker. The pattern of mineralization of the outer 150 micron of the cut labial enamel was assessed using microhardness testing. The SEM appearance of the acid-etched outer enamel was compared in S and M zones in 5 teeth. The enamel of the C tooth was translucent. Diffuse opacities, similar in appearance to human fluorosis, were present in all fluoride-treated teeth. Hardness values in the outer 70 micron of the enamel decreased as the fluoride dose increased and, in the HF teeth, were lower in the S zone than in the M zone. Fluoride given during the M phase induced a surface hypomineralization which increased in degree and depth when fluoride was also given during the S phase. The SEM appearance of M and S enamel was similar in 2 LF and 1 HF teeth but, in the other HF tooth, S enamel but not M enamel had a disordered prism structure and loosely-packed crystals in an abnormal organic matrix. Histological examination revealed that ameloblasts remained in only 4 of the 7 teeth and that their regression and the formation of the cementum adjacent only to the labial enamel were progressing abnormally.

Ameloblasts↗
PubMed1976

[Ultrastructural changes in cells of the inner enamel epithelium, stratum intermedium and reticulum stellatum in the enamel organ of the upper incisor of the Wistar rat at different phases of amelogenesis].

An electronmicroscopical study of the enamel organ of the upper incisors germs of Wistar rats was performed to analyse the ultrastructural features of the cells of the inner epithelium, the intermediate layer and the stellate reticulum, during preimary, young, transitional and mineralized enamel phases of amelogenesis. So, it was observed that the mitochondria in the ameloblasts are ovoid before the beginning of the enamel matrix formation and in the primary and young enamel phases. However, in the transitional and mineralized phases, these organelles are long and tortuous and some are characterized by a compact structure. In the cells of intermediate layer and stellate reticulum, the mitochondria are ovoid until the beginning of the mineralized phase. At the ending of this phase, these organelles are very long and present irregular form; many of them show also a compact structure. The "zonula adhaerens" could be observed only in the ameloblasts of the primary and young enamel phase. The cytoplasm of ameloblasts, during primary and young enamel phases is characterized by an abundance of free ribosomes and a branular endoplasmic reticulum; but during transitional and mineralized enamel phases, the cytoplasm of these cells shows little granular endoplasmic reticulum and free ribosomes, but ehe agranular endoplasmic reticulum is present. The granular endoplasmic reticulum and free ribosomes are abundant in the cells of the intermediate layer and stellate reticulum at the ending of the young enamel phase, in the transitional enamel phase and in the beginning of the minieralized phase. During different phases of amelogenesis, in the three above referred layers of the enamel organ, were also studied the features of the Golgi apparatus the presence and topographic distribution of the pigment granules, as well as the lysosomes, desmosomes and the tonophibriles.

Ameloblasts↗
PubMed1975

Composition and structure of dental enamel: elemental composition and crystalline structure of dental enamel as they relate to its solubility.

The same elements, 21 in number, were found in both acid-resistant and acid-susceptible enamel specimens by ion microprobe analyses. However, there were differences in the concentrations of 14 elements between groups. Of the 16 trace elements found in enamel, the concentrations of K, F, and Na in parts per million were the greatest. Enamel surface analyses showed V and Zn were more concentrated in acid-resistant specimens by factors of 7.4 and 6.1 respectively, followed by nine other elements, the last molybdenum, that were just slightly more prevalent in acid-resistant enamel. Four elements were equally concentrated in both groups of samples, and only one trace element, B, was more abundant in the acid-susceptible samples by a factor of ten. Ca and P were predominantly more abundant in acid-resistant speciems, and C, H, and O were more concentrated in acid-susceptible samples. The enamel substance in acid-resistant and acid-susceptible groups was found to be similar by these methods. --Ion microprobe: the same elements were detected in both groups. Four trace elements (titanium, lead, Cl, and lithium) were equally abundant in the two groups. --Electron diffraction: the crystal structure type was the same in both groups of samples. --Infrared absorption: the crystalline substance showed the same spectra in both groups. The enamel substance in the two groups of specimens was found to be dissimilar by these methods. --Ion microprobe: the concentrations of 11 trace elements as well as Ca and P were greater in acid-resistant enamel. The concentrations of C, H, O, and B were greater in acid-susceptible enamel. --X-ray diffraction: crystallites in the acid-resistant specimens were larger by a factor of more than two. Enamel solubility appears not to be related to atomic species but associated with one, some, or all elements quantitatively and also with its physical form (crystallite size and probably density).

