The effect of rate of eruption on periodontal ligament glycosylaminoglycan content and enamel formation in the rat incisor

The rate of eruption of rat mandibular incisors was either increased by cutting one tooth out of occlusion or eliminated by means of pinning. The effects of such changes in eruption rate on the sulphated glycosylaminoglycan content of the periodontal ligaments was analysed. The length of the enamel secretory zone and the composition of the developing enamel matrix protein was also compared. Sulphated glycosylaminoglycan content of the periodontal ligament increased fourfold (P<0.001) during accelerated eruption but decreased to a corresponding extent (P<0.001) in the absence of eruption, when compared with controls. The length of the enamel secretory zone was also significantly reduced in the immobilised teeth, although the protein content was similar compared with controls. The results demonstrate the differential response to varied eruption rates of the periodontal ligament and enamel, particularly in respect of the extracellular matrix. The data are consistent with the view that the ground substance of the periodontal ligament plays a role in the generation of the eruptive force.     

Tooth components of mandibular deciduous molars of Homo sapiens sapiens and Homo sapiens neanderthalensis: a radiographic study.

Tooth components of deciduous molars were measured from standardized radiographs of Homo sapiens sapiens and Homo sapiens neanderthalensis. Enamel height and width were greater in deciduous teeth of Homo sapiens sapiens than in Homo sapiens neanderthalensis and the differences were statistically significant (p less than 0.01). Dentin height showed no significant differences between the two groups, but enamel to floor of pulp chamber and pulp height and width dimensions were significantly greater in Homo sapiens neanderthalensis. Discriminant analysis carried out between groups, using deciduous tooth components, showed an accuracy of 98-100% for identification of Homo sapiens sapiens and 83-92% for identification of Homo sapiens neanderthalensis. The results obtained in this study on dental dimensions support the hypothesis of a distinct evolutionary line for Neanderthals.     

THE ENAMEL ULTRASTRUCTURE IN GIGANTOPITHECUS BLACKI FROM GUANGXI, CHINA

RecentlyanalysisoftheenamelprismpatterninanumberofNeogenehominoidsdocumentedthatdistinctdifferencesbetweenthevariantsofPatternⅢprismdoexistandseemtobeusedasataxonomicindicator(Gantt,1982,1983).However,becauseofinadequatesamplingandp0orlyunderstoodprocessesattheu1trastructural1evel,thevalue0fsuchstudieshastogainuniversalacceptabilityfordeterminingrelati0nshipinaconsistentandsystematic1nanner.Thereis0bviouslyconsiderablepotentia1interestinthestudyofename1prismpatternsandenamelmicr0structureinf…     

An enigmatic hypoplastic defect of the deciduous canine

A roughly circular hypoplastic defect restricted to the labial enamel surface of the deciduous canine is described. This pathology is quite common in available samples of Upper Paleolithic and Neolithic children and a cadaver sample of recent Calcuttans, affecting 44% to 70% of individuals. It is rare in a Neanderthal sample and in children from a clinical practice in Vancouver. The lesion occurs twice as commonly in the lower jaw. The defect appears to commence at or after birth owing to localized pressure on thin or nonexistent alveolar bone overlying the bulging crypt of the deciduous canine. Population differences in the incidence of the pathology probably reflect innate and acquired variation in hard and soft tissue thicknesses in this region.     

Factors affecting the distribution of enamel hypoplasias within the human permanent dentition

Frequencies and morphological and chronological distributions of enamel hypoplasias are presented by tooth type (permanent I1 to M2s), based on a sample of 30 prehistoric Amerindians with complete and unworn dentitions. There is nearly a tenfold variation in frequency of defects by tooth, ranging from 0.13 per mandibular second molar to 1.27 per maxillary central incisor. The six anterior teeth average between 0.70 and 1.27 defects/tooth, whereas the eight posterior teeth average between 0.43 and 0.13 defects/tooth. Earlier developing teeth, such as incisors, have earlier peak frequencies of defects (2.0-2.5 years), while later developing teeth, such as second molars, have subsequent peak frequencies (5.0-6.0 years). These variations are relevant when comparing hypoplasia data based on different teeth. Differences in hypoplasia frequencies among teeth are not solely due to variation in time of crown development, as is usually reported. Rather, there is evidence for biological gradients in susceptibility to ameloblastic disruption. Anterior teeth are more hypoplastic than posterior teeth. More developmentally stable "polar" teeth are more hypoplastic than surrounding teeth. Polar teeth may be more susceptible to hypoplasias because their developmental timing is less easily disrupted. In all teeth, hypoplasias are most common in the middle and cervical thirds. Crown development and morphological factors, such as enamel prism length and direction, may influence the development and expression of enamel surface defects.     

Mineral metabolism and microstructural defects in primate teeth.

There are numerous structural defects that occur in primate teeth due to variable calcification during certain growth stages. These interruptions are usually areas of hypomineralization in enamel and dentin which are referred to as Striae of Retzius and Hunter Shreger bands in the enamel or Incremental Lines of von Ebner and Contour Lines of Owen in the case of the dentin. The frequency of occurrence of these variations in mineralization can be related to such factors as growth tempo, dietary quality, state of health, and past disease episodes. Another structure that appears in the dentin is a region that fails to calcify and is referred to as Inter-globular Dentin. Our studies have shown that the microstructural quality of different species' dentition varies widely. Samples obtained from certain fre-ranging cercopithcoids show that these species have the least hypomineralizations while man has the most. Other primate species range between these two extremems with the pongids nearer to man in these characteristics, as previously noted by Sognnaes. Additionally, out initial study shows a great deal of diversity between prehistoric human populations in the microstructural quality of their teeth. We offer the tentative explanation that this variation is due to differences in the calcitying properties of the diet and hence a difference in the general state of their health.     

