Studies on agenesis in the permanent dentition

Tooth dimensions in 104 males and females with agenesis of one or more permanent teeth, other than third molars, have been examined. The amounts of size reduction from normal in mesiodistal and buccolingual tooth diameters appear to be independent. Also some apparent differences from normal tooth size variability were noted. Interestingly, first molars and canines, both considered to be stable components of the dentition, showed significant variability in tooth size. In addition the incidence of individual tooth agenesis within this sample was noted and maxillary lateral incisor was most frequently absent in both sexes.     

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.     

Morphometrics of the anterior dentition in strepsirhine primates

Size variations in the anterior dentition were analyzed for 26 species of strepsirhine primates. The upper and lower incisor rows of strepsirhines, like those of anthropoid primates, scale isometrically with body size. Within the order Primates, strepsirhines exhibit the smallest incisors relative to body size, followed in increasing size by tarsiers, platyrrhines, and catarrhines. If the lateral teeth of the indriid toothcomb are interpreted as incisors and not canines, correlations between mandibular tooth size variables and body weight are maximized. The upper incisors of strepsirhines are extremely small and frequently widely separated, most likely to minimize occlusion with the toothcomb. Species deviations for assorted size variables of the anterior dentition generally fail to reflect functional variations in the use of the anterior teeth; some of the variables, however, do reflect taxonomic differences within the Strepsirhini. Although toothcomb size variations among extant strepsirhines are more readily interpreted in terms of gum feeding and bark scraping than they are in terms of grooming, anterior dental morphology as a whole is more easily explained by a grooming hypothesis when existing models of toothcomb origins are considered.     

Morphological features of Jat dentition

Observations on morphological characters of milk and permanent teeth, based on 648 pairs of dental casts of 356 male and 292 female Jat children of Haryana (India) are reported. Deciduous teeth show high frequencies of bilateral winging of maxillary central incisor, Carabelli's cusp of maxillary second molar, and deflecting wrinkle of mandibular second molar. Reduction of maxillary molar cusps is more marked in males than in females. Y pattern is very common in deciduous molars. Permanent teeth have high frequencies of grooved cingulum of incisors, cingular nodule of lateral incisors and canines, and distal accessary ridge of canines. Low frequencies of Carabelli's cusp and winging are also common. The tendency towards faintly developed shovelling in milk incisors occurs more often than in the permanent teeth.     

Developmental origins and homologies of the hyracoid dentition

Understanding the origins of morphological specializations in mammals is a key goal in evolutionary biology. It can be accomplished by studying dental homology, which is at the core of most evolutionary and developmental studies. Here, we focused on the evolution and development of the specialized dentition of hyraxes for which dental homologies have long been debated, and could have implications on early placental evolution. Specifically, we analysed dental mineralization sequences of the three living genera of hyraxes and 17 fossil species using X‐ray computed microtomography. Our results point out the labile position of vestigial upper teeth on jaw bones in extant species, associated with the frequently unusual premolar shape of deciduous canines over 50 Ma of hyracoid evolution. We proposed two evolutionary and developmental hypotheses to explain these original hyracoid dental characteristics. (a) The presence of a vestigial teeth on the maxilla in front of a complex deciduous canine could be interpreted as extra‐teeth reminiscent of early placental evolution or sirenians, an order phylogenetically close to hyracoids and showing five premolars. (b) These vestigial teeth could also correspond to third incisors with a position unusually shifted on the maxilla, which could be explained by the dual developmental origin of these most posterior incisors and their degenerated condition. This integrative study allows discussion on the current evolutionary and developmental paradigms associated with the mammalian dentition. It also highlights the importance of nonmodel species to understand dental homologies.     

Formation of anterior maxillary teeth in 0-3-year-old children with cleft lip and palate and prenatal risk factors for delayed development

Formation of deciduous and permanent maxillary incisors and canines was studied in 361 children with cleft lip and palate. Altogether, 704 occlusal X rays of the children aged from 2 weeks to 41 months were assessed using a 13-stage scale. The early timing of tooth development was in both dentitions close to that reported for healthy children. However, developmental asymmetry was noted between contralateral teeth on the cleft and noncleft sides. In the unilateral cleft lip and palate group, every tenth cleft-side deciduous central incisor, deciduous canine, and permanent central incisor was delayed compared to the corresponding contralateral tooth. The formation timing was also compared within 11 prenatal and hereditary variables. Risk factors for delayed development were low placental weight, short gestation, mother's use of drugs during pregnancy, first in birth order, cleft with multiple additional malformations, and relatives having malformations other than oral clefts. However, the associations between a risk factor and tooth development were weak.     

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.     

