Primary tooth size asymmetry in twins and singletons.

OBJECTIVES: To explore asymmetry values of antimeric deciduous tooth crown dimensions in three types of twins: monozygotic (MZ), dizygotic same-sex (DZ) and opposite-sex (OS) vs. single-born controls. SETTING AND SAMPLE POPULATION: Mesiodistal and labio-lingual crown dimensions of second deciduous molars and mesiodistal canine and first molar crown dimensions of 2159 children at 6-12 years of age were evaluated, originating from the US cross-sectional Collaborative Perinatal Study from the 1970s, including altogether MZ (n = 28), DZ same-sex (n = 33) and OS (n = 39) pairs. Single born (n = 1959) were used as controls. MATERIAL AND METHODS: Dental casts were measured for comparison of variance relationships calculated from antimeric teeth, exhibiting fluctuating (FA), and directional (DA) asymmetry using anova. RESULTS: Significant differences appeared in MZ and OS girls in DA of deciduous canines, which gain size in the first and second trimester, and deciduous second molars, which finally stop crown growth during the early post-natal period. Significantly, increased FA values appeared for lower deciduous canines and second molars, indicating greatest environmental stress in OS girls, MZ girls and DZ boys. Twin girls had more fluctuating and directional crown asymmetry than twin boys, but in some dimensions, the twins were more symmetric than controls. CONCLUSIONS: Transmembrane hormonal influence between opposite-sex twins, and late gestational stress factors, caused by placental malfunction and/or monochorionicity, may be involved in asymmetric growth of antimers, during critical periods of crown size gain.

A three-dimensional comparison of the modifying effects of familial genetic contribution in Turner syndrome.

Comparison of individuals affected by chromosomal aneuploidies with controls has already confirmed the differential action of X and Y chromosomes during dental ontogeny. Permanent enamel and dentin structures are formed during the development of the dentition and these reflect the combined effects of both genetic and environmental factors during the prenatal and early postnatal period. It can provide key information on the effect of developmental assaults such as chromosomal aneuploidy as it is not subject to subsequent resorption or remodelling like other skeletal structures within the body. Dental features seen in Turner syndrome (TS) include significantly smaller teeth than controls and a narrow, deeply vaulted palate. Familial genetic contribution is known to have a modifying effect on features such as palate width. During the last two decades imaging and analysis techniques have undergone rapid evolution. Each development offers new possibilities for describing and defining structures within the body. This pilot study used a novel 3D system to measure the dentition of 10 individuals with TS and 10 unrelated female controls. The reliability of the method and its effectiveness in quantitatively describing differences between the two groups was verified. A larger study involving TS individuals, their first degree unaffected female relatives and female controls (n=35 each group) is underway which will use the new 3D system to describe the surface morphology, volume and contours of the dentition in order to quantify the effect of TS on dental development and to assess any modifying effects of familial genetic contribution.

Open bite in prematurely born children.

PURPOSE: The aims of this study were to: examine the expression of open bite in prematurely born children and discuss the etiological factors that may lead to bite it. METHODS: The subjects were 328 prematurely born (<37 gestational weeks) Caucasoid and African American children and 1,804 full-term control children, who participated in the cross-sectional study of the Collaborative Perinatal Project in the 1960s and 1970s. Dental documents, including casts and photographs, were taken once at the age of 6-12 years in the mixed dentition. The occlusion was recorded by examining and measuring the hard stone casts. Vertical open bite was recorded only for full erupted teeth. The statistical method used was chi-square analysis. RESULTS: Significant differences in the incidence of anterior open bite (from left to right canine) was found between the preterm and control groups and between gender and ethnic groups. The prevalence of anterior open bite was nearly 9% in the preterm group and almost 7% in the control group. African Americans (9%) had a significantly greater incidence of open bite than Caucasians (3%; P<.0001). Generally, girls had a greater incidence of open bite than boys (8% vs 6%; P<.11). When the study groups were divided by prematurity, gender, and ethnic group, the prevalence of open bite was increased--especially in preterm African American boys compared to controls (11% vs 8%). CONCLUSIONS: The results show differences in the development of anterior open bite between ethnic and gender groups. Premature birth may also influence dental occlusal development. Of importance are the patient's: general health condition; respiratory infections; inadequate nasal- and mouth-breathing; oral habits; and other medical problems. Preterm children may be relatively more predisposed to etiological factors for the development of anterior open bite.

