Facial soft tissue thickness in forensic facial reconstruction: Impact of regional differences in Brazil.

Forensic facial reconstruction aims to assemble and provide the appearance of a face over a skull, in order to lead to recognition of that individual, making possible the application of primary identification methods. The scientific literature presents facial soft tissue thickness (FSTT) tables for reference from a range of different geographic regions. However, the consensus on its importance or on how to use specific population data related to FSTT is not unanimous. Brazil is formed by geographic regions with diverse populations, which are reflected in facial features. This paper aimed to measure and compare FSTT of distinct Brazilian samples to ascertain the need for specific data sets for different regions. A specific protocol for cone beam computed tomography was used to standardize measurement, and it was applied in a sample of 101 subjects. The FSTT measurements of a Brazilian population from the Midwest Region was compared to a previous sample from Southeast, which was collected using the same protocol. High compatibility was observed when comparing the averages of FSTT among samples of these two different geographic regions. Regarding age groups, notable differences on the medium and inferior face were observed in females. Minor variances found are unlikely to affect the practice of forensic facial reconstruction. Facial features, such as eyes, lips, nose, and skin may also be relevant in the differentiation of people from these two areas in Brazil. Therefore, concerning the Southeast and Midwest Brazilian regions, the need to apply different data sets is unnecessary.

Introduction

The forensic facial reconstruction (FFR) has an important role in recognizing individuals who are unable to be identified by other methods. Advanced postmortem decomposition process or the lack of antemortem information are its main indication for forensic purposes [1, 2]. The technique is based on the assembling of an approximated soft tissue topography over the unknown skull, with the intent of reconstructing its characteristics to be as similar as possible to the individual at the time of their death. Once the reconstruction is finished, a public campaign is issued, aiming to illicit a response from the public as to whom the remains might belong. Following this, a formal identification can then take place [1, 3, 4].

An approximated face is achievable by using various techniques. The 2D representation is based on a picture of the skull, whereas the 3D representation can be divided into manual or digital methods. The manual method involves direct modelling and sculpture, applying clay or Plasticine over the skull or a model of the skull [1]. More recently, a computerized face sculpture can be generated by using specialized modeling software, and different user interfaces can adapt the procedures to resemble manual modeling. Tablets and the assistance of haptic devices may be used in the 3D context to add soft tissues to a model of the skull [5]. However, independently of the method used, it is imperative to establish parameters and guidance such as the facial soft tissue thickness (FSTT), that serves as reference over specific craniometric landmarks [6], Those FSTT measurements are usually populational-based averages, but from this general information it is often expected to deliver a precise and reliable assistance during FFR [7].

FSTT charts in the scientific literature cover many craniometric landmarks, allowing it to be organized by sex, age, ancestry, BMI, among other facial features considered to be significant in an FFR. Many aspects of the method that seem to be related to the success rate or to the probability of recognition of the reconstructed faces. Studies have indicated that FSTT data are particularly influenced by the population groups under study [8-12], but the debate on the subject has far from achieved a consensus. Therefore, the expert should consider using of FSTT based on the population to which the body can be correlated by previous anthropological exams because specific FSTT charts could produce better results. However, in those studies, it is remarkable that many describe different methodologies, including the original measurement protocols, the source and type of imaging exam and the relation of regional charts, and the success of the FFR has not yet been established. Some researchers do not believe there is enough evidence to justify the use of different population data [13], but it is unclear how this might apply in countries like Brazil, with diverse and complex demographics.

The Brazilian territory has continental proportions, and it is divided into geographical regions (north, northeast, southeast, south, and Midwest), each one with its diverse environments and populations.

To understand the local context better, it is important to remember that the original population was based on several Indigenous Brazilian with different anthropological features among the groups found in the territory. The European colonization favored the concept of a mixed ancestry population, mostly influenced by the presence of Portuguese, Dutch and French. After the world wars of the 20th century, the presence of immigrants from Japan, Eastern Europe, the Middle East, Italy and Germany became important [14]. Their distribution was not even among the regions and, therefore, it is clear that each segment of Brazil has its own physical features that represent the dominant population groups, with different characteristics [15]. The increasing and continuous lack of ancestral uniformity, as it is observed in Brazil, raises the question whether or not the use of a single STT chart is appropriate for the estimation of facial morphology [16].

This study considers that the craniofacial morphology is determined by hereditary features and influenced by the environment [11], affecting the skull and the face. The combination of these anatomical differences makes the individual unique, leading to a wide variation of facial profiles across the country [17]. This justifies deeper investigation and the collection of data from different regions. With the intent of verifying the need for various FSTT charts on reconstruction from each geographic region, this research aimed to measure the FSTT in a Brazilian sample from the Midwest region and to compare to a previous sample from the Southeast region [18] using the same cone-beam computed tomography (CBCT) measuring protocol.

Materials and methods

The sample was composed of 101 CBCT exams of Brazilian subjects from the Midwest region, available in a previously established anonymous data bank in Digital Imaging Communication in Medicine (DICOM) format. Table 1 shows sample distribution.

