reduced tooth size in 45,x (turner syndrome) females

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 65:367-371(1984)

Reduced Tooth Size in 45,X (Turner Syndrome) Females GRANT TOWNSEND, BIRGIT LETH JENSEN, A N D LASS1 ALVESALO Department ofDentistry, The University ofAdelaide, Adelaide, South Australiq 5000 (G. T) , Institute of Orthodontics, Royal Dental College, DK- 2100 Copenhagen, Denmark (B.L. J.), Institute of Dentistry, University of Turku, SF-20520 Turku, Finland (L.A.), and Institute of Dentistry, University o f Kuopio, SF-70211 Kuopio, Finland (L.A.1

KEY WORDS Enamel thickness

Turner syndrome, Tooth size, X chromosome,

ABSTRACT Mean values and variances of deciduous and permanent tooth dimensions were compared between 121 45,X (Turner syndrome) females and 171 control subjects to clarify the role of the X chromosome on dental development. Although deciduous molars tended to be smaller than normal in 45,X females, there was no evidence of a reduction in tooth size for deciduous anterior teeth. In the permanent dentition, all mesiodistal dimensions were significantly smaller in 45,X females but only some of the buccolingual dimensions were smaller. The findings for deciduous tooth-size may reflect a sampling effect related to the extremely high frequency of spontaneous abortion in 45,X individuals. Results for permanent teeth are consistent with the concept of a decrease in enamel thickness in 45,X females.

In addition to ovarian dysgenesis and web- bing of the neck, females with 45,X chromosomal constitution exhibit a variety of somatic anomalies which reflect a basic dis- turbance in growth. Adult stature is typi- cally very short, mean height being about 140 cm, and birth weight also tends to be below average (Hamerton, 1971). Further- more, craniofacial morphology is altered, with facial retrognathism and flattening of the cranial base (Gorlin et al., 1965; Filipsson et al., 1965). XO individuals also tend to show retardation in skeletal maturation (Tanner et al., 1959; Park et al., 1983).

Few studies of the dentition in 45,X females have been published. Filipsson et al. (1965) and Jensen (1974) both noted a significant reduction in the mesiodistal dimension of permanent teeth and Filipsson et al. (1965) also found a tendency for earlier tooth eruption, while Kari et al. (1980) noted a trend toward smaller deciduous teeth in a small sample of 45,X girls. No gross abnormalities in dental morphology have been reported, although Kirveskari and Alvesalo (1982) described modifications in the expression of certain nonmetric crown traits, including shovel-shape, hypocone reduction and lower molar cusp number, which suggested a tendency for morphological dental reduction.

This study provides a comprehensive de- scription of tooth size in a large sample of 45,X females, including a n analysis of mesiodistal and buccolingual dimensions of all deciduous and permanent teeth, except third molars. Measurements obtained from the 45,X sample were compared tooth by tooth with a control group to clarify the role of the X chromosome on dental development.

MATERIALS AND METHODS

The 45,X (Turner syndrome) sample con- sisted of 121 girls and adults, all confirmed by cytogenetic tests as having only one X chromosome. Measurements were recorded from dental casts obtained from collections a t the Royal Dental College, Copenhagen, and the University of Turku, Finland. The Danish group was composed of 35 individuals, while the Finnish group included 86 subjects. Initial comparisons of mean tooth diameters using t-tests showed no significant differences between the groups, which were combined for subsequent analysis. The control group comprised 171 females with no history of serious medical problems, including 20 first-degree relatives of the 45,X fe-

@ 1984 ALAN R. LISS, INC

368 G. TOWNSEND, B.L. JENSEN. A N D L. ALVESALO

males. Average tooth size of the relatives was not significantly different from the rest of the controls, indicating that altered tooth size in 45,X subjects was not a familial fea- ture. All subjects, both 45,X and controls, were of Caucasian ancestry.

Mesiodistal and buccolingual tooth diameters were recorded by the one investigator (G.T.) to an accuracy of 0.10 mm according to the definitions of Seipel(1946) and Moorrees et al. (1957) using specially modified dial cal- ipers. Any teeth which had not fully erupted or which showed evidence of attrition, including interstitial wear, were excluded. No measurement was attempted where caries, restorations, or dental plaque obscured a dimension. Measurements were obtained for teeth on both sides of the dental arch, but as there were no statistically significant differences between sides, values averaged from right and left measurements were used in the final analysis. If a tooth was missing, the measurement obtained from its antimere, if present, was accepted. Unfortunately, very few deciduous incisors of 45,X girls were available for measurement, most casts rep- resenting individuals with either mixed or permanent dentitions. For some subjects, se- rial dental casts were available, enabling measurement of both deciduous teeth and their permanent successors.

