An Overview of 3D Printing in Forensic Science: The Tangible Third-Dimension

There has been a rapid development and utilization of three-dimensional (3D) printing technologies in engineering, health care, and dentistry. Like many technologies in overlapping disciplines, these techniques have proved to be useful and hence incorporated into the forensic sciences. Therefore, this paper describes how the potential of using 3D printing is being recognized within the various sub-disciplines of forensic science and suggests areas for future applications. For instance, the application can create a permanent record of an object or scene that can be used as demonstrative evidence, preserving the integrity of the actual object or scene. Likewise, 3D printing can help with the visualization of evidential spatial relationships within a scene and increase the understanding of complex terminology within a courtroom. However, while the application of 3D printing to forensic science is beneficial, currently there is limited research demonstrated in the literature and a lack of reporting skewing the visibility of the applications. Therefore, this article highlights the need to create good practice for 3D printing across the forensic science process, the need to develop accurate and admissible 3D printed models while exploring the techniques, accuracy and bias within the courtroom, and calls for the alignment of future research and agendas perhaps in the form of a specialist working group.     

The Accuracy and Applicability of 3D Modeling and Printing Blunt Force Cranial Injuries

The purpose of this study was to determine the factors affecting the accuracy of 3D models and 3D prints of cranial blunt force trauma, to evaluate the applicability and limitations of modeling such injuries. Three types of cranial blunt force lesions were documented (hinge, depressed, and comminuted) using three forms of surface scanning (laser, structured light scanner, and photogrammetry) at two different quality settings (standard and high). 3D printed models of the lesions were produced using two different materials (a gypsum‐like composite powder called VisiJet^® PXL and an acrylic engineered composite plastic called VisiJet^® M3 in crystal colour). The results of these analyzes indicate the prints in this study exhibit some statistically significant differences from the actual bone lesions, but details of the lesions can be reproduced to within 2 mm accuracy.     

Testing a Novel 3D Printed Radiographic Imaging Device for Use in Forensic Odontology

There are specific challenges related to forensic dental radiology and difficulties in aligning X‐ray equipment to teeth of interest. Researchers used 3D printing to create a new device, the combined holding and aiming device (CHAD), to address the positioning limitations of current dental X‐ray devices. Participants (N = 24) used the CHAD, soft dental wax, and a modified external aiming device (MEAD) to determine device preference, radiographer's efficiency, and technique errors. Each participant exposed six X‐rays per device for a total of 432 X‐rays scored. A significant difference was found at the 0.05 level between the three devices (p = 0.0015), with the MEAD having the least amount of total errors and soft dental wax taking the least amount of time. Total errors were highest when participants used soft dental wax—both the MEAD and the CHAD performed best overall. Further research in forensic dental radiology and use of holding devices is needed.     

Accuracy of 3D Scanners in Tooth Mark Analysis

The objective of this study was to compare the accuracy of contact and laser 3D scanners in tooth mark analysis. Ten dental casts were scanned with both 3D scanners. Seven linear measurements were made from the 3D images of dental casts and biting edges generated with DentalPrint© software (University of Granada, Granada, Spain). The uncertainty value for contact 3D scanning was 0.833 for the upper dental cast and 0.660 mm for the lower cast; similar uncertainty values were found for 3D-laser scanning. Slightly higher uncertainty values were obtained for the 3D biting edges generated. The uncertainty values for single measurements ranged from 0.1 to 0.3 mm with the exception of the intercanine distance, in which higher values were obtained. Knowledge of the error rate in the 3D scanning of dental casts and biting edges is especially relevant to be applied in practical forensic cases.     

Introducing 3D Printed Models as Demonstrative Evidence at Criminal Trials

This case report presents one of the first reported uses of a 3D printed exhibit in an English homicide trial, in which two defendants were accused of beating their victim to death. The investigation of this crime included a micro‐CT scan of the victim's skull, which assisted the pathologist to determine the circumstances of the assault, in particular regarding the number of assault weapons and perpetrators. The scan showed two distinct injury shapes, suggesting the use of either two weapons or a single weapon with geometrically distinct surfaces. It subsequently served as the basis for a 3D print, which was shown in court in one of the first examples that 3D printed physical models have been introduced as evidence in a criminal trial in the United Kingdom. This paper presents the decision‐making process of whether to use 3D printed evidence or not.     

