3d Facial Analysis

ORIGINAL ARTICLE

J. Djordjevic

M. Jadallah

A. I. Zhurov

A. M. Toma

S. Richmond

Three-dimensional analysis of facial

shape and symmetry in twins using

laser surface scanning

Authors' affiliation:J. Djordjevic, M. Jadallah, A. I. Zhurov,

A. M. Toma, S. Richmond, Department of

Applied Clinical Research and Public

Health, Cardiff University Dental Hospital,

Cardiff, Wales, UK

Correspondence to:Dr Jelena Djordjevic

Department of Applied Clinical Research

and Public Health

Cardiff University Dental Hospital,

1st floor, room 112, Heath Park,

Cardiff, CF14 4XY, Wales

UK

E-mail: [email protected]

Djordjevic J., Jadallah M., Zhurov A. I., Toma A. M., Richmond S.

Three-dimensional analysis of facial shape and symmetry in twins using

laser surface scanning

Orthod Craniofac Res 2012. © 2012 John Wiley & Sons A/S. Published by

Blackwell Publishing Ltd

Structured Abstract

Objectives – Three-dimensional analysis of facial shape and symmetry in

twins.

Setting and Sample Population – Faces of 37 twin pairs [19 monozy-

gotic (MZ) and 18 dizygotic (DZ)] were laser scanned at the age of 15

during a follow-up of the Avon Longitudinal Study of Parents and Children

(ALSPAC), South West of England.

Material and Methods – Facial shape was analysed using two methods:

1) Procrustes analysis of landmark configurations (63 x, y and z coordi-

nates of 21 facial landmarks) and 2) three-dimensional comparisons of

facial surfaces within each twin pair. Monozygotic and DZ twins were

compared using ellipsoids representing 95% of the variation in landmark

configurations and surface-based average faces. Facial symmetry was

analysed by superimposing the original and mirror facial images.

Results – Both analyses showed greater similarity of facial shape inMZ twins,

with lower third being the least similar. Procrustes analysis did not reveal any

significant difference in facial landmark configurations of MZ andDZ twins.

The average faces of MZ andDZmales were coincident in the forehead,

supraorbital and infraorbital ridges, the bridge of the nose and lower lip. In MZ

andDZ females, the eyes, supraorbital and infraorbital ridges, philtrum and

lower part of the cheeks were coincident. Zygosity did not seem to influence

the amount of facial symmetry. Lower facial third was themost asymmetrical.

Conclusion – Three-dimensional analyses revealed differences in

facial shapes of MZ and DZ twins. The relative contribution of genetic

and environmental factors is different for the upper, middle and lower

facial thirds.

Key words: 3D imaging; ALSPAC; face; shape analysis; surface laser

scanning; symmetry; twins

Date:Accepted 6 November 2012

DOI: 10.1111/ocr.12012

© 2012 John Wiley & Sons A/S. Published by

Blackwell Publishing Ltd

Introduction

From the pioneering work of Francis Galton (1) to

the modern-day human genome (2) and phenome

projects (3), genetic and environmental determi-

nants of craniofacial morphology have not ceased

to intrigue scientists. Research efforts have been

supported by the clinical interest of orthodontists

in altering unfavourable facial growth. The success

of such undertaking would depend on the possibil-

ity to influence facial hard and soft tissues within

genetic limitations. In the last few decades, herita-

bility of facial features has been investigated

through twin (4–9) and family studies (10–14),

which shed some light on this complex research

area. However, individual genetic variants that

affect normal variation in human facial features

have yet to be identified (15).

The majority of twin studies in orthodontics

have relied on two-dimensional data collected

from lateral cephalograms of participants. Small

number of landmarks has been used to describe

facial hard tissue morphology. Linear distances

between landmarks have been used as an esti-

mate of facial size and the angles between inter-

secting lines drawn between landmarks as an

estimate of facial shape (16). It is clear that most

information about the facial shape has been

simply ignored (17).

Three-dimensional imaging capture techniques

have the potential to overcome some of the draw-

backs of two-dimensional studies (17, 18). One of

the first three-dimensional studies exploring

facial morphology of twins was performed by

Burke (19). Using stereophotogrammetry, he

analysed 13 parameters on facial contour maps of

18 twin pairs and concluded that dizygotic (DZ)

twin pairs had larger mean intrapair differences

in facial parameters than the monozygotic (MZ)

pairs. The author identified important facial

parameters to distinguish between the two groups

and used them to calculate a ‘facial similarity

index’. Investigations of three-dimensional sym-

metry in twins have also started with stereophoto-

grammetry. In a 9-year longitudinal study, three

pairs of bilateral facial parameters were measured

in six pairs of MZ twins (20). The authors found

that asymmetry was very small, amounting at

most to a few millimetres, and not much larger

than the measuring error of the method. Asym-

metry could not be related to twin zygosity, ado-

lescence or age.

More recent studies have used laser surface

scanning to capture three-dimensional facial data

of twins. Naini and Moss (21) analysed faces of 10

MZ twin pairs and 16 DZ twin pairs using two

methods. Analysis of 28 interlandmark distances

revealed significant genetic determination for

midfacial parameters. The second method (analy-

sis of facial surface shape) showed the strongest

genetic determination for a triangular area of the

midface encompassing the orbital rims, intercan-

thal area and nose. The authors also concluded

that the concordance for vertical and anteropos-

terior facial parameters was greater in MZ twins

than in DZ twins. Moss (22) analysed 10 MZ and

10 DZ twin pairs using the fixed optical surface

scanner. Facial surfaces of MZ twins exhibited

similarities in shape of the brows, bridge of the

nose and infraorbital ridges, whereas the lower

parts of the face (cheeks, chin, and lips) were con-

siderably different. In DZ twins, the areas around

the eyes were different in shape as well as the

lower part of the face.

