Discussions

Facial soft tissue thickness (FSTT) is an index used in forensic facial reconstruction (FFR), and values vary between different populations [1, 2, 5, 17], [40, 51, 52]. Approximated population values of FSTT are commonly used in FFR [52]. It has been postulated that the differences in FSTT values between different populations are due to variations in the type of imaging modality, such as magnetic resonance imaging, computed tomography (CT), ultrasound, and cone beam computed tomography [52] or slight differences in bone morphology between populations. Computed tomography images are very reliable at demonstrating craniofacial bone and soft tissues [24, 43, 52]. In this study, the computed tomography machine was the same as that used in the previous FSTT publication on the combined Nigerian male adult (CNME) data [43].

In comparing the findings of this study with any other published population data, similar to the CNME study, acceptable point variation should be at least a value of 1.5 mm. Previous studies have stated that a difference of less than 1 mm is an insignificant benchmark [43, 52]. In comparison to other studies (Table 1), this study has included an average number of subjects. When compared to previous studies in Africa, a greater number of FSTT points have been used (Table 9), and this should increase coverage of the facial contours. Furthermore, none of the African studies measured or compared the right and left sides of the face in the Nigerian female adult.

Population studied | Image type/number of FSTT points | M/F | Number of patients, age range (years) | Study name/year(abbreviation)
Zulus (South Africa) | Lateral and oblique cephalometric + ultrasound scan/54 | M | 55, 20 to 35 | Aulsebrook et al., 1995 (A°) [26]
Mixed population, White and Black (Cape areas, South Africa) | Computed tomography scan at 5 mm slides whilst using about 20 slides per patient/32 | M/F | 32 (16 male, 16 female), 12 to 71 | Phillip and Smith, 1996(P & S) [40]
Black Population (Gauteng region, South Africa) | The computed tomography thickness of the slides is not stated. Measurements were from 28 FSTT points midline, 10 of which were midline/28 | F | 154 CT scans, 18 to 35 | Cavanagh and Steyn, 2011 (C & S)[39]
Sudanese ethnicGroup | Plane Cephalogram/20 | M/F | 233, 18 to 35 | Hamid and Abuaffan, 2016 (H & A) [35]
Egyptian | Ultrasound/17 | M/F | 204, 20–35 | El-Mehallawi and Soliman [37]
Egyptian | Cone-beam computed tomography/18 (10 midline, 8 bilaterally) | M/F | 20 (M = 10, F = 10)/17–33 | Shehata et al., 2023[41]
Nigerian | Computed tomography/50 | M | 55, 18–100 | Adegbite et al. [43]
Nigerian | Computed tomography/50 | F | 32, 18 to 96 | This study

The RadiAnt software used for estimating the distance from bone to skin at each FSTT point produces a good 3-D reformat of the images, thereby allowing for the elimination of some scans and optimising measurements and results.

Analysis and comparison of the midline data

The soft tissue thickness point with the lowest value for the combined Nigerian female adult (CNFE) is at the rh point with a value of 2.59 mm; this is lower than the 3.35 mm value for the Nigerian male adult (CNME). Studies, including the (CNME), have reported this as the point with the lowest value [38, 42, 43]. The FSTT with the highest value is at the lm point. This is similar to the CNME, which had its highest and similar values at the mp and lm points. As illustrated in Table 5; Fig. 7, CNME displayed marginally higher values at most midline points and with more significant differences at the mp (1.84) and ls (1.52), respectively; except for an insignificantly higher CNFE value at the me (10.81 mm) as compared to the CNME (10.36 mm).

Fig. 7: Points with more soft tissue in Nigerian males (defined by the end of the green arrowhead)

Despite the hair-woven pulling pattern in the CNFE, Fig. 5, the CNME displaced more value at the vertex (5.54 mm vs. 6.39 mm). The CNME report shows slightly more soft tissue beneath the chin (mn) point than the CNFE; this is contrary to the previous report by Wilkinson [1] that females are likely to have greater volume of soft tissue at this point. One previous study has shown that, based on the same body mass index (BMI), females tend to have more facial soft tissue thickness than males [53]. It should be noted that detailed BMI has not been investigated in this study.

