47,XXX females, sex chromosomes, and tooth crown structure

Gender determination using mandibular intercanine distance and mesiodistal width of right mandibular molar

Background

Forensic odontology plays an important role in mass disasters, house fires, criminal deaths, identification of missing persons, and child abuse cases. Teeth are the most stable part of the human body and are resistant to thermal, mechanical, and chemical insults. The aim of this study was to evaluate the effectiveness of mandibular intercanine distance and mesiodistal width of mandibular first molar in gender determination.

Materials and Methods

The study comprised 100 participants (50 males and 50 females) in the age group of 18-23 years. The mandibular impressions were made, and casts were prepared using dental stone. The intercanine distance and mesiodistal width of the right mandibular first molar were measured using digital vernier callipers. The data obtained was statistically analysed using SPSS software version 23.

Results

The mean mandibular intercanine distance was found to be 27.2 ± 2.3 in males and 25.94 ± 1.76 in females (P = 0.03). There was no statistical difference in the mesiodistal width of the mandibular molar between males and females (P = 0.166). However, the mean mesiodistal width of males was higher when compared to females.

Conclusion

Males have a greater intercanine width and mesiodistal dimension when compared to females. This result will be helpful in forensic medicine, anthropology, orthodontic treatments, and clinical dentistry.

Crown heights in the permanent teeth of 47,XXY males and 47,XXX females

OBJECTIVE

Earlier results based on dental casts and radiographs have shown that additional X and Y chromosomes influence permanent and deciduous tooth crown sizes, with 47,XYY males exhibiting greater crown heights than 46,XY males. We studied here the effect of both X and Y chromosomes on tooth crown heights.

MATERIAL AND METHODS

The series consisted of 48 47,XXY males, 22 of their male relatives, and seven 47,XXX females with five female relatives. The population controls consisted of 27 males and 33 females. Measurements of all applicable teeth except for the third molars on both sides of the jaws were made on panoramic radiographs with a sliding digital calliper.

RESULTS

Apart from a few teeth, the mean crown heights in the 47,XXY males were greater than those in the male population controls, the differences being statistically significant for one tooth in the maxilla and ten teeth in the mandible. With the exception of two teeth, the 47,XXX females had taller tooth crowns than the female population controls, the differences in the two teeth being statistically significant. The 47,XXY males had greater tooth crown heights than the 47,XXX females, except in one tooth, and the differences were significant in two teeth. The tooth crown heights of the male relatives of the 47,XXY males and the female relatives of the 47,XXX females were close to those in the general population.

CONCLUSIONS

The present results demonstrated the effect of additional X and Y chromosomes in increasing crown heights. The differences between the 47,XXY males and 47,XXX females indicated a stronger effect of a Y chromosome on tooth crown height than of an X chromosome.

Dimorphism in dental tissues: Sex differences in archaeological individuals for multiple tooth types

OBJECTIVES

Dimorphism in the dentition has been observed in human populations worldwide. However, research has largely focused on traditional linear crown measurements. As imaging systems, such as micro-computed tomography (micro-CT), become increasingly more accessible, new dental measurements such as dental tissue size and proportions can be obtained. This research investigates the variation of dental tissues and proportions by sex in archaeological samples.

MATERIALS AND METHODS

Upper and lower first incisor to second premolar tooth rows were obtained from 30 individuals (n = 300), from 3 archaeological samples. The teeth were micro-CT scanned and surface area and volumetric measurements were obtained from the surface meshes extracted. Dental wear was also recorded and differences between sexes determined.

RESULTS

Enamel and crown measurements were found to be larger in females. Conversely, dentine and root measurements were larger in males.

DISCUSSION

The findings support the potential use of dental tissues to estimate sex of individuals from archaeological samples, while also indicating that individuals aged using current dental aging methods may be underaged or overaged due to sex differences in enamel thickness.

Tooth Crown Morphology in Turner and Klinefelter Syndrome Individuals from a Croatian Sample

OBJECTIVE

Turner syndrome (TS) and Klinefelter syndrome (KS) represent the two most common X chromosome aneuploidies, each associated with systemic disruptions to growth and development. Effects of these conditions on tooth crown morphology are explored in a sample of Croatian individuals.

MATERIALS AND METHODS

The sample included 57 TS, 37 KS and 88 control individuals. Dental crown morphology was scored on dental casts according to the Turner-Scott Dental Anthropology System.

RESULTS

Incisor shoveling and the hypocone were significantly different between TS individuals and both control and KS individuals. Individuals with TS exhibit lower grades of expression than either group. Furthermore, the number of lingual cusps on the mandibular premolars, the hypoconulid on the mandibular second molar, and cusp 7 on the mandibular first molar were significantly different, though pair-wise comparisons did not elucidate these differences. Tuberculum dentale, distal accessory ridge, and Carabelli's trait were expressed similarly to the control. KS individuals were not significantly different from control individuals for any trait, though this may be related to sample size.

CONCLUSIONS

Previous studies suggest the loss of an X chromosome has a reducing effect on dental crown morphology, which is confirmed in this research. TS individuals exhibit generally simpler dental morphology compared to the control sample, though some traits are expressed comparably to the control sample. The effects of KS are less clear. Though previous studies suggest that the presence of an extra X chromosome increases dental crown dimensions, there was no notable effect on crown morphology in this study.

Comparing Different Methods to Estimate the Combined Mesiodistal Widths of Maxillary and Mandibular Incisors

Objective

This study aimed to develop regression equations to predict the combined mesiodistal widths of maxillary and mandibular incisors from each other and compare them with other methods.

Methods

One hundred pairs of study models from 100 Iraqi subjects with normal occlusion were used in this study. The individualized mesiodistal widths of maxillary and mandibular incisors were measured using electronic digital calipers. The combined mesiodistal widths of maxillary and mandibular incisors were calculated according to Tonn's and Abhi's formulas and from regression equations to be compared with the actual one.