Table 1

Sample distribution by sex and age group.

Sex	Male	Female	Total
Age group
18 to 30 years	18	22	40
31 to 40 years	13	14	27
41 and older	14	20	34
Total	45	56	101

The exams were acquired from records of clinical diagnosis, and, therefore, no participant was exposed to ionizing radiation for this research. The image protocol had a 23 cm x 17 cm FOV field of view, allowing the visualization of all included anatomical structures and landmarks from the supraglabellare to menton in the vertical axis and posterior to the supraglenoid structure. The images were obtained with an i-CAT Next Generation tomograph with 17.8 second exposition and voxel of 0.3 mm, and they were exported on Digital Imaging and Communication in Medicine (DICOM) format. CBCT scans allow image acquisitions with the individual in a sitting or standing position. Despite containing stabilizing devices for the head, such as the cephalostat and the chin support, these were not used in our sample, in order to avoid the effects of compression of facial soft tissues.

The research was approved by the Committee of Ethics in Research of the School of Dentistry of University of São Paulo (CAAE 33433320.8.0000.007 and 33433320.8.0000.0075). The inclusion criteria were established by observing the facial integrity of the research subjects. Therefore, this project included the exams of adult patients (18 and older) with required presence of certain structures: the central incisors and second molars (including both natural and prosthetically rehabilitated elements), no visible facial syndromes (hard or soft tissue), with no severe asymmetry and that had not been submitted to orthognathic surgery. Furthermore, the research included exams of both male and female patients in balanced groups. Thus, the exclusion criteria rejected exams that did not fit all the inclusion criteria or had quality issues that could prejudice the measuring of soft tissues.

The selection and measurements were performed with the assistance of the Horos software (version 3.3.6, 64 bit, Horos Project, Purview, Annapolis, USA) installed on an iMac computer (macOS Catalina–version 10.25.2, a 3,4 GHz Intel Core i7 Quad-Core processor, 16 GB RAM) and the 3D reconstruction tool 3D volume rendering through the skin and bone filters. Horos software is an open access version of OsiriX (DICOM viewer software) and has demonstrated to be a good alternative for craniofacial anthropological analyses, both in hard and soft tissues [19].

The exams were divided by sex into three age groups (from 18 to 30 years old, from 31 to 40 years old, 41 and older) following the original research group divisions [18], whose control sample, from Southeast Brazilian region, was composed of 100 exams equally distributed among the groups.

The protocol established by Beaini et al. [18] was used to create a standardized measurements of FSTT in CBCT. In this guide, the skull images were positioned with the Frankfurt Horizontal Plane to avoid the influence of misplacement on multiplanar view. The measurements of FSTT were executed in the same craniometric landmarks studied by Rhine and Campbell [20]. Thirty-two craniometric landmarks were measured, ten located on the midline and eleven bilateral landmarks. Figs 1–3 present the craniometric landmarks and measurement direction, whereas Table 2 describes each landmark and the measurement directions according to the applied protocol.

Fig 1

Craniometric landmarks measured.

Fig 3

Bilateral landmarks measurements.

Table 2

Craniometric landmarks, descriptions, and measurement direction.

	Landmark	Description	Measurement direction
	Median points
1	Supraglabellare	Deepest part of the supraglabella fossa in the median plane	Perpendicular to the bone surface
2	Glabella	Most projecting median point on lower edge of the frontal bone	Perpendicular to the bone surface
3	Nasion	Intersection of the nasofrontal sutures in the median plane	Nasal soft tissue fold
4	Rhinion	Most rostral point on the internasal suture	Perpendicular to the bone surface
5	Mid-Philtrum	Deepest point of the maxillary alveolar bone	Mid-Philtrum or subnasale
6	Prosthion	Median point between the central incisors on the anterior margin of the maxillary alveolar rim	Upper vermilion border
7	Infradentale	Median point at the superior tip of the septum between the mandibular central incisors	Lower vermilion border
8	Supramentale	Deepest median point in the groove superior to the mental eminence	Chin fold
9	Pogonion	Most anterior median point on the mental eminence of the mandible	Perpendicular to the bone surface
10	Menton	Most inferior median point of the mental symphysis	Vertical direction or to neck fold
	Bilateral Points
11	Frontal Eminence	Most projecting point of the frontal bone, at a line that vertically bisects the orbit	Perpendicular to the bone surface
12	Mid-supraorbital	Point on the anterior aspect of the superior orbital rim, at a line that vertically bisects the orbit	Orthoradial direction
13	Mid-infraorbital	Point on the anterior aspect of the inferior orbital rim, at a line that vertically bisects the orbit	Orthoradial direction
14	Malar	Intersection of the maxillary alveolar process and zygomatic process, at a line that vertically bisects the orbit	Perpendicular to the bone surface
15	Lateral Orbital	On the center of the zygomatic bone, at a line that vertically crosses the lateral orbital margin	Orthoradial direction
16	Zygion	The most lateral point on the zygomatic arch	Orthoradial direction
17	Supraglenoid	Most rostral point on the superior rim of the glenoid cavity	Orthoradial direction
18	Gonion	Point on the rounded margin of the angle of the mandible, bisecting two lines one following vertical margin of ramus and one following horizontal margin of the corpus of mandible	Perpendicular to the bone surface
19	Ectomolare2	Most lateral point on the buccal alveolar margin, at the center of the superior second molar position	Orthoradial direction
20	Occlusal Line	Most anterior point on the mandibular ramus, where the occlusal line meets de mandible	Orthoradial direction
21	Ectomolare₂	Most lateral point on the buccal alveolar margin, at the center of the inferior second molar position	Orthoradial direction