Estimates of skewness and kurtosis were calculated to assess the forms of distributions, and descriptive statistics including means, standard deviations, and coefficients of variation derived for tooth dimensions. The significance of differences between mean values was tested by Student’s t-test where sample sizes permitted.

Experimental errors were analysed by a replicability trial in which 20 sets of casts, selected a t random, were measured on two occasions. Measurement errors were small, the standard deviation of a single determi- nation (Dahlberg, 1940) averaging 0.08 mm, and were therefore unlikely to bias tooth measurements.

RESULTS

Estimates of skewness and kurtosis, calculated where sample sizes permitted, indicated that the distributions of tooth measurements were normal and could therefore be described adequately in terms of mean values and standard deviations.

Table 1 provides a comparison of mean diameters of deciduous teeth between the 45,X females and control subjects. Although the sample size for deciduous incisors in the 45,X

group was small, no statistical comparisons with controls being attempted, an interesting trend emerged. There was no evidence of a reduction in tooth size of deciduous incisors or canines in 45, X females; in fact, the buccolingual dimension of the maxillary canine was significantly larger in the 45,X group than normal controls. On the other hand, there was a tendency for deciduous molars in 45,X females to be smaller than normal, five of the eight comparisons showing significant differences (P < 0.01). There was no obvious difference in the patterns of coefficients of variation between the two groups, 11 values being smaller in 45,X females and seven larger.

Table 2 summarizes results for the permanent dentition. Again, an interesting result was noted when mean values and coefficients of variation were compared. All mediodistal dimensions were significantly smaller in the 45,X females compared with normal controls (P < 0.011, but only some of the buccolingual dimensions were smaller. Buccolingual dimensions of both maxillary and mandibular permanent molars showed significant reductions in size in the 45,X group, as did central incisors. However, no significant difference was noted in the buccolingual size of either maxillary or mandibular canines and three other buccolingual dimensions were not significantly different between the groups.

Percentage reductions in permanent mesiodistal dimensions ranged from 2.6% for maxillary canines to 9.3% for maxillary first molars; molars and incisors generally showed greatest percentage reductions whereas canines showed least. The average percentage reduction for mesiodistal dimensions was 6.1%. For buccolingual dimensions, size differences ranged from a slight increase for maxillary canines in 45,X females, to a 6.9% reduction for mandibular second molars. Again, molars showed greatest reduction and canines least, but the average percentage reduction overall for buccolingual dimensions was only 2.6%.

Furthermore, when coefficients of variation were compared, ten of a possible 14 comparisons yielded higher values in the 45,X females for mesiodistal dimensions, whereas only one of 14 comparisons was larger in the 45,X group for buccolingual dimensions. When the pattern of values for coefficients of variation was considered between teeth, maxillary lateral incisors showed greatest variability and first molars least in both groups, a result consistent with the field the- ory of Butler (1939) and Dahlberg (1945).

REDUCED TOOTH SIZE IN TURNER SYNDROME 369

TABLE 1. Crown diameters of deciduous teeth zn 45,XO females and fernale control SUbJeCtS'

45,XO Controls - - Tooth n X SD CV n X

Mesindistal Maxilla

di'

dc dm dm'

di'

Mandible di diz dc dm I dmz

Maxilla di I di2 dc dm' dm2

Buccolingual

5 9

20 19 23

3 5

19 17 18

1 5

17 19 23

2 3

13 14 16

6.50 5.20 6.78 6.87 8.46"

3 75 4 36 5.73 7 19' 9 19'

5.50 4.65 6.37 8.55 9.64

Mandible di I diz dc

dm2 dm 1

-

' n refers to number of teeth measured. Mean value significantly smaller at P < 0.01

3.63 4.37 5.70 6.88* 8.14'

21 .42 2 4 .38 .40

.22

.48

.29

.39

.54

-

.25

.41

.47

.48

-

.08

.31

.30

.38

3.2 8.0 3.6 5.5 4.7

5.8 11.0 5.1 5.5 5.9

~

5.4 6.5 5.4 5.0

-

1.7 5.5 4.4 4.6

35 43 74 63 76

24 37 66 60 65

36 41 72 69 78

22 35 65 65 72

6.38 5.19 6.74 6.99 8.81

3.99 4.63 5.69 7.69 9.82

4.93 4.72

8.49 9.75

6.07:;:

3.69 4.29 5.56 7.22 8.72

DISCUSSION

In a previous study of deciduous tooth-size in 11 Finnish 45,X females, Kari et al. (1980) noted that six of 20 tooth dimensions were significantly smaller in 45,X individuals. Significant differences all related to deciduous molar dimensions, whereas the canines were similar in size in both groups. Our results confirm that there is no significant reduction in deciduous canine size in 45,X girls; in fact, one canine dimension was significantly larger. Furthermore, it appears that deciduous incisors in 45,X girls are also at least as large as normal, although the small sample size available must be taken into account.

