AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 87:161-165 (1992)
Occlusion in1 47,XXY (Klinefelter Syndrome) Men LASS1 ALVESALO AND TELLERVO M I N E Department of Oral Development and orthodontics, Institute of Dentistry, University of Oulu, SF-90220 Oulu, Finland (L.A.1;Department of Orthodontics, Faculty of Dentistry, University of Kuopio, SF-70210 Kuopio,Finland IT.L.)
KEY WORDS Human, Sex chromosomes, Sex chromosome anomaly, Oral development, Cranio-facial growth ABSTRACT Occlusal morphology of permanent dentitions in 29 men with a 47,XXY chromosome complement (Klinefelter syndrome) was determined from dental casts. The results showed that a relatively frequent occlusal anomaly was mesial molar occlusion. Incisal open bite was also more common than in controls. Based on the present and previous observations of occlusal anomalies in various sex chromosome anomaly groups and normal controls, it is suggested that the presence of the Y chromosome in the genome is at least as important as the X chromosome for the development of harmonious occlusal morphology. The tendency towards sexual dimorphism in occlusal phenotype might result from a differential effect of the X and Y chromosomes on cellular activity which leads to different growth patterns. Previous studies on occlusal morphology in patients with sex chromosome aberrations have generally suggested deviation from normal variation. The results of our study in 45,X females (Turner’s syndrome) have shown that Lateral cross bite and distal molar occlusion were the most common occlusal anomalies .amongthem and that large maxillary overjet and a tendency t o open bite were also present (Laine et al., 1986). In a recent study (Harju e t al., 1989) occlusal morphology in women with a mosaic 45,Z 46,XX chromosome complement and in 46,XJXq) women with one normal X and a n isochromosome X (consisting of two long arms and no short arm) was evaluated. The most common type of malocclusion in both study groups was lateral cross bite. Also, distal molar occlusion, increased maxillary overjet and, in mosaics, open bite were found. In a n earlier study on occlusal morphology in Turner syndrome patients, Horowitz and Morishima (1974) reported twice the incidence of Class I1 division 1malocclusion, compared with the normal population. However, contrary to these findings in females with X chromosome anomalies, 47,XYY men seemed to have generally good occlusal morphology (Laine and Alvesalo, 19851, though they may show increased prevalence of mandibular overjet and incisal
@
1992 WILEY-LISS, INC.
open bite compared with control men. The sample size of fourteen 47,XYY individuals was small for the purpose, and therefore the results show tendencies at best. In the present paper occlusal morphology in a sample of 47,XXY (Klinefelter syndrome) men is reported. SUBJECTS AND METHODS The probands were twenty-nine Finnish men with a 47,XXY chromosome complement and the controls thirteen first-degree normal male relatives (fathers and brothers). Undergraduate male students (n = 126)were used as a population control group. A description of this group has been published earlier (Laine and Hausen, 1985).The diaffnoses of the patients were cytogenetically determined. Mean ages of the Klinefelter patients, male relatives, and population control men were 26.0,35.5, and 23.8 years, respectively (Table 1).The proportion of subjects with previous orthodontic treatment and loss of different types of permanent teeth varied to some extent between
Address reprint requests to Lassi Alvesalo, University of Oulu, Institute of Dentistry, Aapistie 3 , SF-90220 Oulu, Finland. Received December 6,1990; accepted July 12,1991.
