The effect of prenatal factors on crown dimensions

As shown in 870 white participants in the National Collaborative Perinatal Project (NCPP), maternal health status during pregnancy and birth size are systematically related to mesiodistal and buccolingual crown dimensions of I1, I2, dc, dm1, dm2 and M1. Maternal diabetes, maternal hypothyroidism and large size at birth are associated with larger maxillary and mandibular teeth in white children. Conversely, deciduous and permanent crown diameters are diminished in maternal hypertension, and in low birthweight and small birth-length conditions. These findings suggest that maternal and fetal (or gestational) determinants of both deciduous and permanent tooth crown dimensions may account for as much as half of crown-size variability with major implications to population comparisons and historical odontometric differences and trends.     

Sexual dimorphism of cusp dimensions in human maxillary molars

Cusp dimensions of human maxillary molars were compared between males and females to determine whether the later-developed, distal cusps displayed greater sexual dimorphism than the earlier-developed, mesial cusps, and whether the later-forming second molar displayed greater sexual dimorphism than the first molar. First and second permanent molar crowns (M1 and M2) were measured indirectly, using dental casts obtained from 117 Japanese (65 males and 52 females). Measurements included maximum mesiodistal and buccolingual crown diameters and the diameters of the four main cusps: the paracone, protocone, metacone, and hypocone. Mean values of crown dimensions were larger in males than in females for both M1 and M2, but the sexual difference in protocone diameter of M1 was not significant. The protocone in M1 showed the least amount of sexual dimorphism, followed by the metacone, hypocone, and paracone, while in M2, the percentage sexual dimorphism corresponded to the order of cusp formation: paracone, protocone, metacone, and hypocone. With the exception of the paracone diameter, M2 showed greater sexual dimorphism than M1. Sexual dimorphism was not always greater in the later-developed, distal cusps of M1 or M2, but the protocone, the most important cusp in terms of occlusal function, displayed the least dimorphism in M1.     

Contours of maxillary molars studied in Australian aboriginals

Distances from the central pit to the perimeter of the crown of permanent upper molars were measured on standardized occlusal photographs of dental casts representing 210 male and 181 female Aboriginals from Yuendumu in the Northern Territory of Australia. In both males and females the first molar was the largest tooth but it showed least variability. Variabilities of the distances tended to be greater for radii constructed in the buccolingual direction than for the transverse mesiodistal radii. The most marked size reduction in the molar series from first to third related to the distolingual part of the crown, which was also the most variable region. Size differences between molars in the mesial contour radii were not marked. Sexual dimorphism was evident in most crown radii, being most marked for the second molar.     

A principal components analysis of human odontometrics

It has long been recognized that tooth crown diameters in hominoids are all positively intercorrelated one with another. This study reports on sex-specific correlation matrices derived from 2,650 individuals from the Solomon Islands, Melanesia. Mesiodistal and buccolingual diameters of all permanent teeth from one side are used, excluding third molars. Analysis discloses significant sex dimorphism in the strengths of the intercorrelations, with females being better integrated. Principal components analysis (PCA) provides an objective means of data reduction (shown here to be preferable to simple size summation methods) and decorrelation of the resulting linear combinations. Four components are extracted (with results being virtually identical in the two sexes) and arguments are put forth that varimax rotation to "a simpler solution" may be counterproductive. Before rotation, the four components are 1) overall size, 2) buccolingual widths contrasted with mesiodistal lengths, 3) anterior (I,C) contrasted with posterior (P,M) teeth, and 4) premolars contrasted with molars. Most of the explained (shared) variance (63%) extracted by PCA is in overall size of the dentition. There is a strong urge to view the results of these principal components analyses as reflective of biologically and genetically meaningful entities.     

