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A comparative study between xerographic, computer-assisted overlay generation and animated-superimposition methods in bite mark analyses
Legal Medicine 22 (2016) 42–48
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Legal Medicine journal homepage: www.elsevier.com/locate/legalmed
A comparative study between xerographic, computer-assisted overlay generation and animated-superimposition methods in bite mark analyses Meng Wei Tai, Zhen Feng Chong, Muhammad Khan Asif, Rabiah A. Rahmat, Phrabhakaran Nambiar ⇑ Department Oral and Maxillofacial Clinical Sciences, University of Malaya, Kuala Lumpur, Malaysia
a r t i c l e
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Article history: Received 16 May 2016 Received in revised form 21 July 2016 Accepted 27 July 2016 Available online 30 July 2016 Keywords: Forensic odontology Bite mark Human skin Xerographic Computer-assisted analysis Adobe PhotoshopÒ CS6 GIF-AnimatorÓ
a b s t r a c t This study was to compare the suitability and precision of xerographic and computer-assisted methods for bite mark investigations. Eleven subjects were asked to bite on their forearm and the bite marks were photographically recorded. Alginate impressions of the subjects’ dentition were taken and their casts were made using dental stone. The overlays generated by xerographic method were obtained by photocopying the subjects’ casts and the incisal edge outlines were then transferred on a transparent sheet. The bite mark images were imported into Adobe PhotoshopÒ software and printed to life-size. The bite mark analyses using xerographically generated overlays were done by comparing an overlay to the corresponding printed bite mark images manually. In computer-assisted method, the subjects’ casts were scanned into Adobe PhotoshopÒ. The bite mark analyses using computer-assisted overlay generation were done by matching an overlay and the corresponding bite mark images digitally using Adobe PhotoshopÒ. Another comparison method was superimposing the cast images with corresponding bite mark images employing the Adobe PhotoshopÒ CS6 and GIF-AnimatorÓ. A score with a range of 0–3 was given during analysis to each precision-determining criterion and the score was increased with better matching. The Kruskal Wallis H test showed significant difference between the three sets of data (H = 18.761, p < 0.05). In conclusion, bite mark analysis using the computer-assisted animated-superimposition method was the most accurate, followed by the computer-assisted overlay generation and lastly the xerographic method. The superior precision contributed by digital method is discernible despite the human skin being a poor recording medium of bite marks. Ó 2016 Elsevier Ireland Ltd. All rights reserved.
1. Introduction Scientific examination of a bite injury or a tooth mark plays an important role in many criminal investigations such as rape, murder, robbery and other forms of physical and sexual violence. The American Board of Forensic Odontology defined bite mark as ‘‘A representative pattern left in an object or tissue by the dental structures of an animal or human” [1]. On the other hand, Mac Donald explained it as a mark left by teeth either by itself or combined with other oral structures [2]. Subbiah SK et al. and Pillay VV et al. [3,4] advocated that a bite mark is an essential forensic evidence which constitutes a popular form of dental evidence presented in criminal court. However, National Academy of Sciences (NAS) reported that bite mark analysis has been heavily criticized ⇑ Corresponding author at: Department Oral and Maxillofacial Clinical Sciences, Faculty of Dentistry, University of Malaya, 50603 Kuala Lumpur, Malaysia. E-mail address: [email protected] (P. Nambiar). http://dx.doi.org/10.1016/j.legalmed.2016.07.009 1344-6223/Ó 2016 Elsevier Ireland Ltd. All rights reserved.
for its principles. One of the main reasons was the insufficient fundamental research that investigates the scientific basis of this method [5,6]. The Innocence Project is convinced that all forensic disciplines need to be verified in a scientific way whereby methodologies are used in criminal cases after genuine independent research and peer reviews were done [7]. Furthermore, subjectivity, operators’ incompetence, or inadequate internal controls can affect the integrity of the results despite the demonstrated methods used. Bite mark analysis is especially plagued due to the almost total absence of any rules, regulations, or processes to accredit experts or the testimony they provide in developing standards. It is common knowledge that very few government-related bodies in any country has ever scrutinized the validity and reliability of bite mark evidence. ‘‘Bite mark analysis has never passed through the rigorous scientific examination that is common to most normal sciences,” citing from the book entitled Modern Scientific Evidence: The Law and Science of Expert Testimony [8].
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Bite mark mechanism is when the teeth apply pressure on the skin with a varied force. It begins with closure of mandible, followed by a negative pressure from the suction of skin, and the tongue thrust from the opposite direction; therefore, there would be projection of teeth edges and palatal surfaces [9]. When an individual bites something, the superior teeth stabilize the object whilst the inferior teeth try to cut it. The indentation created by the superior teeth is significantly important in order to obtain information such as: dental alignment, size and shape of dentition [10]. Bite mark analysis relies on two assumptions; (a) the teeth alignment that produce a bite mark is individualistic, (b) the skin records adequate information of the bite mark to match the corresponding anterior dentition [11]. It has been approximated (by the use of computer technology) that there were more than two billion possibilities to chart an adult dentition [12,13]. This would certainly rule out the chances of two adults having completely identical dentition [14]. However, caution must be expressed as skin is a poor recording medium, it tends to experience visco-elastic, anisotropic, non-linear responses to stresses like bite forces [15,16]. The common method to investigate bite mark is dependent on interpreting photographic evidence in which the dental casts of the teeth of the suspect is matched with the bite mark [17]. The process of bite mark matching with a suspect’s dentition includes parameters such as size, shape and position of each tooth [18]. Xerography has been demonstrated by Kouble et al. [19] and Maloth et al. [20] to be significantly more accurate in bite mark analysis as compared to the conventional hand-tracing on plastic films placed over the dental casts of the offender. Xerography is performed by making a life-size image (using a photocopier) of the biting edges of teeth from the study casts. Subsequently the print-outs are then illuminated by a radiograph view-box, and the incisal margins are hand-traced onto transparent film to make an overlay for analysis. This is sometimes referred as the ‘‘hollowvolume tracing.” Similarly, Sweet et al. [21], Anne et al. [22], Wu et al. [23] and Starvianos et al. [20] have demonstrated in their studies that the computer-assisted overlay generation was an accurate method. By using computer image-processing software, such as ImageJ or Adobe PhotoshopÒ ‘‘magic wand” tool, a mask of selected areas was created from the biter’s dental casts and then a hollow-volume tracing was produced from the mask. Given the unfavourable criticism received from NAS (lack of fundamental forensic research), the present study was conducted to contribute to bite mark investigations by comparing the different overlay generation methods and computer-assisted animated-superimposition method to determine the most accurate method for analysis. Although much of the past literature has focused on validating the best method of overlay generation, in this study, comparison was made using overlay generated by different methods against the images of self-inflicted bite mark. This was to evaluate whether xerographic overlays or computer-assisted methods provides the most superior precision given the fact that the human skin is a poor registration material.
