The Neandertal lower right deciduous second molar from Trou de l'Abîme at Couvin, Belgium

A human lower right deciduous second molar was discovered in 1984 at the entrance of Trou de l'Abîme at Couvin (Belgium). In subsequent years the interpretation of this fossil remained difficult for various reasons: (1) the lack of taxonomically diagnostic elements which would support its attribution to either Homo (sapiens) neanderthalensis or H. s. sapiens; (2) the absence of any reliable chronostratigraphic interpretation of the sedimentary sequence of the site; (3) the contradiction between archaeological interpretations, which attributed the lithic industry to a transitional facies between the Middle and Early Upper Palaeolithic, and the radiocarbon date of 46,820 ± 3,290 BP obtained from animal bone remains associated with the tooth and the flint tools.Thanks to recent progress regarding these three aspects, the tooth from Trou de l'Abîme may now be studied in detail. Analyses of the morphology and enamel thickness of the fossil yielded diagnostic characters consistent with an attribution to Neandertals. Re-examination of the lithic industry of Couvin shows that it corresponds to the late Middle Palaeolithic rather than a transitional facies. Furthermore, a new analysis of the site stratigraphy indicates that the unit situated above the archaeological layer in which the tooth was found is probably a palaeosol of brown soil type. Comparison with the regional cave sequences as well as with the reference sequence from the Belgian loess belt tends to show that the most recent palaeosol of this type is dated between 42,000 and 40,000 BP. This is consistent with both a recently obtained AMS result at 44,500 BP and the published conventional date.     

A survey of carbonic anhydrase mRNA expression in enamel cells

Enamel formation requires rigid control of pH homeostasis during all stages of development to prevent disruptions to crystal growth. The acceleration of the generation of bicarbonate by carbonic anhydrases (CA) has been suggested as one of the pathways used by ameloblasts cells to regulate extracellular pH yet only two isozymes (CA II and CA VI) have been reported to date during enamel formation. The mammalian CA family contains 16 different isoforms of which 13 are enzymatically active. We have conducted a systematic screening by RT-PCR on the expression of all known CA isoforms in mouse enamel organ epithelium (EOE) cells dissected from new born, in secretory ameloblasts derived from 7-day-old animals, and in the LS8 ameloblast cell line. Results show that all CA isoforms are expressed by EOE/ameloblast cells in vivo. The most highly expressed are the catalytic isozymes CA II, VI, IX, and XIII, and the acatalytic CA XI isoform. Only minor differences were found in CA expression levels between 1-day EOE cells and 7-day-old secretory-stage ameloblasts, whereas LS8 cells expressed fewer CA isoforms than both of these. The broad expression of CAs by ameloblasts reported here contributes to our understanding of pH homeostasis during enamel development and demonstrates its complexity. Our results also highlight the critical role that regulation of pH plays during the development of enamel.     

Development of Amelogenin-chitosan Hydrogel for In Vitro Enamel Regrowth with a Dense Interface

Biomimetic enamel reconstruction is a significant topic in material science and dentistry as a novel approach for the treatment of dental caries or erosion. Amelogenin has been proven to be a critical protein for controlling the organized growth of apatite crystals. In this paper, we present a detailed protocol for superficial enamel reconstruction by using a novel amelogenin-chitosan hydrogel. Compared to other conventional treatments, such as topical fluoride and mouthwash, this method not only has the potential to prevent the development of dental caries but also promotes significant and durable enamel restoration. The organized enamel-like microstructure regulated by amelogenin assemblies can significantly improve the mechanical properties of etched enamel, while the dense enamel-restoration interface formed by an in situ regrowth of apatite crystals can improve the effectiveness and durability of restorations. Furthermore, chitosan hydrogel is easy to use and can suppress bacterial infection, which is the major risk factor for the occurrence of dental caries. Therefore, this biocompatible and biodegradable amelogenin-chitosan hydrogel shows promise as a biomaterial for the prevention, restoration, and treatment of defective enamel.     

