3D-3D facial superimposition between monozygotic twins: A novel morphological approach to the assessment of differences due to environmental factors

3D-3D superimposition techniques in personal identification: A ten-year systematic literature review

The 3D-3D superimposition technique offers a comprehensive comparison and quantification of the similarity between two 3D models, making it a promising approach for forensic science. This systematic review aims to explore scanning techniques, 3D analysis software, and 3D-3D superimposition methods, along with providing an overview of their applications and performance in personal identification. We searched four databases (PubMed, Scopus, Web of Science, and Embase) for articles published between January 2014 and May 2024. QUADAS-2 was adopted to assess the risk of bias in the included studies. After applying the eligibility criteria, a total of 25 articles were selected for our review. From these articles, we identified six scanning techniques and eight software programs. These diverse scanning technologies and 3D software significantly streamline the process of 3D data registration and similarity calculations. The surface-based registration was the most frequently utilized approach and was considered more suitable for forensic research. Studies have shown that 3D-3D superimposition has emerged as a valuable tool in various fields, including the antemortem (AM) and postmortem (PM) comparison, pair-matching, re-association, craniofacial superimposition, and face identification. It is anticipated that further research involving a broader range of sample types and standardized protocols will further enhance the applicability of 3D-3D superimposition technology in forensic practice.

Facial morphology differences in monozygotic twins: a retrospective stereophotogrammetric study

OBJECTIVE

To assess soft tissue differences between monozygotic twins (MZ) for the total face and between facial regions using three-dimensional (3D) stereophotogrammetry and quantitative surface-based 3D deviation analyses.

MATERIALS AND METHODS

The study sample consisted of 14 untreated MZ twins (6 males, 8 females, mean age: 14.75 years) from the archive of Marmara University, Department of Orthodontics. The images were taken by the 3dMDface system, and 3dMDvultus software was used for removal of undesired areas and approximation of the images. Then, stereolithography (.stl) format images were superimposed using the best-fit algorithm using 3-matic software. The face was divided into facial thirds, and upper lip and lower lip + chin regions were created. For the comparison, 3D deviation analyses were performed, and a color map and histogram were created. The data were presented as mean deviation, root mean square (RMS), median, and interquartile range.

RESULTS

Between the facial thirds, there was no significant difference in soft tissue differences for mean deviation. A statistically significant difference was found between the upper and lower face for the RMS value. For the comparison of upper lip and lower lip + chin region, the only significant difference was for the RMS. When the data were presented as median and interquartile range, there were no statistically significant differences between any facial regions.

CONCLUSIONS

Lower facial third and lower lip + chin regions had the greatest differences within MZ twin pairs. The genetic and environmental influences might not be the same for different parts of the face.

A Longitudinal 3D Investigation on Facial Similarity among Two Monozygotic Twins in Their First Childhood: An Application of the 3D-3D Facial Superimposition Technique

Children affected by orofacial disorders mix functional alterations with morphological problems, and suitable techniques should be devised for their analysis. Stereophotogrammetry and 3D-3D facial superimposition have already proven to reliably assess morphological differences even between twin siblings, separating the effect of genetic and environmental factors. However, little information is available about twin babies. We longitudinally analyzed a couple of healthy monozygotic twin sisters aged 6 months to 5 years (height time points). The entire 3D facial models of the two sisters were registered according to the least point-to-point distance, and the relevant RMS (root mean square) distance between the facial models was calculated at each time and compared with reference data recorded from adult twins (Mann-Whitney test, p < 0.05). RMS values in the twin sisters were on average 1.18 ± 0.21 mm, and 1.86 ± 0.53 mm in adults, with a significant difference (p < 0.01). Results showed that twins are more similar in early childhood when environmental factors are supposed to have not influenced facial morphology sufficiently. Additionally, the technique seems adequate to detect even small differences: the faces of the twin sisters were not fully identical. 3D-3D facial superimposition techniques can objectively quantify facial dissimilarity even in monozygotic twins. The method may be applied to the faces of twins discordant for some orofacial and maxillofacial pathology and potentially separate genetic and environmental factors.

Can a spontaneous smile invalidate facial identification by photo-anthropometry?

Purpose

Using images in the facial image comparison process poses a challenge for forensic experts due to limitations such as the presence of facial expressions. The aims of this study were to analyze how morphometric changes in the face during a spontaneous smile influence the facial image comparison process and to evaluate the reproducibility of measurements obtained by digital stereophotogrammetry in these situations.

Materials and Methods

Three examiners used digital stereophotogrammetry to obtain 3-dimensional images of the faces of 10 female participants (aged between 23 and 45 years). Photographs of the participants' faces were captured with their faces at rest (group 1) and with a spontaneous smile (group 2), resulting in a total of 60 3-dimensional images. The digital stereophotogrammetry device obtained the images with a 3.5-ms capture time, which prevented undesirable movements of the participants. Linear measurements between facial landmarks were made, in units of millimeters, and the data were subjected to multivariate and univariate statistical analyses using Pirouette® version 4.5 (InfoMetrix Inc., Woodinville, WA, USA) and Microsoft Excel® (Microsoft Corp., Redmond, WA, USA), respectively.

Results

The measurements that most strongly influenced the separation of the groups were related to the labial/buccal region. In general, the data showed low standard deviations, which differed by less than 10% from the measured mean values, demonstrating that the digital stereophotogrammetry technique was reproducible.

Conclusion

The impact of spontaneous smiles on the facial image comparison process should be considered, and digital stereophotogrammetry provided good reproducibility.

Facial Anthropometric Proportion of Chinese Han Nationality

Facial anthropometric measurements play an important part not only in forensic cases but also in clinical treatments. The utilization of 2D photograph methods in facial anthropometric studies to found database with age, gender, ethnicity, and region was expanded by other races but little for Han nationality. This study was undertaken to describe reference ranges of facial anthropometric proportions of Han nationality and compare the anthropometric characteristics with other ethnicities. Our subjects focused on full-face photos of Han nationality in South China which consisted of 1176 healthy person (425 adult males, 421 adult females and 157 underage boys and 173 underage girls). Eight anthropometric landmarks on photos were examined by ImageJ software, and 7 anthropometric ratios were analyzed. The results indicated sex- and age- and ethnics-related anthropometric variations in Chinese Han nationality in South China. For adults, females have larger ratios in intercanthal-nasal width and lip height index and smaller nose width index; for impubes, boys were larger in lip height index and smaller in lip width ratios than girls, but as age achieved, the underage boys and girls exhibited a significantly larger nose width index and lip width index, smaller canthal index, intercanthal-nasal width and lip height index. Comparing with Japanese, India, North American and Persian, Chinese Han showed great difference in facial anthropometric proportions.