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Canadian Eskimo permanent tooth emergence timing.

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Canadian Eskimo Permanent Tooth Emergence Timing
J . T. MAYHALL, P. L. BELIER AND M. F. MAYHALL
Faculty of Dentistry and Department of Anthropology, Uniuersity of Toronto,
Toronto, Ontario, Canada M5G 1G6
K E Y WORDS Inuit
eruption
Eskimos
-
Tooth emergence
.
Tooth
ABSTRACT
To identify the times of emergence of the permanent teeth of
Canadian Eskimos (Inuit), 368 children and adolescents were examined. The
presence or absence of all permanent teeth except the third molars was recorded and these data subjected to probit analysis. Female emergence times
were advanced over males. Generally, the Inuit of both sexes showed statistically significant earlier emergence times than Montreal children, except for the
incisors. The present results do not support hypotheses indicating that premature extraction of the deciduous teeth advances the emergence of their succedaneous counterparts. There is some indication the controls of deciduous
tooth emergence continue to play some part in emergence of the permanent
dentition, especially the first permanent teeth that emerge.
There is an increasing volume of reports on
the time of tooth emergence for human, primate and mammalian groups. These are
broadening our knowledge of the diversity in
the timing of the appearance of the teeth in
the oral cavity and are valuable in assisting in
the explanation of the diversity seen between
populations. We are presenting these data on
the time of permanent tooth emergence in Canadian Eskimos (Inuit) to contribute further
t o the knowledge of human diversity and t o
provide data that may be of assistance to the
clinician.
Only one comprehensive study of Eskimo
tooth emergence times (Boesen et al., '76) has
appeared t o our knowledge. This study was of
two Greenland Eskimo populations. Unfortunately, this study does not include the times
of emergence of some of the more important
teeth, central incisors and first molars. Because of the increasing availability of sophisticated dental care t o Inuit throughout the
world and their increasing awareness of, and
demand for, good dental services, the need for
such data is becoming more apparent.
Although there are various definitions of
the terms emergence and eruption, in this
paper time of emergence refers to the moment
any portion of the tooth crown pierces the gingiva and is visible in the oral cavity. This
makes it possible to accurately record the
AM. J. PHYS. ANTHROP. (1978)49: 211-216.
event. The term eruption refers to the movement of a tooth toward its final occlusal position. Thus, eruption includes movement within the maxilla before emergence, as well as
movement toward the final occlusal position
after emergence.
Thompson and his co-workers ('75) and
Sapoka and Demirjian ('71) have stated, as
have others, that tooth mineralization stages
are preferable to the ages of emergence in the
assessment of dental maturity because mineralization is affected much less by local environmental influences and is measurable over
a longer period of time. This is undoubtedly
true, but with isolated populations and lack of
a source of radiographs required for determining the mineralization stages one must use
readily identifiable clinical signs t o assess
maturity. Further, the clinical appearance of
the teeth and their relative position in the oral
cavity allows the observer to make quick,
accurate assessments of dental age.
Initially, we considered basing the time of
emergence on semi-longitudinal studies of the
yearly stone models of the Eskimo children in
the study, and, in fact, produced a previous
study using these data (Mayhall et al., '75).
However, the observations of the time of emergence were drastically limited by small sample sizes. It would have been impossible to
enlarge the samples without considerable
211
212
J. T. MAYHALL, P. L. BELIER A N D M. F. MAYHALL
error in the estimation of the age of emergence, and it would have required the inclusion of much larger numbers of individuals
than were available in the area. Now with the
use of sophisticated statistical techniques i t is
possible t o determine accurately the time of
emergence by being able t o include individuals without longitudinal records.
MATERIALS A N D METHODS
Two closely related communities in the
northern Foxe Basin area of the Northwest
Territories were chosen as the targets for a
multidisciplinary study of the adaptability of
Eskimos. Between 1968 and 1973 the settlements of Igloolik and Hall Beach were visited
yearly by teams of investigators which included dental, medical and anthropological
personnel. The records from the initial oral examination for each individual under 22 years
of age were studied to determine the status of
each tooth in the oral cavity. This was recorded as unerupted, partially erupted, fully
erupted and in occlusion, congenitally missing, or extracted. These categories could be
confirmed by reference to the stone models obtained at the time of examination and presently stored in Toronto. A total of 368 children
were examined at least once and are included
in this study. This represents approximately
95%of the total population in this age range
within the communities.
