British Journal of Orthodontics

ISSN: 0301-228X (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/yjor19

Proportional Analysis of the Facial Profile in Natural Head Position in Caucasian and Chinese Children Anders Lundström L.D.S., Ph.D., D.Sc., D.D.Sc, F.D.S. & Michael S. Cooke Ph.D., D.Orth., D.D.P.H., F.D.S., F.F.D. To cite this article: Anders Lundström L.D.S., Ph.D., D.Sc., D.D.Sc, F.D.S. & Michael S. Cooke Ph.D., D.Orth., D.D.P.H., F.D.S., F.F.D. (1991) Proportional Analysis of the Facial Profile in Natural Head Position in Caucasian and Chinese Children, British Journal of Orthodontics, 18:1, 43-49, DOI: 10.1179/bjo.18.1.43 To link to this article: http://dx.doi.org/10.1179/bjo.18.1.43

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Date: 25 October 2016, At: 07:22

British Journal of Orthodontics/ Vol. IB/1991/41-49

Proportional Analysis of the Facial Profile in Natural Head Position in Caucasian and Chinese Children ANDERS LUNDSTRi)M, L.D.S., PH.D., D.Sc., D.D.Sc., F.D.S. Department of Orthodontics, Karolinska Institutct, Stockholm, Sweden MICHAEL

s. COOKE, PH.D., D.ORTH., D.D.P.H., F.D.S., F.F.D.

Department 'of Children's Dentistry and Orthodontics, University of Hong Kong, Hong Kong Received for publication December 1989

Abstract. A proportional analysis of the facial soft tissue pr£?file in natural head position involving 11 indices (ratios), was applied to 80 Caucasian, and 80 Chinese male andfemale 12-year-old children in Hong Kong. The analysis is based on the true horizontal and the porion vertical, and has the advantage that its foundation lies on a mor£' stable (less growth affected) region l?{ the head compared to pro,file soft tissue landmarks. Measurements were made on cephalograms recorded in natural head position. M ale subjects were larger than the femalesfor most of the horizontal measurements, but for both population samples the vertical measurements displayed virtually no significant intersex differences at 12 years. No very sign(ficant intersex differences were found for the proportional indices. Ethnic differences were mainly found with the horizontal measurements. Relative to the porion vertical the Caucasian children were more protrusive over S£?{t tissue nasion, nose tip, and sulcus labia/is superior, whilst the Chinese displayed more protrusion over the lower lip and sulcus labia/is inferior. Ethnic proportional differences relative to nasion were combined with a shorter porion-nasion distance in the Chinese as compared with the Caucasian children. The se/la-nasion line was found to be more forwards-upwards inclined in Chinese than Caucasian children. It was concluded that a proportional soft tissue profile analysis, based on natural head position, is a useful method for the comparison of ethnic population groups. This study ampl(fied ethnic differences previously reported by Cooke ( 1986) and Cooke and Wei ( /989). Index words: Profile Analysis, Natural Head Position, Proportional Analysis, Caucasian, Chinese.

Introduction Variation of the facial soft tissue profile has traditionally been studied less than the corresponding skeletal profile. This is understandable in that the teeth are closely related to the apical bases and through them to the total osteological base of the head. As facial aesthetics are an important consideration for many patients, more attention needs to be paid to individual soft tissue profile variation. This study is therefore focused on the facial soft tissue profile. The concept of natural head position (NHP) was introduced into the orthodontic literature in the 1950s by Downs (1956), Bjerin (1957), and Moor-

rees and Kean ( 1958). In the two latter publications it was shown that NHP was reproducible in adults with a standard error of close to 2°, while cephalometric reference planes such as the sella-nasion line and the Frankfort horizontal had il standard deviation of 4-6" when related to a true horizontal or vertical. The same level of reproducibility of NHP has been confirmed by several authors (Lundstrom and Lundstrom, 1989). A growing recognition ofNHP as a suitable basis for cephalometric analysis has been demonstrated in the orthodontic literature (Solow and Tallgren, 1971, 1976; Legan and Burstone, 1980; Scheideman et al., 1980; Lundstrom, 1981; Spradley et al., 1981; Moorees, 1985; Bell et al., 1986; Cooke, 1986;

Correspondence: Clinical Research Centre. F: 68, Huddinge Hospital, S-14186 Huddinge, Sweden. 030 1·228X/91/004000 + 00502.00

(() 1991 British Society for the Study of Orthodontics

44 A. Lundstrom and M. S. Cooke

BJO Vol. 18 No. I

Cooke and Wei, 1988a-c; Cooke, 1988, 1989; Cole, 1988; Lundstrom and Lundstrom, 1989). The aims of the study were: (1) to apply a system for proportional analysis of the soft tissue profile, developed by A. Lundstrom for analysis of cases with facial abnormality, to an ethnic comparison of two population groups (southern Chinese and Caucasian 12-year-old children in Hong Kong); (2) to produce soft tissue profile standards for Caucasian and Chinese children, based on nonselected subjects at an age when many orthodontic treatments start; (3) to compare the results with earlier published data (Cooke, 1986; Cooke and Wei, 1988c; Cooke, 1989) in order to evaluate differences in methodological approach.

~

({~ ~------:--\

In the choice of method the following considerations were taken into account. 1. Profiles should be characterized in the horizontal and vertical directions. Due to the large variation demonstrated for angles between the true vertical and traditional cephalometric reference lines (SD 4-6°, Lundstrom and Lundstrom, 1989) natural head position was chosen as the basic reference for horizontal and vertical measurements (Fig. 1). 2. The type of analysis chosen should be applicable to groups of individuals, making it possible to compare, for instance, males and females, different age groups, ethnic populations, etc. 3. The analysis should express facial proportions and, thus, be independent of differences in general size between individuals.

