MATERIAL AND METHODS
The sample comprised the lateral cephalograms of 106 white and black untreated young Brazilian subjects presenting normal occlusion and well-balanced faces. The whole sample was obtained from the Growth Center at Bauru Dental School, University of São Paulo, and divided into two groups: Group 1 included 50 white subjects (25 of each gender) at a mean age of 13.17 years (standard deviation 1.07, range from 11.40 to 14.90), and group 2 included 56 black subjects (28 of each gender) at a mean age of 13.24 years (standard deviation 0.56, range from 12.08 to 14.33). All subjects presented all permanent teeth up to the second molars and normal occlusion, i.e., normal molar and canine relationship, absence of crowding and crossbites, normal overjet and overbite, wellbalanced face and without previous history of orthodontic treatment. Their data were collected some years ago when there were lighter restrictions on human studies.
The subjects of both ethnic groups were selected as pure as possible from the same geographic boundary, and the parents of each correspondent subject were from the same ethnic group. The Brazilian black subjects had their origin mainly from the African coast, where Bantu population is prevalent. Brazilian whites were Mediterranean descents.
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It is important to study the population characteristics and the origin of the Brazilian ethnic groups, analyzing the respective somatic traits. Other relevant factor is the historic mixture of innumerous populations and races in America, which hinders the biological definition of each group16. The miscegenation in Brazil among the Portuguese, the indigenes and black individuals resulted in the formation, since the early times of History, of a diversified population. Each one of the three basic groups is far from representing a pure ethnic group. By the geographic origin, one can have an idea of the racial affiliation of the imported individuals of the black group. In the African coast the Bantus are predominant, who were selected by the present sample, formed by the mixture of nigricians and paleonegroids, divided in occidental, oriental and meridional, with great or less influence. The Brazil stands as one of the few American countries that received African people of all origins. Three regions of Africa, the west, center-west and southeast coasts contributed with slave workers to Brazil until 185029.
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Regarding the cephalic index and stature, the following ethnic groups were distinguished in the Negroid group:
1. The Nigrician, with high percentage of tall and dolichocephalic individuals; concentrated in Sudan and Guinea;
2. The Paleonegroid, with high percentage of short and mesocephalic individuals; concentrated in the forest regions of Congo, Senegal and Angola;
3. The Nilotic, with really tall and dolichocephalic individuals; dispersed in regions of High Nilo and great lakes;
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4. The Khoisan, with high percentage of short and mesocephalic individuals; dispersed in South Africa, as well as the forest and desert regions.
The cephalometric tracings and landmark identifications were performed on acetate paper by a single investigator (LMAF) and digitized (Numonics AccuGrid XNT, model A30TL.F- Numonics Corporation, Montgomeryville, Pa). These data were then stored on a computer and analyzed with Dentofacial Planner 7.02 (Dentofacial Planner Software Inc., Toronto, Ontario, Canada), which corrected the magnification factor of the radiographic images (6% for both groups). Skeletal, dentoalveolar and soft tissue cephalometric measurements are shown in Figure 1 and less usual variables are shown in Figure 2.
The mean and standard deviation (SD) for the ages and for each variable were calculated for both groups. Normal distribution was verified by the Kolmogorov-Smirnov test. The results of the tests were non-significant for all variables. Therefore, intergroup comparisons were performed by independent t tests. All statistical analyses were performed on Statistica software (Statistica for Windows 6.0; Statsoft, Tulsa, Okla), with a level of significance of 5%.
After 1-month interval from the first measurement, thirty randomly selected cephalograms were retraced and re-measured by the same examiner (LMAF). Random errors were calculated according to Dahlberg’s formula10 (Se2= Σd2/2n) where Se2 is the error variance and d is the difference between the two determinations of the same variable, and the systematic errors were evaluated with dependent t tests19, for p<0.05.
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