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.     

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.     

Carabelli's trait in contemporary Slovenes and inhabitants of a medieval settlement (Sredisce by the Drava River)

The objectives of this study were to determine the total frequency, expression and asymmetry of Carabelli's trait in permanent dentitions of contemporary Slovenes and a medieval skeletal population from northeastern Slovenia. A total of 254 dental casts from contemporary Slovene children were examined. The population of a medieval settlement (10th-15th centuries), was represented by 94 skeletons. A modification of the method of Alvesalo and associates was used to classify Carabelli's trait on a five-grade scale. The trait was expressed on the upper first molars of 79.7% of the contemporary subjects and 75.8% of the medieval sample. Positive expressions of the trait were found in 10.1% of the contemporary subjects and 15.2% of the medieval sample. While the observed total frequency of the trait in both samples is characteristic of Europeans, the rates of positive expressions are surprisingly low but consistent with data from a recently published worldwide literature survey. Both populations showed a low rate of left-right fluctuating asymmetry of the trait. This finding might reflect a pronounced ability of individuals in the medieval population to buffer unfavourable influences from the environment and a relatively low level of environmental stress in the contemporary population.     

Incidence of Carabelli's trait in Kenyan Africans and Asians

Examination for incidence of Carabelli's trait was done on 1267 Africans and 781 Asian school children, 298 dental plaster casts and 248 skulls of Africans. The African sample is composed of 80% Bantu, 20% Nilote, and Nilo-Hamitic people. When observed intraorally, the trait is present in 31–35% of Africans and 26–27% of Asians. In the dental casts and skull sample of Africans, the trait is present as pit in 23–28%, groove in 20%, and as tubercle and cusp in 22%. The total trait frequency in Africans is 68%.     

Logistic analysis of the effects of shovel trait on Carabelli's trait in a mongoloid population

Mongoloid populations differ from Caucasoids by having a high prevalence of shovel trait and a low prevalence of Carabelli's trait. This study was conducted to investigate the effects of the shovel trait on Carabelli's trait in a Mongoloid population. The research design sought a population that resides in an isolated area and exhibits low admixture with neighboring populations. The Mongoloid group selected for study was the Bunun tribe of aborigines who inhabit an alpine area in Taiwan. The effects of sex and age on Carabelli's trait were controlled in this investigation, as was the association between tooth size and Carabelli's trait. Results show that males were more likely to have Carabelli's trait expressed on teeth than females. The buccolingual diameter of Carabelli's trait teeth was larger than that of teeth without the trait. After adjusting for sex, age, and tooth size, the existence of the shovel trait increased the likelihood of having Carabelli's trait by a factor of three, an effect that is significant. © 1996 Wiley-Liss, Inc.     

Three-dimensional analysis of the maxillary first molar crowns of Canadian Inuit

The maxillary first molar crowns of 48 male and 38 female Canadian Inuit (Eskimos) were analyzed three-dimensionally by using moiré contourography methods. Cusp heights were significantly higher in males while the mesial and distal marginal ridges were more proximally placed in males. The metacone and the oblique ridge appeared to be better developed in the males. Comparison of the present results with published results for Dutch and Japanese indicated that the Japanese and Inuit had lower cusps that were more widely spaced than the Dutch. Correlation coefficients suggest that height measurements were positively correlated as were linear measurements. However, there were few significant correlations between height and linear determinations, suggesting that the development of the "width" of a crown is nearly independent of the development of the height of the cusps and crown.     

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.     

High frequencies and grade expressions of Carabelli's trait in a sample of the Croatian population

Although it is generally accepted that Europeans exhibit the highest frequencies of Carabelli's trait (70-90%), these values represent the expression of all possible morphological grades. When only a well-defined trait expression is considered (grades 5th, 6th and 7th), the frequency is much lower, not more than 19.2% for the 5th grade, and significantly less for the 6th and 7th grades. Our observations based on the study of the Croatian (Central European) populations show the highest frequencies for grade of the trait (exceeding 23%). Comparative data for European or European derived populations demonstrate significant variation in grade expression. While the previously published data suggest that the highest grade of the trait expression does not exceed 10%, our figures show the highest yet known frequency of a well-defined trait.     