L. ALVESALO AND T. M I N E
162
TABLE 1. Age Age (years)
of
the subjects
47,XXY males (n = 29)
Male relatives (n = 13)
Population control males (n = 126)
26.0 (10.7) 10-58
35.5 (16.0) 13-67
23.8 (3.0) 20-35
Mean (SD) Range
TABLE 2. Subjects with histories 47,XXY males
No treatment Previous treatment Orthodontic treatment Loss of one or more permanent first molars Loss of one or more permanent teeth anterior to the first molars Loss of one or more permanent teeth
of
dental treatment Male relatives (n)
%
(4
%
38
(11)
46
69
(20)
76
(22)
groups (Table 2 ) . None of the 47,XXY men or male relatives, and 5% of the population controls had undergone orthodontic treatment. Incidence of loss of one or more permanent teeth anterior to the first molars and loss of one or more permanent teeth was largest in Klinefelter patients. However, the number of lost teeth was usually only one or two. Occlusal anomalies of permanent dentitions were determined by the same examiner (TL) from hard stone casts using the method described by Bjork et al. (1964) with slight modifications; in contrast to their limit of 6 mm for extreme maxillary overjet and 5 mm for deep bite, 7 and 6 mm, respectively, were used. In Figures 1 and 2, occlusion of a 47,XXY patient is shown. Analyses of variance were used to compare the degree of overjet and overbite (mm). A logistic risk function was fitted to assess differences in proportions of subjects with different types of occlusal anomalies between the groups, with age, history of orthodontic treatment, and number of lost permanent teeth as possible confounding factors. RESULTS
The results in Table 3 show that the adjusted mean value of overjet was lower in 47,XXY men than in their male relatives and of similar magnitude as in population control males. Overbite was also smaller in Klinefelter patients than in relatives, but similar
Controls %
(nf
(6)
28
(35)
31
(4)
23
(29)
62
(8)
39
(49)
size t o the population controls. However, none of the differences reached statistical significance. Redistribution of different types of occlusal anomalies in the three study groups is presented in Table 4. It is apparent that a relatively common occlusal anomaly in 47,XXY males is mesial molar occlusion. Also, incisal open and deep bite were more common in 47,XXY males than in population controls (Table 4). The best fitted logistic regression model showed that the difference between 47,XXY men and the population controls was significant only for mesial molar occlusion, 47,XXY men being clearly more prone to have mesial molar occlusion than normal men. The effect of age was considered (Table 5). The relatives’ occlusal morphology was quite dissimilar from that of 47,XXY males (Table 4)in that distal molar occlusion occurred only in 10% of X X Y men, but in 62% of relatives, while only mesial molar occlusion occurred in 28% of X X Y males and no relatives. The logistic regression model (Table 6) showed that 47,XXY men had a somewhat higher risk of having mesial molar occlusion, but were less prone to have incisal open bite and especially distal molar occlusion than their relatives. DISCUSSION
In general, the present results indicate increased prevalence of occlusal anomalies
OCCLUSION IN 47,XXY MEN
163
Fig. 1. Anterior occlusal view of a 47,XXY man.
Fig. 2. Lateral occlusal view of a 47,XXY man (same as in Fig. 1).
in 47,XXY men compared with the normal population. The most frequent trait was mesial molar o c ~ l ~ ~ s i owhich n, was fourteen times as comm.on as in normal men. This finding can be considered in parallel with cephalometric clbservations by Ingerslev and Kreiborg (1978). According to them, Kline-
felter patients showed increased mandibular prognathism together with increased maxillary prognathism, which could be related to the altered shape of the cranial base rather than the altered size and position ofthe jaws. Also, Gorlin et al. (1965)have suggested that the loss or addition of a n X chromosome
164
L. ALVESALO AND T. M I N E
TABLE 3. Variation in overjet and overbite in 4 7 , X X Y males, first-degree relatives, and controls
Incisal occlusion Overjet (mm) adjusted' Mean (SE) Range Overbite (mm) adjusted' Mean (SE) Ranae
47,XXY males (n = 29)
Male relatives (n = 13)
Population control males (n = 126)
2.9 (0.5) -3 to 10
4.0 (0.6) 1 to 8
3.0 (0.2) 0 to 11
0.158
3.2 (0.5) -3 to 10
4.0 (0.6) 0 to 7
3.3 (0.2) -1 to 10
0.563
P'
'By analyses of covariance (history of orthodontic treatment a s cofactors, age and number of lost teeth a s covariates)
TABLE 4. Percent distribution o f different types of occlusal anomalies among 4 7 , X X Y males, first-degree relatiues. and controls Type of occlusal anomalv
47,XXY males (n = 29)
Male relatives (n = 13)
Population control males (n = 126)
10 28 10 10
62 0 23 0
11 2 7 3
21 17 0
39 8 0
11 4 3
14 7
0 8
16 6
Sagittal Distal molar occlusion Mesial molar occlusion Extreme maxillary overjet Mandibular overjet Vertical Deep bite Incisal open bite Lateral open bite Transversal Cross bite Scissors bite
TABLE 5. Relationship between occlusal anomalies (no = 0, yes = I ) , previous orthodontic treatment (no = 0, yes = 1) between 4 7 , X X Y men (group = 1) and population controls (group = 0) as estimates o f logistic regression model Variable Age (years) Mesial molar occlusion
Regression coefficient
S.E.
