|FORENSIC ODONTOLOGY: ORIGINAL RESEARCH ARTICLE
|Year : 2020 | Volume
| Issue : 3 | Page : 259-265
Precision of 3D laser optical in assimilation of experimental bite marks in chocolate
Alekhya Kanaparthi1, Manasa Anand Meundi2, Chaya M David2, Datturao Ramanand Mahesh2, Soujanya L Krishnappa2, Ramya Katyayani Kastala3
1 Department of Oral Medicine and Radiology, MNR Dental College and Hospital, Sangareddy, Telangana, India
2 Department of Oral Medicine and Radiology, Dayananda Sagar College of Dental Sciences, Bengaluru, Karnataka, India
3 Department of Oral Medicine and Radiology, Sharavathi Dental College and Hospital, Shimoga, Karnataka, India
|Date of Submission||05-May-2020|
|Date of Acceptance||13-Jul-2020|
|Date of Web Publication||29-Sep-2020|
Dr. Alekhya Kanaparthi
Department of Oral Medicine and Radiology, MNR Dental College & Hospital, Sangareddy -502 001, Telangana
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Aims: To analyze the accuracy of a three-dimensional (3D) optical scanner-GOM® (Gesellschaft für Optische; Messtechnik, Braunschweig Germany) model-ATOS triple II optical Scanner (Advanced topometric Sensor) in examination and identification of experimental bite marks (BM) in chocolate using Styrofoam exemplar (SE). Materials and Methods: The study was conducted with 25 volunteers from whom the dental cast exemplar (CE), SE, and experimental BMs in chocolate, were made. These were then digitized using the GOM® ATOS optical scanner and 3D models were generated using GOM® ATOS software. Data analysis was performed using independent t-test for inferential statistics. Results: On 3D analysis, the experimental BM matched with the presumed biters correctly using both SE and CE. The mean percentage matching of BM vs SE was found to be 92.55 ± 1.757, and in BM vs CE, the mean matching percentage was found to be 96.09 ± 1.311. Statistical analysis of the data was obtained using independent t-test, and the mean difference in percentage matching was significant (P < 0.05) Conclusion: Three-dimensional BM analysis using 3D optical scanner proved to be a reliable, accurate, and permanent method of documentation compared to the conventional two-dimensional methods.
Keywords: Bite mark analysis, chocolate, exemplars and food stuff, forensic odontology, three dimensional, Styrofoam
|How to cite this article:|
Kanaparthi A, Meundi MA, David CM, Mahesh DR, Krishnappa SL, Kastala RK. Precision of 3D laser optical in assimilation of experimental bite marks in chocolate. J Indian Acad Oral Med Radiol 2020;32:259-65
|How to cite this URL:|
Kanaparthi A, Meundi MA, David CM, Mahesh DR, Krishnappa SL, Kastala RK. Precision of 3D laser optical in assimilation of experimental bite marks in chocolate. J Indian Acad Oral Med Radiol [serial online] 2020 [cited 2020 Dec 3];32:259-65. Available from: https://www.jiaomr.in/text.asp?2020/32/3/259/296594
| Introduction|| |
The forensic analysis of patterned injury such as bite marks (BMs) includes: first, recognition of a patterned injury as a bite mark; second, the individuality of a suspect's dentition within a closed population; third, the accuracy in transferring the shape of biting surfaces of anterior teeth on to the substrate; and fourth, the accurate image capturing of both injury (on victim) and the dental cast of the suspect's teeth., Even though, bite mark evidence is considered universally accepted in court of justice, recent criticism of this evidence as reliable scientific tool has been raised owing to subjective nature of the comparative analysis. Complexities of interaction of teeth on human skin/inanimate objects, type of distortion during biting process (primary distortion), time-related changes, body position, and quality of photographic evidence (secondary distortion) often raises concern regarding the accuracy of this evidence.
Several techniques have been proposed for comparing BMs to the dentition of the possible assailants. Direct technique involves comparison of life-sized overlays from the suspect's teeth to detect similarities or differences with the Bite mark., On the other hand, indirect technique involves the use of computer-based techniques to produce bitemark comparison overlays, dental casts are scanned using a two-dimensional scanner (2D), and images were then analyzed in software. The most commonly used method to analyze BMs against suspect's dentition are overlay techniques, using Adobe Photoshop software. Dental casts are the most commonly used exemplar in BM analysis. Nevertheless, American Board of Forensic Odontology suggested exemplars made from bite registration materials such as aluwax, base plate wax, Styrofoam sheets, fruits, and clay. Among bite registration materials, Styrofoam seems to fulfill the prerequisites for being close to an ideal exemplar and obtaining the exemplar is a single step procedure unlike a cast exemplar (CE).