The DICOM files from CBCT were imported into the Horos software, according to the protocol by Beaini et al. [18], a window level of 500 e window width of 3500 were applied to all exams to favor the visualization of both hard and soft tissue limits. The acquired volume was reconstructed on a 3D MPR window (multiplanar reconstruction) and visualized with the aid of a MIP tool (maximum intensity projection) to perform the volume repositioning to the Frankfurt Horizontal Plane, as previously mentioned.

An initial calibration was made in the form of inter- and intraobserver tests. The measurements for this research were collected only with a high concordance between observers. The evaluation and adjustment of inter and intra-examiners were achieved by testing the thirty-two landmarks in fifteen exams (15% of the sample) and testing the intraclass correlation coefficient (ICC) for each point. Regarding intra-examiner assessment, the main examiner measured the fifteen exams twice, considering a one week time interval between the measurements. The main examiner’s previous training of the method was consistent with the original examiner.

The data were organized in a spreadsheet, using the software Microsoft Excel, and statistical analysis was performed with aid of the SPSS statistic pack, establishing a reliability level of 95%.

Using the Shapiro-Wilk test, the normality distribution sample was checked for every landmark, with P < 0.05, which implies alteration of normality. In the nonnormal distribution landmarks, the bootstrap method was used (1000 resampling– 95% CI BCa) to obtain reliable average values.

To search for sex related differences, the t-test was applied on landmarks with normal distribution, whereas the Mann-Whitney test was used with nonnormal distribution data. The variance analysis from a one-way ANOVA was applied to investigate any differences among the average FSTT, by landmark, on the three age groups (18 to 30 years, 31 to 40 years and 41 and older).

Concerning the regional differences, the research data were compared to the raw data of the Southeast region [18] to which full access was granted. A t-test was applied on the comparison of FSTT averages among the Southeastern [18] and Midwestern (this study) regions, for both sexes.

Results

The concordance of the measurements verified by the ICC according to each landmark measurement revealed intra- and interexaminer agreement above 95% (data in S1 Table), demonstrating reliability among the measurements. Fig 4 presents the individual ICC records.

Fig 4

Concordance level for each landmark in intra- and interobserver analysis.

For male subjects, the Shapiro-Wilk test revealed that, from the thirty-two analyzed landmarks, two presented nonnormal distribution (lateral orbital and ectomolare2). Female subjects presented nonnormal distribution at the landmarks rhinion, mid-infraorbital, zygion and gonion. In nonnormal distribution landmarks, the bootstrap method (1000 resamples– 95% CI BCa) was used to obtain reliable mean values. Such statistical procedure assigns consistent results, through the process of random resampling, because the process tends to correct normality deviations of the sample [21].

Table 3 exhibits the FSTT averages as the main result of this research. It has been divided by sex with SD, SE and P values, corresponding to each test, verifying statistically significant differences between the female and male averages, after bootstrapping procedure.

Table 3

Mean FSTT (millimeters and percentage), SD, and SE divided by sex.

