The effect of unerupted permanent tooth crowns on the distribution of masticatory stress in children

Human mothers wean their children from breast milk at an earlier developmental stage than do ape mothers, resulting in human children chewing solid and semi-solid foods using the deciduous dentition. Mechanical forces generated by chewing solid foods during the post-weaning period travel through not only the deciduous teeth, but also the enamel caps of the developing permanent teeth within the maxilla and mandible, which are not present in the adult face. The effects of mechanical stress propagating through these very stiff structures have yet to be examined. Based on a heuristic model, we predicted that the enamel of the embedded developing teeth would act to reduce stresses in the surrounding bony elements of the juvenile face. We tested this hypothesis by simulating occlusal loading in a finite element (FE) model of a child's cranium with a complete set of deciduous teeth and the first permanent molars embedded in the bony crypt in the maxilla. We modeled bone and enamel with appropriate material properties and assessed the effect of embedding high-stiffness enamel structures on stress distribution in the juvenile face. Against expectation, the presence of unerupted enamel caps does not affect the magnitude or location of stresses in the juvenile face. Our results do not support the hypothesis that the unerupted secondary teeth act to moderate stresses in the juvenile face.     

Age and sequence of permanent-tooth emergence among Khasis

The times and emergence of permanent teeth were ascertained by examining 1,263 Khasi children (615 males and 648 females), aged 5 to 15 years. Gingival emergence of the first 28 permanent teeth was recorded and the data were subjected to probit analysis to compute the mean (and standard deviation) emergence time of each individual tooth. Tooth emergence in females was markedly earlier than in males, and canines were most advanced in this respect. Females acquired all their teeth in shorter time span (5.5 years) than males (6.5 years). There were no decisive sex differences in the sequence of tooth emergence. The differences in emergence times between antimeres were statistically nonsignificant. The length of hiatus between two active emergence dental stages was shorter for the maxilla than for the mandible. It occurred between lateral incisor and first premolar in the maxilla of both the sexes, while in case of the mandible, it was spaced between lateral incisor and canine. The Khasis showed early emergence when compared to other populations. The findings support the earlier reports that the controls of deciduous-tooth emergence continue to play some part in emergence of the permanent dentition, especially the first permanent teeth that emerge.     

Dental developmental pattern of the Neanderthal child from Roc de Marsal: a high-resolution 3D analysis

The assessment of the degree of similarity or difference between Neanderthals and modern humans in their patterns of dental development remains a controversial matter. Here we report results from the microtomographic-based (SR-μCT) high-resolution structural investigation of the maxilla and mandible of the Neanderthal child from Roc de Marsal, Dordogne, France (likely from OIS 5a). Following their virtual extraction and 3D rendering, we assessed the maturational stage of each of the 41 dental elements (20 deciduous and 21 permanent) forming its mixed dentition. By using a Bayesian approach, we calculated the probability that its deciduous and permanent mandibular sequences are found within the extant human variation as illustrated by a tomographic CT-based sub-sample of 32 children (deciduous dentition) and a panoramic radiographic- and CT-based whole sample of 343 living children (permanent dentition). Results show that neither the deciduous nor the permanent mandibular sequences displayed by Roc de Marsal are precisely found within our modern comparative files. In both sequences, the most influential factor is represented by a slight discrepancy in the Neanderthal child between the stage of mineralization of the first molar, which is proportionally advanced, and the maturational level reached by its incisors, which are proportionally delayed. Following a quantitative volumetric analysis of the deciduous teeth, we suggest that this characteristic may be related to differences between Neanderthals and modern humans in absolute dental size and relative size proportions between front and cheek teeth, as well as to structural differences in dental tissue proportions.     

Sequences and timing of dental eruption in Bolivian captive-born squirrel monkeys (Saimiri sciureus)

Squirrel monkeys, colony-born from Bolivian parents, were studied to establish the sequences and timing of eruption for deciduous and permanent teeth. Infants were born with a naked gingiva, and in only one monkey was di₁ present at birth. The eruption of the lower deciduous teeth preceded their upper counterparts with the exception of di2, dc, and dpm2. No significant differences were found between the right and left quadrants of the mandible and maxilla. No significant sexual differences were found in the age of eruption. By the age of 14 weeks, all deciduous teeth had erupted. The sequence of eruption of the replacement teeth was different from that of milk teeth. The differences lie in the delayed eruption of canine teeth and in the inverted sequence, from the back to the front, of the premolar series. Significant sexual differences were found in total eruption (TE) for PM₃ and I² (P < 0.05) and highly significant differences (P < 0.01) in TE and initial eruption (IE) for C¹, females being more precocious than males. The age at which monkeys completed dental eruption was highly variable, 103–119 weeks for males and 89–112 weeks for females. Differences were found when our results were compared with those of Long and Cooper [1968] for Colombian squirrel monkeys.     

