Scanning electron microscopic studies of the rat incisor odontoblastema

Summary A scanning electron microscopic technique was used to investigate the surface structure of dentinogenically active odontoblasts.Thin pieces of rat incisors were fixed, rapidly frozen, freezedried at -70° C and fractured to expose new surfaces prior to examination in the SEM. Differences in the appearance of odontoblastic cell surfaces were seen, with the most extensive ridge formations at the distal part of the sides of the odontoblasts. The predentine area displayed a spongy structure which contrasted to the compact appearance of dentine. Results are discussed in relation to previous studies at the light microscopic and transmission electron microscopic levels.This study was supported by the Swedish Medical Research Council and the Faculty of Odontology, University of Göteborg, Göteborg, Sweden.     

中国近代人群上颌前臼齿釉质-齿质连接面形状的三维几何形态测量

牙齿的釉质-齿质连接面(EDJ或Enamel-dentine junction)是釉质表面(OES或Outer enamel surface)形态的发生基础,其形态特征在牙齿发育早期形成,与遗传因素密切相关。为探讨EDJ形状在近代人群中的变异特点,本文使用显微断层扫描技术(micro-CT或micro-computed tomography)扫描了100例采自华中地区近代农业人群的上颌前臼齿(P~3和P~4各50例),并复原了EDJ表面三维结构。采用基于30个标志点(landmark)和半标志点(semi-landmark)的三维几何形态测量量化了上颌前臼齿EDJ表面形状。结果显示,牙齿内部舌侧尖区域变异程度较颊侧尖大。在人群内部,上颌前臼齿的变异方式主要表现在1)颊舌尖相互靠近或远离造成的咬合面深浅的差别;2)颊舌尖齿质最高点(dentine horn)相对高度的差异;3)舌侧尖近远中方向尺寸的变化;4)P~3颊侧尖近中脊的内收与外扩造成的整个轮廓形状的对称性变化;5)P~4整个咬合面轮廓MD/BL比值的大小差别。基于以上发现,本文进一步探讨了上颌前臼齿EDJ形状在两性或不同时代标本之间是否存在差异。平均形状的比较发现男性上颌前臼齿的舌尖相对较宽,颊侧尖近中脊相对较低。但主成分分析(Principal component analysis)和置换检验(Permutation test)显示两性差异未达到显著水平。同样,从新石器时代以来的各样本组之间在EDJ形状上的差别也没有达到统计上的显著水平。这一结果提示中国近代人群上颌前臼齿EDJ表面形状的变异特点至少可以追溯到全新世早期(本文使用标本最早来自距今6000-7000年前的新石器时代阶段)。未来EDJ的三维几何形态测量可通过扩大标本数量进一步探讨不同性别、不同地区人群、不同演化阶段之间的差异。     

Tusk abnormalities in wild boar (<Emphasis Type="Italic">Sus scrofa</Emphasis> L.)

This paper describes pathological alterations in the permanent canines (tusks) of four male wild boars. The mandibular tusks of all individuals, and also some of the maxillary tusks, exhibited an extended enamel hypoplasia in their apical portion, denoting an impairment of secretory ameloblast function. Moreover, the pulp cavities of the mandibular tusks were exposed through cleft-like openings in the wear (whetting) surfaces of the teeth. Presence of a plug of reparative dentine within the pulp cavity was observed in a split mandibular tusk of one individual. In a second boar, the presence of a plug of reparative dentine within the pulp cavity of the mandibular tusks was indicated radiographically. These findings suggested a reparation process attempting to demarcate a vital, apical pulp portion from a necrotic, incisal portion. The enamel hypoplasias observed in the teeth are regarded to be sequelae of the pulp inflammation caused by bacterial invasion in the mandibular tusks. Most likely, bacterial invasion of the dental pulp occurred through the cleft-like openings in the tusks whetting surfaces, the openings resulting from insufficient formation of secondary dentine. It is, however, also conceivable that pulp inflammation and partial necrosis occurred as a consequence of bacterial invasion of patent dentinal tubules, and that the openings in the whetting surface developed secondarily as a consequence of the pulp changes. One mandibular tusk showed marked signs of resorption apically, suggesting a spread of the inflammation from the pulp into the periodontium.     