sign a consent form to participate in this research. They were selected based on the criteria below: a) Inclusion criteria: Healthy volunteers with complete set of natural permanent upper and lower anterior teeth. b) Exclusion criteria: Subjects with impaired mouth opening, compromised periodontal status, orthodontic appliances, intra-oral prosthesis and impression material intolerance. 2.2. Bite mark registration The volunteers were asked to bite on their forearm with moderate force (area of contact disinfected with alcohol swab), thereby leaving indentations on the skin of the forearm without causing any abrasion or any other type of wound. A label was placed beside the bite mark for identification purposes. The bite marks were recorded employing a Canon EOS 600D DSLR camera (Canon, Ohta-ku, Tokyo, Japan), with the ABFO No. 2 photomacrographic scale (Lightning Powder Co., Inc. 13386 International Parkway, Jacksonville, Florida 32218, USA) placed adjacent as a laterality marker. Two separate images for each bite were photographed perpendicular to the scale, recording the upper and lower arches respectively. Alginate impressions (Aroma Fine Plus Normal Set Alginate Impression Material, GC Corporation, Tokyo, Japan) of both the maxillary and mandibular dentitions of the volunteers were taken using stainless steel perforated stock tray. The impressions were then rinsed under running water in the spittoon of dental chair and then soaked in impression disinfectant (DentaseptÒ Impression, Unident SA, Switzerland) for infection control. Dental stone models were then made immediately and each of them was serially numbered. 2.3. Preparation of bite mark images The bite mark images taken were downloaded into a laptop installed with Adobe PhotoshopÒ CS6 (Adobe Systems Inc, San Jose, USA, http://www.adobe.com) software. All the images were properly labelled and segregated. The images were cropped, rotated and resized to 1:1 scale. Any unneeded area was cropped and any distortion was scrutinized and corrected. The final bite mark image was labelled accordingly (Fig. 1) and saved in CMYK (Cyan, Magenta, Yellow and Key) color model.
2. Materials and methods 2.1. Subjects’ selection Ethical approval (Reference number: DF DP1503/0057(U)) was granted by the Medical Ethics Committee, Faculty of Dentistry for this research. Eleven subjects, consisting of eleven students (five males and six females), from the Faculty of Dentistry, University of Malaya agreed to participate in our study. They were given an explanation about the purpose and procedures involved in this study. At the end of the explanation, each subject was required to
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Fig. 1. Final bite mark image after digital adjustment.
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2.4. Scanning of dental casts Dental casts were placed on the scanner plate of a scanner (Canon Pixma MG2170 3-in-1 Printer-Scanner-Photocopier) such that incisal edges of the anterior dentition contacted the plate. The dental casts were placed in a way that they were scanned from the lingual to the buccal surfaces, to give a sharper ‘‘edge-image” to the biting margins of the teeth [24]. Sufficient weight was applied on the top of the dental cast to maximize contact of the anterior biting edges with the glass plate. ABFO No. 2 photomacrographic scale was placed beside the cast. This set up was covered with a piece of white cloth to eliminate any ambient light. 2.5. Bite mark analysis using overlay generated by xerographic method For xerographic method the dental cast images were prepared by photocopying directly onto a plain A4 sized paper in life-size. A transparent sheet was placed on top of the photocopied cast image on a radiograph view-box and the teeth edge outlines were traced using ultra-fine tip permanent ink marker (Fig. 2). The life-size bite mark images recorded earlier were printed out after digital adjustment in the computer. The bite mark analysis was done by comparing the xerographically generated overlay with the correspondingly printed bite mark images. 2.6. Bite mark analysis using overlay generated by the computerassisted method In this technique, the dental casts were scanned and uploaded in the Adobe PhotoshopÒ CS6 software, with a resolution of 600 dpi in RGB (Red, Green and Blue) color model. A pre-scanning was done to ensure proper positioning of the cast with the ABFO scale. Subsequent adjustments were done to the scanned images; including removing unneeded area and labelling of the images (Fig. 3). Prepared cast images were converted to CMYK color model presentation. Biting edges in the cast images were selected. The selection tolerance was set at 18 [25]. Here, one of the biting edges was first chosen and the Adobe PhotoshopÒ CS6 software will select all the similar pixels within the entire image by default.
Fig. 3. Prepared digital image of casts.
The selected site was converted to an overlay (Fig. 4). The overlay image was then flipped horizontally and compared with the corresponding bite mark image in the software (Fig. 5). Both images were adjusted to exact life-size by referring to the ABFO scale. Either image is rotated (if required) to obtain best matching of the overlay and the bite mark. The bite mark images were converted to greyscale during the matching for better definition of the marks.
Fig. 2. Teeth edges (white arrow) were traced on a radiograph view-box.
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of the dental cast image (if required) was done to obtain superior matching with the bite mark. The dental cast image was altered in different opacities to obtain the best superimposition. Different opacities (0%, 5%, 10%, 15%, 20%, 25% (Fig. 6), 30%, 35%, 40%, 45% and 45% and 50% (Fig. 7) were employed and labelled accordingly. Ensure the bite mark image was converted to greyscale during the matching. Subsequently an animated graphic video was produced with GIF-AnimatorÓ (GIF Animator, http://www.gif-animator.com/) using the outcome images (GIF-Graphics Interchange Format). Bite mark analyses were then
Fig. 4. Overlay image produced using computer-assisted method.
