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.     

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.     

Gaining New Insights into How Genetic Factors Influence Human Dental Development by Studying Twins

Many previous attempts to quantify the contribution of genetic factors to human dental variation using the classical twin design have been based on untested assumptions that lead to unreliable estimates of heritability. We have applied structural equation modelling to several different dental phenotypes in a sample of over 600 pairs of Australian twins, enabling the goodness-of-fit of the data to be tested against genetic models incorporating different components of genetic and environmental variance. Our results indicate that the contribution of additive genetic effects to phenotypic variation differs considerably between different dental traits. Heritability estimates for intercuspal distances of molar teeth and for incisal overbite and overjet are low to moderate in magnitude, whereas heritabilities for overall molar crown size and arch dimensions are moderate to high. We propose that after formation of the enamel knots during odontogenesis, the emerging pattern of molar cusps results from a cascade of local epigenetic events, rather than being under direct genetic control. Variation in molar crown size is explained best by a model incorporating additive genetic effects, as well as environmental influences that are both unique and common to co-twins. These environmental influences presumably operate in utero during the early stages of molar odontogenesis prior to crown calcification. The relatively low heritabilities noted for occlusal traits are consistent with the importance of masticatory activity and muscle function in determining the interrelationships between teeth in opposing dental arches. We believe that well-designed studies of twins, coupled with modern genome-scanning approaches, offer great potential to identify key “dental” genes and to clarify how these genes interact with the environment during development.     

Dental structure of the Giant lantern shark <Emphasis Type="Italic">Etmopterus baxteri</Emphasis> (Chondrichthyes: Squaliformes) and its taxonomic implications

Dogfish sharks (Squaliformes) are a highly diverse group of neoselachians occurring in a wide range of marine environments and are common members of deep-sea faunas. The order Squaliformes comprises six families with approximately 98 extant species. The dentition of most squaliforms is characterized by a strong dignathic heterodonty and dental variation yielding a suite of potential tooth characters that could be used for taxonomic and systematic purposes. So far, no detailed study has been carried out to analyse the use of tooth morphologies in reconstructing the phylogeny of squaliforms. Also, the degree of characteristics of intraspecific variability of tooth morphologies is still unclear. Here, we analysed the dental differences between juveniles and adults and between the sexes of the Giant lantern shark, Etmopterus baxteri, and tested these dental characters for taxonomic purposes employing different statistical procedures. The results show that upper teeth of adult females and males differ morphologically in that those of females are bigger and display a lanceolate central cusp, whereas male specimens have thin and needle-like central cusps. Upper teeth of males have a higher number and a more pronounced variability of lateral cusplets than those of females. Moreover, an ontogenetic heterodonty might be developed in male specimens with sexually immature males displaying similar dental morphologies to those of adult females. Lower teeth, conversely, do not differ morphologically between the sexes. Results indicate that tooth morphologies of squaliform sharks bear high potential for phylogenetic purposes if tooth variations are considered, but have to be treated with care, if no variation is analysed.     

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.     

Longitudinal analysis of deciduous tooth emergence: III. Sexual dimorphism in Bangladeshi, Guatemalan, Japanese, and Javanese children

Previous studies, mostly in European populations, found sex differences in the pattern of deciduous tooth emergence. Most studies find that the anterior dentition in males is precocial relative to the female dentition, and the pattern reverses so that females lead males in the emergence of the posterior deciduous dentition. Less is known about sex differences in the dental development and emergence of non-European populations. Here we examine the pattern of sex differences in deciduous tooth emergence in Japanese, Javanese, Guatemalan, and Bangladeshi children. The data come from four longitudinal or mixed longitudinal studies using similar study protocols. Survival analysis was used to estimate parameters of a log-normal distribution of emergence for each of the 10 teeth of the left dentition, and sexual dimorphism was assessed by sex-specific differences in mean emergence times and by Bennett's index. The results support the pattern of developmental cross-over observed in other populations. We conclude that there is little evidence to support the hypothesis of Tanguay et al. ([1984] J. Dent. Res. 63:65-68) that ethnic factors mediate sex differences in the emergence of deciduous teeth.     

