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Crown size and hypodontia in the permanent dentition of modern Skolt Lapps.

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Crown Size and Hypodontia in the Permanent Dentition of
Modern Skolt Lapps
PENTI KIRVESKARI.' HASSE HANSSON.2 BJORN HEDEGARD *
AND ULF KARLSSON 2
' Institute of Dentistry, Uncverscty of Turku, SF 20520 Turko 52, Finland
and Odontoloaiska Klcnzken, University of Gothenburg, S 400 33
Gothenburg 33, Sweden
K E Y WORDS Odontometrics
Lapps
. Hypodontia
Secular changes
ABSTRACT
The teeth of modern Skolt Lapps from northern Finland are considerably larger than those of their ancestors of the Eighteenth Century. The increase is probably attributable to improved nutrition. One or more teeth, excluding the third molars, were congenitally missing in 18.8%of the population aged 5
to 20 years. Relative to a standard the anterior teeth are larger than the posterior
teeth, particularly the premolars. This accords well with the hypodontia pattern
which is dominated by premolar agenesis.
Skolt Lapps are one of the several Lapp
tribes living in northern Scandinavia and
Kola Peninsula (fig. 1). Part of them used to
live in the Petsamo area which belonged to
Finland before World War 11. When Petsamo
was ceded to the Soviet Union, Skolt Lapps of
that area moved to their present settlements
in Finland, Sevettijarvi and Nellim.
The origin of the Lapps is not fully known.
They are believed to be Caucasoids (Coon, '62:
pp. 65-68), and recent studies of their genetic
traits (Eriksson, '73; Steinberg e t al., '74) and
dental morphology (Zubov, '72; Kirveskari,
'74) bear this out, although the Lapps also
show some traits that are common in Mongoloid populations. Skolt Lapps have been isolated from other Lapp tribes until very recent
times, chiefly by geography and religion (Lewin, '71a). Marriages between second cousins
are common. The minimum inbreeding coefficient for the whole population is 0.0045,
calculated from a genealogical chart extending back three t o five generations (Vollenbruck e t al., '74).
Smallness of the teeth is one of the usual
characteristics mentioned in anthropological
texts on the Lapps. The odontometrics of the
Lapps was studied from skulls of the Eighteenth Century (Kajava, '12; Selmer-Olsen,
'49). We collected odontological data and maAM. J. PHYS. ANTHROP. (1978)48: 107-112.
terials on modern Skolt Lapps in connection
with the IBP/Human Adaptability studies in
Finnish Lapland in 1967-1970.
Concomitant with the ongoing cultural
change, the Lapps show a secular increase
of stature and craniofacial dimensions (Lewin
et al., '73). We were interested in possible
changes in tooth dimensions. We also studied
the occurrence of agenesis of different teeth t o
see whether the pattern of morphological reduction and hypodontia were similar.
MATERIALS AND METHODS
The total number of Skolt Lapps living in
Finland was 515 in 1967, according to the population census. We aimed a t examining all of
them, and succeeded in well over 90%.A few
persons had moved from the area, and some
were unable or unwilling to attend the examinations. The organization and the scope of the
studies, as well as the demography of the Skolt
Lapp population have been reported in detail
(Lewin and Hedegard, '71; Lewin et al., '71).
W:: prepared dental hard stone casts in the
field from alginate impressions according t o
manufacturer's instructions. All Skolt Lapps
were included in the odontometric part of the
study provided that at least one tooth dimension was measurable from the cast. All measurements were taken by the same worker
107
108
P. KIRVESKARI, H. HANSSON, 11.
.
HEDEGARD
AND
u.
KARLSSON
traoral radiographs, dental records and casts
from earlier examinations usually confirmed
the diagnosis. We made the diagnosis of a
tooth agenesis without documentation from
earlier years in four instances in which there
was no reason for doubt. Because of the high
rate of extractions we limited the hypodontia
study to persons 5 to 20 years of age (66boys
and 62 girls). We further limited the study of
third molar agenesis to persons 1 2 to 20 years
of age (40 boys and 32 girls).