Three-dimensional analyses of facial character-

istics of twins are rare and suffer from small, unrep-

resentative samples, with a wide age range and

different ethnicity. Therefore, the aim of this study

was to analyse three-dimensional facial shape and

symmetry of MZ and DZ twins, identified from a

cohort of 15-year-old white British adolescents,

using anon-invasive laser surface scanning.

Material and methodsParticipants

Participants were recruited from the Avon Longi-

tudinal Study of Parents and Children (ALSPAC),

a UK-based longitudinal birth cohort study

designed to explore genetic and environmental

influences on health and well-being (23). All preg-

nant women resident in the old administrative

county of Avon (centred around the city of Bristol

in the South West of England), and their resulting

2 | Orthod Craniofac Res 2012

Djordjevic et al. 3D analysis of facial shape and symmetry in twins

children were eligible to participate in ALSPAC if

their estimated delivery date fell between 1 April

1991 and 31 December 1992 inclusive (23, 24). Of

the initial 14 541 pregnancies, all but 69 had

known birth outcome. Of these 14 472 pregnan-

cies, 14 062 were live births and 13 988 were alive

at 1 year. The total number of twin pairs in the

ALSPAC study sample is 204 (24).

During 2006 and 2007, invitations to attend the

annual recall clinic were sent to 9985 15-year-old

adolescents. Of 5253 adolescents who attended,

4784 facial scans were collected. After exclusion

of poor-quality scans and those with obvious

facial dysmorphology, facial scans of 4747 adoles-

cents (2233 males and 2514 females) were

retained (25). Among these, 43 twin pairs were

identified based on their mothers’ reports to the

questionnaires. Zygosity was checked using

genetic testing. DNA samples were not available

for six twin pairs, and therefore, these were

excluded from the analyses. The final sample con-

sisted of 37 twin pairs, 19 MZ pairs (nine male-

male and 10 female-female) and 18 DZ pairs

(seven male-male, three female-female and eight

mixed). The mean age of MZ twins was 184.7 (SD

1.6) months and the mean age of DZ twins was

184.9 (SD 2.1) months (Table 1). The study was

approved by the ALSPAC Ethics and Law Com-

mittee and the Local Research Ethics Committee.

The consent forms were signed by the parents.

Laser scanning

Two laser scanning devices Vivid 900 (Konica

Minolta Sensing Europe, Milton Keynes, UK)

were used. Accuracy and reliability of this

system (series Vivid 700, 900, and 910) were

tested and proved suitable for clinical applica-

tions (26–31). Participants were instructed to sit

still on a stool with adjustable height, 135 cm in

front of the mirror placed between the scanners.

They were told to adopt neutral expression, with

relaxed facial musculature. Natural head position

was obtained by asking them to look at the mir-

ror and level their eyes to the horizontal mark

on the mirror (by adjusting the stool height),

and to level their facial midline to the vertical

mark on the mirror (by moving the stool slightly

left or right). They were also asked not to wear

any make-up on the day of scanning, and had to

take off the hats and glasses. Also, any hair over-

lying the face had to be moved away by a hair-

band or tightened by hairpins. Prior to scanning,

participants were told to swallow hard (in order

to bring their mandible in rest position) and

close their lips. All twins fulfilled these requests.

The scanning took approximately 8 s. If the per-

son incidentally moved, smiled or changed facial

expression, scanning was repeated. Medium-

range lenses with a focal length of 14.5 mm were

used. Scanning was controlled by MultiScan

software (Cebas Computer, GmBH, Eppelheim,

Germany). For each participant, two files in

VIVID format were obtained, which contained

left and right facial halves. The data were saved

on the computer memory for further analysis.

Processing of facial scans

Facial images were imported into Rapidform

2006 (INUS Technology Inc., Seoul, South Korea)

and processed using an in-house-developed

Table 1. Characteristics of the study sample

Monozygotic twins Dizygotic twins

N (pairs)

Age (months)

N (pairs)

Age (months)

Mean (SD) Range Mean (SD) Range

Males 9 184.6 (1.4) 183–187 Males 7 183.4 (1.2) 182–185

Females 10 184.8 (1.8) 182–188 Females 3 185.3 (1.4) 184–187

Mixed 8 186.0 (2.3) 184–191

Total 19 184.7 (1.6) 182–188 Total 18 184.9 (2.1) 182–191

Orthod Craniofac Res 2012 | 3


subroutine. This technique has been tested on a

plaster cast face, several adults and 40 children

(32–34). The raw data imported represents a

cluster of a large number of unconnected shells.

The term shell is used by the software to denote

a triangulated surface or several surfaces treated

as one (32). Therefore, the cluster first had to be

separated into shells, and then all irrelevant

shells removed (background objects, bits of

clothes, hair, ears and neck). The raw face

obtained by scanning has a rough surface and

therefore was smoothed, while preserving shape

and volume (32). The next step was registration

of the two facial halves using the best-fit algo-

rithm. The quality of the scans was checked

prior to merging facial halves. Only scans that

fulfilled the criteria of at least 70% matching in

the overlap area within 0.5 mm, and at least

95% matching within 1 mm, were further pro-

cessed (35). Finally, the holes in the surface

meshes were filled in (eyebrows, eyes, nostrils)

and two facial halves were merged (32).

Prior to any analysis, the position of faces

needed to be standardized. It was accomplished

by fitting them into the same reference frame,

with the point halfway between the inner canthi

of the eyes as the origin. Coronal plane (xy) was

determined by the cylinder that fitted all data

points of the original-mirror face structure and

therefore was based on the natural head position

registered during the scanning. Sagittal plane

(yz) was passing through the middle of the face.

