Changes in the soft tissue chin after orthodontic treatment Ruchi Nanda Singh, DDS, MS Garden Grove, Calif. The study envisages changes in the contour of the soft tissue chin immediately and 5 years after orthodontic treatment in a group of 31 male and 29 female patients. The group was classified according to facial types and whether treatment involved extraction of first premolar teeth. The average age before treatment was 10 years 7 months, immediately after treatment it was 14 years 6 months, and 5 years after treatment was 21 years 6 months. The chin contour was studied from cephalometric x-ray tracings. The facial types--mesofacial, brachyfacial, and dolichofacialNwere identified on the basis of cephalometric analysis. The chin thickness was registered at six different locations around the symphysis, from the point on the soft tissue chin corresponding to B point to the chin point corresponding to menton. Statistical means and standard deviations for all of the six chin thicknesses were calculated. It was found that the overall soft tissue chin thickness increased after orthodontic treatment. The females had less increase at all levels than the males. The dolichofacial group showed a greater increase in the soft tissue chin thickness after treatment. The mesofacial and brachyfacial groups of females showed no statistically significant increases. Regression tests of independent variables, including age, sex, facial type, and such other cephalometric measurements as T - A Pog, I to A Pog, mandibular plane, mandibular arc, facial axis, lower face height, and classification of malocclusion, indicated that age, sex, and facial type were the only variables that influenced the soft tissue chin thickness. (AMJ ORTHOD DENTOFAC ORTHOP 1990;98:41-6.)
H a r m o n i o u s soft tissue profile, an important treatment goal in orthodontics, is sometimes difficult to attain because the soft tissue overlying the teeth and bones is highly variable in its thickness. These variations not only are due to imbalance of the dental and skeletal structures but are also a result of individual variations in the thickness and tone of the soft tissues. Disharmonies and disproportions of the face, as well as imbalances of the lips and their surrounding musculature, have been classified in various ways by Burstone, ~ Ricketts, 2"3 Peck and Peck, 4 and Midtgard et al.,5 among others. Muscle pull and oral habits have a strong influence on the contours of the facial integument. Attempts by patients with protrusion of the maxillary and/or mandibular incisors to gain lip closure result in lip strain, which is accompanied by mentalis function and elevation of the integument of the chin. In most instances orthodontic treatment can correct this problem and produce a smooth contour of the soft tissue chin.
Partially supported by a grant from the Foundation for Orthodontic Research. 8/1/12936
Research on growth 6-9 and development of the dentition, facial skeleton, and related soft tissues indicates that in girls most of the growth is completed by the age of 15 years, whereas boys continue to grow past the age of 18 years. Also, girls do not attain the same degree of straightness in the facial profile that boys do. Growth in thickness of the soft tissue over the chin between the ages of 3 and 18 years has been reported by Subtelny, '° who found that the total increase was 2.4 mm in boys and 1.0 mm in girls. Burstone ~1 found soft tissue thickness at supramentale (B point) of 0.2 mm in boys and 0.9 mm in girls; at the level of pogonion (Po) the increase was 0.8 mm for both sexes. These changes were minimal because the sample included adolescents (14.7 years) and adults. Bowker and Meredith t2 found an increment of soft tissue thickness of 0.0 mm at supramentale for boys and 0.2 mm for girls between the ages of 5 and 14 years; at pogonion, the increment was 1 mm for both sexes. Nanda et al. ~3 reported a study on a longitudinal sample of 40 subjects between the ages of 7 and 18 years. They found that the total increment in thickness of the lip at supramentale, on average, was 2.8 mm for boys and 1.6 mm for girls; at pogonion, it was 2.4 mm for boys and 1.5 mm for girls. i
41
Am. J. Orthod. Dentofac. Orthop. July 1990
Singh
42
Table I. Mean soft tissue thickness (in millimeters) according to facial type and sex Mesofacial
SoB tissue point
B a b c d e
Treatment time
Tt I"2 T5 Tt "I"2 T~ T~ T2 T~ Tt "1"2 T~ Tj "1"2 T5 T~ "1"2 T~
Brachffacial
Dolichofacial
F
M
Both sexes
F
M
Both sexes
F
I M
Both sexes
12.8(1.4) 12.6(1.3) 13.1(1.8) 12.8(2.0) 13.0(1.8) 13.5(2.7) 12.4(2.1) 12.5(2.2) 12,2(2.3) 10.4(2,4) 10.9(2.4) 9.9(2.1) 8.6(2.6) 9.0(2,2) 7.8(I.4) 7.9(3.0) 8.4(2.5) 7.2(1.0)
12,0(1.8) 13,3(1.6) 13.6(0.9) 11.3(1.6) 11.7(1.6) 12.1(i.6) 10.6(1.6) 10.6(1.8) 11.1(1.8) 8,7(1.6) 8.3(1.7) 9.6(1.7) 6.8(1.2) 6.8(0.9) 8.3(1.9) 7.0(1.3) 7.0(1.0) 8.5(2.5)
12.4(1.7) 13.0(1.5) 13.4(1.4) 12.0(1.9) 12.3(1.8) 12.7(2.2) 11.4(2.0) 11.5(2.2) 11.6(2.0) 9.5(2.1) 9.4(2.4) 9.7(1.8) 7.6(2.1) 7.8(1.9) 8.1(1.7) 7.3(2.2) 7.6(1.9) 7.9(2.0)
11.2(1.5) 11,7(1.5) 12.2(1.7) 11.6(1.0) 11.8(1.0) 11.9(1.1) 10.8(1.4) 11.0(0.8) 11.4(1.2) 9.2(1.3) 9.1(0.8) 9.7(1.2) 7.3(0.9) 7.7(0.6) 8.0(0.8) 6.8(1.7) 7.7(1.2) 7.6(I.6)
11.8(1.9) 12.9(2.3) 13.4(1.6) 11.2(1.9) 11.7(2.2) 13.6(1.5) 10.1(1.6) 9.4(1.3) 12.6(1.6) 8.8(1.3) 9.4(1.3) 11,0(1.2) 6.9(1.0) 7.6(i.2) 8.7(1.3) 6.7(I.2) 7.5(1.1) 8.8(1.0)
11.5(1.7) 12.3(1.6) 12.8(1.8) 11.4(1.5) 12.3(1.9) 12.7(1,5) 10.5(1.5) 11.3(1.7) 12.0(1.5) 9.0(1.3) 9.1(1.1) 10.3(1,3) 7.1(0.9) 7.6(0.9) 8.4(1.1) 6.8(1.2) 7.6(1.1) 8.2(1.4)
12.8(2.6) 13.7(1.9) 13.4(12.9) 11.5(2.3) 12.8(1.6) 12.9(2.0) 10.5(2.4) 11.7(1.4) 11.3(2.2) 7.9(2.5) 8.6(1.4) 8.9(2.0) 6.1(1.7) 6.6(I,3) 7.1(1.5) 6.0(1.8) 6.6(1.7) 7.1(2.0)
12.7(1.5) 13.8(1.7) 14.6(2.0) 11,8(1.6) 12.7(1.6) 13.4(2.0) 10.1(2.1) 11.3(1.6) 12.0(2.0) 7.1(1.5) 8.6(I.4) 9.5(1.2) 5.7(0.9) 7.0(1.0) 8.2(1.3) 6.1(1.0) 6.9(i.0) 8.7(1.6)
12.8(2.1) 13.7(2.3) 14.0(2.4) 11.7(1.9) 12.7(1.6) 13.1(2.0) 10.3(2.2) 11.5(1.5) 11.7(2.0) 7.5(2.1) 8.6(1.4) 9.2(1.7) 5.9(1.3) 6.8(1.1) 7.6(1.5) 6.1(1.4) 6.7(1.4) 7.9(2.0)
Standard deviations are given in parentheses. F, Female; M, male.