U
S
S
R
RESULTS
/
\
- -
Fig. 1 Map of northern Scandinavia. S, Sevettijarvi;
NE, Nellim; N, Neiden; and P, Pasvik.
with a sliding calliper with sharpened beaks,
and the readings were rounded off to the
nearest 0.05 mm. Moorrees' ('57: pp. 78-80)
definitions of the mesiodistal and buccolingual diameters were adhered to. Only morphologically normal, fully erupted permanent
teeth were measured. Teeth with carious
lesions, dental calculus, bacterial plaque accumulations, or fillings were rejected, unless the
measurement could be taken between intact
surfaces. Only the right side of the dental arch
was used; in cases of missing teeth, the antimeres were measured whenever possible.
Selmer-Olsen's ('49) material included subpopulations also from old Skolt Lapp territories, Neiden and Pasvik (fig. 1). We can conclude from the known history of modern Finnish Skolt Lapps (Lewin, '71a) that part of
their ancestors came from Neiden-Pasvik
area. We therefore assume some genetic continuity between the populations, and compare
Skolt Lapp tooth sizes to those of the combined Neiden-Pasvik skeletal population instead of the whole Norwegian Lapp material.
We based the diagnosis of a tooth agenesis
on orthopantomograms taken in 1970. In-
The mesiodistal (table 1) and buccolingual
(table 2) crown diameters of modern Skolt
Lapps were consistently larger than the corresponding measurements in the skeletal
Neiden-Pasvik population. The difference was
larger than that between the sexes, except in
the mandibular canines and the MD diameter
of the mandibular central incisor.
The sexual dimorphism of the MD diameter
reached statistical significance a t the 5% level
in all teeth except third molars and upper premolars. The BL diameters differed even more;
only the lower third molars failed to show significant dimorphism.
The coefficients of variation varied according to the field concept (Dahlberg, '45)in the
molars. In the maxillary premolars the MD diameter varied a little more in P1 than in P2,
in other respects the premolar variability followed the field concept. The incisor variability
showed the well-known exception, the lower
central incisors varying more than the lateral
ones, but only with respect to the BL diameter.
Excluding the third molars, we found hypodontia in 18.8%of the Skolt Lapps (table 3).
Agenesis of one tooth occurred in 7 persons
(29x1, of two teeth in 10 persons (42%), of
three teeth in 3 persons (13%),and of four
teeth in 4 persons (17%). The agenesis was
unilateral in 12 (38%)and symmetric bilateral
in 20 (63%)cases. Most of the missing teeth
were second premolars (table 4).
Third molar agenesis occurred in 19%(table
5). None of the persons with third molar
agenesis showed agenesis of other teeth, and
none of the persons with agenesis of any tooth
showed peg-shaped upper lateral incisors.
DISCUSSION
Skolt Lapps have become considerably taller, and their craniofacial dimensions have in-
109
LAPP TOOTH SIZE A N D HYPODONTIA
TABLE 1
Mesiodistal diameter (in mm) of the permanent teeth in modern Skolt Lapps
Skolt Lapps
Neidan-Panvik Lapps
Tooth
d
P
'3 +P
s
P
dSP
d
P
d +4
d
P
d +Y
d
P
d +P
d
9
d +Y
d
9
d +P
d
P
d +P
d
P
d +P
6
P
d +P
d
P
d +P
d
P
d +P
d
P
d +P
d
P
d +P
d
0
d +P
d
0
d +P
N
Mean
S.D.
C.V.
