A serial study of normal facial asymmetry in monozygotic twins.

Asymmetry of the soft tissues of the face was measured by comparing three pairs of bilateral facial parameters connecting the landmarks external canthus, tip of nose and angle of mouth. The subjects were six pairs of monozygotic twins (eight girls and four boys) in the age range 8-19 years. A clinical contour mapping technique known as short-base stereophotogrammetry provided life-size facial maps on which the parameters were measured in three dimensions. The study was based on annual serial records over an average period of 9 years for each pair, and was almost entirely longitudinal. The asymmetry in millimetres was given a positive or negative sign, depending on whether right or left side dominated. Asymmetry in the facial parameters was found to be very small, amounting at most to a few millimetres, and was not much larger than the measuring error of the method. Nevertheless, asymmetry was statistically significant (p < 0.05) in 12 out of 60 indicators, and of these seven were at p < 0.01 level. Asymmetry could not be related to twin zygosity, adolescence or age.

Serial observation of asymmetry in the growing face.

Three children suffering from facial asymmetry were observed annually using facial stereophotogrammetry before, during, and after their general skeletal adolescent growth spurt. Stereophotogrammetry allows accurate three-dimensional measurements between identifiable facial landmarks. Five pairs of bilateral parameters connecting external canthi and angles of the mouth to alae and tip of nose, and to each other, allowed a positive sign (right-side larger) or a negative (left-side larger) assessment of parameter asymmetry. Their total, taking sign into account, assessed mid-facial asymmetry. Serial observation showed that: (1) in patient no. 1 suffering from post-traumatic condylar hypoplasia, the facial asymmetry resolved; (2) in patient no. 2 suffering from unilateral facial hypoplasia, the asymmetry, which was severe, reduced with adolescence, but did not resolve; (3) in patient no. 3 suffering from fibro-osseous dysplasia of left maxilla, the asymmetry was reduced by surgery, but the full effects of the surgery were not measurable until over 1 year after operation; subsequently, the asymmetry began to increase again.

Improvement in the deformity of the face in Paget's disease treated with diphosphonates.

We studied nine patients with Paget's disease affecting the skull or facial bones, who were subsequently treated with either dichloromethylene diphosphonate (clodronate) or ethylene-1-hydroxy-1,1-diphosphonate (etidronate). Long-term treatment induced a clinical and biochemical improvement in eight, and this was associated with a reduction in maxillary or skull volume as assessed by quantitative stereophotogrammetry. The one patient whose disease was resistant to treatment with diphosphonate, showed no change in maxillary shape. These studies suggest that the long-term control of disease activity attained with diphosphonates, results in the improvement of skeletal deformity.

Stereophotogrammetric study of growth and development of the nose.

A total of 269 contour maps of the face were measured in three dimensions to study growth and development of the nose. The maps were derived from a mixed longitudinal study of 26 boys and 26 girls between the ages of 9 and 16 years, and were recorded annually. Various nasal parameters were measured to study growth of linear parameters and external nasal volume. Apart from dorsum of the nose between 9 and 11 years of age, all linear parameters were larger for boys by an amount increasing with age. The early growth in girls and late growth in boys suggested the presence of an adolescent growth spurt in the nose, which was confirmed by volumetric measurements. Developmentally the greatest change occurred in anteroposterior prominence of nasal tip in both sexes and the least change occurred in intercanthal width.

Developmental changes in the facial soft tissues.

Short-base stereophotogrammetry was used to study differential growth and development of the soft tissues of the face. Thirteen facial parameters were measured at ages 9, 11, 13, 15, and 16 years on 170 facial contour maps selected from a mixed longitudinal study of 26 boys and 26 girls. Each parameter was measured three-dimensionally, and its developmental progress at the earlier stages was expressed as a percentage of its value at 16 years of age. Standing height development was assessed in the same way. Three parameters that measured soft tissues surrounding the eyes grew little but were very advanced in their development, following a "neural" pattern. The remaining facial parameters grew more but were less advanced, and standing height was least advanced. There appeared to be three separate patterns of development, "neural," "facial," and "skeletal." Girls were, in general, smaller than boys, but their development was more advanced when measured as a percentage of size at 16 years compared with boys.

Intrapair facial differences in twins.