Soft tissue contours of the chin also vary among the three facial types. T M Dolichofacial patients have a vertical growth pattern. Such a patient may have greater alveolar height, a retrognathic chin, and a long and narrow chin symphysis. The brachyfacial patient usually has a symphysis with thick and square lines. The chin of the brachyfacial patient appears to be unaffected by orthodontic treatment, except for the adaptation of the alveolar plane, the alveolar bone, and B point? This is a retrospective study designed to evaluate changes in the soft tissue chin that may have accompanied orthodontic therapy and their overall effect on the facial profile. Changes in the soft tissue chin were considered in their relationship to the facial profile. Differences in the soft tissue morphology between the various facial types were also studied. MATERIAL AND METHODS
A sample of 60 whit e patients with cephalometric records obtained before, immediately after, and 5 years after treatment was selected from the files of the Rocky Mountain Data System. There were 31 male and 29 female subjects. The 60 patients were classified according to facial types. 14 The mesofacial group consisted of eleven male and nine female subjects and the braehyfacial and dolichofaeial groups consisted of 10 male and 10 female subjects each. Twenty-three pa-
tients were treated with extraction of four first premolars, and the remaining thirty-seven underwent nonextraction treatment. The average age before treatment was 10 years 7 months (SD 2 years 1 month). The average age after treatment was 14 years 6 months (SD 2 years I month), and the average age 5 years after treatment was 21 years 6 months (SD 3 years 5 months). To locate the various points on the cephalometric x-ray tracings of soft tissue contour Of the chin, vertical and diagonal extensions were made from the hard tissue chin to the soft tissue chin at various designated points on the symphysis. The horizontal lineswere parallel to the Frankfort horizontal plane, and the vertical extensions were parallel to the pterygoid vertical plane. The chin thickness was registered at six different locations around the symphysis. For simplicity of measurement, the alphabetical symbols B, a, b, c, d, and e are used for each of the soft tissue chin landmarks as shown in Fig. 1. The horizontal extensions were made to the soft tissue from the supramentalis point at B, protuberance menti point at a, and pogonion point at b, respectively. The vertical extension, from menton to the soft tissue chin was e. To label c and d, the horizontal extension of point b was extended horizontally to meet the vertical extension of point e. The angles formed by the intersection of the aformentioned lines were divided into thirds and
Volume 98 Number 1
Changes bz soft tissue chhz after treatment
43
Total
F
M
Both sexes
! 2.2(2.0) 12.7(2. l) 12.9(2.2) 12.0(I.9) 12.5(1.5) 12.7(2.0) I 1.2(2. l)
12.2(1.7) 13.3(1.6) 13.8(1.6) I 1.4(!.6) 12.3(1.9) 13.0(1.8) 10.3(1.7)
12.2(1.9) 13.0(I.9) 13.4(I.9) 11.7(1.8) 12.4(1.8) 12.9(1.9) 10.7(2.0)
11.7(1.6) 11.6(1.9)
11.2(1.9) 11.9(1.8)
I 1.4(1.8) 11.8(1.9)
9.1(2.3) 9.5(1.9) 9.5(1.8) 7.3(2.0) 7.7(1.7) 7.6(! .3) 6.9(2.1) 7.6(1.9) 7.3(I .6)
8.2(1.6) 8.7( 1.5) 10.0(1.5) 6.5(1.3) 7.1(1.0) 8.4(I .5) 6.6(1.2) 7.1(1.0) 8.6(1.8)
8.7(2.0) 9. l (1.7) 9.8(1.7) 6.9(1.6) 7.4(1.4) 8.0(I .4) 6.7(1.7) 7.3(1.5) 8.0(1.8) Fig. 1. Cephalometric landmarks used in the measurement of the soft tissue chin thickness. Note location of points B, a, b, c, d, and e.
extensions were drawn to the soft tissue chin to form c and d. Hard tissue to soft tissue distances were measured for each point from B to e (in millimeters) before treatment (TO, immediately after treatment (T2), and 5 years after treatment ('1"5). The recordings were measured to the nearest 0.5 mm. Statistical means and standard deviations were computed for the thickness of the soft tissue drapes at B, a, b, c, d, and e at Tt, T2, and 1"5. The changes in the soft tissue chin, according to the different facial types and for males and females, were studied with an analysis of variance test. The error of measurement for the soft tissue thicknesses was measured and found to be insignificant.
RESULTS Averages and standard deviations for the various linear dimensions from point B to e were calculated for the total sample with the different facial types and for both sexes at each treatment time (Table I). Mean dimensional changes in the soft tissue chin thickness at points B to e after treatment and 5 years after treatment are shown in Table II. The underlined numbers are the distances that showed a significant increase in the soft tissue chin thickness. It was discovered that immediately after treatment the chin thickness varies at all points on the symphysis except for the two points d and e, which are at and closest to menton (Table II). Analysis of the data revealed that soft tissue thicknesses were similar according to sex, facial type, and treatment
time. It was found that c was the most variable; lengths B and a and d and e were most often similar. Females on the whole, had a more even soft tissue chin thickness than males. After treatment, especially 5 years after treatment, the soft tissue chin thickness evens out more for the females than for the males. The results of the present study showed in the total sample that, overall, the soft tissue chin thickness increases after orthodontic treatment. The females had less increase at all levels than the males. In the dolichofacial group females showed a greater increase in the soft tissue chin thickness after treatment (T2) (Table II). Females in the mesofacial and brachyfacial groups showed no statistically significant increase in the soft tissue chin thickness. When 5-year postretention records ('1"5) were compared with those taken at the end of treatment (T2), the total female sample showed no statistically significant increase in the soft tissue thickness of the chin. The total male sample did show an increase in the soft tissue thickness of the chin when T2 and T5 records were compared (Table II). After comparison of the three facial types in males and females, as shown in Table II, it was discovered that the soft tissue chin thickness increased most in the dolichofacial group at T2 and "I"5. The mesofacial group showed the least amount of change in the soft tissue chin thickness at T2 and Ts. Regression tests were per-
44
Singh
Am. J.