Talon cusp from two archaic period cemeteries in North America: implications for comparative evolutionary morphology

Talon cusps are rare morphological features of the anterior dentition that represent a spectrum of lingual cingulum diversity. In this paper, talon cusp prevalence is described in two Archaic period North American samples, Windover Pond (Florida) and Buckeye Knoll (Texas). Given the early date of these cemeteries (~7500 BP), these specimens represent the oldest reported cases of lingual talon cusp in the New World, and perhaps globally. Windover preserves three cases of talon cusp (representing three different individuals) affecting the permanent maxillary lateral incisors. The sample frequencies were 1.8% and 3.1% for the left and right maxillary lateral incisors, respectively. Buckeye Knoll preserves four cases of talon cusp representing three individuals. Talon cusps at this site were distributed throughout the maxillary anterior dentition, including a permanent maxillary central incisor, bilateral permanent maxillary lateral incisors, and a deciduous maxillary lateral incisor. The multicomponent nature of this site complicates sample frequency calculation with by-tooth estimates ranging from 3.6% to 25%. This paper discusses the difficulties with comparative frequency estimation, resulting from a proliferation of terminology that is discipline-specific. Understanding the evolutionary basis and significance of dental morphological variation requires an inclusive approach to the comparative literature that focuses on homology within the context of odontogenetic process.     

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.     

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.     

Sequences and timing of dental eruption in semi-free-ranging mandrills (Mandrillus sphinx)

The chronology of tooth emergence is often used to examine the growth and development of individuals and to compare life histories across species. Emergence patterns are also used to age animals and to infer life history influences for extinct species. However, comparative studies of primates are hindered by a lack of dental development data for many species. Here we describe the sequences and timing of tooth emergence for a large sample of semi-free-ranging mandrills (Mandrillus sphinx) and compare this with other life history variables for this species. Deciduous dentition emerged in the sequence i1 i2 c p3 p4. The augmented sequence (including information about variability in emergence sequence) was i1 i2 [c p3] p4 for the female maxilla and the male mandible, and i1 i2 c p3 p4 for the female mandible and the male maxilla. Deciduous dentition was complete by 5.0 months in females and 6.4 months in males. The permanent dentition began to emerge at 26 months, and complete adult dentition had emerged by 68 months for males and 85 months for females. Sex differences occurred in the augmented eruption sequences: females M1 I1 I2 [M2 C] P3 P4 M3, males M1 I1 [I2 M2] [P4 = P3 = C] M3. The order of tooth eruption and the occurrence of sequence polymorphisms were very similar to those observed for baboons and macaques. Comparison with life history variables showed that mandrills have complete deciduous dentition at weaning, females possess both adult incisors and M1 when they first reproduce, but still have deciduous canines and premolars, and that both sexes have full adult dentition before they attain their full adult stature and mass.     

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.     

A comparative study of incisor procumbency and mandibular morphology in vampire bats

The three species of vampire bats (Phyllostomidae: Desmodontinae), Desmodus rotundus, Diaemus youngi, and Diphylla ecaudata, are the only mammals that obtain all nutrition from vertebrate blood (sanguinivory). Because of the unique challenges of this dietary niche, vampire bats possess a suite of behavioral, physiological, and morphological specializations. Morphological specializations include a dentition characterized by small, bladelike, non‐occlusive cheek teeth, large canines, and extremely large, procumbent, sickle‐shaped upper central incisors. The tips of these incisors rest in cuplike pits in the mandible behind the lower incisors (mandibular pits). Here, we use microCT scanning and high‐resolution radiography to describe the morphology of the mandible and anterior dentition in vampire bats, focusing on the relationship between symphyseal fusion, mandibular pit size, incisor size, and procumbency. In Desmodus and Diaemus, highly procumbent upper incisors are associated with relatively small mandibular pits, an unfused mandibular symphysis with substantial bony interdigitations linking the dentaries, and a diastema between the lower central incisors that helps to facilitate the lapping of blood from a wound. In Diphylla, less procumbent upper incisors are associated with relatively large mandibular pits, a completely fused mandibular symphysis, and a continuous lower toothrow lacking a central diastema. We hypothesize that symphyseal morphology and the presence or absence of the diastema are associated with the angle of upper incisor procumbency and mandibular pit development, and that spatial constraints influence the morphology of the symphysis. Finally, this morphological variation suggests that Diphylla utilizes a different feeding strategy as compared to Desmodus and Diaemus, possibly resulting from the functional demands of specialization on avian, rather than mammalian, blood. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.     