Carabelli's trait and tooth size of human maxillary first molars

Carabelli's trait is a morphological feature that can occur on the protocone of human maxillary molars. This study tests the hypothesis that Carabelli's trait is correlated statistically with the dimensions of the crown's four principal cusps or whether, as a cingular feature, the trait truly accretes onto an otherwise unaffected crown. Computer-assisted image analysis was used to measure the 6 intercusp distances and 12 angular relationships among cusp tips on the permanent first molar of 300 young adult American whites. Carabelli's complex was scored using an 8-grade ordinal scheme. Crown size was quantified in three ways, namely as 1) maximum mesiodistal and buccolingual diameters, 2) the 6 intercusp distances, and 3) the 12 angular cusp arrangements. There was no sex difference in the morphological expression of Carabelli's trait in this sample. Overall crown size and intercusp distances were significantly and progressively larger in molars with larger Carabelli's trait expressions. There are graded size responses between crown size (mesiodistal and buccolingual diameters), sizes of the four principal cusps, and morphological stage of Carabelli's complex, though the statistical relationships are appreciably stronger in males than females. Carabelli's trait occurs preferentially in larger molars. In contrast, angular (shape) relationships among cusp tips are not discernibly affected by trait size in either sex. There is the situation, then, that Carabelli's trait is developmentally correlated with crown size, but with no apparent alteration of cusp arrangements, suggesting that the increases are isometric across the occlusal table. Why the association is much weaker in females remains speculative, but these data provide yet another line of evidence that, within a population, tooth size is associated in a positive fashion with crown complexity.     

Studies on agenesis in the permanent dentition

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

Intercusp relationships of the permanent maxillary first and second molars in American whites

Much of a human molar's morphology is concentrated on its occlusal surface. In view of embryologists' recent attention on the determination of crown morphology by enamel knots that initiate cusp formation, we were interested in the arrangement of cusp apices in the definitive tooth. Computer-assisted image analysis was used to measure intercusp distances and angles on permanent maxillary M1 and M2 in a sample of 160 contemporary North American whites. The intent was to generate normative data and to compare the size and variability gradients from M1 to M2. There is little sexual dimorphism in intercusp distances or angles, even though the conventional mesiodistal (MD) and buccolingual (BL) crown size is 2.0% and 4.0% larger in males, respectively, in these same teeth. Dimensions decreased in size and increased in variability from M1 to M2, but differentially. Cusps of the trigon were more stable between teeth, especially the paracone-protocone relationship. Principal components analysis on the six M1 distances disclosed only one eigenvalue above 1.0, indicating that overall crown size itself is the paramount controlling factor in this tooth that almost invariably exhibits a hypocone. In contrast, four components were extracted from among the 12 angular cusp relationships in M1. These axes of variation may prove useful in studies of intergroup differences. A shape difference occurs in M2, depending on whether the hypocone is present; when absent, the metacone is moved lingually, creating more of an isosceles arrangement for the cusps of the trigon. Statistically, correlations are low between occlusal intercusp relationships and conventional crown diameters measured at the margins of the crowns that form later. Weak statistical dependence between cusp relationships and traditional MD and BL diameters suggest that separate stage- and location-specific molecular signals control these different parts (and different stages) of crown formation.     

Morphologic characteristics of the Alaskan Eskimo dentition: IV. Cusp number and groove patterns of mandibular molars

Data on the permanent dentition of 63 coastal and 33 inland Alaskan Eskimos are presented. The number of cusps and groove pattern of the mandibular molars were recorded. Agenesis of the mandibular third molars was classified and the mesiodistal and buccolingual crown diameter was measured on the first and the second mandibular molars. The predominant pattern of the lower first molars was Y5, while for the second molar the dominating patterns were +5 and +4. In the lower third molar, +5 was found in the majority of cases. For M1 and M2, men showed a stronger tendency toward a conservative pattern than did women. In the case of M2, the inland population exhibited a more conservative trait than did the coastal population. No connection was seen between the groove pattern and agenesis of M3, however, a reduction in the mesiodistal crown diameter for the second molars was seen when the number of cusps is reduced from 5 to 4.     

Development and size of the teeth of Macaca mulatta.