Orthod.Dentofac.Orthop. July 1990
Table II. Mean changes (in millimeters) in soft tissue thickness between treatment time periods with their standard deviations according to facial type, sex, and treatment time SoO
Mesofacial
Brach)facial
tissue point
Treatment time
F
B
2-1 5-1 5-2
-0.3(1.3) 0.3(2.1) 0.6(2.0)
1.3(i.5) 1.6(1,5) 0.3(1.2)
0.6(1.6) 1.0(1.9) 0.4(1.6)
2-I 5-1 5-2 2-1 5-1 5-2 2-1 5-1 5-2 2-1 5-1 5-2
0.2 (1.4) 0.7(3.2) 0.5(2.6) 0.1(0.6) -0.2(2.1) -0.30.3) 0.5(1.5) -0.5(2.8) - 1.0(1.7) 0.4(1.1) -0,7(2.6) -1.2(2.0)
0.4(1.2) 0.8(1.5) 0.4(2.0) 0.1(1.2) 0.5(1.8) 0.5(1.7) -0.5(1.5) 0.9(2.0) 1.3(1.4) 0(1.2) 1.5(1.3) 1.5(1.6)
2-1 5-1 5-2
0.5(2.0) -0.7(2.8) -1.2(2.2)
0(1.8) 1.5(2.3) 1.5(2.6)
a
b
C
d
e
31
I Both sexes
I
Dolichofacial
31
Both sexes
F
0.5(1.9) 1.0(1.6) 0.5(0.9)
1.1(1.2) 1.6(1.7) 0.5(1.2)
0.8(1.6) 1.3(1.6) 1.5(1.0)
0.3(1.3) 0.7(2.3) 0.4(2.3) 0.1(1.3) 0.2(2.0) 0.1(1.5) 0(1.5) 0.2(2.4) 0.3(2.0) 0.2(1.2) 0.5(2.2) 0.3(2.2)
0.2(!.i) 0.3(1.0) 0.1(0.7) 0.1(1.1) 0.5(1.2) 0.4(0.9) --0.1(1.6) 0.5(I.7) 0.6(1.3) 0.4(1.1) 0.7(0.8) 0.3(1.0)
1.5(1.8) 2.4(1.5) 0.9(1.5) 1.6(1.5) 2.6(1.5) 1,0(1.4)
0.2(1.8) 0.5(2.7) 0.3(2.8)
0.9(1.3) 0.8(1,5) -0.1(.8)
0.6(1.3) 2.1(1.2) i.5(1.3) 0.7(1.3) 1.8(1.5) 1.1(1.8) 0.8(1.4) 2.0(1.9) 1.2(1.6)
F
I
M
Both sexes
0.9(1.3) 0.6(1.6) --0.3(1.1)
1.1(1.1) 1.9(1.8) 0.8(1.1)
1.0(1.2) 1.2(1.8) 0.2(1.2)
0.9(i.6) 1.4(1.6) 0.5(1.2) 0.8(1.5) 1.5(1.7) 0.7(1.2)
1.3(1.6) 1.3(1.2) 0(1.4) 1.2(1.5) 0.8(2.4) 0.4(1.9)
0.8(1.6) 1.6(1.1) 0.7(1.3) 1.2(2.1) 1.9(1.5) 0.7(1.3)
1.1(1.6) 1.4(1.1) 0.4(1.4) 1.2(1.8) 1.4(2.0) 0.2(1.7)
0.3(1.5) 1.3(1.6) 1.1(1.4) 0.5(1.2) 1.2(1.3) 0.7(1.5) 0.8(1.3) 1.4(i.8) 0.6(I.8)
0.7(1.8) 1.0(2.7) 0.3(1.7) 0.4(1.3) 0.9(1.4) 0.5(1.0) 0.5(1.3) 1.0(1.4) 0.5(0.9)
1.4(1.7) 2.4(1.8) 1.0(1.3) 1.3(1.2) 2.5(1.7) 1.2(1.2)
1.0(1.7) 1.7(2.4) 0.6(1.5) 0.9(1.3) 1.7(1.7) 0.8(1.1)
0.8(1.0) 2,6(1.4) 1.7(!.5)
0.7(1.1)
i.8(1.6) 1.1(1.3)
The underlined figures axe increments that were statistically significant at p > 0.05. F, Female; M, male.
formed to find if the independent variables of age, sex, facial type, various other cephalometric measurements, such as ]'-A-Poe, l_-APog, mandibular plane, mandibular arc, facial axis, and lower face height, and classification of malocclusion affected the points a - e at T~, T2, or Ts. It was determined that only variables of age, sex, and facial type influenced the points B to e. DISCUSSION
The soft tissue thickness for the total sample, as demonstrated in Table II, increased immediately and 5 years after treatment, with a range of 0.4 to 1.2 mm on points B to e. The total mesofacial soft tissue chin thickness increased only at points B and a, which were within a range of 0.3 to 0.6 mm immediately after treatment; the 5-year posttreatment range was 0.7 to 1.0 mm. In brachyfacial patients soft tissue chin thickness increased at all points; the range was 0.3 to 0.9 mm immediately after treatment and 1.2 to 1.5 mm 5 years after treatment. The greatest increase in soft tissue chin thickness was in the dolichofacial group. All points around the symphysis increased, with a range of 0.7 to 1.2 mm immediately after treatment and 1.2 to 1.89 mm 5 years
after treatment. Dolichofacial males showed the greatest amount of increase at the end of treatment, with a range of 0.9 to 1.4 ram; there was a range of 1.6 to 2.5 mm 5 years after treatment. These changes may be attributed to the reduction of overjet and/or bimaxillary protrusion. Previous research ~5a6shows that the soft tissue chin is closely related to the degree of prognathism of the chin symphysis. In nearly all cases studied, however, the distribution of the soft tissue of the chin over the symphysis changed as the teeth were moved) °'7 The soft tissue chin of the total male sample increased uniformly in all facial types, whereas the total female sample did not show any significant increase in the thickness of the soft tissue chin (Table II). The soft tissue follows the bony contour in females more closely than it does in males and in the mesofacial group more than in the other two groups. Merrifield 7 stated, on the basis of his measurements, that adult males have 2.4 mm more "total chin" than females. He measured this "total chin" between the line NB and the soft tissue pogonion. A longitudinal study by Nanda et el? 3 on the thickness of soft tissue chin at points supramentale and pogonion shows total incre-
Volume98 Number 1
Changes in soft tissue chin after treatment
Total F 0.4(I .6) 0.6(1.7) 0.2(1.4) 0.6(I .4) 0.8(2.0)
I
M
I
Both sexes
!. 1(1.2) 1.7(1.6) 0.5(I .2) 0.9(I .6) 1.6(I .5)
0.8(1.5) 1.2( 1.7) 0.4(1.3) 0.7(1.5) 1.2(1.8)
O. 1(1.7)
0.7(1.6)
0.4(1.6)
0.5(1.4) 0.4(2.0)
0.9(1.7) 1.6(I.8)
0.7(1.6) 1.0(2.0)
- 0.1(1.4)
0.7(1.4)
0.3(1.5)
0.4(1.6) 0.3(2.4)
0.4(1.6) 1.8(1.8)
0.4(1.6) 1.1(2.2)
- 0.2( 1.7)
1.3(1.3)
0.7(1.6)
0.4(1.1) 0.3(1.8)
0.6(1.3) 1.9(1.5)
0.5(1.2) 1.1(1.8)
- 0.8(1.5)
t.3(I.5)
0.6(1.6)
0.7(1.5) 0.4(2.0) - 0.2( 1.8)
0.5(1.4) 2.0(I .9) 1.5(1.9)
0.6(I.5) 1.2(2.1) 0.7(2.0)
ments of 2.8 mm for the males and 1.6 mm for the females and 2.4 mm for the males and 1.5 mm for the females, respectively. Previous studies 1°-~2 on the growth changes in the integument of the chin show even smaller increments. None of the studies, however, have reported changes based on the classification of facial type. The current investigation shows that the soft tissue changes after orthodontic treatment (T2-T0 were significant and that consideration of facial type is important in estimating posttreatment changes at the chin. A Student t test performed on females, showed that at the age of 15 years and older, there is no significant difference between the posttreatment and 5-year posttreatment measurements at the various points from B to e on the chin. The results of T~ and T2 show that the overall soft tissue chin thickness was greater in the brachyfacial sample than the dolichofacial sample at points c, d, and e (Table I). The overall tissue distance around the symphysis in the brachyfacial sample was equal to, or less than, that of the mesofacial sample. The fact that the brachyfacial sample has no clear advantage in the thickness of soft tissue chin as compared to the mesofacial group does not correlate with the fact that, because of the short vertical growth pattern evident in the brachyfacial pattern, this sample would be expected to have
45
