|Year : 2009 | Volume
| Issue : 2 | Page : 66-72
Bitemark analysis: Use of polyether in evidence collection, conservation, and comparison
Gabriel M Fonseca1, Martin A Farah2, Sabrina V Orellano-Blaskovich1
1 Department of Oral Pathology and Forensic Dentistry Team, Cordoba, Argentina
2 Department of Dental Materials and Forensic Dentistry Team, School of Dentistry, National University of Cordoba, Cordoba, Argentina
|Date of Web Publication||8-Mar-2010|
Gabriel M Fonseca
Artigas 818, Departamento A, Cordoba (5000)
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Background: While bitemarks are categorical identification evidence, the dynamics of biting, the anatomical location of the bite, and failures in wound records can introduce distorted images and mislead crime investigation. Materials and Methods: In this study, 20 bitemarks were performed on dead pig skin and subsequently photographed, excised, conserved, and analyzed using digital comparison (Adobe Photoshop™ 8.0), following the standard procedures (ABFO); physical comparison was also done using polyether (Impregum™; 3M) casts. Study plaster casts of the upper and lower jaws of each subject were taken using type IV yellow densite stone. Polyether was used as impression material to obtain bitemarks, and casts were made from densite stone and polyether. Results: Because of its elasticity, polyether casts can compensate for primary or secondary distortions, so that there is a better degree of match when positioning the subject's dental cast. Conclusion: Polyether is an alternative impression material and is an excellent option for creating positive casts of the wound for physical dynamic comparison.
Keywords: Bitemarks, crime identification, forensic odontology, polyether casts, stone casts, physical comparison, skin distortion
|How to cite this article:|
Fonseca GM, Farah MA, Orellano-Blaskovich SV. Bitemark analysis: Use of polyether in evidence collection, conservation, and comparison. J Forensic Dent Sci 2009;1:66-72
|How to cite this URL:|
Fonseca GM, Farah MA, Orellano-Blaskovich SV. Bitemark analysis: Use of polyether in evidence collection, conservation, and comparison. J Forensic Dent Sci [serial online] 2009 [cited 2019 Sep 24];1:66-72. Available from: http://www.jfds.org/text.asp?2009/1/2/66/60376
| Introduction|| |
Bitemarks are defined as patterns made by teeth in skin, food, or firm but compressible substrates. , The nature of this bite contact has a major influence on the resultant bitemark.  Most bitemarks of forensic interest involve contact between human teeth and skin , and its analysis assumes that the uniqueness of dentition can be accurately recorded on skin.  Bitemarks are observed primarily in violent crimes, especially those involving sexual assault. The perpetrator may bite the victim or the victim may bite the assailant in self-defense. Females are bitten more often than males, ,,, with most of the bites occurring on the breast (33%) and the arms (19%). ,
Depending on the anatomic location, the constitution of the skin, and the victim's reaction, a bitemark may become distorted because of the dynamics of biting, particularly the arch size and shape. ,,,, In 1984, Rawson and Brooks  proposed a classification of human breast morphology owing to its great variability in size and resiliency, both necessary elements for understanding distortion effects. In 2001, Sheasby and MacDonald  conducted a forensic classification of bitemark distortions in primary (at the time of biting) and secondary (when the bitemark is examined or recorded) bites. They report that 'dynamics and tissue distortion are complex and unpredictable phenomena which are closely related because of their simultaneous occurrence during the episode of contact between the dentition and the skin.' They categorically emphasize the need for reconstruction of the victim's known position at the time of biting. However, the reconstruction of a range of positional possibilities is most suitable for the live victim. In dead victim cases, the body position is unknown and the reconstruction of a range of body positions is not readily achieved. Therefore, the potential occurrence of a posture distortion may even be more difficult to explain in the case of dead victims.
Several basic procedures to preserve the forensic dental information are to discern the injury as a potential bitemark; taking photographs and impressions and the eventual excision and preservation of the potential bitemark. , The clarity and shape of the bitemark may change in a relatively short period in both living and dead victims.  While photographs provide the most reliable means of preserving information, they have the inherent limitation that they seek to represent a three-dimensional object on a two-dimensional film.  Computer techniques have been used to analyze, calibrate, and record dental images and can prevent mistakes by pattern-associated comparison. ,,, Clearly, these size-matching techniques are only applicable to bitemarks exhibiting minimal distortion. , The preservation of the three-dimensional nature of the bitten area by making custom trays to take impressions, which are then poured in type II stone, has therefore been described as a study aid. ,, Additional casts may be made with appropriate materials for special studies  to simulate bites in different body parts. Use of the suspect's dental casts has also been recommended.  Pig skin has been suggested as a good analogue for human skin in forensic research. 
