Outer Enamel Layer Research Articles

On the initial propagation of dental caries.

A multi-dimensional model for dental caries is applied to study the shape of caries lesions in a realistic tooth geometry and to examine the rate of progress of caries. An upgraded model, taking into account the outer prismless enamel layer, is derived and solved. The model demonstrates the importance of this layer in delaying the onset of caries. The conclusions are discussed in light of experimental results.

Spatial distribution of the human enamel fracture toughness with aging

A better understanding of the fracture toughness (KIC) of human enamel and the changes induced by aging is important for the clinical treatment of teeth cracks and fractures. We conducted microindentation tests and chemical content measurements on molar teeth from “young” (18≤age≤25) and “old” (55≤age) patients. The KIC and the mineral contents (calcium and phosphorus) in the outer, the middle, and the inner enamel layers within the cuspal and the intercuspal regions of the crown were measured through the Vickers toughness test and Energy Dispersive X-Ray Spectroscopy (EDS), respectively. The elastic modulus used for the KIC calculation was measured through atomic force microscope (AFM)-based nanoindentation tests. In the outer enamel layer, two direction-specific values of the KIC were calculated separately (direction I, crack running parallel to the occlusal surface; direction II, perpendicular to direction I). The mean KIC of the outer enamel layer was lower than that of the internal layers (p<0.05). No other region-related differences in the mechanical properties were found in both groups. In the outer enamel layer, old enamel has a lower KIC, II and higher mineral contents than young enamel (p<0.05). The enamel surface becomes more prone to cracks with aging partly due to the reduction in the interprismatic organic matrix observed with the maturation of enamel.

Electrochemical behavior of enamel-coated carbon steel in simulated concrete pore water solution with various chloride concentrations

The electrochemical behavior of enamel coated carbon steel in simulated concrete pore water solution with various chloride concentrations was investigated by open circuit potential, linear polarization resistance, and electrochemical impedance spectroscopy tests. The phase composition, microstructure, and tensile strength of enamels were characterized by X-ray diffraction, scanning electron microscopy, and pull-off tests. Three types of coatings with pure, mixed, and double enamels were studied and compared for their corrosion behavior. Test results indicated that all three types of enamel coatings can reduce the corrosion current density of carbon steel in an alkaline environment with chloride; the pure and double coatings are superior to the mixed enamel coating. Cohesive failures were observed within the three coatings while their interface with the steel substrate remained intact. In comparison with the pure enamel, the mixed enamel was stronger with smaller open channels formed due to the addition of calcium silicate and the double enamel was weaker with larger air bubbles trapped in the inner pure enamel layer by the outer mixed enamel layer.

Ultrastructure of enamel and dentine in extant dolphins (Cetacea: Delphinoidea and Inioidea)

Longitudinal and cross sections of teeth from 17 species of the Recent dolphins (Delphinoidea and Inioidea) were examined under scanning electron microscope to study the arrangement and ultrastructure of dental tissues with reference to phylogenetic and functional constraints. For most species, enamel had a simple bi-layered structure of radial enamel and an outer layer of prismless enamel. The outer prismless layer varied from 5 to 30 % of enamel thickness. The enamel of Burmeister’s porpoise (Phocoena spinipinnis) was entirely prismless. The prisms had an open sheath; tubules and tuft-like structures were common at the enamel-dentine junction. Cetacean dentine was characterized by irregularly distributed dentinal tubules in a relatively homogenous dentinal matrix. Radial enamel was observed in all Delphinoidea and in the franciscana (Pontoporia blainvillei), whereas the Amazon river dolphin (Inia geoffrensis) had prisms organized in Hunter–Schreger bands. HSB in enamel are regarded as a device for resisting propagation of cracks. These may occur due to increased functional demands, possibly related to the hardness of the species diet. Simplification in tooth shape and reduced biomechanical demands plausibly explain the primitive radial organization among delphinoids and Pontoporia. The HSB structure in the Amazon river dolphin, similar to those of extinct archaeocetes, seems to have secondary functional implications. However, the distribution of HSB in more-basal odontocetes is too poorly known to judge whether the HSB of Inia are a retained plesiomorphic feature or convergence.