It was determined as the symmetry plane of the

original-mirror face structure. Transverse plane

(xz) was passing through the inner canthi of the

eyes and was perpendicular to previous two

planes. Standardisation of the faces was fully

automated (17). Twenty-one facial landmarks, as

defined by Farkas (36), were manually identified

on the facial scans by one experienced operator

(Fig. 1). For each face, 63 coordinates (x, y and z

coordinates of 21 facial landmarks) were

recorded and saved.

Facial shape analysis

Facial shape analysis was performed using two

methods: landmark-based and surface-based.

Similarities and differences in facial shape

within- and between-twin pairs were explored.

For within-pair comparisons, the data was col-

lected only from the same gender twins: 19 MZ

pairs (nine male-male and 10 female-female)

and 10 DZ pairs (seven male-male and three

female-female). Eight pairs of DZ mixed twins

were excluded from this analysis, as previous

three-dimensional study showed that there is a

gender difference in facial shape of 15.5-year-old

ALSPAC adolescents (35).

The first method (landmark-based) comprised

Generalized Procrustes Analysis (GPA), which

was used to register (align) the sets of 21 facial

landmarks by removing translation and rotation

(37, 38). As facial form consists of size and

shape, size differences were removed by scaling,

separately for males and females in the sample.

Within each twin pair, two landmark configura-

tions were compared and the overall similarity

in facial shape measured as the Procrustes

Fig. 1. Anthropometric landmarks that were identified on the

facial scans. (1) Glabella (g); (2) Nasion (n); (3) Endocanthion

left (enl); (4) Endocanthion right (enr); (5) Exocanthion left

(exl); (6) Exocanthion right (exr); (7) Palpebrale superius left

(psl); (8) Palpebrale superius right (psr); (9) Palpebrale inferi-

us left (pil); (10) Palpebrale inferius right (pir); (11) Pronasale

(prn); (12) Subnasale (sn); (13) Alare left (all); (14) Alare right

(alr); (15) Labiale superius (ls); (16) Crista philtri left (cphl);

(17) Crista philtri right (cphr); (18) Labiale inferius (li); (19)

Cheilion left (chl); (20) Cheilion right (chr); (21) Pogonion

(pg). Definitions by Farkas (36) were used.



distance. The lower the Procrustes distance

between the two landmark configurations, the

more similar facial shapes of two twins were.

In order to visualize the differences between

MZ and DZ twins, four sets of ellipsoids were

constructed for: MZ males (n = 18), MZ females

(n = 20), DZ males (n = 22, 14 from male-male

and eight from mixed pairs) and DZ females

(n = 14, six from female-female and eight from

mixed pairs). Each ellipsoid represented 95% of

the variation (two standard deviations from the

mean) in a position of a given facial landmark.

Landmark configurations were aligned on mid-

endocanthion (a point halfway between the

inner canthi of the eyes) and compared.

The second method (surface-based) consisted

of comparison of faces using all available data

points (several thousands) captured by the laser

scanning device. As in the first method

described, the faces were first scaled to the aver-

age Procrustes size calculated from the land-

marks (for males and females separately). The

two faces of twins were then superimposed using

best-fit registration, a standard tool in Rapidform

2006, based on the iterative closest point algo-

rithm. Absolute distances between all pairs of

points of the two superimposed facial surfaces

were automatically collected and the average dis-

tance between them calculated. The lower the

average distance between the two facial surfaces,

the more similar facial shapes of two twins were.

In addition, coincidence of the two faces was

expressed as a percentage. A colour deviation

map and a histogram were generated for each

twin pair to visualize and quantify the differences

in two facial shapes (Fig. 2). The same two

parameters were obtained for the upper, middle

and lower facial thirds. The upper third was

located above a horizontal line connecting inner

corners of the eyes (endocanthion left and right).

The middle third occupied the area between the

horizontal line connecting inner corners of the

eyes and a horizontal line connecting corners of

the mouth (cheilion left and right). The lower

third was located below the horizontal line con-

necting corners of the mouth.

The differences between MZ and DZ twins

were analysed using average faces. These were

constructed for the aforementioned groups of

twins: MZ males (n = 18), MZ females (n = 20),

DZ males (n = 22, 14 from male-male and eight

from mixed pairs), and DZ females (n = 14, six

from female-female and eight from mixed pairs).

Iterative averaging in the local normal direction

to a template was performed using another

internally developed subroutine for Rapidform

2006. This ensured that the line of averaging met

all faces at nearly right angles, thus providing

maximum accuracy (17). Three iterations were

performed. The average faces were aligned on

Fig. 2. The colour map and the histogram show the differences in three-dimensional facial shape of two monozygotic female

twins. Faces of twins were scaled to the average Procrustes size for females (calculated from 21 facial landmarks) and superim-

posed in Rapidform 2006 (Inus Technology Inc., Seoul, South Korea) using best-fit algorithm. The average distance between the

two facial surfaces was 0.73 mm (calculated using internally developed subroutine) and the coincidence within 0.5 mm tolerance

level was 41.42% (grey area on the colour map). Shades of blue (minimum value �1.96 mm) represent negative difference for the

face of the first twin (which is a reference) and the shades of red represent positive difference (maximum value 3.98 mm). Dotted

lines on the middle image (which connect inner corners of the eyes and corners of the mouth) divide the face into the upper,

middle and lower thirds.



the mid-endocanthion. The differences in facial

shape of MZ and DZ twins were visualized and

quantified on colour maps and histograms,

respectively.

Facial symmetry analysis

Facial symmetry analysis was performed using

aforementioned in-house-developed subroutine

for Rapidform 2006. In this part of the study,

only the three-dimensional facial surface was

considered. For each participant, the amount of

three-dimensional symmetry was calculated after

superimposing (best-fit registering) the original

face with its mirror image (Fig. 3). The average

distance between the original and the mirror

faces and the percentage of coincidence were

measured for the whole face, the upper, middle

and lower facial thirds, as previously described

(39, 40). The data was collected from all partici-

pating twins.