Root lengths in 47,XYY males' permanent teeth.

Studies on individuals with sex chromosome anomalies have demonstrated the promoting effect of the Y chromosome on tooth crown enamel and dentin growth. The present research investigated permanent tooth root lengths in 47,XYY males. The measurements were made from panoramic radiographs. The results indicate longer tooth roots in 47,XYY males compared with those in control males and females. The promoting effect of the Y chromosome on dental growth thus continues in the form of root dentin after the completion of crown growth. The results, together with those on tooth crown sizes in 47,XYY males, suggest that growth excesses are evident and final, beginning a few months after birth and continuing up to the age of 14 years, at least. The excess root dentin growth in 47,XYY males, as well as sexual dimorphism in the growth of crown and root dentin, might be caused by the same factor on the Y chromosome.

Unilateral Angle II in functional lateralities.

The aim of this study was to explore unilateral Angle II-type malocclusion prevalences in functionally true right-sided (TRS) and non-right-sided (NRS) children having one or more left-sided functions (eye, hand, foot). A half cusp sagittal relationship of the upper and lower M1 and Dm2 was determined on dental casts of 1423 young American black and white children in a cross-sectional sample with the mean age of 8.5 years (range 6-12 years). Hand, foot and eye preferences were recorded at the age of 4 years during the Collaborative Perinatal Study. The prevalences of symmetric bilateral Angle I and II and asymmetric unilateral Angle II right and Angle II left cases were compared between TRS and NRS children using Chi-square analysis. In general, unilateral Angle II right occurred in 9 per cent of the population and Angle II left in 6.5 per cent. In moderate non-right sideness (two-thirds of left dominant functions), these proportions were 17 and 3 per cent, respectively, and in true right sidedness 8 and 6 per cent, respectively. TRS subjects were more symmetric (bilateral Angle I or II in 85 per cent of cases) than NRS children (80 per cent), and the differences were statistically significant (P < 0.02). These results highlight the anatomical relationships of structures supporting the occlusion and the symmetry/asymmetry of the neurocranium, cranial base, masticatory apparatus, and probably also the sidedness and the growth-stimulating effect of lateralized jaw function. Based on the results and considering earlier observations on brain asymmetry in functional lateralities, it can be hypothesized that a normal symmetric sagittal occlusal relationship is based on unilateral sagittal compensatory growth to maintain optimal bite, challenging early preventive orthodontic treatment in suspect unilateral Angle II cases.

Deciduous tooth crown size and asymmetry in strabismic children.

OBJECTIVES: To explore deciduous tooth crown dimensions in strabismic children and the relationship between the type of strabismus and tooth crown mesio-distal (M-D) and labio-lingual (L-L) size asymmetries. MATERIAL: Dental casts at mixed dentition of 2159 Collaborative Perinatal Study black and white children were measured, 123 of them strabismic at 1 year of age, age ranging from 6 to 12 years. METHODS: Directional and fluctuating asymmetries in antimeric teeth were explored in various types of strabismus having unilateral, bilateral or alternating expression. ANOVA and T-square test were used for size comparisons and calculated asymmetries were explored by comparing the variances and Pearson correlations. RESULTS: Strabismus was associated with significant M-D size increase of deciduous maxillary canines in black boys and white girls, black girls had size reduction in their mandibular canine, but white boys were unaffected. Right side size dominance was found in the strabismic children in the lower second deciduous molar M-D dimensions and in the children with alternating strabismus in their upper deciduous canine M-D dimensions. Children with unilateral strabismus had random fluctuating dental asymmetry in their upper deciduous second molar L-L dimensions when compared with healthy normals. Higher left-right correlations were found in lower second deciduous molar dimensions in strabismic girls when compared with that in controls and in strabismic boys, suggesting better developmental canalization in female. CONCLUSIONS: Asymmetries in the head area, such as promoted here in strabismic children, may have associations with asymmetries in the dentition, focusing the embryonal origins and timing of developmental processes.

Tooth eruption symmetry in functional lateralities.