	Female			Male
	Mean	SD	SE	Mean	SD	SE	Mean difference (mm) **	Mean difference (%) ***	P value
Supraglabella	4.5	0.97	0.14	5.5	1.14	0.23	-1	18.1	0.00* T
Glabella	4.9	0.77	0.1	5.9	0.95	0.14	-1	16.9	0.00* T
Nasion	6.2	0.97	0.13	8.1	1.24	0.18	-1.9	23.4	0.00* T
Rhinion	1.7	0.43	0.06	2.3	0.58	0.09	-0.5	26.0	0.00* M
Mid-Philtrum	13.1	1.82	0.24	15.7	2.22	0.33	-2.7	16.5	0.00* T
Prosthion	10	1.58	0.21	13.3	2	0.3	-3.3	24.8	0.00* T
Infradentale	9.8	1.34	0.18	11.9	1.5	0.22	-2.1	17.6	0.00* T
Supramentale	11.9	1.53	0.2	12.9	1.85	0.28	-1.1	7.7	0.00* T
Pogonion	9.8	2.18	0.29	11.4	2.25	0.34	-1.6	14.0	0.00* T
Menton	7	1.73	0.24	9	2.08	0.33	-2	22.2	0.00* T
Frontal Eminence R	4.1	0.89	0.14	5	1.23	0.33	-0.9	18.0	0.00* T
Frontal Eminence L	4.2	1.11	0.18	4.9	1.2	0.32	-0.7	14.2	0.04* T
Mid-supraorbital R	6.5	1.27	0.17	8.6	1.33	0.2	-2.1	24.4	0.00* T
Mid-supraorbital L	6.4	1.37	0.18	8.7	1.33	0.2	-2.4	26.4	0.00* T
Mid-infraorbital R	5.3	1.47	0.2	5.8	1.51	0.23	-0.5	8.6	0.07 M
Mid-infraorbital L	5.5	1.58	0.21	5.9	1.65	0.25	-0.4	6.7	0.07 M
Malar R	21.4	2.57	0.34	22.8	2.75	0.41	-1.4	6.1	0.01* T
Malar L	21.7	2.38	0.32	22.9	2.8	0.42	-1.2	5.2	0.02* T
Lateral Orbital R	9.1	1.73	0.23	8.3	1.46	0.22	0.8	-9.6	0.02* M
Lateral Orbital L	9.2	1.74	0.23	8.3	1.36	0.2	0.8	-10.8	0.02* M
Zygion R	7.8	1.79	0.24	9.2	1.85	0.28	-1.4	15.2	0.00* M
Zygion L	7.8	1.9	0.25	9.1	1.87	0.28	-1.3	14.2	0.00* M
Supraglenoid R	10.7	1.9	0.25	12.8	1.57	0.23	-2.1	16.4	0.00* T
Supraglenoid L	10.7	1.84	0.25	12.8	1.6	0.24	-2.1	16.4	0.00* T
Gonion R	12.8	3.65	0.49	18.3	5.54	0.83	-5.5	30.0	0.00* M
Gonion L	13	3.88	0.52	17.8	5.49	0.82	-4.8	26.9	0.00* M
Ectomolare2 R	27	3.62	0.48	30.3	3.29	0.49	-3.3	10.8	0.00* M
Ectomolare2 L	27.2	3.64	0.49	30.2	3.44	0.51	-2.9	9.9	0.00* M
Occlusal Line R	20.3	2.82	0.38	24.6	3.17	0.47	-4.4	17.4	0.00* T
Occlusal Line L	20.4	2.86	0.38	24.3	3.21	0.48	-3.8	16.0	0.00* T
Ectomolare₂ R	24.9	3.06	0.41	28.2	3.96	0.59	-3.4	11.7	0.00* T
Ectomolare₂ L	24.8	3.2	0.43	28.4	3.48	0.52	-3.6	12.6	0.00* T

R–right; L–left; T–t-test; M–Mann Whitney.

* P < 0.05.

**; ***Differences were calculated between female means compared to male means.

The FSTT analysis indicates the male sample exhibited higher FSTT values compared to the female sample, except for the orbital lateral, which demonstrated a difference among the averages of 0.8 mm. The major thickness discrepancies between the sexes were found on landmarks the gonion, ectomolare2, ectomolare2 and occlusal line, in which mean differences were above 3 mm.

Regarding age, an ANOVA was used, on both sexes, to compare averages between the age groups (18 to 30 years, 31 to 40 years and 41 and older). A direct relation between FSTT and ageing process can be seen, particularly among females. The mid-philtrum, prosthion an ectomolare2 landmarks presented a decrease of FSTT as the age advanced.

Figs 5 and 6 (data in S2 Table) show the comparison by sex among age groups. Quantitatively, a direct relation is noted between age and divergence of FSTT specifically for females, on mid-philtrum, prosthion and ectomolare2 landmarks, which showed a decrease of FSTT as the age advanced.

Fig 5

FSTT means: Comparison among age groups in males.

Fig 6

FSTT means: Comparison among age groups in females.

Table 4 presents FSTT averages, on each landmark in comparison to the Southeastern sample (SE) [18] and the Midwestern (MW) (this paper), by sex, as well as P values (t test).

Table 4

FSTT (in millimeters) comparison among SE and MW regions, in both sexes.

