Exploring the feasibility of smartphone cameras for 3D modelling of bite patterns in forensic dental identification

The field of bitemark analysis involves examining physical alterations in a medium resulting from contact with teeth and other oral structures. Various techniques, such as 2D and 3D imaging, have been developed in recent decades to ensure precise analysis of bitemarks. This study assessed the precision of using a smartphone camera to generate 3D models of bitemark patterns. A 3D model of the bite mark pattern was created using 3Shape TRIOSTM and a smartphone camera combined with monoscopic photogrammetry. The mesiodistal dimensions of the anterior teeth were measured using Rapidform Explorer and OrtogOnBlender, and the collected data were analyzed using IBM® SPSS® Statistics version 23.0. The mean mesiodistal dimension of the anterior teeth, as measured on the 3D model from 3Shape TRIOSTM and smartphone cameras, was found to be 6.95 ± 0.7667 mm and 6.94 ± 0.7639 mm, respectively. Statistical analysis revealed no significant difference between the two measurement methods, p > 0.05. The outcomes derived from this study unequivocally illustrate that a smartphone camera possessing the specific parameters detailed in this study can create a 3D representation of bite patterns with an accuracy level on par with the outputs of a 3D intraoral camera. These findings underscore the promising trajectory of merging smartphone cameras and monoscopic photogrammetry techniques, positioning them as a budget-friendly avenue for 3D bitemark analysis. Notably, the monoscopic photogrammetry methodology assumes substantial significance within forensic odontology due to its capacity for precise 3D reconstructions and the preservation of critical measurement data.

Superimposed polygonal approximation analysis comparing 2D photography and 3D scanned images of bite marks on human skin

Background

Preservation of bite marks evidence has always been a major problem in forensic odontology due to progressive loss of details as time passes. The use of 2D photographs has been widely used to document forensic evidence and preserving bite marks; however, there are limitations to this method. This study aims to measure the accuracy of the 3D scanned image in comparison to 2D photograph registration of experimental bite marks. Thirty volunteers performed self-exertions of a bite mark on the respective forearm of subjects. A 2D photograph and 3D scanned image was immediately registered following bite mark exercise using a conventional camera and Afinia EinScan-Pro 2X PLUS Handheld 3D Scanner, respectively. The outlines of the bite mark were transformed into a polygonal shape. Next, the polygonal approximation analysis was performed by an arbitrary superimposition method. The difference between surface areas of both images was calculated (2D photographs ̶ 3D scanned images).

Results

A paired t test was used to measure significance with α = 0.05. The mean surface area of 2D photographs and 3D scanned images is 31.535 cm2 and 31.822 cm2, respectively. No statistical difference was found between both mean surface areas (p > 0.05). The mean error (ME) is 0.287 ± 3.424 cm2 and the mean absolute error (MAE) is 1.733 ± 1.149 cm2.

Conclusion

Bite marks registered with the 3D scanned image are comparable to the standard 2D photograph for bite mark evaluations. The use of a 3D scan may be adopted as a standard operating procedure in the forensic application, especially for evidence preservation.

Determining the effective number and surfaces of teeth for forensic dental identification through the 3D point cloud data analysis

Background

The assimilation between three-dimensional (3D) imaging techniques and dental forensic science can provide rich and stable information for human identification. This study aimed to determine the effective number and surfaces of teeth for dental identification through the 3D imaging approach.

Material and methods

In the present study, maxillary dental casts were fabricated from subjects who met the inclusion criteria and scanned using a 3D scanner Vivid 910. Rapidform XOS/SCAN software was used to create and trim the 3D point cloud data. Subsequently, two types of 3D surface data of dental casts were registered and the root mean square errors (RMSEs) between subjects were calculated using iterative closest point (ICP) algorithm in MATLAB. Two sets of experiments with 120 combinations of the superimposed 3D dataset were designed, termed as experiments 1 and 2.

