Sexual dimorphism in soft tissue facial form as captured by digital three-dimensional photogrammetry by



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Figure 2: Example of 3D mesh obtained via stereophotogrammetry

A series of 26 anatomical surface landmarks were then collected from each participant’s 3D facial scan, and the corresponding x,y,z coordinates saved. From these landmark coordinates, a set of 29 simple linear distances were calculated using simple Euclidean geometry. These 29 distances are equivalent to standard facial anthropometric measurements (Farkas 1994; Kolar and Salter, 1997) and are shown above in Table 1 and Table 2.

In addition to simple linear distance measures, seven commonly used anthropometric indices were calculated from these distances (shown below in Table 3). These proportions provide a rudimentary way of capturing shape information on the face (Farkas and Munro, 1987).



Table 3: List of craniofacial indices used in the present study

Index

Definition

Interpretation

Cephalic

Maximum head width x 100 / Maximum head length

Higher values indicate more brachycephalic head shape

Facial

Morphological face height x 100 / Maximum face width

Higher values indicate relatively longer and/or narrower face

Upper Facial

Upper face height x 100 / Maximum face width

Higher values indicate relatively longer and/or narrower upper face

Upper-middle face depth

Upper facial depth x 100 /

Middle facial depth



Higher values indicate relatively protruded upper face and/or retruded middle face

Middle-lower face depth

Middle facial depth x 100 /

Lower facial depth



Higher values indicate greater increased maxillary projection and/or mandibular retrusion

Intercanthal

Intercanthal width x 100 / Outercanthal width

Higher values indicate greater relative hypertelorism

Nasal

Nasal width x 100 /

Nasal height



Higher values indicate a relatively shorter and/or wider nose
    1. statistical methods


Simple univariate statistics were run to compare males and females across the entire set of 41 craniofacial measurements and indices (5 distances from direct anthropometry; 29 distances from 3D photogrammetry; and 7 indices). Tests were run two different ways: (1) independent samples t-tests were performed and (2) analysis of covariance (ANCOVA) was carried out on the same variables, with the subject’s height included as a covariate. The second set of tests was performed to assess whether any craniofacial measures were significantly different even after adjusting for the effects of overall body size, since it is well known that males are larger on average. Comparing height in our dataset revealed this same pattern, with males showing a mean height increase of 15.4 cm over females (p < 0.001). To adjust for multiple comparisons, a Bonferonni correction was applied to the p-value and the threshold for statistical significance was set to 0.001 (.05/41).
  1. results


The descriptive statistics of the five direct anthropometric measurements and 29 3D surface-derived measurements are presented in Table 4. Of note, the positive mean difference values were all signed positive, indicating that all 34 dimensions were larger in our male sample. The inferential statistics are presented in Table 5. The t-tests showed that mean difference between males and females was significant for 32 of the 34 measurements at the p < 0.001 level. Only two of the 34 measurements were found to be non-significant, and these were upper vermilion height (p = 0.109) and lower vermilion height (p = 0.046), both relating to the vermillion segment of the lips. When the means were adjusted for the covariate ‘height’, the analysis of covariance (ANCOVA) still revealed significant differences for 27 of the 34 measurements at the p < 0.001 level. Five of the 34 measurements were no longer found to be statistically significant, and these were minimum frontal width (p = 0.011), palpebral fissure length (right) (p = 0.203), palpebral fissure length (left) (p = 0.277), nasal protrusion (p = 0.01), and nasal height (p = 0.014). Both upper vermilion height (p = 0.940) and lower vermilion height (p = 0.202) remained non-significant.

Table 6 summarizes the seven calculated craniofacial indices as well as the results of the accompanying t-tests. Males were found to have larger facial, intercanthal, and nasal indices while females were found to have larger cephalic, upper facial, upper-middle facial depth, and middle-lower facial depth indices. Of the 7 indices calculated, four were found to be non-significant, and these were the cephalic (p = 0.103), facial (p = 0.094), upper facial (p = 0.082), and intercanthal (p = 0.444) indices. Conversely, the remaining three indices (upper-middle facial depth, middle-lower facial depth, and nasal) were found to be significant at the p < 0.001 level.


Table 4: Descriptive statistics on all 34 craniofacial measurements (mm)






Males

Females




Measurement

Mean

sd

Mean

sd

Mean diff

Maximum cranial width

153.67

7.05

145.75

5.80

7.92

Minimum frontal width

107.84

8.47

102.84

7.57

5.00

Maximum cranial length

197.80

9.24

186.85

7.33

10.95

Maximum facial width

138.63

6.90

129.76

5.95

8.88

Mandibular width

106.16

7.11

97.48

6.43

8.68

Cranial base width

148.67

6.58

138.68

4.62

9.98

Upper facial depth (Right)

127.97

4.98

119.75

3.92

8.22

Upper facial depth (Left)

128.11

5.01

119.88

4.00

8.23

Middle facial depth (Right)

133.90

5.21

124.16

4.02

9.74

Middle facial depth (Left)

133.60

5.24

124.11

4.07

9.49

Lower facial depth (Right)

152.84

6.72

139.76

5.45

13.07

Lower facial depth (Left)