		Female					Male
Landmark	SE	MW	Mean Difference (mm)**	Mean Difference (%)***	T Test Sig.	SE	MW	Mean Difference (mm)**	Mean Difference (%)***	T Test Sig.
Supraglabellare	3.4	4.5	-1.1	-24.4	0.00*	4.3	5.5	-1.2	-21.8	0.00*
Glabella	5	4.9	0	0.0	0.94	5.8	5.9	-0.2	-3.4	0.45
Nasion	5.9	6.2	-0.3	-4.8	0.11	7.2	8.1	-1	-12.3	0.00*
Rhinion	1.7	1.7	0	0.0	0.61	1.9	2.3	-0.3	-13.0	0.01*
Mid-Philtrum	12.3	13.1	-0.7	-5.3	0.02*	15.1	15.7	-0.6	-3.8	0.16
Prosthion	9.5	10	-0.5	-5.0	0.17	12.4	13.3	-0.9	-6.8	0.02*
Infradentale	11.3	9.8	1.5	15.3	0.29	11.2	11.9	-0.8	-6.7	0.05*
Supramentale	10.8	11.9	-1.1	-9.2	0.00*	11.4	12.9	-1.5	-11.6	0.00*
Pogonion	9.4	9.8	-0.4	-4.1	0.42	10.8	11.4	-0.7	-6.1	0.21
Menton	6.9	7	-0.1	-1.4	0.87	8.6	9	-0.4	-4.4	0.38
Frontal Eminence R	3.5	4.1	-0.6	-14.6	0.00*	4.4	5	-0.6	-12.0	0.09
Frontal Eminence L	3.4	4.2	-0.8	-19.0	0.00*	4.5	4.9	-0.5	-10.2	0.21
Mid-supraorbital R	6.2	6.5	-0.3	-4.6	0.22	7.3	8.6	-1.3	-15.1	0.00*
Mid-supraorbital L	6.1	6.4	-0.2	-3.1	0.33	7.2	8.7	-1.6	-18.4	0.00*
Mid-infraorbital R	5	5.3	-0.3	-5.7	0.32	5.4	5.8	-0.4	-6.9	0.16
Mid-infraorbital L	4.8	5.5	-0.6	-10.9	0.03	5.4	5.9	-0.5	-8.5	0.07
Malar R	19.4	21.4	-2	-9.3	0.00*	20.3	22.8	-2.5	-11.0	0.00*
Malar L	18.7	21.7	-3	-13.8	0.00*	20.3	22.9	-2.6	-11.4	0.00*
Lateral Orbital R	9	9.1	-0.1	-1.1	0.76	7.5	8.3	-0.8	-9.6	0.01*
Lateral Orbital L	10.4	9.2	1.2	13.0	0.38	7.3	8.3	-1	-12.0	0.00*
Zygion R	7.4	7.8	-0.4	-5.1	0.27	8.1	9.2	-1.1	-12.0	0.01*
Zygion L	7.5	7.8	-0.3	-3.8	0.43	7.8	9.1	-1.4	-15.4	0.00*
Supraglenoid R	10	10.7	-0.7	-6.5	0.06	11.4	12.8	-1.4	-10.9	0.00*
Supraglenoid L	9.9	10.7	-0.8	-7.5	0.04*	11.1	12.8	-1.6	-12.5	0.00*
Gonion R	13.2	12.8	0.3	2.3	0.66	16.9	18.3	-1.4	-7.7	0.21
Gonion L	13.2	13	0.2	1.5	0.73	17.2	17.8	-0.6	-3.4	0.55
Ectomolare2 R	26	27	-1	-3.7	0.11	28.2	30.3	-2.2	-7.3	0.01*
Ectomolare2 L	26.3	27.2	-0.9	-3.3	0.17	28.2	30.2	-1.9	-6.3	0.01*
Occlusal Line R	20.1	20.3	-0.2	-1.0	0.73	22.8	24.6	-1.8	-7.3	0.01*
Occlusal Line L	20.4	20.4	0	0.0	0.93	23	24.3	-1.3	-5.3	0.07
Ectomolare₂ R	23.5	24.9	-1.3	-5.2	0.03*	25.1	28.2	-3.1	-11.0	0.00*
Ectomolare₂ L	24	24.8	-0.8	-3.2	0.18	25.5	28.4	-2.9	-10.2	0.00*

*P < 0.05.

**; *** Differences calculated between the averages of SE sample compared to MW sample.

Discussion

FSTT is one of the most studied subjects in the FFR field [22]. It provides quantitative data for the technique [13], but there are still some geographical regions that have not been studied. Studies have confirmed that FSTT measures obtained by using CBCT result in reliable and reproducible data [7, 18, 23, 24].

Several studies have verified the presence of FSTT variances among different populations, suggesting the importance of using specific values for each one [8, 10–12, 25, 26]. Some of these studies compared data of FSTT averages that were obtained with different measurement protocols with inevitable bias to those conclusions [13]. This may explain why there are other studies that contradict this hypothesis and do not support that specific FSTTs are needed for different populations for the FFR [27-29]. The FSTT measurement method is important to the analysis of the specificity among different studies [29]. Our study was able to compare regional FSTT using the same method from a previous study, eliminating the method variant.

The concordance results from the interexaminer ICC analysis showed the Beaini protocol [18] can provide reproducibility and that it is recommended for future research. The intra-examiner ICC analysis demonstrated high concordance on the measurements made by the main examiner, in accordance with other studies that utilized the CBCT with the same objective [18, 30]. Nevertheless, it was a result of practical experience gained on previous training, which may be necessary and well demonstrated in future studies.

Compared to the previous research [18], that produced a FSTT chart from a Brazilian Southeastern sample, it was clear that the heterogeneity of the Brazilian population is marked by a diverse population affinity [2]. Analyzing the average of the differences among the Southeastern and Midwestern samples, the negative variation shows a predominance of deeper FSTTs among the Midwestern sample when compared to the Southeastern sample.

