Introduction

Forensic facial reconstruction (FFR) is the reproduction of the face of the deceased person from their skull. This is commonly achieved by building the soft tissues onto the skull. This practice has been an aid in recognition since the 1370 BC (Before Christ) Egyptian burial ceremony as a death mask [1]. This technique also existed during the 2nd and 3rd centuries BC (Before Christ) as part of Roman entombment rituals and in the bronze portrait age in the passé Christian era [1].

Different methods for forensic facial reconstruction have been used. This can broadly be classified into two techniques: two-dimensional [1, 2] and three-dimensional [1–3]. These techniques are either manual or computer-based. The standard practice of FFR is the reproduction of the face conventionally by using the facial soft tissue thickness (FSTT) dataset derived from the same population.

Typically, facial soft tissue thickness (FSTT) is measured at defined anatomical points from the skull [1–9] and usually with the skull placed in the Frankfurt position [1, 3–10]. The Frankfurt position is the horizontal plane passing between the lowest point on the margin of the orbit (Ro) and the highest point on the brim of the auditory meatus (Po). The measurements are usually taken at 90° from the defined soft tissue points on the skull to the skin [1, 11, 12].

However, there is no consensus on an optimal number of FSTT points for forensic facial reconstruction. A range of points have been used in published works, varying from as low as 9 [1] to 60 [13]. Most authors have at least studied midline facial soft tissue thickness [14, 15], but commonly a combination of midline and lateral points [4–6, 13]; this combination will produce a wider coverage of the face, although not all published works stated which side of the face was studied.

Facial soft tissue thickness are a variable of several factors including population affinity [1, 2, 4–6, 14–26], sex [1, 2, 13], age [1, 27] and body mass index (BMI) [1, 2, 5, 14–20, 27], Table 1. Reports have shown that dental malocclusion is also a significant factor [35]. There are appreciable differences in facial soft tissue thickness values between different populations; hence, population-based values are often used (Table 1) [1, 2, 13, 22, 36]. Some authors have argued that the slight millimetre differences are of no practical significance [8], and others believe the differences in the rendered appearance are due to the underlying population-based bony differences.

Study name(abbreviation) | Adult population studied | M/F | Image (scan)/number of FSTT points | Number of subjects, age brackets (years) | BMI as stated
Hwang et al. [28] | Koreans | M/F | Cone-beam computed tomography/31 | 100 (M = 50, F = 50)/20 to 36 | 
Ruiz [18] | Colombians | M/F | Cone-beam computed tomography/17 | 30 (M = 26, F = 4)/18 to 35 | 
Lodha et al. [29] | Gujarati, Indians | M/F | Computed tomography/25 | 489 (M = 324, F = 165)/17 to 65 | 
Moritsugui et al. [30] | Brazilians (mid-west region) | M/F | Cone-beam computed tomography/21 | 101 (M = 45, F = 56)/18 to > 41 | 
Sahni et al. [5] | Indian (north-west) | M/F | Magnetic resonance imaging/29 | 300 (M = 173, F = 127)/18 to 70 | 
Eftekhari-Moghadam et al. [14] | Iranian (south-west) | M/F | Magnetic resonance imaging/ | 100 (M = 160, F = 63)/18 to 50 | 
Bulut et al. [2] | Turkish | M/F | Computed tomography/31 | 320 (M = 160, F = 160)/18 to 80 | < 20, > 20 – <25, > 25 (L, N, OB)
Manhein et al. [31] | Black and White Americans/midline and right | M/F | Ultrasound/19 | 197, 19 to 55 | 
Deng et al. [13] | Yangtze River delta Han (China) | M/F | Cone-beam computed tomography/60 | 424 (M = 130, F = 294)/21 to 50 | 
Guyomarc’h et al. [20] | French (France) | M/F | Computed tomography/37(Reported no difference btw m/f) | 500 (M = 265, F = 235)/18 to 96 | < 25, > 25 (N, OV)
Navic et al. [32] | Thai (Thailand) | M/F | Needle puncture technique (12 h since death)/27 | 100 (M = 50, F = 50)/51 to 95 | 
Tedeschi-Oliveira et al. [23] | Guarulhos, São Paulo (but of mixed ethnicity) (Brazil) | M/F | Needle puncture technique (12 h since death)/32 | 40 (M = 26, F = 14)/17 to 90 | < 20, > 20 – <25, > 25 - <29.9, > 30 (obese)
Codinha et al. [19] | Lisbon, Portuguese | M/F | Needle puncture technique (24 h since death)/20 (8 midline & 12 bilateral) | 151 (M = 103, F = 48)/20 to 99 | < 20, > 20 – <25, > 25 (L, N, OV)
De Greef et al. [33] | Belgium | M/F | Ultrasound/52 | 967 (M = 457, F = 510)/20 to 99 | < 20, > 20 – <25, > 25 (L, N, OB)
Coskun et al. [34] | Greek | M/F | Computed tomography/22 (5 midline, 17 laterally) | 100 (M = 50, F = 50)/18 to 99 | 
Domaracki and Stephan, [24] | Australian | M/F | Sooted needle puncture technique (embalmed for > 6 months)/13 (7 midline, 3 bilaterally) | 33 (M = 19, F = 14)/46–92 | 