Due to the reported inconsistencies of Bite mark as evidence, revoking of exonerations in the past and frequent questions raised against BMs as pseudoscience; researchers across the globe are in search of newer methods to overcome the drawbacks of conventional methods of analysis. One such method in three-dimensional (3D) Bite Mark analysis is the use of 3D optical scanning system for generating 3D models that provide permanent documentation of the evidence, retrievable any time for examination.,,,,,
Three-dimensional scanning systems are commonly used to digitize models in automobile industries, which records the geometry of the object and reconstructs it to a digital model with high accuracy and precision.,,,, This digitized model can be retrieved and used for analysis at any point of time. Specialized software of such scanning systems allows virtual maneuvering of the digitized model and also has metric tools for calculation of linear and angulation measurements enabling automatic percentage degree of matching, along with color code match mapping.,,,
The present study was aimed to analyze the accuracy of a 3D optical scanner-GOM® (Gesellschaft für Optische;Messtechnik, BraunschweigGermany; model-ATOS triple II optical Scanner (Advanced topometric Sensor) in examination and identification of experimental BMs in chocolate using Styrofoam exemplar (SE).
| Materials and Methods|| |
This study was conducted at a private dental college, India. All the participants were informed about the purpose of the study, and written and informed consent was obtained before the start of the study.
Study population and sample size
The cross-sectional study was conducted among dental students who were willing to volunteer to be a part of the study. Sample size was calculated with G power software v. 18.104.22.168 computer program. Sample size determination revealed that, for Chi square test on a sample with an effect size (Cohen'd) of 0.8, a minimum of 25 subjects was required. Randomized sampling methodology was employed to include the study subjects. A final sample size of 25 was included in the study. Volunteers with completely missing anterior teeth were excluded from the study as the process of biting requires at least the presence of incisor's and canines.
The materials used in the study for impression making were impression trays; rubber bowl; spatula; alginate (Algitex, DPI), dental stone (Kalstone, Kalabhai) for dental cast [Figure 1], Styrofoam sheets were obtained from the manufacturer of disposable thermocol plates. They were of 0.4 cm thickness and were cut into the size of 57 mm × 76 mm for SE [Figure 2] for the experimental BM in chocolate (Plain Cadbury Dairy milk of 8 mm thickness) [Figure 3] and for the digitalization, a 3D optical scanner-GOM® (Gesellschaft für Optische ; Messtechnik, BraunschweigGermany; model-ATOS Triple II (Advanced topometric Sensor) 3D surface scanning system (www.gom.com, Braunschweig, Germany.) [Figure 4].
|Figure 1: Procedure of acquiring a cast exemplar (CE) a) Alginate impression and b) Dental stone cast|
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|Figure 2: a) Procedure of acquiring Styrofoam exemplar (SE) b) Styrofoam exemplar (SE)|
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|Figure 3: a) Procedure of acquiring experimental bite mark in chocolate (BM) and b) Experimental bite mark (BM)|
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First, all the 25 subjects underwent procedures for acquisition of exemplars followed by Experimental BMs.
a. Patient preparation and exemplar acquisition: The procedure was explained to the volunteers prior to performing the technique. Two exemplars from two different materials were generated from each volunteer: A) dental cast B) Styrofoam.
The CE was obtained by making the maxillary teeth impression using alginate followed by preparing a cast using dental stone as per the manufacturer's guidelines [Figure 1]. Though elastomeric impression materials are dimensionally more stable; in this study, we used alginate with a practical consideration of being a less expensive and readily available material. However, extra caution was taken to pour the dental casts immediately after taking the impression to prevent any loss of information due to dimensional changes.
The SE was obtained by instructing the volunteer to position the disinfected sheet of 0.4-cm-thick sheet of 57 × 76 mm dimension in between their teeth and bite it to register the marks of the upper anterior teeth [Figure 2]. To disinfect the exemplar, it was washed and dried using absorbent paper and gently wiped off with a spirit swab and placed in a sealed polythene bag.
b) Experimental BM acquisition: Each volunteer was instructed to hold the central portion of the chocolate (Cadbury Dairy Milk) in between the front teeth and bite off some chocolate to obtain the sliding bite and prevent the chocolate from breaking [Figure 3]. The marks within the remaining portion of the chocolate were considered as “bite mark” (BM). The acquired experimental BMs were placed in a sealed polythene bag and were stored in a Thermocol™ box.