Considering the differences related to sex in the samples of the Southeastern [18] and Midwestern regions (this paper), statistical differentiation was observed. In males, differences were more evident in five landmarks on the midline and eight bilateral points. Quantitatively, that variance did not surpass 2.5 mm, except the ectomolare2 with 3.1 mm. Proportionally, it varied between 10 to 15% in most cases with a few landmarks showing higher values. Within females, studies indicate fewer divergent landmarks (three on the midline and eight bilateral) where only malar showed a difference above 2.5 mm (3.0 mm). These results reveal high compatibility among the samples, considering that errors lower than 2.5 mm, may result in high correspondence on a facial pool [31] and differences between 2.5 ≤ 2.9 mm have minimal practical impact [32].

Whether reconstructions should match local facial traits is not under debate, and the use of FSTT tables of a specific ancestry FSTT charts may provide better FFR. However, local changes should not be exclusively related to FSTT [33]. Eyes, lips, nose, and skin features could also be relevant in the differentiation of people from these two different areas in Brazil.

Investigating further into our results, they support that previous to the FFR, a careful anthropological evaluation of the skull regarding sex, age and ancestry variance remain necessary [6] because it provides important information to the forensic professional. However, the use of FSTT mean values divided by sex, age, and ancestry is no guarantee of better recognition rates, and awareness of the complexity of soft tissue displacement caused by aging [34]. The assessment of the age variant was originally made to reduce sample distribution bias when compared to the Southeastern sample [18] but it presented interesting results. Our results show that attention to this matter should not be neglected on reconstructed faces [27].

The same was planned to verify sex differences because the Southeastern research showed statistically significant changes in STT related to sex. In this research, in agreement with previous studies [18, 35–37], the analysis among sexes revealed males tend to possess larger depths than females, excepting the lateral orbital landmark, in which it has been observed a mean difference of 0.8 mm.

However, such statistical difference may not be the only reason for sexual dimorphism features [9, 36, 38]. Landmarks showed FSTT averages variate thickness within a small quantitative interval (<6% average), leaving sex variance among the individuals to skull formation [38].

The variation between males and females was no greater than 3 mm in most points. Only four landmarks exhibited greater discrepancies and those were located at anatomical regions most influenced by the BMI [37], such as gonion (5.5 mm), ectomare2 (3.3 mm), ectomloare2 (3.6 mm) and occlusal line (4.4 mm). Hence, sexual dimorphism was not clearly evidenced in the variation of depths of soft tissue. Despite the statistical differences, the authors found that male and female individuals appear to share similar averages [38]. The human skull is the third best reference for determining sex, after the pelvic bone and postcranial dimensions [39]. Therefore, the differences verified in this study indicate that sexual dimorphism is probably based, mainly, on the skull morphology.

Multiple facial morphological and physiological alterations act on the ageing process of the face. The initiation and progression vary between individuals, sexes, and populations [40]. In this study, meaningful differences were observed in the FSTT among the age groups, notably in females, at the landmarks located on the medium and inferior face. The FSTT averages of the landmarks mid-philtrum, prosthion and ectomolare2 tend to decrease progressively with age, reproducing the morphological alteration patterns that occur in facial ageing, demonstrating a coherence among the data. With the advancing of age, the average face volume is permanently lost from both from superficial and deep fat tissue [41], and a redistribution of this volume occurs that causes slenderizing of the superior lip more than the inferior [42]. Bone remodeling in that region results in a decrease of the overlying soft tissue support area. This phenomenon, along with the effect of gravity, characterizes the average ageing of the face [34, 43].

Conclusions

The measurements analyzed in this research, when compared to those collected in the Southeast region of Brazil, are statistically different at many landmarks. However, observing the averages in a specific FSTT chart, indicated that regional differences between the two samples are quantitatively small and they should have minimal influence on facial reconstructions. Therefore, the use of specific FSTT charts is not necessary when performing FFR of individuals from Southeast and Midwest Brazil.

ICC intra- and interexaminer.

(PDF)

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FSTT means in age groups in both sexes.

(PDF)

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23 Feb 2022

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Reviewer #1: Thank you for the opportunity to review this paper.

Language editing needed – I indicated these by yellow highlighting in the attached document as they were too much to correct.

Overall, I think the research is sound, although not very innovative in the sense that it repeats what others have said before. We will need a better discussion of the results, and based on this and other studies clear guidance on the way forward with regard to the use of STT tables. What is the most important – age? Sex? Population?

Below are some comments, which should be read in conjunction with the comments in the text itself (made as sticky notes and highlights in yellow).

Title: Add “in Brazil” at the end

Abstract:

Needs editing as indicated in the attached document. Please provide the sample sizes.

Introduction:

The debate about the use of population-specific STT is not fully explored. This needs more detail.

We need to know more as to why the two populations are expected to be different – i.e., the background of the samples.

