Aspects of dental development in the orangutan prior to eruption of the permanent dentition

In spite of a resurgence of interest in the interpretation of the sequences of dental development and eruption in various Plio-Pleistocene hominoids as being either “modern human” or “ape-like,” the body of comparative material on the extant hominoids remains deficient in critical areas. In concert with recent attempts to rectify this situation, we present the results of our studies on dental morphogenesis in the orangutan. We have focused on the growth and eruption of the deciduous dentition as well as early stages of permanent tooth formation and have found that 1) many permanent teeth develop earlier than was thought, 2) differences exist between development in the upper and in the lower jaw, and 3) states of tooth formation can vary significantly among individuals of similar chronological age or tooth eruption status.     

Deciduous dentition and eruption pattern in late Miocene Pachyrukhinae (Hegetotheriidae,Notoungulata) from La Pampa Province,Argentina

The study of juvenile remains of Paedotherium Burmeister from Cerro Azul Formation (La Pampa Province, Argentina; late Miocene) is presented. Upper and lower deciduous dentition (or permanent molars supposed to be associated with non-preserved deciduous teeth) are recognised. Several ontogenetic stages are distinguished among juveniles, according to the degree of wear and the replaced deciduous teeth. Besides, some morphological and metrical differences are observed along the crown height. Deciduous cheek teeth are high-crowned and placed covering the apex of the corresponding permanent tooth. The height of the crown and the degree of wear allow establishing the pattern of dental replacement of deciduous and permanent premolars in a posterior–anterior direction (DP/dp4–2 and P/p4–2), as well as the eruption of M/m3 before DP/dp4 is replaced. Some of the studied remains are recognised as young individuals of Tremacyllus Ameghino, but with complete permanent dentition, which leads to propose a different timing in the dental replacement with respect to Paedotherium; they also allow the establishment of an opposite premolar eruption pattern, from P/p2 to P/p4. This knowledge of the deciduous dentition of Paedotherium suggests the need of revising the morphological and metrical characters previously used for defining species within this taxon.     

Changes in the Distribution of Periodontal Nerve Fibers during Dentition Transition in the Cat

The periodontal ligament has a rich sensory nerve supply which originates from the trigeminal ganglion and trigeminal mesencephalic nucleus. Although various types of mechanoreceptors have been reported in the periodontal ligament, the Ruffini ending is an essential one. It is unknown whether the distribution of periodontal nerve fibers in deciduous teeth is identical to that in permanent teeth or not. Moreover, morphological changes in the distribution of periodontal nerve fibers during resorption of deciduous teeth and eruption of successional permanent teeth in diphyodont animals have not been reported in detail. Therefore, in this study, we examined changes in the distribution of periodontal nerve fibers in the cat during changes in dentition (i.e., deciduous, mixed and permanent dentition) by immunohistochemistry of protein gene product 9.5. During deciduous dentition, periodontal nerve fibers were concentrated at the apical portion, and sparsely distributed in the periodontal ligament of deciduous molars. During mixed dentition, the periodontal nerve fibers of deciduous molars showed degenerative profiles during resorption. In permanent dentition, the periodontal nerve fibers of permanent premolars, the successors of deciduous molars, increased in number. Similar to permanent premolars, the periodontal nerve fibers of permanent molars, having no predecessors, increased in number, and were densely present in the apical portion. The present results indicate that the distribution of periodontal nerve fibers in deciduous dentition is almost identical to that in permanent dentition although the number of periodontal nerve fibers in deciduous dentition was low. The sparse distribution of periodontal nerve fibers in deciduous dentition agrees with clinical evidence that children are less sensitive to tooth stimulation than adults.     

MANDIBULAR DENTAL ONTOGENY OF RINGED SEALS (PHOCA HISPIDA)

X-rays of mandibles from ringed seal fetuses ( n = 15), newborns ( n = 12), and young-of-the-year ( n = 11), collected up to early June, were examined for the presence, location, and eruption patterns of deciduous and permanent teeth. The presence of a neonatal line and cementum in permanent canines was determined microscopically. Fetuses sampled in October-November had only unerupted, deciduous tooth germs, but by late January there were robust, deciduous teeth at il-2 pc2-4 and small permanent teeth at 11-2 Cl PCl-5. In newborns collected in early April, 109 of 143 (76%) deciduous teeth were resorbed completely. The remaining 34 deciduous teeth were partially resorbed; six (18%) had erupted and likely would be shed. By late April young-of-the-year had no deciduous teeth remaining. In newborns 54% of the permanent teeth (102/188) were erupted < 2 mm, and by late May the permanent dentition was erupted fully. The neonatal line first appeared in the canine teeth of young-of-the-year collected in mid-April and was 100% present after early May. There was no cementum apparent on any canine collected up to early June. Two seals were missing one and two permanent incisors, respectively. No supernumerary teeth or morphological variants were observed.     