In relation to the permanent dentition, all mesiodistal dimensions were significantly smaller in the 45,X group, confirming the findings of Filipsson et al. (1965). However, there was not a uniform reduction in tooth size throughout the dentition. Not only were some teeth reduced in size to a greater extent than others in 45,X females (for example, first molars compared with canines) but there was also a definite trend for mesiodistal dimensions in general to show greater reduc-

SD

.33

.29

.34

.43

.47

.oo

.28

.26

.36

.50

.29

.36

.40

.42

.45

.25 2 3 .32 .41 .43

5.1 5 5 5.0 6.2 5.3

7.4 6.0 4.5 4.7 5.1

5.8 7.6 6.6 5.0 4.6

6.7 5.3 5.7 5.7 4.9

~

tions than buccolingual(6.1% compared with 2.6%).

The results of a radiographic study of enamel thickness in 45,X permanent teeth by Alvesalo and Tammisalo (1981) provide a possible explanation for the observed differ- ential reduction of mesiodistal and buccolingual dimensions. They found that the enamel layer was definitely thinner in incisors and canines of 45,X females compared with control males and females. However, the dis- tance between mesial and distal dentino- enamel junctions, which reflects dentine thickness, was similar in 45,X females and normal control females. In other words, the reduction in overall tooth size in 45,X females could be attributed to a decrease in enamel thickness. Our results are consistent with this concept, particularly if the data on enamel thickness provided by Shillingburg and Grace (1973) are also considered.

Shillingburg and Grace measured the normal thickness of enamel on the mesial, labial, distal and lingual aspects of all permanent teeth, except third molars, at different crown levels. Total enamel thickness in the region of maximum mesiodistal diameter (occlusal or incisal third of crowns) was

370 G. TOWNSEND, B.L. JENSEN, AND 1,. ALVESALO

TABLE 2. Crown dianaeters ofpermanerit teeth in 45,XO females and female control suhlects'

Tooth

Mesiodistal Maxilla

I' I2 C PM' PYZ M M2

Mandible

PM, MI Mz

Buccolingual Maxilla

I' IZ C PM' PM' M' M2

I , Mandible

P M , PMi MI M .;

__ n __

109 112 110 103 98 93 46

103 110 112 111 103 86 46

82 79 91

101 102 102 58

80 89 92

105 107 94 55

4 9 8 5 54' 6 40- ' 6 79' ' 6 66* ' 9 991 9 593 '

6 9 3 ' * 6 26 8 21 8 971 9 11

10 91" 1090 '

5 86 6 05' 7 42 7 80 8 25 9 92 9 67

' n refirs to the number (if teeth mt.:iiurrd. 'Mean valui, significantly smal ler at P < 0.05

*- 'Mean value significantly siiiiiller a t €' < 0.01

~~. ..

SD

.53 5 6 .40 3 9 .36 .43 .53

3 2 .37 .33 .37 .39 .53 .48

.43

.45

.51

.47

.48

.47

.59

.35 3 1 .47 .48 .50 .43 .5 1

approximately 2-3 mm on average, whereas enamel thickness in those areas correspond- ing to the maximum buccolingual diameter (gingival third of crowns) averaged less than 1 mm. That is, the thickness of enamel nor- mally contributes considerably more to the maximum mesiodistal size of teeth than to the buccolinpal diameter. If the absence of an X chromosome does indeed lead to a uniform percentage decrease in enamel thickness of all teeth (for instance, a 15% reduction) one would expect a more marked effect on the maximum absolute mesiodistal crown diameter than the buccolingual. It is also interesting in this regard to note that according to Shillingburg and Grace the enamel layer on the labial and lingual aspects of canines in the region of the gingival third of the crown is particularly thin, less than 1 mm in total, and that the buccolingual dimension of this particular tooth showed no evidence of reduction in the 45,X group. Our finding that variability in tooth size, as re-

~~

CV ~~~

6.6 8.9 5.3 5.9 5.7 4.6 5.8

6.5 6.6 5.1 5.4 5.8 5.3 5.0

6.2 7.2 6.2 5.3 5.2 4.3 5.4

6.0 5.1 6.4 6.2 6.1 4.3 5.3

flected

n

125 111 81 77 77

107 47

123 122 87 82 78 74 50

85 77 78 81 82

121 64

91 89 77 84 85

116 58

____ - X ~-

8 61 6 69 7 73 6 97 6 61

10 35 9 96

5 41 5 97 6 66 7 06 7 03

10 96 10 46

7 15 6 39 8 19 9 21 9 20

11 41 11 41

5 99 6 32 7 53 7 81 8 40

10 50 10 34

Controls - __ SD

~

.55

.55

.35

.38 34 .47 .60

3 1 .37 .33 .40 .38 .6:3 .63

.46

.50

.45

.4Y

.54 5 0 .63

.42

.4 1

.5 1 5 4 .53 .47 5 5

bv coefficients of

CV

6.4 8.3 4.6 5.4 5.2 4.5 6.1

5.8 6.1 4.9 5.6 5.4 5.8 6.1

6.4 7.8 5.5 5.3 5.9 4.4 5.5

6.9 6.4 6.8 6.8 6.3 4.5 5.3

.-

variation. was greater than normal for mesiodist,al dimensions but less than normal for buccolingual dimensions is difficult to interpret but may also result from a reduction in enamel thickness affecting crown dimensions differen- tially.