Enamel hypoplasia in the Middle Pleistocene hominids from Atapuerca (Spain)

The prevalence and chronology of enamel hypoplasias were studied in a hominid dental sample from the Sima de los Huesos (SH) Middle Pleistocene site at the Sierra de Atapuerca (Burgos, northern Spain). A total of 89 permanent maxillary teeth, 143 permanent mandibular teeth, and one deciduous lower canine, belonging to a minimum of 29 individuals, were examined. Excluding the antimeres (16 maxillary and 37 mandibular cases) from the sample, the prevalence of hypoplasias in the permanent dentition is 12.8% (23/179), whereas the deciduous tooth also showed an enamel defect. No statistically significant differences were found between both arcades and between the anterior and postcanine teeth for the prevalence of hypoplasias. In both the maxilla and the mandible the highest frequency of enamel hypoplasias was recorded in the canines. Only one tooth (a permanent upper canine) showed two different enamel defects, and most of the hypoplasias were expressed as faint linear horizontal defects. Taking into account the limitations that the incompleteness of virtually all permanent dentitions imposes, we have estimated that the frequency by individual in the SH hominid sample was not greater than 40%. Most of the hypoplasias occurred between birth and 7 years (N = 18, X = 3.5, SD = 1.3). Both the prevalence and severity of the hypoplasias of the SH hominid sample are significantly less than those of a large Neandertal sample. Furthermore, prehistoric hunter-gatherers and historic agricultural and industrial populations exhibit a prevalence of hypoplasias generally higher than that of the SH hominids. Implications for the survival strategies and life quality of the SH hominids are also discussed. © 1995 Wiley-Liss, Inc.     

Age determination and body growth of the Common duiker Sylvicapra grimmia(Mammalia)

Age determination in the Common duiker Sylvicapra grimmia was investigated by analysis of tooth eruption and replacement sequence, incremental lines of tooth cementum and tooth wear in a unique collection of 48 known-age skulls, and also by analysis by post-natal body growth in known-age duiker. In both the mandible and maxilla, permanent molariform teeth were fully erupted and in wear by 26 months of age. There was little variation in the age of eruption and replacement of all molariform teeth, making this a particularly useful feature of the duiker for age determination purposes. In contrast, the variability in eruption of the incisiforms, coupled with the difficulty in distinguishing deciduous incisiforms from the permanent counterparts, placed an unexpected limitation on the use of these teeth. Although the apparent linear relationship between tooth attrition and age has potential for further investigation as an age determination technique, the cementum annuli were not correlated with chronological age. Theoretical Von Bertalanffy equations were used to analyse body growth with age. It was concluded that because the asymptote of growth was reached at such an early age, and because there is so much individual variation in growth, body growth, including horn growth, is of very limited value for age determination. Female duiker were significantly larger than males.     

Localized enamel hypoplasia of human deciduous canine teeth: prevalence and pattern of expression in rural Pakistan

Localized hypoplasia of the labial surface of deciduous canine teeth is a widely reported enamel defect, the etiology of which remains enigmatic. Published frequencies for this defect are based on small or biased samples from prehistoric and clinical contexts. In this study I report the prevalence and pattern of expression of this defect among 113 schoolchildren of Harappa village, Punjab Province, Pakistan. The labial surface of deciduous canines of children between the ages of 5 and 8 years was examined using a penlight; age, sex, stature, and socioeconomic status were also recorded. The defect occurs in 34.5% of the subjects studied and in 14.6% of the teeth examined. No significant association was found between the presence of the defect and gender, socioeconomic status, stature, or side of the jaw. The hypoplastic lesion occurs more frequently in the mandible than in the maxilla, and bilateral expressions are less common than unilateral expressions. These results confirm specific aspects of earlier studies and imply that localized (circular) enamel hypoplasia of deciduous teeth, unlike linear enamel hypoplasia, is not a marker of systemic growth disruption.     