Dental casts and oral photographs from a cross-sectional sample of 2092 young North Americans with detailed information on functional lateralities (eyedness, handedness and footedness) were examined to compare the proportions of symmetrical and asymmetrical eruption of the antimeric (left-right, contralateral pair) permanent teeth using a four-grade eruption scale. The proportion of symmetrically erupting antimeric teeth was higher for some teeth in those with non-right-sidedness of the feet and eyes, but not significantly so in the case of handedness. Left-footedness was significantly (95% confidence interval) associated with an increased proportion of symmetrical pairs of the maxillary first molar and mandibular lateral incisor, and non-right-eyedness with an increased proportion of symmetrical eruption and left/right non-balanced proportions of asymmetrical eruption in maxillary central incisors. True right-sidedness (hand, foot and eye) was significantly (P< or =0.05) associated with advanced eruption of the left mandibular first molar. It is suggested that while the timing of antimeric tooth emergence and clinical eruption is primarily programmed before crown mineralization, starting approximately at the 30th gestational week in the case of first permanent molars, symmetrical/asymmetrical tooth emergence and eruption may provide information a posteriori on prenatal and early postnatal growth and development.

Permanent tooth crown dimensions in prematurely born children.

AIM: The aim was to examine the effect of preterm birth on permanent tooth crown dimensions. MATERIALS AND METHODS: The data consisted of 328 prematurely born white and black children and 1804 control children who participated in the cross-sectional study of the Collaborative Perinatal Project (USA) in the early 1960s and 1970s. The dental examinations were carried out in a standardized fashion at ages varying from 6 to 12 years in 95% of cases. Tooth crown size measurements were performed on the dental casts with an electronic measuring device and readout by two experienced observers according to precise definitions generally quoted in the anthropological and genetic literature. The preterm and control groups were divided by sex and race. RESULTS: The results show both increased and decreased tooth crown dimensions in the prematurely born children. Significantly increased dimensions were found in the means of the intercuspal distances of the first permanent molars in the white boys and in the mesiodistal dimensions (MD) of the lower lateral incisors and the upper left first molar in the black girls. By contrast, there were decreased intercuspal distances, MD and labiolingual (LL) tooth crown dimensions in the white girls and black boys. The statistical method used was the Mann-Whitney's U-test (Willcoxon Rank-Sums test). CONCLUSIONS: The findings partly support previous reports of decreased tooth crown dimensions in preterm infants, but the increased dimensions found in the preterm white boys and black girls differ from earlier reports. Our results indicate the importance of environmental factors including neonatal factors in determining permanent tooth crown dimensions. Growth patterns, the buffering capacity and the timing of sensitive moments in tooth crown volume gain may vary between the sexes and ethnic groups and the possible effect of the accelerated growth period in preterm infants (catch-up growth) may influence the determination of permanent tooth crown dimensions.

The relationship of handedness to asymmetry in the occlusal morphology of first permanent molars.

Handedness has been shown to be related to a number of systematic asymmetries in body dimensions, dermatoglyphic patterns and cerebral morphology. The aim here was to compare linear and angular tooth crown asymmetries of the permanent molars in healthy right-handed and left-handed subjects. The material comprised 27 children with recorded concordant left-side dominance of hand, eye and foot. The controls were an age- and sex-matched group with right side dominance. The material is based on the Collaborative Perinatal Project where detailed medical records and the dentitions, including accurate dental impressions, of over two thousand American children were examined in the USA in the sixties. Machine vision technique was used to obtain accurate three-dimensional information from the occlusal surfaces of the first permanent upper and lower molars. The directional asymmetry values of angular measurements of mandibular first molars showed evidence of asymmetry of opposite direction between the two examined groups. The results indicate that occlusal morphology of first permanent molars may be affected by handedness, and this tendency is most evident in the angular measurements of the mandibular molars. Fluctuating asymmetry did not differ significantly between the examined groups.

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 karyotype 46,XY females.