Results

Both sums of the maxillary and mandibular incisors were significantly correlated. There were significantly high differences between the actual and calculated sum widths, and also between the calculated and predicted ones. On the other hand, a non-significant difference was obtained between the actual and predicted sum widths of maxillary and mandibular incisors.

Conclusion

Tonn's and Abhi's methods are not reliable methods to calculate the sum widths of maxillary and mandibular incisors. New regression equations are developed to predict the sum widths of maxillary and mandibular incisors from each other.

Influence of long and short arms of X chromosome on maxillary molar crown morphology

Although genes on the human X chromosome reportedly influence tooth crown morphology, little is known about X chromosome activation or inactivation systems relevant to morphological variations. We assessed the relationships between tooth crown size and crown morphological traits in females with Turner syndrome, the variants of which include complete absence of one X chromosome, lack of the short arm (Xp), or duplication of the long arms (Xq), and then estimated the functions of Xp and Xq in the process of unilateral X chromosome inactivation during tooth crown development. The mesiodistal and buccolingual diameters in the maxillary first (M1) and second (M2) permanent molars were compared among X chromosome karyotypes by multiple regression analyses, and their relationships with the development of Carabelli’s cusp and the distolingual cusp were analyzed using logistic regression analysis.

The crown sizes increased in the order of the 46,X,i(Xq) karyotype, 45,X and 45,X/46,XX karyotypes, and control group. A lower frequency of Carabelli’s cusp and higher frequency of a reduced distolingual cusp in M1 were characteristics of Turner syndrome. The overall M1 and M2 crown sizes differed among the X chromosome karyotypes, whereas a smaller crown size was associated with a reduced distolingual cusp but not with Carabelli’s cusp. Considering the differences in chromosome arrangement among females with Turner syndrome and the process of unilateral X chromosome inactivation, the observed results can be considered in terms of quantity or number of promoters/inhibitors during tooth crown development.

The X chromosome karyotypes have a strong influence on the overall crown sizes of the M1 and M2 molars because those karyotypes with variable numbers of active gene regions directly influence tooth germ development in an early stage of human odontogenesis. The later forming cusps, such as the distolingual cusp and Carabelli’s cusp, may be affected by this developmental prerequisite.

Crown heights in the permanent teeth of 47,XYY males

OBJECTIVE

The results in human sex chromosome aneuploidies had shown that the extra Y chromosome increases permanent and deciduous tooth crown sizes in the mesiodistal and labiolingual directions. The hypothesis of the study was that the additional Y chromosome increases the permanent tooth crown growth in a vertical dimension. We also aimed to observe possible sex difference in the permanent tooth crown height.

MATERIAL AND METHODS

Data on 15 47,XYY males or males with an extra Y chromosome, nine male relatives (five brothers and four fathers) and 45 male and 48 female population controls had been gathered previously for Professor Lassi Alvesalo's KVANTTI Research Project. The measurements from panoramic radiographs were performed of all the applicable teeth, except the third molars on both sides of the jaws with a sliding digital calliper.

RESULTS

All the mean tooth crown heights in the 47,XYY males were larger than in the male population controls and the differences were statistically significant in six teeth in the maxilla and 10 teeth in the mandible. Apart from few teeth, the crown heights in the 47,XYY males were larger than in their male relatives, but the difference between these groups was significant only in one tooth. The differences between sexes were statistically significant in eight teeth in the maxilla.

CONCLUSIONS

Based on previous investigations and this work, it is evident that the impact of the extra Y chromosome during tooth crown development is holistic, increasing permanent tooth sizes in three dimensions in a balanced manner.

Linear Odontometric Analysis of Permanent Dentition as A Forensic Aid: A Retrospective Study

INTRODUCTION

Sex determination in forensic anthropology is an essential step for medico-legal purposes and crucial for identification as the number of possible matches is reduced to 50%. Teeth are an excellent material for anthropological, genetic, odontological and forensic investigations as they are known to resist a variety of ante-mortem and post-mortem insults. Sexual dimorphism in tooth size and the accuracy of odontometric sex prediction is found to vary in different population and therefore it is necessary to determine specific population values in order to make identification possible. Hence, the present study was undertaken to evaluate the existence of sexual dimorphism in South Kerala population.

AIM

To evaluate and estimate the degree of odontometric sexual dimorphism in all permanent teeth except third molars and the variations in odontometric dimensions between the left and right side teeth of the maxillary and mandibular arches in male and female groups.

MATERIALS AND METHODS

The MesioDistal (MD) and BuccoLingual (BL) measurements of 28 teeth were estimated from the preorthodontic casts of 132 subjects; male group (66 males) and female group (66 females) of age range 15-25 years using digital Verniers' Caliper. The data obtained were analysed using SPSS version 17 and the Students' t-test for two independent samples.

RESULTS

The MesioDistal (MD) and BuccoLingual (BL) parameters of all permanent teeth in the study group showed sexual dimorphism. Over 39% of the tooth variables showed reverse dimorphism. The comparison of mean values of MD and BL diameters of the maxillary and mandibular, right and left side teeth in male and female groups showed statistical significance in males whereas females show non-significant values in both MD and BL diameters.

CONCLUSION

The study showed a varied percentage of sexual dimorphism and variation in the mean values of MD and BL dimensions in males, but not in females between right and left side teeth of the maxillary and mandibular arches of the study population.

Crown heights in the permanent teeth of 45,X and 45,X/46,XX females

OBJECTIVE

Previous results regarding human sex chromosome aneuploidies have shown that the X and Y chromosomes affect tooth size and morphology. This study looked for the effect of sex chromosome deficiency on permanent tooth crown heights.