Calcium Phosphates↗
PubMed1989

No effect of waxed dental floss on enamel fluoride uptake or on enamel dissolution changes.

Enamel specimens were flossed in vitro with "waxed" dental floss and then treated with water, Act, Meridol, or Elmex Gel to evaluate the effect of "waxed" floss on the enamel fluoride uptake and on the enamel dissolution rate. The flossed and treated enamel was etched 4 times successively in 2N HCl for 5, 10, 15 and another 15 s. The concentrations of fluoride, calcium and phosphorus were assayed in the etching solutions. The enamel fluoride concentration was significantly increased in only the first layer of the Elmex Gel group compared to the other 3 groups. Respective etching depths were similar for the water, Act and Elmex Gel groups. However, the first layer in the Meridol group was less etched than that in the 3 other groups. This study showed that "waxed" dental floss did not compromise the fluoride uptake by surface enamel after treatment with a concentrated acidic topical fluoridating agent. Moreover, previously reported results showing that Meridol solution containing SnF2 and amine fluoride 297 significantly decreased the in vitro dissolution rate of enamel were confirmed by the present study. Even though the enamel was first treated with "waxed" dental floss, the SnF2/amine fluoride 297 still produced a decreased enamel dissolution rate.

Acid Etching, Dental↗
PubMed1986

Comparison of tryptophan-labeled constituents of developing rodent molar enamel matrix, non-enamel occlusal cusp, Hertwig's epithelial root sheath, and presumptive root furcation regions: light microscopic autoradiography.

During the process of organogenesis involving the developing rodent molar and incisor tooth organs, novel gene products termed enamel proteins are expressed by ectodermally-derived enamel organ epithelia at precise times and positions within the course of morphogenesis. The present studies were designed to identify the relative distribution of tryptophan-labeled, non-collagenous, epithelial-derived proteins associated with rat maxillary first molar crown (M') and initial root formation. Our experimental strategy was to utilize semi-quantitative autoradiography methods to compare and contrast the distribution of silver grains resulting from tryptophan incorporation into developing postnatal pups associated with enamel matrix, non-enamel occlusal cusp, Hertwig's Epithelial Root Sheath (HERS), and presumptive root furcation regions of M'. Five-day-old Wistar rats were injected with 14C-labeled tryptophan. Four animals were sacrificed at 15 minutes and then at 1, 2, 4, and 24 hour intervals following the administration of this essential aromatic amino acid. Following fixation and subsequent processing for autoradiography, semiquantitative analyses were performed of the silver grain distribution localized within selected regions of the developing M' tooth organs. All enamel organ epithelia were found to incorporate tryptophan and silver grains were identified (above background) in the extracellular matrices (ECM) of the enamel matrix, non-enamel occlusal cusp adjacent to the inner enamel epithelia, and the ECM (2-4, micron) adjacent to presumptive root furcation and HERS regions. Tryptophan incorporation was not significant in the odontoblasts or dentine ECM of the crown or forming presumptive root regions. These results support the hypothesis that inner enamel epithelia associated with rat molar crown formation, as well as HERS, synthesize tryptophan-labeled, non-collagenous, ECM molecules. We speculate that HERS participates in root development by possibly producing non-collagenous proteins for intermediate cementum formation.

Amelogenesis↗
PubMed1989

[Enamel abrasion and enamel tears by porcelain brackets].

Orthodontic brackets manufactured of poly- or monocrystalline alumina ceramics are aesthetically appealing, but unfortunately show disadvantages for clinical application primarily causing (1) Abrasions of the enamel of antagonistic teeth, and (2) Tear-outs of the underlying enamel through debonding. To determine whether hardness and/or textural and structural qualities of the ceramics (as characterized by SEM investigations) are responsible for the deleterious clinical effects of abrasion, the amount of decrease of the height of human enamel-molar-cusps was measured. Enamel loss was shown to be significantly more than 100 microns at 10 min. operating time in an abrasive testing device. Also debonding of the ceramic brackets proved to be problematic. Whereas metals and polymeric brackets allow some deflection of the material in addition to the tensile stress, separating the bracket from the enamel at the bracket-to-adhesive interface, or within the adhesive composite, the lacking workability in the ceramic brackets may induce a shift of the break-line during debonding to the adhesive-enamel interface or even into the dental enamel. Development and clinical application of ceramic brackets should improve safety for the enamel. Regardless of ceramic brand the abrasiveness endangers enamel through ceramic/enamel interferences. To avoid tear-out defects, brackets should debond at the ceramic-adhesive interface.

