McNamara analysis cephalometric parameters in White-Brazilians, Japanese and Japanese-Brazilians with normal occlusion

ABSTRACT Introduction: McNamara’s Jr. cephalometric analysis is a tool to diagnose dental and skeletal discrepancies and is widely used, guiding diagnosis for surgical procedures to be performed or for the use of functional devices. Few studies have shown that different ethnic groups have different cephalometric patterns. Thus, single characteristics should be respected to support the diagnosis and to help the treatment plan for different ethnic groups and their different patterns of miscegenation. Objective: Obtain normal values for McNamara’s cephalometric analysis for adolescent Japanese-Brazilian descents with normal occlusion, as well as to compare this sample with similar samples of White-Brazilian and Japanese. Methods: Lateral headfilms from 40 White-Brazilian, 33 Japanese and 32 Japanese-Brazilian descents were selected. The three groups were composed by individuals with normal occlusion, well-balanced profiles and were separated by sex. The data were statistically analyzed with ANOVA, t-test, ANCOVA and MANCOVA tests. Results: White-Brazilian males had significantly greater nasolabial angle than Japanese males. Japanese-Brazilian displayed an intermediate value between White-Brazilian and Japanese. Conclusion: White-Brazilian, Japanese and Japanese-Brazilian present different cephalometric characteristics of McNamara analysis. Japanese males have a significantly more acute nasolabial angle than White-Brazilian subjects.


INTRODUCTION
In Orthodontics, several resources are available to aid diagnosis and the choice of treatment. [1][2][3][4] Lateral headfilms, for example, have been very useful in determining a more precise diagnosis, because radiograph images can now be reproduced with a minimum of distortion, facilitating orthodontic evaluation.
In 1941, Margolis 5 presented an evaluation method that allowed the study of the facial outline, the mandible and the facial bones and their relationship with the teeth before and after orthodontic treatment, using cephalometric lateral headfilms and a profile photograph. In 1943, he verified that the incisor mandibular plane angle (IMPA) had to be 90º in a pleasant skeletal pattern. 3 Nowadays, it is known that cephalometric analysis does not serve as a fixed and unique parameter for the examination of an individual and in the determination of orthodontic diagnosis and planning. 6 McNamara Jr. analysis is widely known among orthodontists. 7 It has some advantages over other analyzes, such as linear evaluations of apical base discrepancy and dental to apical base discrepancies. This analysis assists in the diagnosis and treatment planning of orthopedic or surgical cases. Population migration between different countries increases each year and, currently, Brazil is the country with the largest number of Japanese outside Japan. Based on that, it is extremely important to differentiate the variations that dento-skeletal structures may present due to the union between different ethnic groups. Because of the considerable increase of the Japanese-Brazilian population, there is a need for studies to support the diagnosis and facilitate the treatment plan for these group. Therefore, the main purpose of this study is to compare three ethnic groups, White Brazilian, Japanese and Japanese-Brazilian, regarding the parameters of McNamara's cephalometric analysis. The sample selection criteria included pleasing and balanced profiles with passive lip competence, facial symmetry, presence of normal occlusion or incipient Angle Class I malocclusion with normal overjet-overbite, absence or a minimal crowding of less than 2mm, presence of all permanent teeth (except the third molars), as judged using study models.

MATERIAL AND METHODS
In order to confirm the absence of racial miscegenation, the grandparents and parents of the White-Brazilian and Japanese samples should not have had any miscegenation.
The Japanese-Brazilian sample should be descendant of both Brazilians and Japanese, without previous miscegenation.  The Japanese-Brazilian sample was constituted by 32 lateral headfilms of 17 females (mean age 13.22 ± 1.04 years) and 15 males (mean age of 14.79 ± 1.01 years). The inclusion criteria were the same as the other groups but in this case, all had to be children or grandchildren from the union of Japanese and White-Brazilians.

CEPHALOMETRIC ANALYSIS
The lateral headfilms were taken with the teeth in maximum intercuspation, in accordance with the norms of the Discipline of Radiology of the institution.

METHOD ERROR
In order to evaluate the method error, 30% of the sample was randomly selected and re-measured after a 30-day interval by the same investigator. To estimate the random errors, the Storniolo-Souza JM, Seminario MP, Pinzan-Vercelino CRM, Pinzan A, Janson G -McNamara analysis cephalometric parameters in White-Brazilians, Japanese and Japanese-Brazilians with normal occlusion formula proposed by Dalberg 8 (S 2 = Σd 2 /2n, where S 2 is the error variance and "d" is the difference between two determinations of the same variable) was applied. Systematic errors were evaluated with dependent t-tests, at p < 0.05. 9

STATISTICAL ANALYSES
Normal distribution of the variables was evaluated with Kolmogorov-Smirnov tests. All variables presented normal distribution.
Sexual dimorphism within each ethnic group was evaluated with t-tests. Ethnic intergroup comparison within males and females was performed with ANCOVA, using the age as co-variable, followed by Tukey tests and multivariate analysis of covariance (MANCOVA).