VERT

VERT 1CA L OIS TAN CES

HOR

Subjects and Methods Samples The material was described in detail by Cooke (1986), and Cooke and Wei (1988c). The subjects consisted of 240 Chinese children, from which 80 children (40 boys and 40 girls) were selected at random to form a Chinese sample of the same size as the whole Caucasian sample. All children were between 12 and 13 years of age. The Caucasian children were residents in Hong Kong with both parents originated from the United Kingdom. All the children had not received orthodontic treatment (originally 8·7 per cent of the British males and 12·5 per cent of the British females had to be rejected due to previous orthodontic treatment).

VERT FIG. I (a) Horizontal distances from Porion (uppermost point of ear post) to: soft tissue nasion (N), pro nasion (PRN), sulcus labialis superior (SLS), labrale superior (LS), la bra le inferior (LI), sulcus labia lis inferior(SLI), pogonion (PG N ). The variables were defined relative to the true horizontal in natural head position. (b) Vertical distances used in this study: (I) nasion-menton (N-ME); (2) nasion-subnasion (N-SbN); (3) subnasion-menton (SbNME); (4) subnasion-stomion (SbN-ST); (5) stomion-menton (ST-ME).

Proportional Facial Analysis 45

BJO February /99 I

Method of analysis All individuals had standardized lateral roentogenographic cephalograms taken with the teeth in centric occlusion and the lips in light contact. Each child was carefully instructed in how to attain a natural, relaxed, standing position in front of a vertical mirror and to look into their own eyes. A plumb line anterior to the facial midline helped to orient the subjects. Earposts of the cephalostat were inserted with care taken not to disturb the natural head position. This and details of the cephalostat and digitizer have been described previously by Cooke ( 1986), and Cooke and Wei ( 1988c). The upper and lower plumb line points and the landmark§ shown in Fig. I were digitized and stored. A computer program was designed to produce the 12 distance variables specified in Fig. I. All variables were corrected for enlargement. Means and standard errors of means were calculated for each of the variables in the following subgroups: Caucasian boys, Caucasian girls. Chinese boys, Chinese girls. Profile proportions were calculated in the form of indices for eight horizontal, two vertical, and one vertical/horizontal proportions as listed in Table I. In order to demonstrate mean differences between the groups for the whole profiles. computer plottings were produced as mean profiles based on a series of digitized landmarks from the upper part of the forehead down to the lower part of the chin (McWilliam, 1989). This co-ordinate system had sella ·as origin and the true vertical in natural head position asy-axis. In this way mean profile plottings could be produced for each of the four subgroups. Curvatures between the digitized points were adapted to the 'best fit' of the landmark data. TABLE

I.

2. 3. 4. 5. 6. 7. 8.

I

Method errors (m.e.) were calculated from differences between measurements on duplicate head films from I 0 subjects. The first and second films were taken within 4-10 minutes or 1-2 hours intervals as part of a complementary study ofNHP reproducibility (Cooke, 1986; Cooke and Wei, 1988b). Error variances were calculated according to the formula:

I:.d2 m.e.2= 2n where d is the difference between observations and n the number of subjects. The error variance was related as a percentage to the total variance for the 160 subjects. Results Errors For horizontal distances error variance/total variance percentages were quite small (0·5-2·3 percent). The vertical distances varied between 3·9 and 10·4 per cent for four of them and 17·8 per cent for one (nasion-subnasion). The horizontal proportions varied between 1·2 and 6·0 per cent while vertical and vertical/horizontal proportions varied between 8·4 and 13·3 per cent. Intersex differences Among the Caucasian children 3 out of 11 proportions showed some sex difference, although only on the 5 per cent level of significance (Table 2):

Indices expressing facial proportions ( cf Fig. 1)

Index

Definition

Horizontal Nasal prominence Upper jaw prominence Lower jaw prominence Upper to lower jaw Lip relationship Chin eminence Chin prominence Facial convexity

PO-PRN/PO-N x 100 (or PRN/N) PO-SLS/PO-N x 100 (or SLS/N) PO-SLI/PO-N x 100 (or SLI/N) PO-SLS/PO-SLI x 100 (or SLS/SLI) PO-LS/PO-LI x 100 (or LS/LI) PO-PG/PO-SLI x 100 (or PG/SLI) PO-PG/PO-N x 100 (or PG/N) PO-SLS/i (PO-N +PO-PG) x lOO

Vertical 9. Upper to lower facial height 10. Upper to lower jaw height

N-SN/SN-GN X 100 SN-ST/ST-GN X 100

Vert ica/f Horizontal 11. Facial/height to depth

N-GN/PO-PG X 100

46

A. Lundstrom and M. S. Cooke

BJO Vol. 18 No. I

TABLE2

Intersex dijj'erences for facial proportions (index units) for Caucasian and Chinese 12-yearold children ( 40 boys and 40 girls in each group)

Caucasian Variable

Boys (i±SE)

Chinese Girls

Significance

(Xi SE)

(P)

117·1 ±0·7 116·6±0·5 PRN/N SLS/N 101·5±0·8 98·9±0·6 89·5± 1·6 86·2±0·8 SLI/N SLS/SLI 113-8±0·7 114·9±0·6 LS/LI 104·7±0·3 104·9±0·3 PG/SLI 101·2±0·3 101·2±0·2 PG/N 87-2±0·8 .. 90·6±1·1 Convexity 108·2±0·4 108·3±0·3 N-SbN/ShN-ME 77-6±1·3 82·5± 1·4 SbN-ST/ST-ME 51·4±1·0 47·9± 1·0 N-ME/PO-PG 125·2± 1·2 128·6± 1·4