Error of the method

An earlier study has shown that the Vivid 900

scanner is accurate to a level of 0.56 � 0.25 mm

and that the error in computerized registration

of left and right scans is 0.13 � 0.18 mm (26). In

all facial surface comparisons, any difference

<0.5 mm was considered insignificant and was

therefore chosen as the tolerance level. The

quality of facial scans was compared within and

between MZ and DZ pairs. In order to examine

the intra-operator reliability in landmark identi-

fication, facial scans of 30 individuals (15 males

and 15 females) were randomly selected from

the final sample of 74 twins and landmarked on

two occasions, 2 weeks apart. The reliability of

the landmarks was determined using Bland–Alt-

man plots, as described previously (41).

Statistical analysis

Procrustes analysis was performed in R project,

the open source software. Mean and standard

deviations of all landmarks in the x-, y- and

z-directions were calculated after scaling male and

female subsamples. The distribution of all other

data was checked using histograms, Q-Q plots

and Shapiro–Wilk test. As the distribution was

not normal and the subsamples were relatively

small, the transformation of the data was not

attempted. The data is presented as median and

interquartile range (25th percentile, 75th percen-

tile). Non-parametric Mann–Whitney U test was

used for all comparisons between MZ and DZ

twin pairs. The upper, middle and lower facial

thirds within twin pairs were compared using

Fig. 3. The colour map and the histogram show three-dimensional facial symmetry in a 15-year-old monozygotic male. The ori-

ginal face (left) and the mirror face (right) were superimposed (best-fit registered) in Rapidform 2006 (Inus Technology Inc.,

Seoul, South Korea). The average distance between the original and the mirror faces was 0.84 mm (calculated using internally

developed subroutine) and the coincidence within 0.5 mm tolerance level was 63.15% (represented by grey area on the colour

map). Shades of blue (minimum value �2.07 mm) and shades of red (maximum value 2.13 mm) represent asymmetrical parts of

the face.



Kruskal–Wallis one-way analysis of variance test.

When a statistically significant difference was

noticed, Mann–Whitney U test was used to

explore it further. P value <0.05 was considered

statistically significant. These statistical analyses

were performed in the Statistical Package for

Social Sciences Software version 17.0 (SPSS Inc.,

Chicago, IL, USA).

Results

There was no statistically significant difference

in the quality of the scans within and between

the twin groups (p > 0.05). Landmark identifica-

tion error was <1 mm for majority of land-

marks’ coordinates. The results of both analyses

(landmark-based and surface-based) showed

greater similarity of facial shape within MZ twin

pairs in comparison with DZ twin pairs

(Table 2). Landmark-based analysis revealed

that there was an overlap in the interquartile

ranges (25th to 75th percentile) for Procrustes

distances of landmark configurations between

MZ and DZ males. However, according to the

surface-based method, the interquartile ranges

for similarity of facial shapes of the two twin

groups were distinct and no overlap could be

noticed.

Further investigation revealed that within MZ

male pairs lower facial third was the least simi-

lar, whereas in females, no such difference was

noticed (Table 3). In DZ male pairs, the upper

facial third was the most similar. The same anal-

ysis was not performed separately for females

due to only three observations. When the data

for DZ males and females were combined, the

results showed that lower facial third was the

least similar within DZ twin pairs.

Facial shape of MZ and DZ twins was com-

pared separately for males and females. After

scaling and generalized Procrustes registration,

the results showed that standard deviations of

21 facial landmarks were very similar between

MZ and DZ twins (Tables 4 and 5). This is illus-

trated on ellipsoid plots, which represent 95%

of the variation in landmark configurations

(Fig. 4).

Table 2. Within-pair comparisons of facial shapes in monozygotic and dizygotic twins assessed by landmark-based and sur-face-based methods

Parameter


N Median

25th

perc.

75th

perc. N Median

25th

perc.

75th

perc. p Value†

Landmark-based method

Pr. dist. (mm) Males 9 9.86 9.19 11.99 7 10.73 10.53 13.76 0.233 (NS)

Females 10 9.86 9.20 11.51 3 – – – –

All 19 9.31 7.48 10.44 10 10.71 10.37 14.16 0.004

Surface-based method

Av. dist. (mm) Males 9 0.87 0.74 0.99 7 1.30 1.12 1.51 0.001

Females 10 0.77 0.63 1.12 3 – – – –

All 19 0.82 0.73 1.04 10 1.30 1.12 1.60 <0.001

Coincid. (%) Males 9 38.94 36.46 41.98 7 24.84 21.86 29.55 0.001

Females 10 43.00 31.45 51.66 3 – – – –

All 19 39.39 36.43 44.08 10 24.80 18.62 30.93 <0.001

N, number of within-pair observations; perc., percentile; Pr. dist., Procrustes distance between two landmark configurations within atwin pair; Av. dist., average distance between the two faces of twins; Coincid., the percentage of coincidence between the two faces oftwins (see text and Fig. 2 for further explanation).Eight mixed dizygotic pairs were excluded from the analysis (see text for further explanation) and the data for dizygotic females werenot analysed separately due to only three observations.NS, not statistically significant.†Mann–Whitney U test was performed.



Average faces of MZ and DZ twins of both gen-

ders are presented in Fig. 5. Monozygotic males

tend to have wider face and nose with prominent

upper lip when compared with DZ males, with a

maximum difference of 1.8 mm. On the other

hand, DZ males tend to have more prominent

eyes, upper part of the forehead and central part

of the chin, with a maximum difference of

1.2 mm. The two average male faces coincide

34.1%, mainly in the forehead, supraorbital and

infraorbital ridges, the bridge of the nose and

lower lip. Monozygotic females tend to have

wider lower part of the face, wider nose and more

prominent lips when compared with DZ females,

with a maximum difference of 1.5 mm. Dizygotic

females tend to have more prominent forehead,

the bridge of the nose, malar area and lower part

of the chin, with a maximum difference of

1.1 mm. The two average female faces coincide

61.1%, mainly in the eyes, supraorbital and infra-

orbital ridges, philtrum of the upper lip and lower

part of the cheeks.