Ontogeny and homology of the dentition in dasyurid marsupials: Development inSminthopsis virginiae

Histological analysis of an ontogenetic series of the dasyurid marsupial,Sminthopsis virginiae, from birt to 60 days old, was undertaken to assess the developmental homologies of the deciduous and successional teeth. This period covers the time from the initiation of all teeth as epithelial buds up until the time of early eruption of some teeth. In addition, two older specimens, aged 81 and 97 days, were examined to provide additional information on the state of differentiation of the unerupted third premolar. In the postcanine dentition, only a single tooth position, dP3, was characterized by the later development of a replacing successional tooth (P3), following developmental pathways identical to those in eutherian mammals. In contrast, the anterior dentition is characterized by the formation of rudimentary, nonerupting deciduous incisors and canines, and by the accelerated development of normal, erupting successional incisors and canines in both jaws. Comparison of relative developmental stages for each tooth position throughout its preeruptive ontogeny suggests thatheterochrony (both developmental acceleration and retardation) has played an important role in the evolutionary history of the dasyurid dentition. Differing aspects of this phenomenon are identified and discussed for the anterior dentition, the anterior two premolars, P3, and the lower molars. Further evidence is presented to corroborate the identification of the anterior two premolars in the adult as dP1 and dP2, based on the relative retardation of their initiation and their lack of successor tooth germs. This developmental heterochrony has probably occurred in all three-premolared marsupials.     

Homologies of the anterior teeth in Indriidae and a functional basis for dental reduction in primates

In a recent paper Schwartz ('74) proposes revised homologies of the deciduous and permanent teeth in living lemuriform primates of the family Indriidae. However, new evidence provided by the deciduous dentition ofAvahi suggests that the traditional interpretations are correct, specifically: (1) the lateral teeth in the dental scraper of Indriidae are homologous with the incisors of Lemuridae and Lorisidae, not the canines; (2) the dental formula for the lower deciduous teeth of indriids is 2.1.3; (3) the dental formula for the lower permanent teeth of indriids is 2.0.2.3; and (4) decrease in number of incisors during primate evolution was usually in the sequence I3, then I2, then I1. It appears that dental reduction during primate evolution occurred at the ends of integrated incisor and cheek tooth units to minimize disruption of their functional integrity.     

Numeric anomalies of teeth in concomitant hypodontia and hyperdontia

Variations in tooth number in children, each of whom had supernumerary teeth and agenesis of teeth, is described. Among the 11, seven had cleft lip and palate, and two had clefting syndromes; two children had dental anomalies only. Only children who had both supernumerary teeth and congenitally missing teeth outside the area of the cleft alveolus were included. Concomitant hypodontia and hyperdontia were observed in the same dentition in nine subjects, in the same jaw in eight subjects, and in the same jaw quadrant in only three subjects. Supernumerary teeth and agenesis of teeth were observed simultaneously more often in the permanent dentitions than in the deciduous dentitions or in both dentitions simultaneously. The overall number of supernumeraries was 10 in the deciduous dentition and 14 in the permanent dentition of the 11 subjects. The number of congenitally absent teeth was 14 in the deciduous dentition and 40 in the permanent dentition. The etiology of concomitant hypodontia and hyperdontia is difficult to explain. It may result from disturbances in migration, proliferation, and differentiation of neural crest cells or interactions between the epithelial and mesenchymal cells during the initiation of odontogenesis.     

Dental fluctuating asymmetry in the Gullah: tests of hypotheses regarding developmental stability in deciduous vs. permanent and male vs. female teeth

