Tooth eruption in Reeves' muntjac (Muntiacus reevesi) and its use as a method of age estimation (Mammalia: Cervidae)

The sequence of tooth eruption and replacement in Reeves' muntjac was determined from captive animals of known age. Pronounced sexual dimorphism is shown by the permanent upper canine which in the male is large, tusk-like and is used as a weapon. The upper canine was the first deciduous tooth to be replaced in males, at approximately 21 weeks of age, compared with 53–57 weeks in the female. The permanent mandibular teeth erupted in the order: molars, first and second incisors, premolars, third incisor and canine. The maxillary teeth erupted in the order: first molar, canine (in male), second and third molars, canine (in female), premolars. The full complement of 34 functional permanent teeth was attained by 83–92 weeks of age.     

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.     

Masculinization of the eruption pattern of permanent mandibular canines in opposite sex twin girls

The aim of this study is to explore the effect of prenatal androgenization on the clinical eruption of permanent teeth expressing dimorphism and bimaturism. The eruption curves of permanent teeth (except third molars), including those that make up the canine complex (permanent canines, lower first premolars), are compared among opposite sex twins (OS twins) relative to single‐born boys and girls. The comparisons are made with regard to three phases of eruption (pierced mucosa, half‐ erupted, and completely erupted) from a cross‐sectional sample of dental casts, using Kaplan–Meier survival and Cox regression analyzes. The casts were collected from 2159 school children from the US Collaborative Perinatal Project, including 39 pairs of OS‐twins, of which 12 pairs (30.8%) were Euro‐Americans and 27 pairs (69.2%) were of African‐American ancestry. The eruption patterns of the incisors, upper first molars, and lower canines were found to be significantly masculinized (delayed) among OS twin girls. The differences in most other teeth were either not significant, or the number of observations of active eruption phases were too few, such as in the upper first molars and incisors, to yield strong evidence and meaningful results. The masculinization of the tooth eruption pattern in OS twin girls is intriguing because of the lower canine responses during puberty, as well as canine primordial formation during early fetal androgenization of their co‐twin during the 8th to 14th gestational weeks. The present results offer a challenge for future research exploring tooth eruption mechanisms, and may also highlight some cases of delayed or ectopic canines, which are biased toward females. Am J Phys Anthropol 151:566–572, 2013. © 2013 Wiley Periodicals, Inc.     

Dental Ontogeny in Macroscelides proboscideus (Afrotheria) and Erinaceus europaeus (Lipotyphla)

We investigated the state of dental eruption in specimens of Macroscelides proboscideus and Erinaceus europaeus of known age. When M. proboscideus reaches adult size and sexual maturity, few or none of its replaced permanent cheek teeth have erupted. The approximate sequence of upper tooth eruption is P1, [I3, C, M1], [I1–2], M2, P4, [P2, P3]. Chronologically, E. europaeus erupts its molars and most premolars prior to M. proboscideus; but its first two upper incisors erupt after those of M. proboscideus, and its canines erupt around the same time. The approximate sequence of upper tooth eruption in E. europaeus is [M1, M2, P2, I3], C, M3, P4, P3, I2, I1. Unlike M. proboscideus, E. europaeus does not reach adult size until all permanent teeth except for the anterior incisors have erupted. While not unique among mammals, the attainment of adult body size prior to complete eruption of the permanent cheek teeth is particularly common among macroscelidids and other afrotherians.     