All of the 75 samples (including 25 samples of both cast and SEs, and 25 experimental BMs in chocolate) were subjected to 3D scanning using a 3D ATOS triple II optical scanner.
c) Three-dimensional scanning of exemplars and experimental BMs:
The 3D documentation of the objects was performed using the ATOS™ Triple II scanning system. The detailed specifications regarding this device are reviewed at the patent website
Use of the optical scanner and associated equipment required a certain degree of training. Prior to the digitization of the study samples, the author's practiced using the equipment and software commands to digitize the samples and tools for metric measurements and color mapping used for BM analysis.
First, the exemplars and experimental BMs were placed manually on an automated rotation table, which rotates until the whole object is scanned. The ATOS modeling software automatically merges the single data set using reference targets placed around the object to create high-precision coordinates of up to 5 million surface points into 3D polygon meshes. The polygon models of cast [Figure 5]a, experimental BMs [Figure 5]b and SEs [Figure 5]c will be generated and saved in stereolithography (stl) formats.
|Figure 5: Polygon mesh models of a) Cast exemplar (CE), b) Experimental bite mark (BM), and c) Styrofoam exemplar (SE)|
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For the CE and SE and experimental BMs in chocolate (BM), the measuring volume of 170 × 130 × 130 mm3 with a resulting point spacing of 0.07 mm was used for registering finer details.
After scanning, 3D models of BM and both CE and SE were coded by another observer. The experimental BMs in chocolate were numbered sequentially from 1 to 25 (BM1, BM2,…, BM25), whereas both the exemplars (CE and SE) were given a number randomly between 1 and 25.
e) Three-dimensional comparative analysis of BM-CE and BM-SE:
During analysis, the 3D models generated using the ATOS modeling software of the 25 CEs and 25 SEs were compared to the 3D models of each of the 25 experimental BMs in question (e.g.: BM1). For the comparison of the experimental BMs, the GOM inspect was used [Figure 6] and [Figure 7].
|Figure 6: Three-dimensional matching of the experimental bite mark (BM) and Cast exemplar (CE) showing the percentage matching|
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|Figure 7: Three-dimensional matching of the experimental bite mark (BM) and Styrofoam exemplar (SE) showing the percentage matching|
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The 3D models saved in stereolithography (Stl) file format were superimposed into the corresponding positions of the BM to draw conclusions about the matching.
In this 3D pattern-associated comparison, the pattern of the upper anterior teeth, as well as the relationship to the surrounding teeth, was compared. The width and shape of the maxillary arch, width and shape of incisive edges, cuspal tips, and other distinguishing characteristics of the teeth (position, rotation, spacing) were analyzed. The 3D models of one bite mark (BM) are superimposed into the corresponding position using a best fit registration tool by the software [Figure 6] and [Figure 7]. This comparison allowed maneuvering of these models in all the directions to allow examination of the intricate scratch mark within the chocolate right from the initial tooth contact to the surface intact with exemplars. This was repeated for the remaining 24 experimental BMs to which all the 25 CE and SE are once again compared individually for possible matching. Following comparison, conclusions were made based on the ABFO standards (ABFO, 2017). To describe the relation of a BM to the biter, following terms were used: 1) not excluded as biter (N), 2) inconclusive (I), and 3) excluded (E) as the biter.
In cases of an inconclusive relationship, GOM Inspect used to calculate the degree of the correlation between the BM in question and probable CE and SE. The results are displayed as a color-coded polygon mesh along with degree of matching expressed as percentages. Green represents the highest degree of surface matching and red represents poor matching. The percentage matching of BM vs SE and BM vs CE were tabulated [Table 1] and subjected to statistical analysis.
|Table 1: Matching percentages of experimental bite marks (BM) with Styrofoam exemplar (SE) and Cast exemplar (CE)|
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Results and statistical analysis
The statistical analyses were performed using SPSS version 21 software (SPSS, Chicago, Illinois). The results were computed statistically using independent t-test to test the mean difference of matching between CE and SE. In a total of 25 study subjects, there was matching between all of the BM vs CE and BM vs SE. The mean matching between BM vs CE was 96.09 with a standard deviation of 1.311, and the mean matching of BM vs SE was found to be 92.55 with a standard deviation of 1.757 [Table 2], [Graph 1]. The “p” value obtained was 0.000, which was <0.05 accepted as indicating a high level of statistical significance [Table 3].
| Discussion|| |
BMs are the physical alterations within the medium caused by the forceful contact of teeth either alone or in combination with other parts of the mouth. This dental evidence, if processed properly, can help in solving a crime.