MATERIALS AND METHODS

The material, from the Finnish KVANTTI Research Project, consisted of 97 45,X females and 15 45,X/46,XX females. The controls were 32 sisters and 28 mothers of the 45,X females, eight sisters and two mothers of the 45,X/46,XX females and 35 female population controls. Crown heights of all the available teeth except third molars on both sides of the jaws were measured from panoramic radiographs with a digital calliper according to the defined procedure.

RESULTS

The tooth crown heights were significantly smaller in the 45,X females than in the female population controls, except for the incisors and one canine in the maxilla, whereas the tooth crown heights of the 45,X/46,XX females were close to those of the normal control females. The differences between the 45,X and 45,X/46,XX females were statistically significant, excluding the upper incisor area and a few teeth in the mandible.

CONCLUSIONS

The effect of the sex chromosome deficiency on permanent tooth crown height is due to the magnitude of lacking sex chromosome material. The present results regarding the 45,X females are parallel to previous findings in Turner patients regarding reduced mesiodistal and labiolingual dimensions and tooth crown heights in the permanent dentition.

Root lengths in the permanent teeth of 45,X females

OBJECTIVE

Studies in permanent and deciduous tooth crowns and permanent tooth roots in individuals with sex chromosome anomalies and in their relatives have given proof that the X chromosome affects enamel formation, root length and crown and root morphology. The present research studies the effects of sex chromosome deficiency on the development of permanent tooth root.

MATERIALS AND METHODS

This research investigated tooth root lengths in a group of 97 45,X females. As controls there were 32 sisters and 28 mothers of the 45,X females, 45 female and 42 male population controls and 15 45,X/46,XX females from the KVANTTI research project. Tooth root lengths on both sides of the jaws were measured from panoramic radiographs in each acceptable instance.

RESULTS

The results showed significantly shorter tooth root lengths in the 45,X females than in the female and male controls in all teeth measured, whereas in the female relatives tooth root lengths were shifted towards the aneuploids in relation to that in the general population. The tooth root lengths in the 45,X females differed more from those found in their sisters than in their mothers.

CONCLUSIONS

These results with the large pure sample size of the whole dentitions in patients with monosomy X confirm the earlier findings of short tooth roots in 45,X females. The fact that in most instances there were no significant differences in tooth root lengths between 45,X and 45,X/46,XX females comes close to the earlier findings regarding mesio-distal tooth crown sizes.

Sexual dimorphism in permanent teeth of modern Greeks

Sex determination is considered an important step in reconstructing the biological profile of unknown individuals from a forensic context. Forensic anthropologists have long used teeth as an additional tool for sex determination as they resist postmortem destruction. In this case the use of population-specific data is necessary since sexual dimorphism varies between different populations. Currently there are no odontometric standards for determining sex in Greek populations. The purpose of this study is to examine the degree of sexual dimorphism in permanent teeth of modern Greeks. A total of 839 permanent teeth in 133 individuals (70 males and 63 females) from the Athens Collection were examined. Mesiodistal and buccolingual crown and cervical diameters of both maxillary and mandibular teeth were measured. It was found that males have bigger teeth than females and in 65 out of 88 dimensions measured, male teeth exceeded female teeth significantly (P<0.05). Canines were the most dimorphic teeth followed by first premolars, maxillary second premolar and mandibular second molar. Although other teeth were also sexually dimorphic they did not have a statistically significant difference in all dimensions. The most dimorphic dimension was buccolingual cervical diameter followed by buccolingual crown diameter. A comparison of sexual dimorphism in teeth between different populations showed that it differs among different groups. European population groups presented the highest degree of sexual dimorphism in teeth whereas Native South Americans the lowest.

Root length in the permanent teeth of women with an additional X chromosome (47,XXX females)

OBJECTIVE

Previous studies have demonstrated differential effects of the X and Y chromosomes on dental development. The expression of sexual dimorphism in terms of tooth size, shape, number and developmental timing has been explained especially by Y chromosome influence. The Y chromosome promotes enamel, crown and root dentin development. The X chromosome has an effect on enamel deposition. The aim of this research is to study the influence of the extra X chromosome on the development of permanent tooth root length.

MATERIAL AND METHODS

The study subjects (all of whom were from the Kvantti Dental Research Project) were seven 47,XXX females, five female relatives and 51 and 52 population control men and women, respectively. Measurements were made from panoramic radiographs on available permanent teeth by a digital calliper according to established procedures.

RESULTS

The results showed that the maxillary root lengths of the 47,XXX females were of the same magnitude as those in normal women, but the mandibular root lengths were longer in 47,XXX females than in normal men or women.

CONCLUSIONS

Increased enamel thickness in the teeth of 47,XXX females is apparently caused by the active enamel gene in all X chromosomes having no increased influence on crown dentin formation. These results in 47,XXX females indicate an increase in root dentin development, at least in the mandible, which together with the data on crown formation reflects a continuous long-lasting effect of the X chromosome on dental development.

Altering biomineralization by protein design

To create a bioceramic with unique materials properties, biomineralization exploits cells to create a tissue-specific protein matrix to control the crystal habit, timing, and position of the mineral phase. The biomineralized covering of vertebrate teeth is enamel, a distinctive tissue of ectodermal origin that is collagen-free. In forming enamel, amelogenin is the abundant protein that undergoes self-assembly to contribute to a matrix that guides its own replacement by mineral. Conserved domains in amelogenin suggest their importance to biomineralization. We used gene targeting in mice to replace native amelogenin with one of two engineered amelogenins. Replacement changed enamel organization by altering protein-to-crystallite interactions and crystallite stacking while diminishing the ability of the ameloblast to interact with the matrix. These data demonstrate that ameloblasts must continuously interact with the developing matrix to provide amelogenin-specific protein to protein, protein to mineral, and protein to membrane interactions critical to biomineralization and enamel architecture while suggesting that mutations within conserved amelogenin domains could account for enamel variations preserved in the fossil record.

