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Upper Central Incisor and Canine Tooth Crown Size in 47,XXY Males L. Alvesalo, E. Tammisalo and G. Townsend J DENT RES 1991 70: 1057 DOI: 10.1177/00220345910700070801 The online version of this article can be found at: http://jdr.sagepub.com/content/70/7/1057

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Upper Central Incisor and Canine Tooth Crown Size in 47,XXY Males L. ALVESALO, E. TAMMISALO', and G. TOWNSEND2 Institute of Dentistry, University of Oulu, Aapistie 3, SF-90220 Oulu, Finland; 'Institute of Dentistry, University of Turku, Lemminkdisenkatu 2, SF-20520 Turku, Finland; and 2Department of Dentistry, The University ofAdelaide, G.P. O. Box 498, Adelaide, South Australia 5001

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. J Dent Res 70(7):1057-1060, July, 1991

Introduction. It has commonly been assumed that human sex chromosomes contain genes that influence the determination of final height (e.g., Ferguson-Smith, 1965; Simpson, 1976). Investigations of skeletal development in Klinefelter and Turner syndromes have indicated that the Y chromosome might possess genes that cause a retardation of skeletal maturation (Tanner et at., 1959), and X linkage for rate and timing of ossification has also been suggested (Gain and Rohmann, 1962). Evidence is now accumulating that growth and development of dental structures are affected by sex chromosomes, independently of secondary hormonal influences. For example, X-linkage for tooth crown size and dental development has been proposed based on correlative studies of normal relatives (Garn and Rohmann, 1962; Garn et at., 1965; Alvesalo, 1971). The results on relatives have also indicated the effect of the Y chromosome on tooth growth, and observed sexual dimorphism in average tooth size has been connected with this effect (Alvesalo, 1971). Teeth are particularly suited for the study of developmental events occurring from fetal life to adolescence, since human dental development begins with the formation of deciduous incisors at about four weeks in utero, followed by that of the other deciduous and permanent teeth, each of which passes through a series of well-defined developmental stages. All tooth crowns, apart from third molars, have reached their final shape and size between the ages of two months and eight years, and, consequently, sexual dimorphism in final average crown size is expressed at early and different stages of development. Measurements of tooth crown size obtained from dental models have shown that the teeth of 47,XYY males and 47,XXY males are generally larger than those of normal males, while 45,X and 45,X/46,XX females have smaller teeth than do normal females (Filipsson et al., 1965; Alvesalo et at., 1975; Received for publication March 13, 1990 Accepted for publication March 5, 1991 This study was supported by the Academy of Finland and the University of Turku Foundation.

Alvesalo and Kari, 1977; Alvesalo and Portin, 1980; Kari et al., 1980; Townsend et al., 1984; Alvesalo, 1985; Townsend and Alvesalo, 1985a, b; Townsend et al., 1988; Varrela et al., 1988). Females with complete testicular-feminizing syndrome (46,XY females) have teeth with sizes similar to those of normal males (Alvesalo and Varrela, 1980). These results support the concept that both X and Y chromosomes have growth-promoting effects on tooth size and that they operate from early during development. The location of a growth-promoting region within the X chromosome is probably in the short arm (Mayhall et al., 1991), and within the Y chromosome, conceivably on the proximal, non-fluorescent portion of the long arm (Alvesalo and de la Chapelle, 1981). The determination of the thickness of enamel and dentin of tooth crowns from standardized intra-oral radiographs provides an insight into the nature of the growth-modifying effects of the sex chromosomes. The distance across the dentino-enamel junctions is determined at an early stage of crown development at the time when amelogenesis is beginning, and mitotic activity of the cells of the inner enamel epithelium is the decisive factor in determination of this distance (Kraus and Jordan, 1965). Enamel thickness provides a measure of the secretary activity of post-mitotic, highly differentiated ameloblasts, whereas "dentin" thickness reflects growth due to mitotic activity of the developing tooth germs. As a whole, the results of the measurements on enamel and dentin thicknesses of tooth crowns in individuals with various kinds of sex chromosome anomalies-including 45,X, 45,X/ 46,XX, 47,XXX, and 46,XY females and 47,XYY males indicate that the X chromosome influences mainly enamel thickness, whereas the Y chromosome promotes both enamel deposition and dentin growth (Alvesalo and Tammisalo, 1981; Alvesalo, 1985; Alvesalo et al., 1985, 1987). Results at the molecular level suggest that human amelogenin gene loci are on the sex chromosomes, on the distal short arm of the X chromosome, and possibly at the proximal long arm region of the Y chromosome (Lau et al., 1989). Interestingly enough, dermatoglyphic investigations have suggested that human sex chromosomes may directly influence the development of the palmar patterns of loops and triradii (Polani and Polani, 1979), and it.has also been postulated that the Y chromosome may regulate the rate of growth of the primitive gonad, pointing to a more general regulatory role for the Y chromosome (Mittwoch, 1985). Differential ontogenesis of the sexes has been proposed to depend entirely on a regulatory effect of the Y chromosome (Ounsted and Taylor, 1972).