Sexual differences in the anterior dentition in African primates

A study was made of ranges of variation of the anterior dentition of various African nonhuman primates. Comparisons of the dentitions were made between different species and sex differences within each species were determined. Among the nonhuman primate groups studied were: Gorilla gorilla gorilla, Pan troglodytes, Pan paniscus, Cercopithecus nictitans, Cercocebus albigena and Colobus badius. In monkeys the canine teeth of the males are considerably larger than those of the females. There are also considerable differences in size in the rest of the anterior dentition. In apes, and specifically only gorillas, distinct sex differences are only found in the maxillary canines. In the chimpanzees, sex differences in the dentition are much smaller and there is considerable overlap in the ranges of variation. There are no fundamental differences in the size of the rest of the anterior dentition in the apes. The present study shows that differences due to sex in the anterior dentition, excluding the canine, are not as great as has been considered. If we consider the fossil record of man, whose morphological complex includes a much reduced canine, the probability will be that sex differences in the rest of the dentition will be negligible. Given the fragmentary nature of the fossil record, it is, therefore, highly unlikely that the determination of the sex of any fossil hominid specimen can be accurately made based solely on the evidence of its dentition.     

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.     

Brief communication: on the optimum number of metacarpals for roentgenogrammetric measurement

Interpretation of dental development of fossil hominids requires understanding of and comparison with the pattern and timing of dental development among living humans and pongids. We report the first study of crown and root calcification in the lower permanent molar teeth among chimpanzees (Pan troglodytes) of known chronological age. A series of 99 lateral head radiographs of 16 captive-born chimpanzees were analyzed. Radiographs were taken at irregular intervals throughout the entire postnatal period of dental development from birth to 13 years of age. Permanent mandibular molars were rated on an eight-point maturation scale from initial radiographic appearance through crown and root calcification and apical closure of the root canals. In addition, we were able to document initial crown calcification and completion, as well as root completion and apical closure in incisors, canines, and premolars. Our results show several differences from the widely cited developmental schedule for pongid dentitions of Dean and Wood (Folia Primatol. 36:111–127, 1981). We found a much greater degree of temporal overlap in calcification of the crowns of adjacent molars, a pattern very unlike that usually seen in human dental development, which is characterized by delays between the onset of crown calcification in the molar series. Also, the ages and durations of crown and root formation in our chimp sample differ from the estimates proposed by Dean and Wood. By more clearly establishing the nature of developmental schedules and the timing of major events in the pongid dentition, these results should aid in the ongoing controversies concerning the human or pongid nature of dental development among Plio-Pleistocene hominids.     

Dental fast track: Prenatal enamel growth,incisor eruption,and weaning in human infants

Correlation between the timing of permanent first molar eruption and weaning age in extant primates has provided a way to infer a life history event in fossil species, but recent debate has questioned whether the same link is present in human infants. Deciduous incisors erupt at an age when breast milk can be supplemented with additional foods (mixed feeding), and weaning is typically complete before permanent first molars erupt. Here, I use histological methods to calculate the prenatal rate by which enamel increases in thickness and height on human deciduous incisors, canines, and molars (n = 125). Growth trajectories for each tooth type are related to the trimesters and assessed against the eruption sequence and final crown height. Analyses show that central incisors initiate early in the second trimester with significantly faster secretion rates relative to canines and second molars, which initiate closer to birth. Even though initial extension rates were correlated with crown height and scaled with positive allometry within each tooth class, the relatively short incisors still increased in height at a significantly faster rate than the taller canines and molars. The incisor prenatal “fast track” produces a greater proportion of the crown before birth than all other tooth types. This growth mechanism likely facilitates early incisor eruption at a time when the mixed feeding of infants can be initiated as part of the weaning process. Findings provide a basis from which to explore new links between developmental trends along the tooth row and mixed feeding age in other primates. Am J Phys Anthropol 156:407–421, 2015. © 2014 Wiley Periodicals, Inc.     

Sex estimation based on deciduous and permanent dentition in a contemporary spanish population

Sex estimation of skeletal remains with satisfactory allocation accuracy represents an essential step in reconstructing the biological profile of unknown individuals in archaeological research and forensic practice. Teeth are among the most frequently recovered physical elements of an individual that remain after death due to their hardness, durability, and resistance to postmortem insults. This study was based on the deciduous and permanent dentition of 269 individuals (150 males and 119 females) from the Granada osteological collection of identified infants, young children, and adults (Granada, Spain). Mesiodistal, buccolingual, and diagonal crown and cervical diameters of both dentitions were measured, and logistic regression analyses were performed to create equations for sex discrimination. The results show that the first and second deciduous molars and the permanent canines are the teeth with the greatest sexual dimorphism, providing percentages of correct assignment of sex between 78.1 and 93.1% in deciduous dentition and between 79.4 and 92.6% in permanent teeth, depending on the dimensions used. The results indicate that this method may be applicable as an adjunct with other accepted procedures for sex estimation when fragmentary skeletal remains are encountered in archaeological excavations and in forensic contexts. Am J Phys Anthropol 152:163–164, 2013. © 2013 Wiley Periodicals, Inc.     

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.     

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.