Historically, several 2D methods of analysis of the BMs included evaluation of these patterned marks from the hand-drawn, photocopied, scanned, or computer-assisted overlay generation techniques. These overlays are later superimposed onto 1:1 life-sized photographs or the casts are directly matched by the manual docking method to compare and analyze the BMs. These 2D methods have the limitations of possible human error due to observer bias, manipulation of the data during overlay generation, the possibility of distortions during photographic documentation and the need to use ABFO scale 2 for documentation of evidences.,,,,,,,,
The act of biting is a 3D, dynamic procedure due to the movement of the jaws of the biter and the reaction of the bitten person or consistency of the material on which the bite is inflated., This entire process may not be assessed clearly during a 2D photographic documentation, as suggested in earlier studies by Thali MJ et al.; Nather S et al.; Blackwell SA et al.,,
Thali MJ et al. and Prystanska A et al. demonstrated the potential for 3D scanning with an advanced GOM ATOS® scanner and suggested the ease of use and reliability of these scanners in 3D BM analysis., In the current study, using the GOM ATOS® optical scanner, we also created the 3D models that were similar to the original test bites and all were effective in registering the BMs that allowed positive identification of the presumed biters within the experimental model.
Using the GOM® software, each of the SEs was compared to one experimental BM. On comparison out of 25 SE, 19 matched unambiguously to the corresponding experimental BMs using the best fit registration tool and could be concluded as “not excluded as biters (N).” There was confusion between six experimental BMs that were marked as Inconclusive (I), that were later confirmed as biters using the GOM inspect tool, which calculated the surface area matching as percentages.
Similarly, in the initial assessment on 3D comparison of CE with BM, 20 out of 25 samples matched unambiguously to the corresponding experimental BMs, and the remaining five experimental BMs were marked as inconclusive (I) initially. Later, the GOM inspect tool enabled identification of the exact biters in cases of inconclusive match, while also confirming the initially concluded biters. It is important to note that the 3D software not only identified the biters but also automatically displayed the percentage matching along with colorimetric scales that was not possible in previously reported 2D BM studies.
In our study, even though all experimental BMs correctly identified their respective CE and SE, the mean matching of the BM vs CE was more than BM vs SE [Table 1]. This could be due to the increased surface registered within the experimental BM by the CE that registered both the incisal edge and some amount of the labial surface of the dentition in the thickness of the BM against only the surface area matching of the BM with the incisal edges registered within the SE, further supporting the ability of 3D software to register finer details and 3D information with no data loss.
The validity of using 3D BM analysis has been demonstrated in the previous studies by Thali MJ et al., Evans ST et al., Nather S et al., Przystanska A et al., and Blackwell SA et al. that allowed successful identification of the biters, and the results of our study are in agreement with these studies and it can be said that this 3 D method of BM analysis could be applied in real crime scenes as it is relatively automated and may show less chance of subjective human error.
Though there are several proven 2D studies in the assessment of BMs, the current study put forth the importance of registering the third dimension using a 3D laser scanner. In this study, the process of comparison was relatively automated, and the software not only aided the initial comparison but also assisted in identification of the biter in cases of confusion. The 3D BM analysis proved to be relatively quick, reliable, accurate, and an efficient method in BM comparative analysis.
Recent innovations in technologies evaluated by few authors reported the use of Cone Beam Computed Tomography, in 3D BM analysis., However, this method of analysis has a drawback of radiation dosage, instrument portability to practically apply it in real crime scene, and chances of subjective error during data interpretation.
Another addition to the path of innovation is the use of intraoral scanners for digital impression of teeth, thereby reducing the need of laborious lab work and ease of obtaining the digital models in dental office itself. Though it has shown potential use, more evidence is required to further explore its application in BM analysis, and our research group has already started a preliminary study in this regard.
| Conclusion|| |
The role of BM analysis in the identification of the suspect is a complex procedure. Biting is a 3D process that cannot be fully registered into two dimensions during documentation as a valuable evidence. With the advent of digital technologies, it is now possible to acquire 3D models that have minimal error in data acquisition, comparison, and storage (particularly in perishable materials like food stuffs) and the use of GOM ATOS scanner to digitize the experimental BMs seems indispensable. The data exchange in file formats also enables instant data evaluation between investigating authorities at any point of time. From our study, it can be concluded that the accuracy, degree of precision, relative automation, and reproducibility of the results in this technique definitely proves its edge over other traditional 2D techniques of BM analysis. We further recommend studies to be carried out using 3D comparison to assess the reliability of the currently available 3D scanning systems and software in a larger sample size with different exemplars and simulated BMs in other materials.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient (s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
A heartfelt thanks to Mr. Suresh Murthy, Asst Manager, APM technologies, Bengaluru, Karnataka, India for his kind support and guidance to prepare the three-dimensional data for this study.
The present study was approved by the Institutional Ethical Committee (Ref no: DSCDS/2015- 16/293A).
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
[Table 1], [Table 2], [Table 3]