The Intro needs to better reflect current debates around the issues raised.

M and M

We need info on the age and sex distribution of the sample (found this later in Results – should be in M and M). Sample sizes in each sex-age cohort quite small (as few as n = 13). This is a shortcoming that should be discussed later on. We also need an indication of the sample sizes of the comparative sample.

I don’t know the software used – cant comment on it

I assume the individuals were in a sitting position when scanned? – this needs better discussion also with regards to best practice and current guidelines.

Inter- and intra-observer repeatability assessment needs better explanation

Comparison between the two regions – are the people from the two regions supposed to be different? Why would we expect them to be different? This needs explanation.

Results

The inter- and intra-observer results are too uninformative, we need the actual results. Inter-observer above 95% is really unusual.

Table with sample sizes should be in the M and M. In the end, the sample size per sex-age group is really small (with as few as 13 individuals)

Differences between the two compared groups should be discussed in more detail – how many measurements differed significantly? It seems there were quite a few. When does one decide that these differences are enough to use population-specific data? How much difference would this make in an actual reconstruction? In the literature it was suggested that one should look not so much at the absolute difference in mm, but rather in % of the actual difference (e.g., a 2 mm difference in a measurement of 10 mm may not make much of a difference in a reconstruction, but 2 mm when the average is 5 mm will be more pronounced). Think it was a paper by Briers? This warrants better Discussion (in the Discussion section).

Discussion

Changes with age cannot be ascribed to bone losses only – the soft tissues as well as the hard tissues undergo changes. Changes with age needs a more thorough discussion with reference to the literature– seems that in this study this was more important than differences between populations from different regions – would you advise that separate tables are used for older and younger groups? But not for different populations?

Miscegenation is a strong word to use, with negative connotations. Please rephrase.

It is stated that the regional differences have an insignificant impact on facial soft tissue thicknesses and consequently on FFR result. This last part – the actual result – has not been tested in this study and this statement can thus not be substantiated. It may be suggested, but was not proven by this study.

Overall, we need to be advised on the way forward, based on the results from this (and other) studies. The last sentence of the conclusion seems to contradict all of what had gone before – do we still need to take population, sex etc into account or not?

Reviewer #2: Overall, the manuscript is written well and logically laid out. The authors have provided details of demonstrated rigour with regards to the experimental design and subsequent analysis through inter and intra observer error, tests for normality, and bootstrapping where appropriate. A narrative is built up throughout the paper by describing the methodology in a chronological fashion, which I found to be well considered. All supporting data appears to have been made fully available.

The consideration of the level of specificity and granularity required with FSTTs is an important one, and it was interesting to see that the differences at regional level for Brazil were insufficient to justify multiple FSTT datasets.

I’ve noted a few suggestions below. Additionally, I have made some suggested edits for the English, as in some cases it was a little unclear what you were intending to say. These are small suggestions for the authors to consider, but I would encourage the inclusion of further clarification around some of the points raised:

General comments:

• You cover the literature in terms of the ‘success’ of population specific datasets in FFR, and that incongruent FSTTs still yield a recognisable face, but that congruent population specific datasets might result in a more ‘accurate’ FFR, although differences in protocols might suggest insufficient evidence for this. I wonder if you could provide some more background on the importance of FSTTs in the recognition process. I.e. FSTTs mainly cover the contours of the face, not the estimation of facial features. Literature suggests facial features and their configuration are more important for familiar face recognition. Furthermore, given the variation of FSTTs in the facial contour due to BMI and ageing, we have a greater tolerance for inaccuracies in these areas. I think it would be useful for you to provide some background on this and to discuss the relative importance of FSTT datasets in the Facial reconstruction and subsequent recognition process. You touch on this briefly in the discussion, but more is needed.

• Lines 273 – 283: Can you provide information of the distribution of samples in the above 41yrs age bracket? i.e. the range? As you mention, age-related changes to the soft tissues change in ‘type’ as age increases. For example, someone in their 40s may have superficial age related changes, caused by a change to the dermis. But those in their 60s and 70s are more likely to also exhibit more extreme volume/morphological changes, such as ptosis etc. which would have a bigger impact on the position of FSTTs. Given this, it would be useful to know the age range for that bracket, and if there was a wide range, why the sample was collapsed into one group. Especially given that a large portion of this manuscript discusses age-related changes.

• Do you anticipate any plans for future research in this area? Given that you observe morphological variation in faces between regions of Brazil, enough to warrant your investigation into FSTTs, might it be worth investigating parameters for feature estimation between these regions? It would be great to see this research carried out.

Formatting edits:

• Perhaps increase the size of the annotation text on figures 2 and 3? If I download the figures I can see it more clearly when zoomed in, but they are barely readable when in article format.

• Ectomolare could be better differentiated rather than using superscript and subscript 2. Whilst it represents upper and lower, I think it’s quite hard to see visually. Maybe 1 and 2 is better?

