A detailed review of forensic facial reconstruction techniques

Abstract

Facial reconstruction is an effective forensic technique that can help recreate a victim’s facial appearance from the skull. It is typically used to assist law enforcement agencies to identify missing deceased persons. Reconstruction techniques are usually based on the relationship between the underlying hard tissues, such as bone structure, and soft tissues such as the facial muscles and facial features. Facial reconstruction can be a feasible alternative to identify the remains from a decomposed, mutilated, or skeletonised corpse. It is important to remember that although the outcomes are empirical in nature, the technique has been applied widely in many situations. Recent advancements in technology and computer-based techniques have increased the accuracy and validity of this forensic discipline. We consider the most commonly used facial reconstruction techniques in this paper, with a detailed description of manual 3D techniques.

Keywords

Forensic facial reconstruction two-dimensional reconstruction three-dimensional reconstruction identification forensic sciences

Introduction

Facial reconstruction is an effective forensic technique that can help to recreate a victim’s facial appearance from the skull sufficiently accurately to achieve identification.^1,2 A combination of both scientific methods and artistic skills can be used to this end in forensic investigations where conventional identification techniques are not useful and few clues are available.^3–7

Facial reconstruction, however, cannot be used on its own for positive identification and should be supported by other established techniques, such as DNA assessment, dental record analysis or other valid identification methods.^7,8 Based on the relationship between the soft facial tissues and the underlying hard tissue of the cranium, different procedures have been developed. However, a lack of understanding of the relationship between them is the main cause of continuing disputes on the accuracy of these techniques.⁹

The methods of facial reconstruction can be divided into two basic groups:

Two-dimensional (2D)

Three-dimensional (3D)

Two-dimensional facial reconstruction

The face is drawn and created on overlays that are later superimposed on the skull images or craniographs. Frontal and lateral profile views are produced using this technique.^10,11 Few practitioners use the Manchester facial reconstruction approach to draw the facial musculature onto an initial overlay before attempting the finished facial morphology for greater precision in the process;¹² on the other side, some prefer to draw a finished face directly over the skull photographs.¹³ Facial features can be developed from visual or sketched images; with the advent of technology, they are then blended digitally into the skull using computer softwares. Various facial outlines and features are chosen from a database in the computer aided system, and the proportions of the skull are used to assess the overall face form and appearance^14–16 (Figure 1).

Figure 1.

(a) Two-dimensional facial reconstruction, (b) Three-dimensional facial reconstruction (Photo courtesy: Michael W. Streed).

Three-dimensional facial reconstruction

Facial structure is never sculpted on an original skull but always done on its replica. Some prefer an anatomical approach^17–19 where facial muscle modelling is performed before a skin layer is added to shape the face, while others favour a morphometric approach using standard measurements of tissue depth to create a facial surface contour into which the facial features are produced.^8,10,11 Some also use a combination of an anatomical approach along with mean tissue depth data as guides.^{4,10,11,17,19,20}

Recently, various technologies have been built to produce facial reconstruction using computer software that improves versatility, performance and speed. The first digital technique was developed by Moss for forensic purposes.²¹ Digital or computerised facial reconstruction systems can be divided into two types – automated systems and modelling systems. Automated systems focus on anthropometrical data and/or templates of skeletal morphology and include facial templates depending upon factors like sex, age and the ethnic group of the skull.^7,22,23 3D modelling software uses 3D animation software^24–26 to model the face on the skull to approximate the manual facial reconstruction processes, while other solutions use computer sculpture systems and haptic feedback^27,28 (Figure 1).

Regardless of the method used, forensic facial reconstruction procedures can be divided into three basic schools of thought.

Anthropometrical American Method/Tissue Depth Method: Krogman developed the procedure in 1946, using average tissue thickness at various points on the skull to direct the reconstruction of soft tissue. This approach is widely used by law enforcement authorities for forensic facial reconstruction.²⁹

Anatomical Russian Method: In 1971, Gerasimov developed this approach by carving muscles, glands and cartilage layer by layer onto the skull. This technique is much slower than the technique of tissue depth and a greater degree of anatomical expertise is required. This approach has been used to recreate prehistoric skulls.²⁹

Combination Manchester Method/British Method: The procedure was developed by Neave in 1977 to take into account both the thickness of soft tissue and facial muscles.²⁹

However, forensic facial reconstruction procedures require a few basic guidelines.^17,19,30

Preparatory phase

Specific skull preparation procedures should be maintained whether the reconstruction will be done in 2D or 3D. A file should be maintained for each skull to be reconstructed. The file should include:

○Case number with a proper certificate from the legal entity from which the skull is collected with the signature and date of the official involved, or a letter from the university head if the skull is obtained from the archives of the institution concerned for scientific purposes. It should also have a report of age, sex and ancestry information.

○Details of dentition are recorded; as teeth play an important role in estimating age and provide insight into a person's lifestyle. Proper skeletal and dental photographs with precise descriptions should be recorded.