greater linear soft tissue distances at points B to e at each treatment time. Only at T5 were the soft tissue distances at points b, c, and e larger in the brachyfacial group than in the mesofacial group and the points b, c, d, and e had larger distances in the brachyfacial group than in the dolichofacial group. Before treatment (T1) the total (male and female) dolichofaeial sample measurements from the hard to the soft tissue chin were as much as 2 mm less than those of the mesofacial and brachyfacial groups, especially at points c, d, and e (Table I). The dolichofacial group at T2 showed a consistent increase in the distances from the hard to the soft tissue chin, especially at points a, b, and c. At some points (a, b, c, and d) the dolichofacial group showed a greater increase in the distances at the soft and hard tissue chin than did the mesofacial and brachyfacial groups. The mentalis muscle is more likely to be strained in the pretreatment dolichofacial group and, as orthodontic treatment relieves the strain, the chin thickness at points c, d, and e increases. Patients at pretreatment ages of less than 9 years would be expected to have smaller linear soft tissue chin dimensions. There were 22 patients below 9 years of age and 38 above 9 years at Ti. A t test applied to the various soft tissue chin dimensions between the two age groups showed that only the thickness at B point was larger in the older group. The data in this study indicate that the soft tissue chin thickness varies in different individual facial types, as well as in the two sexes (Table I). After adjustment for sex and age, the facial type was the primary determinant in the amount of change that occurred in the soft tissue chin after orthodontic treatment. Holdaway 9 stressed that one of the fundamental traits associated with facial beauty includes a soft tissue chin that is nicely positioned in the facial profile. He recorded the horizontal measurement of the soft tisstie chin thickness (suprapogonion to the soft tissue suprapogonion) and determined the average to be 10 to 12 mm. However, there has been virtually no discussion of the soft tissue on the chin covering the entire symphysis. In previous studies, the horizontal thickness of the soft tissue on the chin has been measured only from pogonion, Ricketts' suprapogonion point, and B point. This research gives averages for various additional soft tissue landmarks on the chin as well as demonstrates the changes between sexes and the three facial types. The differential changes recorded after treatment at different points on the symphysis emphasize the need to consider the chin integument not only at points B and
46
Am. J. Orthod. Dentofac. Orthop. July 1990
Singh
pogonion but also at other points suggested in this study. CONCLUSIONS After orthodontic treatment, the soft tissue chin thickness increased at all the points measured around the symphysis of the chin in both male and female patients. Males showed a greater increase than the females in the thickness of the soft tissue chin at all points, B to e, and "1"2and "1"5. The soft tissue chin thickness increased most in the dolichofacial group of males at T2 and Ts. The mesofacial females showed the least amount of increase in the soft tissue chin thickness at T2 and 'I"5. The brachyfacial pattern has a larger soft tissue chin thickness than the dolichofacial pattern at points c, d, and e at Tt, "['2, and T~. However, the posttreatment change in the dolichofacial group was significantly greater at these points. No facial type showed an even thickness of soft tissue chin around the symphysis before treatment or immediately and 5 years after treatment. The soft tissue chin thickness did not seem to increase after the age of 15 years in female patients. If the lip and chin thickness is recognized to be excessively thin or heavy at the onset of treatment, it may mean the difference between esthetic success and failure of the soft tissue treatment. It must be emphasized that changes in the basic position of the soft tissue nose and the soft tissue chin occur primarily as a function of growth, and there is little that an orthodontist can do to alter them. Within reason, the clinician can possibly exert some control over the soft tissue chin. This study shows that limited changes in different parts of the soft tissue integument of the chin can be obtained with judicious treatment procedures. This article is based on a master's thesis submitted to the faculty of the Graduate College, Loma Linda University,
1984. The assistance of Dr. Ram S. Nanda in the preparation of this manuscript is appreciated. REFERENCES 1. BurstoneCJ. The integumentalprofile. AngleOrthod 1958;44:125. 2. Ricketts RM. The influenceof orthodontic treatment on facial growth and development. AM J ORTHOD1960;30:103-33. 3. Rickens RM. Esthetics, environmentand the law of lip relation. Ar,I J ORa'HOD1968;54:272-89. 4. Peck H, Peck S. A concept of facial esthetics. Angle Orthod 1970;40:284-318. 5. MidtgardJ, BjorkG, Linder-AronsenS. Reproducibilityofcephalometriclandmarksand errors of measurementof cephalometric cranial distances. Angle Orthod 1974;44:56-61. 6. Nanda RS. Growth changes in skeletal-facial profile and their significance in orthodontic diagnosis. AM J Oarnoo 1971; 59:501-13. 7. MerrifieldLL. The profile line as an aid in criticallyevaluating facial esthetics. AM J ORTHOD1966;52:804-21. 8. Neger M. A quantitativemethod of the evaluationof the soft tissue facial profile. AM J OaTHOD1959;45:738-51. 9. HoldawayRH. Soft tissue cephalometricanalysisand its use in orthodontic treatmentplanning. AM J ORTHOD1983;84:1-36. 10. SubtelnyJD. A longitudinalstudy of soft tissue facial structures and their profile characteristics defined in relationto underlying structures. AM J ORTHOD1959;45:481-507. 11. Burstone CJ. Integumental contour and extension patterns. Angle
Orthod 1959;29:93-104. 12. BowkerWD, Meredith HV. A metric analysisof the facial profile. Angle Orthod 1959;29:149-160. 13. Nanda RS, Meng HP, Kapila S, Goorhuis Y. Growth changes in the soft tissue facial profile. Accepted for publication,Angle Orthod 1989. 14. Ricketts RM. Cephalometric synthesis. AM J ORTnOD 1960; 46:647-73. 15. HambletonRS. The soft-tissuecoveringof the skeletal face as related to orthodonticproblems. A.~tJ OaTnoo 1964;50:405-20. 16. HillesundE, Fjeld D, ZachrissonBU. Reliabilityof soft tissue profile in cephalometrics. Ar,l J ORTHOD1978;74:537-50. 17. Riedel RA. Esthetics and its relation to orthodontic therapy. Angle Orthod 1950;22:168-78. Reprint requests to: Dr. Ruehi Nanda Singh 12570 Brookhurst St. Suite 3 Garden Grove, CA 92640
H a r m o n i o u s soft tissue profile, an important treatment goal in orthodontics, is sometimes difficult to attain because the soft tissue overlying the teeth and bones is highly variable in its thickness. These variations not only are due to imbalance of the dental and skeletal structures but are also a result of individual variations in the thickness and tone of the soft tissues. Disharmonies and disproportions of the face, as well as imbalances of the lips and their surrounding musculature, have been classified in various ways by Burstone, ~ Ricketts, 2"3 Peck and Peck, 4 and Midtgard et al.,5 among others. Muscle pull and oral habits have a strong influence on the contours of the facial integument. Attempts by patients with protrusion of the maxillary and/or mandibular incisors to gain lip closure result in lip strain, which is accompanied by mentalis function and elevation of the integument of the chin. In most instances orthodontic treatment can correct this problem and produce a smooth contour of the soft tissue chin.