In its guidelines the American Board of Forensic Odontology (ABFO) recommends taking dental impressions of the bite site; the impression materials used should have American Dental Association specifications and must be prepared according to the manufacturer's instructions.  The common impression materials listed are hydrocolloids and light-body vinyl polysiloxane (VPS).  Polyether, has been reported to have excellent accuracy, long-term stability, good elastic recovery, and excellent tear resistance. , Its excellent hydrophilicity ensures impressions with superior detail reproduction in wet surfaces, including areas that are difficult to access. ,,,,, The objective of this report is to demonstrate the accuracy of bitemark impressions obtained using a polyether impression material composing elastic casts. As the material has similar elasticity to that of human skin, it is useful in the analysis of bitemarks having the potential for distortion.
| Materials and Methods|| |
Twenty bitemarks were performed by different human subjects on selected resilient-consistency dead pig skin according to the ethical standards of the committee on human experimentation. The pig skin was excised prior to biting. The evidence collection and conservation procedures were undertaken as described in the bitemark investigation protocol. This protocol is designed according to the chronologic basic steps in forensic investigation.
The bitemark: All 20 bitemarks were photographed by the same operator with a digital camera (Coolpix 2100 Nikon™) using the ABFO No. 2 scale in 300 dpi resolution [Figure 1]. Polyether light-bodied consistency (Impregum™ 31750 - Refill Pack; 3M) and heavy-bodied consistency (Impregum™ 31749 - Refill Pack; 3M) were used as impression material of the skin bitemarks as shown in [Figure 2]. Only one impression from the bitemark was taken to avoid unnecessary manipulation, distortion, and loss of evidence. This procedure to record the marks (evidence preservation) was done as bitemarks have a natural tendency to disappear due to tissue regeneration (live victim) or putrefaction (dead body). A monophase technique was performed according to the manufacturer's recommendations  and custom trays were hot-water adapted (60°C) with extra-hard pink wax (Beauty Pink™, Moyco Technologies Inc.). As this was an experimental design, no swabs for DNA recovery were considered. However, the authors recommend that in actual investigations the basic steps and protocols be followed.
The biter suspect: Study plaster casts of the upper and lower jaw from each individual were made using type IV yellow densite stone (Prima Rock™). Casts were scanned using a flatbed scanner (Hewlett-Packard™ Scanjet 3770) with the same metric reference as shown in [Figure 3]a and b.
First die cast (densite stone casts - control sample): Each polyether impression was carefully poured using type IV yellow densite stone (Prima Rock™) and slight vibration. The densite type IV die stone was chosen for its good physical properties. The small particle size as well as the powder/water ratio (100 gr/20 ml) shows the quality of the material. The working time is approximately 6-8 min, while the setting time is 12 min. Another characteristic of the densite type IV die stone is its low expansion, which reaches 0.13%. Furthermore, its compressive strength increases from 55 to 117 Mpa in just 48 h. These properties ensure dimensional stability and durability. Two densite stone casts were poured. The first one was considered as an ‛examination cast' and second one as an ‛untouched cast' (preserved and stored in a secure place). The examination casts were scanned using ABFO No. 2 scale as shown in [Figure 3]c.
Second die cast (polyether model): After the examination and the creation of the densite stone casts, their impressions were obtained using the polyether technique as described in the section A above. Positive casts were poured with polyether light-bodied consistency (Impregum™ 31750 - Refill Pack; 3M) using a paintbrush and slight vibration to ensure the flow of the polyether. [Figure 3]d shows models scanned using the ABFO No. 2 scale.
The same operator performed all the impressions, and mixed and poured all the casts according to the manufacturer's instructions.
Digital photographs of skin bitemarks and the scanned images of first and second (densite stone and polyether) die casts of the same subject were compared using Adobe Photoshop 8.0™ software (Adobe System Inc., USA) with superimposition as the method. Metric references were calibrated, but no digital imaging methods were used to adjust for angular distortion.