In this investigation, deciduous teeth (canines, c; first molars, m1; second molars, m2) and their permanent successors (canines, C; first premolars, P1; second premolars, P2) were used to test two related hypotheses about fluctuating asymmetry (FA). First, based on the biology of the developing dentition, it was predicted that deciduous teeth would be more developmentally stable and thus exhibit less dimensional FA than their permanent successors. Second, based on sex differences in tooth development, it was predicted that female canines would have greater developmental stability (less FA) than male canines. Bucco-lingual measurements were made on dental casts from a single Gullah population. Using a repeated-measures study design (n = 3 repeated measures), we tested these hypotheses on sample sizes ranging from 63-82 antimeric pairs. Neither hypothesis was supported by our data. In most cases, Gullah deciduous teeth did not exhibit statistically significantly less FA than their permanent successors; indeed, statistically significant differences were found for only 3 of 12 deciduous vs. permanent contrasts, and in two cases, the deciduous tooth had greater FA. Female mandibular canines exhibited statistically significantly greater FA than those of males, while there was no statistically significant sex difference in FA for the maxillary canine. FA in these Gullah samples is high when compared to Archaic and late prehistoric Ohio Valley Native Americans, consistent with historical and archaeological evidence that environmental stress was relatively higher in the Gullah population. We suggest that when environmental stress in a population is high, the impact of differences in tooth formation time spans and developmental buffering upon FA may be minor relative to the effect of developmental noise.     

From Embryo to Adult: The Complete Development and Unusual Replacement of the Dentition of the Tammar Wallaby (Macropus eugenii)

Unlike their reptile-like ancestors with continuous tooth replacement, mammals have evolved to replace each tooth either only once, or not at all. In previous large-scale comparative studies, it has been suggested that this tooth replacement only occurs from a successional dental lamina produced lingually to the primary tooth. This study aims to document the complete tooth development and replacement pattern of the tammar wallaby (Macropus eugenii). The tammar wallaby is a diprotodont marsupial, a group defined by their two procumbent lower incisors. To provide a comprehensive documentation of the spatio-temporal pattern of tooth development, we used Lugol’s Iodine staining and microCT scanning (diceCT) of embryos and pouch young into adulthood, resulting in high resolution 3D models for both soft and mineralised stages of development for all tooth positions. Our results reveal that the eponymous lower incisors are the successional generation at the third incisor locus, where the primary dentition initiates but never erupts. Furthermore, we track the development of the only replacement tooth, the permanent third premolar (P3), from initiation to eruption, and found it develops from the primary dental lamina, mesial to the dP3. This is contrary to the conventional view of lingual replacement from successional lamina in mammals. Our findings indicate that no functional tooth replacement occurs in the tammar wallaby, and expands the diversity of tooth replacement patterns found in mammals. We also conclude that since almost all marsupial and placental mammals produce replacement teeth from the distalmost deciduous premolar, this tooth should be considered homologous in these two groups.

     

Growth, function and homology: aspects of dental replacement in toothcombed strepsirhines.

In maturing juvenile lemurs and lorises, it was found that the anteriormost lower deciduous premolar migrates forward and may become associated with the teeth of the toothcomb; this is similar to previous observations on the dentition of indriines. The mesial shift of dp2 appears to be associated with the eruption of P2 but, more importantly, also with replacement of the deciduous by the permanent teeth of the toothcomb--which is a period of functional disruption at the front of the jaw. It is suggested that this growth-related phenomenon should not be confused with other aspects of dental development and eruption which might be indicative of homology.     

Reduced tooth size in 45,X (Turner syndrome) females

Mean values and variances of deciduous and permanent tooth dimensions were compared between 121 45,X (Turner syndrome) females and 171 control subjects to clarify the role of the X chromosome on dental development. Although deciduous molars tended to be smaller than normal in 45,X females, there was no evidence of a reduction in tooth size for deciduous anterior teeth. In the permanent dentition, all mesiodistal dimensions were significantly smaller in 45,X females but only some of the buccolingual dimensions were smaller. The findings for deciduous tooth-size may reflect a sampling effect related to the extremely high frequency of spontaneous abortion in 45,X individuals. Results for permanent teeth are consistent with the concept of a decrease in enamel thickness in 45,X females.     

The eruption times of permanent teeth in boys and girls in the Stormarn District, Schleswig-Holstein (Germany)

In a longitudinal study in two small towns in southern Schleswig-Holstein (Ammersbek and Ahrensburg, District Stormarn; 9155 inhabitants) we investigated 2832 oral findings of 1396 patients (711 males, 685 females). The minimum age was 1.51 years, and the maximum age was 25.50 years. The dental findings were collected over a period of about 20 years (1982-2002). The oral findings per child were assessed between one and eight times. The eruption times of teeth in females are earlier than those for the same teeth in males. Further, the permanent dentition in females is completed earlier than in males. In both sexes the tooth eruption occurs symmetrically in both jaws. The comparison of both jaws revealed a slightly advanced eruption of the lower jaw teeth in both sexes. There is a noteworthy change in the eruption sequence of the teeth. In contrast to other reports we observed that the eruption of the canine proceeds the eruption of the second molar. We found no acceleration of the dentition when compared with other reports and could confirm the rules of tooth eruption in man. Conclusion: Oral examination of teeth is a simple tool to calculate tooth eruption intervals. This first investigation on a population of Schleswig-Holstein revealed a change in the eruption sequence of permanent teeth. These findings are relevant for dental treatment planning and should be reconfirmed at certain intervals.     