Trophic ecology of two savanna grazers,blue wildebeest <Emphasis Type="Italic">Connochaetes taurinus</Emphasis> and black wildebeest <Emphasis Type="Italic">Connochaetes gnou</Emphasis>

The feeding niches and trophic ecology of two South African grazers, blue wildebeest Connochaetes taurinus and black wildebeest Connochaetes gnou, are compared using stable carbon and nitrogen isotope data from feces and tooth dentine collagen. As sympatric, closely related taxa predicted to occupy similar trophic positions, the blue and black wildebeest provide a good model for studying the mechanisms of coexistence and macroevolution in mammals. Data from feces collected from a single reserve in the Free State Province reveal different trophic behaviors between two herds of blue wildebeest and between both compared with a single herd of black wildebeest. These data suggest that sympatric coexistence of blue and black wildebeest is facilitated by differential niche occupation at family group or herd levels, rather than between species. However, such separation does not occur over longer time scales: results from dentine collagen support the hypothesis that the two species are indistinct in terms of trophic behavior, although blue wildebeest show more feeding flexibility, probably because of their wider habitat tolerance range. Similarities in premaxillary width of males and females of both species also suggest that both species are adapted to similar feeding styles. Thus, it is unlikely that changes in trophic behavior provided the trigger for divergence of the black from the blue wildebeest lineage in the Middle Pleistocene. We argue that the case of these two species represents an example of speciation that was not driven by resource competition, as is often assumed for many turnover events in mammalian evolution. We briefly discuss a previous suggestion that links black wildebeest evolution to their more territorial breeding behavior associated with Middle-to-Late Pleistocene landscape changes in southern Africa.     

A radiographic and histological study of modern human lower first permanent molar root growth during the supraosseous eruptive phase

There is increasing focus on the relationship between root growth and the eruptive process in studies of primate dental development, and the first permanent molar (M1) is regarded as a key tooth in many of these comparative studies. In this study of modern human M(1)s, histological and radiographic data were compared. Rates of root extension were determined histologically in 20 M(1)s from individuals of known sex using data for daily incremental markings and the orientation of accentuated lines in root dentine. Mean values at the mesiobuccal enamel cervix were 4.3-5.4 microm per day and then rose to a maximum of 6.7-8.4 microm per day during the first 5mm of root growth before gradually declining again to 2.8-3.6 microm per day towards apical closure. A sample of 101 orthopantomograms of children, where M(1)s were between the stages of alveolar eruption and complete eruption, were then used to determine total mesial tooth height and mesial and distal root lengths at four successive stages of eruption. At complete eruption, mean values for mesial and distal root lengths were 8-10mm, respectively. Expressed as a percentage total of mesial tooth height these averaged 45.6-56.2%. Maximum rates of M(1) eruption occur just prior to gingival emergence but did not coincide with maximum rates of root extension in this study. These results emphasise that rates of eruption and rates of root growth do not follow the same pattern of change during the supraosseous eruptive phase. They highlight the need for greater consideration of the role of the eruptive process in explaining differences in gingival emergence times in comparative studies of modern humans and fossil hominins.     

A three-phase liquid chromatographic method for δC analysis of amino acids from biological protein hydrolysates using liquid chromatography–isotope ratio mass spectrometry

We report a three-phase chromatographic method for the separation and analysis of δ¹³C values of underivatized amino acids from biological proteins (keratin, collagen, and casein) using liquid chromatography–isotope ratio mass spectrometry (LC–IRMS). Both precision and accuracy of δ¹³C values for standard amino acid mixtures over the range of approximately 8 to 1320 ng of carbon per amino acid on the column were assessed. The precision of δ¹³C values of amino acids was found to be better at higher concentrations, whereas accuracy improved at lower concentrations. The optimal performance for this method was achieved with between 80 and 660 ng of carbon of each amino acid on the column. At amino acid amounts lower than 20 ng of carbon on the column, precision and accuracy may become compromised. The application of this new three-phase chromatographic technique will allow the analysis of δ¹³C of amino acids to be carried out as a routine method and benefit fields of research such as biomedicine, forensics, ecology, nutrition, and palaeodiet reconstruction in archaeology.     

Induction of transforming growth factor-beta 1 on dentine pulp cells in different culture patterns

Recent studies have documented that TGF-beta1 takes part in dental pulp tissue repair. Moreover, dental pulp cells have the potential to differentiate into odontoblast-like cells and produce reparative dentine in this process. However, the molecular mechanisms and potential interactions between TGF-beta1 and dental pulp cells are not clear due to the complexity of the pulp/dentine microenvironment. In this study, we investigated the induction of TGF-beta1 on the dental pulp cells in cell culture, tissue culture and three-dimensional culture patterns. These results demonstrated that TGF-beta1 significantly increased the proliferation of cells and activity of ALPase. Dental pulp cells cultured in the presence of TGF-beta1 formed mineralization nodules. In the organ culture, dental pulp cells treated with TGF-beta1 differentiated into odontoblast-like cells and formed a pulp-dentinal complex; and TGF-beta1 significantly induced synthesis of dentine relative proteins DSPP, DMP-1. The dental pulp cells share some characteristics of the odontoblast, such as a parallel arrangement with columnar form and a unilateral cell process. Together, these data indicate that TGF-beta1 can make dental pulp cells differentiated into odontoblast-like cells and form the pulp-dentinal complex. Moreover, these results suggest that TGF-beta1 is an important regulatory factor in odontoblast differentiation during tooth development and pulp repair.     