Traits were categorized by three operators (to assess inter- and intra-observer agreement) into one of the following types:
- Extreme-degree match
- High-degree match
- Probable-degree match
- Poor-degree match
- Dissimilar-degree match
The subjects' dental casts were positioned on the bitemarks in the polyether and plaster casts and categorized (degree of match) using the described method. The procedure was performed to minimize the initially distorted patterns of skin. Finger pressure was applied in the polyether casts on the side opposite the bitemark, thus attenuating the expanded areas. Matches need to be achieved easily and should be unforced (accuracy factor).
Descriptive statistics (i.e., arithmetic mean, standard deviation, variance, range, maxima, and minima) were used to describe the obtained data. Tabular description and graphical display of data were used to facilitate comparisons.
The manual comparison of the polyether models of all 20 subjects was categorized into one of five types according to degree of match. Category 5 (dissimilar-degree match) was considered a negative match and categories 1-4 (extreme-/high-/probable-/poor-degree match) were considered false-positive matches.
| Results|| |
[Table 1],[Table 2],[Table 3] and [Figure 4] show the differences between the manual comparison with polyether models and the other comparisons. The digital and manual comparisons of the densite stone casts reveal the distortions at the time of biting (primary distortions) [Figure 5]. [Figure 6] shows that the polyether cast compensates for these distortions because of its elasticity, providing a better degree match when positioning the subject's dental cast.
After digital comparison of the bitemark photographs, cases 1, 8, 9, 12, 14, 15, and 19 (35%) were categorized as type 1 or 2 (i.e., extreme- or high-degree match); cases 2, 5, 10, 16, and 20 (25%) were categorized as type 3 (i.e., probable-degree match); and cases 3, 4, 6, 7, 11, 13, 17, and 18 (40%) were categorized as type 4 or 5 (i.e., poor-degree or dissimilar-degree match).
There are no substantial differences between digital comparison of densite stone casts, and polyether casts. Cases 3, 11, and 13 (15%) achieved better matches in digital comparisons of densite stone casts and polyether models than the digital comparison with photographs.
While manual comparison with densite stone casts did not show better results than with digital comparison as shown in [Figure 7], the polyether models (on manual comparison) show type 1 or 2 matches (i.e., extreme- or high-degree matches) in 100% of the cases [Figure 8].
Comparison of the results of all 20 subjects show that there were no false-positive matches.
| Discussion|| |
While bitemarks produced in a firm substrate such as cheese or chocolate can be analyzed by the standard quantitative techniques because there is minimal distortion, bitemarks on a highly deformable substrate like skin are more difficult to analyze. ,, In fact, many authors have established that human skin is a very poor substrate for retaining clear impressions, making it impossible to use in a scientific analysis of skin wounds. ,, In the authors' experience, primary distortions have been found in photographs, densite stone casts, polyether casts, and all the comparisons of the subject's plaster casts. The scanning of casts may decrease the risk of error in the bitemark photographic record (secondary distortions) as seen in cases 3, 11, and 13. In forensics, there are invasive procedures that allow the preservation of three-dimensional images of bitten areas; , obviously, this may be performed on a deceased victim's skin and after the pathologist has completed the autopsy. ,
According to Pretty and Sweet,  bitemark evidence is not sufficiently reliable, given the inaccuracy of techniques and errors in protocol. Literature reports many cases of technical infractions in the processing and recording of bitemarks. ,,, Pretty also  indicates that there are over 60 reported bitemarks per year, of which only an average of 15 are suitable for further work and only 10 hold sufficient unique detail for a precise analysis.
When investigators or authorities have identified the potential biter, his or her dental records provide the basis for comparison with the bitemark. Ideally, a suspect's dental casts would be directly compared to the tooth-created indentations in the patterned injury on the skin, but this situation is extremely rare.  Impression of the mark poured in dental stone to create models is the first step for comparison. , According to the literature, since 1963 it has become customary to construct two casts (untouched and examination casts) and to use a rubber model to study dynamic bite action.  The ABFO has recommended the creation of additional casts in appropriate materials for special studies.  A first die stone cast provides primary bitemark conservation because of its dimensional stability. The need for reproducing the elasticity and deformability of skin surface is achieved using polyether die-cast impressions of the densite stone casts, which can withstand longer time periods benefiting comparison procedures. Because it can attain its original size and shape even in highly deformable rates, polyether is a good alternative both as an impression and pouring material. It has the capacity for superior detail reproduction. When correctly processed, it is an excellent option when obtaining positive models of the wound for physical dynamic comparison.