Assessment of the accuracy of dental enamel thickness measurements using microfocal X-ray computed tomography

Tooth enamel thickness has long been an important character in studies of primate and especially hominin phylogeny, taxonomy, and adaptation. Current methods for accurately assessing enamel thickness involve the physical sectioning of teeth, because measurements of enamel thickness using some radiographic techniques are unreliable. However, because destructive methods limit sample sizes and access to important fossil specimens, it is desirable that they be replaced with nondestructive techniques. Although microfocal X-ray computed tomography (mCT) has been used recently in studies of enamel thickness, the accuracy of this technique has yet to be established. The present research compares physical sections to computer-generated mCT sections of teeth from a variety of primate and nonprimate, recent and fossil taxa to examine whether enamel thickness, tooth size, and diagenetic remineralization (fossilization) impact the ability of mCT to measure enamel thickness accurately. Results indicate that recent teeth of varying size and thickness are clearly and accurately depicted in mCT scans, with measurements from nearly identical planes in physical and mCT sections differing by 3-5%. A fossil papionin molar (ca. 2 Myr) was also accurately measured using mCT scans, although thinner enamel in much older therapsid (ca. 263-241 Myr) teeth could not be distinguished from dentine. mCT is thus an accurate technique for measuring enamel thickness in recent taxa, although heavily mineralized teeth pose an obstacle to the ability of mCT to distinguish dental tissues. Moreover, absolutely thin enamel (less than approximately 0.10 mm) is difficult to resolve adequately in raw mCT images based on pixel values alone. Therefore, caution must be exercised in the application of mCT to the study of fossilized teeth.

Root growth in the teeth of 46,XY females

The subjects of this study are women with a male sex chromosome complement or 46,XY females who show the complete form of the testicular feminization syndrome (CTF). The basic endocrine defect is end organ insensitivity to androgens. They are on average tall individuals and also show an increase in head and face dimensions relative to normal females. A size increase is likewise evident in permanent tooth crowns and here we report permanent tooth root lengths in eight 46,XY females, their five female relatives and population control females and males. Measurements were made from panoramic radiographs by a digital calliper according to established procedures on both sides of the jaws. The results show increased root lengths of 46,XY females relative to control females with values similar to those in population control males. The root and crown findings point to evident irreversible growth excesses in 46,XY females beginning 3 years after birth up to the age of 14 years expressing an effect which apparently is influencing in a continuous way. Excess root growth conceivably would develop independently of the possible androgen influence, and it is suggested that the increase results from the direct effect of the genes on the Y chromosome. It is possible that these genes on the Y chromosome are the same that promote tooth crown growth.

Sexual dimorphism in modern human permanent teeth

On average, males possess larger tooth crowns than females in contemporary human populations, although the degree of dimorphism varies within different populations. In previous studies, different amounts of either enamel or dentine were implicated as the cause of this dimorphism. In this study, we attempt to determine the nature of sexual dimorphism in the crowns of permanent modern human teeth and to determine if two contrasting tooth types (permanent third molars and canines) show identical patterns of dimorphism in enamel and dentine distribution. We estimated the relative contributions of both enamel and dentine to total crown size, from buccolingual sections of teeth. Our sample consisted of a total of 144 mandibular permanent third molars and 25 permanent mandibular canines of known sex. We show that sexual dimorphism is likely due, in part, to the presence of relatively more dentine in the crowns of male teeth. However, whatever the underlying cause, dimorphism in both tooth root and tooth crown size should produce measurable dimorphism in tooth weight, though this has not been previously explored. Therefore, we provide some preliminary data that indicate the usefulness of wet tooth weight as a measure of sexual dimorphism. Both male permanent third molars and canines are significantly heavier than those of females. The weight dimorphism reported here for both classes of teeth may prove a useful finding for future forensic studies. In particular, weights of canines may be more useful as a means of sexing modern human skeletal material than linear or area measurements of teeth.

The effect of hereditary disorders on tooth components: a radiographic morphometric study of two syndromes

OBJECTIVE

The purpose of this study was to compare tooth components (enamel and dentin) in Familial Dysautonomia (FD) and Down syndrome (DS) in order to assess the extent to which each was affected.

DESIGN

The design was cross-sectional. The sample consisted of 20 FD patients and 45 DS patients. The control group comprised 250 healthy subjects. Mesio-distal crown width (CW), enamel and dentin thickness and pulp chamber dimensions were measured on standardized bitewing radiographs of mandibular second primary and first permanent molars. Statistical analyses were performed between groups using SAS programs.

RESULTS

CW was reduced in both hereditary disorders. In the DS group enamel height (EH) and dentin thickness were reduced. In FD enamel thickness in the primary and permanent molars as well as dentin height (DH) in permanent molars was increased.

CONCLUSIONS

In both syndromes the reduction in CW suggests reduced proliferation during tooth germ formation. However, the differences in enamel and dentin thickness suggest that ameloblasts and odontoblasts were affected differently in the later phases of cell function. In FD cell function is stimulated resulting in thicker enamel and dentin. In DS cell function is reduced resulting in thin enamel and dentin.

Integrating the genotype and phenotype in hominid paleontology

Competing interpretations of human origins and evolution have recently proliferated despite the accelerated pace of fossil discovery. These controversies parallel those involving other vertebrate families and result from the difficulty of studying evolution among closely related species. Recent advances in developmental and quantitative genetics show that some conventions routinely used by hominid and other mammalian paleontologists are unwarranted. These same advances provide ways to integrate knowledge of the genotype into the study of the phenotype. The result is an approach that promises to yield a fuller understanding of evolution below the family level.