Genome-wide association study identifies four loci associated with eruption of permanent teeth

The sequence and timing of permanent tooth eruption is thought to be highly heritable and can have important implications for the risk of malocclusion, crowding, and periodontal disease. We conducted a genome-wide association study of number of permanent teeth erupted between age 6 and 14 years, analyzed as age-adjusted standard deviation score averaged over multiple time points, based on childhood records for 5,104 women from the Danish National Birth Cohort. Four loci showed association at P<5×10(-8) and were replicated in four independent study groups from the United States and Denmark with a total of 3,762 individuals; all combined P-values were below 10(-11). Two loci agreed with previous findings in primary tooth eruption and were also known to influence height and breast cancer, respectively. The two other loci pointed to genomic regions without any previous significant genome-wide association study results. The intronic SNP rs7924176 in ADK could be linked to gene expression in monocytes. The combined effect of the four genetic variants was most pronounced between age 10 and 12 years, where children with 6 to 8 delayed tooth eruption alleles had on average 3.5 (95% confidence interval: 2.9-4.1) fewer permanent teeth than children with 0 or 1 of these alleles.     

Permanent tooth emergence in Gujjars of Punjab, India.

Patterns of permanent tooth emergence in Gujjars were studied in a cross-sectional sample of 483 children ranging in age from 6 to 13 years. Females were markedly advanced in permanent tooth emergence times over males, but no such sex differences were observed in sequence of emergence. Differences between median emergence times of right and left side antimers were significant for only 4 of 28 instances (14.29%), namely central incisors, mandibular first molars in males and lateral maxillary incisors in females. In general mandibular teeth except premolars tended to emerge earlier than their maxillary counterparts. The quiescent period between first and second tooth emergence stages was longer in males than in females. Mandibular depth and morphological facial length were very significantly correlated (p < 0.01) with the number of permanent teeth present in the oral cavity.     

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.     

Eruption of permanent teeth in Brazilian Whites and Blacks

A total of 302 White and 904 Black children six, nine and 12 years of age were studied for the eruption of their permanent teeth. Differences between the two ethnic groups were not large, but the Black subjects were generally more precocious at the beginning of the process (especially the girls, both in the upper and lower incisors). At nine and 12 years of age, however, these dissimilarities disappear. The latter do not seem to be related to distinct rates of extraction or agenesis of deciduous teeth. No significant differences were observed in the degree of asymmetry present in the permanent dentition of the White and Black individuals studied.     

树鼩(Tupaia belangeri chinensis)生长发育的初步观察

本文对39只树鼩的个体生长发育作了描述。新生幼仔生长发育迅速,在出生后头一个月内,体重可增长3—6倍,其体重的增长与饮奶量有关。出生后4个月性成熟,7个月龄时可繁殖产仔。性器官的重量有明显的季节性变化,1—6月间睾丸、子宫、卵巢重量最大,性行为活跃,其余月份重量下降,性功能出现渐进性衰退。辜丸重和体重的比值小于0.01,表明树鼩是单雄交配繁殖。乳齿的萌发为下颚先于上颚,门齿最先萌发,其次是犬齿,前臼齿,最后是臼齿。与Lyon(1913)和Shigehara(1980)提出的恒齿萌发次序不同。     

The timing of eruption of the primary dentition in Nigerian children

The objectives of this study were to clarify the eruption time and sequence for primary teeth in Nigerian children. It also investigated the effect of sex and socioeconomic status on the timing and sequence of eruption. A random sample of 1,657 children from ages of 3-40 months were examined--921 (55.6%) males and 736 (44.4%) females. The age of eruption of the teeth was estimated using probit regression. The results show that there was no effect of sex, socioeconomic status or breastfeeding status on the timing of eruption and pattern of teeth eruption in Nigerian children. Left and right teeth had similar eruption times. Eruption times of the lateral incisor, canine, and molars were similar for upper and lower teeth. Interpopulation studies however showed that though the sequence of eruption of primary teeth in Nigerian population is similar to that of their peers in other compared populations, there are observable sex differences in the timing of tooth eruption.     