Prevalence and age at development of enamel hypoplasias in Mexican children

Enamel hypoplasias, deficiencies in enamel thickness resulting from disturbances during the secretory phase of enamel development, are generally believed to result from nonspecific metabolic and nutritional disruptions. However, data are scare on the prevalence and chronological distributions. of hypoplasias in populations experiencing mild to moderate malnutrition. The purpose of this article is to present baseline data on the prevalences and chronological distributions of enamel hypoplasias, by sex and for all deciduous and permanent anterior teeth, in 300 5 to 15-year-old rural Mexican children. Identification of hypoplasias was aided by comparison to a published standard (Federation Dentaire Internationale: Int. Dent. J. 32(2):159-167, 1982). The location of defects, by transverse sixths of tooth crowns, was used to construct distributions of defects by age at development. One or more hypoplasias were detected in 46.7% (95% CI = 40.9-52.5%) of children. Among the unworn and completely erupted teeth, the highest prevalence of defects was found on the permanent maxillary central incisors (44.4% with one or more hypoplasias), followed by the permanent maxillary canine (28.0%) and the remaining permanent teeth (26.2 to 22.2%) Only 6.1% of the completely erupted and unworn deciduous teeth were hypoplastic. The prevalence of enamel defects on the permanent teeth was up to tenfold greater than that found in studies of less marginal populations that used the FDI method. The prevalence of defects in transverse zones suggests a peak frequency of hypoplasias during the second and third years for the permanent teeth, corresponding to the age at weaning in this group. In the deciduous teeth, a smaller peak occurs between 30 and 40 weeks post gestation. The frequency of defects after three years of age is slightly higher in females than males, suggesting a sex difference in access to critical resources.     

Aluminum concentrations in human deciduous enamel and dentin related to dental caries

The aluminum (Al) concentrations in the enamel and dentin of 314 human deciduous teeth were determined in order to examine the relationship between Al and dental caries. The sample teeth were divided into three groups: the sound tooth group, carious tooth group and filled tooth group. The teeth of the carious tooth group were further classified into three groups depending on the stage of caries. The Al content was determined using graphite furnace atomic absorption spectrometry. In both the enamel and dentin, the Al concentrations were unaffected by sex, but did depend on tooth type. In enamel, the Al concentration was significantly higher in the sound tooth group (42.8 +/- 37.3 microg/g) than in the three carious groups (20.7 +/- 17.1-24.9 +/- 22.0 microg/g) and the filled tooth group (27.3 +/- 25.5 microg/g). As for dentin, the Al concentration was also significantly higher in the sound tooth group (36.2 +/- 35.1 microg/g) than in the three carious groups (15.1 +/- 13.3-24.5 +/- 23.4 microg/g) and the filled tooth group (17.2 +/- 20.6 microg/g). Even when analyzing incisors alone, the Al concentrations were significantly higher in the sound tooth group than in the other groups, for both enamel and dentin. Furthermore, the Al levels in carious enamel and dentin did not decrease with the advance of caries. These findings indicated that the deciduous teeth containing higher Al concentrations on average had less caries than the teeth with lower Al concentrations, and suggest that Al acts as a possible cariostatic agent by itself.     

Fibrils in marsupial enamel tubules

Summary Serial etching of cross-sectioned prisms in undecalcified adult marsupial enamel from different species, revealed distinct cylindrical acid-resistant fibrils that were demonstrable by light microscopy and by scanning electron microscopy. No fibrils were found in the enamel of Vombatus.The fibrils and the organic matrix in the remainder of the enamel stain differently. The fibrils project from the center of prisms or the borderline between prisms and interprismatic substance.It is concluded that the fibrils are chemically different from the organic matrix in the enamel, that they constitute the compact, homogenous, and morphologically well defined organic contents of the tubules in adult marsupial enamel.Since most of the material was obtained from dry museum crania, it is concluded that the fibrils are not destroyed by prolonged drying.The scanning electron micrographs were taken at the Electron Microscopical Unit for Biological Sciences, Oslo, Norway.     