Coronal breadth of human primary anterior teeth

Original data for mesiodistal diameter of deciduous anterior teeth on 180 White children show: (1) mean size is smallest for the lower central incisor and largest for the upper canine, (2) means from combining widths on the left anterior teeth of each arch are larger in the maxilla than the mandible by 4.0 mm, (3) individual differences for widths of the upper central and lateral incisors extend from one child with these teeth of similar size to another child with the central incisor larger than the lateral by 2.3 mm, and (4) anterior tooth correlations are positive, varying from r = 0.4 for upper canine width with width of lower central incisor, to r = 0.8 for combined widths of left anterior teeth in the maxilla with combined widths of their antagonists. Comparative findings are drawn from investigations on Australian aborigines, South African Bushmen, Liberian Negroes, Tristan da Cunha islanders, Japanese, Japanese-Negro admixtures, Japanese-White admixtures, White groups living in several parts of Europe, and North American Whites. Among these ethnic groups, Australian aborigines have the largest deciduous anterior teeth. Composite means on each sex for North American Whites show boys to have slightly larger anterior deciduous teeth than girls.     

Associations in emergence age among permenent teeth

Associations in the timing of emergence among the permanent teeth of Boston children were obtained from a mixed longitudinal growth study of 414 Caucasian twin pairs examined annually. Correlations were estimated by the method of maximum likelihood for corresponding left-right teeth, upper-lower teeth, and all paired combinations from central incisor to second molar in a jaw quadrant of each sex. Strong positive correlations in emergence timing prevailed throughout the dentition. Principal component analyses on correlation matrices of jaw quadrant relations for boys and girls in the maxilla and mandible showed that three components effectively explained the emergence associations among the seven permanent teeth in each jaw quadrant. Factor analytic techniques further illustrated the nature of the three components and showed the emergence relations to be essentially the same in the maxilla and mandible for both sexes. The first component was a general maturation factor influencing all of an individual's teeth to be simultaneously early or late in emerging. The remaining two components were a molar factor, affecting almost exclusively the emergence timing of the permanent first and second molars, and a duration factor that affected the duration of the emergence process for non-molar teeth, contrasting particularly the incisors and premolars.     

Concentration of selected elements in the roots and crowns of both primary and permanent teeth with caries disease

We examined the differences between the concentrations of chemical elements in caries-changed primary teeth and permanent ones with a division into the root and the crown. The study comprised 27 children aged from 4 to 11 yr and 36 adults aged from 36 to 71 yr. We examined the elements with the total reflection X-ray fluorescence method. The lowest concentrations of calcium, manganese, strontium, lead, and copper were in the roots of primary teeth compared to the roots of permanent ones. The calcium, nickel, zinc, lead, and copper concentrations were significantly higher in the roots of primary teeth than in the roots of permanent teeth. However, the zinc concentration was higher both in the root and crown of primary teeth than in permanent teeth. On the basis of our investigations, we can conclude that the content of some elements (manganese, copper, strontium, and lead) is higher in caries permanent teeth than in primary ones. The nickel and zinc concentrations are higher in the teeth of the children than the adults. However, the content of other elements (calcium, chromium, iron) is similar in both kinds of teeth.     

Orthodontic status and head morphology in young males

Complete anthropometrical data on a sample of 111 Russian males aged 20.0+/-2.3 years were obtained to investigate craniofacial morphology according to individual orthodontic status (OS). Subsample analyses were performed, using a variety of grouping factors. a) 1-spacing on both dental arches; 2-absence of crowding, spacing, rotation, or displacement of teeth on both dental arches; 3-crowding on both dental arches; b) 1-spacing on mandible; 2-absence of crowding, spacing, rotation, or displacement of teeth on mandible; 3-crowding on mandible; c) 1-spacing on maxilla; 2-absence of crowding, spacing, rotation, or displacement of teeth on maxilla; 3-crowding on maxilla. Wilks' Lambdas were found to be 0.29 to 0.59; all were significant. CONCLUSIONS: 1. Significant positive and negative correlations were found between craniofacial measurements and an individual's OS. 2. Measurements exhibited statistically significant differences between the groups with different OS at the p<0.05 level and some at p<0.01. 3. Using forward stepwise discriminant analysis, a high difference in craniofacial architecture between the groups with different OS was found. Canonical discriminant analysis indicates the face pattern connected to crowding: relatively high medial vertical mandible height in combination with a vertically long and narrow face; to spacing: a wide face with wide nose and high upper lip is combined with shortened medial vertical mandible height. 4. Depending upon the grouping factor, 10 to 12 variables were chosen in the canonical discriminant model. Classification functions and means of canonical roots were calculated; morphological interpretations of canonical roots were performed. 5. Definitive OS is a complicated product of interaction during the ontogenesis of jaws between the time of teeth eruption and the growth of two growth fields (alveolar and corpus) under the simultaneous influence of hormonal status and the chronological age of the individual.     