Analysis and comparison of bilateral data

The facial soft tissue thickness (FSTT) data for both sides of the face were analysed and compared with the CNME data and other populations’ published data. Like the CNME, the CNFE’s lowest FSTT value was at the mid-lateral orbit (mlo). CNFE’s highest FSTT value was at the lateral maxilla (lm) point; this is dissimilar to the CNME, which had its highest value at the mid-masseter (mm) point.

Comparing the Nigerian female and male represented as mean difference (comparison column) in Table 6 shows that males have marginally more soft tissue at more FSTT points, except at the lateral points of the face where females shows marginally more soft tissues, including at the lm (22.20 vs. 20.09), sm2 (21.64 vs. 19.93), lo (7.65 vs. 6.06), io (10.41 vs. 9.44), and za (6.76 vs. 6.26), respectively (Table 8; Fig. 8). The increased values at the zygomatic arch, lateral orbit, lateral maxilla, and supra-M2 in the CNFE is consistent with previous studies, including studies on Japanese, white Europeans, black and white Americans [1, 21, 31, 38].

Fig. 8: Points with more soft tissue in Nigerian females (defined by the end of the green arrowhead)

Similar to the male, the differences between the right and left faces of the Nigerian female consistently reveal (marginally) more soft tissues on the left side at all FSTT points (Table 6, comparative Table), also seen in Cohen’s D difference. The highest differences between left and right sides of the face are at the supra-M2, lateral maxilla, and the infra-M2 points with differential values of 1.41, 1.4, and 1.16 mm, respectively.

The Nigerian adult female FSTT points with the least relative percentage difference were at the infraorbital (0.85%), lateral glabella (2.42%), and frontal eminence (2.43%) regions, Table 6. The highest relative percentage difference was at the zygomatic arch (9.28%), the mid-lateral orbit (7.58%) and the supra-M2 (6.64%). This is different to the Nigerian males, the FSTT point with the least relative difference is at the mid-masseter (1.53%), and the highest is at the frontal eminence (8.18%), Table 6.

These Nigerian adult female (CNFE) bilateral data were compared with other population studies that have compared the right and left sides of the face (Table 10). At least for this Nigerian adult female and male, these differences were not due to the head position because the same machine was used and each subject was scanned in a supine position with the head centred by equal support to both the left and right sides of the face. Those that were not well-centred were rejected from the dataset as the measurement could not be standardised.