Size and shape of the human first permanent molar: a Fourier analysis of the occlusal and equatorial outlines

Form can be viewed as a combination of size and shape. Shape refers to the boundary outline independently from its orientation, relation to reference planes, and dimension (or size). Shape and its changes could be quantified by mathematical methods such as the Fourier series. In this investigation, Fourier analysis has been used to quantify the morphologic characteristics (size and shape) of the outline of the occlusal surface and maximum circumference (equator) in 259 normal, healthy human first permanent maxillary and mandibular molars and to assess the effect of sex. Large within-group variability was found in the Fourier coefficients. Both equatorial and occlusal molar areas were on average larger in male than in female homologous teeth, but the difference was statistically significant only for the equatorial areas. The mean ratios between equatorial and occlusal dental areas were independent from arch (maxillary and mandibular), side, or sex. Both equatorial and occlusal outlines of left and right homologous molars within sex and arch were similar, without size and shape differences. Similarly, no sex differences in shape were found in the comparison of homologous teeth. The method used in the present study could supply information about dental shape in both its entirety and local variations. In particular, the method is extremely sensitive to local variations in dental shape, and it could be usefully employed to compare single teeth to a standard.     

Identification of quantitative trait loci for agronomically important traits and their association with genic-microsatellite markers in sorghum

The identification of quantitative trait loci (QTLs) affecting agronomically important traits enable to understand their underlying genetic mechanisms and genetic basis of their complex interactions. The aim of the present study was to detect QTLs for 12 agronomic traits related to staygreen, plant early development, grain yield and its components, and some growth characters by analyzing replicated phenotypic datasets from three crop seasons, using the population of 168 F₇ RILs of the cross 296B × IS18551. In addition, we report mapping of a subset of genic-microsatellite markers. A linkage map was constructed with 152 marker loci comprising 149 microsatellites (100 genomic- and 49 genic-microsatellites) and three morphological markers. QTL analysis was performed by using MQM approach. Forty-nine QTLs were detected, across environments or in individual environments, with 1–9 QTLs for each trait. Individual QTL accounted for 5.2–50.4% of phenotypic variance. Several genomic regions affected multiple traits, suggesting the phenomenon of pleiotropy or tight linkage. Stable QTLs were identified for studied traits across different environments, and genetic backgrounds by comparing the QTLs in the study with previously reported QTLs in sorghum. Of the 49 mapped genic-markers, 18 were detected associating either closely or exactly as the QTL positions of agronomic traits. EST marker Dsenhsbm19, coding for a key regulator (EIL-1) of ethylene biosynthesis, was identified co-located with the QTLs for plant early development and staygreen trait, a probable candidate gene for these traits. Similarly, such exact co-locations between EST markers and QTLs were observed in four other instances. Collectively, the QTLs/markers identified in the study are likely candidates for improving the sorghum performance through MAS and map-based gene isolations.     

A radiographic and histological study of modern human lower first permanent molar root growth during the supraosseous eruptive phase

There is increasing focus on the relationship between root growth and the eruptive process in studies of primate dental development, and the first permanent molar (M1) is regarded as a key tooth in many of these comparative studies. In this study of modern human M(1)s, histological and radiographic data were compared. Rates of root extension were determined histologically in 20 M(1)s from individuals of known sex using data for daily incremental markings and the orientation of accentuated lines in root dentine. Mean values at the mesiobuccal enamel cervix were 4.3-5.4 microm per day and then rose to a maximum of 6.7-8.4 microm per day during the first 5mm of root growth before gradually declining again to 2.8-3.6 microm per day towards apical closure. A sample of 101 orthopantomograms of children, where M(1)s were between the stages of alveolar eruption and complete eruption, were then used to determine total mesial tooth height and mesial and distal root lengths at four successive stages of eruption. At complete eruption, mean values for mesial and distal root lengths were 8-10mm, respectively. Expressed as a percentage total of mesial tooth height these averaged 45.6-56.2%. Maximum rates of M(1) eruption occur just prior to gingival emergence but did not coincide with maximum rates of root extension in this study. These results emphasise that rates of eruption and rates of root growth do not follow the same pattern of change during the supraosseous eruptive phase. They highlight the need for greater consideration of the role of the eruptive process in explaining differences in gingival emergence times in comparative studies of modern humans and fossil hominins.     

