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Cephalometric analysis of the craniofacial region of the northern Foxe Basin Eskimo.

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Cephalometric Analysis of the Craniofacial Region of
the Northern Foxe Basin Eskimo
W. B. COLBY AND J. F. CLEALL
D e p a r t m e n t of O r t h o d o n t i c s , U n i v e r s i t y of M a n i t o b a , W i n n i p e g ,
Manitoba, Canada
KEY WORDS
Cephalometric Eskimo.
ABSTRACT
Past investigations of the Eskimo have indicated that there are
marked morphological differences in the craniofacial skeleton of this relatively
isolated ethnic group compared to other ethnic and racial groups. This study,
using cephalometric radiography, attempted to characterize the craniofacial
phenotype of the Eskimo living in the northern Foxe Basin, Northwest Territories, Canada. Age changes were examined on a cross-sectional basis with
comparisons being made with a Winnipeg Caucasian group.
This investigation indicates that the Igloolik Eskimo has a phenotype, established
early in life, and is distinct from the Winnipeg group. The overall size of the
Eskimo craniofacial complex was significantly larger at three years of age and
remained larger through the ages studied. Development of the craniofacial
region, however, was fairly similar i n rate and direction for both populations.
The greatest differences between the Eskimo and Caucasian groups were
found in the linear measurements assessing cranial width, facial width, mandibular length, facial height, protrusion of the incisors, chin point development,
and nasal morphology. Differences between the two groups in the morphological
relationships of the component structures include the angular relationships of
the maxilla and nasal bones to the anterior cranial base, the gonial angle of
the mandible, and the angle of facial convexity.
Anthropologists, interested in man's
physical characteristics and their differences among various ethnic groups, have
paid considerable attention to the craniofacial region. The technique of radiographic cephalometry is particularly applicable as it makes possible the examination
of the internal craniofacial structures of
viable populations.
The Arctic Eskimo has been the subject
of numerous anthropometric investigations. Laughlin ('66) describes the Eskimo
phenotype from a synthesis of previous
studies as medium in stature with short
extremities, with a large face, a straight
nasal profile, and a high frequency of
epicanthic folds. Other authors (Cameron,
'23; Oschinsky, '62; Hrdlieka, '28, '40;
Scott, '67) commented on the extremely
wide face and large mandible of these
people. Scott ('67) has demonstrated that
the Eskimo possesses one of the largest
mandibles known to modern man.
The purpose of the present study was
AM. J. PHYS. ANTHROP,40
159-170
to describe and cephalometrically characterize the craniofacial region of the northern Foxe Basin Eskimo. An attempt was
also made to describe growth (on a crosssectional basis) of the craniofacial complex of this relatively isolated group by
age and sex and to compare the morphology of the craniofacial complex of the
northern Foxe Basin Eskimo to that of a
Winnipeg Caucasian sample.
METHODS AND MATERIALS
The population studied was drrpwn from
the Eskimos living in the settlement of
Igloolik, Northwest Territories, Canada.
The sample consisted of 192 individuals
(108 males and 84 females) which ranged
in age from three years to 59 years. No
known craniofacial abnormalities were
included in the sample and, although all
the Igloolik subjects are termed Eskimos
and have been living as Eskimos, it is
probable that some of them have some
159
160
W. B. COLBY AND J. F. CLEALL
ancestral Caucasian gene admixture. To
facilitate studying the craniofacial growth
and development of this population, the
sample was divided by sex and subgrouped
into the following age ranges: 3-5, 6-9,
10-14, 15-21,22-29,30-59.
For comparative purposes a Caucasian
sample, matching the Eskimo population
in age and sex, was collected from the
Winnipeg, Manitoba, area. This sample
numbered 143 subjects (73 males and 70
females) and has been used as a “control”
sample for other studies and will be so
designated.