Three-dimensional symmetry analysis showed

that there was no statistically significant

difference in the amount of facial symmetry

between MZ and DZ twins (Table 6). When

upper, middle and lower facial thirds were com-

pared, lower facial third was found to be the

most asymmetrical in both twin groups

(Table 7).

Discussion

In this exploratory cross-sectional study, three-

dimensional facial shape and symmetry of 37

twin pairs was investigated using non-invasive

laser surface scanning. Facial analysis was per-

formed using two methods. The first method

was based on geometric morphometrics, which

employs GPA to register (align) sets of landmark

configurations. Although powerful, Procrustes

registration is not an ideal technique to superim-

pose numerous faces, as it relies only on limited

Table 3. Facial shape similarity by facial thirds within monozygotic and dizygotic twin pairs

Twins N Parameter

Upper facial third Middle facial third Lower facial third

p Value†Median

25th

perc.

75th

perc. Median

25th

perc.

75th

perc. Median

25th

perc.

75th

perc.

MZ males 9 Av. dist. (mm) 0.80 0.65 0.93 0.80 0.74 0.97 0.98 0.79 1.34 0.188 (NS)

Coincid. (%) 36.85 34.98 46.13 41.18 36.24 42.31 28.60 26.34 36.34 0.032

MZ females 10 Av. dist. (mm) 0.67 0.53 1.00 0.72 0.66 1.30 0.80 0.70 1.35 0.384 (NS)

Coincid. (%) 47.51 33.18 55.78 43.96 28.24 48.80 37.32 21.20 44.47 0.325 (NS)

MZ all 19 Av. dist. (mm) 0.78 0.56 0.92 0.79 0.70 0.98 0.93 0.75 1.27 0.140 (NS)

Coincid. (%) 42.05 35.40 51.80 41.18 35.24 47.06 32.99 25.30 41.99 0.064 (NS)

DZ males 7 Av. dist. (mm) 0.90 0.68 1.22 1.56 1.05 1.78 1.57 1.27 1.89 0.019

Coincid. (%) 32.67 26.90 45.63 19.95 14.66 31.72 17.34 11.28 22.70 0.010

DZ females‡ 3 Av. dist. (mm) – – – – – – – – – –

Coincid. (%) – – – – – – – – – –

DZ same

gender§

10 Av. dist. (mm) 1.11 0.81 1.47 1.64 1.03 1.79 1.79 1.36 2.00 0.013

Coincid. (%) 29.62 20.59 38.29 19.25 15.55 31.91 17.34 13.15 21.98 0.030

N, number of within-pair observations; perc., percentile; MZ, monozygotic; DZ, dizygotic; Av. dist., average distance between the twofaces of twins in a given facial third; Coincid., the percentage of coincidence between the two faces of twins in a given facial third.NS, not statistically significant.Figures in bold indicate facial third which was significantly different from the other two (Mann–Whitney U test was applied).†Kruskal–Wallis test was performed.‡The data for dizygotic females were not analysed separately due to only three observations.§Eight mixed dizygotic pairs were excluded from the analysis (see text for further explanation).



number of landmarks and therefore does not

take into account other information available

(17). This is certainly the case when laser scan-

ning devices are used, as these can capture at

least 40 000 points on the facial surface (42).

These points do not have fixed positions and

hence cannot be used as landmarks (17). For

this reason, the second method used in this

study relied on the comparison of facial surfaces.

Two different superimposition techniques were

used and this requires further explanation.

The first method of superimposition (the best-

fit alignment) was performed to compare faces

of twins within each pair. The presumption was

that the faces of twins will be very much alike

and that slight differences can be registered

using this approach. The best-fit method is

based on the iterative closest point algorithm, a

built-in feature of the commercial software.

Essentially, it is a mathematical least-squares

method. Automatic comparison took into

account all pairs of points on the facial surfaces

captured by the devices (several thousands). We

are unaware of any study, which specifically

investigated the reliability of this software tool,

although it has been used before (17, 35, 42).

There is a theoretical possibility that different

piece of software would produce slightly differ-

ent superimposition results. This could be inves-

tigated in future studies.

The second method of superimposition was

used to compare average faces of MZ and DZ

twins. The faces were aligned on mid-endocan-

thion, the point halfway between the inner cor-

ners of the eyes. As previous research has

shown, this point can be used as a relatively

Table 4. Mean and standard deviation of 21 facial landmarks in x-, y- and z-directions for monozygotic and dizygotic malesafter scaling and Generalized Procrustes registration

Landmark

Monozygotic males (N = 18) Dizygotic males (N = 22)

X Y Z X Y Z

Mean (SD) Mean (SD) Mean (SD) Mean (SD) Mean (SD) Mean (SD)

Glabella (g) 0.07 (0.66) 48.91 (1.68) 4.41 (1.62) 0.32 (0.74) 48.58 (1.90) 3.99 (1.97)

Nasion (n) 0.29 (0.60) 38.04 (1.35) 3.54 (1.28) 0.43 (0.66) 38.12 (1.62) 3.31 (1.48)

Endocanthion left (enl) 16.92 (1.32) 27.35 (0.61) �12.34 (1.12) 16.91 (1.15) 27.58 (0.71) �12.54 (1.05)

Endocanthion right (enr) �16.76 (1.31) 26.47 (0.88) �11.34 (1.12) �16.55 (1.17) 27.70 (0.77) �12.55 (1.47)

