Introduction

Covid-19 has presented new challenges in every sphere of life including the science of bite mark analysis. The pandemic has seen an increase in the number of domestic violence cases, murders, cases involving sexual assault, child abuse, and the neglect of the elderly [1,2,3,4]. Human bite marks were observed in many of these cases [5].

Currently collecting evidence for bite marks poses a risk of occupational exposure to Covid-19 infection for the forensic dentist in a mortuary setting, particularly if the necessary precautionary measures are lacking [6, 7]. The use of alternative methods, such as three-dimensional (3D) scanning technology which are less invasive, digitally transferrable, and equally accurate to conventional methods should now be considered. Since the onset of Covid-19, the Pretoria team of forensic odontologists have included 3D scanning of both, the bite marks and the suspect’s dentition in their analysis of the relevant cases. Bitemarks will always undergo a degree of warpage, shrinkage, and distortion with time [8,9,10]. A 3D scan is thus, a representation of a distorted bite mark [11] in either skin or an inanimate object. A 3D scan is a snapshot in time that will capture and freeze the images that we know are already distorted. A 3D scanner generates point clouds from geometric data gathered from the surface of an object. The object’s shape is reconstructed from the digital data on the known spatial position of each measurement point. Different scanning and processing software programs are used to generate comparison of dental casts and scanned dentition [12].

This systematic review aims to investigate the practical utilization of different 3D scanners in recording bite marks in skin- and inanimate objects and the use of computer-assisted methods in human bite mark analyzes during and after the Covid-19 pandemic.

Methods

In August 2020, during the height of the South African pandemic, a systematic review of the literature was performed using an online search in three scientific databases: MEDLINEOvid®, Pubmed®, and Google Scholar. As a result of rapid development of technology, only articles from 2011 onwards were considered relevant. Key words such as “human bite mark,”, “bite mark analyzes”, “3D analyzes”, “3D scanning”, “forensic odontology”, and “forensic dentistry” were searched. The search was expanded by checking the reference lists of the articles. Additional mining of above mentioned databases was conducted in February 2021 for the purpose of this review. The articles obtained by the search were screened and selected by two operators. Only English language full-text articles with indexed abstracts published in ISI-accredited dental, forensic, and legal medicine journals were included. Short communications, letters to the editor, case reports, ordinary, and systematic reviews were excluded from the results.

From the articles that fulfilled the criteria, the following data were extracted: (1) the aim of the study, (2) the sample size, (3) the bite mark substrate (4) registration techniques and the scanners used, (5) software, and (6) the study outcome.

Results

The initial search yielded 263 full-text articles, of which 248 did not meet the selection criteria. A PRISMA[13] flowchart is presented in a Fig. 1.

Fig. 1
figure 1

Flow diagram of the search and selection process [13].

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The year of publication, authors, titles, and journals are presented in the Table 1.

Table 1 Studies included in this systematic review
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Fifteen eligible articles were divided on a basis of the analysis target as follows:

  1. A

    Studies assessing the reliability of measurements of different 3D scanners are presented in the Table 2 (6 articles) 

    Table 2 Overview of the studies on the reliability of different 3D scanners
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  2. B

    Studies utilizing 3D comparison of the dental crown morphology of the anterior dentition are presented in the Table 3 (3 articles)

    Table 3 Overview of studies utilizing 3D comparison of the dental crown morphology of the anterior dentition
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  3. C

    Studies on suitability of different computer-assisted methods for bitemark analyzes are presented in the Table 4 (6 articles)

    Table 4 Overview of the studies on computer-assisted methods for bitemark analyzes
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Discussion

From the search it became clear that 3D digital scanning of bite marks enables accurate and fast recording of the bite marks in soft substances such as cheese, chocolate, pears, apples, and human skin without further distortion of the evidence during impression taking [10, 11]. While using digital scanners, an exposure to pathogens can be minimized and several steps can be eliminated. These include mixing an impression material, waiting for setting of impressions and casting of models from impressions [27]. Taking impressions of the suspect’s dentition can sometimes be problematic due to noncompliance and gagging which can be alleviated by the small heads available in some of the scanners [28, 29]. Maintaining a chain of evidence becomes far simpler and can be digitally traced. A digital file can be uploaded to a cloud server for immediate communication with the forensic team members [30]. It minimizes the number of people being exposed to the evidence or suspect from a pandemic control point of view and allows the team to work remotely via cloud server. It also enables for the virtual presentation of the expert witness in a court of law [31].