Lateral and posterior-anterior cephalometric radiographs were obtained for all
subjects using a technique similar to that
described by Broadbent (‘31). The remoteness of this Eskimo community necessitated using a portable cephalometer. The
anode-to-subject and subject-to-film dis-
tance varied somewhat between the portable cephalometer and the standard cephalometrix cephalometer in the Orthodontic
Department, University of Manitoba. As
a result, a different magnification factor
for each set of cephalograms was calculated (Adams, ’40) and later applied to the
coordinates of the landmarks selected for
study to allow direct comparisons of linear
measurements. The average correction
factor for the Eskimo and Caucasian
radiographs was 7% and 9% respectively.
Radiographs were taken by a team of two
operators.
Landmark identification was made on
a varying intensity illuminator; the coordinates for these landmarks were then
transferred directly to IBM computer
cards by a Ruscom Logics Limited strip
chart digitizer in a preselected order. The
landmarks and Teference planes used in
Y PLANE
0.
Prn
Li
Fig. 1 Landmarks and reference planes for the analysis of the lateral cephalometric
radiographs.
CRANIOFACIAL REGION OF ESKIMO
this study are illustrated in figures 1 and
2. All points and lines were identified according to accepted definitions and criteria (Salzmann, '66; Bjork, '47).
Calculation of all linear and angular
measurements was performed by computer
using the method of analysis described by
Cleall and Chebib ('71). Using this system,
all digitized coordinates of landmarks of
individual subjects were mathematically
superimposed on a common set of axes
which permitted computation and comparison of linear and angular variables.
Thirteen angular and 24 linear variables
were used to compare the craniofacial
complex of the two groups, these variables
(figs. 3-5) being obtained by synthesizing
the work of many authors (Krogman and
Sassouni, '57).
The pertinent cephalometric landmarks,
reference planes, and linear measurements
are shown in figures 1, 2, 3, 4, and 5 and
explained as follows:
1 . Lateral cephalogram.
0-Y plane Posterior point on cranium
to perpendicular to the sella-nasion line.
F-Y plane Frontale to Y plane.
S-Na Anterior cranial base. Sella to
Nasion.
Ba-S
Posterior cranial base. Sella to
Basion.
ANS-PNS Length of palate.
Rp-Pog
Corpus length from posterior
point on ramus to pogonion.
Tip of nasal bone to SN line.
Nt-SN
Measures the height of convexF-SN
ity of frontal bone in relation to the anterior cranial base.
ANS-SN
Height of maxilla from anterior nasal spine to SN.
Me-SN Anterior face height from
menton to SN.
Y PLANE
O i
S N PLANE
Baf
/
Rp\;
6;
Fig. 2
161
Linear variables used in the lateral cephalometric analysis.
162
W. B. COLBY AND J. F. CLEALL
Fig. 3
Angular variables used in the lateral cephalometric analysis.
PNS-SN Posterior height of maxilla
from posterior nasal spine to SN.
Bi-SN Posterior height of the face
from most inferior point on body of mandible between the antigonial notch and
gonion and SN.
Prn-NP Horizontal development of
the soft tissue nose (pronasale) in relation
to the facial plane (nasion to pogonion).
Ls-NP Labrale superius to facial
plane.
Li-NP Labrale inferious to facial
plane.
PS-NP Soft tissue pogonion to facial
plane.
Pog-MnP
Height ofpogonion to mandibular plane.
Pog-NB
Chin development. Pogonion
to mandibular apical base.
Is-NP
Tip of upper incisor to facial
plane.
Ii-Nt
Tip of lower incisor to facial
plane.
Na-Nt
Length of nasal bone.
2. Pos tero-anterior radiograph.
Tr-T1 Width of cranium.
Zr-Z1 Distance between zygomatic
processes.
Gr-G1 Width of mandible.
X point A geometrically constructed
point located at the intersection of the
supraorbital plane and a perpendicular
line erected to this plane and passing
through the midpoint of the root of crista
galli.