Intrapopulation variation in macro tooth wear patterns—a case study from Igloolik,Canada

The pattern of human tooth wear—the way it varies between teeth in the mouth—is crucial to our understanding of important questions in archeology and paleoanthropology, such as the contrasts in diet and behavior between Neanderthals and early modern humans in Europe and Asia, or with the adoption of agriculture in the Americas. Little is known, however, about the way in which wear patterns develop with increasing age or the way in which they differ between males and females. One explanation is that few living people show the high rates of tooth wear seen worldwide throughout the preindustrial archaeological record. The study described here investigates the macroscopic pattern of tooth wear in a unique group of known age and sex dental casts from living Canadian Inuit from Igloolik. The results show that the Igloolik people possessed a pattern of extremely heavy anterior tooth wear, relative to the first molar and the other posterior teeth, which is attributed to the use of the anterior teeth in cultural practices as well as the extreme and marginal environments in which they lived. Heavy anterior tooth wear was established at an early age and maintained throughout life; statistically significant differences were found between the wear patterns of males and females and are explained in terms of sexual division of labor within the community. This study highlights the need to understand both intra‐ and interpopulation variation in tooth wear patterns when interpreting patterns in past human groups. Am J Phys Anthropol, 2012. © 2012 Wiley Periodicals, Inc.     

Sizes of deciduous teeth in 47,XYY males.

Deciduous teeth of six 47,XYY males have been examined, and the tooth sizes were found to be larger than those of controls. We concluded that a factor or factors which influence excess dental growth in 47,XYY males are probably in effect before the age of a few months. The time needed for the achievement of final tooth growth excess seems to be limited to a 9--18 month period. It also became evident that excess dental growth of 47,XYY individuals is a developmentally stable process, and the Y chromosome apparently regulates quantitative variation of the teeth in normal males [2]. These observations on tooth sizes in 47,XYY males suggest a chromosomal influence on dental determination.     

A genetic analysis of body size in pink salmon (Oncorhynchus gorbuscha)

Two small-sized and two large-sized male pink salmon (Oncorhynchus gorbuscha) were mated to each of four females, producing eight families sired by small males and eight sired by large males. The juveniles were reared for 500 d after fry emergence. Juvenile weight in the two male size classes was similar until the spring of the year of maturity, when juveniles sired by large males grew faster than those sired by small ones. Heritability estimates of weight based upon the dam component of variance increased during 500 d of rearing from 0.4 to 0.8. Heritability of weight based upon the sire component of variance generally ranged between 0.1 and 0.3. The large variation in male body size in spawning pink salmon populations may have resulted from different male breeding strategies.     

Dental caries prevalence as evidence for agriculture and subsistence variation during the Yayoi period in prehistoric Japan: biocultural interpretations of an economy in transition

The Yayoi period represents the earliest point of agricultural dependence in Japan, dating from approximately 2500 BP to AD 300. Yayoi period people consumed wet-rice as a primary subsistence base. This article uses dental caries prevalence to interpret the biocultural implications of agriculture among these people by testing the following hypotheses: 1) Yayoi period agriculturalists had greater frequencies of carious teeth than Jomon period foragers, 2) regional variation in carious tooth frequencies will be observed among Yayoi period agriculturalists, while 3) variation in carious tooth frequencies will be observed between male and female agriculturalists. Statistically significant differences in carious teeth were observed between the agriculturalists from Southern Honshu and all other samples. These differences suggest greater reliance on cariogenic plants among farmers from Southern Honshu and are consistent with an agricultural economy. The people of the Yayoi period from Tanegashima Island and Northern Kyushu did not have significantly different carious tooth frequencies compared to Jomon period foragers. This suggests that rice alone was not a more cariogenic dietary substance than those consumed by Jomon period foragers but a cariogenic food nonetheless. Dietary heterogeneity between the prehistoric people of the Yayoi period from Southern Honshu and those from Northern Kyushu and Tanegashima Island is also inferred from these differences. Significantly greater frequencies of carious teeth among older aged Yayoi period females compared with males suggest dietary differences between the sexes.     