Exocanthion left (exl) 44.54 (1.31) 26.95 (0.96) �18.57 (1.24) 43.99 (2.19) 27.29 (1.03) �17.81 (1.97)

Exocanthion right (exr) �45.14 (1.49) 27.49 (1.20) �18.53 (1.26) �44.25 (1.89) 28.02 (0.97) �17.89 (1.49)

Palpebrale superius left (psl) 31.09 (1.03) 34.66 (0.94) �8.83 (1.41) 30.09 (1.51) 34.48 (1.16) �7.76 (1.10)

Palpebrale superius right (psr) �31.22 (1.37) 34.25 (0.96) �7.75 (1.08) �30.97 (1.42) 34.66 (1.30) �7.11 (1.42)

Palpebrale inferius left (pil) 31.25 (1.16) 22.63 (1.06) �10.68 (0.83) 30.42 (1.64) 22.76 (1.22) �10.83 (1.25)

Palpebrale inferius right (pir) �31.14 (1.40) 22.23 (1.00) �10.70 (1.28) �30.89 (1.45) 22.87 (1.22) �10.55 (1.19)

Pronasale (prn) 0.09 (0.85) �2.68 (2.10) 26.48 (2.00) 0.06 (0.80) �2.97 (1.82) 26.38 (2.04)

Subnasale (sn) 0.38 (0.71) �15.20 (1.85) 12.06 (1.52) 0.34 (0.59) �15.42 (2.38) 12.68 (1.86)

Allare left (all) 17.29 (1.14) �6.31 (1.06) 5.68 (1.82) 16.98 (1.63) �6.74 (1.51) 4.20 (1.07)

Allare right (alr) �17.06 (1.38) �6.05 (0.99) 6.01 (1.79) �16.74 (1.39) �6.91 (1.31) 4.47 (1.70)

Labiale superius (ls) 0.13 (0.46) �30.85 (1.14) 12.85 (1.38) 0.06 (0.39) �30.93 (1.18) 13.15 (0.88)

Labiale inferius (li) 0.04 (0.43) �45.88 (2.22) 8.24 (1.23) 0.21 (0.40) �46.33 (1.25) 9.24 (1.48)

Crista philtri left (cphl) 6.17 (1.54) �29.47 (1.18) 12.26 (1.38) 6.09 (1.16) �29.07 (1.29) 12.34 (0.90)

Crista philtri right (cphr) �6.42 (1.42) �29.22 (1.19) 12.09 (1.37) �6.64 (1.17) �29.05 (1.21) 12.25 (0.84)

Cheilion left (chl) 24.05 (2.21) �38.40 (0.96) �3.03 (2.30) 24.47 (2.13) �38.75 (1.42) �4.28 (1.77)

Cheilion right (chr) �24.44 (1.72) �37.89 (0.98) �2.91 (1.77) �24.46 (2.13) 38.81 (1.65) �3.11 (1.44)

Pogonion (pg) �0.13 (0.59) �67.05 (2.99) 1.05 (3.49) 0.14 (0.50) �67.07 (2.64) 2.39 (2.46)



stable reference during facial growth (42). The

expected level of similarity of facial features

between MZ and DZ twins was less than within

the twin pairs. In this case, the best-fit approach

would tend to decrease the difference between

the average MZ and DZ faces. On the other

hand, similarity that was demonstrated by

superimposition on mid-endocanthion point had

a greater chance of representing a true effect.

Surface-based average faces have already been

applied in orthodontics and maxillofacial surgery

to illustrate facial anomalies, evaluate facial

growth, analyse treatment effects, compare facial

morphologies between genders and among dif-

ferent populations (17, 18, 25, 35).

Both facial analyses (landmark-based and sur-

face-based) revealed greater similarity of facial

surfaces in MZ twins than in DZ twins. This is

in agreement with previous studies (19, 21, 22).

Instead of presenting only descriptive data

(obtained from colour maps), facial shape simi-

larity within twin pairs was further investigated

by dividing the faces into thirds and analysing

facial shape parameters statistically. In MZ

males, the lower facial third was the least simi-

lar, whereas in MZ females, no statistically sig-

nificant difference was determined. In DZ

males, upper facial third had the most similar

shape within twin pairs. These findings can

indicate that the influence of genetic and envi-

ronmental factors and their interaction on soft

tissue shape is not the same in all facial

regions.

The amount of three-dimensional facial sym-

metry measured in MZ and DZ twins was similar

as the one measured in 270 singletons from the

same population (40). The study failed to show

significant differences in facial symmetry

between MZ and DZ twin groups. It can either

be due to small sample size, which prevents

detection of any difference (possible type II

error) or an indication that facial soft tissue

symmetry of healthy individuals is not under

strong genetic control. The latter statement is

supported by previous study (20). More studies

with larger samples are needed to reach a defi-

A

B

Fig. 4. The 95% of the variation in scaled 21 facial landmarks for 74 monozygotic and dizygotic 15-year-old twins. (A) Front (x

and y coordinates) and profile view (y and z coordinates) for male facial landmarks (18 monozygotic males represented by light

grey ellipsoids and 22 dizygotic males represented by dark grey ellipsoids). (B) Front (x and y coordinates) and profile view (y

and z coordinates) for female facial landmarks (20 monozygotic females represented by light grey ellipsoids and 14 dizygotic

females represented by dark grey ellipsoids). The data were aligned on the mid-endocanthion, a point halfway between the inner

canthi of the eyes. For names of landmarks refer to Figure 1.



nite conclusion. Lower facial third was found to

be the most asymmetric, contrary to the findings

of previous study on 270 singletons (40), which

showed no statistically significant difference in

the amount of symmetry among upper, middle

and lower facial thirds. There is no consensus in

the literature on the most asymmetric part of

the face (39, 40).