Association of relatively delayed emergence of mandibular molars with molar reduction and molar position

Among 234 children examined annually from age three to 20 years at the Burlington Growth Centre, there was statistically significant cooccurrence of early and late emergence sequences of the permanent first and second molars relative to the central incisors and second premolars in the same jaw and in both jaws. Alternatively, mandibular molar delay was not accompanied by corresponding maxillary molar delay, and the mandibular molars emerged later than the maxillary molars. This was strongly associated with Angle Class II malocclusion, indicating a relationship between relative time of emergence and relative position of opposing molars. Delay of the mandibular molar relative to the successional teeth or maxillary molars was associated with increased frequency of four cusped first and second molars and agenesis of third molars, indicating a tendency for co-occurrence of delay in timing of molar emergence with reduction in structure of the molars. These relationships were evident even though emergences were affected by early loss of a deciduous second molar which increased M1I1 and M2P2 sequences by earlier emergence of M1 and delayed emergence of P2.     

Dental developmental status of southern Chinese girls in Hong Kong

Dental developmental status of the permanent canines, premolars and second molars were studied in one hundred and two twelve-year-old Southern Chinese girls born and brought up in Hong Kong. Eruption of these teeth were defined as gingival emergence during the clinical examination while the root development was assessed from orthopantomographs. Root resorption pattern of the primary canines and molars were also studied with the aid of the orthopantomographs. Two-thirds of girls presented with permanent dentition stage. The root resorption patterns of the primary teeth were different from their order of exfoliation. The mandibular permanent teeth were in advanced in both eruption and root development than the corresponding maxillary teeth, except the first premolars.     

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.     

Dental eruption in captive-bornCebus apella: From birth to 30 months old

This work reports on the ages of gingival eruption of deciduous and permanent teeth observed from the time of birth until 30 months old, captive-born individuals. All of the animals were born with the protrusive di₁ already through the gingival border. The dmp⁴ were the last teeth of the deciduous series which emerged at 24.5±3.11 weeks in the males and 27.8±2.95 weeks in the females. Significant sexual differences were found between the eruption period of the dpm₂, dmp⁴ (p<0.05), and dpm₄ (p<0.01), with the males being more precocious than the females. The first permanent tooth that emerged, usually, was the M₁ at 13.50±2.12 months in the males, and 14.00±0.82 months in the females. At 30 months of age, not one individual had replaced his deciduous canine or premolar teeth with the permanent ones, and, moreover, the M ₃ ³ had not yet emerged.     

Evolutionary Implications of Dental Eruption in Dasypus (Xenarthra)

Late eruption of the permanent dentition was recently proposed as a shared anatomical feature of endemic African mammals (Afrotheria), with anecdotal reports indicating that it is also present in dasypodids (armadillos). In order to clarify this question, and address the possiblity that late eruption is shared by afrotherians and dasypodids, we quantified the eruption of permanent teeth in Dasypus, focusing on growth series of D. hybridus and D. novemcinctus. This genus is the only known xenarthran that retains two functional generations of teeth. Its adult dentition typically consists of eight upper and eight lower ever-growing (or euhypsodont) molariforms, with no premaxillary teeth. All but the posterior-most tooth are replaced, consistent with the identification of a single molar locus in each series. Comparison of dental replacement and skull metrics reveals that most specimens reach adult size with none or few erupted permanent teeth. This pattern of growth occurring prior to the full eruption of the dentition is similar to that observed in most afrotherians. The condition observed in Dasypus and many afrotherians differs from that of most other mammals, in which the permanent dentition erupts during (not after) growth, and is complete at or near the attainment of sexual maturity and adult body size. The suture closure sequence of basicranial and postcranial epiphyses does not correlate well with dental eruption. The basal phylogenetic position of the taxon within dasypodids suggests that diphyodonty and late dental replacement represent the condition of early xenarthrans. Additionally, the inferred reduction in the number of molars to a single locus and the multiplication of premolars represent rare features for any living mammal, but may represent apomorphic characters for Dasypus.     