Blackwell et al. affirm 'the natural tendency to see what one wants to see, thereby tempting examiners to over-interpret bitemark evidence, has led to serious difficulties when bringing such evidence before the courts.'  This work does not intend to suggest that the conventional impression, photographic, or digital techniques be replaced. While an objective method  of analysis has emerged with the advent of DNA analysis, polyether may supplement DNA procedures within the limits of its application because of its strength in recovering bitemarks.
| References|| |
|1.||Bernstein ML. Nature of Bitemarks. In: Dorion RB, editor. Bitemark Evidence. New York: Marcel Dekker; 2004. p. 59-60. |
|2.||Martin-de las Heras S, Valenzuela A, Ogayar C, Valverde AJ, Torres JC. Computer-based production of comparison overlays from 3D-scanned dental casts for bite mark analysis. J Forensic Sci 2005;50:127-33. |
|3.||Sheasby DR, MacDonald DG. A forensic classification of distortion in human bite marks. Forensic Sci Int 2001;122:75-8. |
|4.||Freeman AJ, Senn DR, Arendt DM. Seven hundred seventy eight bite marks: analysis by anatomic location, victim and biter demographics, type of crime, and legal disposition. J Forensic Sci 2005;50:1436-43. |
|5.||Vale GL, Noguchi TT. Anatomical distribution of human bite marks in a series of 67 cases. J Forensic Sci 1983;28:61-9. |
|6.||Lessig R, Wenzel V, Weber M. Bite mark analysis in forensic routine case work. EXCLI J 2006;5:93-102. |
|7.||Pretty IA, Sweet D. Anatomical location of bitemarks and associated findings in 101 cases from the United States. J Forensic Sci 2000;45:812-4. |
|8.||Dorion RBJ. Human Bitemarks. In: Dorion RB, editor. Bitemark Evidence. New York: Marcel Dekker; 2004. p. 323. |
|9.||Sakoda S, Fujita MQ, Zhu BL, Oritani S, Ishida K, Taniguchi M, et al. Wounding dynamics in distorted bitemarks: two case reports. J Forensic Odontostomatol 2000;18:46-51. |
|10.||Rothwell BR. Bite marks in forensic dentistry: a review of legal, scientific issues. J Am Dent Assoc 1995;126:223-32. |
|11.||Al-Talabani N, Al-Moussawy ND, Baker FA, Mohammed HA. Digital analysis of experimental human bitemarks: application of two new methods. J Forensic Sci 2006;51:1372-5. |
|12.||Rawson RD, Brooks S. Classification of human breast morphology important to bite mark investigation. Am J Forensic Med Pathol 1984;5:19-24. |
|13.||American Board of Forensic Odontology. ABFO Bitemark Guidelines, 2009 January; http://www.forensicdentistryonline.org/Forensic_pages_1/bitemark_guidelines.htm . [Cited in 2009 Jan]. |
|14.||Delattre VF. Teamwork in Bitemark Investigation. In: Dorion RB, editor. Bitemark Evidence. New York: Marcel Dekker; 2004. p. 56. |
|15.||Bernitz H, van Heerden WF, Solheim T, Owen JH. A technique to capture, analyze, and quantify anterior teeth rotations for application in court cases involving tooth marks. J Forensic Sci 2006;51:624-9. |
|16.||Bowers CM, Johansen RJ. Digital analysis of bite marks and human identification. Dent Clin North Am 2001;45:327-42. |
|17.||Bowers CM, Johansen RJ. Photographic evidence protocol: the use of digital imaging methods to rectify angular distortion and create life size reproductions of bite mark evidence. J Forensic Sci 2002;47:178-85. |
|18.||Martin-de las Heras S, Valenzuela A, Javier Valverde A, Torres JC, Luna-del-Castillo JD. Effectiveness of comparison overlays generated with DentalPrint software in bite mark analysis. J Forensic Sci 2007;52:151-6. |
|19.||Dorion RB. Bitemark Impressions. Noninvasive analyses. In: Dorion RB, editor. Bitemark Evidence. New York: Marcel Dekker; 2004. p. 203-8. |
|20.||Avon SL, Wood RE. Porcine skin as an in-vivo model for ageing of human bite marks. J Forensic Odontostomatol 2005;23:30-9. |