A cross-sectional sample of 151 skulls from Macaca mulatta of known age and similar rearing in U.S. Primate Centers was analyzed to determine age-related "norms" of stages of development and size of teeth. The stages of development from the follicle of a deciduous incisor in the fetus to completion of the root with apex closed of the permanent third molar were related to age. The age range observed for eruption of each tooth was noted and related to its stage of development. The crown of each erupted tooth was found to be completely developed, but growth of its root continued for a longer, indeterminate period. When a deciduous tooth was exfoliated, the crown of the permanent successor was found to be completed and root growth had begun. Measurements of both mesiodistal and faciolingual diameters and of crown length of the teeth in situ and of total length and root length on roentgenograms were examined for sexual dimorphism. The faciolingual diameter of the deciduous mandibular second incisor and of both second molars showed the greatest sexual dimorphism among both diameters of all deciduous teeth. The mesiodistal and faciolingual diameters of the mandibular premolars were found to be the best dimensions in discriminant functions for identifying sex in the absence of permanent canines.     

Reduction of maxillary molars in Homo sapiens sapiens: a different perspective.

Crown and cusp areas, and buccolingual and mesiodistal diameters of maxillary molars of complete upper tooth rows (30 males, 30 females) were analysed in order to quantify changes in size and shape from the first to the third molar. Uni- and multivariate analyses revealed the mesial cusps, in particular the protocone (mesiolingual cusp), to be more stable than the other cusps. Although there is a gradient in size from the first to third molar, shape changes were found to be marked. Overall, the findings are in keeping with the field theory and the hypotheses of environmental constraints on later developing teeth. However, not all of the results could be entirely explained by these concepts. Functional aspects seem to account for the relative stability of the protocone and the buccolingual crown diameter. It appears that this functional complex is relatively stable despite the overall reduction of tooth size, which is probably secondary to processes occurring in the jaws and the cranium. This finding may have implications for studies on tooth reduction between populations of different time periods.     

Associations between Carabelli trait and cusp areas in human permanent maxillary first molars

Few dental anthropological studies have investigated the associations between tooth crown size and crown traits in humans using quantitative methods. We tested several hypotheses about overall crown size, individual cusp areas, and expression of Carabelli cusps in human permanent first molars by obtaining data from standardized occlusal photographs of 308 Australians of European descent (171 males and 137 females). Specifically, we aimed to calculate the areas of the four main molar cusps, and also Carabelli cusp, and to compare the relative variability of cusp areas in relation to timing of development. We also aimed to compare cusp areas between males and females and to describe how Carabelli cusp interacted with other molar cusps. Measurements included maximum crown diameters (mesiodistal and buccolingual crown diameters), the areas of the four main cusps, and the area of Carabelli cusp. The pattern of relative variability in absolute areas of molar cusps corresponded with their order of formation, the first-forming paracone displaying the least variation, and the last-forming Carabelli cusp showing the greatest. Overall crown size and areas of individual cusps all showed sexual dimorphism, with values in males exceeding those in females. Sexual dimorphism was smallest for paracone area and greatest for Carabelli cusp area. Overall crown size and cusp areas were larger in individuals displaying a Carabelli cusp, especially the hypocone area. Although the combined area of the protocone and a Carabelli cusp was greater in cuspal forms than noncuspal forms, protocone area alone was significantly smaller in the former. Our findings lead us to propose that, in individuals with the genotype for Carabelli trait expression, larger molar crowns are more likely to display Carabelli cusps, whereas molars with smaller crowns are more likely to display reduced forms of expression of the trait. We suggest that the pattern of folding of the internal enamel epithelium in developing molar crowns, particularly in the protocone region, can be modified by a developing Carabelli cusp.     