RESULTS
The random errors ranged from 0.26mm (Lower incisor to A-Po line) to 0.74 mm (P-Nperp), and from 0.63º (Facial axis angle) to 1.6º (Nasolabial angle), and were within acceptable ranges. 10,11 There were no significant systematic errors.
The Japanese sample was significantly older than the Japanese-Brazilian sample ( Table 2).
There were significant ethnic intergroup differences among females (Table 6).

White-Brazilians had significantly greater Nasolabial angle than
Japanese and significant ethnic intergroup differences among males (Table 7).  Table 4: Japanese inter-sex comparison (t-tests).
Storniolo-Souza JM, Seminario MP, Pinzan-Vercelino CRM, Pinzan A, Janson G -McNamara analysis cephalometric parameters in White-Brazilians, Japanese and Japanese-Brazilians with normal occlusion Table 5: Japanese-Brazilian inter-sex comparison (t-tests).    Differences were found between male and female in the literature and in the present study. 11,14,15 For this reason, the ethnic group comparisons had to be separated by sex.

SEX DIFFERENCE
In the White-Brazilian sample, no significant differences between males and females were found (Table 3). Nevertheless, males presented higher values, compared to females. Similar findings were reported by Miyajima et al., 16 indicating that the dentoskeletal variables in males and females with ideal occlusion tend to be larger in males.
There was significantly greater retrusion of the maxilla in males than in females in the Japanese sample (Table 4). These characteristics of the skeletal tissues were confirmed by previous research. 17 The midfacial length (Co-A), mandibular length (Co-Gn) and the maxillo-mandibular difference were significantly larger in males than in females. Similar findings were reported by Miyajima et al. 16 and Bronfman et al., 18 who noticed significant sexual dimorphism in the midface and in mandibular length. Because the midface and the mandibular length were larger, the maxillo-mandibular difference was also larger in males than in females. The Japanese-Brazilian sample presented dimorphism for some skeletal variables, with the highest values found for males (

ETHNIC DIFFERENCES
The samples were separated by sex to obtain a more specific and useful cephalometric normative values of each ethnic group. 16,17,[20][21][22] In males and females, the lower anterior face height was not significantly different between the three samples, which corroborates with the results of Nezu et al. 23 and Alcalde et al. 17 ( Tables 6 and 7).
No significant differences in the dentition variables between the three samples could be noticed (Tables 6 and 7). The results found by Sathler et al. 24 also demonstrated no differences in the upper incisor position between the Japanese-Brazilian and Caucasian sample. However, findings of Miura et al., 25 Miyajima et al., 16 and Ioi et al. 19 found that Japanese-Brazilians have greater protrusion of the mandibular incisors. Among the studied samples, only the nasolabial angle in males was significantly more acute in Japanese than in White-Brazilian ( Table 7). The Japanese-Brazilian presented an average value intermediate to the group of White-Brazilian and Japanese. These results coincide with Bronfman et al. 18 and Miyajima et al., 16 that also observed a more acute nasolabial angle in Japanese.
McNamara Jr. 7 reports that separate evaluation of soft and skeletal tissues usually leads to the same diagnosis, so a patient with an acute nasolabial angle also has a protruded maxila. In this study, the male Japanese group that presented more acute nasolabial angle also had the greatest maxillary protrusion, which has been previously observed. 24 In addittion, Miyajima et al. 16 concluded that Japanese presents greater lip protrusion.
Results showed significant differences between White-Brazilian, Japanese and Japanese-Brazilian using MANCOVA test (Tables 6   and 7). This test compares the three ethnic groups comparing all the variables together, in order to find differences between them. Previous studies found differences between Caucasians and Japanese sample 16,18,24,25 that confirm the present findings.
Therefore, the orthodontist must be careful and individualize each ethnic group during diagnosis and treatment planning. 26,27 Storniolo-Souza JM, Seminario MP, Pinzan-Vercelino CRM, Pinzan A, Janson G -McNamara analysis cephalometric parameters in White-Brazilians, Japanese and Japanese-Brazilians with normal occlusion