Cement-modified enamel coating for enhanced corrosion resistance of steel reinforcing bars

Abstract The corrosion performance of smooth steel rebar coated with pure enamel, mixed enamel, and double enamel, and embedded in mortar cylinders were quantified in 3.5 wt.% NaCl solution using open-circuit potential (OCP), linear polarization resistance (LPR), and electrochemical impedance spectroscope (EIS) tests over a period of 173 days. The mixed enamel was prepared by adding calcium silicate contained in cement into the pure enamel. The double enamel consisted of an inner pure enamel layer and an outer mixed enamel layer. Results indicated that after 27 days of immersion, corrosion initiated and was rapidly developed in uncoated and the mixed enamel coated specimens. Although the OCP indicated a high likelihood of corrosion initiation, the pure enamel and double enamel coated rebar had significantly lower corrosion current densities, and thus remained in passivity throughout the entire test period. This behavior was further verified by the forensic study and EIS results.

Dens evaginatus on maxillary first premolar: Report of a rare clinical case

Dens evaginatus (DE) is an odontogenic developmental anomaly that can be defined as a tubercle or protuberance from the involved surface of the affected tooth consisting of an outer layer of enamel, a core of dentin, and may contain a slender extension of pulp tissue. Early diagnosis and management of DE is important in order to prevent occlusal interference, compromised esthetics, carious developmental grooves, periodontal problems due to excessive occlusal forces, or irritation of the tongue during speech and mastication. DE usually affects the mandibular second premolars as an accessory cusp or a protuberance between the buccal and lingual cusps. Reports of DE on maxillary premolar are rare in the literature. We report one such extremely rare case of DE on maxillary first premolar.

Mineral densities and elemental content in different layers of healthy human enamel with varying teeth age

ObjectivesThis study aims to evaluate the mineral density, calcium (Ca), and phosphorus (P) weight percent of healthy human enamel of varying human teeth age and enamel layers. MethodsTwenty human teeth were divided into “young” (18–24years) and “old” (55≤ years) age groups. From each tooth, one enamel slab (approximately 8mm×2mm×1.5mm) was obtained. All enamel slabs were embedded and scanned by micro-computed tomography. The scanned slices were reconstructed into a 3D image and regions of interest (ROIs) were defined. Then, the mineral density for each ROI was calculated. The Ca and P weight percent in the outer, middle, and inner enamel layers were quantified by scanning electron microscopy with energy dispersive spectroscopy. Finally, the data were analysed using one-way ANOVA and Student's t-test. ResultsIn the two age groups, the mineral density, Ca and P weight percent decreased from outer to the inner enamel layer. The mineral density, Ca and P weight percent in the outer enamel layer in the old age group were significantly higher than those in the young age group (P<0.05); however, no age-dependent differences were observed for these properties in the middle and inner enamel layers (P>0.05). ConclusionsThe mineral density, Ca and P weight percent decreased from the outer to the inner enamel layers in the two age groups. In the outer enamel layer, the differences in these properties between the two age groups were significantly different; however, no region-dependent differences were observed in the middle and inner enamel layers.

Stress Distribution in Teeth Due to Dimensional Changes of the Restorative Material