Fig. 6. Superimposition of cast image (opacity at 25%) with bite mark image.
Fig. 5. Comparison of overlay generated by computer-assisted method.
2.7. Bite mark analysis using computer-assisted animatedsuperimposition method Another method of computer-assisted comparison was done by directly superimposing the dental cast image (Fig. 3) with the corresponding life-size bite mark image. The bite mark image was first secured to prevent any accidental modification whereas the dental cast image was adjusted (life-size) as the bite mark image. Rotation
Fig. 7. Superimposition of cast image (opacity at 50%) with bite mark image.
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Table 1 Chart for scoring according to the different criteria. Each criteria was given a score of 0–3, where 0 is totally unmatched or excluded, 1 is the possible match, 2 is the probable match and 3 is the definite match. Criteria
Score
Size and shape of arch All teeth represented in the mark are present in the subject’s mouth Tooth mark in the bite correlates with tooth position in subject’s mouth Spacing of marks in the bite compared to spacing of subject’s teeth Other distinctive features like missing teeth e.g. peg shape etc.
0–3 0–3 0–3 0–3 0–3
Table 2 Total score of bite mark analysis using overlay generated by xerographic, computerassisted and superimposition methods. Case number
Xerographic method in overlay generation
Computerassisted overlay generation
Computer-assisted animated superimposition
01 02 03 04 05 06 07 08 09 10 11 Total
16 20 12 8 8 16 12 12 16 8 20 148
19 15 12 15 16 17 15 22 22 17 14 184
23 22 20 24 21 22 22 23 21 22 21 241
performed satisfactorily by observing the comparison of the animated GIF format outcome images and bite-marks.
Table 3 Ranking score from the data obtained from Table 2. Case number
Xerographic method in overlay generation
Computer-assisted overlay generation
Computer-assisted animated superimposition
01 02 03 04 05 06 07 08 09 10 11 Rank Sum (R)
20.5 14.0 28.5 32.0 32.0 20.5 28.5 28.5 20.5 32.0 14.0 271.0 6676.45
16.0 24.0 28.5 24.0 20.5 17.5 24.0 6.5 6.5 17.5 26.0 211.0 4047.36
2.5 6.5 14.0 1.0 11.0 6.5 6.5 2.5 11.0 6.5 11.0 79.0 567.36
R2 n
overlay generation and computer-assisted animatedsuperimposition methods in bite mark analyses. The total score for computer-assisted animated superimposition had the highest score, followed by computer-assisted overlay generation which had much higher score than xerographic overlay comparison. In general the numbers of probable and definite matching cases were higher in both the computer-assisted methods. As the data was analysed with Kruskal Wallis H test, the results showed that both the H values and p value were outside the critical value. Therefore, there is a significant difference in precision of xerographic overlay and computer-assisted overlay as well as superimposition methods, thus the null hypothesis was rejected (Tables 2 and 3). 4. Total score of comparisons in different methods
2.8. Bite mark analyses Comparison of the bite marks were done by the two first authors separately. Five criteria were evaluated for a bite mark analysis. Firstly, the total number of teeth present in the bite mark image in comparison to the teeth of subject, the shape and size of the arch, spacing between teeth, tooth position and other distinctive features. Each criteria was given a score of 0–3, where 0 is totally unmatched or excluded, 1 a possible match, 2 a probable match and 3 is a definite match. The comparison was evaluated according to the criteria stated in Table 1 and all the findings were recorded without bias according to the scale provided. The data was analysed by Kruskal Wallis H test to determine if there is any significant differences (statistically) between these 3 sets of data. The null hypothesis is that no difference will be noticed between the xerographic, computer-assisted overlay and computer-assisted animated superimposition methods in bite mark analyses. 3. Results In our study, 8 out of the 11 cases recorded bite mark where the indentation of the lower first premolar was visible. The rest of them recorded only the six anterior teeth in each arch. The bite mark produced by the lower arch was clearer, and the incisal edges were slightly wider unlike those produced by the upper arch in all cases. Five out of 11 cases presented with lingual markings of the upper anterior teeth. Besides that, we found that bite mark on subjects with fair skin tone were easier to distinguish than those on subjects of darker skin tone. Interestingly, both the examiners were getting corresponding results during their comparisons. Total score of comparison and Kruskal Wallis H test were used to determine the suitability and precision of xerographic, computer-assisted
For statistical analysis, Kruskal Wallis H test was used. Null and alternative hypotheses were defined as: H0: There is no difference between the xerographic, computerassisted overlay and computer-assisted animated superimposition method in bite mark analysis. H1: There is a difference between the xerographic, computerassisted overlay and computer-assisted animated superimposition method in bite mark analysis.
a = 0.05
Degree of freedom; df ¼ k 1 (k = number of methods used) )df ¼ 2 (critical value in Chi-Square Table = 5.99)
The following is the ranking of data obtained from the total scoring in Table 2. 5. Ranking of data from Table 2 Group Size (n) = 11, Total Sample Size (N) = 3(11) = 33
X R2 n
!
¼ 11291:18 PTn1 2
12 By using the equation H ¼ NðNþ1 Þ
H¼
! 3ðN þ 1Þ,
12 ð11291:18Þ 3ð33 þ 1Þ 33ð33 þ 1Þ
H = 18.761 Since H = 18.761 > 5.99, the null hypothesis is rejected. ) There is significant difference among the three methods, H = 18.761, p < 0.05.