○If available, other accessories such as hair samples, eyeglasses, dentures, jewellery or any ante-mortem photo should be included.

To avoid contamination, the skull should be kept in a controlled and protected environment and should be handled with gloves. In addition, the skull should be handled with a humanitarian approach.

Skull stabilisation can be achieved with a sandbag, clay or cork ring. Avoid picking up the skull with the fingers positioned in the orbit or nasal aperture; instead use both hands to handle the skull or place thumb in the foramen magnum with the palm holding the base of the skull (Figure 2).

Figure 2.

(a, b) Proper handling of skull; (c) use of clay ring to stabilise skull and positioning for the edentulous mandible (lateral view); (d) positioning for the edentulous mandible (basal view).

Teeth may become loose occasionally or may slip out of the socket. In such situations, the loose teeth should be cleaned, and the teeth should be held in the socket using clay.

For positioning the mandible with the skull, 3–6 mm space should be allowed to mimic the living condition. The mandible is positioned with a pencil from the opposite mandibular notch in cases of an edentulous mandible (Figure 2). When the mandible is edentulous, but dentures are available, missing gingiva is simulated with a sheet of clay before positioning the denture.¹⁷

Figure 3.

Various types of skull replica; (a) made of dental stone, (b) and (c) 3D printed skull.

Orifices such as orbit, nasal aperture, foremen magnum and any crack or wound opening should be taped if duplication is to be done with materials like alginate or silicon impression material. However, with the advent of technologies, 3D imaging and 3D printing can help to replicate the skull better and more reliably even without touching or tampering with it^31,32 (Figure 3). This technique is beneficial if the skull is in a bad condition. The pieces have to be re-assembled using non-permanent glue in cases of fragmented skulls.¹⁷ Any incomplete areas are wax-modelled, but certain errors can exist.

Figure 4.

Frankfort horizontal plane.

Working on a skull replica allows us to:

Reduce the chance of damage to the original skull.

Allows study of the skull during the entire reconstructive procedure.

Leaves a record of the specimen after reconstruction is completed.

Reconstruction phase

The skull must be oriented in the Frankfort horizontal plane (Figure 4), an anthropological standard position that closely approximates the natural position of the head in living individuals.^17,19

Figure 5.

Aligning and setting the prosthetic eye (frontal and lateral view).

An important preliminary aspect of forensic facial reconstruction is setting up the prosthetic eye. By means of a small amount of clay attached to the back of the prosthetic eye, the eye is mounted onto the orbit of the skull. The outer edge of the cornea of the eye should be nearly tangent to the upper and lower eye socket margins¹⁷ (Figure 5).

Techniques for anthropometrical American method/tissue depth method

The following tissue depth markers are positioned on the skull's landmark spot; however certain landmarks in different populations may vary (Table 1).^17,30 The tissue depths are joined by strips of clay; the thickness of the tissue depth marker is followed by positioning the strips of clay over and on the sides of the head. The eyes, nose, lips and ears are sculpted appropriately and texturing, where available, is achieved with the inclusion of a few accessories such as hair, caps, eyeglasses, jewellery (Figure 6).

Figure 6.

Tissue depth method; (a) skull with tissue depth markers (front view), (b) left lateral view, (c) right lateral view, (d) left lateral view of skull showing tissue depth markers connected with clay blocks, (e) completed facial reconstruction.

Table 1.

Soft tissue landmarks on the skull.

Serial no.	Name of landmark	Description
1	Supraglabella	Point above glabella.
2	Glabella (G)	The most prominent point between the supraorbital ridges in the midsagittal plane above the frontonasal suture.
3	Nasion (N)	The midline of the suture between the frontal and the two nasal bones.
4	End of nasals (nasals or Na)	The most anterior tip or point of the nasal bone.
5	Mid-philtrum	The midline of the maxilla placed below the curvature of the anterior nasal spine.
6	Upper lip margin (Supradentale or Sd,or Alveolare)	Centred between the maxillary (upper) central incisors at the level of the Cemento Enamel Junction (CEJ)
7	Lower lip margin (Infradentale or Id)	Centred between the mandibular (lower) central incisors at the level of the Cemento Enamel Junction (CEJ)
8	Chin–lip fold (Supramentale)	The deepest midline point of indentation on the mandible between the mandibular teeth and the chin protrusion
9	Mental eminence (Pogonion or Pog)	The most anterior or projecting point in the midline on the chin.
10	Beneath chin (Menton or Me)	The lowest point on the mandible.
11	Frontal eminence	Place on the most anterior projections at both sides of the forehead.
12	Supraorbital	Centred on the upper most margin or border of the orbit.
13	Suborbital	Centred on the lower most margin or border of the orbit.
14	Inferior malar	The lower portion of the maxilla, still on the “cheekbone”. This point is not actually on the malar or zygomatic bone, but rather on the maxilla.
15	Lateral orbit	Draw a line from the outer margin of the orbit and place the marker about 10 mm below the orbit.
16	Zygomatic arch, midway	Halfway along the zygomatic arch or point at which the lateral surface projects farthest away from the calvarium. This is not necessarily correspondent to the suture line between the zygomatic and temporal bones. It is generally the most projecting point on the arch when viewed from above.
17	Supraglenoid	Above and slightly anterior to the external auditory meatus at the deepest point.
18	Gonion (Go)	The most lateral prominent point on the mandibular angle.
19	Supra 2nd molar (M2)	Above the second maxillary molar. If the second molar is missing, the marker should be placed in the estimated area where it would have been.
20	Occlusal line	On the mandible in alignment with the line where the teeth occlude or “bite”, below the coronoid process.
21	Sub 2nd molar (M2)	Below the second mandibular molar. If the second molar is missing, the marker should be placed in the estimated area where it would have been.