Studies assessing the reliability of different 3D scanners

The study on contact 3D scanners showed that the contact between the scanner and the bitemark was problematic as the evidence could inadvertently be damaged. Contact scanners were also unable to capture surfaces with marked concavity [12]. This has led to increased interest in noncontact methods such as laser scanning. The 3D laser scanners have proved their precision for different applications. However, the difficulty detecting sharp edges, especially incisal edge of the anterior incisors may provide false presentation of the tooth morphology. While using the 3D laser scanners for dental casts and biting edges in practical forensic cases, the margin of the error should be considered [12].

Utilization of fringe pattern protection scanners, also known as optical surface scanners such as Gom ATOS III (Gom, Braunschweig, Germany) in 3D documentation of bite marks was reported in two articles [10, 15]. The method is noninvasive, displays high resolution results, and does not damage the evidence [10]. The difficulties of capturing tiny areas and deep structures of the surface and the cost of equipment have been reported in the literature [10, 32].

The evidence suggests that intra- and inter- arch measurements obtained from digital dental models using intraoral scanners is equivalent to dental plaster models or digital images generated from conventional dental impressions [33]. Zfx InraScan intraoral 3D scanner and it’s virtual measuring tool was found valid for measuring key features in dental casts [20]. The studies done by Fournier et. al. [23, 25] proposed a protocol for the bite-mark analyzes using Planmeca Emerald® intraoral scanner. In a validation study it was found reliable on wax, cheese, and chocolate, but yielded the poorest results in apples. The use of any type of scanner and associated equipment always requires a high degree of training and expertise. These devices showed an excellent potential for use in bite-mark analysis.

The CBCT-assisted analysis of bite marks was considered a nondestructive, accurate, and simple. Ali et al. [21] concluded that CBCT images of bite marks displayed no distortion artifacts and enabled accurate 3D measurements. Corte-Real et. al. [22] showed in their study that bite mark analysis could be done through software that searches for matching dentitions in a CBCT database. This could add value in the identification process of potential suspects where countries have one or more national databases for all the performed radiographic images. Using ionizing radiation may pose potential risk to the operator and the suspect [34]. This obviously does not apply to the bitemarks on the bodies observed and investigated in the mortuary. The availability of the CBCT machines and the cost of the procedure might be an obstacle for utilizing this novel approach in less developed countries. In spite of these shortcomings, CBCT could provide a potential alternative modality for recording the bite marks in forensic odontology, especially on foodstuffs [35].

Photogrammetry in 3D documentation of skin bite marks was published for the first time in 2003 by Thali et al. [36]. A series of overlapping photos from different points of view around a targeted object are taken and the 2D photographs are combined into a true-to-scale 3D model of the object. Simplicity, inexpensiveness, free software, and somewhat trivial technical requirements of photogrammetry enable us to create a textured 3D surface model [37]. The accuracy of this technique has been proven to be comparable to the laser scanners [38]. Photogrammetry has been routinely utilized in forensic 3D documentation of skin injuries [39,40,41]. The use of photogrammetry was demonstrated by De Sainte Croix et al. [16] in our systematic review.

Studies utilizing 3D comparison of the dental crown morphology of the anterior dentition.

The uniqueness of human dentition (UHD) could be assessed using 2D (flatbed scanning and photography) and 3D (laser scanning and intraoral scanning) image registration [42]. Chong et al. [17] used intraoral 3D scanner and 3D analyzes software to investigate the UHD in the orthodontically treated study population on human anterior dentition. The authors found that anterior dentition was unique within their study population as no perfect matches were detected. They concluded that using 3D scanner and commercially available 3D analyzes software were highly encouraging methods in bite-mark analyzes particularly in the absence of any positive DNA assay [17]. In two studies by Franco et al. [18, 19] they investigated the uniqueness of the human dentition utilizing 3D methods in randomly selected subjects. The subjects included orthodontically treated patients and twins to increase the reliability of the study [18]. The first study analyzing incisal edges did not show uniqueness, but when the complete crowns of the anterior teeth were included, UHD was demonstrated [18, 19].