Behavioral correlates of tooth eruption in Madagascar lemurs

Observations on the sequence and timing of gingival tooth eruption are reported for six species of Madagascar lemurs. Complete sequences of eruption were obtained for the deciduous dentition, and partial to complete sequences were recorded for the permanent dentition. In Cheirogaleus medius and in four species of the genus Lemur, the deciduous teeth erupt in front-to-back sequence, with the toothcomb emerging near birth as an integrated complex. In Propithecus verreauxi the same pattern is exhibited, but the small peglike lower canine and dp₃ erupt last. Eruption of the permanent dentition in Lemur species takes place in two distinct stages. In the first stage the upper incisors, toothcomb, and first two molars penetrate the gingiva. After an interval of 3 to 4 months, the remaining permanent teeth erupt. Deciduous premolars erupt when young animals are being weaned. The eruption of the deciduous toothcomb appears unrelated to feeding or grooming behavior. In L. catta and L. fulvus, the first stage of permanent tooth eruption occurs at approximately 6 months of age, when the growth rate slows down and (in wild populations) the rainy season is ending. This suggests that eruption of the anterior molars is timed to coincide with a shift from a more frugivorous to a more folivorous dietary regime, which occurs during the dry season. No further tooth eruption occurs until approximately 1 year of age, when the growth rate increases and the rainy season returns for wild populations. Thus, the second wave of permanent tooth eruption in these species again appears linked to changing climatic conditions which lead to a shift in dietary preferences.     

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.     

Growth and development in the saddle-back tamarin: The sequence and timing of dental eruption and epiphyseal union

A cross-sectional sample of 121 colony-born saddle-back tamarins, Saguinus fuscicollis, was examined to identify the sequence and timing of dental eruption and epiphyseal union. The state of dental development of the deciduous and permanent dentitions was recorded as erupted or non-erupted on the basis of gingival penetration. Eighteen areas of union of long bone epiphyseal and other secondary centers, the union of the primary elements of the innominate, and the spheno-occipital synchondrosis were examined. The state of union at the areas was recorded on a three-point scale of not united, uniting, and united. The data indicated that deciduous incisors and canines were present at birth and that all deciduous teeth were erupted by 12 weeks. The first permanent tooth, M(1), erupted between weeks 16 and 23; the permanent dentition was fully erupted by 45 weeks. Union of the long bone epiphyses began in the third month at the distal humerus and continued until the first quarter of the second year. The secondary centers at the ischial tuberosity and iliac crest were united slightly later than four and six years of age, respectively. Regression analysis of the data indicate their potential use as parameters for predicting age in feral specimens.     

Reconstructing infant weaning histories at Roman period Kellis, Egypt using stable isotope analysis of dentition

Studies of infant feeding and weaning patterns in past populations that rely on a cross-sectional approach must make the assumption that no infant mortality bias exists. Previous investigations of infant weaning patterns at the Dakhleh Oasis, Egypt, relied on cross-sectional isotope data. In this study, we re-examine this weaning pattern, using a simulated longitudinal approach, which does not require any assumptions regarding potential infant mortality biases. This involves examining the dental isotopic signatures of individuals who survived the weaning process. Stable isotope signatures from juveniles and adults (102 individuals, 297 teeth) were examined to reconstruct the weaning history of those that survived the weaning process. Both deciduous and permanent teeth were sampled. Homogenized enamel and dentin samples were isolated from each tooth and analyzed for delta(13)C(ap) and delta(18)O(ap) from the enamel and delta(15)N(coll) and delta(13)C(coll) from dentin collagen. We investigate differences between in utero versus postbirth, preweaning versus postweaning, and juvenile versus adult stable isotope values as reflected in the dentition. A random permutation procedure was used to test for statistically significant differences in stable isotope values between tooth types. Statistically significant differences were observed in all stable isotopes between permanent and deciduous teeth, and between early and later forming permanent teeth in delta(13)C(ap) and delta(15)N(coll) isotopes. These results indicate dietary change between in utero and postbirth, and changes occurring during the weaning period. These results provide a more comprehensive picture of infant weaning practices at Kellis and provide further support that complete weaning occurred by 3 years of age.     