Odontometric variations of permanent crown in Punjabi and U.S. twins

The study reports odontometric variations within and between Punjabi and U.S. twins. The data are based on 23 MZ and 35 DZ Punjabi twin pairs and 32 MZ and 43 DZ U.S. pairs. None of the t' tests indicates differences between MZ and DZ mean dental dimensions in either sample. Mean tooth dimensions of Punjabi twins are in general greater than those of U.S. twins with significant differences for about 25% of the traits. Coefficient of variation is highest in lateral incisors and canines and lowest in first molars in both samples. The two samples differ more in their variances than in their means. The results indicate that buccolingual dimensions of mandibular traits are under relatively greater selection pressure.     

Comparing sensory experience in bitter taste perception of phenylthiocarbamide within and between human twins and singletons: intrapair differences in thresholds and genetic variance estimates

BACKGROUND: Quantitative genetic studies revealed that not all of the phenotypic variance in PTC taste perception is heritable. AIM: To study quantitative variations in PTC tasting ability in twins and to estimate heritability of PTC taste perception on the taste of twin data on males and females sexes separately. SUBJECTS AND METHODS: The data for PTC taste sensitivity following the classic method of Harris & Kalmus (1949) were collected on a sample of 141 twin pairs (66 MZ and 75 DZ) and 275 singletons (128 males and 147 females) from Chandigarh, India. Genetic analyses were performed following Christian (1979), Donner (1986) and Sham (1998). RESULTS: Frequency of non-tasters was similar in twins (33 %) and singletons (32 %), but significant sex differences were observed. No differences were found between zygosities for mean thresholds. Similarly, no evidence of variance heterogeneity and environmental covariance was seen between zygosities. Since no basic assumption of the twin method was found violated, within-pair estimates of genetic variance would be unbiased. These estimates were highly significant in both males and females. However, dominance and additive components of genetic variance were found to differ between sexes. CONCLUSION: PTC thresholds do not seem to be significantly affected by environmental factors as no variance inequality was observed between twin zygosities. Intensity of bitterness (scalar dimensions) of PTC is a separate trait having no commonality with the genetic basis of recognition threshold for PTC tasting ability. The receptors recognizing bitter taste are different from the receptors determining intensity of taste. The absolute difference between co-twins in PTC thresholds can be used as a simple tool in the twin zygosity diagnosis. The results show that none of the MZ co-twins had manifested difference of more than 3 in their PTC threshold.     

Teeth emergence in wild olive baboons in Kenya and formulation of a dental schedule for aging wild baboon populations

Teeth emergence schedules are presented from analysis of 95 wild olive baboons Papio anubis (age range 2–120 months) and compared to recently published results for wild and captive yellow baboons (P. cynocephalus; Phillips-Conroy and Jolly: American Journal of Primatology 15:17–29, 1988). Age at emergence of M1 (20.5 months males, 19.5 months females), I1 (32.5 and 33.5 months) and I2 (40.0 and 39 months) of olive baboons was earlier than in the wild yellow baboons and similar to captive yellow baboons. However, the later emerging teeth were delayed considerably relative to the captive animals and were similar in age of emergence to those of wild yellow baboons. Considerable variation in age of emergence occurred in the later emerging teeth especially among males. Regression analysis of dental scores with age demonstrated differences between olive baboons and captive yellow baboons but not between olive baboons and wild yellow baboons. Combined data on dental scores for wild yellow, olive, and hamadryas baboons provide schedules of AGE (months) = {SCORE – 11.79} ÷ 0.4405 and AGE (months) = {SCORE – 11.24} ÷ 0.4797 for males and females, respectively, which may be used for aging wild baboons. Full permanent dentition in wild baboons is predicted to occur over 1 year later than in captive animals.     