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6. Discussion Bite mark analysis is based on the principle two human dentitions not same and hence no two bite marks made are same either. In the past, the only method to generate overlay (around 1966), was the hand-traced manual method. In 1991, Dailey [26] discovered a time and cost efficient, yet an accurate technique to generate overlay with the help of the office photocopier. Naru and Dykes [22] later presented the computer-assisted overlay generation method for bite mark investigations. In this study, we introduce the computer-assisted animated-superimposition as a new method in bite mark investigations. One of the common findings in bite mark examination is that teeth in the lower arch occur more clearly than those in the upper arch. This is probably because the biting mechanism consist of moving mandible and a stationary maxilla [27]. Moreover, although the lower anterior teeth marks were clearer, they had slightly wider incisal edge indentations compared to those produced by the anterior teeth of the maxilla. This is because the anterior teeth from the lower arch moved and stretched the flexible human skin. However caution must be expressed here as the biting mechanisms of the subjects were in a controlled manner without causing any abrasions. According to Sperber, when food like corn-on-the-cob are eaten, the mandible needs to be protruded so that the incisal edges can approximate each other as they incised, whereas a piece of soft food can be incised in centric relationship [28]. The latter might produce palatal indentations of the anterior teeth of the maxilla as evident in this study. In generating a xerographic overlay, there is some degree of operator’s ability involved. Hence, the examiner requires a certain level of expertise to produce the xerographic overlay. As such the overlay is not reproducible exactly each time a new overlay was drawn over the same dental cast. This can be challenged because the xerographic method of overlay generation in bite mark analysis may have compromised on the precision. However, the reason why we have chosen xerographic method is because Kouble et al. [19] and Maloth et al. [20] found that photocopier-generated overlay had superior precision to the hand-tracing method. As a matter of fact, Sweet and Bowers have concluded in their study that subjective process of hand tracing directly on the casts should not be used altogether [29,24]. For computer-assisted overlay generation method in bite mark analysis, the results are found to be more accurate than xerographic method. Since the selection of biting edges are fully done by the software Adobe PhotoshopÒ CS6, there is no subjective bias from the operator. However, the pixel-based selection by the software is fully dependent on the clarity of the image and the surrounding light during the scanning. The clearer the image scanned, the more accurate the biting edge selection can be done. Selection of the first pixel is critical as it will become the reference for the software to determine other pixels with similar values. With Adobe PhotoshopÒ CS6, we can set the selection tolerance wherein the software will select pixels that are similar or almost similar to the pixel we have selected. The selection tolerance should be stated in the forensic odontological report if this method was used to analyse the bite mark [25]. On the other hand, the clarity of the image also depends on how we position the cast on the scanner. The biting edge of incisors, especially the central incisor, is used as a reference in which the weight will put on top on the cast to ensure the incisor edge touches fully on the scanner [25]. However, in some cases, the most prominent tooth of the overall occlusal plane may not necessary be the incisal edge. Hence this can alter the clarity of the cast image scanned. With regards to computer-assisted animated-superimposition method, it was the most accurate method in bite mark analysis
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among the 3 methods studied. With this method, we can compare not only the biting edges but also some of the lingual or palatal markings. As stated earlier, palatal markings become evident during suction of the tissues during biting. Moreover, using the superimposition method, we were able to observe all the teeth during matching while in the other two methods each tooth was compared individually to each mark noticed in the arch marks produced. More importantly producing images in GIF animated format makes the analyses easier as it will be played infinitely enabling examination of the criteria of matching rapidly and precisely. Xerographic overlay generation method is more suitable for those who are cost conscious and do not have a forensic laboratory or need a preliminary assessment prior to the comparison. Computer-assisted method on the other hand requires experience in superimposing either the overlay with the bite mark or the cast image with the bite mark. Proper training for adjusting the size of the bite mark and the cast images is required. A similarity in the size of the images in computer-assisted bite mark analysis is crucial as it will affect the accuracy of the superimpositions. It must be emphasized here that the bite marks produced in our study had indentations with bruises, but in most forensic cases there will be abrasions or lacerations which will hinder the determination of the outline of the bite mark. Furthermore, bite mark images were photographed immediately after it was produced; however, in real cases, the forensic investigations are delayed causing healing of the marks. It is evident in this research that computer-assisted methods in bite mark analyses are superior than xerographic overlay generation method. There should be more training in forensic odontology regarding computer-assisted methods in bite mark analysis. In addition, more research should be undertaken on animatedsuperimposition techniques as this is a promising method of bite mark investigation.
7. Conclusion Xerographic overlay generation method requires experience in tracing precisely the biting edge on the dental casts, whereas, computer-assisted bite mark analysis methods require expensive computer, scanner equipment and software skills to produce the best comparisons. In addition, you got to rely on the capability of the scanner to produce a high quality scanned cast images. These machines can be expensive but higher the quality of the scanning, the better the image resolution and clearer the image produced. Computer-assisted animated-superimposition bite mark analysis produced the most accurate comparison in this study. Bite marks inflicted on human skin are especially transient in nature but significant matching is possible if the investigation is done rapidly.
Conflict of interest The authors have no relevant conflicts of interest to declare.
Acknowledgment We would like to express our gratitude to the clinical staffs from the Polyclinics, Faculty of Dentistry, University of Malaya and student volunteers for helping us during this clinical research. We are also thankful to the Ministry of Higher Education Malaysia for providing the High Impact Research Grant No: UM.C/HIR/ MOHE/Dent/19 to undertake this study.