Materials and methods. Measurements of enamel and dentin thicknesses of permanent maxillary central incisors and canines were made in 37 Finnish 47,XXY (Klinefelter syndrome) males. Controls were first-degree male and female relatives of the study subjects and also population males and females, including dental students and patients at the Institute of Dentistry, University of Turku,

Finland. Determinations of enamel and dentin thicknesses were made

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from standardized intra-oral radiographs of permanent maxillary central incisors and canines on both sides of the jaw. These teeth were selected for technical reasons and also, with canines, for their developmental stability (Osborne et al., 1958). The following techniques were used: A piece of film (size, 2 x 3 cm) was attached with wax to the palatal surface of the tooth crown, and the central x-ray beam was directed to the mid-point of the labial surface perpendicular to the plane bisecting the angle between the film and the long axis of the tooth crown. An open-ended cylindrical metal cone limited the diameter of the radiation field to 28 mm and gave a targetfilm distance of 32 cm. The exposure time was 0.5 s, and other exposure factors were 55 kVp and 15 mA. Film was developed by an automatic x-ray processor, and a dental x-ray viewer (Realist) was used to magnify the radiographs ten-fold for measurement. Maximum mesiodistal diameters and the thicknesses of mesial and distal enamel layers of the tooth crowns were measured perpendicular to the long axis of the tooth crown. The accuracy of the measurements (after magnification) was to the nearest 0.5 mm, and all measurements were performed by the same investigator. As a test of the replicability of the method, 50 control subjects were radiographed a second time after an interval of a few days. No statistically significant differences were found between the means of the measurements at the 5% probability level, and error variances were less than 6% of total observed variances for all variables. Measurements made on the right side of the jaw were used for this study. However, if mea-

J Dent Res July 1991 TABLE 1 MEAN MESIODISTAL TOOTH-CROWN SIZES IN MAXILLARY CENTRAL INCISORS AND CANINES OF 47,XXY MALES AND CONTROLS MEASURED FROM THE RADIOGRAPHS Tooth Crown Size (mm) I C Group Mean SD N Mean SD N 47,XXY males ***9.47 0.59 37 ***8.68 0.51 28 46,XY males 9.43 0.57 85 8.78 0.49 84 9.00 0.50 93 46,XX females 8.35 0.47 94 Subsample 47,XXY males 9.38 0.57 9 8.37 0.50 7 Male relatives 9.48 0.54 9 8.56 0.73 7 Subsample 47,XXY males 9.56 0.96 8 8.72 0.48 6 Female relatives 8.99 0.66 8 8.25 0.58 6 I, maxillary central incisor; C, maxillary canine. F-values: I, 17.00, p

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 max...
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