Regression coefficient/S.E.
0.04006 1.66671
0.01942 0.42584
2.06331 3.9 1396
TABLE 6. Relationship between occlusal anomalies (no = 0, yes = 1) among 4 7 , X X Y men (group = 1) and firstdegree male relatives (group =0) as estimates of logistic regression model Variable
Distal molar occlusion Mesial molar occ1usion Incisal open bite
Regression coefficient
S.E.
Regression coefficient/S.E.
-1.18354
0.43898
-2.69613
4.54196 -0.34646
influences mandibular and possibly maxillary prognathism. Thus, according to Gorlin et a]., Klinefelter patients should exhibit increased facial prognathism, whereas pa-
17.68090 0.67305
0.25689 -0.51476
tients with Turner's syndrome should exhibit facial retrognathism. Surveys of different types of occlusal anomalies in various sex-chromosome-
165
OCCLUSION IN 47,XXY MEN
anomaly groups, including 47,xxY men (this study), 45,Xwomen (Laine et al., 19861, and 47,XYY men (L(aineand Alvesalo, 19851, as well as in normal men and women (Laine and Hausen, 19851, indicate that, overall, the occlusal malrphology most deviant from that of normal males or females appears in 45,X females; 47,XXY males also show increased occurrence of malocclusion, whereas 47,XYY males have relatively low frequencies of occlusal anomalies. The prevalence of distal molar occlusion is clearly highest in 45,X females, where it is closer to that in normal women than men. Mesial molar occlusion is highest in 47,XXY men and closer to that in normal women than men. Lateral cross bite occurs most frequently (in about half of the cases) in 45,X females, rather less often in normal women and men, and least in 47,XXY and 47,.KYY men. Incisal open bite is a relatively common finding in all sex chromosome anomaly groups. The comparisons between normal males and females show that the frequencies of most of the occlusal anomalies differ between the sexes, although the differences are quite subtle. Certainly, sa:mple sizes of these patient groups, with thle exception of 45,X females, are quite small, especially in the case of XYY-males, and inspection, for example, of oral habits o r other locally acting mechanisms was not included in the study protocol. Despite these shortcomings of the available data, we suggest that the presence of the Y chromosome in the genome is at least as important as thLe X chromosome for the development of balanced occlusal morphology in sagittal, trainsverse, and vertical directions. From correlative studies of normal relatives, there is now increasing evidence for the presence of dental growth genes within the human sex chromosomes (Garn et al., 1965; Alvesalo, 1971). The X chromosome promotes enamel formation, but has little or no influence on growth of dentin, whereas the Y chromosome promotes growth of both enamel and dentin, in the latter case probably through cell proliferation. This appears to be the consequence of a relatively high mitotic potentiail in the presence of a Y chromosome. This potential may explain, for example, larger average tooth crown sizes in males than females and sex predilection for males in the number of supernumerary and ordinary teeth (Alvesalo and Tammisalo, 1981; Alvesalo, 1985; Alvesalo et al., 1985,
1987,1991). It is possible that gene(s) influencing dental growth might also control other events in the process of growth and development (Alvesalo, 1985). We suggest therefore that the tendency towards sexual dimorphism in occlusal phenotype might result from the differential effect of the X and Y chromosomes on cellular activity, which ultimately leads to different growth patterns a t various locations in the developing craniofacia1 complex. ACKNOWLEDGMENTS