Statistical evaluation of the data consisted of calculation of the means, the
standard deviation and the standard error
of the means for each variable according
to group, sex, and age. The numerical
value of each variable for each subject
was recorded on computer cards and the
163
CRANIOFACIAL REGION OF ESKIMO
TABLE 1
Linear variables significant a t t h e 1 % level as revealed b y the analysis of variance
Group
Source of
variation
Between
groups
(Eskimo or
control)
Between
sexes
(male or
female)
Among
ages
(6 age
ranges)
1
1
5
Degrees of
freedom
X
Group
Group
Sex
sex
X
X
X
X
sex
age
age
age
1
5
5
5
Craniofacial width
TI-TI
Zr-Z1
Gr-G1
Cranial depth
F-Y plane
0-Y plane
Cranial base
S-Na
Ba-S
Facial height
F-SN
Me-SN
ANS-SN
Bi-SN
PNS-SN
Nasal complex
Na-Nt
Nt-SN
Maxillary complex
ANS-PNS
Mandible
RPPog
Pog-MnP
Bony profile
IS-NP
li-NP
POg-NB
Soft tissue profile
Prn-NP
LFNP
Li-NP
Ps-NP
-
* ,Significant at 1%level.
data for each variable analyzed independently as a three-factorial experiment with
uneven subgroups. The factors were
grouped at two levels (Eskimo and control),
sex at two levels (males and females), and
age at six levels (3-5, 6-9, 10-14, 15-21,
22-29 and 30-59). All main effects and
interactions were calculated and tested
for statistical significance. The mean
squares were adjusted for unequal subclass numbers by the harmonic mean
method suggested by Snedecor ('56). Main
effects and interactions showing a difference at the 1% level of confidence were
deemed a real or significant difference.
RESULTS
Of the 24 linear variables studied highly
significant differences were detected in
22 of the 24 variables when groups (Eskimo and control) were compared, in 17
variables when sexes (male and female)
were compared, and in 23 variables when
age (6 age ranges) was considered. Highly
significant group by sex interaction was
found in only one variable, while group
by age and sex by age interactions were
observed more frequently, occurring in
11 and 13 variables, respectively. The fiequency of significant interactions was reduced in the angular measurements. The
levels of significance €or the linear and
angular measurements are summarized.
in tables 1 and 2. Due to the general lack
of interaction between group by sex, i t
was deemed proper to pool males and fe-
164
W. B. COLBY AND J. F. CLEALL
TABLE 2
Angular variables significant a t the 1 % level a s revealed b y t h e analysis of variance
Group
Source of
variation
Between
groups
(Eskimo or
control)
Between
sexes
(male or
female)
Among
ages
(68ge
ranges)
Group
X
X
X
X
sex
age
age
age
1
1
5
1
5
5
5
Degrees of
freedom
X
Group
Sex
sex
Cranial base
BaSNa
Nasal complex
SNaNT
NaNt-NP
Maxillary complex
SNA
PP-SN
Mandible
SNB
SNPog
MnP-SN
ArRp-BiMe
Bony profile
NaA-AP
ANB
Li-MnP
Soft tissue profile
NSAS-ASPS
*, Significant a1 the 1%
level.
males of both groups in the presentation
of the data.
For presentation purposes, the variables
were grouped into the following areas or
morphological units: (1) craniofacial width;
(2) cranial depth; (3) cranial base; (4)
facial height; (5) nasal complex; (6) maxillary complex; (7) mandible; (8) bony
profile; and (9) soft tissue profile. Mean
measurements for each of the variables
are presented in tables 3 and 4, while developmental changes for each age group
are presented in polygon form in figure 4.
Craniofacial uiidth
Results of the measurements assessing
craniofacial widths confirm the frequently
reported immensity of the Eskimo craniofacial complex. Development of the width
measurements (Tr-TI, Zr-Z1, and Gr-G1)
followed a similar pattern in both groups.
When compared to the adults in their
respective groups, the three to five year
Eskimos exhibited 93.8 % completion of
the intertemporal dimension, 76.6% completion of the bizygomatic dimension, and
73.4% completion of the bigonial dimension. Similar proportions of total transverse
craniofacial growth noted in the Caucasian
sample have also been reported by other
investigators (Salzmann, '66; Meredith,
'60). Growth of the intertemporal dimension (Tr-Tl), as expected, was developmentally ahead of the other width dimen-
TR
~ i 4 ~ Measurements
.
made on the posteroanterior (PA) cephalometric radiographs.