The objective of this paper is to theoretically investigate the stress distribution in a tooth model due to expansion or contraction of the filler material. Finite element calculations were carried out to determine the stresses and deformations in a model of the tooth. The tooth was modelled to consist of two concentric cylinders, an inner cylinder of 7 mm diameter dentine and an outer layer of 1 mm thick enamel. The two cylinders were assumed to be rigidly fixed at the bottom end and the top end was free. Different sizes of occlusal cavities (2, 4 and 7 mm) as well as mesial-occlusal and mesial-occlusal-distal were simulated through removal of dentine from the centre. The fillings were subjected to an internal pressure of 1 MPa and a chewing pressure of 1 MPa. Since the cylinders were rigidly fixed at one end, the inner part of the cavity (dentine) tended to bend outwards, thus compressing the outer (enamel) layer. This behaviour, coupled with a strong mismatch of the elastic moduli of dentine and enamel, leads to widely different distributions of stress in the tooth as the cavity sizes and filling types are varied. The radial deformations were of the order of microns, most of it occurring in the softer dentine. The maximum stresses occur in the stiffer enamel layer when a chewing pressure is applied, without a chewing pressure the stresses are more evenly distributed.

Research on the remineralization of partially decalcified enamel surfaces using extracted tooth with calcifying solution

The recovery of tooth enamel after acid etching was examined in vitro using enamel powder in order to maximize the contact surface area. The weight of the powder decreased due to acid etching and then increased when the powder was exposed to a calcifying solution. The increase in weight was due to the formation of needle like crystals. According to thermal gravimetric analysis, the newly formed enamel layer was very stable, and was suggested to be apatite by X-ray diffraction and FT-Raman analysis. There was no distinct difference between the newly formed layer and the original tooth in terms of composite X-ray image (CaK α and PK α ). The new layer appeared to be a crystallized extension of the tooth enamel, as determined from SEM observations. However, the outer layer of tooth enamel was damaged by acid etching, and the crystallization had deteriorated 48 hours later when compared with that of a non-etched sample. On the other hand, we were unable to confirm the effectiveness of the recovery. From these results, the recovery of damage caused by acid etching cannot be expected when a tooth is exposed to a calcifying solution. However, the finding demonstrated that the crystallized layer was apatite.

Scanning electron microscopy and energy-dispersive X-ray analysis of defects in mature rat incisor enamel after thyroparathyroidectomy

The surface and the structure of the erupted enamel of the continuously growing rat incisor were studied by scanning electron microscopy (SEM) to analyse the effect of thyroparathyroidectomy on enamel formation. Ten male 21-day-old Wistar rats were thyroparathyroidectomized and five sham-operated rats were used as controls. Two months after surgery the rats were perfused with 1% glutaraldehyde and their mandibles dissected. The erupted ends of the incisors were cut off and routinely processed for SEM. An energy-dispersive analysis of X-rays (EDX analysis) was performed for the calcium:iron ratio of the enamel surface defects. Thyroparathyroidectomy induced surface defects and structural abnormalities in the outer layer of the mature erupted enamel. It was established that the surface and structural defects were related. The EDX analysis of the outer enamel showed that the enamel defects were associated with an abnormal elevation of the iron content. The SEM appearance and the EDX analyses indicated that these defects were hypomineralized and rich in iron. The reddish colour of the enamel is due to the high concentrations of iron.

Immunochemical and biochemical characteristics of enamel proteins in hypocalcified amelogenesis imperfecta

Amelogenesis imperfecta is a hereditary disease of the enamel that is unassociated with generalized defects. Cases of the condition are clinically classified into three groups: hypoplastic, hypomaturation, and hypocalcified. In this study, soluble protein fractions of the enamel from three patients with hypocalcified amelogenesis imperfecta were examined through the use of immunochemical and biochemical techniques. In immunochemical analyses done with a polyclonal anti-amelogenin antibody, all samples from enamel in which there was amelogenesis imperfecta were found to contain considerable amounts of amelogenin peptides. When an enamel sample from one patient was examined by Western-blot transfer and immunobinding analysis, the amelogenin fraction was found to consist of a 26-kDa molecule thought to be normally present in the outer layer of secretory-stage enamel. This enamel was also found to contain albumin as one of the major constituents of the protein fraction. These results suggest that hypocalcified amelogenesis imperfecta may in part be caused by a disturbance in matrix protein degradation during the maturation phase.

Porcine amelogenins.