One of the strengths of this study is that facial

analysis was performed in a sample of twins of

the same age, with confirmed zygosity, who were

born and raised in the same geographical region.

Hence, the sample was more homologous than

in previous three-dimensional studies on facial

morphology of twins. The accuracy of the laser

scanning method enables quantification of even

subtle differences in facial morphology and sym-

metry, which has not been feasible previously

using two-dimensional data from photographs

or lateral cephalograms. In order to use the full

potential of this technology, future studies on

heritability of facial features will have to adopt

some method of three-dimensional facial

analysis.

As with any observational study, there are

some limitations. The sample comes from a

longitudinal population-based study, in which

twins constitute approximately 1.3% of the

cohort (24). As facial laser scanning was orga-

nized only during one follow-up clinic, sample

size could not be increased. In addition, many

confounding factors could not be controlled. In

facial analysis, some of these factors might be

related to body mass index, medical conditions,

orthodontic treatment and trauma. In future

studies, these factors should be carefully moni-

tored to ensure the consistency of the results.

It has been argued that twin results need to be

interpreted with great caution, and that other

family relations should be taken into account,

A

B

Fig. 5. Average faces for monozygotic and dizygotic 15-year-old twins. (A) Average face for 18 monozygotic males (left), average

face for 22 dizygotic males (centre) and the colour map and the histogram (right), which show the difference in facial shape of

the two male twin groups. (B) Average face for 20 monozygotic females (left), average face for 14 dizygotic females (centre) and

the colour map and the histogram (right), which show the difference in facial shape of the two female twin groups. Average faces

were aligned on mid-endocanthion, and monozygotic average face in both genders was taken as the reference. Shades of blue

represent negative (minimum �2 mm), and shades of red positive differences (maximum 2 mm) in facial shape. Grey area repre-

sents the parts of two facial surfaces, which coincide within 0.5 mm (34.1% in males and 62.1% in females).



especially comparisons between parents and

children (14). An ongoing project aims at

exploring this aspect of the problem, and the

faces of approximately 1300 fathers of ALSPAC

children are currently being laser scanned.

Genome-wide associations will have a major

Table 5. Mean and standard deviation of 21 facial landmarks in x-, y- and z-directions for monozygotic and dizygotic femalesafter scaling and Generalized Procrustes registration

Landmark

Monozygotic females (N = 20) Dizygotic females (N = 14)

X Y Z X Y Z

Mean (SD) Mean (SD) Mean (SD) Mean (SD) Mean (SD) Mean (SD)

Glabella (g) 0.47 (0.65) 48.65 (2.05) 3.91 (1.33) 0.27 (0.64) 48.15 (1.48) 4.39 (1.38)

Nasion (n) 0.60 (0.64) 37.59 (2.03) 2.68 (1.26) 0.35 (0.57) 37.86 (1.77) 3.60 (1.05)

Endocanthion left (enl) 16.40 (0.95) 25.89 (0.72) �10.43 (0.82) 16.99 (1.26) 26.14 (0.63) �10.73 (0.67)

Endocanthion right (enr) �15.98 (1.11) 26.40 (0.75) �9.84 (0.75) �16.17 (1.06) 26.38 (0.82) �10.03 (0.84)

Exocanthion left (exl) 43.87 (1.85) 25.33 (0.88) �15.86 (1.39) 43.28 (1.16) 25.86 (0.51) �15.67 (1.28)

Exocanthion right (exr) �43.72 (1.95) 27.01 (0.74) �15.99 (1.59) �43.30 (1.62) 27.16 (0.57) �15.80 (1.01)

Palpebrale superius left (psl) 30.08 (1.17) 33.40 (0.86) �6.03 (1.54) 30.00 (1.13) 33.06 (1.13) �7.47 (0.77)

Palpebrale superius right (psr) �30.34 (1.51) 33.98 (1.04) �5.79 (1.31) �29.99 (1.31) 33.86 (1.27) �6.82 (0.90)

Palpebrale inferius left (pil) 30.34 (1.34) 21.25 (0.96) �8.52 (0.96) 30.22 (1.09) 21.76 (0.88) �8.51 (0.88)

Palpebrale inferius right (pir) �30.36 (1.47) 21.96 (0.84) �8.42 (1.06) �29.96 (1.27) 22.11 (0.77) �8.29 (0.87)

Pronasale (prn) �0.21 (0.73) �2.49 (1.37) 23.68 (2.02) �0.15 (0.46) �2.80 (1.49) 24.86 (1.93)

Subnasale (sn) 0.13 (0.57) �15.28 (1.46) 10.26 (1.68) 0.08 (0.50) �15.75 (1.28) 11.23 (1.53)

Allare left (all) 16.20 (1.51) �7.01 (0.90) 3.84 (0.96) 15.81 (1.21) �7.21 (1.24) 3.74 (1.06)

Allare right (alr) �16.28 (1.02) �6.87 (1.23) 3.56 (0.88) �15.78 (1.02) �6.94 (1.54) 3.45 (0.89)

Labiale superius (ls) �0.12 (0.29) �29.07 (1.48) 11.53 (1.26) �0.10 (0.33) �29.42 (1.35) 11.49 (0.92)

Labiale inferius (li) �0.06 (0.40) �45.20 (1.64) 7.88 (1.07) �0.02 (0.39) �44.42 (1.83) 7.41 (1.58)

Crista philtri left (cphl) 5.36 (0.80) �27.68 (1.40) 10.54 (1.05) 5.34 (1.09) �28.09 (1.19) 10.74 (0.92)

Crista philtri right (cphr) �5.75 (0.63) �27.41 (1.41) 10.61 (1.10) �5.86 (0.92) �27.95 (1.02) 10.70 (0.88)

Cheilion left (chl) 22.79 (2.09) �38.10 (1.50) �4.59 (1.54) 23.65 (1.39) �37.87 (1.34) �5.38 (1.59)

Cheilion right (chr) �23.16 (2.54) �37.53 (0.85) �3.79 (1.59) �24.14 (1.38) �37.38 (1.64) �5.02 (1.28)

Pogonion (pg) �0.27 (0.54) �64.84 (1.96) 0.76 (2.68) �0.53 (0.39) �64.50 (1.45) 2.12 (2.41)

Table 6. Three-dimensional facial symmetry in monozygotic and dizygotic twins

Parameter


p Value*N Median 25th perc. 75th perc. N Median 25th perc. 75th perc.