165
CRANIOFACIAL REGION OF ESKIMO
TABLE 3
Eskimo and control groups m e a n s and standard error of t h e m e a n s in
millimeters for t h e 24 linear variables
Variable
Craniofacial width
TY-Tl
Zr-Z1
Gr-Gl
Cranial depth
F-Y plane
0-Y plane
Cranial base
S-Na
Ba-S
Facial height
F-SN
Me-SN
ANS-SN
Bi-SN
PNS-SN
Nasal complex
Na-Nt
Nt-SN
Maxillary complex
ANS-PNS
Mandible
RPPog
PoeMnP
Bon;profile
Is-NP
Ii-NP
Pog-NB
Soft tissue profile
Prn-NP
Ls-NP
Li-NP
PS-NP
Eskimo
SE
Control
SE
142.87
125.02
96.04
0.46
0.49
0.57
138.33
116.19
85.94
0.44
0.43
0.54
67.80
110.32
0.21
0.44
69.08
103.09
0.25
0.58
62.49
40.07
0.20
0.19
64.20
39.94
0.23
0.23
11.67
108.59
48.55
74.02
41.79
0.18
0.39
0.22
0.34
0.17
9.94
99.22
46.11
70.92
39.56
0.21
0.44
0.26
0.40
0.20
23.88
22.68
0.19
0.20
20.77
19.07
0.23
47.80
0.21
48.11
0.24
77.62
8.41
0.33
0.12
73.47
7.02
0.38
0.14
9.48
7.07
0.94
0.26
0.21
0.12
5.73
2.69
1.31
0.30
0.24
0.14
28.94
23.78
21.60
12.12
0.26
0.31
0.29
0.23
29.34
18.58
16.37
10.95
0.26
0.31
0.27
0.21
sions as calvarial growth closely parallels
neural growth.
Cranial d e p t h
Posterior cranial depth was larger in
the Eskimo group than in the control
group at all age levels while anterior cranial depth (fig. 2, F-Y plane) tended to be
slightly larger in the Caucasian group.
Cranial base
The anterior cranial base was shorter
while the posterior cranial base tended to
be larger in the Eskimo group than in the
Caucasian group. Cameron ('23) and Connolly ('28) have demonstrated longer anterior cranial bases in Caucasians than
in Negroes and Eskimos. Slight variations
were noted in the cranial base angle between the age ranges, but these differences were attributed to the cross-sectional
nature of the data.
0.21
Facial heights
All vertical measurements of facial
height were found to be greater in the
Eskimo group at all age ranges. This seems
to be in keeping with Cameron's ('23) description of the Central Eskimo skull as
dolichocephalic. The difference in total
anterior facial height appears to be due
primarily to greater differential development of the mandible.
Nasal c o m p l e x
Development of the nasal complex in
both populations was in accordance with
descriptions of normal nasal growth (Subtelny, '59; Posen, '64). However, the nasal
bones were found to be less prominent in
the profile at all age levels in the Eskimo
population. Previous anthropometric descriptions (Laughlin, '66; HrdliEka, '28)
have also noted this decreased prominence
in the nasal area of the Eskimo.
166
W. B. COLBY AND J. F. CLEALL
TABLE 4
Eskimo a n d control groups m e a n s a n d standard error of t h e m e a n s i n
degrees f o r t h e 1 3 angular variables
~
Variable
Cranial b a s e
BaSNa
Nasal complex
SNaNt
NaNt-NP
Maxillary complex
SNA
PP-SN
Mandible
SNB
SNPog
MnP-SN
ArRpBiMe
Bony profile
NaA-AP
ANB
L1-MnP
Soft tissue profile
NSAS-ASPS
~
~~
~
Eskimo
SE
Control
SE
133.86
0.37
132.77
0.44
106.48
144.47
0.45
0.44
111.82
139.02
0.51
0.50
83.25
8.23
0.27
0.24
81.67
7.71
0.31
0.27
78.78
78.23
39.72
127.61
0.26
0.26
0.40
0.51
78.12
78.84
33.28
125.66
0.30
0.31
0.46
0.57
10.07
4.42
89.28
0.42
0.19
0.56
5.83
3.49
94.14
0.49
0.22
0.61
17.36
0.57
16.41
0.49
Maxillary complex
The maxillary process translated in a
downward and forward direction with increasing age. While development was generally similar in the two populations, differences in the morphology of the area
were apparent. One of the more notable
differences was found in the anteroposterior position of the maxillary complex.