The craniofacial cephalometric dimensions, angles and dimensional ratios of five Finnish individuals with complete testicular feminization (CTF) were compared with their first-degree relatives and population female and male controls. The linear and angular measurements were made from standardized lateral cephalograms of patients and normal population controls from the 'Kvantti Study' series. The women with CTF tended to have cranial base and maxillary complex dimensions between those of the normal control females and males. Their mandibular corpus was found to be longer than in normal control females, while their ramus was shorter compared with that of normal males. They also showed a smaller sagittal length ratio of the maxilla to the mandible, a smaller ANB angle and a more acute gonial angle than in both normal control females and males. Comparison of the women CTF with their first-degree female relatives showed basically the same trends as when comparing them with normal female controls. As the phenotype in these females with CTF is due to insensitivity to, or lack of androgens, it is suggested that the presence of the Y chromosome in these females leads to craniofacial dimensions between those of normal females and males which influences the growth of the mandibular corpus. This follows the same general metric pattern that is observed in many of their adult head and body dimensions as well as in their dental arches.

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.

Dental occlusion and arch size and shape in karyotype 46,XY females.

The dental arch dimensions and occlusion of five Finnish individuals with complete testicular feminization were compared with their first-degree relatives and population female and male controls. The women with complete testicular feminization tended to have larger maxillary arch dimensions in all three spatial planes than the female and male controls, and larger mandibular arch dimensions in the transversal plane than the female controls. The results also suggested that the height/width ratio in the maxillary arch and width/length ratio in the mandibular arch would be greater in these females than in population females. Both the molar and canine sagittal relationships were more mesial than in the female and male population controls. As the phenotype in these 46,XY females is due to insensitivity to, or lack of androgens, it is suggested that the presence of the Y chromosome in these females leads to arch dimensions falling between those of normal females and males. This follows the same general dimensional pattern observed in their adult stature.

Maternal smoking and tooth formation in the foetus. III. Thin mandibular incisors and delayed motor development at 1 year of age.

Dental casts from 2159 black and white Americans with detailed neurological data available from the Collaborative Perinatal Study were examined to investigate the relationship of maternal smoking during pregnancy and delayed motor development at 1 year of age to morphological traits in the dentition. Earlier results have indicated that maternal smoking during pregnancy may cause selected tooth size metric reductions in the deciduous dentition and at least in some of the permanent teeth with prenatal crown formation, these features being influenced by sex and race differences. The present results suggest that a thinning of the incisal parts of the permanent mandibular incisors is associated with heavy maternal smoking during pregnancy, and those white girls, in whom this dental variant is found, have probably experienced more severe central damage during the smoking sensitive gestational months, as is also seen in a delayed motor development at the age of 1 year.

Sex chromosomes and human growth. A dental approach.

Studies on tooth crown size and structure of individuals with various sex chromosome anomalies and their normal male and female relatives have demonstrated differential direct effects on growth of genes on the human X and Y chromosomes. The Y chromosome promotes growth of both tooth enamel and dentin, whereas the effect of the X chromosome on tooth growth seems to be restricted to enamel formation. Enamel growth is decisively influenced by cell secretory function and dentin growth by cell proliferation. It is suggested that these differential effects of the X and Y chromosomes on growth explain the expression of sexual dimorphism in various somatic features, such as the size, shape and number of teeth, and, under the assumption of genetic pleiotropy, torus mandibularis, statural growth, and sex ratio. Future questions concern, among other topics, the Y chromosome and the mineralization process, concentric control of enamel and dentin growth, and gene expression.

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.

Maternal smoking and tooth formation in the foetus. II. Tooth crown size in the permanent dentition.

Altogether 2159 pregnancies among black and white Americans in the Collaborative Perinatal Study and dental casts from their children at the age of 6-12 years were studied to determine the effect of maternal smoking on permanent tooth crown dimensions. A trend of reduction, similar to that observed in the deciduous second molars, was found in the permanent first molars and also in the mesio-distal dimension of permanent incisors in relation to sex and race of the children and smoking habits of the mother. In terms of peak in their mitotic growth, the results can be interpreted to indicate a sensitive period of intra uterine development from the 24th to 28th gestational weeks. Comparisons of postnatal body size and differential correlation patterns in affected tooth dimensions with early postnatal body and head size between smokers and non-smokers, suggests that maternal smoking during pregnancy may have an effect on basic growth of the head and body and/or the developmental process that impacts tooth development at some specific sensitive period also during the postnatal formation of these tooth crowns.