Incremental enamel development in modern human deciduous anterior teeth

This study reconstructs incremental enamel development for a sample of modern human deciduous mandibular (n = 42) and maxillary (n = 42) anterior (incisors and canines) teeth. Results are compared between anterior teeth, and with previous research for deciduous molars (Mahoney: Am J Phys Anthropol 144 (2011) 204-214) to identify developmental differences along the tooth row. Two hypotheses are tested: Retzius line periodicity will remain constant in teeth from the same jaw and range from 6 to 12 days among individuals, as in human permanent teeth; daily enamel secretion rates (DSRs) will not vary between deciduous teeth, as in some human permanent tooth types. A further aim is to search for links between deciduous incremental enamel development and the previously reported eruptionsequence. Retzius line periodicity in anterior teeth ranged between 5 and 6 days, but did not differ between an incisor and molar of one individual. Intradian line periodicity was 12 h. Mean cuspal DSRs varied slightly between equivalent regions along the tooth row. Mandibular incisors initiated enamel formation first, had the fastest mean DSRs, the greatest prenatal formation time, and based upon prior studies are the first deciduous tooth to erupt. Relatively rapid development in mandibular incisors in advance of early eruption may explain some of the variation in DSRs along the tooth row that cannot be explained by birth. Links between DSRs, enamel initiation times, and the deciduous eruption sequence are proposed. Anterior crown formation times presented here can contribute toward human infant age-at-death estimates. Regression equations for reconstructing formation time in worn incisors are given.     

The deciduous dentition of Griphopithecus alpani from Paşalar, Turkey

Seventy-four hominoid primary teeth have been recovered from the middle Miocene site of Pa?alar, Turkey, constituting the largest sample of deciduous teeth for any species of fossil ape. Morphological features that characterize the permanent teeth of Griphopithecus alpani from the site have also been identified in some of these deciduous teeth, including a lingual pillar on the di(1)s. These features plus the overwhelming preponderance of G. alpani permanent teeth at the site suggest that all of the deciduous teeth belong to this species. Contrary to the situation in the permanent teeth, nothing in the morphology of the primary dentition suggests the representation of a second species. The age profile of the non-adult hominoids was reconstructed based on the degree and type of wear recorded on the dp4s, the most abundant deciduous tooth in the sample, assuming a similar eruption chronology to that of Pan troglodytes. This analysis indicates underrepresentation of very young individuals in the sample and high mortality for individuals belonging to the 3-5-years age cohort, a situation that could be due to the effects of stress related to weaning. The coefficient of variation and range-index values obtained for the majority of tooth types are equal to or greater than the comparable values in a sample of P. troglodytes, in some cases at much smaller sample sizes. One possible explanation for this is that there was greater sexual dimorphism in the G. alpani deciduous dentition than in Pan, which would mirror the condition of the permanent dentition.     

Plate-like permanent dental laminae of upper jaw dentition in adult gobiid fish, Sicyopterus japonicus

Sicyopterus japonicus (Teleostei, Gobiidae) possesses a unique upper jaw dentition different from that known for any other teleosts. In the adults, many (up to 30) replacement teeth, from initiation to attachment, are arranged orderly in a semicircular-like strand within a capsule of connective tissue on the labial side of each premaxillary bone. We have applied histological, ultrastructural, and three-dimensional imaging from serial sections to obtain insights into the distribution and morphological features of the dental lamina in the upper jaw dentition of adult S. japonicus. The adult fish has numerous permanent dental laminae, each of which is an infolding of the oral epithelium at the labial side of the functional tooth and forms a thin plate-like structure with a wavy contour. All replacement teeth of a semicircular-like strand are connected to the plate-like dental lamina by the outer dental epithelium and form a tooth family; neighboring tooth families are completely separated from each other. The new tooth germ directly buds off from the ventro-labial margin of the dental lamina, whereas no distinct free end of the dental lamina is present, even adjacent to this region. Cell proliferation concentrated at the ventro-labial margin of the dental lamina suggests that this region is the site for repeated tooth initiation. During tooth development, the replacement tooth migrates along a semicircular-like strand and eventually erupts through the dental lamina into the oral epithelium at the labial side of the functional tooth. This unique thin plate-like permanent dental lamina and the semicircular-like strand of replacement teeth in the upper jaw dentition of adult S. japonicus probably evolved as a dental adaptation related to the rapid replacement of teeth dictated by the specialized feeding habit of this algae-scraping fish.