Grammatical edits:

• Table 1: description for Occlusal line. “where the occlusal line meets de mandible”. EDIT to “where the occlusal line meets the mandible”

• LINE 30: “…reconstruction aims to assemble”

• LINE 31: It’s not just next of kin, it could be friends etc. I would rephrase this

• LINE 38: “…which are reflected in the facial features” (see my third general comment as well)

• LINE 38: “This paper aimed to measure and compare….”

• LINE39:”…to ascertain the need for specific datasets for different regions”

• LINE 44: “As the age of the participants increased…”

• LINE 48: High compatibility was observed when comparing…..

• LINE 51: “Therefore, considering these two geographic regions, the need for applying different datasets has been shown to be unnecessary”

• LINE 58: “Forensic Facial Reconstruction (FFR) has an important role in helping to identify individuals that are unable to be identified by primary methods due to post-mortem changes, or by lack of ante-mortem information.”

• LINE 63: “…a public campaign is issued, aiming to illicit a response from the public as to who the remains may belong to. Following this, a formal identification can then take place”.

• LINE 69: “More recently, computerised face sculpture can be adopted by using digital modelling software, …”

• LINE 75: “In scientific literature….”

• LINE 91: I think “miscegenation” might be considered a derogatory term, and also relates more closely to Race rather than Ancestry. Consider rephrasing/choosing another term. It’s also used again throughout the manuscript.

• LINE 103: “The sample was composed of 101 cone beam…”

• LINE 133: “The Beaini et al……”

• LINE 137: “In total….”

• LINE 148: …CBCT were imported into the software….”

• LINE 153: “Prior to the gathering...”

• LINE 161: “spreadsheet Microsoft Excel for MAC was used….”

• LINE 163: “establishing…..”

• LINE 169: “…., and with non-normal data…”

• LINE 170: “analysis from a one-way ANOVA was applied to investigate any differences among the…..”

• LINES 181-183: “ ..composed of 101 exams, was divided into subgroups for age and sex, shown in Table 3.”

• LINES 205-6: …” that the male sample exhibited higher FSTT values compared to the female sample, except for Orbital Lateral…..”

• LINES 207-8:” The major thickness discrepancies between the sexes were found on….

• LINES 211 – 212: “Regarding age, an ANOVA was used, on both sexes, to compare averages between the age groups…”

• LINE 216: “Figs 4 and 5…”

• LINE 218: “specifically for females…”

• LINE 229: “..a predominance of higher mean FSTTs on the MW sample…..”

• LINE 234: “….using CBCT result in reliable….”

• LINES 236-7: “….showed that the Beaini protocol (17) yields excellent general reproducibility.”

• LINE 245: Consider using “Practitioner” rather than “forensic professional”

• LINES 250-251: “…revealed a tendency for males to exhibit greater tissue depths than females, except the Lateral….”

• LINES 252-255: Consider rephrasing. It’s not overly clear what is meant here?

• LINES 256-257: “…showed slight differences which were less than 3mm. Only four landmarks…..”

• LINE 261: “….variation of the soft tissue depths.”

• LINE 272: “..located in the mid and lower face.” Same for LINE 275

• LINE 309: “…divided into five regions..”

• LINE 312: “… of settlement and continuous migration….”

• LINE 321: “..differences were observed for both sexes. In males, differences were observed for five landmarks on the midline…”

• LINE 330: “…differences between the two studied….”

• LINE 331: “…Nonetheless, the ageing process…”

• LINE 333: “…The establishment of a biological profile…”

• LINE 335: “ …before selecting a FSTT dataset for FFR.”

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29 Apr 2022

The authors would like to thank the reviewers for their valuable comments and excellent suggestions to improve the quality of our manuscript.

The authors have revised all points brought by the reviewers. We sincerely hope that the information presented in this manuscript provides some answers and opens novel questions to advance future research.

Submitted filename: Response to Reviewers.docx

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8 Jun 2022

Submitted filename: PONE-D-22-02392_R1.pdf

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10 Jun 2022

The authors would like to thank the reviewers and the Editor for their valuable comments that definitely improved the quality of the manuscript entitled “Facial soft tissue thickness in forensic facial reconstruction: Impact of regional differences in Brazil” (PONE-D-22-02392R1).

Additional Editor Comments:

Further minor changes necessary - these are highlighted in the attached document.

Action: As requested by the Editor, the authors revised the paper and all the necessary changes (highlighted) were made.

Submitted filename: Response to Reviewers.docx

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17 Jun 2022

17 Jun 2022

The authors would like to apologize for this lapse, and as requested by the Editor, the authors revised the paper and the correction in Line 27 (highlighted) was made.

Submitted filename: Response to Reviewers.docx

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22 Jun 2022

Facial Soft Tissue thickness in Forensic Facial Reconstruction: Impact of regional differences in Brazil

PONE-D-22-02392R3

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Reviewers' comments:

7 Jul 2022

PONE-D-22-02392R3

Facial soft tissue thickness in forensic facial reconstruction: impact of regional differences in Brazil

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