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References [1] American Board of Forensic Odontology, inc. Diplomates Reference manual. Section 1: Preface, Acknowledgments, Background, Functions and Purposes, Jan 2013 ed., p. 118. [2] D.G. Mac Donald, Bitemark recognition and interpretation, J. For. Sci. Soc. 14 (1974) 229–233. [3] V.V. Pillay, Alexander, Value of bite mark analysis in forensic investigations. An overview, JIDA 73 (2002) 111–115. [4] S.K. Subbiah, Bite mark injury: a review, J. Forensic. Odontol. 1 (1) (2008) 23– 25. [5] National Research Council and Committee on Identifying the Needs of the Forensic Sciences Community, Strengthening Forensic Science in the United States: A Path Forward, National Academics Press, Washington, DC, 2009. [6] I.A. Pretty, D. Sweet, The scientific basis for human bitemark analyses – a critical review, Sci. Justice 41 (2001) 85–92. [7] Cases Where DNA Revealed that Bite Mark Analysis Led to Wrongful Arrests and Convictions. (n.d.). Retrieved November 23, 2015, from http://www. innocenceproject.org/news-events-exonerations/cases-where-dna-revealedthat-bite-mark-analysis-led-to-wrongful-arrests-and-convictions. [8] D. Faigman, Modern Scientific Evidence. The law and Science of Expert Testimony, 2011-2012 ed., West, St. Paul, Minn., 2012. [9] J.W. Beckstead, R.D. Rawson, W.S. Giles, Review of bite mark evidence, J. Am. Dent. Assoc. 99 (1979) 69–71. [10] G.L. Vale, Dentistry, bite marks and the investigation of crime, J. Calif. Dent. Assoc. 24 (1996) 29–34. [11] Committee on Identifying the Needs of the Forensic Sciences Community, National Research Council. Strengthening Forensic Science in the United States: A Path Forward, National Academics Press, Washington, DC, 2009. [12] R.W. Frearnead, Facilities for forensic odontology, Med. Sci. Law. 1 (1961) 273. [13] S.M. Heras, A. Valenzuela, C. Ogayar, A.J. Valverda, J.C. Torras, Computer based production of comparison overlays from 3D-scanned dental casts for bite marks analysis, J. Forensic. Sci. 50 (1) (2005) 1–7. [14] D.W. Wright, J.C. Dailey, Human bite marks in Forensic dentistry, Den. Clin. N. Am. 45 (2) (2001) 365–395. [15] G.L. Wilkes, I.A. Brown, R.H. Wildnauer, The biomechanical properties of skin, Crit. Rev. Bioeng. 1 (4) (1973) 453–495.
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Legal Medicine journal homepage: www.elsevier.com/locate/legalmed
A comparative study between xerographic, computer-assisted overlay generation and animated-superimposition methods in bite mark analyses Meng Wei Tai, Zhen Feng Chong, Muhammad Khan Asif, Rabiah A. Rahmat, Phrabhakaran Nambiar ⇑ Department Oral and Maxillofacial Clinical Sciences, University of Malaya, Kuala Lumpur, Malaysia
a r t i c l e
i n f o
Article history: Received 16 May 2016 Received in revised form 21 July 2016 Accepted 27 July 2016 Available online 30 July 2016 Keywords: Forensic odontology Bite mark Human skin Xerographic Computer-assisted analysis Adobe PhotoshopÒ CS6 GIF-AnimatorÓ
a b s t r a c t This study was to compare the suitability and precision of xerographic and computer-assisted methods for bite mark investigations. Eleven subjects were asked to bite on their forearm and the bite marks were photographically recorded. Alginate impressions of the subjects’ dentition were taken and their casts were made using dental stone. The overlays generated by xerographic method were obtained by photocopying the subjects’ casts and the incisal edge outlines were then transferred on a transparent sheet. The bite mark images were imported into Adobe PhotoshopÒ software and printed to life-size. The bite mark analyses using xerographically generated overlays were done by comparing an overlay to the corresponding printed bite mark images manually. In computer-assisted method, the subjects’ casts were scanned into Adobe PhotoshopÒ. The bite mark analyses using computer-assisted overlay generation were done by matching an overlay and the corresponding bite mark images digitally using Adobe PhotoshopÒ. Another comparison method was superimposing the cast images with corresponding bite mark images employing the Adobe PhotoshopÒ CS6 and GIF-AnimatorÓ. A score with a range of 0–3 was given during analysis to each precision-determining criterion and the score was increased with better matching. The Kruskal Wallis H test showed significant difference between the three sets of data (H = 18.761, p < 0.05). In conclusion, bite mark analysis using the computer-assisted animated-superimposition method was the most accurate, followed by the computer-assisted overlay generation and lastly the xerographic method. The superior precision contributed by digital method is discernible despite the human skin being a poor recording medium of bite marks. Ó 2016 Elsevier Ireland Ltd. All rights reserved.
1. Introduction Scientific examination of a bite injury or a tooth mark plays an important role in many criminal investigations such as rape, murder, robbery and other forms of physical and sexual violence. The American Board of Forensic Odontology defined bite mark as ‘‘A representative pattern left in an object or tissue by the dental structures of an animal or human” [1]. On the other hand, Mac Donald explained it as a mark left by teeth either by itself or combined with other oral structures [2]. Subbiah SK et al. and Pillay VV et al. [3,4] advocated that a bite mark is an essential forensic evidence which constitutes a popular form of dental evidence presented in criminal court. However, National Academy of Sciences (NAS) reported that bite mark analysis has been heavily criticized ⇑ Corresponding author at: Department Oral and Maxillofacial Clinical Sciences, Faculty of Dentistry, University of Malaya, 50603 Kuala Lumpur, Malaysia. E-mail address: [email protected] (P. Nambiar). http://dx.doi.org/10.1016/j.legalmed.2016.07.009 1344-6223/Ó 2016 Elsevier Ireland Ltd. All rights reserved.
for its principles. One of the main reasons was the insufficient fundamental research that investigates the scientific basis of this method [5,6]. The Innocence Project is convinced that all forensic disciplines need to be verified in a scientific way whereby methodologies are used in criminal cases after genuine independent research and peer reviews were done [7]. Furthermore, subjectivity, operators’ incompetence, or inadequate internal controls can affect the integrity of the results despite the demonstrated methods used. Bite mark analysis is especially plagued due to the almost total absence of any rules, regulations, or processes to accredit experts or the testimony they provide in developing standards. It is common knowledge that very few government-related bodies in any country has ever scrutinized the validity and reliability of bite mark evidence. ‘‘Bite mark analysis has never passed through the rigorous scientific examination that is common to most normal sciences,” citing from the book entitled Modern Scientific Evidence: The Law and Science of Expert Testimony [8].