Annual serial records in the form of facial contour maps were examined for 18 like-sexed twin pairs of near equal zygosity distribution. Zygosity diagnosis was based primarily on hematological reports for 26 of the 36 children and the remainder were diagnosed on a basis of the concordance or discordance of various physical characteristics: standing height, finger print ridge count, tooth size, and hair and eye colour. Thirteen facial parameters were measured on 274 maps. After age correcting and three-point smoothing, more than 1,150 intrapair differences of individual facial parameters were measured. In general, the dizygotic twin pairs had the larger mean intrapair differences in facial parameters and the monozygotic twin pairs had the smaller intrapair mean differences. The more important facial parameters for distinguishing the two groups were identified and used to calculate a "facial similarity index".

The adolescent growth spurt in the soft tissues of the face.

The faces of 8 boys and 8 girls were recorded annually by short base stereophotogrammetry. The output for the 16 children consisted of 158 life-size facial maps allowing the serial three-dimensional measurement of 13 soft tissue facial parameters. Three of these parameters (1, 2 and 3) measured the width of the palpebral fissures and the intercanthal distance and were therefore related to the eyes, and 'neural' in character. The remaining 10 parameters (4-13) measured facial characteristics. Standing height was also recorded. The values for each characteristic were age-corrected. Means for the different soft tissue facial parameters are reported for ages 9-16 years. The original individual readings were then three-point smoothed and related first to the year in which peak growth was achieved in standing height, second to the two years preceding and, third, to the two years following that year. The means for the 10 facial parameter growth velocities extending below the eyes showed an adolescent growth spurt related to that in standing height, although not necessarily coinciding with that year. Of the 10 parameters, 5 peaked in PHV year, 3 in -1 PHV year and 2 in +1 PHV year. The facial parameters at eye level, which are really 'neural' parameters, showed much smaller growth velocities and no spurt.

The growth and development of the soft tissues of the human face.

The complexity of shape, soft nature of the facial tissues and the sensitivity of the eyes make their accurate direct measurement difficult. Short base stereophotogrammetry is three dimensional and non-invasive. This technique was used to measure the faces of 52 like-sexed twins between the ages of 9 and 16 years in a mixed longitudinal study. Certain vertical and horizontal parameters defining the eyes, the nose, the mouth and overall facial shape were remeasured and plotted for this study. Relative to the intercanthal line, the alae of nose and angles of mouth are displaced by growth, on or very near to straight lines which were not parallel, indicating a small change of proportion between nose and mouth. Their steepness is a measure of the dominance of vertical over lateral growth. Knowledge of normal growth changes will help to predict soft tissue changes produced by orthodontic or surgical treatment in the faces of children.

Angular distortion in the orthopantomogram.

The orthopantomogram is in popular use in orthodontic diagnosis and monitoring treatment progress. Being a laminographic-type radiograph, its image suffers from a variable degree of linear distortion and this has limited its use as a research tool. A wire-mesh frame shaped to represent the curvature of the dentition in the jaws, with lead shots representing the long axes of the teeth as well as certain skeletal landmarks, was used to investigate the accuracy of projection of its structures on to the X-ray film of the orthopantomograph. Angular parameters were used to identify and assess both the magnitude and distribution of angular distortion of the radiographic image. The canine--premolar region of both arches expressed the greatest amount of angular distortion and variability. The third molar regions, together with the landmarks projected at a lower level on the radiograph, were the least variable. The applications and implications of the findings are discussed.

Stereophotographic measurement of change in facial soft tissue morphology following surgery.

Changes in soft tissue morphology induced by surgery are generally analysed using midline profiles only, derived from photographs and cephalometric radiographs. Full face photographs supplement these records. Soft tissues and their changes can be measured in three dimensions using stereophotography. This report described how the three dimensional changes produced by facial surgery were measured for a patient undergoing surgery to the mandible.

Quantitative assessment of the occlusal features.

There is no widely accepted quantitative method for assessing occlusion. The wide variation in epidemiological studies is due to the use of quantitative terms, which are subjective and allow a broad range of interpretation. A new, simple reproducible and valid quantitative method of assessing occlusion which is suitable for epidemiological and clinical use is described. Four instruments are used for direct measurement of occlusal traits. An overbite gauge has been devised and three other measuring instruments have been modified to measure overjet and crowding of the teeth. Each dental arch is divided into three segments, an incisal segment and two buccal segments. Each segment is assessed in terms of intra-arch alignment and inter-arch relationship (in occlusion). The method has been field tested and proved to be practical and valid.