Partially supported by a grant from the Foundation for Orthodontic Research. 8/1/12936
Research on growth 6-9 and development of the dentition, facial skeleton, and related soft tissues indicates that in girls most of the growth is completed by the age of 15 years, whereas boys continue to grow past the age of 18 years. Also, girls do not attain the same degree of straightness in the facial profile that boys do. Growth in thickness of the soft tissue over the chin between the ages of 3 and 18 years has been reported by Subtelny, '° who found that the total increase was 2.4 mm in boys and 1.0 mm in girls. Burstone ~1 found soft tissue thickness at supramentale (B point) of 0.2 mm in boys and 0.9 mm in girls; at the level of pogonion (Po) the increase was 0.8 mm for both sexes. These changes were minimal because the sample included adolescents (14.7 years) and adults. Bowker and Meredith t2 found an increment of soft tissue thickness of 0.0 mm at supramentale for boys and 0.2 mm for girls between the ages of 5 and 14 years; at pogonion, the increment was 1 mm for both sexes. Nanda et al. ~3 reported a study on a longitudinal sample of 40 subjects between the ages of 7 and 18 years. They found that the total increment in thickness of the lip at supramentale, on average, was 2.8 mm for boys and 1.6 mm for girls; at pogonion, it was 2.4 mm for boys and 1.5 mm for girls. i
41
Am. J. Orthod. Dentofac. Orthop. July 1990
Singh
42
Table I. Mean soft tissue thickness (in millimeters) according to facial type and sex Mesofacial
SoB tissue point
B a b c d e
Treatment time
Tt I"2 T5 Tt "I"2 T~ T~ T2 T~ Tt "1"2 T~ Tj "1"2 T5 T~ "1"2 T~
Brachffacial
Dolichofacial
F
M
Both sexes
F
M
Both sexes
F
I M
Both sexes
12.8(1.4) 12.6(1.3) 13.1(1.8) 12.8(2.0) 13.0(1.8) 13.5(2.7) 12.4(2.1) 12.5(2.2) 12,2(2.3) 10.4(2,4) 10.9(2.4) 9.9(2.1) 8.6(2.6) 9.0(2,2) 7.8(I.4) 7.9(3.0) 8.4(2.5) 7.2(1.0)
12,0(1.8) 13,3(1.6) 13.6(0.9) 11.3(1.6) 11.7(1.6) 12.1(i.6) 10.6(1.6) 10.6(1.8) 11.1(1.8) 8,7(1.6) 8.3(1.7) 9.6(1.7) 6.8(1.2) 6.8(0.9) 8.3(1.9) 7.0(1.3) 7.0(1.0) 8.5(2.5)
12.4(1.7) 13.0(1.5) 13.4(1.4) 12.0(1.9) 12.3(1.8) 12.7(2.2) 11.4(2.0) 11.5(2.2) 11.6(2.0) 9.5(2.1) 9.4(2.4) 9.7(1.8) 7.6(2.1) 7.8(1.9) 8.1(1.7) 7.3(2.2) 7.6(1.9) 7.9(2.0)
11.2(1.5) 11,7(1.5) 12.2(1.7) 11.6(1.0) 11.8(1.0) 11.9(1.1) 10.8(1.4) 11.0(0.8) 11.4(1.2) 9.2(1.3) 9.1(0.8) 9.7(1.2) 7.3(0.9) 7.7(0.6) 8.0(0.8) 6.8(1.7) 7.7(1.2) 7.6(I.6)
11.8(1.9) 12.9(2.3) 13.4(1.6) 11.2(1.9) 11.7(2.2) 13.6(1.5) 10.1(1.6) 9.4(1.3) 12.6(1.6) 8.8(1.3) 9.4(1.3) 11,0(1.2) 6.9(1.0) 7.6(i.2) 8.7(1.3) 6.7(I.2) 7.5(1.1) 8.8(1.0)
11.5(1.7) 12.3(1.6) 12.8(1.8) 11.4(1.5) 12.3(1.9) 12.7(1,5) 10.5(1.5) 11.3(1.7) 12.0(1.5) 9.0(1.3) 9.1(1.1) 10.3(1,3) 7.1(0.9) 7.6(0.9) 8.4(1.1) 6.8(1.2) 7.6(1.1) 8.2(1.4)
12.8(2.6) 13.7(1.9) 13.4(12.9) 11.5(2.3) 12.8(1.6) 12.9(2.0) 10.5(2.4) 11.7(1.4) 11.3(2.2) 7.9(2.5) 8.6(1.4) 8.9(2.0) 6.1(1.7) 6.6(I,3) 7.1(1.5) 6.0(1.8) 6.6(1.7) 7.1(2.0)
12.7(1.5) 13.8(1.7) 14.6(2.0) 11,8(1.6) 12.7(1.6) 13.4(2.0) 10.1(2.1) 11.3(1.6) 12.0(2.0) 7.1(1.5) 8.6(I.4) 9.5(1.2) 5.7(0.9) 7.0(1.0) 8.2(1.3) 6.1(1.0) 6.9(i.0) 8.7(1.6)
12.8(2.1) 13.7(2.3) 14.0(2.4) 11.7(1.9) 12.7(1.6) 13.1(2.0) 10.3(2.2) 11.5(1.5) 11.7(2.0) 7.5(2.1) 8.6(1.4) 9.2(1.7) 5.9(1.3) 6.8(1.1) 7.6(1.5) 6.1(1.4) 6.7(1.4) 7.9(2.0)
Standard deviations are given in parentheses. F, Female; M, male.
