Cephalometric analysis of the craniofacial region of the northern Foxe Basin Eskimo.код для вставкиСкачать
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. 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