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Bite mark mechanism is when the teeth apply pressure on the skin with a varied force. It begins with closure of mandible, followed by a negative pressure from the suction of skin, and the tongue thrust from the opposite direction; therefore, there would be projection of teeth edges and palatal surfaces [9]. When an individual bites something, the superior teeth stabilize the object whilst the inferior teeth try to cut it. The indentation created by the superior teeth is significantly important in order to obtain information such as: dental alignment, size and shape of dentition [10]. Bite mark analysis relies on two assumptions; (a) the teeth alignment that produce a bite mark is individualistic, (b) the skin records adequate information of the bite mark to match the corresponding anterior dentition [11]. It has been approximated (by the use of computer technology) that there were more than two billion possibilities to chart an adult dentition [12,13]. This would certainly rule out the chances of two adults having completely identical dentition [14]. However, caution must be expressed as skin is a poor recording medium, it tends to experience visco-elastic, anisotropic, non-linear responses to stresses like bite forces [15,16]. The common method to investigate bite mark is dependent on interpreting photographic evidence in which the dental casts of the teeth of the suspect is matched with the bite mark [17]. The process of bite mark matching with a suspect’s dentition includes parameters such as size, shape and position of each tooth [18]. Xerography has been demonstrated by Kouble et al. [19] and Maloth et al. [20] to be significantly more accurate in bite mark analysis as compared to the conventional hand-tracing on plastic films placed over the dental casts of the offender. Xerography is performed by making a life-size image (using a photocopier) of the biting edges of teeth from the study casts. Subsequently the print-outs are then illuminated by a radiograph view-box, and the incisal margins are hand-traced onto transparent film to make an overlay for analysis. This is sometimes referred as the ‘‘hollowvolume tracing.” Similarly, Sweet et al. [21], Anne et al. [22], Wu et al. [23] and Starvianos et al. [20] have demonstrated in their studies that the computer-assisted overlay generation was an accurate method. By using computer image-processing software, such as ImageJ or Adobe PhotoshopÒ ‘‘magic wand” tool, a mask of selected areas was created from the biter’s dental casts and then a hollow-volume tracing was produced from the mask. Given the unfavourable criticism received from NAS (lack of fundamental forensic research), the present study was conducted to contribute to bite mark investigations by comparing the different overlay generation methods and computer-assisted animated-superimposition method to determine the most accurate method for analysis. Although much of the past literature has focused on validating the best method of overlay generation, in this study, comparison was made using overlay generated by different methods against the images of self-inflicted bite mark. This was to evaluate whether xerographic overlays or computer-assisted methods provides the most superior precision given the fact that the human skin is a poor registration material.
sign a consent form to participate in this research. They were selected based on the criteria below: a) Inclusion criteria: Healthy volunteers with complete set of natural permanent upper and lower anterior teeth. b) Exclusion criteria: Subjects with impaired mouth opening, compromised periodontal status, orthodontic appliances, intra-oral prosthesis and impression material intolerance. 2.2. Bite mark registration The volunteers were asked to bite on their forearm with moderate force (area of contact disinfected with alcohol swab), thereby leaving indentations on the skin of the forearm without causing any abrasion or any other type of wound. A label was placed beside the bite mark for identification purposes. The bite marks were recorded employing a Canon EOS 600D DSLR camera (Canon, Ohta-ku, Tokyo, Japan), with the ABFO No. 2 photomacrographic scale (Lightning Powder Co., Inc. 13386 International Parkway, Jacksonville, Florida 32218, USA) placed adjacent as a laterality marker. Two separate images for each bite were photographed perpendicular to the scale, recording the upper and lower arches respectively. Alginate impressions (Aroma Fine Plus Normal Set Alginate Impression Material, GC Corporation, Tokyo, Japan) of both the maxillary and mandibular dentitions of the volunteers were taken using stainless steel perforated stock tray. The impressions were then rinsed under running water in the spittoon of dental chair and then soaked in impression disinfectant (DentaseptÒ Impression, Unident SA, Switzerland) for infection control. Dental stone models were then made immediately and each of them was serially numbered. 2.3. Preparation of bite mark images The bite mark images taken were downloaded into a laptop installed with Adobe PhotoshopÒ CS6 (Adobe Systems Inc, San Jose, USA, http://www.adobe.com) software. All the images were properly labelled and segregated. The images were cropped, rotated and resized to 1:1 scale. Any unneeded area was cropped and any distortion was scrutinized and corrected. The final bite mark image was labelled accordingly (Fig. 1) and saved in CMYK (Cyan, Magenta, Yellow and Key) color model.
2. Materials and methods 2.1. Subjects’ selection Ethical approval (Reference number: DF DP1503/0057(U)) was granted by the Medical Ethics Committee, Faculty of Dentistry for this research. Eleven subjects, consisting of eleven students (five males and six females), from the Faculty of Dentistry, University of Malaya agreed to participate in our study. They were given an explanation about the purpose and procedures involved in this study. At the end of the explanation, each subject was required to
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Fig. 1. Final bite mark image after digital adjustment.
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2.4. Scanning of dental casts Dental casts were placed on the scanner plate of a scanner (Canon Pixma MG2170 3-in-1 Printer-Scanner-Photocopier) such that incisal edges of the anterior dentition contacted the plate. The dental casts were placed in a way that they were scanned from the lingual to the buccal surfaces, to give a sharper ‘‘edge-image” to the biting margins of the teeth [24]. Sufficient weight was applied on the top of the dental cast to maximize contact of the anterior biting edges with the glass plate. ABFO No. 2 photomacrographic scale was placed beside the cast. This set up was covered with a piece of white cloth to eliminate any ambient light. 2.5. Bite mark analysis using overlay generated by xerographic method For xerographic method the dental cast images were prepared by photocopying directly onto a plain A4 sized paper in life-size. A transparent sheet was placed on top of the photocopied cast image on a radiograph view-box and the teeth edge outlines were traced using ultra-fine tip permanent ink marker (Fig. 2). The life-size bite mark images recorded earlier were printed out after digital adjustment in the computer. The bite mark analysis was done by comparing the xerographically generated overlay with the correspondingly printed bite mark images. 2.6. Bite mark analysis using overlay generated by the computerassisted method In this technique, the dental casts were scanned and uploaded in the Adobe PhotoshopÒ CS6 software, with a resolution of 600 dpi in RGB (Red, Green and Blue) color model. A pre-scanning was done to ensure proper positioning of the cast with the ABFO scale. Subsequent adjustments were done to the scanned images; including removing unneeded area and labelling of the images (Fig. 3). Prepared cast images were converted to CMYK color model presentation. Biting edges in the cast images were selected. The selection tolerance was set at 18 [25]. Here, one of the biting edges was first chosen and the Adobe PhotoshopÒ CS6 software will select all the similar pixels within the entire image by default.