The subjects were classified into age categories a t the time of examination, and each
tooth was recorded as present or absent in the
oral cavity. The former category included any
manifestation of the crown apparent, while
the latter one excluded extracted and congenitally missing teeth. When all teeth had
been classified, the range of the age of
emergence was recorded with the upper and
lower limits for each tooth - that age group
by which the tooth had emerged in all subjects
and that in which it had not yet emerged in
any of the subjects. The categories between
the extremes were then ordered in six month
intervals and the analysis performed.
To arrive at the mean emergence time for a
tooth the probit analysis program of Dixon
(’73) was used. This procedure transforms the
proportion of teeth present at given ages into
probits and then uses these to derive a regression line. This line is then described arithmetically and, through a series of iterations,
the best slope is obtained. That becomes the
basis for determining the estimated mean age
of emergence and the estimated standard
deviation. Since the data are “normalized” the
estimated mean and the median are the same.
In addition, a maximum likelihood test is performed to determine whether the various age
samples are sufficiently homogeneous to be
accepted as randomly drawn from a population represented by the adjusted regression
line.
The use of probit analysis has been successfully applied to emergence data for Pima
Indians (Dahlberg and Menegaz-Bock, ’581,
French-Canadians (Perreault et al., ’741, and
Cree and Ojibway Indians (Mayhall et al.,
’77).We have chosen the data on the children
of Montreal as our reference population.
We are fully aware of the problems of comparing the results of the study population
with a “norm,” and we have chosen the
French-Canadian sample for the comparisons
because of the similarity of collection and
analysis techniques. Perreault and his coworkers (‘74, ’75) demonstrate that their results differ somewhat from those of other
North American studies. However, this in no
way negates the use of the Montreal children
as our comparative group as most populations
will show some variation, and we are using
them for illustrative purposes only. The important figures are those for the Eskimos
which may be compared with any other population in which similar analyses and data collection techniques were used.
RESULTS
The comparison of the times of emergence
in Eskimo males and females (table 1) shows
that females are advanced in their emergence
times except for those teeth emerging first:
the maxillary first molars, the mandibular
first molars, and the central incisors. These
teeth show no statistically significant difference between the sexes in their emergence
timing. Among the Inuit males the sequence
of the mean emergence times for the mandible
is: M,-1,-I,-C-Pm,-M,-Pm, while the maxillary sequence is: M1-I’-IZ-Pm‘-Pm2-C-M2.
The
sequences are the same for the females with
the exception of the reversal of the mandibular second molar and second premolar. Also, i t
can be seen that the pattern of the mandibular
canine appearing before the maxillary first
premolar generally found in females (Tanner
’62) is present in both sexes, although the difference in emergence times is quite small.
Tables 2 and 3 present the results of the
213
ESKIMO TOOTH EMERGENCE TIMING
TABLE I
Eskimo sex differences in tooth emergence (female mean age in years minus male mean1
-.
Maxilla
Tooth
Difference
11
- 0.50
-0.80
12
c
-1.09
-0.55
-0.87
-0.03
-0.70
h
l
Pm,
Mi
M2
Mandible
__
t-value
Significance
Difference
t-value
Significance
3.776
4.422
2
- 0.24
-0.34
1.391
2.083
N.S.
2
5.236
2.789
4.118
0.175
3.249
2
-0.62
- 1.35
- 1.02
+0.14
-0.33
3.269
5.021
4.789
0.829
1.591
2
2
2
N.S.
I
2
>
N.S.
N.S.
' Statistically significant
difference at 95 percent level of confidence.
Statistically significant difference at 99 percent level of confidence.
TABLE 2'
Age of emergence o f permanent teeth - males
French-Canadians '
Foxe Baain Eskimo
EskimoIFrench Canadian
N
Mean
S.D.
.v
Mean
S.D.
t-value
Significance
63
38
64
67
92
50
51
7.43
8.47
11.10
9.57
10.70
5.61
11.39
0.76
0.57
1.52
1.62
1.66
0.64
1.36
103
102
74
96
96
102
88
7.33
8.24
11.11
10.19
10.04
6.22
12.14
1.11
1.12
1.12
1.14
1.13
1.14
1.13
0.504
1.227
0.051
3.369
3.722
3.552
3.868
N.S.
42
60
67
112
67
63
71
6.32
7.20
9.52
10.32
11.38
5.40
10.78
0.67
0.85
1.27
1.84
2.46
0.87
1.43
102
103
96
96
96
102
88
6.27
7.42
10.45
11.08
11.61
6.22
11.72
1.11
1.11
1.11
1.15
1.16
1.15
1.11
0.275
1.342
5.388
4.251
4.828
5.010
5.265
N.S,
N.S.