Strong association between polymorphisms in ANKH locus and skeletal size traits

Loss of bone strength is the main determinant of bone fragility. Bone strength is directly dependent on bone size (BS). A substantial portion of BS variation is attributable to genetic effects. However, the list of genes and allelic variants involved in the determination of BS variation is far from being complete. Polymorphisms in the ANKH gene have been shown to be associated with radiographic hand BS-related phenotypes. The present study examined the possible association of the ANKH gene with skeletal size and shape in order to test the universality of the ANKH effect on BS traits. Our sample consisted of a total of 212 ethnically homogeneous nuclear families (743 individuals) of European origin. Each individual was measured for body height, weight, and several other anthropometrical measurements, and genotyped for nine polymorphic markers (the average heterozygosity level was 0.4). We observed significant associations with practically all the anthropometrical phenotypes studied. More specifically, we found associations with body weight and height, limb length (P≤0.001; promoter region). After adjustment for body height, we demonstrated the substantial association increase for biacromial breadth (P=0.0012; some 140 kb downstream from ANKH) and vertebral column length (P=0.0008; exons 2–7 region). The majority of the observed associations persisted even after correction for multiple testing. For the first time the reliable evidence in support of universality of ANKH gene polymorphisms effect on bone size was provided.     

On the eruption pattern of the permanent incisors and first permanent molars in Paranthropus

It has been claimed recently that Australopithecus exhibited a pattern of permanent tooth eruption like that of extant great apes, whereas a significantly different pattern was shared by Paranthropus and Homo (Dean, 1985). More particularly, each of the four Paranthropus specimens examined in that study was held to show advanced development and eruption of the permanent incisors relative to the first molar. It is demonstrated here that the eruption sequence that was posited for at least one of these four Paranthropus specimens (SK 61) is clearly erroneous, while the developmental/eruption sequences manifested by the other three specimens would appear to be more ambiguous than was claimed. Another juvenile specimen of Paranthropus (KNM-ER 1820) that was not included in Dean's study also does not necessarily support the eruption pattern that was said to characterize that taxon.     

The Patterning Cascade Model and Carabelli's trait expression in metameres of the mixed human dentition: exploring a morphogenetic model

Since ancient times the Mediterranean island of Sardinia has been known for harboring a population with an average body height shorter than almost every other ethnic group in Europe. After over a century of investigations, the cause(s) at the origin of this uniqueness are not yet clear. The shorter stature of Sardinians appears to have been documented since prehistoric times, as revealed by the analysis of skeletal remains discovered in archaeological sites on the island. Recently, a number of genetic, hormonal, environmental, infective and nutritional factors have been put forward to explain this unique anthropometric feature, which persisted for a long time, even when environmental and living conditions improved around 1960. Although some of the putative factors are supported by sound empirical evidence, weaker support is available for others. The recent advent of whole genome analysis techniques shed new light on specific variants at the origin of this short stature. However, the marked geographical variability of stature across time and space within the island, and the well‐known presence of pockets of short height in the population of the southern districts, are still puzzling findings that have attracted the interest of anthropologists and geneticists. The purpose of this review is to focus on the state‐of‐the‐art research on stature, as well as the factors that made Sardinians the shortest among Europeans.     

A new statistic for the analysis of association between trait and polymorphic marker loci

Inference for detecting the existence of an association between a diallelic marker and a trait locus is based on the chi-squared statistic with one degree of freedom. For polymorphic markers with m alleles (2), three approaches are mainly used in practice. First, one may use Pearson's chi-squared statistic with m-1 degrees of freedom (d.f.) but this leads to a loss in test power. Second, one can select an allele to be the most associated and then collapse the other allele categories into a single class. This reduces in a biased way, the locus to a diallelic system. Third, one may use the Terwilliger [J.D. Terwilliger, Am. J. Hum. Genet. 56 (1995) 777] likelihood ratio statistic which has a non-standard unknown limiting probability distribution. In this paper, we propose a new statistic, L(D), based on the second testing approach. We derive the asymptotic probability distribution of L(D) in an easy way. Simulation studies show that L(D) is more powerful than Pearson's chi-squared statistic with m-1 d.f.