This study was supported by the Academy of Finland. LITERATURE CITED Alvesalo L (1971) The influence of sex-chromosome genes on tooth size in man. Proc. Finn. Dent. Soc. 67:3-54. Alvesalo L (1985)Dental growth in 47,XYY males and in conditions with other sex-chromosome anomalies. In AA Sandberg (ed.):T h e y Chromosome, Part B: Clinical Aspects of the Y Chromosome Abnormalities. New York: Alan R. Liss, Inc., pp. 277-300. Alvesalo L, and Tammisalo E (1981)Enamel thickness in 45,X females’ permanent teeth. Am. J. Hum. Genet. 33r464469. Alvesalo L, Tammisalo E, and Hakola P (1985) Enamel thickness in 47,XYY males’ permanent teeth. Ann. Hum. Biol. 12:421-427. Alvesalo L, Tammisalo E, and Therman E (1987)47,XXX females, sex chromosomes, and tooth crown structure. Hum. Genet. 77:345-348. Alvesalo L, Tammisalo E, and Townsend G (19911 Upper central incisor and canine tooth crown size in 47,XXY males. J. Dent. Res. 70(73:1057-1060. Bjork A, Krebs A, and Solow B (1964) A method for epidemiological registration of malocclusion. Acta Odontol. Scand. 22:2741. Garn SM, Lewis AB, and Kerewsky RS (1965) X-linked inheritance of tooth size. J. Dent. Res. 44:439-441. Gorlin FLJ, RedmanRS, and Shapiro BL(1965)Effect ofX chromosome aneuploidy on jaw growth. J. Dent. Res. 44269-282. Harju M, Laine T, and Alvesalo L (1989) Occlusal anomalies in 45,X/46,XX - and 46,Xi (Xq) - women (Turner’s syndrome). Scand. J. Dent. Res. 97:387-391. Horowitz S, and Morishima A (1974) Palatal abnormalities in syndrome of gonadal dysgenesis and its variants and in Noonan’s syndrome. J. Oral Surg. 38:839844. Ingerslev CH, and Kreiborg S (1978) Craniofacial morphology in Klinefelter syndrome. A roenfgencephalometric investigation. Cleft Palate J. 15t100-108. Laine T, and Alvesalo L (1985) Occlusion in 47,XYY males. J. Dent. Res. 64:324 (abstract). Laine T, and Hausen H (1985) Occlusal anomalies in Finnish students related to age, sex, absent permanent teeth, and orthodontic treatment. Eur. J. Orthod. 5:125-13 1. Laine T, Alvesalo L, Savolainen A, and Lammi S (1986) Occlusal anomalies in Finnish 45,X females. J. Craniofac. Genet. Dev. Biol. 6:351-355.
Occlusion in1 47,XXY (Klinefelter Syndrome) Men LASS1 ALVESALO AND TELLERVO M I N E Department of Oral Development and orthodontics, Institute of Dentistry, University of Oulu, SF-90220 Oulu, Finland (L.A.1;Department of Orthodontics, Faculty of Dentistry, University of Kuopio, SF-70210 Kuopio,Finland IT.L.)
KEY WORDS Human, Sex chromosomes, Sex chromosome anomaly, Oral development, Cranio-facial growth ABSTRACT Occlusal morphology of permanent dentitions in 29 men with a 47,XXY chromosome complement (Klinefelter syndrome) was determined from dental casts. The results showed that a relatively frequent occlusal anomaly was mesial molar occlusion. Incisal open bite was also more common than in controls. Based on the present and previous observations of occlusal anomalies in various sex chromosome anomaly groups and normal controls, it is suggested that the presence of the Y chromosome in the genome is at least as important as the X chromosome for the development of harmonious occlusal morphology. The tendency towards sexual dimorphism in occlusal phenotype might result from a differential effect of the X and Y chromosomes on cellular activity which leads to different growth patterns. Previous studies on occlusal morphology in patients with sex chromosome aberrations have generally suggested deviation from normal variation. The results of our study in 45,X females (Turner’s syndrome) have shown that Lateral cross bite and distal molar occlusion were the most common occlusal anomalies .amongthem and that large maxillary overjet and a tendency t o open bite were also present (Laine et al., 1986). In a recent study (Harju e t al., 1989) occlusal morphology in women with a mosaic 45,Z 46,XX chromosome complement and in 46,XJXq) women with one normal X and a n isochromosome X (consisting of two long arms and no short arm) was evaluated. The most common type of malocclusion in both study groups was lateral cross bite. Also, distal molar occlusion, increased maxillary overjet and, in mosaics, open bite were found. In a n earlier study on occlusal morphology in Turner syndrome patients, Horowitz and Morishima (1974) reported twice the incidence of Class I1 division 1malocclusion, compared with the normal population. However, contrary to these findings in females with X chromosome anomalies, 47,XYY men seemed to have generally good occlusal morphology (Laine and Alvesalo, 19851, though they may show increased prevalence of mandibular overjet and incisal
