Arthur B. Lewis

Genetic, Nutritional, and Maturational Correlates of Dental Development

useful in their own right, fail to explain the extent to which size and timing are dependent upon endogenous and exogenous factors, respectively. For such work, particular research designs must be selected. Nutrition can be explained within a population where one or more nutritional parameters can be quantified. Genetic factors can be investigated both between populations (if nutritional status is known) and within populations, using sibling and twin comparisons and correcting for attenuation due to measurement error. Sex-specific sibling comparisons (sister-sister, brother-brother) and parentchild comparisons (father-daughter, father-son, etc.) help to uncover Xand Y-linked genetic mediation. S. M. G.

Sex Difference in Tooth Size

In connection with continuing studies on X-chromosomal determination of intraindividual tooth-size variability, we became concerned with the sex difference in absolute tooth size, using mesiodistal crown diameters of 243 middle-class, Ohio, white children, measured by one of us (ABL) throughout. With mean values generally comparable to those reported by Moorrees (The Dentition of the Growing Child [Cambridge: Harvard University Press, 1959], p. 82), the sex difference in tooth size for the Ohio white children from a single geographical area was 4 per cent, intermediate between the 3 per cent sex difference in tooth formation timing and the 5 per cent difference in tooth eruption, but in the opposite

The gradient and the pattern of crown-size reduction in simple hypodontia.

Abstract No Abstract Available. From the Center for Human Growth and Development, University of Michigan and Fels Research Institute, Yellow Springs, Ohio

Sexual Dimorphism in the Buccolingual Tooth Diameter

In recent years attention has been given to mechanisms controlling over-all tooth size. Reduction in tooth number has been related to reduced size and morphological complexity of the remaining teeth (S. M. GARN, A. B. LEwis, and R. S. KEREWSKY, Nature, 200:488, 1963; H. J. KEENE, Angle Orthodont., 35:289, 1965; K. HANIHARA, T. MASUDA, and T. TANAKA, J. Anthropol. Soc. [Nipponj, 73:72, 1965). While sex clearly affects tooth size throughout the dentition, dimorphism is particularly large for

Third Molar Agenesis and Reduction in the Number of Other Teeth

Agenesis of one or more third molar teeth is relatively common, occurring in 7-26 per cent of white populations studied radiographically (Goblirsch, J.A.D.A., 17:1849, 1930; Banks, Angle Orthodont., 4:223, 1934; Hellman, D. Cosmos, 78:750, 1936; Nanda, Am. J. Orthodont., 40:698, 1954). On theoretical grounds an increased incidence of other missing teeth might be expected where M1 is absent (H. GrUneberg, The Genetics of the Mouse [2d ed.; The Hague: Nijhoff, 1952]). Data were assembled on a total of 100 individuals lacking one or more third molar teeth. Seventyeight came from a private orthodontic practice (A. B. L.). Twenty-two were taken from the Fels Longtitudinal Series and lacked lower left M3 in every case. Of the total of 100 individuals so characterized, 53 teeth of other classes proved to be congenitally absent by direct and radiographic observation. Only M1 was consistently present in this group. Agenesis of one or more teeth was confirmed for L, J, C, P1, P2, and M2 (see table).

Late Growth Changes in the Craniofacial Skeleton

Analysis of serial radiographs shows that growth in the cranial base and in the mandible continues into the third decade. Variations in rate and timing are great, and the total increments after 18 years are usually small.

Intrinsic Craniofacial Compensations

Abstract No Abstract Available. *Supported in part by United States Public Health Service Grant DE-02272.

Pubertal spurts in cranial base and mandible. Comparisons within individuals.

Serial data from cephalometric radiographs were analyzed for 34 boys and 33 girls who had cephalometric radiographs annually near each birthday from at least age 7 through 18 years. Spurts were defined for this study as increases between successive cranial base increments that exceeded 0.75mm/year in boys or 0.5mm/year in girls. The corresponding criterion for the mandible was 1.0mm/year in either sex. Pubescence was defined as the 4- year period spanning 2 years before and after peak height velocity. Spurts during pubescence were common, tending to occur about 1.6yr earlier in girls than boys. The mean increments at first pubertal spurt (FPS) and the mean sizes of FPS were about 25% to 33% greater in the boys than in the girls. The rate of growth during the year before FPS tended to be greater in the girls, while in the year after FPS it tended to be greater in the boys. The timing of FPS in either cranial base of mandible was not closely related to the onset of ossification in the ulnar sesamoid, the age at peak height velocity, or age at menarche. FPS generally occurred after the onset of ossification of the ulnar sesamoid, but before peak height velocity and menarche. There was no evidence of difference between craniofacial EPS in children who passed rapidly or slowly through pubescence, nor was any difference noted between the size of pubertal spurts in tall or short boys. larger total increments after peak height velocity were found in the short boys. Significant correlations were identified between the cranial base and the mandible in the timing but not in the magnitude of FPS. The children were approximately equally divided between those in whom cranial base spurts occurred first, those in whom mandibular spurts were first, and those in whom FPS occurred in both areas within the same annual interval.

Comparisons between dental and skeletal ages.

Data from 694 untreated children seen in a private orthodontic practice were used to analyze associations between dental and skeletal maturity. Dental ages were obtained by comparison with Bolton Standards; skeletal ages were assessed using the Greulich-Pyle atlas. In some children the difference between the dental and skeletal ages was as large as 36 months; the difference was less than 6 months in fewer than 40% of the children. Regression analyses showed only moderate associations between these measures. One measure of maturity cannot be inferred from the other.

PHYLOGENETIC AND INTRA-SPECIFIC VARIATIONS IN TOOTH SEQUENCE POLYMORPHISM

Publisher Summary This chapter reviews phylogenetic and intraspecific variations in tooth sequence polymorphism. The sequence of eruption of the permanent teeth shows a remarkable shift through the order primates. At one end, in the insectivores, the posterior or molar teeth add themselves to the dental arcade before the deciduous anterior teeth even begin replacement. At the other end, typified by the textbook European, the deciduous anterior teeth are largely replaced by their permanent successors before the second and third molar teeth extend the effective size of the dental arch. This distinction in eruption order between early primate and modern man is paralleled by a less dramatic but comparable difference between ape and man. The discovery of immature paleoanthropic hominids directed attention to their still-developing if fossilized teeth. There appeared to be a neat developmental difference that put paleoanthropic man in one eruption set and neanthropic man in another, except perhaps for the copper-age Greeks. But this neat differentiation between fossil and modern hominids based on the presumed order of eruption in a few juvenile fossil mandibles and the average age at eruption from norms for Europeans proved to be one of the credible but incorrect myths. In living apes, or preserved specimens, gingival eruption has been the point of record. Available data and data summarizations, thus, combine alveolar eruption, gingival eruption, estimates of eruption order based on the relative heights of the erupted teeth, and radiological assessments.