Molar size sequence in Australian Aboriginals

Percentage frequencies for molar size sequence of first and second molars were calculated in a group of contemporary Australian Aboriginals using mesiodistal and buccolingual dimensions, as well as crown areas. Comparisons were made between sexes, arches, and dimensions within the Aboriginal groups and also between Aboriginal data and those published for other populations. The frequencies of the M2 > M1 molar size sequence in the Aboriginals fell within the range of frequencies reported for other contemporary populations. Differences in the frequencies of the M2 > M1 sequence between the sexes and between arches, together with the relatively high frequency of asymmetry in molar size sequence within Aboriginals, supported the notion that local environmental conditions acting during odontogenesis, together with differential responses to other environmental influences, play an important role in determining observed patterns of molar tooth size.     

Alternative dental measurements: proposals and relationships with other measurements

Most archaeological and fossil teeth are heavily worn, and this greatly limits the usefulness of tooth crown diameter measurements, as they are usually defined at the widest points of the crown. There are alternatives, particularly measurements at the cervix of the tooth, where the crown joints the root, and measurements along a diagonal axis in molars, that are much less affected by wear. These would allow a wider range of specimens to be included, e.g., in the study of dental reduction in Upper Palaeolithic and Mesolithic Homo sapiens. In addition, they would allow the little-worn teeth of children to be compared directly with well-worn teeth in adults. These alternatives, however, have been little used, and as yet there have not been any studies of the repeatability with which they can be measured, or of the extent to which they are related to the more usual crown diameters. The present study is based on a group of unworn teeth, where direct comparisons could be made between the alternative measurements, which are not much affected by wear, with the usual crown diameters, which are very much affected. In an interobserver-error study of this material, cervical and diagonal measurements could be recorded as reliably as the usual crown diameters. The buccolingual cervical measurement was strongly correlated with the normal bucclingual crown diameter in all teeth, whereas the mesiodistal cervical measurement was highly correlated with the normal mesiodistal crown diameter in incisors and canines, but less so in premolars and molars. The molar diagonal measurements showed high correlations with all other measurements. Crown areas (robustness index) calculated from the usual diameters were strongly correlated with crown areas calculated from cervical measurements, and crown areas calculated from molar diagonals were strongly correlated with both other areas. Despite the long usage of the more usual maximum crown diameters, the alternative dental measurements could be measured just as reliably, could record similar information about tooth crown size, and would be better measures for the worn dentitions seen in archaeological and fossil material.     

The dentition of the Indian Knoll skeletal population: odontometrics and cusp number.

Data on the permanent dentition of 153 individuals from the well known Indian Knoll skeletal population are presented. Mesiodistal and buccolingual measurements were taken with a Helios dial caliper. Cusp number of maxillary and mandibular molars are recorded. The Indian Knoll dentition is larger than many modern groups but smaller than Australoid or Mesolithic groups. With the exception of maxillary 12, males have larger teeth than females in both dimensions. The lower canine is the most dimorphic tooth. Through rank order correlation, an association was shown between the sexual dimorphism of the mesiodistal and buccolingual dimensions. Compared to modern groups, the Indian Knoll population displays a moderate degree of sexual dimorphism in tooth size. In general, the coefficients of variation were greater for the more distal teeth within morphological classes. Amounts of size variability did not differ significantly between the sexes; moreover, rank order correlations indicated that patterns of variability in both dimensions were similar for males and females. The predominant cusp number pattern for upper molars is 4-3-3 and for lowers 5-5(4)-5. No sex differences were shown for cusp occurrence or bilateral asymmetry in cusp number.     

Crown diameters of the deciduous teeth in Australian Aboriginals

Mesiodistal and buccolingual crown diameters were measured from dental casts representing the deciduous dentitions of 197 Aboriginal children from the Northern Territory of Australia. Double determination analysis indicated that the semi-automatic recording procedure used was reliable leading to observer errors of no practical significance. Tooth-size was greater in the male subjects but the sexual dimorphism was less marked than in the permanent teeth of the same subjects. The mandibular teeth were more uniform than maxillary with respect to buccolingual size relative to mesiodistal. Extremes of general tooth-size were more marked in the deciduous dentition than in the permanent as a consequence of the relatively large deciduous second molar which in Aboriginals approximates in size the permanent first molar of many other ethnic groups.     