@
1992 WILEY-LISS, INC.
open bite compared with control men. The sample size of fourteen 47,XYY individuals was small for the purpose, and therefore the results show tendencies at best. In the present paper occlusal morphology in a sample of 47,XXY (Klinefelter syndrome) men is reported. SUBJECTS AND METHODS The probands were twenty-nine Finnish men with a 47,XXY chromosome complement and the controls thirteen first-degree normal male relatives (fathers and brothers). Undergraduate male students (n = 126)were used as a population control group. A description of this group has been published earlier (Laine and Hausen, 1985).The diaffnoses of the patients were cytogenetically determined. Mean ages of the Klinefelter patients, male relatives, and population control men were 26.0,35.5, and 23.8 years, respectively (Table 1).The proportion of subjects with previous orthodontic treatment and loss of different types of permanent teeth varied to some extent between
Address reprint requests to Lassi Alvesalo, University of Oulu, Institute of Dentistry, Aapistie 3 , SF-90220 Oulu, Finland. Received December 6,1990; accepted July 12,1991.
L. ALVESALO AND T. M I N E
162
TABLE 1. Age Age (years)
of
the subjects
47,XXY males (n = 29)
Male relatives (n = 13)
Population control males (n = 126)
26.0 (10.7) 10-58
35.5 (16.0) 13-67
23.8 (3.0) 20-35
Mean (SD) Range
TABLE 2. Subjects with histories 47,XXY males
No treatment Previous treatment Orthodontic treatment Loss of one or more permanent first molars Loss of one or more permanent teeth anterior to the first molars Loss of one or more permanent teeth
of
dental treatment Male relatives (n)
%
(4
%
38
(11)
46
69
(20)
76
(22)
groups (Table 2 ) . None of the 47,XXY men or male relatives, and 5% of the population controls had undergone orthodontic treatment. Incidence of loss of one or more permanent teeth anterior to the first molars and loss of one or more permanent teeth was largest in Klinefelter patients. However, the number of lost teeth was usually only one or two. Occlusal anomalies of permanent dentitions were determined by the same examiner (TL) from hard stone casts using the method described by Bjork et al. (1964) with slight modifications; in contrast to their limit of 6 mm for extreme maxillary overjet and 5 mm for deep bite, 7 and 6 mm, respectively, were used. In Figures 1 and 2, occlusion of a 47,XXY patient is shown. Analyses of variance were used to compare the degree of overjet and overbite (mm). A logistic risk function was fitted to assess differences in proportions of subjects with different types of occlusal anomalies between the groups, with age, history of orthodontic treatment, and number of lost permanent teeth as possible confounding factors. RESULTS
The results in Table 3 show that the adjusted mean value of overjet was lower in 47,XXY men than in their male relatives and of similar magnitude as in population control males. Overbite was also smaller in Klinefelter patients than in relatives, but similar
Controls %
(nf
(6)
28
(35)
31
(4)
23
(29)
62
(8)
39
(49)
size t o the population controls. However, none of the differences reached statistical significance. Redistribution of different types of occlusal anomalies in the three study groups is presented in Table 4. It is apparent that a relatively common occlusal anomaly in 47,XXY males is mesial molar occlusion. Also, incisal open and deep bite were more common in 47,XXY males than in population controls (Table 4). The best fitted logistic regression model showed that the difference between 47,XXY men and the population controls was significant only for mesial molar occlusion, 47,XXY men being clearly more prone to have mesial molar occlusion than normal men. The effect of age was considered (Table 5). The relatives’ occlusal morphology was quite dissimilar from that of 47,XXY males (Table 4)in that distal molar occlusion occurred only in 10% of X X Y men, but in 62% of relatives, while only mesial molar occlusion occurred in 28% of X X Y males and no relatives. The logistic regression model (Table 6) showed that 47,XXY men had a somewhat higher risk of having mesial molar occlusion, but were less prone to have incisal open bite and especially distal molar occlusion than their relatives. DISCUSSION
In general, the present results indicate increased prevalence of occlusal anomalies
OCCLUSION IN 47,XXY MEN
163
Fig. 1. Anterior occlusal view of a 47,XXY man.