Angle SNA was significantly larger in the
Eskimo group at all ages and reflects the
maxillary prognathism which seems to
characterize this ethnic group. The depth
of the maxillary complex (ANS-PNS), in
keeping with the previously mentioned
anterior cranial depths, was smaller in
the Eskimo group.
than in the Caucasian population. In relation to the anterior facial plane (NP),
the maxillary and mandibular incisors
were positioned more anteriorly in the
Eskimo profile. An increase in the anterior
position of these teeth was demonstrated
at all age levels studied in the Eskimo
group (fig. 5). This contrasted with the
control group which exhibited the usual
Caucasian developmental pattern. In this
latter group, the incisors tended to become more upright and less prominent in
the profile with increasing age. The chin
point in the Eskimo group was observed
to be less prominent than in the Caucasian
group. At no point along the age continuum was the Eskimo chin point found to
protrude beyond the NB plane. DevelopMandible
ment of the chin, however, was similar
The results of this study showed that in both populations in that it tended to
in relation to the Caucasian control popu- become more prominent with age. Bony
lation the Eskimo mandible was larger convexity, when considered independent
and more robust in all linear measure- of the incisors, decreased with age as exments. Spacial orientation of the Eskimo pected in a normally developing craniomandible in relation to the anterior cra- facial complex.
nial base (angles SNB and SNPog), howSoft tissue profile
ever, was similar for both populations.
The contour of the soft tissues covering
Bony profile
the face in the Eskimo population generGreater convexity of the bony profile ally reflected the contours of the underwas observed in the Eskimo population lying bony and dental structures in both
ESKIMO
-
Fig. 5 Facial polygons of the Caucasian (control) and Eskimo groups showing the developmental
changes occurring i n the craniofacial complex at each of the six age ranges studied. Polygons are
oriented on the NS line and are registered at sella. Landmarks are designated only on the first (3-5
years) age range. Where lines are superimposed, only the Eskimo plot is shown.
........CONTROL
0
r
168
W. B. COLBY AND J. F. CLEALL
ing age, assuming as it develops a proportionately greater amount of the total craniofacial complex. With the exception of
some size and shape differences, the developmental pattern was found to be essentially the same as that previously described for Caucasians (Broadbent, '37).
Mean values were used to construct these
developmental patterns from cross-sectional data, and hence individual variations
in rate and direction of growth could
DISCUSSION
not be determined. The existence, howAll measurements of facial height and ever, of such variation between the indicraniofacial width were greater in the viduals of each population is recognized
Eskimo group as was posterior cranial and acknowledged.
The greater overall size of the Eskimo
depth. However, the measurements assessing anterior cranial and anterior cra- craniofacial complex was apparent in the
nial base depth were generally greater in earliest age ranges and in all probability
was present at birth. The Eskimo in the
the Caucasian group,
Development of the facial region of both 30-59 age range (fig. 6 ) showed a relathe Eskimo and control groups in the tively less prominent craniofacial complex
sagittal plane is illustrated in figures 5 with smaller dimensions of all facial depth
and 6. In both groups the face emerges measurements than the Eskimo 22-29
from beneath the cranium with increas- age range which may be representative
populations. The only notable exception
was found in the area immediately anterior to A point where greater thickening
of the soft tissue was observed. The effect
of this differential thickening was observed by comparing the bony angle of
convexity (NA-AP) and the soft tissue
angle of convexity (NSAS-ASPS) and noting the increased amount of soft tissue
convexity.
.-*-
........
-
3 - 5 YEARS
10-14YEARS
22-29 YEARS
30-59YEARS
Fig. 6 Composite developmental patterns of the Eskimo and Caucasian (control) groups at selected
age ranges illustrating the downward and forward development of the face. Polygons are oriented on
the NS line and registered at sella. Other landmarks are similar to those i n figure 5. Marked bimaxillary
protrusion of the dental area is evident throughout the Eskimo population. Lower craniofacial depth
measurements i n the Eskimo 30-59 age group suggests, perhaps, the possibility of a secular trend
occurring in this population.