Fig. 3. Prepared digital image of casts.
The selected site was converted to an overlay (Fig. 4). The overlay image was then flipped horizontally and compared with the corresponding bite mark image in the software (Fig. 5). Both images were adjusted to exact life-size by referring to the ABFO scale. Either image is rotated (if required) to obtain best matching of the overlay and the bite mark. The bite mark images were converted to greyscale during the matching for better definition of the marks.
Fig. 2. Teeth edges (white arrow) were traced on a radiograph view-box.
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of the dental cast image (if required) was done to obtain superior matching with the bite mark. The dental cast image was altered in different opacities to obtain the best superimposition. Different opacities (0%, 5%, 10%, 15%, 20%, 25% (Fig. 6), 30%, 35%, 40%, 45% and 45% and 50% (Fig. 7) were employed and labelled accordingly. Ensure the bite mark image was converted to greyscale during the matching. Subsequently an animated graphic video was produced with GIF-AnimatorÓ (GIF Animator, http://www.gif-animator.com/) using the outcome images (GIF-Graphics Interchange Format). Bite mark analyses were then
Fig. 4. Overlay image produced using computer-assisted method.
Fig. 6. Superimposition of cast image (opacity at 25%) with bite mark image.
Fig. 5. Comparison of overlay generated by computer-assisted method.
2.7. Bite mark analysis using computer-assisted animatedsuperimposition method Another method of computer-assisted comparison was done by directly superimposing the dental cast image (Fig. 3) with the corresponding life-size bite mark image. The bite mark image was first secured to prevent any accidental modification whereas the dental cast image was adjusted (life-size) as the bite mark image. Rotation
Fig. 7. Superimposition of cast image (opacity at 50%) with bite mark image.
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Table 1 Chart for scoring according to the different criteria. Each criteria was given a score of 0–3, where 0 is totally unmatched or excluded, 1 is the possible match, 2 is the probable match and 3 is the definite match. Criteria
Score
Size and shape of arch All teeth represented in the mark are present in the subject’s mouth Tooth mark in the bite correlates with tooth position in subject’s mouth Spacing of marks in the bite compared to spacing of subject’s teeth Other distinctive features like missing teeth e.g. peg shape etc.
0–3 0–3 0–3 0–3 0–3
Table 2 Total score of bite mark analysis using overlay generated by xerographic, computerassisted and superimposition methods. Case number
Xerographic method in overlay generation
Computerassisted overlay generation
Computer-assisted animated superimposition
01 02 03 04 05 06 07 08 09 10 11 Total
16 20 12 8 8 16 12 12 16 8 20 148
19 15 12 15 16 17 15 22 22 17 14 184
23 22 20 24 21 22 22 23 21 22 21 241
performed satisfactorily by observing the comparison of the animated GIF format outcome images and bite-marks.
Table 3 Ranking score from the data obtained from Table 2. Case number
Xerographic method in overlay generation
Computer-assisted overlay generation
Computer-assisted animated superimposition
01 02 03 04 05 06 07 08 09 10 11 Rank Sum (R)
20.5 14.0 28.5 32.0 32.0 20.5 28.5 28.5 20.5 32.0 14.0 271.0 6676.45
16.0 24.0 28.5 24.0 20.5 17.5 24.0 6.5 6.5 17.5 26.0 211.0 4047.36
2.5 6.5 14.0 1.0 11.0 6.5 6.5 2.5 11.0 6.5 11.0 79.0 567.36
R2 n
overlay generation and computer-assisted animatedsuperimposition methods in bite mark analyses. The total score for computer-assisted animated superimposition had the highest score, followed by computer-assisted overlay generation which had much higher score than xerographic overlay comparison. In general the numbers of probable and definite matching cases were higher in both the computer-assisted methods. As the data was analysed with Kruskal Wallis H test, the results showed that both the H values and p value were outside the critical value. Therefore, there is a significant difference in precision of xerographic overlay and computer-assisted overlay as well as superimposition methods, thus the null hypothesis was rejected (Tables 2 and 3). 4. Total score of comparisons in different methods
2.8. Bite mark analyses Comparison of the bite marks were done by the two first authors separately. Five criteria were evaluated for a bite mark analysis. Firstly, the total number of teeth present in the bite mark image in comparison to the teeth of subject, the shape and size of the arch, spacing between teeth, tooth position and other distinctive features. Each criteria was given a score of 0–3, where 0 is totally unmatched or excluded, 1 a possible match, 2 a probable match and 3 is a definite match. The comparison was evaluated according to the criteria stated in Table 1 and all the findings were recorded without bias according to the scale provided. The data was analysed by Kruskal Wallis H test to determine if there is any significant differences (statistically) between these 3 sets of data. The null hypothesis is that no difference will be noticed between the xerographic, computer-assisted overlay and computer-assisted animated superimposition methods in bite mark analyses. 3. Results In our study, 8 out of the 11 cases recorded bite mark where the indentation of the lower first premolar was visible. The rest of them recorded only the six anterior teeth in each arch. The bite mark produced by the lower arch was clearer, and the incisal edges were slightly wider unlike those produced by the upper arch in all cases. Five out of 11 cases presented with lingual markings of the upper anterior teeth. Besides that, we found that bite mark on subjects with fair skin tone were easier to distinguish than those on subjects of darker skin tone. Interestingly, both the examiners were getting corresponding results during their comparisons. Total score of comparison and Kruskal Wallis H test were used to determine the suitability and precision of xerographic, computer-assisted
For statistical analysis, Kruskal Wallis H test was used. Null and alternative hypotheses were defined as: H0: There is no difference between the xerographic, computerassisted overlay and computer-assisted animated superimposition method in bite mark analysis. H1: There is a difference between the xerographic, computerassisted overlay and computer-assisted animated superimposition method in bite mark analysis.
a = 0.05
Degree of freedom; df ¼ k 1 (k = number of methods used) )df ¼ 2 (critical value in Chi-Square Table = 5.99)
The following is the ranking of data obtained from the total scoring in Table 2. 5. Ranking of data from Table 2 Group Size (n) = 11, Total Sample Size (N) = 3(11) = 33
X R2 n
!