Dental Bonding↗
PubMed1992

Localization of glycosylated matrix proteins in secretory porcine enamel and their possible functional roles in enamel mineralization.

The present study was undertaken to investigate glycosylation of porcine enamel proteins secreted in the secretory stage of amelogenesis and to gain insight into functional roles of glycosylated proteins in enamel mineralization. Enamel proteins, isolated from various zones of the secretory enamel, were separated by SDS-PAGE and then transferred on to a nitrocellulose membrane. The transblotted proteins were visualized with either antibodies against porcine amelogenins or various biotin-conjugated lectins. The lectins used were Con-A, GS-II, STA, WGA, s-WGA, GS-I, MPA, VVA, PNA, RCA-I, DBA, SJA, UEA-I, Lotus-A and LPA. The results of the immuno- and lectin blottings revealed that most of the lectins did not bind to porcine amelogenins, while a large number of non-amelogenins having various molecular masses were stained strongly with the conjugated WGA, Con A and MPA lectins. On the basis of the binding specificity with the lectins, porcine non-amelogenins were classified into two groups: WGA (and Con A)-binding moieties at 60-90 kDa (WGA-HMW); and MPA-binding moieties at 13-17 kDa (MPA-LMW). These two groups of non-amelogenins differed distinctly in terms of their localization and stability in the secretory tissue and their adsorption properties onto hydroxyapatite. The WGA-HMW were concentrated in the outer region adjacent to the ameloblasts and disappeared (due to degradation) in the underlying inner secretory enamel. In contrast, the MPA-LMW were found in all zones of the secretory enamel and their quantity remained relatively constant. Histochemical studies using FITC-conjugated WGA and MPA showed that the fluorescence-labelling of WGA was localized in the core region of prism rods, while the fluorescence-labelling of MPA was locally limited at the rim of prism rods or at the prism sheath. In separate adsorption studies, it was found that the WGA-HMW, as well as the intact amelogenins, displayed a high adsorption affinity on to apatite crystals, whereas the MPA-LMW showed only marginal adsorption on to apatitic surfaces. The overall results indicate that part of the heterogeneity found in porcine enamel proteins can be ascribed to variations of carbohydrate moieties attached to non-amelogenins.(ABSTRACT TRUNCATED AT 400 WORDS)

Adsorption↗
PubMed1991

Enamel structure and microwear: an experimental study of the response of enamel to shearing force.

The anisotropic fracturing and differential wear properties of enamel microstructure represent factors that can obscure the predictive relationship between dental microwear and diet. To assess the impact of enamel structure on microwear, this in vitro experimental study examines the relative contributions to wear of three factors: 1) species differences in microstructure, 2) direction of shearing force relative to enamel prisms and crystallites, and 3) size of abrasive particles. Teeth of Lemur, Ovis, Homo, and Crocodylus, representing, respectively, the structural categories of prismatic patterns 1, 2, and 3 and nonprismatic enamel, were abraded by shearing forces (forces having a component directed parallel to abraded surfaces) and examined by scanning electron microscopy. Striation width increased with particle size for nonprismatic, but not for prismatic, specimens. Direction of shear relative to prism and crystallite orientation had a significant influence on striation width in only some prismatic enamels. The different responses of prismatic and nonprismatic enamels to abrasion reflect the influence of structure, but at the level of organization of crystallites rather than prisms per se. Such interactions explain in part the inability of striation width to discriminate among animals with different dietary habits. Heteroscedasticity and deviations from normality also may confound parametric analyses of microwear variables. Variation in crystallite orientation in prismatic enamels may contribute to optimal dental function through the property of differential wear in functionally distinct regions of teeth.

Alligators and Crocodiles↗