Soft tissue contours of the chin also vary among the three facial types. T M Dolichofacial patients have a vertical growth pattern. Such a patient may have greater alveolar height, a retrognathic chin, and a long and narrow chin symphysis. The brachyfacial patient usually has a symphysis with thick and square lines. The chin of the brachyfacial patient appears to be unaffected by orthodontic treatment, except for the adaptation of the alveolar plane, the alveolar bone, and B point? This is a retrospective study designed to evaluate changes in the soft tissue chin that may have accompanied orthodontic therapy and their overall effect on the facial profile. Changes in the soft tissue chin were considered in their relationship to the facial profile. Differences in the soft tissue morphology between the various facial types were also studied. MATERIAL AND METHODS
A sample of 60 whit e patients with cephalometric records obtained before, immediately after, and 5 years after treatment was selected from the files of the Rocky Mountain Data System. There were 31 male and 29 female subjects. The 60 patients were classified according to facial types. 14 The mesofacial group consisted of eleven male and nine female subjects and the braehyfacial and dolichofaeial groups consisted of 10 male and 10 female subjects each. Twenty-three pa-
tients were treated with extraction of four first premolars, and the remaining thirty-seven underwent nonextraction treatment. The average age before treatment was 10 years 7 months (SD 2 years 1 month). The average age after treatment was 14 years 6 months (SD 2 years I month), and the average age 5 years after treatment was 21 years 6 months (SD 3 years 5 months). To locate the various points on the cephalometric x-ray tracings of soft tissue contour Of the chin, vertical and diagonal extensions were made from the hard tissue chin to the soft tissue chin at various designated points on the symphysis. The horizontal lineswere parallel to the Frankfort horizontal plane, and the vertical extensions were parallel to the pterygoid vertical plane. The chin thickness was registered at six different locations around the symphysis. For simplicity of measurement, the alphabetical symbols B, a, b, c, d, and e are used for each of the soft tissue chin landmarks as shown in Fig. 1. The horizontal extensions were made to the soft tissue from the supramentalis point at B, protuberance menti point at a, and pogonion point at b, respectively. The vertical extension, from menton to the soft tissue chin was e. To label c and d, the horizontal extension of point b was extended horizontally to meet the vertical extension of point e. The angles formed by the intersection of the aformentioned lines were divided into thirds and
Volume 98 Number 1
Changes bz soft tissue chhz after treatment
43
Total
F
M
Both sexes
! 2.2(2.0) 12.7(2. l) 12.9(2.2) 12.0(I.9) 12.5(1.5) 12.7(2.0) I 1.2(2. l)
12.2(1.7) 13.3(1.6) 13.8(1.6) I 1.4(!.6) 12.3(1.9) 13.0(1.8) 10.3(1.7)
12.2(1.9) 13.0(I.9) 13.4(I.9) 11.7(1.8) 12.4(1.8) 12.9(1.9) 10.7(2.0)
11.7(1.6) 11.6(1.9)
11.2(1.9) 11.9(1.8)
I 1.4(1.8) 11.8(1.9)
9.1(2.3) 9.5(1.9) 9.5(1.8) 7.3(2.0) 7.7(1.7) 7.6(! .3) 6.9(2.1) 7.6(1.9) 7.3(I .6)
8.2(1.6) 8.7( 1.5) 10.0(1.5) 6.5(1.3) 7.1(1.0) 8.4(I .5) 6.6(1.2) 7.1(1.0) 8.6(1.8)
8.7(2.0) 9. l (1.7) 9.8(1.7) 6.9(1.6) 7.4(1.4) 8.0(I .4) 6.7(1.7) 7.3(1.5) 8.0(1.8) Fig. 1. Cephalometric landmarks used in the measurement of the soft tissue chin thickness. Note location of points B, a, b, c, d, and e.
extensions were drawn to the soft tissue chin to form c and d. Hard tissue to soft tissue distances were measured for each point from B to e (in millimeters) before treatment (TO, immediately after treatment (T2), and 5 years after treatment ('1"5). The recordings were measured to the nearest 0.5 mm. Statistical means and standard deviations were computed for the thickness of the soft tissue drapes at B, a, b, c, d, and e at Tt, T2, and 1"5. The changes in the soft tissue chin, according to the different facial types and for males and females, were studied with an analysis of variance test. The error of measurement for the soft tissue thicknesses was measured and found to be insignificant.
RESULTS Averages and standard deviations for the various linear dimensions from point B to e were calculated for the total sample with the different facial types and for both sexes at each treatment time (Table I). Mean dimensional changes in the soft tissue chin thickness at points B to e after treatment and 5 years after treatment are shown in Table II. The underlined numbers are the distances that showed a significant increase in the soft tissue chin thickness. It was discovered that immediately after treatment the chin thickness varies at all points on the symphysis except for the two points d and e, which are at and closest to menton (Table II). Analysis of the data revealed that soft tissue thicknesses were similar according to sex, facial type, and treatment
time. It was found that c was the most variable; lengths B and a and d and e were most often similar. Females on the whole, had a more even soft tissue chin thickness than males. After treatment, especially 5 years after treatment, the soft tissue chin thickness evens out more for the females than for the males. The results of the present study showed in the total sample that, overall, the soft tissue chin thickness increases after orthodontic treatment. The females had less increase at all levels than the males. In the dolichofacial group females showed a greater increase in the soft tissue chin thickness after treatment (T2) (Table II). Females in the mesofacial and brachyfacial groups showed no statistically significant increase in the soft tissue chin thickness. When 5-year postretention records ('1"5) were compared with those taken at the end of treatment (T2), the total female sample showed no statistically significant increase in the soft tissue thickness of the chin. The total male sample did show an increase in the soft tissue thickness of the chin when T2 and T5 records were compared (Table II). After comparison of the three facial types in males and females, as shown in Table II, it was discovered that the soft tissue chin thickness increased most in the dolichofacial group at T2 and "I"5. The mesofacial group showed the least amount of change in the soft tissue chin thickness at T2 and Ts. Regression tests were per-
44
Singh
Am. J.
