Experimental design

Thirty-five landmarks were used. Fifteen of the landmarks were identified in the midsagittal plane ( n = 15) and were bilateral ( n = 20). Most of these landmarks were defined according to Farkas ( Fig. 1 ). The landmarks were marked with a pen on the skin of the volunteers by the same observer in order to compare exactly the same point in the different head positions. After this procedure, the subjects were scanned in the sitting, standing, and supine body positions with a 3D light scanner.

(A) Soft tissue landmarks marked on the skin, the common origin, and defined x , y , and z axes. (B) Schematic description and abbreviations for the soft tissue landmarks.

3D scanning

An Artec EVA 3D light scanner (2013; Artec Group, Luxembourg) was used for the face scanning. The working distance of the scanner is between 0.4 m and 1 m, the 3D accuracy is up to 0.05 mm, and the 3D resolution is up to 0.1 mm. During scanning, a computer and Artec EVA Studio software (version . . .15; Artec Group) was used to host the Artec EVA. Scanning was performed in the sitting, standing, and supine positions. The sitting and standing scans were performed in the natural head position. The natural head position was determined by the subjects own feeling of a natural head balance. The supine scans were performed after the head of the subject was oriented horizontally ( Fig. 2 ).

The positions of the subject and the scanner: (A) sitting, (B) standing, and (C) supine body positions.

Soft tissue analyses

The scanned data from the three positions were imported into the same workspace of the Artec Studio software. The corresponding scans for each position were aligned manually using translation and rotation in all three directions, and then merged onto each other using the surface mapping algorithm. For alignment, the mid-endocanthion point (a point halfway between the inner corners of the eyes), which has been found to be the statistically most stable point of the face, was used as the common origin of the x , y , and z axes. The transverse, vertical, and sagittal anatomical axes of the head were defined as the x -, y -, and z -axis, respectively. The marked landmarks were used to bring the scans into the same position and give them the same orientation. For each landmark, the differences between the sitting and supine, standing and supine, and sitting and standing positions were calculated along the x , y , and z axes. In addition, the standard deviations (SD) of the landmarks were obtained for the 35 landmarks. The root mean square (RMS), the mean absolute deviation (MAD), and the mean signed distance (MSD) values were also calculated automatically by the software; these were then used to compare the superimposed scans. Figure 3 shows an example of the deviation colour maps derived from the superimposition of facial masks obtained from the scans.

Mask to mask deviation colour maps derived from the superimposition of facial masks in (A) the sitting and standing body positions, (B) the sitting and supine body positions, and (C) the standing and supine body positions. The coloured deviation map legend in the upper left corner shows the millimetre scale. The map changes in colour from blue, which corresponds to negative distance, to red, which corresponds to positive distance; green means that the distance between surfaces at that particular point is close to zero.

Statistical analysis

The statistical analysis was performed using GraphPad Prism version .05 software (GraphPad Software Inc., San Diego, CA, USA). The results were expressed as the mean ± SD. The D’Agostino–Pearson test was used to assess whether the data were normally distributed. Two-way analysis of the variance (ANOVA) was used to compare the masks between the different body positions and in the x , y , and z axes. Variations in the landmarks within the different body positions were evaluated by one-way ANOVA for repeated measurements. The differences between the measurements were tested with Tukey’s post hoc test. Friedman ANOVA for repeated measurements and Dunn’s multiple comparison test were used for those not suited for normal dispersion. A P -value of ≤0.0001 was considered statistically significant. Comparisons of the mean differences between the genders were carried out with the t -test or the Mann–Whitney U -test.

Reproducibility of landmark identification

The 3D scans obtained for each body position acquired from randomly selected subjects (five male and five female) were used in order to test the accuracy of observer landmark identification. The landmarks were labelled and the identifications were repeated two times by two different observers (UO, RS) with a 1-week gap between digitization sessions. The reliability of the observers was assessed using the two-way random intra-class correlation coefficient. A value of 0. or higher was considered to signify reliability.

Intra- and inter-observer reliability of the body positions

The intra-observer and inter-observer reliability for the three body positions was acceptable. The correlation coefficient between the first and second measurements of the sitting position ranged between 0.919 and (average 0.986) for intra-observer reliability, and between 0.914 and 0.999 (average 0.974) for inter-observer reliability. In the standing position, the values ranged between 0.90 and 0.998 (average 0.946) for intra-observer reliability, and between 0.903 and 0.989 (average 0.938) for inter-observer reliability. In the supine position, the results ranged between 0.912 and 0.962 (average 0.946) for intra-observer reliability, and between 0.91 and 0.999 (average 0.965) for inter-observer reliability.