Effect of undernutrition on deciduous tooth emergence among Rajput children of Shimla District of Himachal Pradesh, India

This article examines the influence of nutritional status on the emergence of deciduous dentition in a cross-sectional sample of 510 rural Rajput children from the Jubbal and Kotkhai Tehsils, Shimla District, Himachal Pradesh, India. The nutritional status of each child was evaluated using Z-scores of height/supine length-for-age (HAZ), weight-for-age (WAZ), and weight-for-height (WHZ). The effects of sex and side on deciduous dental emergence were not statistically significant. Partial correlation indicates that the number of emerged teeth (T) was more strongly correlated with height than with other anthropometric variables. In most age groups, the stunted boys and girls (HAZ <-2) had fewer emerged teeth than nonstunted age peers (HAZ >-2). The mean T in underweight children was also less than that of the normal children, with a few exceptions. The stunted children have a significantly greater likelihood of delayed emergence of deciduous dentition. Measures of linear growth status are more closely related to dental development than measures of growth in mass. The findings indicate that even moderate undernutrition can delay deciduous tooth emergence.     

Recapture of male and female dragonflies in relation to parasitism by mites, time of season, wing length and wing cell symmetry

For aquatic mites parasitic on dragonflies, completion of their life cycle depends on their being returned to appropriate water bodies by their hosts, after completion of engorgement. We examined whether differences among hosts in timing of emergence or phenotypic attributes might affect their probability of return to an emergence pond, and hence success of mites. Parasitized males and females of the dragonfly Sympetrum obtrusum (Hagen) did not differ in overall recapture rates. Females that had wing cell symmetry and emerged early were more likely to be recaptured than females that emerged later or had wing cell asymmetry, but there were no consistent relations between these variables and parasitism by mites. No such relations between wing cell asymmetry, emergence date, and recapture likelihood were found for males. Using randomization tests, we found that mean intensities of Arrenurus planus (Marshall) mites at host emergence were the same for recaptured females and females not recaptured; however, males that were recaptured had lower mean intensities of mites at emergence than males not recaptured. Further, mature females carried more mites than mature males, and the latter had fewer mites than newly emerged males not recaptured. Biases in detachment of engorging mites do not explain the differences in parasitism between mature males and females, nor the differences in mite numbers between mature males and newly emerged males that were not recaptured. Rather, heavily parasitized males appear to disperse or die and are not recaptured, which should have implications for dispersal of mites and fitness of male hosts.     

Dental health of elderly confederate veterans: evidence from the Texas State Cemetery

Analysis of the skeletal remains of 50 Confederate veterans provided a unique opportunity to explore the dental health of a geriatric sample. These men, who died between 1907-1932, had an average age at death of 76.7 years. Ninety percent were institutionalized at the Confederate Home for Men (Austin, TX) prior to their deaths. This elderly sample was assessed in terms of caries, antemortem tooth loss (AMTL), abscesses, and linear enamel hypoplasias. On a per tooth basis, the AMTL rate was 57.2%. Of 39 dentate men, 33 (84.6%) had dental caries, and 24.4% (121 of 496) of teeth were carious. Ten (25.0%) of the dentate men had hypoplastic teeth. At least one abscess was seen in 14 (28%) of 50 individuals. Results from this geriatric institutionalized sample are compared to contemporaneous historical samples. Disparities in dental health among these groups may be due to differences in average age at death, and these comparisons allow a better understanding of dental changes that occur with age. The sample is also compared to modern elderly samples: modern groups have higher caries rates, possibly because they retained more teeth. This finding may be due in part to diets in the United States becoming increasingly cariogenic over time. In addition, dental care has moved from the reactive practices seen in the nineteenth and early twentieth centuries (such as tooth extractions) to modern proactive solutions dedicated to preserving and restoring teeth (such as tooth brushing, fluoride treatments, and dental fillings).     