Orthod.Dentofac.Orthop. July 1990
Table II. Mean changes (in millimeters) in soft tissue thickness between treatment time periods with their standard deviations according to facial type, sex, and treatment time SoO
Mesofacial
Brach)facial
tissue point
Treatment time
F
B
2-1 5-1 5-2
-0.3(1.3) 0.3(2.1) 0.6(2.0)
1.3(i.5) 1.6(1,5) 0.3(1.2)
0.6(1.6) 1.0(1.9) 0.4(1.6)
2-I 5-1 5-2 2-1 5-1 5-2 2-1 5-1 5-2 2-1 5-1 5-2
0.2 (1.4) 0.7(3.2) 0.5(2.6) 0.1(0.6) -0.2(2.1) -0.30.3) 0.5(1.5) -0.5(2.8) - 1.0(1.7) 0.4(1.1) -0,7(2.6) -1.2(2.0)
0.4(1.2) 0.8(1.5) 0.4(2.0) 0.1(1.2) 0.5(1.8) 0.5(1.7) -0.5(1.5) 0.9(2.0) 1.3(1.4) 0(1.2) 1.5(1.3) 1.5(1.6)
2-1 5-1 5-2
0.5(2.0) -0.7(2.8) -1.2(2.2)
0(1.8) 1.5(2.3) 1.5(2.6)
a
b
C
d
e
31
I Both sexes
I
Dolichofacial
31
Both sexes
F
0.5(1.9) 1.0(1.6) 0.5(0.9)
1.1(1.2) 1.6(1.7) 0.5(1.2)
0.8(1.6) 1.3(1.6) 1.5(1.0)
0.3(1.3) 0.7(2.3) 0.4(2.3) 0.1(1.3) 0.2(2.0) 0.1(1.5) 0(1.5) 0.2(2.4) 0.3(2.0) 0.2(1.2) 0.5(2.2) 0.3(2.2)
0.2(!.i) 0.3(1.0) 0.1(0.7) 0.1(1.1) 0.5(1.2) 0.4(0.9) --0.1(1.6) 0.5(I.7) 0.6(1.3) 0.4(1.1) 0.7(0.8) 0.3(1.0)
1.5(1.8) 2.4(1.5) 0.9(1.5) 1.6(1.5) 2.6(1.5) 1,0(1.4)
0.2(1.8) 0.5(2.7) 0.3(2.8)
0.9(1.3) 0.8(1,5) -0.1(.8)
0.6(1.3) 2.1(1.2) i.5(1.3) 0.7(1.3) 1.8(1.5) 1.1(1.8) 0.8(1.4) 2.0(1.9) 1.2(1.6)
F
I
M
Both sexes
0.9(1.3) 0.6(1.6) --0.3(1.1)
1.1(1.1) 1.9(1.8) 0.8(1.1)
1.0(1.2) 1.2(1.8) 0.2(1.2)
0.9(i.6) 1.4(1.6) 0.5(1.2) 0.8(1.5) 1.5(1.7) 0.7(1.2)
1.3(1.6) 1.3(1.2) 0(1.4) 1.2(1.5) 0.8(2.4) 0.4(1.9)
0.8(1.6) 1.6(1.1) 0.7(1.3) 1.2(2.1) 1.9(1.5) 0.7(1.3)
1.1(1.6) 1.4(1.1) 0.4(1.4) 1.2(1.8) 1.4(2.0) 0.2(1.7)
0.3(1.5) 1.3(1.6) 1.1(1.4) 0.5(1.2) 1.2(1.3) 0.7(1.5) 0.8(1.3) 1.4(i.8) 0.6(I.8)
0.7(1.8) 1.0(2.7) 0.3(1.7) 0.4(1.3) 0.9(1.4) 0.5(1.0) 0.5(1.3) 1.0(1.4) 0.5(0.9)
1.4(1.7) 2.4(1.8) 1.0(1.3) 1.3(1.2) 2.5(1.7) 1.2(1.2)
1.0(1.7) 1.7(2.4) 0.6(1.5) 0.9(1.3) 1.7(1.7) 0.8(1.1)
0.8(1.0) 2,6(1.4) 1.7(!.5)
0.7(1.1)
i.8(1.6) 1.1(1.3)
The underlined figures axe increments that were statistically significant at p > 0.05. F, Female; M, male.
formed to find if the independent variables of age, sex, facial type, various other cephalometric measurements, such as ]'-A-Poe, l_-APog, mandibular plane, mandibular arc, facial axis, and lower face height, and classification of malocclusion affected the points a - e at T~, T2, or Ts. It was determined that only variables of age, sex, and facial type influenced the points B to e. DISCUSSION
The soft tissue thickness for the total sample, as demonstrated in Table II, increased immediately and 5 years after treatment, with a range of 0.4 to 1.2 mm on points B to e. The total mesofacial soft tissue chin thickness increased only at points B and a, which were within a range of 0.3 to 0.6 mm immediately after treatment; the 5-year posttreatment range was 0.7 to 1.0 mm. In brachyfacial patients soft tissue chin thickness increased at all points; the range was 0.3 to 0.9 mm immediately after treatment and 1.2 to 1.5 mm 5 years after treatment. The greatest increase in soft tissue chin thickness was in the dolichofacial group. All points around the symphysis increased, with a range of 0.7 to 1.2 mm immediately after treatment and 1.2 to 1.89 mm 5 years
after treatment. Dolichofacial males showed the greatest amount of increase at the end of treatment, with a range of 0.9 to 1.4 ram; there was a range of 1.6 to 2.5 mm 5 years after treatment. These changes may be attributed to the reduction of overjet and/or bimaxillary protrusion. Previous research ~5a6shows that the soft tissue chin is closely related to the degree of prognathism of the chin symphysis. In nearly all cases studied, however, the distribution of the soft tissue of the chin over the symphysis changed as the teeth were moved) °'7 The soft tissue chin of the total male sample increased uniformly in all facial types, whereas the total female sample did not show any significant increase in the thickness of the soft tissue chin (Table II). The soft tissue follows the bony contour in females more closely than it does in males and in the mesofacial group more than in the other two groups. Merrifield 7 stated, on the basis of his measurements, that adult males have 2.4 mm more "total chin" than females. He measured this "total chin" between the line NB and the soft tissue pogonion. A longitudinal study by Nanda et el? 3 on the thickness of soft tissue chin at points supramentale and pogonion shows total incre-
Volume98 Number 1
Changes in soft tissue chin after treatment
Total F 0.4(I .6) 0.6(1.7) 0.2(1.4) 0.6(I .4) 0.8(2.0)
I
M
I
Both sexes
!. 1(1.2) 1.7(1.6) 0.5(I .2) 0.9(I .6) 1.6(I .5)
0.8(1.5) 1.2( 1.7) 0.4(1.3) 0.7(1.5) 1.2(1.8)
O. 1(1.7)
0.7(1.6)
0.4(1.6)
0.5(1.4) 0.4(2.0)
0.9(1.7) 1.6(I.8)
0.7(1.6) 1.0(2.0)
- 0.1(1.4)
0.7(1.4)
0.3(1.5)
0.4(1.6) 0.3(2.4)
0.4(1.6) 1.8(1.8)
0.4(1.6) 1.1(2.2)
- 0.2( 1.7)
1.3(1.3)
0.7(1.6)
0.4(1.1) 0.3(1.8)
0.6(1.3) 1.9(1.5)
0.5(1.2) 1.1(1.8)
- 0.8(1.5)
t.3(I.5)
0.6(1.6)
0.7(1.5) 0.4(2.0) - 0.2( 1.8)
0.5(1.4) 2.0(I .9) 1.5(1.9)
0.6(I.5) 1.2(2.1) 0.7(2.0)
ments of 2.8 mm for the males and 1.6 mm for the females and 2.4 mm for the males and 1.5 mm for the females, respectively. Previous studies 1°-~2 on the growth changes in the integument of the chin show even smaller increments. None of the studies, however, have reported changes based on the classification of facial type. The current investigation shows that the soft tissue changes after orthodontic treatment (T2-T0 were significant and that consideration of facial type is important in estimating posttreatment changes at the chin. A Student t test performed on females, showed that at the age of 15 years and older, there is no significant difference between the posttreatment and 5-year posttreatment measurements at the various points from B to e on the chin. The results of T~ and T2 show that the overall soft tissue chin thickness was greater in the brachyfacial sample than the dolichofacial sample at points c, d, and e (Table I). The overall tissue distance around the symphysis in the brachyfacial sample was equal to, or less than, that of the mesofacial sample. The fact that the brachyfacial sample has no clear advantage in the thickness of soft tissue chin as compared to the mesofacial group does not correlate with the fact that, because of the short vertical growth pattern evident in the brachyfacial pattern, this sample would be expected to have
45