Genetics and the evolution of primate enamel thickness: A baboon model

The thickness of mammalian tooth enamel plays a prominent role in paleontology because it correlates with diet, and thicker enamel protects against tooth breakage and wear. Hominid evolutionary studies have stressed the importance of this character for over 30 years, from the identification of "Ramapithecus" as an early Miocene hominid, to the recent discovery that the earliest hominids display molar enamel intermediate in thickness between extant chimpanzees and Australopithecus. Enamel thickness remains largely unexplored for nonhominoid primate fossils, though there is significant variation across modern species. Despite the importance of enamel thickness variation to primate evolution, the mechanisms underlying variation in this trait have not yet been elucidated. We report here on the first quantitative genetic analysis of primate enamel thickness, an analysis based on 506 pedigreed baboons from a captive breeding colony. Computed tomography analysis of 44 Papio mandibular molars shows a zone of sufficiently uniform enamel thickness on the lateral surface of the protoconid. With this knowledge, we developed a caliper metric measurement protocol for use on baboon molars worn to within this zone, enabling the collection of a data set large enough for genetic analyses. Quantitative genetic analyses show that a significant portion of the phenotypic variance in enamel thickness is due to the additive effects of genes and is independent of sex and tooth size. Our models predict that enamel thickness could rapidly track dietary adaptive shifts through geological time, thus increasing the potential for homoplasy in this character. These results have implications for analyses of hominoid enamel thickness variation, and provide a foundation from which to explore the evolution of this phenotype in the papionin fossil record.

Increased primary tooth size in a 47,XXY male: a first case report

Increased tooth size has previously been reported in association with Klinefelter syndrome. However, until now, this observation has been restricted to the permanent dentition. In this paper, we report increased mesio-distal width in the primary incisor and molar teeth of a 47,XXY male.

An evaluation of dental radiograph accuracy in the measurement of enamel thickness

Many studies have employed lateral radiographs to measure the thickness of tooth enamel in recent human and fossil hominid samples, but the accuracy of measurements obtained by this technique has not been assessed. In this study, 20 isolated human maxillary permanent molars were radiographed using the parallel film technique. The crowns were then sectioned longitudinally through the tips of the buccal cusps. Measurements of enamel cap area, and of linear enamel thickness in the occlusal basin and over the metacone apex, were made from the radiographs and corresponding sectioned surfaces. Comparisons of the two sets of values revealed that radiographs generally overestimated enamel thickness but there was considerable variability in the error by which measurements from radiographs either under- or overestimated the true value. Lateral radiographs may provide a rough visual impression of whether a tooth has thin or thick enamel but they do not generally provide for accurate measurement of enamel thickness. Quantitative data on enamel thickness from studies that have employed lateral radiographs should be viewed with circumspection.

Tissue contributions to sex and race: differences in tooth crown size of deciduous molars

This study describes size of constituent deciduous tooth crown components (enamel, dentine, and pulp) to address the manner in which males characteristically have larger teeth than females, and the observation that teeth of American blacks are larger than those of American whites. Measurements were collected (n = 333 individuals) from bitewing radiographs using computer-aided image analysis. Tissue thicknesses (enamel, dentine, pulp) were measured at the crown's mesial and distal heights of contour. Deciduous mesiodistal molar crown length is composed of about 1/7 enamel, 1/3 dentine, and 1/2 pulp. Details differ by tooth type, but males typically have significantly larger dentine and pulp dimensions than females; there is no sexual dimorphism in marginal enamel thickness. Males scale isometrically with females for all variables tested here. Blacks significantly exceed whites in size of all tissues, but tissue types scale isometrically with blacks and whites with one exception: enamel thickness is disproportionately thick in blacks. While the absolute difference is small (5.56 mm of enamel in blacks summed over all four deciduous molar tooth types vs. 5.04 mm in whites), the statistical difference is considerable (P < 0.001). Aside from enamel, crown size in blacks is increased proportionately vis-à-vis whites. Principal components analysis confirmed these univariate relationships and emphasizes the statistical independence of crown component thicknesses, which is in keeping with the sequential growth and separate embryonic origins of the tissues contributing to a tooth crown. Results direct attention to the rates of enamel and dentine deposition (of which little is known), since the literature suggests that blacks (with larger crowns and thicker enamel) spend less time in tooth formation than whites.

Interpreting sex differences in enamel hypoplasia in human and non-human primates: Developmental, environmental, and cultural considerations

The purpose of this review is to provide a synoptic, critical evaluation of the evidence of, and potential etiological factors contributing to, sex differences in the expression of enamel hypoplasia (EH). Specifically, this review considers theoretical expectations and empirical evidence bearing on two central issues. The first of these is the impact of a theorized inherent male vulnerability to physiological stress on sex differences in EH. The second issue is the potential contribution to sex differences in EH of intrinsic differences in male and female enamel composition and development. To address this first issue, EH frequencies by sex are examined in samples subject to a high degree of physiological stress. Based on the concept of inherent male vulnerability (or female buffering), males in stressful environments would be expected to exhibit higher EH frequencies than females. This expectation is evaluated in light of cultural practices of sex-biased investment that mediate the relationship between environmental stress and EH expression. Defects forming prenatally afford an opportunity to study this relationship without the confounding effects of sex-biased postnatal investment. Data bearing on this issue derive from previously conducted studies of EH in permanent and deciduous teeth in both modern and archaeological samples as well as from new data on Indian schoolchildren. To address the second issue, fundamental male-female enamel differences are evaluated for their potential impact on EH expression. A large sex difference in the duration of canine crown formation in non-human primates suggests that male canines may have greater opportunity to record stress events than those of females. This expectation is examined in great apes, whose canines often record multiple episodes of stress and are sexually dimorphic in crown formation times. With respect to the first issue, in most studies, sex differences in EH prevalence are statistically nonsignificant. However, when sex differences are significant, there is a slight trend for them to be greater in males than in females, suggesting a weak influence of greater male vulnerability. Cultural practices of sex-biased investment in children appear to have greater impact on EH expression than does male vulnerability/female buffering. With respect to the second issue, sex differences in the composition and development of enamel were reviewed and determined to have limited or unknown impact on EH expression. Of these factors, only the duration of crown formation was expected to affect EH expression by sex within the great apes. The data support an association between higher defect counts in the canines of great ape males relative to those of females that may be the result of longer crown formation times in the canines of great ape males. This review concludes with an assessment of the nature of the evidence currently available to examine these issues and suggests future avenues for research focused on elucidating them.