Comparison of facial masks

The similarity of the surfaces was analyzed by comparing the RMS, the MAD, and the MSD.

The results for the merged masks are shown in Fig. 4 . The RMS values between the scans were .001 ± 0.397 for sitting to supine (Sit–Sup), .033 ± 0.408 for standing to supine (Stn–Sup), and .051 ± 0.326 for sitting to standing (Sit–Stn). The results of the MAD were .133 ± 0.362 for Sit–Sup, .2 ± 0.385 for the Stn–Sup, and .165 ± 0.2519 for the Sit–Stn. The MSD values were 0.619 ± 0.267 for Sit–Sup, 0.694 ± 0.278 for Stn–Sup, and −0.073 ± 0.171 for Sit–Stn. Comparisons between the Sit–Sup and the Stn–Sup groups showed no significant differences. The results for Sit–Stn were significantly lower than those of both of the other groups. Comparisons in the x , y , and the z axes were also performed and are shown in Fig. 4 .

Comparison of standing (Stn), sitting (Sit), and supine (Sup) body positions. Differences among the positions were compared using the root mean square (RMS), mean absolute deviation (MAD), and mean signed distance (MSD). *Significantly different from Sit–Sup; ^# significantly different from Stn–Sup ( P < 0.0001).

Comparison of the landmarks

With further analysis of the data, the mean differences of landmarks in the x , y , and z coordinates were compared among the three body positions. The data are shown in Table 1 and the results are summarized in Table 2 .