FSTT points | Study name
LtRt
 | CNFE | R & C (female) [38] | R & C (male) [38] | De Geoff et al., [33] | Hwang et al., [28] | Toneva et al.,(female) [51] | Toneva et al.,(male) [51]
Frontal eminence | 4.474.36 | 8.008.00 | 8.258.75 | 4.14.3 | 5.96.0 | -- | --
Supraorbital | 5.585.43 | 4.504.50 | 4.754.75 | 5.65.4 | 6.76.8 | 6.736.96 | 7.597.79
Infraorbital | 10.5010.41 | 8.508.25 | 7.507.75 | 9.59.4 | 7.67.5 | 5.115.28 | 5.405.27
Supraglenoid | 12.9812.24 | 12.0012.25 | 11.7511.75 | 9.99.5 | 12.212.1 | -- | --
Zygomatic arch | 7.396.76 | 9.259.00 | 8.758.50 | 6.56.7 | 8.58.6 | 8.338.07 | 7.296.98
Lateral Orbit | 8.137.65 | 14.25*12.75 | 13.0013.00 | 8.99.4 | 9.49.3 | 8.758.67 | 7.107.38
Lateral Glabella | 4.554.44 | -- | -- | 5.75.9 | 8.88.6 | -- | --
Lateral nasal | 7.406.95 | -- | -- | 3.83.7 | 6.97.0 | -- | --
lateral maxilla | 23.6022.20 | -- | -- | 17.518.2 | 18.318.3 | -- | --
Lateral nostril | 9.399.11 | -- | -- | 9.79.5 | 13.513.7 | -- | --
Supracanine | 7.987.59 | -- | -- | 9.99.3 | 10.810.9 | -- | --
Infra-canine | 7.847.58 | -- | -- | 10.010.5 | 11.711.9 | -- | --
Mid-lateral orbit | 3.503.25 | -- | -- | 4.84.8 | 5.05.0 | 3.263.44 | 3.183.48
Supra-M2 | 23.0521.64 | 20.7521.25 | 22.2522.00 | 26.626.8 | 27.927.8 | -- | --
Infra-M2 | 19.0217.86 | 16.7517.25 | 15.7516.50 | 17.918.8 | 20.720.6 | -- | --
Mid-masseter | 20.9820.22 | -- | -- | 16.217.8* | 18.317.8 | 18.7119.22 | 20.2119.71
Gonion | 17.5316.75 | 14.2514.25 | 14.2514.75 | 14.215.1 | 13.012.5 | 13.2913.10 | 14.2713.28
Occlusal line | 20.6219.61 | 18.2519.25 | 19.5019.00 | 19.019.5 | 21.921.8 | 21.3021.33 | 22.2722.55
Mid-mandible | 12.6411.88 | -- | -- | 10.612.1* | 7.97.7 | -- | --

There are only very few studies which have reported a consistent increase in soft tissue on the left side of the face at all FSTT points; this includes the Sahni et al. on an adult population in northwest India [5]. Coskun reported that the left side of the Greek adult female face was marginally larger than the right side, although in males, the converse was found, as the right side had more thickness than the left, with the most difference at the zygomaxillary [34].

Table 10 reveals that the differences at FSTT points are marginal and not confined to one side of the face but vary at different points on the right and left, also documented by Coskun, Beaini, and other authors [28, 33, 38, 51].

In conclusion, the CNFE, like the CNME, had more soft tissue thickness on the left than the right; this is similar to Sahni et al. [5]. These differences are generally marginal and less than 6% [53].

Comparative analysis of the CNFE young adult FSTT with other populations of similar age

The young Hausa female 18 to 32 years range (represented as HF°) was compared with the young Nigerian male adults (CNME of age 18 to 32 years) and with other populations (Tables 8 and 11). The CNME 18 to 32 generally displayed greater soft tissue thickness at most FSTT points than the HF° 18–32, but especially at the mm, mp, ol, ln, and ls points with differences of 3.15, 2.23, 2.99, 2.31, and 1.60, respectively (Table 8) and Fig. 9 illustrate the comparison with females in other populations of similar age brackets. The De Geoff female aged 18 to 29 years (Belgium data) represented as De Greef°, when compared with the HF°, shows differences greater than 1.5 mm affecting 10 FSTT points, Table 11.