Directional dental asymmetry in South Sinai Bedouin isolates

Dental casts of 242 Bedouin children were used to study directional asymmetry (DA). Results of Student's t-test pair comparison showed that for permanent dentition, 4 out of 24 DA measures were statistically significant whereas for deciduous dentition, 8 out of 20 measures were significant (p less than 0.05). The magnitude of DA was on the average 1% of the total size of the tooth. No preference regarding dimension (buccolingual, mesiodistal) or jaw (maxilla, mandible) was detected for the DA. PCA results demonstrated the independent nature of DA measures in the dentition.     

Probit and survival analysis of tooth emergence ages in a mixed-longitudinal sample of chimpanzees (Pan troglodytes).

Tooth emergence data from a mixed-longitudinal sample of 58 chimpanzees of known age were analyzed using probit and survival techniques to produce median emergence ages, ranges of variability, and emergence sequences for primary and permanent teeth. Between-group comparisons were made to test for statistically significant differences in emergence ages. No such differences were found between right and left sides, or between maxilla and mandible, for any primary or permanent teeth. Male-female comparisons did demonstrate significant emergence-age differences for some teeth, although they were not always bilaterally symmetrical. More complete data are required to further clarify the nature of sex differences in tooth emergence in chimpanzees. Regression models for age prediction from the number of emerged teeth were generated and indicate that males achieve a given number of emerged teeth at a significantly later age than females. However, when fewer than five teeth have emerged, males are predicted to be younger than females. The sizable root mean square error values for these models suggest that this method of age prediction has limited usefulness owing to the amount of variability in timing of tooth emergence in chimpanzees. The implications of these data for studies on tooth emergence in early hominids are addressed.     

Interrelation between fusions in the primary dentition and agenesis in the succedaneous permanent dentition seen from an embryological point of view

The purpose of the present study was to elucidate the relationship between fusions in the primary dentition and the occurrence of agenesis in the succedaneous permanent dentition in a Danish child population and to elucidate this relationship from the recently described normal embryological development of the anterior parts of the human maxilla and mandible. The material included radiographs, either as intraoral film or as orthopantomograms from a total of 19 primary dentitions with a total of 21 fusions. Radiographs of the permanent dentition in the fusion regions were available for all 19 dentitions. Of 21 fusions, a total of 20 were in the mandible and one in the maxilla. In 15 cases, the fusions were between primary incisors and in six cases between lateral incisors and canines. Agenesis of a permanent lateral incisor always occurred when there had been fusion of a primary lateral incisor and a canine in the primary dentition. When fusion had been between primary incisors, there was only agenesis of an incisor in the permanent dentition in a few cases. The degree of fusion between the involved teeth was not related to the occurrence of agenesis. It is suggested that the intra-jaw differences are related to the recently reported prenatal developmental patterns of the alveoli of the incisors and canines. Moreover, it is suggested that neural crest developmental field differences between the developing maxilla and mandible may explain the inter-jaw differences in phenotypic abnormalities.     

西安鱼化寨史前婴幼儿乳齿的特征

本文通过对西安鱼化寨史前婴幼儿乳齿特征的观察研究,发现人类乳齿与恒齿在种族识别方面具有相同的价值,且乳齿齿冠部分形态特征相较于恒齿表现的更加鲜明。统计分析结果显示,鱼化寨婴幼儿乳齿形态与东北亚人群具有的“中国型牙”接近,同时兼有少量东南亚人群具有的“巽他型牙”特征,这与同时期关中地区其他古代人群颅骨上反映的种族特征基本一致。笔者对这种现象产生的原因进行了分析。此外,本文还针对鱼化寨婴幼儿乳齿的测量数据进行了分析和探讨。     

The presence of a side population and its marker ABCG2 in human deciduous dental pulp cells

Stem cells have been identified using the DNA-binding dye Hoechst 33342 and flow cytometry (FCM) in various tissues known as the side population (SP). The present study shows, for the first time, the presence of side population cells in human deciduous dental pulp cells (DPCs). Flow cytometric identification revealed that 2% of human deciduous DPCs were SP cells and that this SP profile disappeared in the presence of verapamil. The SP marker ABCG2 protein was localized to DPCs in the cell membrane by immunofluorescence staining, and flow cytometric analysis demonstrated that 3.6% of DPCs were ABCG2-positive. Furthermore, quantitative real-time PCR proved that ABCG2 mRNA expression in DPCs isolated from human exfoliated deciduous teeth was higher than in DPCs from permanent teeth. Our findings demonstrate that DPCs from human exfoliated deciduous teeth contain a higher proportion of the SP phenotype than permanent teeth and that they may constitute a stem cell population.     