Fig. 2. Lateral occlusal view of a 47,XXY man (same as in Fig. 1).
in 47,XXY men compared with the normal population. The most frequent trait was mesial molar o c ~ l ~ ~ s i owhich n, was fourteen times as comm.on as in normal men. This finding can be considered in parallel with cephalometric clbservations by Ingerslev and Kreiborg (1978). According to them, Kline-
felter patients showed increased mandibular prognathism together with increased maxillary prognathism, which could be related to the altered shape of the cranial base rather than the altered size and position ofthe jaws. Also, Gorlin et al. (1965)have suggested that the loss or addition of a n X chromosome
164
L. ALVESALO AND T. M I N E
TABLE 3. Variation in overjet and overbite in 4 7 , X X Y males, first-degree relatives, and controls
Incisal occlusion Overjet (mm) adjusted' Mean (SE) Range Overbite (mm) adjusted' Mean (SE) Ranae
47,XXY males (n = 29)
Male relatives (n = 13)
Population control males (n = 126)
2.9 (0.5) -3 to 10
4.0 (0.6) 1 to 8
3.0 (0.2) 0 to 11
0.158
3.2 (0.5) -3 to 10
4.0 (0.6) 0 to 7
3.3 (0.2) -1 to 10
0.563
P'
'By analyses of covariance (history of orthodontic treatment a s cofactors, age and number of lost teeth a s covariates)
TABLE 4. Percent distribution o f different types of occlusal anomalies among 4 7 , X X Y males, first-degree relatiues. and controls Type of occlusal anomalv
47,XXY males (n = 29)
Male relatives (n = 13)
Population control males (n = 126)
10 28 10 10
62 0 23 0
11 2 7 3
21 17 0
39 8 0
11 4 3
14 7
0 8
16 6
Sagittal Distal molar occlusion Mesial molar occlusion Extreme maxillary overjet Mandibular overjet Vertical Deep bite Incisal open bite Lateral open bite Transversal Cross bite Scissors bite
TABLE 5. Relationship between occlusal anomalies (no = 0, yes = I ) , previous orthodontic treatment (no = 0, yes = 1) between 4 7 , X X Y men (group = 1) and population controls (group = 0) as estimates o f logistic regression model Variable Age (years) Mesial molar occlusion
Regression coefficient
S.E.
Regression coefficient/S.E.
0.04006 1.66671
0.01942 0.42584
2.06331 3.9 1396
TABLE 6. Relationship between occlusal anomalies (no = 0, yes = 1) among 4 7 , X X Y men (group = 1) and firstdegree male relatives (group =0) as estimates of logistic regression model Variable
Distal molar occlusion Mesial molar occ1usion Incisal open bite
Regression coefficient
S.E.
Regression coefficient/S.E.
-1.18354
0.43898
-2.69613
4.54196 -0.34646
influences mandibular and possibly maxillary prognathism. Thus, according to Gorlin et a]., Klinefelter patients should exhibit increased facial prognathism, whereas pa-
17.68090 0.67305
0.25689 -0.51476
tients with Turner's syndrome should exhibit facial retrognathism. Surveys of different types of occlusal anomalies in various sex-chromosome-
165
OCCLUSION IN 47,XXY MEN
anomaly groups, including 47,xxY men (this study), 45,Xwomen (Laine et al., 19861, and 47,XYY men (L(aineand Alvesalo, 19851, as well as in normal men and women (Laine and Hausen, 19851, indicate that, overall, the occlusal malrphology most deviant from that of normal males or females appears in 45,X females; 47,XXY males also show increased occurrence of malocclusion, whereas 47,XYY males have relatively low frequencies of occlusal anomalies. The prevalence of distal molar occlusion is clearly highest in 45,X females, where it is closer to that in normal women than men. Mesial molar occlusion is highest in 47,XXY men and closer to that in normal women than men. Lateral cross bite occurs most frequently (in about half of the cases) in 45,X females, rather less often in normal women and men, and least in 47,XXY and 47,.KYY men. Incisal open bite is a relatively common finding in all sex chromosome anomaly groups. The comparisons between normal males and females show that the frequencies of most of the occlusal anomalies differ between the sexes, although the