Different body mass index classifications have been used in FSTT studies (Table 1). Historically, researchers have measured weight rather than body mass index, though in the last decades, most FSTT studies have focused on body mass index [31, 33] rather than weight. Some authors have used only subjects with a normal body mass index (BMI) [37, 38], while others have compared the normal BMI to the overweight subgroup [2, 33]. However, some studies did not investigate body mass index [39], probably because this criterion will increase the number of subjects required. Still, most published literature agrees that facial soft tissue thickness values will increase with BMI increase [1, 2, 36]. However, conflating the facial thickness of the deceased with BMI values may be challenging because BMI may not always be constant.

There is a significant variation in the age ranges in FSTT studies. Publications from Africa have used age ranges in years, such as 20 to 35 [26, 37], 18 to 35 [35, 39], 12 to 71 [40] and 17 to 33 [41] (Table 1). Studies from other continents have used either similar or broader age ranges, such as 20 to 36 [28], 17 to 65 [29], 18 and > 41 [30], 18 to 70 [5] and 18 to 80 [2] (Table 1). There are a lot of variation in the literatures on the effect of age on facial soft tissue thickness.

Sex has also been shown to be a co-determinant of facial soft tissue thickness value [1, 2, 9]. Authors have studied both sexes differently [2, 5, 20, 26, 33, 37, 41] for comparison; some other researchers combined both sexes to generate a single dataset (Table 1). Others have studied either males [26] or only females [39].

Different imaging and measurement techniques have been used in FSTT studies. Historically, facial soft tissue thickness was determined manually from cadavers, but results were inaccurate due to inherent difficulties in palpating for reference points and further complicated by variable shrinkage of tissues [24, 32, 38]. More recently, cadaveric studies have used freshly deceased individuals of less than 12 [38] or 24 h [32]. Further to cadaveric studies, different imaging modalities have been used in measurements of facial soft tissue thickness (Table 1).

Initially, measurements were from cephalometric X-ray by using acetate tracing and a pencil [35]. However, most contemporary studies have used modern imaging of living subjects with magnetic resonance imaging (MRI) [9, 14, 15, 17], ultrasound [33, 37, 42], computed tomography (CT) [1, 2, 4, 29, 34, 39, 40, 43] and most recently cone beam computed tomography (CBCT) [13, 18, 28, 30], Table 1. CT and MRI both give good results. The measurements of FSTT from live scans are manipulated with specialised software packages such as the image tool in Centricity [39], Skull Measure (CyberMed) [28], Amira [2, 34] and iCAT Vision [18].

The number of subjects analysed in facial soft tissue thickness studies has varied considerably, with the highest number reported by De Greef et al. (967) [33], Manhein et al. (907 of 551 children and 256 adults) [31] and Guyomarc’h et al. (500) [20]. Recently, Shehata et al. in 2023 studied 10 males and 10 females [41], and Ruiz reported on 26 males and 4 females [18] (Table 1). The reduced number of subjects may reduce accuracy; however, the accurate imaging and proficient measurements of FSTT with software packages should give more precise results than cadaver studies.

In age classifications, the number of subjects within each age bracket will vary considerably and may be very low; Manhein et al. had 3 subjects in the 35 to 45 age brackets for black adult males of normal weight [31], whilst Coskun et al. had 8 male and female subjects in the 18–34 age range and 5 in the 35–44 age brackets [34], Table 1.

At the time of this study, the authors were unaware of any published facial soft tissue thickness data on the Nigerian female adult population. This study aimed to establish a dataset and analyse the impacts of age, sex, and body mass index (BMI) to allow comparison with data for the Nigerian adult male [43] and other populations. This sex specific FSTT data will enhance forensic facial reconstruction and improve identification of human remains. This is a significant concern because of the ever-increasing death toll of people trying to migrate from Africa to Europe.