Pitfalls of Computed Tomography 3D Reconstruction Models in Cranial Nonmetric Analysis*

Many studies in the literature have highlighted the utility of virtual 3D databanks as a substitute for real skeletal collections and the important application of radiological records in personal identification. However, none have investigated the accuracy of virtual material compared to skeletal remains in nonmetric variant analysis using 3D models. The present study investigates the accuracy of 20 computed tomography (CT) 3D reconstruction models compared to the real crania, focusing on the quality of the reproduction of the real crania and the possibility to detect 29 dental/cranial morphological variations in 3D images. An interobserver analysis was performed to evaluate trait identification, number, position, and shape. Results demonstrate a false bone loss in 3D models in some cranial regions, specifically the maxillary and occipital bones in 85% and 20% of the samples. Additional analyses revealed several difficulties in the detection of cranial nonmetric traits in 3D models, resulting in incorrect identification in circa 70% of the traits. In particular, pitfalls included the detection of erroneous position, error in presence/absence rates, in number, and in shape. The lowest percentages of correct evaluations were found in traits localized in the lateral side of the cranium and for the infraorbital suture, mastoid foramen, and crenulation. The present study highlights important pitfalls in CT scan when compared with the real crania for nonmetric analysis. This may have crucial consequences in cases where 3D databanks are used as a source of reference population data for nonmetric traits and pathologies and during bone-CT comparisons for identification purposes.     

Virtual anthropology: a preliminary test of macroscopic observation versus 3D surface scans and computed tomography (CT) scans

Virtual anthropology (VA) is based on applying anthropological methods currently used to analyse bones to 3D models of human remains. While great advances have been made in this endeavour in the past decade, several interrogations concerning how reliable these models are and what their proper use should be remain unanswered. In this research, a fundamental assumption of VA has been investigated: if the way we perceive and apply an anthropological method is truly similar when looking at bones macroscopically and through various 3D media. In order to answer, 10 skulls of known age and sex were scanned using a computed tomography (CT) scanner and a 3D surface scanner. Two observers separately applied a defined staging method to eight suture sites on these skulls, first looking at the bone macroscopically, then at the 3D surface scan, and finally on the CT scan. Two rounds of observation were carried out by each observer. Intra- and inter-observer error were evaluated, and two sample t-tests used to evaluate if the different types of medium used yielded significantly different observations. The results show a high degree of inter-observer error, and that data obtained from 3D surface scans differ from macroscopic observation (confidence level 95%, P ≤ 0.05). CT scans, in these settings, yielded results comparable to those obtained through macroscopic observations. These results offer many possibilities for future research, including indications on the kind of anthropological methods and anatomical landmarks that might be reliably transferable to the virtual environment. All current methods used in traditional anthropology should be tested, and if they prove unreliable, new techniques to analyse bones from virtual models should be developed.

Key points

• Large discrepancies between observation on dry bones and computer-generated 3D models (surface scans or CT scans) could lead to the re-evaluation of the suitability of traditional anthropological methods for application on 3D models.
• This preliminary study evaluates whether macroscopic, 3D surface scans, and CT scans viewings generate different observations.
• The results indicate that the data are not always coherent across all three media of observation.
• Explanations include the aspect given to the bone by the 3D software, differences between handling bones in real life versus on a computer, and level of expertise of the observers.

     

Citrate Content of Bone for Time Since Death Estimation: Results from Burials with Different Physical Characteristics and Known PMI

A recently introduced method to determine the postmortem interval (PMI) based on quantification of the citrate content in bone was applied on the temporal bones and femora of 20 individuals buried in wooden coffins (WO) and body bags (BB), respectively. Concerning known vs. calculated PMI, a significant difference between the temporal and the femur bone samples of the same individuals was observed in the BB group (p = 0.012). In contrast, differences were insignificant for the WO group (p = 0.400). Moreover, similar levels of underestimation of PMIs resulted from the analysis of the femora for both burial groups (p = 0.247). Also, there was consistently less citrate preserved in the flat temporal bones as compared to the femora, indicating that the cortical layer of the long bones should be preferentially employed for citrate‐based PMI estimations. The results call for additional research on subsurface‐buried and surface‐deposited remains to enhance the accuracy of the published PMI equation.     

Estimating Biological Characteristics With Virtual Laser Data

Laser scanning technology is increasingly being used in forensic anthropological research to obtain virtual data for archival purposes and post hoc measurement collection. This research compared the measurement accuracy of two laser scanners—the FARO Focus^3D 330X and the FARO Freestyle^3D—against traditionally obtained (i.e., by hand) control data (N = 454). Skeletal data were collected to address a novel question: the ability of laser scanning technology to produce measurements useful for biological characteristic estimation, such as sex and stature. Results indicate that both devices produced measurements very similar to control (c. 3‐mm average absolute error), but also illuminate a tendency to under‐measure. Despite these findings, the virtual data produced sex and stature estimates that varied little from control‐produced estimates, signifying the usefulness of virtual data for preliminary biological identification when the skeletal elements are no longer available for physical analysis.     