differences are quite subtle. Certainly, sa:mple sizes of these patient groups, with thle exception of 45,X females, are quite small, especially in the case of XYY-males, and inspection, for example, of oral habits o r other locally acting mechanisms was not included in the study protocol. Despite these shortcomings of the available data, we suggest that the presence of the Y chromosome in the genome is at least as important as thLe X chromosome for the development of balanced occlusal morphology in sagittal, trainsverse, and vertical directions. From correlative studies of normal relatives, there is now increasing evidence for the presence of dental growth genes within the human sex chromosomes (Garn et al., 1965; Alvesalo, 1971). The X chromosome promotes enamel formation, but has little or no influence on growth of dentin, whereas the Y chromosome promotes growth of both enamel and dentin, in the latter case probably through cell proliferation. This appears to be the consequence of a relatively high mitotic potentiail in the presence of a Y chromosome. This potential may explain, for example, larger average tooth crown sizes in males than females and sex predilection for males in the number of supernumerary and ordinary teeth (Alvesalo and Tammisalo, 1981; Alvesalo, 1985; Alvesalo et al., 1985,
1987,1991). It is possible that gene(s) influencing dental growth might also control other events in the process of growth and development (Alvesalo, 1985). We suggest therefore that the tendency towards sexual dimorphism in occlusal phenotype might result from the differential effect of the X and Y chromosomes on cellular activity, which ultimately leads to different growth patterns a t various locations in the developing craniofacia1 complex. ACKNOWLEDGMENTS
This study was supported by the Academy of Finland. LITERATURE CITED Alvesalo L (1971) The influence of sex-chromosome genes on tooth size in man. Proc. Finn. Dent. Soc. 67:3-54. Alvesalo L (1985)Dental growth in 47,XYY males and in conditions with other sex-chromosome anomalies. In AA Sandberg (ed.):T h e y Chromosome, Part B: Clinical Aspects of the Y Chromosome Abnormalities. New York: Alan R. Liss, Inc., pp. 277-300. Alvesalo L, and Tammisalo E (1981)Enamel thickness in 45,X females’ permanent teeth. Am. J. Hum. Genet. 33r464469. Alvesalo L, Tammisalo E, and Hakola P (1985) Enamel thickness in 47,XYY males’ permanent teeth. Ann. Hum. Biol. 12:421-427. Alvesalo L, Tammisalo E, and Therman E (1987)47,XXX females, sex chromosomes, and tooth crown structure. Hum. Genet. 77:345-348. Alvesalo L, Tammisalo E, and Townsend G (19911 Upper central incisor and canine tooth crown size in 47,XXY males. J. Dent. Res. 70(73:1057-1060. Bjork A, Krebs A, and Solow B (1964) A method for epidemiological registration of malocclusion. Acta Odontol. Scand. 22:2741. Garn SM, Lewis AB, and Kerewsky RS (1965) X-linked inheritance of tooth size. J. Dent. Res. 44:439-441. Gorlin FLJ, RedmanRS, and Shapiro BL(1965)Effect ofX chromosome aneuploidy on jaw growth. J. Dent. Res. 44269-282. Harju M, Laine T, and Alvesalo L (1989) Occlusal anomalies in 45,X/46,XX - and 46,Xi (Xq) - women (Turner’s syndrome). Scand. J. Dent. Res. 97:387-391. Horowitz S, and Morishima A (1974) Palatal abnormalities in syndrome of gonadal dysgenesis and its variants and in Noonan’s syndrome. J. Oral Surg. 38:839844. Ingerslev CH, and Kreiborg S (1978) Craniofacial morphology in Klinefelter syndrome. A roenfgencephalometric investigation. Cleft Palate J. 15t100-108. Laine T, and Alvesalo L (1985) Occlusion in 47,XYY males. J. Dent. Res. 64:324 (abstract). Laine T, and Hausen H (1985) Occlusal anomalies in Finnish students related to age, sex, absent permanent teeth, and orthodontic treatment. Eur. J. Orthod. 5:125-13 1. Laine T, Alvesalo L, Savolainen A, and Lammi S (1986) Occlusal anomalies in Finnish 45,X females. J. Craniofac. Genet. Dev. Biol. 6:351-355.
