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



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purpose of the present investigation


It is clear that there is ample evidence of sexual dimorphism in the human craniofacial complex. Prior studies have generally either focused on hard tissue or soft tissue craniofacial measurements. Assessment of the literature revealed that the findings are perhaps more pronounced and more consistent for measures of the skull, compared with the soft-tissue findings. This was particularly true when body size differences were taken into account during the analysis. Given the contrasting results in recent studies examining soft-tissue craniofacial dimorphism, the principal aim of this project is to help elucidate which sex differences, if any, are present in the soft tissues face in a large sample of healthy adults.
  1. Materials and methods

    1. sample description


The sample used for this study was comprised of 586 craniofacially healthy adults (over the age of 18 years). There were 197 males and 389 females in the sample. The mean age of the male sample was 27.2 years (sd = 5.69; range = 18-40). The mean age for female sample was 27.7 years (sd = 5.47; range = 18-40). Age was not found to be significantly different between the two sexes (t = -0.988; p = 0.342). The boxplot in Figure 1 shows the age comparison between males and females.

Figure 1: Boxplot showing the mean age of males and females in the present sample

Subjects were recruited at three US locations: Pittsburgh, PA (University of Pittsburgh), Seattle, WA (Seattle Children’s Research Institute) and Houston, TX (University of Texas Health Sciences Center at Houston). Recruitment was accomplished primarily through a combination of targeted advertisement, word-of-mouth, research registries, and on-site recruitment in public venues. To participate in the study individuals had to be of recent European ancestry (all four grandparents) and could not have any personal history of facial trauma, facial reconstructive or aesthetic plastic surgery, orthographic surgery, or any other medical condition that might affect the structural integrity of the head and face. In addition, there could be no personal of family history of any craniofacial anomalies or syndromes that involve the craniofacial complex. All individuals were screened on these criteria prior to enrollment in the study. IRB approval was obtained at each site prior to recruitment.

    1. data acquisition


Following informed consent, each participant completed a short demographic interview to gather information on age, height, weight and ancestry/ethnicity. Then, using direct anthropometry, a series of five standard craniofacial measurements (Kolar and Salter, 1997) was taken on each participants head and face with spreading calipers (GPM, Switzerland); these measurements are listed in Table 1 and Table 2.

Table 1: Direct anthropometric measurements used in the present study (Kolar and Salter, 1997)

Measurement

Description

Maximum cranial width

eu-eu (euryon = the most lateral point on the head, located in the parietal region)

Minimum frontal width

ft-ft (frontotemporale = the medial point on the temporal crest of the frontal bone)

Maximum cranial length

g-op (glabella = the more prominent point in the median sagittal plane between the supraorbital ridges, identified by palpation; opisthocranion = the most prominent posterior point of the occiput, the point which produces the greatest length of the head from glabella)

Maximum facial width

zy-zy (zygion = the most lateral point on the zygomatic arch)

Mandibular width

go-go (gonion = the most lateral point at the angle of the mandible)

Table 2: Indirect anthropometric measurements used in the present study (Kolar and Salter, 1997)



Measurement

Description

Maximum cranial width

eu-eu (euryon = the most lateral point on the head, located in the parietal region)

Minimum frontal width

ft-ft (frontotemporale = the medial point on the temporal crest of the frontal bone)

Maximum cranial length

g-op (glabella = the more prominent point in the median sagittal plane between the supraorbital ridges, identified by palpation; opisthocranion = the most prominent posterior point of the occiput, the point which produces the greatest length of the head from glabella)

Maximum facial width

zy-zy (zygion = the most lateral point on the zygomatic arch)

Mandibular width

go-go (gonion = the most lateral point at the angle of the mandible)

Cranial base width

t-t (tragion = located at the notch above the tragus of the ear, the cartilaginous projection in front of the external auditory canal, where the upper edge of the cartilage disappears into the skin of the face)

Upper facial depth (Right)

n-t (nasion = midpoint of the nasofrontal suture; tragion)

Upper facial depth (Left)

(same as above)

Middle facial depth (Right)

sn-t (subnasale = the junction between the lower border of the nasal septum, the partition which divides the nostrils, and the cutaneous portion of the upper lip in the midline; tragion)

Middle facial depth (Left)

(same as above)

Lower facial depth (Right)

gn-t (gnathion = lowest point in the midline on the lower border of the chin, a bony landmark; tragion)

Lower facial depth (Left)

(same as above)

Morphological facial height

n-gn (nasion; gnathion)

Upper facial height

n-sto (nasion; stomion = the midpoint of the labial fissure when the lips are closed naturally)

Lower facial height

sn-gn (subnasale; gnathion)

Intercanthal width

en-en (endocanthion = the inner corner of the eye fissure where the eyelids meet, not the caruncles)

Outercanthal width

(Biocular width)



ex-ex (exocanthion = the outer corner of the eye fissure where the eyelids meet)

Palpebral fissure length (Right)

en-ex (endocanthion; exocanthion)


Table 2: (continued)

Palpebral fissure length (Left)

(same as above)

Nasal width

al-al (alare = the most lateral point on the nasal ala)

Subnasal width

sbal-sbal (subalare = the point on the lower margin of the base of the nasal ala where the ala disappears into the upper lip skin)

Nasal protrusion

sn-prn (subnasale; pronasale = the most protruded point of the nasal tip)

Nasal ala length

(Right)


ac-prn (alar curvature point = the most posterolateral point of the curvature of the base of the nasal alae, the lateral flaring walls of the nostrils; pronasale)

Nasal ala length

(Left)


(same as above)

Nasal height

n-sn (nasion; subnasale)

Nasal Bridge Length

n-prn (nasion; pronasale)

Labial fissure width

ch-ch (cheilion = the outer corner of the mouth where the outer edges of the upper and lower vermilions meet)

Philtrum width

cph-cph (crista philtri = the point on the crest of the philtrum, the vertical groove in the median portion of the upper lip, just above the vermilion border)

Philtrum length

sn-ls (subnasale; labiale superius = the midpoint of the vermilion border of the upper lip)

Upper lip height

sn-sto (subnasale; stomion)

Lower lip height

sto-sl (stomion; sublabiale = midpoint along the inferior margin of the cutaneous lower lip, labiomental sulcus)

Upper vermilion height

ls-sto (labiale superius; stomion)

Lower vermilion height

sto-li (stomion; labiale inferius = the midpoint of the vermilion border of the lower lip)

Cutaneuous lower lip height

li-sl (labiale inferius; sublabiale)

Next, each subject had a 3D image acquired of their facial surface using a 3dMD digital stereophotogrammetry system (Atlanta, GA). 3D stereophotogrammetry is a totally non-invasive method for acquiring human facial surface data, with capture speeds well under one second. The 3dMD system captures geometry of the human face as a point cloud, typically containing over 25000 individual points. These points can then be connected creating a 3D mesh and rendered with color, texture and shading to deliver a geometrically accurate facial representation. The 3dMD system has been shown previously to be accurate at the sub-millimeter level (Weinberg et al. 2006). An example of a facial surface is shown in Figure 2 without color and texture to preserve anonymity.



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