Enamel dictates whole tooth deformation: A finite element model study validated by a metrology method

In order to understand whole tooth behavior under load the biomechanical role of enamel and dentin has to be determined. We approach this question by comparing the deformation pattern and stiffness of intact teeth under load with the deformation pattern and stiffness of the same teeth after the enamel has been mechanically compromised by introducing a defect. FE models of intact human premolars, based on high resolution micro-CT scans, were generated and validated by in vitro electronic speckle pattern interferometry (ESPI) experiments. Once a valid FE model was established, we exploit the flexibility of the FE model to gain more insight into whole tooth function. Results show that the enamel cap is an intrinsically stiff biological structure and its morphology dictates the way a whole tooth will mechanically behave under load. The mechanical properties of the enamel cap were sufficient to mechanically maintain almost its entire stiffness function under load even when a small defect (cavity simulating caries) was introduced into its structure and breached the crown integrity. We conclude that for the most part, that enamel and not dentin dictates the mechanical behavior of the whole tooth.     

A mouse model expressing a truncated form of ameloblastin exhibits dental and junctional epithelium defects

Ameloblastin (AMBN) is the second most abundant extracellular matrix protein produced by the epithelial cells called ameloblasts and is found mainly in forming dental enamel. Inactivation of its expression by gene knockout results in absence of the enamel layer and its replacement by a thin layer of dysplastic mineralized matrix. The objective of this study was to further characterize the enamel organ and mineralized matrix produced in the AMBN knockout mouse. However, in the course of our study, we unexpectedly found that this mouse is in fact a mutant that does not express the full-length protein but that produces a truncated form of AMBN. Mandibles from wild type and mutant mice were processed for morphological analyses and immunolabeling. Microdissected enamel organs and associated matrix were also prepared for molecular and biochemical analyses. In incisors from mutants, ameloblasts lost their polarized organization and the enamel organ detached from the tooth surface and became disorganized. A thin layer of dysplastic mineralized material was deposited onto dentin, and mineralized masses were present within the enamel organ. These mineralized materials generated lower backscattered electron contrast than normal enamel, and immunocytochemistry with colloidal gold revealed the presence of amelogenin, bone sialoprotein and osteopontin. In addition, the height of the alveolar bone was reduced, and the junctional epithelium lost its integrity. Immunochemical and RT–PCR results revealed that the altered enamel organ in the mutant mice produced a shorter AMBN protein that is translated from truncated RNA missing exons 5 and 6. These results indicate that absence of full-length protein and/or expression of an incomplete protein have direct/indirect effects beyond structuring of mineral during enamel formation, and highlight potential functional regions on the AMBN molecule.     

鳜牙齿形态结构及与不同种属间比较观察

牙齿是肉食性鱼类重要的摄食器官。为探究鳜(Siniperca chuatsi)牙齿形态结构,采用解剖镜观察了鳜牙齿分布、形态与数量。并比较其与大眼鳜(S. kneri)、斑鳜(S. scherzeri)及中国少鳞鳜(Coreoperca whiteheadi)牙齿差异。采用茜素红染色、组织切片、扫描电镜、X射线能谱及红外光谱观察并检测了鳜牙齿结构、元素组成和化学成分。结果显示,鳜牙齿具上颌齿、下颌齿、犁齿、腭齿和咽齿。其中,上颌齿前端有犬齿,其余为绒毛状齿;下颌齿最内列有犬齿,其余为绒毛状齿;犁齿、腭齿、咽齿均为绒毛状齿。鳜和大眼鳜下颌齿列数为3列,斑鳜和中国少鳞鳜为4列。茜素红染色显示,犬齿和绒毛状齿外层均为透明的牙釉质,内层为包裹髓腔的牙本质;组织切片显示,牙本质结构疏松,内有许多孔隙;牙尖部分形成牙釉质帽;中央为髓腔,内有牙髓组织。扫描电镜显示,犬齿和绒毛状齿表面均由釉柱组成,釉质层有釉柱横纹。X射线能谱显示,犬齿和绒毛状齿主要元素都为碳(C)、氧(O)、氮(N)、钙(Ca)和磷(P)。红外光谱显示,犬齿和绒毛状齿主要无机成分为碳酸羟基磷灰石。结果表明,鳜牙齿较发达,上、下颌齿有犬齿,犬齿和绒毛状齿结构与组成基本相似。