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.     

Tooth dimensions of Southern Chinese.

Teeth in casts of a random sample from the Hong Kong Oral Health Survey of 12-year-old children (n=459; 295 boys and 164 girls) were measured in the mesiodistal, buccolingual, and clinical crown height dimensions. Sexual dimorphism was evident in all tooth types in nearly all tooth dimensions, with the exception of the mesiodistal dimension of mandibular central incisors. The Chinese male tooth dimensions were larger than in females in nearly all characters. The measurements were compared with other human groups. Results showed that the Southern Chinese had larger tooth dimensions than the Japanese and than the White Americans. Hence it is important to have data concerning a relevant human group for purposes of clinical diagnosis and planning of treatment. These data may also be useful in forensic dentistry.     

Small tooth sizes in a nineteenth century South Carolina plantation slave series

Sub-Saharan African (and derived) populations typically exhibit larger mean tooth crown diameters than whites in spite of considerable population variability. We report on a 19th century series of American black slaves from a single cemetery near Charleston, South Carolina, that possessed notably smaller crown sizes. Analysis identifies a characteristic set of differences compared to caucasians, including retention of large maxillary lateral incisors and disproportionately large premolars and molars. Regression of principal components scores (derived from the mesiodistal diameters) on the sum of all diameters (used here as a measure of overall tooth mass) confirms a basic ethnic difference between black and white odontometrics: significantly more of the tooth mass is apportioned to the cheek teeth (premolars, molars) in blacks than whites. The difference (expressed as residuals from linear regression on tooth mass) holds for the several groups assessed here despite considerable intergroup variability in tooth sizes. Potential explanations for the notably small diameters of this plantation series are speculative, but may involve kin-based divergences and/or reflect the natural intergroup differences extant in the African slave sources.     

Improving the spatial orientation of human teeth using a virtual 3D approach

Since teeth are resistant to decomposition processes, they provide important and at times unique sources of information about fossil humans. Fortunately, dental remains reflect significant evolutionary changes. These changes make a very important and often exclusive contribution to the definition of new taxa or the attribution of fossil specimens to existing taxa.The traditional approach to dental morphometric analyses usually focuses on the recording of several measures of the tooth with calipers, especially the two basic crown diameters (buccolingual and mesiodistal). However, since these measures do not adequately represent the complex morphology of the tooth, 2D images and 3D digital models of dental morphology have been used. For both types of analysis, the possibility of correctly comparing homologous teeth depends on the adoption of a common orientation system. The lack of such a system makes it difficult to compare the results of different studies.Here we describe a new method for orienting teeth specifically devised for the upper and lower first molar (M1). Samples of unworn maxillary (n = 15) and mandibular (n = 15) first molars of modern humans were scanned with a Roland Picza 3D digitizer. The 3D virtual models were used to compare our new orientation method with those proposed in the literature. The new orientation system, which meets a geometric criterion, is based on three points identified on the cervical line and ensures acceptable repeatability of the spatial positioning and orientation independent of the shape and wear of the first molar under investigation. This orientation system is a first step toward the creation of a virtual set of hominid and fossil human first molars, which will allow us to make comparisons via a sophisticated and noninvasive approach. This pilot study also provides guidelines to extend the new methodology to the other types of teeth.     

Crown dimensions of deciduous teeth from pre-Columbian Peru

The mean mesiodistal and buccolingual diameters are presented for the deciduous teeth from Pre-Columbian Peru. Generally, the deciduous teeth from Pre-Columbian Peru are larger in most dimensions than the deciduous teeth of modern populations of European descent and smaller than those of modern Australian aboriginals. Differences in crown dimensions between the Pre-Columbian Peruvian deciduous teeth and those from Prehistoric Inamgaon and Mesolithic Europe are inconsistent. However, the maxillary and mandibular second molars are larger in the Peruvian population while the incisors are smaller. Since comparative data for prehistoric deciduous teeth are rare, this paper adds valuable data to the growing literature on deciduous crown dimensions.