|21.||Lu H, Nguyen B, Powers JM. Mechanical properties of 3 hydrophilic addition silicone and polyether elastomeric impression materials. J Prosthet Dent 2004;92:151-4. |
|22.||Aimjirakul P, Masuda T, Takahashi H, Miura H. Gingival sulcus simulation model for evaluating the penetration characteristics of elastomeric impression materials. Int J Prosthodont 2003;16:385-9. |
|23.||Walker MP, Petrie CS, Haj-Ali R, Spencer P, Dumas C, Williams K. Moisture effect on polyether and polyvinylsiloxane dimensional accuracy and detail reproduction. J Prosthodont 2005;14:158-63. |
|24.||Michalakis KX, Bakopoulou A, Hirayama H, Garefis DP, Garefis PD. Pre- and post-set hydrophilicity of elastomeric impression materials. J Prosthodont 2007;16:238-48. |
|25.||McCabe JF, Carrick TE. Recording surface detail on moist surfaces with elastomeric impression materials. Eur J Prosthodont Restor Dent 2006;14:42-6. |
|26.||German MJ, Carrick TE, McCabe JF. Surface detail reproduction of elastomeric impression materials related to rheological properties. Dent Mater 2008;24:951-6. |
|27.||Johnson GH, Lepe X, Aw TC. The effect of surface moisture on detail reproduction of elastomeric impressions. J Prosthet Dent 2003;90:354-64. |
|28.||Mondon M, Ziegler C. Changes in water contact angles during the first phase of setting of dental impression materials. Int J Prosthodont 2003;16:49-53. |
|29.||Impregum TM Soft Polyether Impression Material. Technical Product Profile. 3M Espe. Available from: http://3mespe.pl/files/infotech/Impregum_Soft_E_infotech.pdf [last cited on 2009 Jan]. |
|30.||Blackwell SA, Taylor RV, Gordon I, Ogleby CL, Tanijiri T, Yoshino M, et al. 3-D imaging and quantitative comparison of human dentitions and simulated bite marks. Int J Legal Med 2007;121:9-17. |
|31.||Bernitz H, Owen JH, van Heerden WF, Solheim T. An integrated technique for the analysis of skin bite marks. J Forensic Sci 2008;53:194-8. |
|32.||van der Velden A, Spiessens M, Willems G. Bite mark analysis and comparison using image perception technology. J Forensic Odontostomatol 2006;24:14-7. |
|33.||Thali MJ, Braun M, Markwalder TH, Brueschweiler W, Zollinger U, Malik NJ, et al. Bite mark documentation and analysis: the forensic 3D/CAD supported photogrammetry approach. Forensic Sci Int 2003;135:115-21. |
|34.||Rothwell BR, Thien AV. Analysis of distortion in preserved bite mark skin. J Forensic Sci 2001;46:573-6. |
|35.||Sweet DJ, Bastien RB. Use of an acrylonitrile-butadiene-styrene (ABS) plastic ring as a matrix in the recovery of bite mark evidence. J Forensic Sci 1991;36:1565-71. |
|36.||Dorion RB. Tissue Specimens. Invasive Analyses. In: Dorion RB, editor. Bitemark Evidence. New York: Marcel Dekker; 2004. p. 225. |
|37.||Pretty IA, Sweet DJ. The judicial view of bitemarks within the United States Criminal Justice System. J Forensic Odontostomatol 2006;24:1-11. |
|38.||Bernstein ML. Two bite mark cases with inadequate scale references. J Forensic Sci 1985;30:958-64. |
|39.||Sperry K, Campbell HR Jr. An elliptical incised wound of the breast misinterpreted as a bite injury. J Forensic Sci 1990;35:1226-35. |
|40.||Grey TC. Defibrillator injury suggesting bite mark. Am J Forensic Med Pathol 1989;10:144-5. |
|41.||Pretty IA. Development and validation of a human bitemark severity and significance scale. J Forensic Sci 2007;52:687-91. |
|42.||Dailey JC. The Comparison. In: Dorion RB, editor. Bitemark Evidence. New York: Marcel Dekker; 2004. p. 423-4. |
|43.||Ström F. Investigation of bite-marks. J Dent Res 1963;42:312-6. |
|44.||Pretty IA. Forensic dentistry: 2. Bitemarks and bite injuries. Dent Update 2008;35:48-50, 53-4, 57-8 passim. |
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]
[Table 1], [Table 2], [Table 3]