The developing dentition and tooth structure in hominoids

This review of hominoid dental development is presented in two parts. The first section reviews (1) the general relationship between dental development and life history in hominoids; (2) the methods used to document dental development, and (3) the nature of incremental growth markings in hominoid teeth. The second section builds on this and reviews the contributions to hominoid dental development that have been made by (1) studies of tooth emergence; (2) studies of tooth calcification stages, and (3) histological studies of incremental growth markings made either from sections of teeth or replicas of early hominid teeth prepared for scanning electron microscopy.     

Wear Fast,Die Young: More Worn Teeth and Shorter Lives in Iberian Compared to Scottish Red Deer

Teeth in Cervidae are permanent structures that are not replaceable or repairable; consequently their rate of wear, due to the grinding effect of food and dental attrition, affects their duration and can determine an animal''s lifespan. Tooth wear is also a useful indicator of accumulative life energy investment in intake and mastication and their interactions with diet. Little is known regarding how natural and sexual selection operate on dental structures within a species in contrasting environments and how these relate to life history traits to explain differences in population rates of tooth wear and longevity. We hypothesised that populations under harsh environmental conditions should be selected for more hypsodont teeth while sexual selection may maintain similar sex differences within different populations. We investigated the patterns of tooth wear in males and females of Iberian red deer (Cervus elaphus hispanicus) in Southern Spain and Scottish red deer (C. e. scoticus) across Scotland, that occur in very different environments, using 10343 samples from legal hunting activities. We found higher rates of both incisor and molar wear in the Spanish compared to Scottish populations. However, Scottish red deer had larger incisors at emergence than Iberian red deer, whilst molars emerged at a similar size in both populations and sexes. Iberian and Scottish males had earlier tooth depletion than females, in support of a similar sexual selection process in both populations. However, whilst average lifespan for Iberian males was 4 years shorter than that for Iberian females and Scottish males, Scottish males only showed a reduction of 1 year in average lifespan with respect to Scottish females. More worn molars were associated with larger mandibles in both populations, suggesting that higher intake and/or greater investment in food comminution may have favoured increased body growth, before later loss of tooth efficiency due to severe wear. These results illustrate how independent selection in both subspecies, that diverged 11,700 years BP, has resulted in the evolution of different longevity, although sexual selection has maintained a similar pattern of relative sex differences in tooth depletion. This study opens interesting questions on optimal allocation in life history trade-offs and the independent evolution of allopatric populations.     

Relationship between dental morphology, sex, body length and age in Pontoporia blainvillei and Sotalia fluviatilis (Cetacea) in Northern Rio de Janeiro, Brazil

The relationship between dental morphology, sex, body length and age of small cetaceans can be used to determine ontogeny, sexual dimorphism and geographical variation. The objective of this study was to determine the relationship between dental morphology, sex, body size and age. A total of 91 specimens of P. blainvillei and 80 specimens of S. fluviatilis accidentally captured in fisheries or stranded in northern Rio de Janeiro (21 masculine37'-22 masculine25'S), from September 1988 to November 1996 were analysed. The teeth root diameter in P. blainvillei was significantly different between the sex; the values for females were larger than males. In neither species aid we observed significant in variations dimension and number of teeth, thickness of dentine and cemental layers and in the maximum width of cement as a function of body size. Age was related to increases in tooth length, root and cingulum diameters, and maximum width of cement in individuals of P. blainvillei, and tooth and crown lengths and maximum width of cement in individuals of S. fluviatilis. The observation of a linear growth between maximum width of cement and age in both species indicates that the equations obtained can be used to estimate relative age in P. blainvillei and S. fluviatilis in northern of Rio de Janeiro.