19
17
36
74
48
122
78
80
158
87
85
172
99
94
193
99
91
190
104
92
196
117
98
215
17
13
30
66
60
126
57
61
118
112
97
209
127
111
238
144
129
273
140
133
273
129
119
248
8.76
8.76
8.76
9.87
9.58
9.75
10.53
10.16
10.34
6.64
6.55
6.60
6.95
6.89
6.92
7.88
7.59
7.74
6.88
6.64
6.77
8.79
8.54
8.67
10.53
10.31
10.43
10.85
10.56
10.71
11.26
10.95
11.10
7.01
6.88
6.95
6.97
6.87
6.92
7.04
6.63
6.85
6.07
5.88
5.98
5.50
5.37
5.44
0.84
0.70
0.77
0.58
0.55
0.58
0.54
0.57
0.58
0.40
0.38
0.39
0.38
0.48
0.43
0.45
0.45
0.47
0.57
0.60
0.59
0.58
0.60
0.60
1.23
0.83
1.06
0.63
0.72
0.69
0.55
0.66
0.63
0.35
0.45
0.41
0.38
0.40
0.39
0.36
0.34
0.41
0.33
0.37
0.37
0.32
0.34
0.33
9.59
7.99
8.79
5.88
5.74
5.95
5.13
5.61
5.61
6.02
5.80
5.91
5.47
6.97
6.21
5.71
5.93
6.07
8.28
9.04
8.71
6.60
7.03
6.92
11.68
8.05
10.16
5.81
6.82
6.44
4.88
6.03
5.68
4.99
6.54
5.90
5.45
5.82
5.64
5.11
5.13
5.99
5.44
6.29
6.19
5.82
6.33
6.07
t-value
0.00
2.72
4.21
1.49
1.08
4.39
2.86 '
3.04
0.55
2.36
'
2.77
'
2.34
'
2.13
'
9.67
4.47
3.09
N
Mean
58
47
105
65
65
130
55
60
115
61
58
119
55
62
117
51
53
104
17
36
53
19
28
41
42
43
85
57
56
113
49
51
100
54
49
103
55
59
114
55
58
113
31
41
72
13
16
29
7.78
7.67
7.73
9.12
8.78
8.95
10.06
9.76
9.90
6.24
6.10
6.17
6.52
6.41
6.46
7.53
7.32
7.42
6.51
6.58
6.56
8.31
8.26
8.28
9.77
9.47
9.62
10.40
9.82
10.11
10.85
10.53
10.69
6.64
6.45
6.55
6.62
6.47
6.54
6.70
6.35
6.52
5.84
5.80
5.82
5.47
5.14
5.29
In addition to the mean and standard deviation, coefficient of variation and Student's t-test value indicating eexual dimorphism
are given. Weighted means of the corresponding measurementn in skeletal Neiden and Pasvik subpopulationn (Selmer-Olsen,'49)
are given for cornpariaon.
0.05>P>0.01.
0.013FP> 0.001.
0.0011P.
'
110
P. KIRVESKARI, H. HANSSON, B. HEDEGARD AND U. KARLSSON
TABLE 2
Buccolingual diameter (zn mmi of the permanent teeth in modern Skolt Lapps
Skolt Lapps
Neiden-Pasvik Lapps
Tooth
d
E
d +E
3
E
d +E
s
0
dtP
3
E
d +P
d
?
d +P
d
P
d +P
d
P
d +?
d
P
d +P
d
9
d +E
d
P
d +P
d
P
d +P
d
P
d +P
d
Y
d +P
d
E
d +?
d
0
d t?
d
P
d +E
N
Mean
S D.
C.V.