N.S.
N.S.
I
2
2
'
2
2
2
2
2
' From: Perreault
et d..'74.
Statistically significant at the 99 percent level of nignificance.
analysis for the teeth of the left side and their
comparison with the emergence times for the
French-Canadian children. The Eskimo males
generally display younger ages of emergence
in the canines and posterior dentition, but
there are no statistically significant differences in the incisor timing. For the females
the comparisons between the Eskimo and
Montreal groups are essentially the same as
those for the males. Incisors show no statistically significant differences while the remainder of the dentition is advanced over the
French-Canadians. The comparison of the
right and left emergence times for the Eskimos revealed no statistically significant differences between the antimeres.
Table 4 is a comparison of the present results with those for two other native Ameri-
can groups. The Pima Indians of Arizona were
studied by Dahlberg and Menegaz-Bock ('581,
and we recently reported on the Indians of
northwestern Ontario of Cree and Ojibway
tribal affiliation (Mayhall et al., '77). Similar
techniques were used in all four studies and
the results should be comparable.
The maxillary canine of the male Cree-Ojibway emerges before that of the Eskimo: however, in all other maxillary comparisons, both
male and female, Pima and Cree-Ojibway, the
Inuit demonstrate an earlier mean age at
emergence. The differences tend to be greater
between the female groups than the males.
In the mandible, however, 8 of the 28 comparisons indicate earlier emergence among
the Indians. The greatest of these differences
is only 0.24 years. All occur in the first molar
214
J. T. MAYHALL, P. L. BELIER AND M. F. MAYHALL
TABLE 3
Age of emergence ofpermanent teeth
Foxe Basin Eskimo
Maxilla
I'
12
C
Pm'
Pm'
M'
M'
-
females
French-Canadians'
EakimdFrench-Canadians
N
Mean
S.D.
N
Mean
S.D.
t-value
Significance
75
86
62
1LOO
48
43
65
6.84
7.67
10.01
9.02
9.83
5.58
10.69
0.90
0.99
1.18
1.52
0.92
0.58
1.30
99
99
90
90
90
96
78
6.89
7.80
10.66
10.08
10.81
6.22
12.01
1.11
1.10
1.15
1.16
1.16
1.14
1.13
0.323
0.861
3.091
6.280
5.284
3.544
7.154
N.S.
N.S.
48
69
76
55
92
55
52
6.08
6.86
8.90
8.97
10.36
5.54
10.45
0.66
0.86
1.29
0.69
1.25
0.80
1.10
96
99
90
90
90
96
78
5.98
7.07
9.62
10.44
11.18
5.95
11.32
1.12
1.12
1.11
1.15
1.17
1.16
1.11
0.575
1.330
4.233
8.693
5.028
5.828
4.621
N.S.
N.S.
2
2
2
2
1
Mandible
1,
I2
c
Pml
Pm2
M,
M2
2
2
2
2
2
' From: Perreault
et el., '74.
Statistically significant at the 99 percent level of confidence
TABLE 4
Comparison ofmean ages ofemergence in North American natives
Females
Males
Tooth
Eskimo minus
Pimal
Eskimo minus
Cree-Ojibway '
Eskimo minus
Pima '
- 0.40
-0.27
- 0.56
- 0.51
- 0.63
- 0.37
- 0.28
-0.18
-0.11
0.23
-0.11
- 0.20
- 0.62
- 0.48
-0.63
-0.67
- 0.93
-0.61
- 0.90
- 0.22
-0.69
0.06
0.10
0.02
-0.84
-0.51
-0.05
0.15
- 0.93
- 0.07
- 0.45
- 1.26
-0.11
-0.01
0.01
-0.51
- 0.46
-0.76
- 0.90
- 0.37
0.11
-0.35
Eskimo minus
Cree-Ojibway
-0.57
- 0.56
- 0.66
- 0.64
- 0.23
- 0.30
- 1.21
0.24
-0.08
-0.56
- 1.33
- 0.33
0.05
- 1.19
' From: Dahlherg and Menegaz-Bock, '58
From: Mayhall et al., '77.
or incisor comparisons - the earliest teeth t o
emerge.
DISCUSSION
The advancement of emergence times of the
Eskimo females when compared with the
males follows the general trends noted by previous investigators (Clements et al., '53; Dahlberg and Menegaz-Bock, '58; Lee et al., '65;
Niswander and Sujaku, '60; Nanda, '60).Probably of more interest are those teeth that do
not show significant differences between the
sexes as seen in table 1. These include the
mandibular first molar and central incisor
that showed reversals in the Eskimohdian
comparison. While we have not yet investigated the emergence timing for deciduous
teeth, it has been pointed out previously (Tanner, '62) that deciduous teeth generally display no significant male/female differences.
