Influence of sex and body mass index on facial soft tissue thickness measurements of the northern Chinese adult population

Abstract

Forensic facial reconstruction is a mixture of science and art, as it attempts to reestablish the contours of the soft tissues over the skull. From a forensic point of view, identification of an unknown body relies heavily on this visual aspect of recognition. To obtain acceptable results in forensic facial reconstruction, accurate facial soft tissue thickness data are essential. Until now, despite numerous works related to soft tissue thickness, there is little information in this area for the Chinese population. To this end, this study developed soft tissue thickness data for the Chinese adult population. Spiral computed tomography (CT) data and the body mass index (BMI) of 200 northern Chinese aged 18–32 years were collected. Soft tissue thickness measurements at 20 anthropological landmarks on the skull were taken, based on the three-dimensional models of the skull and face reconstructed from the spiral CT data of each subject. Considering the sex and BMI of the individuals, general descriptive analyses of soft tissue thickness were determined. Statistical analyses were performed between males and females in each BMI group, as well as between each of the BMI categories for males and females, respectively. The results revealed that males have thicker soft tissues than females at most of the anthropological landmarks in the Chinese population, similar to other populations. However, only one-third of these differences were statistically significant between males and females. Taking into consideration the nutritional status, the soft tissue thickness measurements increased with increased BMI levels for both sexes at each landmark, and the statistically significant differences were depicted between the different BMI categories at most of the landmarks. In conclusion, this study has provided useful reference points of the adult northern Chinese population for forensic facial reconstruction, and recommends that the nutritional status of the subject be considered during skull reconstruction procedures.

Introduction

Identification of human remains relies heavily on facial reconstruction, and consequently this technique is of great importance in forensic science [1], [2]. Facial reconstruction is a mixture of science and art, which attempts to recreate an individual's face from a skull or mold of a skull by drawing, sculpture, or computer-assisted methods. Accurate facial reconstruction requires knowledge of the approximate soft tissue thicknesses over various anatomical points of the skull [3].

There has been extensive research on soft tissue thicknesses to date, and many population groups have been investigated. However, Stephan and Simpson [4] indicated that despite the large quantity of data available from such a wide section of the human population, it is unclear which data set is the most appropriate for an individual in a commonly measured population group. Raw data with precise inclusion criteria for subjects and standard measurement methods are therefore still needed for specific population groups. As to the Chinese population, Chen et al. [5] developed soft tissue thickness standards using magnetic resonance imaging (MRI). The age-related and sex × age interactions of soft tissue thicknesses were also discussed in that work. However, the nutritional condition of individuals was not considered.

Facial soft tissues fluctuate in accordance with the nutritional condition of the individual, and facial variations resulting from different body types may limit the effectiveness of facial reconstruction [6], [7], [8], [9], [10]. Several studies incorporated three body type categories (slender, normal, and obese) into their assessments of soft tissue thicknesses, and found that body mass index (BMI) was a major contributing factor in accurately determining differences in facial soft tissue thicknesses between individuals [6], [8], [11]. Consequently, future studies in facial recognition now demand consideration of the different BMI categories when estimating soft tissues thicknesses [3], [12].

Until the mid-1980s, most studies on soft tissue thicknesses employed the needle puncture method on cadaveric samples [13], [14], [15]. However, in the last two decades, several imaging-based methods, including cephalometric radiography [16], [17], [18], [19], [20], ultrasonography [8], [11], [21], [22], [23], computed tomography (CT) [24], [25], [26], and MRI [9], [27] have permitted measurements to be taken on living individuals. As the software performance/quality has advanced, so too has the display technology improved, which can now reconstruct three-dimensional (3D) images of the skull and face using spiral CT data on personal computers. Several studies have measured facial soft tissue thicknesses based on reconstructed CT images, and the similarities as well as differences between this method and the needle puncture method have been evaluated [14], [24], [28].

The purpose of the present study was to add new data to the existing literature and propose average soft tissue thicknesses of the Chinese population, taking individual sex and BMI into account. These results would be useful in forensic science as well as other research applications.