Evaluation of reproduction technique of bitemarks printed in chewing gum for human identification

Forensic Odontology is the science that correlates dental and legal principles, used for processes such as human identification. One of the possible acting fields for Forensic Research, Society and Development, v. 9, n. 12, e40391211177, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i12.11177 2 Odontologists is the analysis and study of patterns and injuries created by human bite marks. This study aimed to show the applicability of dental marks printed in chewing gum for human identification in forensic investigations. A transversal observational study was carried out. The data was collected from 20 volunteers over 18 years old. Each subject had their upper and lower dental casts and was asked to chew a piece of gum for one minute. The pieces of chewing gum were refrigerated at -20oC for a week, and reproduced with addition and condensation silicones using an adapted reproduction technique. The analysis of the chewing gum was made by overlays. The ANOVA test showed no significant differences on width and length between the pieces of chewing gum and their reproductions (greatest width p=0.918, and the length p=0.981). The analysis of the reproductions with plaster mold showed that there was no difference when using addition silicone or condensation silicone. During the analysis, various suspects could be excluded from the investigation (up to 11, depending on the technique used), but it was not possible to confirm one of them as the main suspect. The study showed that the reproduction technique of chewing gum is efficient, viable and easily performed; and can be used in cases of human identification in forensic investigations. However, it is necessary to certify that the chewing gum effectively presents a bite mark and that it is correctly handled to avoid alterations. It also became evident that the process of refrigeration is essential for the analysis proposed in this study.


Introduction
The study of recognition and interpretation of marks and injuries produced by human bites is increasing in Forensic Dentistry (Hinchliffe, 2010). Although some authors affirm that there cannot be two people with the same dental standards, there is still no concrete theory about the individuality of dentitions and the behavior of skin marks (Carvalho & Matoso, The technique for molding and reproduction of chewing gum was according to Silva, Flores and Lino Jr (2014). First, the alginate was manipulated using the manufacturer's recommended measurement, for each half of the cast recipient, a measure of alginate was used. After manipulation, the alginate was inserted into the half of the cast recipient ( Figure   1) and the refrigerated piece of chewing gum was placed in the pink mass of the alginate. After 1 minute, when the alginate became white (Figure 2), another alginate measure was manipulated and it was placed in the disposable syringe, and then, using the syringe, the refrigerated piece of chewing gum was careful covered (Figure 3). Source: Authors (2020). Research, Society andDevelopment, v. 9, n. 12, e40391211177, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i12.11177 6  After setting time of the material, the cast recipient was carefully opened and the piece of chewing gum removed and refrigerated again. After this process, we had a negative reproduction of the piece of chewing gum ( Figure 5). Research, Society and Development, v. 9, n. 12, e40391211177, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i12.11177 This process was carried out with each type of material, using the measurements reported by each company. The elastomers addition silicone in the dispenser, the condensation silicone, the base paste, and the accelerator paste were placed in two strands of the same length on a glass plate and mixed with a spatula. Then it was spread regularly on top of one another.
The distribution of the sample was statistically evaluated by the parametric test Analysis of Variance (ANOVA) using one criterion. In addition, the complementary Tukey Research, Society andDevelopment, v. 9, n. 12, e40391211177, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i12.11177 10 test was used to determine which group had differences between itself. The estimated level of significance was 5%, as provided in Table 2. Analysis of plaster models vs reproductions of chewing gum.
Identification methods used were overlay between the reproductions of chewing gum and plaster models; and overlay with transparency sheets.

Overlay between the reproductions of chewing gum and the plaster models
Each of the 40 reproductions of chewing gum were interposed between the plaster models, trying different ways to find some compatibility between the reproductions and the incisal / occlusal surfaces of plaster models. Thus, each piece of chewing gum made possible 40 interpositions with the plaster models. Considering that there were 20 suspects, 800 clashes performed. This analysis showed possible suspects and excluded other.

Manual overlay with transparency sheet
The 40 dental models, 20 upper and 20 lower, had their cusps painted with a marker.
Later the models were placed in a multifunctional printer Epson Stylus TX430W (Epson ® , Beijing, China) to perform copies. A sheet of transparency was placed on top of each copy and marks of the cusp of each model were transfixed to the sheet, reproducing the occlusal profile to be used for analysis. Research, Society andDevelopment, v. 9, n. 12, e40391211177, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i12.11177 For the photos of the reproductions, the following materials were used: Nikon D3000 camera (Nikon Corporation ™ , Thailand); Tamron 18-200mm lens XR Dill; tripod; remote trigger and ABFO number 2 scale. The pictures were taken by the same investigator, with the camera on a tripod with 85th tilt, fixed lens in 18mm, shutter f22 and trigger 1/200 with builtin flash. The camera was kept still for all the photos, and they were all taken with a remote trigger in order to maintain the quality and sharpness of the images.
The 80 photos of the reproductions of chewing gum were printed, being each one on one side of each reproduction, all in actual size. The transparency sheet was overlapped on the photographs, in order to find matching points, to obtain possible suspects or exclude suspects.

Results
The measurements of samples and reproductions of silicone are in Table I. When comparing the measurements of samples and reproductions of chewing gum, the statistical result using ANOVA, to the greatest width was p=0.918, and the length, p=0.981. For either length or width of the reproductions, the results were not significant, suggesting that the distortions between the pieces of chewing gum were similar to the reproductions. Therefore, these materials can be used for reproduction of chewing gum with confidence.
Overlay between the reproduction of chewing gum and plaster models.
Through overlay of the reproductions of chewing gum and the plaster models, some suspects could be excluded from investigation. However, correspondence could not be confirmed with any of the subjects.
Considering both reproductions (made with addition and condensation silicone), from the 20 pieces of gum chewed by the suspects, 7 led to exclusion in 70 clashes (which corresponds to 35 percent of the analyzed samples and 25 percent of the total of clashes). The other 13 pieces of gum did not allow the exclusion or the identification of the suspect, corresponding to 65 percent of the total sample. Of these, 32.5 percent represented the samples that did not have any bitemarks. These were considered possible for all suspects in the statistical analysis.
A single piece of chewing gum presented differences between the materials of reproduction. More suspects were discarded using the condensation silicone (10 suspects) compared to the addition silicone (4 suspects). This result is explained by the presence of bubbles often observed when using the addition silicone, preventing a better assessment of compatibility. Research, Society andDevelopment, v. 9, n. 12, e40391211177, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i12.11177 12 For the statistical analysis of the difference in the usage of silicone reproductions of condensation or addition, the Pearson's Chi-Squared Test was used. The results showed 100% compatibility in the analyses, suggesting no statistical differences between the usages of addition or condensation silicones and is illustrated in Table 3. Table 3 -Pearson chi-square for manual interposition for overlay between the reproduction of chewing gum and plaster models.

Conclusion
According to the analyses performed, it was concluded that the molding technique of chewing gum and reproduction with both addition and condensation silicones is applicable in forensic routine. However, the expert conclusion will depend on the visible presence of bitemarks on chewing gum and its proper handling and storage, in order to prevent alterations.