Visualization of initial bacterial colonization on dentine and enamel in situ

Bacterial colonization of dentine is of high relevance in cariology, endodontology and periodontology. The aim of the present in situ study was to establish recent methods for visualization and quantification of initial bacterial adherence to dentine in comparison to enamel. For this purpose, bovine enamel and dentine slabs were fixed on buccal sites of individual upper jaw splints worn by 6 subjects for 30 min, 120 min and 360 min, respectively. Adherent bacteria on the slabs were visualized and quantified with DAPI-staining (4′,6-diamidino-2-phenylindole) and fluorescence in situ hybridization (FISH) of streptococci and eubacteria using the CLSM (confocal laser scanning microscopy) as well as an epifluorescence microscope. In addition, the number of colony forming units was quantified after desorption. Representative samples were processed for SEM (scanning electron microscopy) and TEM (transmission electron microscopy). All methods clearly indicated that a significantly higher number of bacteria adhered to dentine than to enamel. Furthermore, the amount of bacteria on the dentine increased with increasing oral exposure time, but remained rather constant on the enamel. The CLSM allowed visualization of bacteria in the dentinal tubules. Bacteria were found preferentially at the openings of the dentine tubules, but were distributed randomly on the enamel.In conclusion, the adopted methods are suitable for visualization and quantification of bacterial adhesion to dentine. Even the initial bacterial colonization of dentine is much more pronounced than bacterial adherence to the enamel.     

The oldest holocephalan (Chondrichthyes) from the Middle Devonian of the Boulonnais (Pas-de-Calais, France)

The Couderousse Member of the Blacourt Formation in the Banc-Noir quarry, Ferques inlier, Boulonnais (Pas-de-Calais, France) has yielded a tooth plate whose morphology is similar to that of Synthetodus, which is considered a holocephalan. Its histology is made of an outer enameloid-like tissue, and an inner trabecular dentine. Its occlusal surface shows a bean-shaped bulge. This tooth plate was prepared from a limestone that is dated from the Middle–Upper varcus Conodont Zone, that is lower upper Givetian. This limestone has also yielded a Pokorninella bricae–Rothpletzella–Tentaculites assemblage, which is indicative of an environment of the inner to middle marine platform boundary. This specimen appears to be the oldest confirmed holocephalan (‘bradyodont’) tooth plate for which the name Melanodus loonesi nov. gen. et sp. is erected.     

Stable carbon and nitrogen isotope ratio profiling of sperm whale teeth reveals ontogenetic movements and trophic ecology

Teeth from male sperm whales (Physeter macrocephalus) stranded in the North-eastern Atlantic were used to determine whether chronological profiles of stable isotope ratios of C (δ¹³C) and N (δ¹⁵N) across dentine growth layers could be used to detect known ontogenetic benchmarks in movements and trophic ecology. Profiles showed a general decrease in δ¹³C (median = 1.91‰) and an increase in δ¹⁵N (median = 2.42‰) with age. A marked decline in δ¹³C occurred for all 11 teeth around 9–10 years and again for six individuals around 20 years. After the early twenties the δ¹³C continued to decline with age for all teeth. These results are consistent with males segregating from natal groups in low latitudes with the onset of puberty between 4 and 15 years and gradually dispersing pole-ward into ¹³C-depleted temperate waters. Penetration into further depleted, productive high latitudes after the age of 20 might facilitate the spurt of accelerated growth rate observed around this age. Breeding migrations back to lower latitudes were not reflected in the δ¹³C profiles possibly due to being short compared to the time spent feeding in high latitudes. The timings of marked isotopic change in the δ¹⁵N profiles reflect those of the δ¹³C profiles, suggesting a link between dietary changes and movements. The observed increase in δ¹⁵N with age is likely to be caused by a trophic level increase as males grow in size, probably feeding on larger prey. An additional explanation could be that, in the higher latitudes of the North Atlantic, the main prey source is the high trophic level squid Gonatus fabricii. Also, the lower latitudes from where males disperse are depleted in basal ¹⁵N. Profiles of δ¹³C and δ¹⁵N in sperm whale teeth gathered from different regions, sexes, and periods in time, could provide a unique way to understand the ecology of this species across different oceans.