Cephalometric norms for the Vietnamese population

INTRODUCTION

Roentgenographic cephalometrics was first introduced to study craniofacial growth and development. Later on, it was used to study facial form and its use gradually extended to the development of cephalometric norms to define the objectives of orthodontic treatment. The introduction of the cephalometer then provided avenues for creation of cephalometric analysis for clinical diagnosis and treatment planning and soon the cephalogram became an indispensable weapon in the armory of an orthodontist for correct diagnosis, treatment planning, prognostic evaluation, and comparative studies. The cephalometric norms for the Caucasians, for many decades, were being applied on the population groups worldwide. However, with time, many investigators concluded that there was variation of the craniofacial morphology between different ethnic groups.^[1,2]

Thus, it became apparent that the widely studied Caucasian norms which were established using various cephalometric analyses were not sufficient to apply to different racial or ethnic groups’ cephalometric studies on different ethnic groups including those of Chan’s on Chinese, Garcia’s on Mexican-Americans,^[3] and Connor et al.’s on American black patients.^[4] Studies by Cooke and Wei and Yeong and Huggare on Chinese,^[5,6] Enlow et al. analysis of Black and Caucasian craniofacial patterns,^[7] Bacon et al. on African Bantu and a Caucasoid population,^[8] Hamdan and Rock on an Arabic population,^[9] Alcalde et al. and Engel and Spolter and Miura et al. on Japanese,^[10-12] Drummond et al. on Negroes^[13] and Park et al.,^[14] and Hwang et al.^[15] on Korean adults had indicated that normal measurements of one group cannot be considered normal for other racial groups. Investigators such as Miura and Alcalde et al. in Japan^[13] and Carlos J Garcia in the USA had established their norms on the basis of Steiner’s analysis. The first cephalometric study on the Indian population was done by Kotak^[16] on Gujarati girls and thereafter Nanda^[17] and John et al.^[18] had done cephalometric studies on various population groups of India.^[19]

However, till date, no study has been conducted on the population of Vietnamese. The Vietnamese are an East Asian ethnic group originating from present-day northern Vietnam and southern China. They are the majority ethnic group of Vietnam, comprising 86% of the population at the 1999 census. Although geographically and linguistically labeled as Southeast Asians, long periods of Chinese domination and influence have placed the Vietnamese culturally closer to East Asians, or more specifically their immediate northern neighbours, the Southern Chinese and other tribes within South China. The unique ethnicity of the Vietnamese mandates separate indicators and norms for applications in forensics, cosmetic surgery and research. It was therefore thought pertinent to undertake such a study for a young population of Vietnamese and observe various hard tissue cephalometric values by means of Steiner’s analysis with a view to use these established norms in clinical practice.

MATERIALS AND METHODS

The material for this study consisted of standardized lateral head roentgenograms of 30 Vietnamese young boys and 30 girls residing in the School of Odonto-Stomatology, Ha Noi Medicine University, Vietnam. They were selected as per the following criteria.

1. A normal acceptable and pleasing profile, 18–25 years of age, normal occlusion^[20] with full complement of erupted teeth up to the second molar in proper intercuspation

2. No history of orthodontic treatment, gross carious lesion, and periodontal disease and no history of facial trauma.

A panel was formed to check the samples required for the study and they gave their consent regarding the fulfillment of the criteria of the samples. The study objective and methods were approved by the University ethical committee.

Landmarks used in the study

• Angular measurements: Angle SNA, SNB, ANB, SND, maxillary I to NA. Mandibular I to NB, maxillary I to mandibular I, occlusal plane to SN, and Go-Gn to SN

• Linear measurements (mm): Maxillary I to NA line, mandibular I to NB line, Pog to NB line, SL line, and SE line [Figure 1].

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Figure 1

Hard and soft tissue analysis

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The patient’s head was positioned in the PantOs 16 XP roentgenographic cephalostat maintaining a target-film distance of 5 feet or 152.4 cm. The X-ray film plate which is enclosed in a light-tight cassette was positioned parallel to the midsagittal plane of the patient such that the X-ray beam was directed perpendicular to it. The ear rods were used to stabilize the head in a vertical plane. The patient’s head was positioned so that the Frankfort Horizontal plane would be parallel to the floor and was instructed to look straight and maintain a relaxed posture with teeth in centric occlusion during the exposure of the films.^[21]

The lateral cephalogram was traced upon an A4 size acetate matte tracing sheet with a 3HB pencil over a well-illuminated viewing screen. Each cephalogram was traced twice and the average measurement is taken into account to minimize the error.^[22]

The linear measurements were recorded with a measuring scale up to 0.05mm correction. The angular measurements were recorded with a protractor up to 0.05 mm correction. Statistical calculations performed included mean, standard deviation (SD), standard error, Student’s t-test for each parameter. Statistical comparisons were done by the t-test and Pearson’s test for reproducibility of values of these variables.

The mean values of this study had been compared with the Steiner’s norms for Caucasian cases. By these data, a complete chart of the Steiner’s analysis was established for young Vietnamese adult population [Figures 2 and 3].

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Figure 2

Photograph showing cephalometric head plate

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Figure 3

The subject was instructed to look straight and maintain arelaxed posture with teeth in centric occlusion during the exposureof the films

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RESULTS

The study sample size was found to be adequate for statistical analysis. The measurements were repeated by 2 seperate authors and the intra examiner variability was found to be statistically insignificant. The results are shown in Tables 1-3.

DISCUSSION

The present study tries to establish a norm or standard for the skeletal and dental pattern of Vietnamese young adults according to the Steiner’s analysis. The results were compared with the Steiner’s norm for the Caucasians. Cephalometerically, nine angular and five linear measurements were used by Steiner. The Steiner’s have been taken from Cecil C. Steiner’s original article “Cephalometrics for you and me” published in the American Journal of Orthodontics, October (1953). The present study revealed that the mean values for the Vietnamese sample were significantly different in all measurable values from the means of Steiner’s analysis of Caucasians.

SUMMARY AND CONCLUSION

From the current study, it is evident that in the Vietnamese population with so-called well-balanced faces, there are some fundamental variations in the craniofacial structure of Vietnamese when compared with Steiner’s norms. These should be established to serve in the diagnosis and treatment of the Vietnamese patients. The results of the present study also support the view that a single standard of facial esthetics should not be supplied to all racial and ethnic groups. The following differences and similarities were demonstrated in the Vietnamese samples as compared to the Caucasians:

1. The anteroposterior position of the apical base of the maxilla and mandible in relation to the anterior cranial base was more anteriorly placed or prognathic as compared to the Caucasians. An increased ANB angle indicated a greater tendency toward bialveolar protrusion

2. The angular relationship of the mandibular plane in relation to the cranial base plane (SN-GoGn angle) was smaller which was suggestive of a strong horizontal growth pattern in the Vietnamese

3. The Vietnamese population, in terms of skeletal- dental correlation, has a tendency of protrusion when compared to Caucasian people

4. The study suggested wide divergence of the SE and SL distance in the Vietnamese population when compared to the Caucasians.

The study concluded that most of the cephalometric measurements of the Vietnamese cases were significantly different from the Steiner’s norms and also from other ethnic groups because the various published methods represent population averages; it is important to consider each patient’s treatment goals and needs during evaluation and treatment planning.