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Craniofacial structure of Japanese and European-American adults with normal occlusions and well-balanced faces

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Abstract

The purpose of this study is to compare two groups of adults from different races who were selected on the basis of having normal (“ideal”) occlusions and well-balanced faces. The lateral cephalometric radiographs of 54 Japanese adults (26 men and 28 women) were compared with a sample of 125 adults (44 men and 81 women) of European-American ancestry. The samples were chosen by orthodontists of the same racial background as the sample selected. Each lateral cephalogram was traced and digitized, and differences between cephalometric measurements between groups were analyzed with completely randomized t tests. In comparison to the European-American sample, the Japanese sample, in general, was smaller in anteroposterior facial dimensions and proportionately larger in vertical facial dimensions. The facial axis angle was more vertical in Japanese subjects, indicating a more downward direction of facial development. On average, the subjects in the Japanese sample were more protrusive dentally, with a more acute nasolabial angle and a greater tendency toward bilabial protrusion. These differences, evident even in groups with so-called “well-balanced faces”, indicate that fundamental variation exists in the craniofacial structure of Japanese and European-Americans. The results of this study support the premise that a single standard of facial esthetics is not appropriate for application to diverse racial and ethnic groups. (Am J Orthod Dentofac Orthop 1996;110:431-8.)

Section snippets

Cephalometric norms

Within the orthodontic community, attempts have been made to quantify facial esthetics through cephalometric analysis, with virtually all the early cephalometric analyses based on sample populations of people of European-American ancestry.1, 2, 3, 4, 5, 6 In addition, most major longitudinal growth studies are based on samples of people of European background.7, 8, 9, 10, 11, 12

The first attempt to apply cephalometric analysis to ethnic groups other than those of European ancestry was published

Purpose

A review of the literature reveals some apparent differences in craniofacial structure between persons of Japanese and European-American ancestry. The cephalometric studies of Japanese cited previously, however, often did not take facial esthetics into consideration when the samples were defined. One study that did select subjects on the basis of facial balance39 analyzed the records of persons who already had undergone orthodontic treatment, and the cephalometric norms used to determine facial

Samples

Two groups of untreated adults were compared in this study, one of Japanese origin and one of European-American origin.

Sexual dimorphism

Table I presents the means and standard deviations of the measurements for the male and female Japanese samples.

Of the 24 craniofacial measurements, 5 showed significant sexual dimorphism, 3 measures of which (Co-Point A, Co-Gn, ANS-Me) apparently reflected the expected average size differential between the men and women. One other notable difference was in the mandible, with the female Japanese subjects having a steeper mandibular plane angle (26.1°) than the male Japanese subjects (22.3°).

Discussion

This investigation is the first to compare samples of untreated Japanese and European-American persons characterized as having normal occlusions and well-balanced faces. No previous study of racial differences has compared so-called “ideal” samples, although several studies have evaluated patients from one ethnic group with normal or ideal occlusions (e.g., European-American: Hellman,48 Downs,2 Riedel,49 Casko and Shepard,50 and Ben-Bassat et al.51 Japanese: Sakamoto,30 Miura et al.,33

Conclusion

The results of this study of two racially diverse groups of persons with so-called “well-balanced faces” indicate that fundamental variations exist in the craniofacial structure of Japanese and European-Americans. The findings of this study support the premise that a single standard of facial esthetics is not appropriate for application to diverse racial and ethnic groups, at least for the present. The long-term effects of increasing global communication and interaction on perceptions of facial

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