18
13
31
80
51
131
88
83
171
96
89
185
99
91
190
82
74
156
75
60
135
89
79
168
17
13
30
68
57
125
61
63
124
105
93
198
111
97
208
111
106
217
96
100
196
99
102
201
10.81
10.08
10.50
11.66
11.23
11.49
11.73
11.29
11.52
9.11
8.89
9.01
9.30
9.05
9.18
8.46
7.97
8.23
6.57
6.36
6.48
7.44
7.09
7.28
10.26
10.09
10.19
10.62
10.35
10.50
10.94
10.68
10.81
8.10
7.88
8.00
7.61
7.42
7.52
7.96
7.36
7.67
6.55
6.32
6.43
6.18
5.88
6.03
0.92
0.88
0.96
0.63
0.66
0.67
0.52
0.58
0.59
0.51
0.65
0.59
0.49
0.60
0.56
0.47
0.50
0.54
0.49
0.50
0.51
0.43
0.44
0.47
0.49
0.67
0.58
0.54
0.56
0.56
0.47
0.50
0.50
0.53
0.66
0.60
0.43
0.50
0.47
0.39
0.42
0.51
0.38
0.39
0.40
0.37
0.39
0.41
8.51
8.73
9.14
5.40
5.88
5.83
4.43
5.14
5.12
5.60
7.31
6.55
5.27
6.63
6.10
5.56
6.27
6.56
7.46
7.86
7.87
5.78
6.21
6.46
4.78
6.64
5.69
5.08
5.41
5.33
4.30
4.68
4.63
6.54
8.38
7.50
5.65
6.74
6.25
4.90
5.71
6.65
5.80
6.17
6.22
5.99
6.63
6.80
t-value
2.23 '
3.78
5.29
2.61 '
3.09
'
6.38
2.51 I
5.23
0.82
N
Mean
54
49
103
63
60
123
55
67
122
44
57
101
45
55
100
45
47
92
23
43
66
32
43
75
36
46
82
9.66
9.14
9.41
10.86
10.14
10.51
11.08
10.57
10.80
8.62
8.36
8.47
8.72
8.58
8.64
7.91
7.42
7.66
6.19
5.87
5.98
6.90
6.57
6.71
9.32
9.19
9.23
9.99
9.50
9.74
10.26
9.95
10.10
7.56
7.45
7.50
7.30
7.06
7.17
7.44
6.79
7.09
6.14
5.89
6.00
5.81
5.45
5.59
64
2.84
3.04
2.52 '
2.97
10.92
4.18
5.49
'
66
130
58
62
120
50
62
112
57
68
125
56
66
122
37
46
83
32
51
83
In addition to the mean and standard deviation, coefficient of variation and Student's t ~ t e s value
t
indicating sexual dimorphiam
are given. Weighted means of the corresponding measurements in skeletal Neiden and Pasvik subpopulations (Selmer-Olsen, '49)
are given for comparison
' 0.05>P>0.01.
2 0.01>P>0.001.
3 O.OOl>P.
LAPP TOOTH SIZE AND HYPODONTIA
TABLE 3
Occurrence of hypodontia in the permanent dentition of
Skolt Lapps (aged 5-20, third molars excluded)
Hypodontia
d
Y
d +P
N
n
(%I
66
62
128
8
16
24
(12.1)
(25.8)
(18.8)
TABLE 4
Occurrence of hypodontia in the permanent dentition of
Skolt Lapps by type oftooth (third molars excluded)
Lower P2
Upper P2
Upper I2
Upper C
Lower I1
Total
8
2
2
2
1
15
0
3 +Q
16
15
2
2
2
37
24
17
4
(46.2)
(32.7)
(7.7)
4
17.R
3
52
(5.8)
(100.0)
(91)
TABLE 5
Occurrence of third molar agenesis in
Skolt Lapps (aged 12-20)
Nurnher of
missing M3
d
P
0
1
2
3
4
1-4
33
1
2
2
2
7
25
2
3
1
1
7
d +?
58
3
5
3
3
14 (19%)
creased during the last few decades. The
changes are attributed solely to the improved
socio-economic conditions (Lewin e t al., '73).
