130
J. Dent. 1991;
19: 130-131
Short Communication
Reproducibility
of natural head position*
C. S. W. Chiu and R. K. F. Clark Department
of Prosthetic
Dentistry,
University
of Hong Kong, The Prince Philip Dental Hospital,
Hong Kong
ABSTRACT The orientation of the head, when the natural head position was adopted, was measured relative to the true vertical on standardized black and white profile photographs. Two methods of obtaining the natural head position were compared and their reproducibility tested. No statistically significant difference was found between the two different methods or at different sittings. KEY WORDS: J. Dent. 1991; 1991)
Natural head position, Chinese, Reproducibility 19: 130-l
31 (Received 20 November 1990;
received 18 December 1990;
accepted 8 January
Correspondence should be addressed to: Dr C. S. W. Chiu, Department of Prosthetic Dentistry, University of Hong Kong, The Prince Philip Dental Hospital, 34 Hospital Road, Hong Kong.
I
INTRODUCTION Anthropomorphic studies of the head whether for research or clinical evaluation require a standard orientation of the skull for reference. The realization that the Frankfort plane may not always be horizontal when the natural head position is adopted (Downs, 1956; Chow, Clark and Cooke, 1985; Moorrees, 1985) has resulted in greater interest in the natural head position itself in cephalometric work. The natural head position has been shown to be reproducible (Moorrees and Keen, 1958; Solow and Tallgren, 1971; Cook and Wei, 1988b) and its use with the true horizontal plane as the reference can avoid individual and racial variations (Moorrees et al., 1976; Foster et al., 1981; Lundstrom, 1981; Cook and Wei, 1988a). As part of a study of the facial soft tissue profile in southern Chinese adults, the reproducibility of natural head posture has been investigated photographically.
MATERIALS AND METHODS Twenty-seven males and 3 1 females, aged 19-30 years and all of whom were Cantonese, were recruited for the study. Each subject stood 1 m in front of a full-length mirror with a plumb line suspended before them (Fig. I). Two triangular pointers were stuck onto the subject’s face to serve as the arbitrary line for assessing the head orientation. *Submitted in partial fultilment for the degree of Master of Dental Surgery, University of Hong Kong. @1991 Butterworth-Heinemann 0300-5712/91/020130-03
Ltd.
i/
subject
Fig.1. Photographic
set-up.
Av
meter ruler
_
matt white background
mirror
Standardized profile views of the tested subjects were taken with a Canon AE-1 camera (Canon, Tokyo, Japan), a Canon FD-100 mm f/2.8 lens and a National electronic flash unit (National, Tokyo, Japan), mounted on a fixed tripod with adjustable vertical height to match each individual. Walking lightly on the spot and tilting the head backwards and forwards with decreasing amplitude as suggested by Solow and Tallgren (1971) helped the subjects to relax the body and the neck muscles. Two photographs were taken. For the first the mirror was covered and the head position was attained by the subject’s own feeling of natural head balance. The second photograph was taken with the mirror uncovered and the subject was told to look into his own eyes in the mirror. These procedures were repeated 4-6 h later on the same day. The triangular pointers were not removed between the first and second sessions.
Chiu and Clark: Reproducibility
of natural head position
131
Table 1. Analysis of variance for the head position obtained with or without looking into the mirror in the two separate photographic sessions Source of variation Between groups Within groups
Sum of squares 56.18 8606.41
All photographs were processed by the Dental Illustration Unit of the Prince Philip Dental Hospital. Life-sized black and white profile views were produced and the plumb line was also included to serve as the true vertical reference (Fig. 2). The orientation of the head position was determined by the angle formed between the line passing through the tips of the two triangular pointers on the subject’s face and the true vertical. The angles obtained from each method of achieving natural head position and from each pair of corresponding photographs taken at the two sittings were compared.
RESULTS The analysis of variance for the natural head position obtained with and without looking into the mirror in the two separate sittings revealed no significant difference (Table I). Hence, the natural head position, obtained with or without looking into the mirror, was found to be reproducible.
DISCUSSION Previous studies of the natural head position have usually employed a cephalometric method which required tested subjects to be exposed to radiation. The present study used a simple photographic technique to evaluate the reproducibility of the natural head position. In posing the
d.f.