Table 1

The mean linear (millimetres) and percentage differences. ^a

	x -axis						y -axis						z -axis
	Sit–Stn	(%)	Sit–Sup	(%)	Stn–Sup	(%)	Sit–Stn	(%)	Sit–Sup	(%)	Stn–Sup	(%)	Sit–Stn	(%)	Sit–Sup	(%)	Stn–Sup	(%)
Midsagittal landmarks
Tri	−0.12	7.55	0.09	5.26	0.21	13.86	−0.59	0.82	0.25	0.35	0.84	1.18	−0.24	6.69	0.30	8.24	0.54*	16.00
G	0.07	9.91	0.07	10.31	−0.00	0.37	−0.34	1.56	0.29	1.33	0.63*	2.94	0.21	1.47	−0.80	5.58	−1.01*	7.15
N	0.02	22.15	0.20	188.50	0.18	136.19	−0.54	4.42	−0.22	1.80	0.32	2.74	0.35	2.53	−0.37	2.67	−0.72*	5.34
Mn	−0.06	41.69	0.21	145.22	0.27	320.54	−0.44	4.64	−0.48	5.05	−0.04	0.40	0.32	1.21	−0.07	0.27	−0.39	1.50
Prn	−0.01	7.40	0.11	55.79	0.13	68.24	−0.16	0.49	−0.48	1.48	−0.32	0.98	0.45	1.17	−0.35	0.91	−0.80*	2.10
Cm	−0.10	23.40	−0.02	5.30	0.07	23.62	−0.19	0.47	−0.60*	1.47	−0.41	1.00	0.45	1.48	−0.08	0.26	−0.53	1.77
Sn	−0.01	3.45	−0.01	3.49	−0.00	0.04	−0.18	0.41	−0.55	1.25	−0.37	0.84	0.35	1.47	0.05	0.21	−0.30	1.28
Ls	−0.01	1.45	0.01	1.50	0.02	3.00	−0.22	0.39	0.24	0.43	0.46	0.82	0.46	1.93	0.27	1.13	−0.19	0.81
Sto	0.06	9.04	0.13	18.74	0.07	8.89	−0.05	0.08	0.56	0.86	0.61*	0.94	0.53	2.58	0.87*	4.23	0.34	1.70
Li	−0.10	14.89	0.12	18.55	0.22	39.29	−0.33	0.44	−0.41	0.55	−0.08	0.11	0.76*	3.91	0.27	1.39	−0.49	2.62
Sm	−0.14	15.81	0.09	10.44	0.23	31.18	−0.07	0.08	−0.41	0.50	−0.34	0.41	0.77*	5.08	0.20	1.32	−0.57*	3.96
Pg	−0.04	6.33	0.23	40.32	0.26	49.80	−0.31	0.31	−0.01	0.01	0.30	0.30	0.71*	4.45	0.03	0.19	−0.68*	4.46
Gn	−0.03	7.75	0.07	15.53	0.10	25.24	−0.10	0.10	0.10	0.10	0.20	0.19	0.61	4.61	−0.33	2.50	−0.94*	7.45
Me	0.01	16.66	0.18	400.80	0.17	329.27	−0.30	0.28	−0.30	0.28	−0.00	0.00	0.70	8.89	−0.33	4.19	−1.03*	14.36
C	0.02	10.07	−0.10	53.70	−0.12	70.91	0.10	0.08	0.40	0.33	0.30	0.25	−1.43	4.74	−2.88*	9.55	−1.45	5.05
Bilateral landmarks
Ex1	0.05	0.10	1.21*	2.35	1.16*	2.25	0.01	0.57	0.69*	28.27	0.68*	27.86	0.31	2.62	0.16	1.35	−0.15	1.24
En1	−0.15	0.85	0.41	2.33	0.56	3.21	0.14	25.44	−0.46	83.05	−0.60	86.49	0.18	479.81	−0.62*	1675.77	−0.80*	371.77
En2	0.17	1.02	−0.20	1.20	−0.37	2.25	−0.01	2.05	−0.58	95.83	−0.57	95.75	0.14	1540.10	−0.69*	7362.22	−0.83*	542.79
Ex2	0.02	0.04	−1.16*	2.28	−1.18*	2.32	−0.21	7.65	0.90*	32.44	1.12*	37.24	0.26	2.27	0.24	2.10	−0.02	0.17
Zy1	−0.01	0.02	2.39*	4.64	2.40*	4.66	0.07	0.28	2.20*	8.91	2.13*	8.66	0.40	8.47	1.04*	22.14	0.64*	12.60
Zy2	0.40	0.76	−2.11*	4.03	−2.51*	4.83	0.04	0.15	2.50*	9.66	2.46*	9.52	0.17	3.05	0.90*	16.28	0.73*	12.84
Al1	0.02	0.12	0.94*	5.42	0.92*	5.30	−0.16	0.46	0.27	0.77	0.43	1.22	0.56	3.30	−0.12	0.71	−0.68*	4.14
Al2	0.13	0.79	−0.88*	5.33	−1.01*	6.17	−0.01	0.03	0.46	1.32	0.47	1.35	0.49	2.95	−0.41	2.47	−0.90*	5.59
Ch1	−0.14	0.50	1.68*	5.94	1.82*	6.47	0.01	0.01	1.09*	1.63	1.08*	1.62	0.45	5.87	1.07*	13.99	0.62*	8.62
Ch2	0.04	0.15	−1.60*	5.86	−1.64*	6.02	−0.02	0.03	0.97*	1.46	0.99*	1.49	0.52	6.63	1.27*	16.26	0.75*	10.31
Sa1	−1.22	1.39	1.02*	1.16	2.24*	2.58	0.62	181.18	0.93	270.92	0.31	31.92	0.80	0.85	2.06*	2.18	1.26*	1.32
Sa2	0.09	0.10	−1.93*	2.18	−2.02*	2.28	0.46	139.59	0.84	255.80	0.38	293.57	−0.02	0.02	2.10*	2.24	2.12*	2.26
Hel1	0.05	0.07	1.94*	2.58	1.89*	2.52	0.30	1.93	0.71	4.56	0.41	2.69	0.40	0.49	1.48*	1.80	1.08*	1.31
Hel2	0.20	0.27	−2.17*	2.88	−2.37*	3.15	0.40	2.40	1.23	7.39	0.83	5.11	0.16	0.20	1.59*	1.94	1.43*	1.74
Tr1	0.04	0.05	1.65*	2.20	1.61*	2.15	0.35	1.23	1.51*	5.33	1.16*	4.14	0.33	0.42	1.75*	2.24	1.42*	1.81
Tr2	0.08	0.11	−1.63*	2.18	−1.71*	2.29	0.44	1.52	1.98*	6.82	1.54*	5.38	0.31	0.40	1.77*	2.28	1.46*	1.87
Sba1	0.38	0.52	4.60*	6.26	4.22*	5.71	0.41	0.78	1.04*	1.98	0.63*	1.21	0.28	0.36	2.27*	2.92	1.99*	2.55
Sba2	0.13	0.18	−4.21*	5.71	−4.34*	5.90	0.25	0.47	1.45*	2.73	1.20*	2.27	0.08	0.10	1.78*	2.31	1.70*	2.21
G1	0.50	0.84	4.16*	6.98	3.66*	6.09	0.43	0.55	3.45*	4.38	3.02*	3.85	0.14	0.25	1.42*	2.55	1.28*	2.29
G2	−0.06	0.10	−4.28*	7.32	−4.22*	7.21	0.32	0.40	3.72*	4.61	3.40*	4.23	−0.41	0.75	1.16*	2.12	1.57*	2.89

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