Because of the early loss of teeth due to caries,
we could not compare tooth sizes between age
groups, and find out whether the increase in
tooth sizes also occurred during the last decades. Secular increase in tooth size has been
observed in Sweden during the last 160 years
(Ebeling et al., '73). Modern British molars are
larger than Anglo-Saxon molars from the
Sixth to Eighth Century, while all other teeth
show decrease of the size (Lavelle, '68). Garn
et al. ('68b) demonstrate a secular increase of
tooth size over two consecutive generations.
In comparison with these, the increase of
Skolt Lapp tooth size is remarkably large. Yet
the crown size profile pattern (cf. Garn et al.,
'68c) has remained virtually the same, in-
111
dicating a uniform increase in the whole dentition (Kirveskari, '77).
We think the improved socio-economic conditions are a plausible explanation of the
increase of tooth size. Admixture can be
ruled out on the basis of the known history of
Skolt Lapps during the last centuries (Lewin,
'71a,b), and selection for larger teeth seems
unlikely (cf. Dahlberg, '63). Theoretically,
random drift, a n increased susceptibility to
environmental variation resulting from increased homozygosity (cf. Bailit, '66; Niswander and Chung, '65), and pleiotropic effects of some unidentified selectively important traits are possible additional explanatory
factors.
The magnitude of sexual dimorphism of the
Lapp tooth size is clearly less than, for instance, in Ohio Caucasians (Garn et al., '66b),
and it seems unchanged. Contrary to the findings of Garn et al. ('66b), the rank order correlation between MD and BL size dimorphism
of the different teeth was high (0.82 when
ranked by t-values). The "field" of size dimorphism surrounding the mandibular canine
(Garn et al., '66a, '68a) did not seem to exist in
Skolt Lapps.
The sex difference in the tooth size variability, the females varying more than the
males, was conspicuous in Skolt Lapps, and in
accordance with the findings of Garn et al.
('68a).
Hypodontia is remarkably common in Skolt
Lapps, 18.8%excluding the third molars. By
comparison, hypodontia occurs in Finns in
7.97% (Haavikko, '711, in Swedes in 6.1%
(Grahnen, '561, and in Norwegians in 10.1%
(Hunstadbraten, '73). When the relative tooth
sizes of Skolt Lapps are compared with a
Caucasian reference population (Garn et al.,
'68c), the premolars of Skolt Lapps are considerably smaller but the incisors equally
large or larger than those of the reference population (Kirveskari, '77). This accords well
with the hypodontia pattern in which the
agenesis of premolars dominates. Agenesis of
the teeth and crown size are known to be associated features (Garn and Lewis, '69, '70). The
hypodontia pattern of Skolt Lapps is also in
good agreement with the crown morphology:
molars show considerable reduction while anterior teeth do not (Kirveskari, '74).
According to Garn et al. ('621, the probability of other teeth missing in third molar
hypodontia is increased 13-fold. We can offer
112
P. KIRVESKARI, H. HANSSON, B. HEDEGARD AND
no explanation why none of the Skolt Lapps
with third molar agenesis showed agenesis of
any other teeth. Even if there were no association between the two, the probability of the
totally separate occurrence is rather low.
The teeth of Skolt Lapps, and probably of
other Lapp populations, are no longer exceptionally small. However, their tooth morphology, relative tooth sizes, and pattern of hypodontia are suggestive of advanced structural
reduction of the posterior part of the dentition. Perzigian ('75) demonstrated both stabilizing and directional selection in the protohistoric Arikara Indian dentition. We have
no hard data to support the view that a n unreduced, strong anterior dentition would have
been a selective advantage in the Lapps. However, a generation or two ago the Lapps still
used their anterior teeth as all-purpose tools,
often wearing them down to the gum. The anterior teeth were undoubtedly more important
than the posterior teeth.
ACKNOWLEDGMENTS
We wish to express our gratitude to Doctor
Thord Lewin who made available the results
of his extensive study of Skolt Lapp genealogies, and to the Finnish Dental Society,
Swedish Medical Council (Project B 7 0 12X2902-01), and Scandia Concernen for financial support.
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