greater linear soft tissue distances at points B to e at each treatment time. Only at T5 were the soft tissue distances at points b, c, and e larger in the brachyfacial group than in the mesofacial group and the points b, c, d, and e had larger distances in the brachyfacial group than in the dolichofacial group. Before treatment (T1) the total (male and female) dolichofaeial sample measurements from the hard to the soft tissue chin were as much as 2 mm less than those of the mesofacial and brachyfacial groups, especially at points c, d, and e (Table I). The dolichofacial group at T2 showed a consistent increase in the distances from the hard to the soft tissue chin, especially at points a, b, and c. At some points (a, b, c, and d) the dolichofacial group showed a greater increase in the distances at the soft and hard tissue chin than did the mesofacial and brachyfacial groups. The mentalis muscle is more likely to be strained in the pretreatment dolichofacial group and, as orthodontic treatment relieves the strain, the chin thickness at points c, d, and e increases. Patients at pretreatment ages of less than 9 years would be expected to have smaller linear soft tissue chin dimensions. There were 22 patients below 9 years of age and 38 above 9 years at Ti. A t test applied to the various soft tissue chin dimensions between the two age groups showed that only the thickness at B point was larger in the older group. The data in this study indicate that the soft tissue chin thickness varies in different individual facial types, as well as in the two sexes (Table I). After adjustment for sex and age, the facial type was the primary determinant in the amount of change that occurred in the soft tissue chin after orthodontic treatment. Holdaway 9 stressed that one of the fundamental traits associated with facial beauty includes a soft tissue chin that is nicely positioned in the facial profile. He recorded the horizontal measurement of the soft tisstie chin thickness (suprapogonion to the soft tissue suprapogonion) and determined the average to be 10 to 12 mm. However, there has been virtually no discussion of the soft tissue on the chin covering the entire symphysis. In previous studies, the horizontal thickness of the soft tissue on the chin has been measured only from pogonion, Ricketts' suprapogonion point, and B point. This research gives averages for various additional soft tissue landmarks on the chin as well as demonstrates the changes between sexes and the three facial types. The differential changes recorded after treatment at different points on the symphysis emphasize the need to consider the chin integument not only at points B and
46
Am. J. Orthod. Dentofac. Orthop. July 1990
Singh
pogonion but also at other points suggested in this study. CONCLUSIONS After orthodontic treatment, the soft tissue chin thickness increased at all the points measured around the symphysis of the chin in both male and female patients. Males showed a greater increase than the females in the thickness of the soft tissue chin at all points, B to e, and "1"2and "1"5. The soft tissue chin thickness increased most in the dolichofacial group of males at T2 and Ts. The mesofacial females showed the least amount of increase in the soft tissue chin thickness at T2 and 'I"5. The brachyfacial pattern has a larger soft tissue chin thickness than the dolichofacial pattern at points c, d, and e at Tt, "['2, and T~. However, the posttreatment change in the dolichofacial group was significantly greater at these points. No facial type showed an even thickness of soft tissue chin around the symphysis before treatment or immediately and 5 years after treatment. The soft tissue chin thickness did not seem to increase after the age of 15 years in female patients. If the lip and chin thickness is recognized to be excessively thin or heavy at the onset of treatment, it may mean the difference between esthetic success and failure of the soft tissue treatment. It must be emphasized that changes in the basic position of the soft tissue nose and the soft tissue chin occur primarily as a function of growth, and there is little that an orthodontist can do to alter them. Within reason, the clinician can possibly exert some control over the soft tissue chin. This study shows that limited changes in different parts of the soft tissue integument of the chin can be obtained with judicious treatment procedures. This article is based on a master's thesis submitted to the faculty of the Graduate College, Loma Linda University,
1984. The assistance of Dr. Ram S. Nanda in the preparation of this manuscript is appreciated. REFERENCES 1. BurstoneCJ. The integumentalprofile. AngleOrthod 1958;44:125. 2. Ricketts RM. The influenceof orthodontic treatment on facial growth and development. AM J ORTHOD1960;30:103-33. 3. Rickens RM. Esthetics, environmentand the law of lip relation. Ar,I J ORa'HOD1968;54:272-89. 4. Peck H, Peck S. A concept of facial esthetics. Angle Orthod 1970;40:284-318. 5. MidtgardJ, BjorkG, Linder-AronsenS. Reproducibilityofcephalometriclandmarksand errors of measurementof cephalometric cranial distances. Angle Orthod 1974;44:56-61. 6. Nanda RS. Growth changes in skeletal-facial profile and their significance in orthodontic diagnosis. AM J Oarnoo 1971; 59:501-13. 7. MerrifieldLL. The profile line as an aid in criticallyevaluating facial esthetics. AM J ORTHOD1966;52:804-21. 8. Neger M. A quantitativemethod of the evaluationof the soft tissue facial profile. AM J OaTHOD1959;45:738-51. 9. HoldawayRH. Soft tissue cephalometricanalysisand its use in orthodontic treatmentplanning. AM J ORTHOD1983;84:1-36. 10. SubtelnyJD. A longitudinalstudy of soft tissue facial structures and their profile characteristics defined in relationto underlying structures. AM J ORTHOD1959;45:481-507. 11. Burstone CJ. Integumental contour and extension patterns. Angle
Orthod 1959;29:93-104. 12. BowkerWD, Meredith HV. A metric analysisof the facial profile. Angle Orthod 1959;29:149-160. 13. Nanda RS, Meng HP, Kapila S, Goorhuis Y. Growth changes in the soft tissue facial profile. Accepted for publication,Angle Orthod 1989. 14. Ricketts RM. Cephalometric synthesis. AM J ORTnOD 1960; 46:647-73. 15. HambletonRS. The soft-tissuecoveringof the skeletal face as related to orthodonticproblems. A.~tJ OaTnoo 1964;50:405-20. 16. HillesundE, Fjeld D, ZachrissonBU. Reliabilityof soft tissue profile in cephalometrics. Ar,l J ORTHOD1978;74:537-50. 17. Riedel RA. Esthetics and its relation to orthodontic therapy. Angle Orthod 1950;22:168-78. Reprint requests to: Dr. Ruehi Nanda Singh 12570 Brookhurst St. Suite 3 Garden Grove, CA 92640