Crown components of mandibular molar teeth in 45,X females (Turner syndrome)

This study was designed to determine the possible effect of one X-chromosome constitution on components of the human permanent and primary molar teeth. Enamel, dentine, pulp and crown dimensions were measured on radiographs of first and second permanent and second primary mandibular molars of 49 Finnish 45,X females (Turner syndrome), their 46 first-degree male and female relatives and 50 non-related males and females. In permanent first and second molars of the 45,X females, crown width and the dimensions of tooth components were less than those of normal females and males. Reduction in size affected first more than second molars, and in both teeth the enamel was relatively as well as absolutely thinner than in the controls. No differences were found in tooth components between normal relatives and unrelated controls. These data agree with previous studies which have demonstrated that the X chromosome promotes enamel apposition and that both X chromosomes in normal females are active in amelogenesis, while the Y chromosome influences both dentine and enamel growth. The relative reduction in "dentine" or the estimated mesiodistal width of the tooth germ in the 45,X females indicates that their tooth development is affected at an early stage of morphogenesis. Taken together with the results already reported for anterior teeth, the present results suggest that there is an inverse correlation between the duration of crown formation and the severity of size reduction.

The craniofacial complex in 45,X/46,XX females

Fourteen Finnish 45,X/46,XX females were compared with population female and male controls, and in addition, nine of them were compared with their first-degree female relatives. Linear and angular measurements were made from standardized lateral cephalograms of patients and normal population controls from the "Kvantti" study series. In both comparisons the results indicated that craniofacial dimensions in 45,X/46,XX females were smaller than those in population female and male controls. The general metric pattern was similar to that observed in relation to the tooth crowns of 45,X/46,XX females. Several of their craniofacial proportions and plane angles differed from those of normal women: shorter anterior and posterior cranial bases and a flatter cranial-base angle, a sagittally shorter maxilla and a sagittally shorter mandible with an enlarged ramus:corpus length ratio, posterior rotation of the mandible and a tendency to bimaxillary retrusion. It is suggested that the reduction of X-chromosomal genetic material in 45,X/46,XX females results in smaller craniofacial dimensions than in normal females, with substantial effects on dimensional ratios and especially plane angles of the cranial base.

Asymmetry in the occlusal morphology of first permanent molars in 45,X/46,XX mosaics

The genetic control of dental morphology is affected by various chromosomal aberrations, and morphological changes familiar to specific aneuploidies can be distinguished in many cases. Asymmetry between bilateral teeth in the dental arch in laboratory animals shows increased expression after exposure to external stress during development. Bilateral asymmetry in occlusal cuspal morphology has not been widely used as a means of odontometric examination, partly because accurate and reliable methods are not commonly available. The aim here was to examine linear and angular variables of the occlusal morphology of maxillary and mandibular first permanent molars in three dimensions in individuals with 45,X/46,XX mosaicism and to find out if this aneuploidism causes deviations from normal development and increased asymmetry in bilateral variables of the occlusal surface. The participants were five females with 45,X/46,XX chromosome constitution, whose karyotypes were confirmed by cytogenetic tests of skin fibroblasts. The controls were 10 first-degree female relatives of the mosaic patients with normal 46,XX chromosome constitution. The method of measuring the three-dimensional morphology of occlusal surfaces was based on a machine-vision technique using a single video-imaging camera. An apparent increase in asymmetry of occlusal morphology in first permanent molars in 45,X/46,XX mosaics was found. As there was evidence of directional asymmetry, it is possible that different cell lines regulated by discrete genes cause the directionality.

The craniofacial complex in 47,XYY males

Eight adult, Finnish 47,XYY males were compared with population male and female controls and, in addition, three of them were compared with first-degree male relatives. Linear and angular measurements were made from standardized lateral cephalograms of patients and normal population controls from the "Kvantti" study series. In both comparisons the craniofacial dimensions in 47,XYY males were larger than those in population male and female controls. Their craniofacial proportions and plane angles were similar to those of normal men except for a larger lower facial height with posterior rotation of the mandible and a tendency to bimaxillary protrusion, a longer cranial base and a lesser cranial-base angle. Thus the supernumerary Y chromosomal gene(s) in 47,XYY males may result in larger craniofacial dimensions than in normal males, without substantial effects on dimensional ratios and plane angles. This general metric pattern is similar to that observed in relation to many adult body and head dimensions, and the dental arches and tooth crowns, of 47,XYY males. The foramen magnum in 47,XYY males was smaller in the sagittal plane than that of normal males and females.

Torus mandibularis in 45,X females (Turner syndrome)

Ninety-three Finnish females with a 45,X chromosome constitution, 78 first-degree female, and 37 first-degree male relatives were examined to determine the frequency and expression of torus mandibularis. The results indicate that among adults the frequency of the trait was significantly lower and the expression weaker in the 45,X females than in male control relatives. A similar trend was observed in comparison to normal females. In juveniles the trend was reversed. Our findings suggest that the sex chromosomes may have an influence on the occurrence, expression, and timing of development of the mandibular torus. Sexual dimorphism in the manifestation of torus mandibularis may result particularly from the effect of the Y chromosome on growth.