CRANIOFACIAL REGION OF ESKIMO
of a secular trend within the population.
Only 28 individuals with equal sex distribution were available in each of these age
ranges and, therefore, while too much
weight should not be placed on this observation, it could reflect the changes in
diet and living conditions which accompany the transition of a nomadic hunting
society to a community centered society.
Several of the specific similarities and
differences between the Eskimo and Caucasian samples were of interest. It was
considered that the greater facial height
found in the Eskimo group was largely
due to greater differential development
of the mandible. The effect of this differential development was observed in the
ratio, upper facial height to total facial
height, where the ratio showed a tendency to decrease in the Eskimo population
indicating an increased prominence of the
lower face. This finding was inconsistent
with the findings of Broadbent (‘37), Salzmann (‘66), and Bjork (‘47) who report
that this ratio remains relatively stable
throughout life in Caucasian samples.
Development of the maxillary complex
in the northern Foxe Basin Eskimo was
similar to that reported by Scott (‘67),
Broadbent (‘37), Brodie (‘41), Salzmann
(‘66), and Bjork (’47) for normal Caucasian development of this area. The exception to this is in the relative prognathism
of the maxilla, a similar finding being
reported by Packard (‘70) in Alaskan
Eskimos.
The mandible was larger in the Eskimo
group. The mean measurements for the
anuglar measurements generally described
a moderately retrognathic mandible which
appears to be inconsistent with anthropometric descriptions (Oschinsky, ’62;
HrdliEka, ’28) of the Eskimo as “flatfaced.” Packard (‘70), however, in his
cephalometric study, showed a similarly
retrognathic mandible in Alaskan Eskimos.
Hrdlieka (‘28) maintains that the size
of the gonial angle characterizes different
ethnic groups. Caucasians are reported to
exhibit the larger gonial angle. They are
followed by the “yellow-browns’’including
the Eskimos. The mean measurement for
the Eskimo population studied was 1.94”
larger than the control sample which was
somewhat inconsistent with HrdliEka’s
findings. With increasing age, the gonial
169
angle was observed to become less obtuse.
This was attributed to a proportionately
greater increase in ramal height than in
mandibular corpus length. Similar reports
of change in the gonial angle have been
reported by Hellman (‘29) and Bjork (‘47).
CONCLUSIONS
The cephalometric investigation was
undertaken to describe the development
and phenotype of the northern Foxe Basin
Eskimo. Linear and angular measurements were used to evaluate and compare
the craniofacial development of this relatively isolated population with a Caucasian
sample. While, in general, development of
the craniofacial region was similar in both
groups, morphological differences were observed, the most notable being:
1. Nearly all linear measurements of
the craniofacial complex were larger in
the Eskimo population.
2. The greater overall size of the Eskimo craniofacial complex was established
before three years of age and in all probability was present at birth.
3 . While greater posterior cranial
depth was noted in the Eskimo sample,
linear measurements of anterior cranial
depth, the anterior cranial base, and midfacial depth were all smaller in the Eskimo population.
4. Mandibular corpus length was
greater in the Eskimo group, but the anteroposterior position of the chin in relation to the anterior cranial base was recessive.
5. The maxillary and mandibular incisors were significantly more procumbent
in the Eskimo group, and together with
the anteriorly positioned maxilla produced
a marked bimaxillary protrusion.
ACKNOWLEDGMENTS
This investigation was supported by
grant MA-3541 from the Medical Research
Council of Canada.
The authors wish to acknowledge the
International Biological Programme-Human Adaptabilities, Canadian Committee
and its medical-dental field team composed of Dr. J. Hildes, M.D.; Dr. J. Mayhall, D.D.S.; Dr. C. Kennedy, D.D.S.; Dr.
0. Schaeffer, M.D.; and Mr. S. Harris,
R.T. for the collection and the use of the
Eskimo radiographs .
170
W. B. COLBY AND J. F. CLEALL
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