Mean square
Variance ratio (F)
18.73
0.50
37.10
(P > 0.05)
subjects, no external physical constraint such as the earrods from the cephalometric machine was used and the tested subjects were allowed to attain a more natural and relaxed head position. In this study, the natural head positions obtained with and without looking into the mirror were found to be reproducible, which is consistent with the previous studies (Moorrees and Kean, 1958; Solow and Tallgren, 1971; Cooke and Wei, 1988b), and no significant difference was found between the natural head positions registered with and without the mirror. The results indicate that in spite of a greater variability in the orientation of other landmarks such as the Frankfort plane (Chow et al., 1985) and the occlusal plane (Chow et al., 1986) the natural head position is reproducible in the southern Chinese ethnic group and is consistent with other ethnic groups in this respect. The use of this simple photographic technique can be justified in future studies involving the analysis of the soft tissue profile, using natural head position and the true vertical as the reference.
References Chow T. W., Clark R. K. F. and Cooke M. S. (1985) Errors in mounting maxillary casts using face-bow records as a result of an anatomical variation. J. Dent. 13, 217-282. Chow T. W., Clark R. K. F. and Cooke M. S. (1986) The orientation of the occlusal plane in Cantonese patients. J.
Dent. 14, 262-265. Cook M. S. and Wei S. H. Y. (1988a) A summary five-factor cephalometric analysis based on natural head posture and the true horizontal. Am. .I Orthod. Dentofac. Orthop. 93,
213-223. Cook M. S. and Wei S. H. Y. (1988b) The reproducibility
of head posture: a methodological study. Am. _I Orthod. Dentofac. 0rthop.93, 280-288. Downs W. B. (1956) Analysis of the dentofacial profile. Angle Orfhod. 26, 191-212. Foster T. D., Howat A P. and Naish P. J. (1981) Variation in cephalometric reference lines. Br. J. Orthod. 8, 183-187. Lundstrom A (1981) Orientation of profile radiographs and photos intended for publication of case reports. Proc. Finn. Dent. Sot. 77, 105-111. Moorrees C. F. A. (1985) Natural head position. In: Jacobson A. and Cantield P. W. (eds), Introduction to Radiographic Cephalometry. Philadelphia, Lea & Febiger, chap. 8. Moorrees C. F. A. and Kean M. R. (1958) Natural head position-a basic consideration in the interpretation of cephalometric radiographs. Am. .I. Phys. Anthropol. 16, 213-234. Moorrees C. F. A, Tandarts M. E. V., Lebret L. M. L. et al. (1976) New norms for the mesh diagram analysis. Am. J. Orthod. 69, 51-71. Solow B. and Tallgren A. (1971) Natural head position in standing subjects. Acta Odontol. Stand. 29, 591-607. natural
Fig. 2. Standard photographic view.
J. Dent. 1991;
19: 130-131
Short Communication
Reproducibility
of natural head position*
C. S. W. Chiu and R. K. F. Clark Department
of Prosthetic
Dentistry,
University
of Hong Kong, The Prince Philip Dental Hospital,
Hong Kong
ABSTRACT The orientation of the head, when the natural head position was adopted, was measured relative to the true vertical on standardized black and white profile photographs. Two methods of obtaining the natural head position were compared and their reproducibility tested. No statistically significant difference was found between the two different methods or at different sittings. KEY WORDS: J. Dent. 1991; 1991)
Natural head position, Chinese, Reproducibility 19: 130-l
31 (Received 20 November 1990;
received 18 December 1990;
accepted 8 January
Correspondence should be addressed to: Dr C. S. W. Chiu, Department of Prosthetic Dentistry, University of Hong Kong, The Prince Philip Dental Hospital, 34 Hospital Road, Hong Kong.
I
INTRODUCTION Anthropomorphic studies of the head whether for research or clinical evaluation require a standard orientation of the skull for reference. The realization that the Frankfort plane may not always be horizontal when the natural head position is adopted (Downs, 1956; Chow, Clark and Cooke, 1985; Moorrees, 1985) has resulted in greater interest in the natural head position itself in cephalometric work. The natural head position has been shown to be reproducible (Moorrees and Keen, 1958; Solow and Tallgren, 1971; Cook and Wei, 1988b) and its use with the true horizontal plane as the reference can avoid individual and racial variations (Moorrees et al., 1976; Foster et al., 1981; Lundstrom, 1981; Cook and Wei, 1988a). As part of a study of the facial soft tissue profile in southern Chinese adults, the reproducibility of natural head posture has been investigated photographically.
MATERIALS AND METHODS Twenty-seven males and 3 1 females, aged 19-30 years and all of whom were Cantonese, were recruited for the study. Each subject stood 1 m in front of a full-length mirror with a plumb line suspended before them (Fig. I). Two triangular pointers were stuck onto the subject’s face to serve as the arbitrary line for assessing the head orientation. *Submitted in partial fultilment for the degree of Master of Dental Surgery, University of Hong Kong. @1991 Butterworth-Heinemann 0300-5712/91/020130-03
Ltd.
i/
subject
Fig.1. Photographic
set-up.