¼ 11291:18 PTn1 2
12 By using the equation H ¼ NðNþ1 Þ
H¼
! 3ðN þ 1Þ,
12 ð11291:18Þ 3ð33 þ 1Þ 33ð33 þ 1Þ
H = 18.761 Since H = 18.761 > 5.99, the null hypothesis is rejected. ) There is significant difference among the three methods, H = 18.761, p < 0.05.
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6. Discussion Bite mark analysis is based on the principle two human dentitions not same and hence no two bite marks made are same either. In the past, the only method to generate overlay (around 1966), was the hand-traced manual method. In 1991, Dailey [26] discovered a time and cost efficient, yet an accurate technique to generate overlay with the help of the office photocopier. Naru and Dykes [22] later presented the computer-assisted overlay generation method for bite mark investigations. In this study, we introduce the computer-assisted animated-superimposition as a new method in bite mark investigations. One of the common findings in bite mark examination is that teeth in the lower arch occur more clearly than those in the upper arch. This is probably because the biting mechanism consist of moving mandible and a stationary maxilla [27]. Moreover, although the lower anterior teeth marks were clearer, they had slightly wider incisal edge indentations compared to those produced by the anterior teeth of the maxilla. This is because the anterior teeth from the lower arch moved and stretched the flexible human skin. However caution must be expressed here as the biting mechanisms of the subjects were in a controlled manner without causing any abrasions. According to Sperber, when food like corn-on-the-cob are eaten, the mandible needs to be protruded so that the incisal edges can approximate each other as they incised, whereas a piece of soft food can be incised in centric relationship [28]. The latter might produce palatal indentations of the anterior teeth of the maxilla as evident in this study. In generating a xerographic overlay, there is some degree of operator’s ability involved. Hence, the examiner requires a certain level of expertise to produce the xerographic overlay. As such the overlay is not reproducible exactly each time a new overlay was drawn over the same dental cast. This can be challenged because the xerographic method of overlay generation in bite mark analysis may have compromised on the precision. However, the reason why we have chosen xerographic method is because Kouble et al. [19] and Maloth et al. [20] found that photocopier-generated overlay had superior precision to the hand-tracing method. As a matter of fact, Sweet and Bowers have concluded in their study that subjective process of hand tracing directly on the casts should not be used altogether [29,24]. For computer-assisted overlay generation method in bite mark analysis, the results are found to be more accurate than xerographic method. Since the selection of biting edges are fully done by the software Adobe PhotoshopÒ CS6, there is no subjective bias from the operator. However, the pixel-based selection by the software is fully dependent on the clarity of the image and the surrounding light during the scanning. The clearer the image scanned, the more accurate the biting edge selection can be done. Selection of the first pixel is critical as it will become the reference for the software to determine other pixels with similar values. With Adobe PhotoshopÒ CS6, we can set the selection tolerance wherein the software will select pixels that are similar or almost similar to the pixel we have selected. The selection tolerance should be stated in the forensic odontological report if this method was used to analyse the bite mark [25]. On the other hand, the clarity of the image also depends on how we position the cast on the scanner. The biting edge of incisors, especially the central incisor, is used as a reference in which the weight will put on top on the cast to ensure the incisor edge touches fully on the scanner [25]. However, in some cases, the most prominent tooth of the overall occlusal plane may not necessary be the incisal edge. Hence this can alter the clarity of the cast image scanned. With regards to computer-assisted animated-superimposition method, it was the most accurate method in bite mark analysis
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among the 3 methods studied. With this method, we can compare not only the biting edges but also some of the lingual or palatal markings. As stated earlier, palatal markings become evident during suction of the tissues during biting. Moreover, using the superimposition method, we were able to observe all the teeth during matching while in the other two methods each tooth was compared individually to each mark noticed in the arch marks produced. More importantly producing images in GIF animated format makes the analyses easier as it will be played infinitely enabling examination of the criteria of matching rapidly and precisely. Xerographic overlay generation method is more suitable for those who are cost conscious and do not have a forensic laboratory or need a preliminary assessment prior to the comparison. Computer-assisted method on the other hand requires experience in superimposing either the overlay with the bite mark or the cast image with the bite mark. Proper training for adjusting the size of the bite mark and the cast images is required. A similarity in the size of the images in computer-assisted bite mark analysis is crucial as it will affect the accuracy of the superimpositions. It must be emphasized here that the bite marks produced in our study had indentations with bruises, but in most forensic cases there will be abrasions or lacerations which will hinder the determination of the outline of the bite mark. Furthermore, bite mark images were photographed immediately after it was produced; however, in real cases, the forensic investigations are delayed causing healing of the marks. It is evident in this research that computer-assisted methods in bite mark analyses are superior than xerographic overlay generation method. There should be more training in forensic odontology regarding computer-assisted methods in bite mark analysis. In addition, more research should be undertaken on animatedsuperimposition techniques as this is a promising method of bite mark investigation.
7. Conclusion Xerographic overlay generation method requires experience in tracing precisely the biting edge on the dental casts, whereas, computer-assisted bite mark analysis methods require expensive computer, scanner equipment and software skills to produce the best comparisons. In addition, you got to rely on the capability of the scanner to produce a high quality scanned cast images. These machines can be expensive but higher the quality of the scanning, the better the image resolution and clearer the image produced. Computer-assisted animated-superimposition bite mark analysis produced the most accurate comparison in this study. Bite marks inflicted on human skin are especially transient in nature but significant matching is possible if the investigation is done rapidly.
Conflict of interest The authors have no relevant conflicts of interest to declare.
Acknowledgment We would like to express our gratitude to the clinical staffs from the Polyclinics, Faculty of Dentistry, University of Malaya and student volunteers for helping us during this clinical research. We are also thankful to the Ministry of Higher Education Malaysia for providing the High Impact Research Grant No: UM.C/HIR/ MOHE/Dent/19 to undertake this study.
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