Amelogenins were extracted from the thin outer layer of porcine secretory enamel and purified by gel filtration and reverse-phase HPLC. The results of amino acid sequencing of the purified porcine amelogenins indicated the presence of at least four prototype amelogenins translated from alternatively spliced transcripts. The results of mass spectroscopy of the CNBr-cleaved peptides derived from the 25 kDa amelogenin indicated that porcine 25 kDa amelogenin is neither phosphorylated nor glycosylated.

Correlation of the arrangement pattern of enamel rods and secretory ameloblasts in pig and monkey teeth: a possible role of the terminal webs in ameloblast movement during secretion.

Enamel rod architecture and ameloblast arrangement were examined in pig and monkey teeth using light microscopy and scanning and transmission electron microscopy. Enamel rods in the pig teeth were arranged in longitudinal straight rows in the initial enamel layer, in longitudinal wavy rows in the inner enamel layer, and in a staggered pattern in the outer enamel layer. Rod decussation was seen only in the inner layer. Cross-sectioned enamel rods in the pig were arcade-shaped in the initial and inner layers, and mostly round in shape with circular boundaries in the outer layer. Arrangement of secretory ameloblasts at the level of the distal terminal web and Tomes' processes, and shape of Tomes' processes, corresponded to those of the enamel rod in the enamel layers. Distal terminal webs were well developed between straight rows of the ameloblasts forming the initial layer and between wavy rows of the ameloblasts forming the inner layer, and less developed within a row. The filament bundles in the distal terminal webs were also oriented along the rows. However, in the ameloblasts forming the outer layer, which lost their row pattern, distal terminal web filaments were distributed uniformly at the cell periphery. A similar arrangement of wavy rows of ameloblasts at the level of distal terminal web and Tomes' processes was also seen in monkey teeth.

Fine Structure and Elemental Analysis of the Enamel in Andrias davidianus (Cryptobranchidae) and Onychodactylus japonicus (Hynobiidae)

Functional teeth from Andrias davidianus and Onychodactylus japonicus were prepared for transmission electron microscopy (TEM) and electron microprobe analyzer (EMPA) of the elements of the enamel layer. The enamel layer is thin and the arrangement of the enamel crystals is regular in the outer enamel layer of Onychodactylus japonicus; on the other hand, the crystals of Andrias davidianus show irregularities in different tooth regions. Based on calcium and magnesium distribution levels using electron microprobe analyzer (EMPA), the enamel layer lacks enameloid in these species. Concentrations of iron and fluoride are located in the outer enamel layer. The presence of trace elements is related to the formation and mineralization of enamel. l of Herpetology, Vol. 25, No. 2, pp. 14 46, 1991 i t 1991 Society for the Study of Amphib ans and Reptiles cture and Elemental Analysi of the Enamel in i s avidianus (Cryptobranchidae) and actylus japonicus (Hynobiidae) O,1 KAZUYUKI SHIMADA,2 ATSUYUKI YOKOI,2 The enamel layers of the amphibian tooth form prismless structures, in contrast to mammalian teeth which have rods in the enamel layer. This material is known as aprismatic enamel, and though it is very thin, it is hypermineralized, as in mammals. In mammals, the enamel crystals are chiefly composed of hydroxyapatite, with iron, fluoride and other trace elements complexed in the surface enamel layer of the tooth (Halse and Selvig, 1974; Selvig and Halse, 1975; Weatherell et al., 1975; Heap et al., 1983; Nelson et al., 1989). A number of different trace elements may be involved in the formation of the apatite crystals. The pigmented layer of rat incisor enamel contains 1-10% iron (Halse and Selvig, 1974) bound to the surface of hydroxyapatite crystals (Selvig and Halse, 1975). Trace elements may also be associated with the mineral component of amphibian enamel. Based on observations using polarizing microscopy, Schmidt (1971) reported that the enamel of Andrias japonicus contains pigments that impart a ena el layers of the amphibian too h prismles structures, in contrast to ma brown color at the tip of the tooth, which he suggested to be an iron oxide. Using transmission electron microscopy (TEM), Kawasaki and Fearnhead (1983) reported the presence of enam loid, a substance previously reported to occur only in fish, beneath the enamel layer in the teeth of the salamanders Hynobius nigrescens and Cynops pyrrhogaster. Enameloid differs from enamel in having a different embryological origin (mesoderm vs. ectoderm), and in having a much lower mineral content (Poole, 1967). The purpose of this study was to look for an interrelationship between the fine structure, concentration, and distribution of trace elements of the enamel layer in Andrias davidianus and Onychodactylus japonicus, and to ascertain the presence or absence of enameloid in these species. MATERIALS AND METHODS Thirteen adult (total length ca. 80 cm) Andrias davidianus (Cryptobranchidae) and ten adult (tocolor at the tip of the tooth, w ich he ested to be an iron oxide. Using transmiselectron microscopy (TEM), K wasaki and head (1983) reported the presence of eloid, a substance previously reported to only in fish, beneath the enamel layer in teeth of the s lamanders Hynobius nigrescens nops py rhogaster. Enameloid differs from el in having a diff rent embryological or( esoderm vs. ectoderm), and in having a lower mineral content (Poole, 1967). urpose of thi study was t look for an relationship between the fine str cture, 141 This content downloaded from 157.55.39.59 on Mon, 17 Oct 2016 04:59:01 UTC All use subject to http://about.jstor.org/terms