Measurements of tooth wear among Australian Aborigines: I. Serial loss of the enamel crown

The dental casts made from Aboriginal children during the course of a longitudinal growth study in Central Australia provided material for analyzing tooth wear under known environmental conditions. The wear facets produced on the occlusal surfaces were clearly preserved on the dental stone casts and recorded the progress of enamel attrition from ages 6 to 18. These casts were photographed and traced by electronic planimetric methods that automatically recorded the location and size of wear facets on the first and second permanent molars. These areas of worn tooth surface were compared to the total tooth surface. The worn surface was regressed on age to calculate wear rates of each tooth. Discriminant analyses were also performed to determine the significance of dental attrition differences between the sexes at each age group. The total wear on each tooth was highly correlated with age as expected but females wore their teeth at a significantly higher rate than males. The mandibular molars wore more rapidly than maxillary teeth in both sexes. The discriminant analysis successfully grouped 91% of the cases according to age and sex. Pattern of wear, the location, and size of wear facets also differed between age groups and sex. The questions of why there is a difference between male and female wear or why there is greater wear on one arch or arch region have no ready answers. The differing rates and pattern of dental wear do suggest that arch shape and growth rates may be the answer though it has yet to be tested. However, the occlusal surface wear is useful for age estimation in a population and provides a record of shifting masticatory forces during growth.     

On the nature of the opaque and translucent enamel regions of some macropodinae (Macropus giganteus,Wallabia bicolor and Peradorcas concinna)

Summary Teeth of three macropod species, M. giganteus, W. bicolor and P. concinna, have been studied using the techniques of light microscopy, scanning- and transmission-electron microscopy and hardness measurement. Light microscope observations showed that the teeth of these species had a translucent enamel region close to the dentine and an outer opaque enamel region at the tooth's surface. These regions were not related to the presence or absence of tubules which are a characteristic feature of marsupial enamel. Hardness tests showed that the opaque enamel was softer than the translucent enamel. Scanning electron microscope observations revealed that there was no correlation between any particular prism packing or orientation and the opaque and translucent enamel regions. Transmission electron microscope observations showed that the translucent enamel region consisted of well defined prisms and well packed, lath-like crystals, whereas the opaque enamel was disrupted by voids (which ranged in size from enlarged micropores to about 2 m in diameter in extreme cases) between crystals and some randomly oriented, loosely packed crystals. This disruption within the opaque enamel region was more common at prism boundaries but pockets of disrupted enamel were also found within prisms and interprismatic regions. The opacity of the enamel was caused by scattering of light from the voids. The ultrastructure of the opaque enamel region indicated that this region was hypomineralized; hardness tests and polarized light microscope observations were consistent with these results.     

Fine structure of the dental enamel in the Family Callitrichidae (Ceboidea,primates)

The fine structure of the dental enamel was intensively examined in the Family Callitrichidae.Leontopithecus rosalia has the nonserial pattern, butCallimico goeldii andSaguinus midas appear more or less modified from the typical nonserial pattern asSaimiri sciureus has (see Figs. 1 & 5). On the other hand,Callithrix jacchus andCebuella pygmaea attain to the primitive stage of the multiserial pattern (see Figs. 4 & 6). So far as the structural patterns of the dental enamel are concerned, a serial trend is confirmed in the Callitrichidae; extending from the genusLeontopithecus through the generaCallimico andSaguinus to the generaCallithrix andCebuella. The genusSaguinus shows extremely wide interspecific variation in the fine structure of the dental enamel, ranging fromS. leucopus with the most primitive features toS. bicolor with the most advanced (see Figs. 2 & 3). The rows of enamel prisms are slightly twisted mesiodistally in the former species, but strongly folded in the latter. This reflects transitional stages from the nonserial pattern to the multiserial. As a whole, however, the genusSaguinus is still regarded as nonserial. Thus, there is a slight, but important gap between the genusSaguinus andCallithrix, as shown by the decussation of clusters (see Fig. 5), as well as by other characters.     

Microevolution of outer and inner structures of upper molars in Late Pleistocene and Early Holocene humans

In this study, we investigate outer and inner variations of upper second molars (UM2) for Late Pleistocene and Early Holocene modern humans, at a key-period in our evolutionary history associated with major sociocultural, economic and environmental changes. Non-metric traits have been recorded on 89 UM2 of 66 Upper Paleolithic, Mesolithic and Neolithic individuals, and 40 UM2 have been microscanned to assess variations in enamel thickness (ET) distribution and enamel–dentine junction (EDJ) shape. Major changes are found between Mesolithic and Neolithic periods: a decrease of the metacone expression combined with an increase of the hypocone development; an increase of the heterogeneity of ET distribution between lingual and buccal cusps; and an increase of the development of the dentine horn tips corresponding to the hypocone and, to a lesser extent, to the metacone. These morphological modifications could be linked to the masticatory functional changes associated with the transition to agriculture.