Av. dist. (mm) Males 18 0.69 0.60 0.82 22 0.71 0.57 0.90 0.849 (NS)

Females 20 0.59 0.46 0.72 14 0.60 0.57 0.76 0.462 (NS)

All 38 0.66 0.51 0.76 36 0.67 0.57 0.82 0.449 (NS)

Coincid. (%) Males 18 49.91 44.52 54.02 22 50.68 42.90 55.73 0.807 (NS)

Females 20 57.26 44.73 64.43 14 53.15 48.79 57.70 0.421 (NS)

All 38 52.23 44.86 61.34 36 52.00 43.17 55.83 0.634 (NS)

N, number of individuals; perc., percentile; Av. dist., average distance between the original and mirror faces of one twin; Coincid., thepercentage of coincidence between the original and mirror faces of one twin (within 0.5 mm of tolerance); NS, not statistically signifi-cant.*Mann–Whitney U test was performed.



role in identifying genetic variants responsible

for normal facial variations. It is believed that

three-dimensional imaging will be of great help

in the quest for further knowledge on genetic

and environmental determinants of facial fea-

tures.

Conclusions

From this study on three-dimensional facial

shape and symmetry of 15-year-old white Brit-

ish twins, the following conclusions can be

drawn:

1. Landmark-based and surface-based three-

dimensional facial analyses can reveal

within- and between-pair differences in facial

soft tissue shapes of MZ and DZ twins.

2. Genetic factors play an important role in

three-dimensional soft tissue shape and the

relative contribution of genetic and

environmental factors is not the same for

the upper, middle and lower facial thirds.

3. Zygosity does not seem to influence the

amount of three-dimensional symmetry of

facial soft tissues. Lower facial third is the

most asymmetrical part of the face in both

MZ and DZ twins.

Clinical relevance

The twin method has been extensively used in

orthodontics in the last few decades to investigate

the relative contribution of genetic and environ-

mental factors to the shape of the craniofacial

complex. Three-dimensional imaging systems

provide a possibility to obtain and analyse facial

soft tissue morphology non-invasively, accurately

and reliably. In this study, laser surface scanning

was used to compare facial shape and symmetry of

MZ and DZ twins. Suggested three-dimensional

facial analyses can reveal differences in facial mor-

phology, which has not been possible previously

using two-dimensional data. This can support fur-

ther research in craniofacial genetics.

Table 7. Three-dimensional symmetry by facial thirds in monozygotic and dizygotic twins

Twins N Parameter

Upper facial third Middle facial third Lower facial third

Median

25th

perc.

75th

perc. Median

25th

perc.

75th

perc. Median

25th

perc.

75th

perc. p Value†

MZ males 18 Av. dist. (mm) 0.52 0.43 0.66 0.57 0.50 0.77 1.00 0.86 1.37 <0.001

Coincid. (%) 58.28 49.70 67.75 53.36 45.18 58.96 29.71 19.57 34.40 <0.001

MZ females 20 Av. dist. (mm) 0.48 0.42 0.59 0.55 0.42 0.67 0.79 0.48 1.43 0.012

Coincid. (%) 62.58 55.76 70.57 56.19 46.76 64.37 38.87 15.40 59.20 0.003

MZ all 38 Av. dist. (mm) 0.49 0.42 0.64 0.56 0.48 0.71 0.94 0.63 1.36 <0.001

Coincid. (%) 60.88 51.73 69.22 54.16 46.80 61.98 31.04 18.89 46.66 <0.001

DZ males 22 Av. dist. (mm) 0.54 0.39 0.65 0.56 0.49 0.79 1.30 0.71 1.84 <0.001

Coincid. (%) 59.18 48.24 70.78 55.53 45.71 57.69 21.30 10.67 38.12 <0.001

DZ females 14 Av. dist. (mm) 0.47 0.40 0.59 0.68 0.48 0.83 0.82 0.48 1.29 0.026

Coincid. (%) 65.36 52.37 75.86 47.02 40.00 59.15 32.63 14.82 59.21 0.007

DZ all 36 Av. dist. (mm) 0.52 0.40 0.59 0.60 0.49 0.79 1.20 0.64 1.62 <0.001

Coincid. (%) 62.86 48.90 71.06 54.11 43.02 57.92 26.07 13.58 43.68 <0.001

N, number of individuals; perc., percentile; Av. dist., average distance between the original and mirror faces of one twin; Coincid., thepercentage of coincidence between the original and mirror faces of one twin (within 0.5 mm of tolerance).Figures in bold indicate facial third which was significantly different from the other two (Mann–Whitney U test was applied).NS, not statistically significant.†Kruskal-Wallis test was performed.



Acknowledgements: We are extremely grateful to all

the families who took part in this study, the midwives

for their help in recruiting them and the whole ALSPAC

study team, which includes interviewers, computer and

laboratory technicians, clerical workers, research scien-

tists, volunteers, managers, receptionists and nurses.

The UK Medical Research Council, the Wellcome Trust

(Grant ref: 092731) and the University of Bristol provide

core support for ALSPAC.

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3d Facial Analysis