Av
meter ruler
_
matt white background
mirror
Standardized profile views of the tested subjects were taken with a Canon AE-1 camera (Canon, Tokyo, Japan), a Canon FD-100 mm f/2.8 lens and a National electronic flash unit (National, Tokyo, Japan), mounted on a fixed tripod with adjustable vertical height to match each individual. Walking lightly on the spot and tilting the head backwards and forwards with decreasing amplitude as suggested by Solow and Tallgren (1971) helped the subjects to relax the body and the neck muscles. Two photographs were taken. For the first the mirror was covered and the head position was attained by the subject’s own feeling of natural head balance. The second photograph was taken with the mirror uncovered and the subject was told to look into his own eyes in the mirror. These procedures were repeated 4-6 h later on the same day. The triangular pointers were not removed between the first and second sessions.
Chiu and Clark: Reproducibility
of natural head position
131
Table 1. Analysis of variance for the head position obtained with or without looking into the mirror in the two separate photographic sessions Source of variation Between groups Within groups
Sum of squares 56.18 8606.41
All photographs were processed by the Dental Illustration Unit of the Prince Philip Dental Hospital. Life-sized black and white profile views were produced and the plumb line was also included to serve as the true vertical reference (Fig. 2). The orientation of the head position was determined by the angle formed between the line passing through the tips of the two triangular pointers on the subject’s face and the true vertical. The angles obtained from each method of achieving natural head position and from each pair of corresponding photographs taken at the two sittings were compared.
RESULTS The analysis of variance for the natural head position obtained with and without looking into the mirror in the two separate sittings revealed no significant difference (Table I). Hence, the natural head position, obtained with or without looking into the mirror, was found to be reproducible.
DISCUSSION Previous studies of the natural head position have usually employed a cephalometric method which required tested subjects to be exposed to radiation. The present study used a simple photographic technique to evaluate the reproducibility of the natural head position. In posing the
d.f.
Mean square
Variance ratio (F)
18.73
0.50
37.10
(P > 0.05)
subjects, no external physical constraint such as the earrods from the cephalometric machine was used and the tested subjects were allowed to attain a more natural and relaxed head position. In this study, the natural head positions obtained with and without looking into the mirror were found to be reproducible, which is consistent with the previous studies (Moorrees and Kean, 1958; Solow and Tallgren, 1971; Cooke and Wei, 1988b), and no significant difference was found between the natural head positions registered with and without the mirror. The results indicate that in spite of a greater variability in the orientation of other landmarks such as the Frankfort plane (Chow et al., 1985) and the occlusal plane (Chow et al., 1986) the natural head position is reproducible in the southern Chinese ethnic group and is consistent with other ethnic groups in this respect. The use of this simple photographic technique can be justified in future studies involving the analysis of the soft tissue profile, using natural head position and the true vertical as the reference.
References Chow T. W., Clark R. K. F. and Cooke M. S. (1985) Errors in mounting maxillary casts using face-bow records as a result of an anatomical variation. J. Dent. 13, 217-282. Chow T. W., Clark R. K. F. and Cooke M. S. (1986) The orientation of the occlusal plane in Cantonese patients. J.
Dent. 14, 262-265. Cook M. S. and Wei S. H. Y. (1988a) A summary five-factor cephalometric analysis based on natural head posture and the true horizontal. Am. .I Orthod. Dentofac. Orthop. 93,
213-223. Cook M. S. and Wei S. H. Y. (1988b) The reproducibility
of head posture: a methodological study. Am. _I Orthod. Dentofac. 0rthop.93, 280-288. Downs W. B. (1956) Analysis of the dentofacial profile. Angle Orfhod. 26, 191-212. Foster T. D., Howat A P. and Naish P. J. (1981) Variation in cephalometric reference lines. Br. J. Orthod. 8, 183-187. Lundstrom A (1981) Orientation of profile radiographs and photos intended for publication of case reports. Proc. Finn. Dent. Sot. 77, 105-111. Moorrees C. F. A. (1985) Natural head position. In: Jacobson A. and Cantield P. W. (eds), Introduction to Radiographic Cephalometry. Philadelphia, Lea & Febiger, chap. 8. Moorrees C. F. A. and Kean M. R. (1958) Natural head position-a basic consideration in the interpretation of cephalometric radiographs. Am. .I. Phys. Anthropol. 16, 213-234. Moorrees C. F. A, Tandarts M. E. V., Lebret L. M. L. et al. (1976) New norms for the mesh diagram analysis. Am. J. Orthod. 69, 51-71. Solow B. and Tallgren A. (1971) Natural head position in standing subjects. Acta Odontol. Stand. 29, 591-607. natural
Fig. 2. Standard photographic view.