It must be understood that the presence of recognizable dental features, nicks, chips, and imperfections are required to correctly match suspects to bitemarks. A lack of features seen in orthodontically treated patients, especially in skin bite cases will create problems in identifying a perpetrator and be impossible to present in the court of law [9].

After considering the research results 3D scanners and computer-assisted methods in bite mark analyszes showed promising results. Small sample size, lacking statistical methods for data comparison, missing intra- and inter-examiner calibrations, nonvalidated software for 3D shape comparison or relatively scarcity of studies performed in vitro present the main limitations in studies included.

Studies on computer-assisted methods for bitemark analyzes

Computer-assisted methods for bitemark analyzes enable experts to work remotely and seek advice from the other team members and colleagues during pandemic. It must be noted, that computers cannot manufacture that which does not exist. Digital analyzes of the bite mark can only enhance existing features and enable the proficient presentation of these features. The use of 3D imaging technology offers practical advantages to the courtroom, specifically with respect to the juror’s understanding of technical language [31].

Biting is a dynamic process. Thus, bite mark analysis is based on a combination of morphological and positional data [43]. Computer assisted graphics and animations have showed the potential for accurate representation of bite marks in all three dimensions, compare the dentitions of presumed biter to the evidence and match the corresponding biter to the bite-mark among several suspects [44]. ATOS software enables an automatic computation of the deviation between the two meshes, thus, allows an easy and very accurate analysis and interpretation of the results. 3D Studio Max software allows dynamic comparison during the animated act of biting, where 3D match or nonmatch is clearly detectable [10].

De Sainte Croix et al. [16] successfully created 3D time-lapse animations, which can be viewed on most electronic devices. The quality of DI3D Photogrammetry system was accurate enough to enable the animations to illustrate the color and shape of bruising. Some distortions were present around the edges of 3D model. The animations can have significant benefit to the photographic evidence presentation in court setting, especially if the presentation has been made virtually [16].

Realistic 3D perspective allows the placement of a higher number of landmarks [44, 45]. Additionally, automated image superimposition and mesh processing leads to improved digital 3D image analyzes and interpretation of bitemarks [18]. 3D capture of the bitemark and digital analysis provide images that have less angular and perspective distortion, which results in less measurement errors [24]. It can be performed using high-tech commercially available as well as special forensic odontology software such as Dentalprint©, BluePrint©, and Biteprint© [12, 24, 26].

Semiautomated BluePrint© software enables the investigator to compare the photographs of a bite mark with the biting edges of a dental cast. It generates data on the dental parameters required for identification (e.g. intercanine distance, rotation, eccentricity, angular position, and distance to the arch of each tooth mark). BitePrint© represents the biting edges of dental casts as a set of geometric coefficients, offering a measurable, semiautomatic, and less subjective analysis. Molina et al. [26] evaluated the accuracy and reproducibility of dental parameters between photographs of bite marks and dental casts using semiautomated technology. The sensitivity of this technology was found to be 92% and specificity 53%. The accuracy of these programs can be applied in practical forensic dentistry and in criminal trials involving human bite mark cases [24, 26].

Conclusion

The global pandemic has forced us to search for new and innovative techniques which are safer to use in our day to day practice of forensic science. Three-dimensional scanners have shown potential advantages and can be used in forensic odontology on the skin and inanimate objects. The analyzes of the bite marks depends on quality, quantity, and the presence of recognizable features in a pattern associated analysis. The latter requires only a degree of accuracy which is standard in the majority of 3D scanners. Training and expertise on 3D scanners and computerized technologies is an absolute prerequisite for forensic dentists to obtain accurate results. The authors believe that in changing world the 3D scanning and analyzing techniques will replace the methods which were derived in a world free of Covid-19, Ebola, HIV, and global connectivity.