Data Table | Comparison Table
FSTT points | HF°(18–32) | C & S(18–35)[39] | Bulut°(18–29)[2] | De Greef°(18–29) [33] | HF° -C & S | HF° - Bulut° | HF° - De Greef°
Vertex | 7.50 | - | - | - | - | - | -
Supraglabella | 3.54 | 4.7 | 3.73 | 4.1 | −1.16 | −0.19 | −0.56
Glabella | 4.76 | 6.3 | 5.72 | 5.1 | −1.54* | −0.96 | −0.34
Nasion | 4.87 | 6.0 | 7.08 | 6.3 | −1.13 | −2.21* | −1.43
Rhinion | 2.56 | 2.7 | 2.49 | 2.6 | −0.14 | 0.07 | −0.04
Midphiltrum | 11.08 | 10.9 | 12.19 | 9.8 | 0.18 | −1.11 | 1.28
Upper lip border | 9.32 | 13.3 | 11.09 | 10.0 | −3.98** | −1.77* | −0.68
Lower lip border | 9.67 | 14.7 | 11.73 | 11.0 | −5.03*** | −2.06* | −1.33
Labiomental | 11.45 | 12.2 | 9.52 | 9.6 | −0.75 | 1.93* | 1.85*
Mental eminence | 10.76 | 10.6 | 10.91 | 9.6 | 0.16 | −0.15 | 1.16
Menton | 4.97 | 6.7 | 5.27 | 5.6 | −1.73* | −0.3 | −0.63
Frontal eminence | 4.53 | 4.8 | 3.75 | 3.9 | −0.27 | 0.78 | 0.63
Supraorbital | 5.80 | 6.8 | 5.99 | 5.4 | −1 | −0.19 | 0.4
Infraorbital | 8.86 | 6.9 | 5.50 | 9.4 | 1.96* | 3.36** | −0.54
Supraglenoid | 11.69 | 12.0 | 11.0 | 9.6 | −0.31 | 0.69 | 2.09*
Zygomatic arch | 6.92 | 8.4 | 8.19 | 6.9 | −1.48 | −1.27 | − 0.02
Lateral Orbit | 7.42 | - | 9.73 | 10.0 | - | −2.31* | −2.58*
Lateral Glabella | 4.65 | - | 5.14 | 5.7 | - | −0.49 | −1.05
Lateral nasal | 6.10 | - | 3.00 | 3.7 | - | 3.1** | 2.4*
lateral maxilla | 20.28 | - | 12.95 | 17.9 | - | 7.33*** | 2.38*
Lateral nostril | 9.46 | - | 9.18 | 9.5 | - | 0.28 | −0.04
Supracanine | 8.34 | - | 9.05 | 9.5 | - | −0.71 | −1.16
Infra-canine | 7.86 | - | 10.04 | 10.3 | - | −2.18* | −2.44*
Mid-lateral orbit | 3.48 | - | 3.62 | 5.0 | - | −0.14 | −1.52*
Supra-M2 | 21.34 | 28.5 | 26.81 | 26.6 | −7.16*** | −5.47*** | −5.26***
Infra-M2 | 18.40 | 21.1 | 20.24 | 19.0 | −2.7* | −1.84* | −0.6
Mid-masseter | 19.34 | 19.5 | 17.51 | 17.2 | −0.16 | 1.83* | 2.14*
Gonion | 15.15 | 14.3 | 14.48 | 14.4 | 0.85 | 0.67 | 0.75
Occlusal line | 17.64 | 22.9 | 22.14 | 19.4 | −5.26*** | −4.5** | −1.76*
Mid-mandible | 10.58 | 7.9 | 9.68 | 11.4 | 2.68* | 0.9 | −0.82

Fig. 9: Compares the (HF°)18–32 with other populations

The South African females aged 18 to 35 years represented as C & S [39] displayed more thickness at some points than the HF° (18 to 32); these include significant differences at the supra-m2 (7.16), li (5.03), ls (3.98), infra-m2 (2.7), io (1.96), mn (1.73) and g (1.54), Fig. 10.

Fig. 10: Points with the most differences between HF° and C & S (defined by the end of the blue arrowhead)

Bulut et al. on subjects aged 18 to 29 years represented as Bulut° (Turkey data) [2] also show more soft tissue thickness than the HF° at points as indicated on the left face by the end of the green arrowhead, Fig. 11. The HF°, however, demonstrates more thickness at other points as defined by the end of the blue arrowhead on the right face.