152.11

6.89

139.55

5.41

12.56

Morphological facial height

128.42

6.10

119.02

5.94

9.40

Upper facial height

79.50

3.98

75.14

4.08

4.37

Lower facial height

73.44

5.13

66.34

4.99

7.11

Intercanthal width

33.64

2.84

32.14

2.63

1.49

Outercanthal width

88.61

4.31

84.94

3.66

3.67

Palpebral fissure length (Right)

28.19

1.81

27.10

1.68

1.09

Palpebral fissure length (Left)

27.87

1.77

26.93

1.77

0.94

Nasal width

36.54

2.72

32.81

2.19

3.73


Table 4: (continued)

Subnasal width

19.93

2.34

17.74

2.09

2.18

Nasal protrusion

20.98

1.88

19.93

1.67

1.05

Nasal ala length (Right)

35.44

2.35

31.52

1.97

3.91

Nasal ala length (Left)

35.44

2.36

31.64

1.94

3.79

Nasal Height

57.46

3.47

55.13

3.44

2.33

Nasal Bridge Length

50.30

3.69

47.80

3.35

2.50

Labial fissure width

50.42

4.12

47.61

3.22

2.80

Philtrum width

13.07

1.76

11.73

1.65

1.34

Philtrum length

16.91

2.34

14.81

2.26

2.10

Upper lip height

23.24

2.28

21.04

2.33

2.20

Lower lip height

19.65

2.77

17.57

2.33

2.09

Upper vermilion height

7.65

1.75

7.42

1.43

0.23

Lower vermilion height

8.78

2.28

8.39

2.09

0.39

Cutaneuous lower lip height

13.14

2.48

11.05

1.98

2.10

Table 5: Results of t-test and ANCOVA for all variables






t-test

ANCOVA1

Measurement

t-value

p

F-value

p

Maximum cranial width

13.603

< 0.001*

67.109

< 0.001*

Minimum frontal width

7.255

< 0.001*

6.448

0.011

Maximum cranial length

15.615

< 0.001*

65.528

< 0.001*

Maximum facial width

15.383

< 0.001*

89.652

< 0.001*

Mandibular width

14.629

< 0.001*

55.989

< 0.001*

Cranial base width

18.822

< 0.001*

165.955

< 0.001*

Upper facial depth (Right)

19.992

< 0.001*

166.703

< 0.001*

Upper facial depth (Left)

19.911

< 0.001*

161.302

< 0.001*

Middle facial depth (Right)

22.746

< 0.001*

224.486

< 0.001*

Middle facial depth (Left)

22.072

< 0.001*

209.567

< 0.001*

Lower facial depth (Right)

23.128

< 0.001*

186.729

< 0.001*

Lower facial depth (Left)

21.937

< 0.001*

163.630

< 0.001*

Morphological facial height

17.751

< 0.001*

69.892

< 0.001*

Upper facial height

12.320

< 0.001*

26.990

< 0.001*

Lower facial height

15.972

< 0.001*

72.847

< 0.001*

Intercanthal width

6.304

< 0.001*

12.274

< 0.001*

Outercanthal width

10.033

< 0.001*

14.454

< 0.001*

Palpebral fissure length (Right)

7.108

< 0.001*

1.627

0.203

Palpebral fissure length (Left)

5.967

< 0.001*

1.182

0.277

Nasal width

16.676

< 0.001*

120.693

< 0.001*


Table 5: (continued)

Subnasal width

11.466

< 0.001*

32.960

< 0.001*

Nasal protrusion

6.885

< 0.001*

6.646

0.01

Nasal ala length (Right)

21.195

< 0.001*

163.339

< 0.001*

Nasal ala length (Left)

19.430

< 0.001*

155.991

< 0.001*

Nasal Height

7.716

< 0.001*

6.109

0.014

Nasal Bridge Length

8.237

< 0.001*

11.978

0.001*

Labial fissure width

8.336

< 0.001*

27.438

< 0.001*

Philtrum width

9.102

< 0.001*

22.852

< 0.001*

Philtrum length

10.500

< 0.001*

44.732

< 0.001*

Upper lip height

10.872

< 0.001*

38.200

< 0.001*

Lower lip height

8.997

< 0.001*

29.896

< 0.001*

Upper vermilion height

1.608

0.109

0.006

0.940

Lower vermilion height

2.059

0.046

1.692

0.202

Cutaneuous lower lip height

10.218

< 0.001*

67.241

< 0.001*

1 results adjusted for height

* significant after correction for multiple testing

Table 6: Descriptive statistics and t-test results for the seven anthropometric indices




Males

Females




Index

Mean

sd

Mean

sd

p

Cephalic

77.47

3.72

77.97

3.04

0.103

Facial

92.60

5.73

91.77

5.58

0.094

Upper facial

57.38

3.87

57.97

3.85

0.082

Upper-middle facial depth

95.75

1.95

96.53

2.04

< 0.001*

Middle-lower facial depth

87.88

2.48

88.94

2.47

< 0.001*

Intercanthal

37.98

2.41

37.81

2.50

0.444

Nasal

63.88

6.05

59.74

5.55

< 0.001*

* significant after correction for multiple testing
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