Immunochemical and immunohistochemical studies, using antisera against porcine 25 kDa amelogenin, 89 kDa enamelin and the 13?17 kDa nonamelogenins, on immature enamel of the pig and rat

Enamel proteins were extracted from the newly formed layer of immature porcine enamel, and the 25 kDa amelogenin, 89 kDa enamelin and 13-17 kDa nonamelogenins were purified. Specific antisera were raised against these proteins. Antibodies specific to the C-terminal region (residues 149-173) of the 25 kDa amelogenin were generated by absorption of the anti-25 kDa amelogenin serum with 20 kDa amelogenin, which contains residues 1-148 of the antigen. Immunoelectro-transfer blotting of the extracted porcine enamel proteins showed that the anti-25 kDa amelogenin serum recognized the 25 kDa and other low and high molecular weight amelogenins. The C-terminal specific anti-25 kDa amelogenin serum reacted only with amelogenins having molecular weights over 23 kDa. The anti-89 kDa enamelin serum recognized the 89 kDa enamelin and lower molecular weight proteins, but neither the amelogenins nor the 13-17 kDa nonamelogenins. The antiserum against the 13-17 kDa nonamelogenins showed no cross reactivity to the 89 kDa enamelin, but recognized higher molecular weight nonamelogenins. In immunohistochemical preparations of the porcine tooth germs, the 25 kDa amelogenin-like immunoreactivity over immature enamel decreased in a gradient from the enamel surface to the middle layer. In the inner layer immunoreactivity was concentrated over the prism sheaths. The C-terminal specific 25 kDa amelogenin-like immunoreactivity was intense at the outer layer of immature enamel and decreased sharply toward the middle layer. Prism sheaths were intensely stained by the antiserum to the 13-17 kDa nonamelogenins.(ABSTRACT TRUNCATED AT 250 WORDS)

Three-dimensional computer graphics of enamel prisms in human teeth.

Using serial focussing transmitted light through a differential interference contrast (DIC) and three-dimensional image analysis, the orientation and the structural changes of normal and abnormal prisms were observed in tangential ground sections of human enamel. The outer layer of permanent enamel consisted of a mild undulation of enamel prisms. The neonatal line of deciduous enamel showed a change in the prism arrangement. The alternation of a constriction and a varicosity with a periodicity of about 3-5 μm was identified as the cross-striations of prisms. Double bordered and spiral prisms in the inner layer of permanent enamel temporarily appeared on the way to the formation of normal arcade prisms. Stunted prisms in the outer layer, however, maintained the shape during a relatively long distance.