Abnormal enamel and pulp dimensions in familial dysautonomia

In familial dysautonomia (FD), a hereditary autonomic and sensory neuropathy, somatic growth is impaired. This study was conducted to explore the possibility that tooth dimensions are altered as a consequence of neural crest dysfunction known to be present in FD. Enamel, dentin, pulp, and tooth size measurements of mandibular primary and permanent molars from FD patients were compared with those of healthy controls. It was found that although tooth size in the FD patients was smaller than normal, the enamel was thicker on the occlusal table, while the pulp chamber was smaller and disproportional to tooth size. Our results suggest distorted tooth dimensions rather than a generalized growth arrest as observed in other hereditary syndromes, such as Down's or Crouzon.

Heterochronic quantitative microevolution: dental divergence in aboriginal Americans

Studies of tooth crown morphology alone have proven valuable in defining human population differentiation. We test the hypothesis that quantitative comparisons of more complex whole tooth structure may prove informative in understanding human diversity. Three disparate populations in Native American genetic history were compared: Kodiak Island Western Eskimos, Peruvian Inca Amerindians, and Southeast Asians. Enamel depth (an increasing gradient extended from Southeast Asians to the Inca) and root parameters were the most discriminating variables. The observed microevolution appears to result from variation in timing of known X-linked, Y-linked, and autosomal genes that affect either ameloblast or odontoblast differentiation. The dental traits were sexually dimorphic, the effect being more pronounced in aboriginal Americans, with male teeth having robust roots and thin enamel compared to female. Southeast Asians were isometrically related. The prominence of sexual dimorphism and the importance of sex-linked genes in the determination of the dental phenotypes suggest that sexual selection was one evolutionary force acting on early Asian populations. Subsequently, the selection appears to have been relaxed in Southeast Asians. Observed divergence of tooth shape among the populations, i.e., differences in the appropriation process of tooth primordia, was mainly the consequence of genetic drift modulating heterochronic regulators of homeotic genes.

Characterisation of molecular defects in X-linked amelogenesis imperfecta (AIH1)

Amelogenins are an heterogenous family of proteins produced by ameloblasts of the enamel organ during tooth development. Disturbances of enamel formation occur in amelogenesis imperfecta, a clinically heterogenous group of inherited disorders characterised by defective enamel biomineralisation. An amelogenin gene, AMGX, has been mapped to the short of the X chromosome (Xp22.1-p22.3) and has been implicated in the molecular pathology of X-linked amelogenesis imperfecta (AIH1). We have identified three families exhibiting AIH1 and screened the AMGX gene for mutations using single-strand conformational polymorphism analysis and DNA sequencing. Three novel mutations were identified: a C-T substitution in exon 5, and a G-T substitution and single cytosine deletion in exon 6, confirming the existence of extensive allelic heterogeneity in this condition. The identification of family-specific mutations will enable early identification of affected individuals and correlation of clinical phenotype with genotype will facilitate an objective system of disease classification.

Sexual dimorphism in mesiodistal dentin and enamel thickness

This study evaluates sexual dimorphism in mesiodistal diameter, enamel thickness and dentin thickness of the permanent posterior mandibular dentition in order to gain a better understanding of variation in mesiodistal tooth size. The results relate to a sample of 59 males and 39 females, 20-35 years of age. Bitewing radiographs of the right permanent mandibular premolars and molars were illuminated and transferred at a fixed magnification to a computer via a video camera. Enamel and dentin landmarks were identified and digitized on the plane representing the maximum mesiodistal diameter of each tooth. The results showed significant sex differences (p < 0.01) in mesiodistal diameter favouring males over females. Dimorphism was more pronounced for the molars than for the premolars. Enamel thickness, which is 0.4-0.7 mm greater for the molars than premolars, shows no significant sex differences. Dentin is significantly thicker in males than females, and is 3.5-4.0 mm thicker in molars than premolars. It is concluded that sexual dimorphism in mesiodistal tooth sizes is due to differences in dentin thickness and not enamel thickness.

Dental morphology of 45,XO human females: molar cusp area, volume, shape and linear measurements

A three-dimensional analysis of the maxillary first molars of five 45,XO females and comparison with normal females and males demonstrated a reduction of cusp areas and volumes in the 45,XO females. Mesiodistal and faciolingual dimensions were also reduced. The reductions in basal area and volume were greater in the later developing, distal cusps. In normal females the second X chromosome apparently does not exert an effect on the cusp height but increases the basal area. The results further indicate that the Y chromosome in normal males increases both cusp height and basal area. The steepest cusps were found in 45,XO females while the shallowest were in the control males. Both sex chromosomes thus seem to affect the shape of the cusp but the resulting phenotypes differ.

Skeletal maturity, dental maturity, and eruption in young patients with Turner syndrome

A major problem for patients with Turner syndrome is their small body height. The rapid biotechnologic development has now made treatment with growth hormone possible at a larger scale. The aim of this investigation was to evaluate skeletal maturity, dental maturity, and eruption in a group of young patients before hormone therapy. The material comprised 33 patients aged 7-16.7 years. The skeletal maturity, as judged from hand radiographs, was on an average 2.3 years retarded (p < 0.001) and showed increasing retardation with increasing age. The dental maturity, assessed from the formation stages of the permanent teeth on panoramic radiographs, was accelerated, with a mean value of 1 year (p < 0.001). The timing of clinical eruption did not differ significantly from that of our reference material; the Turner girls were on an average 3.7 months ahead. Several patients had local eruption problems, especially in the maxillary lateral segments. It is suggested that disharmony between tooth size and arch size may contribute to this problem.