Fig. 11: FSTT points with the most differences between HF° and Bulut et al 18-29° (defined by the end of the green and blue arrowhead)

Other studies, including Manhein et al. have reported greater soft tissue thickness in black American adult males in the age brackets (19 to 34 and 35 to 45 years). In the 19 to 34 group there are differences of 3.8 mm and 2.1 mm at the mp and mn, respectively [31]. For the 35 to 45 age bracket, this was also prominent at the mp, with the male mean value greater than the female by 2.2 mm. Manhein et al. similarly report more tissue thickness in white American adult males in all age categories (19–34, 35–45, 46–55, > 56) except at the rh and mp in the 46–55 where both sexes had same values and in the > 56 years females, with more FSTT values at the me and mn [31]. This is similar to the Nigerian female, which showed marginally more value at the me point.

Comparative analysis of CNFE facial soft tissue with other global adult populations

The Nigerian adult female (CNFE) right side of the face show soft tissue differences (represented in *) when compared with published values for Turkey and Korea populations, in Table 12; Fig. 12. The CNFE tend to displace more soft tissue thickness at the lateral maxilla with difference of 9.32 and 4.7 more than the data by Bulut et al. and Hwang et al., respectively. Also, CNFE have more thickness at the mid-masseter. However, Bulut et al.‘s data show more tissues at the sm2 (21.64 vs. 26.76) and ol (19.61 vs. 21.41), respectively, as indicated with *.

FSTT points | CNFE | Bulut et al. | Hwang et al. | CNFE -Bulut et al. | CNFE -Hwang et al.
Supraglabella | 3.80 | 3.94 | 4.8 | −0.14 | −1
Glabella | 5.39 | 6.03 | 5.3 | −0.64 | 0.09
Nasion | 5.33 | 7.16 | 5.4 | −1.83* | −0.07
Rhinion | 2.59 | 2.38 | 2.2 | 0.21 | 0.39
Midphiltrum | 10.80 | 11.38 | 10.7 | −0.58 | 0.1
Upper lip border | 8.65 | 10.58 | 9.9 | −1.93* | −1.25
Lower lip border | 10.45 | 11.47 | 11.6 | −1.02 | −1.15
Labiomental | 11.79 | 9.56 | 10.2 | 2.23* | 1.59*
Mental eminence | 10.81 | 11.38 | 12.0 | −0.57 | −1.19
Menton | 5.70 | 5.57 | 6.9 | 0.13 | −1.2
Frontal eminence | 4.36 | 4.02 | 5.4 | 0.34 | −1.04
Supraorbital | 5.43 | 6.17 | 6.4 | −0.74 | −0.97
Infraorbital | 10.41 | 5.47 | 7.3 | 4.94*** | 3.11**
Supraglenoid | 12.24 | 11.45 | 11.2 | 0.79 | 1.04
Zygomatic arch | 6.76 | 8.06 | 8.7 | −1.3 | −1.94*
Lateral Orbit | 7.65 | 9.40 | 10.2 | −1.75* | −2.55**
Lateral Glabella | 4.44 | 5.15 | 8.2 | −0.71 | −3.76**
Lateral nasal | 6.95 | 2.77 | 6.5 | 4.18*** | 0.45
lateral maxilla | 22.20 | 12.88 | 17.5 | 9.32*** | 4.7***
Lateral nostril | 9.11 | 9.01 | 12.4 | 0.1 | −3.29**
Supracanine | 7.59 | 8.75 | 10.3 | −1.16 | −2.71*
Infra-canine | 7.58 | 9.67 | 10.8 | −2.09* | −3.22**
Mid-lateral orbit | 3.25 | 3.49 | 5.2 | −0.24 | −1.95*
Supra-M2 | 21.64 | 26.76 | 27.7 | −5.12*** | −6.06***
Infra-M2 | 17.86 | 20.33 | 20.30 | −2.47* | −2.44*
Mid-masseter | 20.22 | 18.38 | 17.50 | 1.84* | 2.72*
Gonion | 16.75 | 14.74 | 12.9 | 2.01* | 3.85**
Occlusal line | 19.61 | 21.41 | 21.2 | −1.8* | −1.59*
Mid-mandible | 11.88 | 9.78 | 7.7 | 2.1* | 4.18**