Properties of phosphorylated 32 kd nonamelogenin proteins isolated from porcine secretory enamel

Enamel proteins were isolated from specific locations of permanent porcine incisors at various developmental stages, namely, the outer (young) and inner (old) secretory, and maturing (chalk-like in appearance) enamel. The selective adsorption of these matrix proteins onto hydroxyapatite (HA) crystals was investigated in the presence of dissociative agents. The results showed that the proteins with the highest adsorption affinity were present at the highest concentration in the vicinity of the ameloblasts, i.e., in the outer enamel layer; a substantial reduction of these proteins was observed in the older (inner) secretory enamel and in the tissue in the maturing stage. An interesting finding was that a group of proteins having molecular masses of 32 kd present only in the inner secretory enamel, adsorbed strongly onto the HA crystals and were potent inhibitors of HA crystal growth. This 32 kd group contains phosphorylated glycoproteins; they are rich in Pro, Glu, Gly, and Asp and the N-terminal sequence was LXQVPGRIPPGYGRPPTP-, having no resemblance to the reported sequences of amelogenins. It was also found that the 32 kd moieties remained only as trace constituents in the maturing enamel, suggesting that most of them were removed as soluble constituents in the tissue fluid or further degraded by enzymatic activity during the late secretory stage. The results obtained support the view that amelogenetic mineralization is regulated by the presence of various organic matter and, importantly, that their efficacy as inhibitors of mineralization may be modulated through their degradation.

Effect of fluoride in the apatitic lattice on adsorption of enamel proteins onto calcium apatites.

The selective adsorption of enamel proteins onto crystalline calcium apatites having different specific surface areas and various degrees of fluoride substitution was investigated. The proteins were obtained from the outer (close to the ameloblast) layer of secretory enamel of porcine permanent incisors. The adsorption of the enamel proteins was not affected markedly by the variation of specific surface area of the hydroxyapatites used as adsorbents, but it was enhanced substantially with increasing fluoride content in the crystalline lattice. Through the use of SDS- and two-dimensional polyacrylamide gel electrophoresis, it was shown that the originally secreted amelogenin (25 kd) as well as 60-90-kd and 5-6-kd molecules adsorbed most selectively onto the hydroxyapatites and that additional moieties having 21-23-kd and 14-18-kd molecular masses commenced to adsorb onto the apatitic surfaces with increasing degrees of fluoride substitution in the lattice. In contrast, the 20-kd amelogenin, a product partially degraded from the 25-kd amelogenin, showed no significant adsorption, even onto the fluoridated apatites. These results suggest that the retention of proteinaceous matrix in the developing enamel might be affected by the nature of the forming crystals.

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.

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Fluoride varnish (F-varnish) has been already used for treatment of hypersensitive dentin in clinic. In this study, F-varnish was examined in vitro the possibility of application for caries inhibition. Experiments were made in vitro of applications of F-varnish, containing 5% NaF or placebo-varnish with the intact enamel surface and fissure, for two weeks at 37°C twice a week, followed by 1, 2 or 3 weeks of washing with distilled water. Fluoride uptake and release, morphological observation, and acid solubility test on enamel blocks following treatment with F-varnish, or after washing were studied by means of electron probe microanalysis (EPMA), chemical analysis and sacanning electron microscopy (SEM).The fluoride uptake of F-varnish-treated enamel surface and fissure were increased, especially a large amount of CaF2 deposited on the outer surface layer and fissure of enamel. Although, CaF2 was released after washing for three weeks, fluoride was taken up at the depth of approximately 40μm. The acid solubility test proved that the acquisition of acid resistance was greater in F-varnish-treated enamel than in the control even after washing for three weeks. SEM of enamel surface showed that CaF2 was formed in the F-varnish-treated enamel, and clearly showed that there was an acid-resistant picture after perchloric acid-etching.Therefore, we suggest that F-varnish which applied to treat hypersensitive dentin may be effective in clinical use for caries inhibition, because the treatment time of enamel can be extended.