Bovine amelogenin message heterogeneity: alternative splicing and Y-chromosomal gene transcription

The amelogenins are the most abundant proteins in developing tooth enamel. Previous analyses have demonstrated that transcriptionally active genes encoding the proteins are located on both the bovine X and the bovine Y chromosomes. We report here the cloning and sequence analysis of the Y-chromosomal gene and corresponding cDNA. The Y-specific mRNA encodes a translation product in which a 21 amino acid domain has been deleted, relative to the X-specific amelogenin, resulting in loss of a structure tentatively described as a beta-spiral. There are also 13 single amino acid differences compared to the X-specific amelogenin. In addition, we have cloned and sequenced an X-chromosomal alternatively spliced amelogenin cDNA that encodes a 43 amino acid amelogenin primary translation product. Hydrophobicity analysis indicates that all analyzed amelogenin proteins have a mean hydrophilic character and the two peptides translated from alternatively spliced messages have significant increases in percentage of hydrophobic amino acids.

Occlusion in 47,XXY (Klinefelter syndrome) men

Occlusal morphology of permanent dentitions in 29 men with a 47,XXY chromosome complement (Klinefelter syndrome) was determined from dental casts. The results showed that a relatively frequent occlusal anomaly was mesial molar occlusion. Incisal open bite was also more common than in controls. Based on the present and previous observations of occlusal anomalies in various sex chromosome anomaly groups and normal controls, it is suggested that the presence of the Y chromosome in the genome is at least as important as the X chromosome for the development of harmonious occlusal morphology. The tendency towards sexual dimorphism in occlusal phenotype might result from a differential effect of the X and Y chromosomes on cellular activity which leads to different growth patterns.

Upper central incisor and canine tooth crown size in 47,XXY males

Enamel and dentin thicknesses were measured in permanent tooth crowns of 47,XXY (Klinefelter syndrome) males. In 47,XXY males, enamel thickness in maxillary central incisors was significantly greater than that in control males or females, and dentin thickness in incisors and canines was significantly greater than that in control females, but smaller than that in normal males. These findings confirm the concept that human dental growth is affected by sex chromosomes. Amelogenesis is promoted by both X and Y chromosome genes, and sexual dimorphism in average tooth size is evidently determined by a promoting effect of the Y chromosome on dentin growth, probably through cell proliferation. This effect can also explain sex predilection for males in the numbers of supernumerary and ordinary teeth.

Tooth crown size in 46, X, i (Xq) human females

Permanent tooth crown sizes of six Finnish females with a 46, X, i(Xq) chromosome constitution (isochromosome for the long arm of the X chromosome) were measured from dental casts and compared with those of normal women, first-degree female relatives and 45, X females. Crown diameters of the 46, X, i(Xq) females were not only smaller than in the normal women but even smaller than the 45, X females. These findings can be considered indirect evidence that X chromosome gene(s) for tooth crown growth are most probably located on the short arm.

Quantitative genetic analysis of longitudinal trends in height: preliminary results from the Louisville Twin Study

A preliminary series of quantitative genetic models was applied to a subset of longitudinal height data, spanning birth to maturity, gathered from twin families in the Louisville Twin Study. Descriptive Cholesky factor parameterization was found to give more satisfactory results than did a system of constraints based on a model of developmental transmission of a time-constant and time-specific factors. The results from application of two autosomal sex-limitation models are contrasted with those from a model specifying both autosomal and sex-chromosomal patterns of inheritance. The latter model was more conducive to parameter reduction. Although these models do not constitute conclusive tests of autosomal sex-limitation versus sex-linkage, the more parsimonious model is consistent with previous research suggesting a stature locus on the long arm of the Y chromosome. Heritability of height is estimated at about 90% or greater from 6 years of age on. Substantial and fairly constant longitudinal genetic correlations are found from 3 years of age on. Shared environmental effects unrelated to parental height were seen for birth length, corrected for gestational age, to height at 3 years of age, but these are not satisfactorily differentiated from possible twin effects in the present sample. The genetic consequences of assortative mating are emphasized since failure to take assortment into account can lead to overestimation of shared environmental effects and under-estimation of genetic effects. The results indicate that about 20% of within-gender variability for mature height can be attributed to the genetic consequences of assortment, even though the phenotypic marital correlation of 0.22 is quite modest. The importance of testing the assumption of multivariate normality underlying the application of the method of maximum-likelihood is also highlighted.

Taurodontism in 45,X females

Orthopantomograms of 87 45,X females, 61 first-degree female relatives of these females, and a population sample of 113 normal females and 44 normal males were examined for the occurrence of taurodontism in mandibular molars. In the sample of 45,X females, two showed taurodont lower molars. In one of them, a hypotaurodont second molar was detected, while hypotaurodont third molars were found in the other. Three of the females' relatives and four of the population control females showed taurodontism, three unilaterally and four bilaterally. In all cases, the affected teeth were hypotaurodont. The results suggest that taurodontism occurs in 45,X females with a frequency similar to that in normal females. This result is not in accordance with the hypothesis that low mitotic activity of the chromosomally abnormal cells is an etiological factor in the development of taurodontism. The present findings, together with earlier results, suggest that the gene content of the X chromosome, rather than the amount of heterochromatin, is the cause of taurodontism in individuals with chromosome aneuploidy.

Occlusal anomalies in 45,X/46,XX- and 46,Xi(Xq)-women (Turner syndrome)

A total of 20 individuals with X-chromosome aberrations, 14 45,X/46,XX-women and six 46,Xi(Xq)-women, were examined for occlusal anomalies. The controls were first-degree woman relatives and population women. The results showed that the most common type of malocclusion in both study groups was lateral cross bite. Also distal molar occlusion, increased maxillary overjet and in 45,X/46,XX-women open bite was found. 45,X/46,XX-women's occlusion seems to be more affected than that of 46,Xi(Xq)-women. Compared to 45,X-women, the present study groups show milder expression of malocclusion. One might speculate that enamel genes of the X-chromosome are involved in occlusal development.