Additional support for the concept that the X chromosome influences enamel thickness comes from a preliminary analysis of dental morpholoby in the 45,X sample. Although no striking morphological crown abnormalities were noted, there were some subtle varia- tions in dental morphology which were suggestive of a decrease in enamel thickness. Admittedly, our analysis was based on dental casts and should therefore be interpreted cautiously. Nevertheless, a number of premolars showed abnormal occlusal groove for- mation, while many mandibular first premolars displayed marked reductions in lingual cusp height. Both these features could be due to a reduction in enamel thickness.

REDUCED TOOTH SIZE IN TURNER SYNDROME 371

Further clinical studies and direct measurements of enamel thickness of the teeth of 45,X females are needed to confirm or reject this conjecture.

Our results regarding the deciduous anterior teeth in 45,X girls need to be interpreted cautiously due to the small sample sizes available. Nevertheless, the apparent lack of reduction in the size of these teeth may reflect a sampling effect, related to the high frequency of spontaneous abortion in 45,X individuals, estimated to be about 97-99% (Polani, 1981). We have only examined the teeth of a very small percentage of survivors, whose cellular activity may not have been severely disrupted during the critical early prenatal period when the deciduous anterior teeth were forming.

Recent odontometric studies of individuals with sex chromosomal aneuploidies (e.g., Al- vesalo and Portin, 1980) have indicated that both the X and Y chromosomes may have a direct effect on growth and development. Whether this genetic effect results from spe- cific genes on the sex chromosomes or is related to a quantitative effect of hetero- chromatin on cell cycle activity is not clearly established. Certainly both the Y chromosome in normal males and the second X in females are largely heterochromatic and there does seem to be a definite dosage effect on various phenotypic features related to the number of sex chromosomes present. For example, if we consider dermatoglyphics, every additional X chromosome depresses total ridge count by about 30 ridges (Penrose, 1967). Dental studies provide added insight into the nature of these effects since final tooth size results from both cellular proliferation of developing enamel organs, as well as deposition of mineralized tissue. Results to date suggest that the Y chromosome may exert more influence on cellular proliferation of developing tooth germs than the X chromosome (Alvesalo and Tammisalo, 19811, whereas both the sex chromosomes seem to be important in controlling amelogenesis in quantitative terms.

ACKNOWLEDGMENTS

This study was supported in part by the National Academy of Finland.

LITERATURE CITED

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Butler, PM (1939) Studies of the mammalian dentition. Differentiation of the postcanine dentition. Proc. Zool. Soc. Lond. 109Btl-36.

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Dahlberg, G (1940) Statistical Methods for Medical and Biological Students. London: Allen and Unwin.

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Gorlin, RJ, Redman, RS, and Shapiro, BL (1965) Effect of Xchromosome aneuploidy on jaw growth. J. Dent. Res. 44:269-282.

Hamerton, JL (1971) Human Cytogenetics, Val. 11, New York: Academic Press, pp. 65-112.

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Moorrees, CFA, Thomsen, SO, Jensen, E, and Yen, PKJ (1957) Mesiodistal crown diameters of the deciduous and permanent teeth in individuals. J . Dent. Res. 36:39-47.

Park, E, Bailey, JD, and Cowell, CA (1983) Growth and maturation of patients with Turner’s syndrome. Pe- diatr. Res. 17:l-7.

Penrose, LS (1967) Finger-print pattern and the sex chromosomes. Lancet 1:298-300.

Polani, PE (1981) Chromosomes and chromosomal mech- anisms in the genesis of maldevelopment. In K J Con- nolly and HFR Prechtl (eds): Maturation and Development: Biological and Psychological Perspec- tives. Clinics in Developmental Medicine No. 77/78. London: William Heinemann Medical Books, pp. 50- 72.

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Tanner, JM, Prader, A, Habich, H, and Ferguson-Smith, MA (1959) Genes on the Y chromosome influencing rate of maturation in man. Skeletal age studies in children with Klinefelter’s (XXY) and Turner’s (XO) syndromes. Lancet 2:141-144.

reduced tooth size in 45,x (turner syndrome) females

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