Canadian Eskimo permanent tooth emergence timing

To identify the times of emergence of the permanent teeth of Canadian Eskimos (Inuit), 368 children and adolescents were examined. The presence or absence of all permanent teeth except the third molars was recorded and these data subjected to probit analysis. Female emergence times were advanced over males. Generally, the Inuit of both sexes showed statistically significant earlier emergence times than Montreal children, except for the incisors. The present results do not support hypotheses indicating that premature extraction of the deciduous teeth advances the emergence of their succedaneous counterparts. There is some indication the controls of deciduous tooth emergence continue to play some part in emergence of the permanent dentition, especially the first permanent teeth that emerge.     

Crown diameters of the deciduous teeth in Australian Aboriginals

Mesiodistal and buccolingual crown diameters were measured from dental casts representing the deciduous dentitions of 197 Aboriginal children from the Northern Territory of Australia. Double determination analysis indicated that the semi-automatic recording procedure used was reliable leading to observer errors of no practical significance. Tooth-size was greater in the male subjects but the sexual dimorphism was less marked than in the permanent teeth of the same subjects. The mandibular teeth were more uniform than maxillary with respect to buccolingual size relative to mesiodistal. Extremes of general tooth-size were more marked in the deciduous dentition than in the permanent as a consequence of the relatively large deciduous second molar which in Aboriginals approximates in size the permanent first molar of many other ethnic groups.     

湖北长阳青铜时代人类乳齿特征的研究

对在湖北长阳县深潭湾崖葬墓出土的青铜时代人类乳齿形态特征的观察研究显示在人类恒齿出现的大多数具有种族识别价值的形态特征在乳齿有相等程度的表现,其中部分特征的出现率和表现程度高于恒齿。与其他地区人群相比,长阳青铜时代人类乳齿特征在总体上与东北亚人类具有的“中国型牙齿”特征接近。同时,在个别牙齿特征上呈现出南亚蒙古人种的特点。作者对产生这种现象的原因进行了分析。本文还就长阳青铜时代人类乳齿测量数据的表现特点进行了探讨。     

Distinctive Genetic Activity Pattern of the Human Dental Pulp between Deciduous and Permanent Teeth

Human deciduous and permanent teeth exhibit different developmental processes, morphologies, histological characteristics and life cycles. In addition, their pulp tissues react differently to external stimuli, such as the pulp sensitivity test, dental trauma and pulp therapy materials. These suggest differences in gene expression and regulation, and in this study we compared gene-expression profiles of the human dental pulp from deciduous and permanent teeth. Pulp tissues from permanent premolars and deciduous molars aged 11–14 years were extirpated and mRNA was isolated for cDNA microarray analysis, and quantitative real-time PCR (qPCR). Other teeth were used for immunohistochemical analysis (IHC). Microarray analysis identified 263 genes with a twofold or greater difference in expression level between the two types of pulp tissue, 43 and 220 of which were more abundant in deciduous and permanent pulp tissues, respectively. qPCR analysis was conducted for eight randomly selected genes, and the findings were consistent with the cDNA microarray results. IHC confirmed that insulin-like growth factor 2 mRNA-binding protein 1 (IGF2BP1) was broadly expressed in deciduous dental pulp tissue, but minimally expressed in permanent dental pulp tissue. Immunohistochemical analysis showed that calbindin 1 (CALB1), leucine-rich repeat-containing G-protein-coupled receptor 5 (LGR5), and gamma-aminobutyric acid A receptor beta 1 (GABRB1) were abundantly expressed in permanent predentin/odontoblasts, but only minimally expressed in deciduous dental pulp tissue. These results show that deciduous and permanent pulp tissues have different characteristics and gene expression, suggesting that they may have different functions and responses to therapies focused on pulp or dentin regeneration.