As the females do show earlier ages for eruption, although not always statistically signifi-
ESKIMO TOOTH EMERGENCE TIMING
cant, in all of the other permanent teeth, perhaps these earliest emerging ones could be
considered to be in a transition period in
which factors controlling emergence of the
permanent teeth are replacing those that control the emergence of the deciduous teeth.
Several authors (Hellman, '43; Fulton and
Price, '54; Godeny, '52; Halikis, '62; Lee et al.,
'65) have divided the sequence of eruption or
emergence into two stages and noted that
there is a hiatus between them. Dental Stage I
includes first molars, central and lateral incisors; while Dental Stage I1 usually encompasses the premolars, canines and second
molars. The length of the hiatus between the
stages in the Eskimos is reduced in comparison with the Montreal children. The male
Eskimos show a hiatus between the stages of
1.10 years for the maxilla and 2.32 years for
the mandible, while the comparable figures
for the French-Canadians are 1.78 years and
3.00 years respectively. This reduction in the
hiatus for Eskimos has the effect of spreading
out the total time of active emergence of the
dentition and correlates with the general
growth trend among the Foxe Basin Inuit
(dePeiia, '71) of a smooth growth curve with
some leveling in the dramatic spurts.
Among the factors influencing tooth emergence timing some have considered climate to
be of some importance. However, conflicting
results are contained among the papers of
Friedlaender and Bailit ('601, Eveleth ('661,
Houpt and co-workers ('67) and Mayhall et al.
('77) casting doubt upon what, if any, influence outdoor temperatures have on emergence
times.
Numerous studies have explored the role of
nutrition andfor socio-economic factors on
emergence times. It seems fair to summarize
these studies by stating that there are no clear
relationships with socio-economic status per
se, and the effect of "better" nutrition afforded by the increase access to money may
depend upon the composition of the dietary.
The exact role of nutrition itself cannot be
assessed accurately in this study due to the
vast differences in the dietary of the Eskimo
and the southern Canadian white. The recent
Nutrition Canada Eskimo Survey report ('75)
that samples Eskimos from throughout the
Canadian Arctic concludes that the median
caloric intakes for children up to age eight
are generally higher t h a n recommended,
and there is no apparent protein deficiency.
Among adolescents, the boys had median
215
caloric intakes very close t o those recommended by the World Health Organization,
but the adolescent girls showed median intakes below the WHO levels. The teenagers of
both sexes had adequate to high levels of protein intake.
Investigations of emergence timing have
usually considered the effects of premature
extraction of the deciduous teeth on the eruption and emergence of their succedaneous
counterparts. There is lack of agreement on
the effects of the premature loss of these
teeth. Niswander and Sujaku ('64) studied the
effects of high caries rates in deciduous teeth
on the acceleration of the emergence of their
permanent successors and suggested that the
high rates could be a factor in determining
emergence timing. However, in the Eskimo
children the caries rates were low at the time
of the initial examination (Mayhall, '70, '75).
Butler ('62) felt that there was no consistent
relationship between early deciduous tooth
loss and the eruption of permanent teeth. Fanning ('62, '64) supported this conclusion in
detailed studies of the effects of premature deciduous tooth extractions on the emergence of
the permanent teeth.
A primary factor accounting for the divergence of the Eskimo tooth emergence timing
from that of other studies may be a hereditary
one. Boesen et al. ('76) found that "practically
unmixed' Greenland Eskimos showed no significant tooth emergence time differences
from those who had a long history of Danish
admixture. However, other studies of extant
populations (Steggerda and Hill, '28; Dahlberg and Menegaz-Bock, '58; Eveleth, '66;
Houpt et al., '67; Perreault et al., '74, '75;
Mayhall et al., '77) have suggested a genetic
origin of earlier or later timing.
ACKNOWLEDGMENTS
The authors wish to express their gratitude
to the Inuit of Hall Beach and Igloolik for
their interest, co-operation and encouragement in the dental studies. We would also like
to thank Doctor D. L. Anderson and Doctor
Frank Popovich for reading drafts of the
manuscript and providing helpful suggestions. This study was funded by the National
Research Council of Canada through a grant
to the Human Adaptability Study of Eskimos,
International Biological Programme.
LITERATURE CITED
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216
J. T. MAYHALL, P. L. BELIER AND M. F. MAYHALL
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