Dentofacial and skeletal pattern in African descendants from southeastern Brazil: clinical prospective study

ABSTRACT Objective: The aim of this study was to evaluate characteristics of African-Brazilians young adults with excellent dental occlusion, including bimaxillary protrusion; compare them to European-American Caucasian standards, and determine whether there is sexual dimorphism in the display of this phenotype. Methods: Lateral cephalometric radiographs were obtained from 43 African-Brazilians within military personnel (28 males and 15 females, average age 22.4 ± 3.4 years) with normal occlusion, selected from a group of 394 volunteers. Thirty-one angular and linear measurements were evaluated. Student’s t-test for independent samples was used to compare results with those established by European-American standards, previously described in the literature. Results: Considering the dentoalveolar pattern, seven angular and six linear measurements showed statistically significant differences (p< 0.001) when compared to Caucasian cephalometric standards. African-Brazilians’ subjects showed lower cranial base angle (SNAr = 119.87 ± 5.66º) and anterior cranial base length (SN-distance = 68.63 ± 4.50 mm) (p< 0.001). The maxilla (SNA = 88.51 ± 3.23º) and the mandible (SNB = 85.06 ± 3.24º) were protruded in relation to the SN line (p< 0.001). Sexual dimorphism was significant for L1.NB (degrees) (p< 0.01), and interincisal angle (U1.L1) (p< 0.05). Conclusion: African-Brazilian young adults presented differences regarding dental and craniofacial characteristics, when compared to European-American norms. It can be stated that Caucasian cephalometric norms should not be applied to African-Brazilian faces.


INTRODUCTION
North American and European cephalometric standards are still widely used in orthodontic planning and extraction decision making, despite the ethnic and racial plurality found in contemporary society. However, cephalometric norms cannot be applied to all individuals due to certain racial characteristics and miscegenation, thus making it necessary to establish specific cephalometric patterns for different ethnic groups. 1,2 Several studies have described dentoalveolar variations in Asian, [3][4][5] Arabic, [6][7][8][9] African, [10][11][12][13][14][15] African-American [16][17][18][19][20] and African-Brazilian 21,22 populations. Thereby, the cephalometric norms for some ethnic groups should be regarded carefully. For instance, the American black population derives from the miscegenation of different races found in the United States, with those from different parts of Africa. 23  Oliveira TCP, Copello FM, Silva IMCC, Nojima LI, Nojima MCG -Dentofacial and skeletal pattern in African descendants from southeastern Brazil: clinical prospective study 5 The 2010 census conducted in Brazil revealed that blacks and browns make up the equivalent of 50.7% of the population.
However, the scientific literature is scarce in relation to the craniofacial morphology of Brazilian Afro-descendants, 22 and the few existing investigations describe only growing subjects.
The intense demand for orthodontic treatment by young adults raises the need to evaluate cephalometric pattern concerning individual's profile of this ethnic group, since some characteristics diagnosed by cephalometric radiographs are highly associated with this population, such as bimaxillary protrusion. 21,22 Bimaxillary protrusion can be described by the forward and proclined positioning of maxillary and mandibular incisors over the basal bone. This condition acts as an important motivating factor for orthodontic treatment, due to the negative esthetic impact of protruding lips and profile convexity. 1  Based on the rising demand for orthodontic treatment by adults and the lack of studies for this specific Brazilian ethnic group, the aims of this study were: (1) to evaluate in 2D images the dental and craniofacial characteristics of African-Brazilian young adults with excellent dental occlusion, including bimaxillary protrusion, and compare them to European-American Caucasian standards; and (2) determine whether there is sexual dimorphism in the display of this phenotype.

This prospective clinical study was approved by the Ethics in
Research Committee of the Institute for General Health Studies at the Federal University of Rio de Janeiro (IESC -UFRJ, statement nº. 66/2011). All subjects gave written informed consent and were aware of the procedures adopted in the present research. The required sample size was determined according to the power analysis at α = 0.05 significance level and 80% power (based on a 5.5º standard deviation and a 4.5º minimum clinically detectable U1.NA difference 24   A 5% level of significance was adopted.
Oliveira TCP, Copello FM, Silva IMCC, Nojima LI, Nojima MCG -Dentofacial and skeletal pattern in African descendants from southeastern Brazil: clinical prospective study

RESULTS
ICC analyses demonstrated excellent rates of reproducibility, with values > 0.9 for all variables.
Considering the dentoalveolar pattern, African-Brazilians presented statistically significant differences compared to Caucasian cephalometric standards (p < 0.001). The maxillary and mandibular incisors were significantly more proclined and protruded in African-Brazilians than in European-Americans, as was observed for linear and angular variables in Table 1. Thus, the interincisal angle was more acute (average = 117 ± 7.2º) compared to Steiner´s norm (U1.L1 = 131º). Bimaxillary protrusion was evidenced in African-Brazilians with excellent occlusion (Table 1). Regarding soft tissue profile, the proclination and protrusion of underlying dentoalveolar structures contributed to a significant decrease of the nasolabial angle (89.04 ± 9.33º) and to the projection of upper and lower lips beyond Rickett's esthetic plane (Table 1)   contributed to an even more acute interincisal angle, giving females a more characteristic aspect of bimaxillary protrusion    Regarding the maxilla and mandible, the African-Brazilians presented maxillary and mandibular bases significantly more protruded than the Caucasian standard ( Table 2). Similar results

DISCUSSION
were found in previous studies that evaluated other melanoderma populations. 12,13,15 High values for SNA and SNB are expected when the cranial base is significantly decreased. 5,6 The maxillary protrusion was confirmed with the A-Nperp distance, however, in a less expressive way, when it was compared to the SNA angle. On the other hand, the mandibular prognathism was not significant when considered Pog-Nperp variable.
Oliveira TCP, Copello FM, Silva IMCC, Nojima LI, Nojima MCG -Dentofacial and skeletal pattern in African descendants from southeastern Brazil: clinical prospective study 18 The present results showed highly significant differences between African-Brazilians and the European-American standards on all variables (linear and angular) (p < 0.001) related to the dentoalveolar pattern (Table 1)  The limitation found in this study was the possible magnification difference of the devices used to obtain the radiographic images between this research and the studies used as European standard.
However, these same standard studies are used in the orthodontist's routine. Besides that, it would be interesting to compare this African-Brazilian group to another African standards and with a control group of white southeastern Brazilians.

CONCLUSIONS
African-Brazilian young adults presented differences regarding dental and craniofacial characteristics when compared to European-American norms.
European-American cephalometric norms do not apply to these individuals and therefore should not be used as references to orthodontic treatment planning for this specific ethnic group, in which a bimaxillary protrusion is more acceptable than for the Caucasian population.
African-Brazilian women revealed larger lower incisor proclination and smaller interincisal angles compared to men. Overall responsibility:

MCGN.
The authors report no commercial, proprietary or financial interest in the products or companies described in this article.