Results

In experiment 1, the difference between subjects was clearly distinguished with a minimum of six teeth of the dental arch. The results of experiment 2 suggest that the labial surfaces of the anterior teeth are sufficient to be used for dental identification.

Conclusion

Through these experiments for all possible pairs of subjects, a clear difference was observed in the RMSE between the genuine and imposter pairs. These results indicate the potential of using the 3D imaging technique to achieve highly accurate human identification. It is suggested that a future study with a larger sample number will evaluate the robustness and accuracy of this method.

Optimising the measurement of bruises in children across conventional and cross polarized images using segmentation analysis techniques in Image J, Photoshop and circle diameter measurements

BACKGROUND

Bruising is a common abusive injury in children, and it is standard practice to image and measure them, yet there is no current standard for measuring bruise size consistently. We aim to identify the optimal method of measuring photographic images of bruises, including computerised measurement techniques.

METHODS

24 children aged <11 years (mean age of 6.9, range 2.5-10 years) with a bruise were recruited from the community. Demographics and bruise details were recorded. Each bruise was measured in vivo using a paper measuring tape. Standardised conventional and cross polarized digital images were obtained. The diameter of bruise images were measured by three computer aided measurement techniques: Image J (segmentation with Simple Interactive Object Extraction (maximum Feret diameter), 'Circular Selection Tool' (Circle diameter), & the Photoshop 'ruler' software (Photoshop diameter)). Inter and intra-observer effects were determined by two individuals repeating 11 electronic measurements, and relevant Intraclass Correlation Coefficient's (ICC's) were used to establish reliability. Spearman's rank correlation was used to compare in vivo with computerised measurements; a comparison of measurement techniques across imaging modalities was conducted using Kolmogorov-Smirnov tests. Significance was set at p < 0.05 for all tests.

RESULTS

Images were available for 38 bruises in vivo, with 48 bruises visible on cross polarized imaging and 46 on conventional imaging (some bruises interpreted as being single in vivo appeared to be multiple in digital images). Correlation coefficients were >0.5 for all techniques, with maximum Feret diameter and maximum Photoshop diameter on conventional images having the strongest correlation with in vivo measurements. There were significant differences between in vivo and computer-aided measurements, but none between different computer-aided measurement techniques. Overall, computer aided measurements appeared larger than in vivo. Inter- and intra-observer agreement was high for all maximum diameter measurements (ICC's > 0.7).

CONCLUSIONS

Whilst there are minimal differences between measurements of images obtained, the most consistent results were obtained when conventional images, segmented by Image J Software, were measured with a Feret diameter. This is therefore proposed as a standard for future research, and forensic practice, with the proviso that all computer aided measurements appear larger than in vivo.

Focussing on the future: survey results on the image capture of patterned cutaneous injuries

An investigator who is involved in assessing the likelihood of physical abuse must make a decision as to whether the injury seen matches the explanation given. In some instances the pattern of these injuries can give the investigator a possible link to the cause of the injury. Photographic imaging is used to record the patterned cutaneous injuries (PCI) and to facilitate forensic interpretation. The current method of capturing PCI often results in some form of distortion that causes a change to the shape of the patterned injury. The Dermatological Patterned Injury Capture and Analysis (DePICA) research group was formed to assess current image capture methods and practices. An online survey was set up to assess the value of localised imaging protocols and training specific to imaging PCI and was made available to law enforcement professionals, forensic investigators and hospital staff. 80 participants responded to the survey. The majority of the survey participants have had training in medical or forensic photography, however 66 (83%) have not had specific training in how to photograph PCI. 41 (51%) of the participants responded that they always use a rigid scale and 34 (43%) position the camera so that it is perpendicular to the scale and injury. Comments made about the quality of images obtained and produced raises concerns about how much knowledge those initiating such images have about image relevance in criminal cases. It is evident that a clear and comprehensive guide to photographing PCIs is required to improve the quality of the photographic evidence that is collected.