Fig. 12: Compares the CNFE FSTT with other population data

Effect of biological sex on facial soft tissue profiles

The CNFE soft tissue points at the lm and sm2 demonstrate the most sexual dimorphism, displaying mean differences of 2.11 and 1.71, respectively, as illustrated in Fig. 8. The published sexual dimorphism for FSTT points differs between populations. Moritsugui et al. data on Midwest Brazil [30] show less tissue thickness in females than males at all points. These differences are at the ns (6.2 vs. 8.1), mp (13.1 vs. 15.7), ls (10 vs. 13.3), li (9.8 vs. 11.9), supramental (11.9 vs. 12.9), pogonion (mn) (9.9 vs. 11.4), me (7.0 vs. 9.0); these are similar to this Nigerian dataset. It is worthwhile to mention that Moritsugui et al. defined the ls as prosthion. Similarly, Beaini et al. on a multi-ancestral Brazilian population [25] report more soft tissue in males than females, except at the lateral orbit (lo) point, where females marginally displayed more tissue. Similarly, Nigerian females have more tissue at the lo than Nigerian males. Sahni et al., northwest India, reported a sexual dimorphism by using 9 variables and sexed with a male accuracy of 88% and female of 76% [5]. Hwang et al.‘s data on Koreans show more soft tissue values in male adults, particularly at the mp (12.5 vs. 10.7), ls (11.7 vs. 9.9), and li (13.0 vs. 11.6) with differences of 1.8, 1.8, and 1.4, respectively. Hwang’s Korean female adult marginally shows more soft tissues at the lateral face (za, mlo and lo); this is similar to the Nigerian adult female and male. However, other researchers argue that these differences will not define identification [53].

Limitations and potential sources of error

Computed tomography (CT) and magnetic resonance imaging (MRI) are both reliable in soft tissue imaging [24]. An accurate soft tissue thickness dataset from any of these will improve FFR [54]. This new dataset for the Nigerian adult female has been generated by the use of computed tomography images. However, the standard supine positioning for craniofacial computed tomography and MRI may have introduced error.

This supine positioning will cause a weight (gravity) pulling effect on the lateral soft tissue, thereby reducing the thickness at the mid-sagittal points and increasing the width of the lateral tissues [52, 55, 56]. CT has been shown to yield higher facial soft tissue thickness (FSTT) values than other imaging modalities, including MRI and ultrasound [52, 57, 58]. These may account for some of the differences in this report. The CT machine in this study had a slice thickness of 1.25 mm; this higher thickness may also have inflated values. Higher slice thicknesses may yield lower resolution [59]; perhaps an average of 0.5 to 0.7 mm thickness will give better resolution.

However, live subjects’ CT is more reliable than using cadavers or other imaging types like lateral cephalograms [8, 24, 32, 38]. Furthermore, in comparison to ultrasound, the direct contact of the gel and probe of ultrasound may cause compression of the soft tissues, thereby giving distorted readings [52, 60]. In future studies, a more sensitive CT or MRI will be used to compare with this dataset. The greater number of FSTT points used in this study will allow for greater coverage of the face, and using its own average FSTT will enhance forensic facial reconstruction as documented in previous studies [56]. Also, specialised software packages employed for measurements may affect measurement accuracy [54, 61].

BMI is not well described in this study. However, as documented in other studies, increases in BMI are more likely to increase soft tissue values [1, 2, 15, 33, 36, 45, 57]. In this Nigerian population, normal weight is quite prevalent rather than underweight, overweight, or obesity [46]. A study has shown that based on the same BMI, females tend to have more soft tissue thickness than males [53]. Some studies have also advocated for producing multiple facial reconstructions of the same face, based on different BMI FSTT data [62].