Techniques for anatomical method

In this procedure, priority is assigned to the formation of the skull and neck musculature in their correct anatomical position. Mastication muscles are modelled over the skull when taking special note of the correct bulk of those muscles. Then, muscles around the mouth, eyes and nose are developed. More specifics are added, such as the parotid glands or the fat tissues. A coating of skin is added to complete the restoration and correct texturing is applied to replicate the original skin¹ (Figures 7 and 8).

Figure 7.

Anatomical method; (a) skull with muscles of mastication and oral region (right lateral view), (b) front view, (c) left lateral view, (d) skull with muscles of orbital and nasal region (right lateral view), (e) front view, (f) left lateral view.

Figure 8.

(a) Skull with facial muscles with parotid glands and fat tissues (right lateral view), (b) front view, (c) left lateral view, (d) completed facial reconstruction.

Eye

The prosthetic eye should be positioned inside the orbit as seen from the front with a line drawn from the medial edge to the lateral margin of the orbit at the junction; and the other line bisecting the orbit between the upper and lower margins. The outer point of the cornea is nearly tangent to a centrally positioned line drawn from the upper and lower margins of the orbit as seen from a lateral perspective.¹⁹ The upper eyelid is more pronounced with more anterior curvature with respect to the total curvature; but for the lower eyelid, the curvature is more towards the lateral angle.³² The angle of curvature is 16.5 mm for the upper eyelid and 22 mm for the lower eyelid.³³ The two canthi are defined by the lacrimal fossa and the malar tubercle³⁴ (Figure 9).

Figure 9.

Formation of soft tissue features: (a) lips, (b) ear, (c) nose, (d) nose.

Mouth

The corners of the mouth would be at the lateral or distal edge to the canine. The width of the lips will be equal to the combined vertical length of the enamel surfaces of the upper and lower teeth¹⁹ (Figure 9).

Nose

The nose shape is obtained from the nasal projection taken as the point at which the tangents from the last part of the nasal root and the nasal spine intersect. Nasal base angle (angle between the upper lip and the columella) is set by the direction of the nasal spine. The end of the soft nose is pointed as the point where a line following the projection of the last part of the nasal bone (at the rhinion) crosses a line following the direction of the nasal spine.¹⁷ The nasal tip bifurcation is associated with a bifid nasal spine.³⁵ First, the overall direction of the nasal spine is observed and a line is drawn to show the general angulation. The depth of mid-philtrum tissue depth marker is transferred to the line of angulation (Figure 9).

Ear

The ears must be positioned on the external auditory meatus with a backward angulation of about 15° behind the angle of the jaw. The ears are closely attached to the anterior portion and posteriorly contoured away from the head^17,19,30 (Figure 9).

Hand stippling with various pointed tools and sandpaper can also be used to produce skin texture. This texture helps to avoid glare problems from the shiny surface of clay during photography. The ears should be left smoother without any texture. The eyebrows should be formed by scraping in the clay with a sharp tool following the natural growth pattern of the eyebrow hair.¹⁹

Forensic facial reconstruction has proved to be a powerful identification tool for law enforcement. While some may question the accuracy of these techniques, the above-mentioned procedures have proved a major advantage for those tasked with identifying missing deceased individuals, particularly when there is no other source of evidence available. The depiction of morphological features should follow scientific procedures aided by some artistic approach. Despite its disadvantages, pitfalls and the fact that the results of a forensic facial reconstruction alone do not prove a positive identification, there are many promising cases that have been solved by using forensic facial reconstruction and which are encouraging its continued use.

Conclusion

Forensic facial reconstruction is a blend of art and science that has evolved greatly over the years. Spurred by the evolution of combining academic study with commercial innovation, practitioners of this valuable forensic discipline have used the results to help move the discipline forward. New and more reliable methods are constantly evolving, aided mostly by advancements in modern technology. Documented success in using forensic facial reconstruction justifies continued research most particularly on the relationship between bony landmarks on the skull and their relationship with facial morphology and how it affects the expression of soft-tissue facial features. Other research topics can also be introduced to further improve precision by confirmation, ease of use and employing technologies and preparation. It offers a valuable forensic recognition method for law enforcement, historical research, museums and others in the science community committed to the analysis and representation of the human face.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

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