Hypodontia: Prevalence amongst Jewish populations of different origin

The teeth of 10,371 male and 11,013 female Israel Jews were examined. Prevalence of all hypodontia was 4.60% with no significant difference between the sexes; 2.11% lacked upper lateral incisors, the females having a significantly higher prevalence than males. Second premolars were missing in 1.87% of the population, with no significant differences between the sexes. Missing lower incisors was diagnosed in 0.68% of the children, with a higher prevalence in males. Prevalence of missing lower incisors was similar in the Ashkenazi and in the non-Ashkenazi. The teeth most frequently missing in descending order were the upper lateral incisors and the lower second premolars.     

Developmental stage of the dentition and speech sound production in a series of first-grade schoolchildren.

This study was undertaken to investigate the effect of developmental stage of the dentition on speech sound production in children with and without articulatory speech disorders. In the whole sample, there were 281 subjects, mean age 7.5 years (SD 0.4). The stage of the eruption of the permanent incisors was calculated as the percentage height of each tooth of the mean crown height of the corresponding tooth in a group of 252 young adults. Eruptional stage of the first permanent molars was classified into three categories. Articulatory disorders were diagnosed by one experienced speech therapist and phoniatrician using the Remes Articulation Test [Remes, 1975] for the Finnish language. The results showed a wide interindividual variation in developmental stage of the dentition in a group of 7-year-old children with a tendency of the first permanent molars but not the incisors to erupt earlier in girls than in boys. Boys had a higher frequency of misarticulations estimated to need treatment than did girls. The present results indicate that during eruption of permanent teeth it is more important to draw attention to symmetrical eruption and to individual timing pattern rather than to the mean values of tooth eruption in subjects of the same age. The findings also suggest a decreasing risk of faulty speech sound production with advancing eruption of some permanent teeth still present in 7-year-old children.     

Brief communication: Emergence chronology of permanent teeth in Nigerian children

This study measured the mean age, duration, and sequence of the emergence of permanent dentition in Nigerian children and compared the findings with other population groups. The cross‐sectional study involved 1,078 Nigerian children, aged 4–16 years old, from selected primary and secondary schools in the Ife Central local government area in Ile‐Ife, Osun State. In general, compared to boys, girls had an earlier mean age of emergence of all the permanent teeth. Children from high socioeconomic class had an earlier mean age of emergence for the maxillary incisors (6.43 and 7.58 years) and mandibular incisors (5.28 and 6.44 years) compared to children from middle and low socioeconomic classes, although socioeconomic effects were more mixed for premolars and molars. Compared to their counterparts in the USA, Australia, Belgium, and Iran, Nigerian children showed an earlier mean age of emergence of all the permanent teeth studied except for Pakistani boys, who had an earlier mean age of emergence of the maxillary premolars and second molar. Poorer economic status has been associated with delayed dental development; however, when compared to other populations, the Nigerian children in this study have earlier mean emergence ages than children from wealthier countries such as the USA and Australia. Am J Phys Anthropol 153:506–511, 2014. © 2013 Wiley Periodicals, Inc.     

Age determination in roe deer — a new approach to tooth wear evaluated on known age in dividuals

A novel, simple, and objective method is presented for ageing roe deerCapreolus capreolus (Linnaeus, 1758) evaluated on 471 lower jaws from roe deer of known age (351 with permanent premolars). It is based on tooth eruption patterns and presence/absence of wear characters in jaws from roe deer integrated in a scoring system. Permanent cheek teeth emerge in May–July in the year af ter birth, which enables precise age determination of individuals with deciduous premolars. For individuals with permanent cheek teeth, the method provides the correct age for all individ uals younger than 13 months and > 80% of all individuals between 13 and 24 months old. For older in dividuals the accuracy decreases, but decent accuracy is achieved to the age of 48 months. Males have higher wear rates than females corroborating recent documentation of sex-specific life history tactics in ungulates. The data originate from two separated Danish roe deer populations exposed to contrasting habitats, but no difference in wear rate is found between populations. Thus, previous concern about the validity of age determination methods based on tooth wear may have been overstated. The findings demonstrate that objective measures of tooth wear can provide the basis for age determination in ungulate species that are otherwise difficult to age.