Latent Print Proficiency Testing: An Examination of Test Respondents,Test-Taking Procedures,and Test Characteristics

Proficiency testing is a key component of quality assurance programs within crime laboratories and can help improve laboratory practices. However, current proficiency testing procedures contain significant limitations and can be misinterpreted by examiners and court personnel (Garrett & Mitchell, 2018). To evaluate some of these limitations, we surveyed latent print examiners (n = 198) after they completed a Collaborative Testing Services, Inc. proficiency test. Additionally, we evaluated test performance and used a quality metric algorithm to evaluate the quality of test prints. Results do not suggest that respondents are dissimilar to the broader examiner population, although they may engage in different behaviors when completing tests versus casework. Findings show that proficiency testing contains prints of high quality and is perceived as both relatively easy and representative of casework. The test discriminated between inexperienced and experienced respondents, and verification procedures were largely ineffective in reducing errors. Objective quality metrics may provide a path forward to improving proficiency testing in a measurable manner.     

应用CT三维重组技术判定胸骨性别的研究

目的建立利用三维重组形态学指标判定胸骨性别来源的方法,并对其判定效果进行评价,考察虚拟骨骼的法医学应用价值。方法应用胸部螺旋CT扫描图像,通过多层面重组法获取胸骨的二维影像,结合容积再现技术得出的三维模型,分别测量胸骨的全长、柄长、体长、柄最大宽、体最大宽、柄最大厚、体最大厚、体上端厚等8项指标,并计算出3个比值指标;筛选出其中有性别差异的指标,建立性别判别方程并评价其判别效果。结果 11个指标的性别差异均具有统计学意义(P0.05),但以胸骨全长、胸骨体长、体最大厚及柄最大宽的判别效果较好。所建方程组中,全指标、长度指标判别方程及逐步判别方程的判别率较高,88.6%的判定率与近期国外有关性别判定研究的报道结果基本一致。结论应用多层螺旋CT三维重组技术判定国人胸骨性别具有较高的可行性和准确性,该技术有望应用于胸骨年龄推断及其它虚拟骨骼的研究。     

Formulae for Estimating Skeletal Height in Modern South‐East Asians

Estimating stature in human skeletal remains of Asian ancestry is problematic for forensic anthropologists due to the paucity and uncertain suitability of regression formulae. To address this issue, our study analyzed 64 individuals from a modern skeletal collection of South‐East Asian origin and developed population‐specific ordinary least squares regression formulae to estimate skeletal height from each of the long bones of the upper and lower limbs, as well as from trunk length. Results indicate that the most accurate estimates of skeletal height from a single bone (as measured by standard error of the estimate—SEE) are from tibial length in males (SEE = 2.40 cm) and from humeral length in females (SEE = 2.59 cm), followed by femoral length (SEE = 2.84 cm). When multiple elements are considered, the combination of femoral and tibial length yields the best estimates in both sexes as well as combined sex samples (male SEE = 2.40 cm; female SEE = 2.77 cm; combined sex SEE = 2.54 cm).     

Effect of Head Position on Facial Soft Tissue Depth Measurements Obtained Using Computed Tomography

Facial soft tissue depth (FSTD) studies employing clinical computed tomography (CT) data frequently rely on depth measurements from raw 2D orthoslices. However, the position of each patient's head was not standardized in this method, potentially decreasing measurement reliability and accuracy. This study measured FSTDs along the original orthoslice plane and compared these measurements to those standardized by the Frankfurt horizontal (FH). Subadult cranial CT scans (n = 115) were used to measure FSTDs at 18 landmarks. Significant differences were observed between the methods at eight of these landmarks (p < 0.05), demonstrating that high‐quality data are not generated simply by employing modern imaging modalities such as CT. Proper technique is crucial to useful results, and maintaining control over head position during FSTD data collection is important. This is easily and most readily achieved in CT techniques by rotating the head to the FH plane after constructing a 3D rendering of the data.     

Recovery Rates of Human Fetal Skeletal Remains Using Varying Mesh Sizes

Human fetal skeletal elements of different gestational ages were screened with multiple mesh sizes (6.4 mm [1/4 inch], 3.2 mm [1/8 inch], 2.0 mm, and 1.0 mm) to determine their recovery rates. All remains were previously macerated, and no significantly damaged elements were used. The 6.4 mm mesh allowed a large loss of elements (63.2% overall), including diagnostic elements, while no diagnostic elements were lost when the 1 mm mesh (0.2%) was used. When using the 3.2 mm mesh, 16.2% of the bones were lost, including some diagnostic elements (primarily tooth crowns), while 7.5% were lost using the 2.0 mm mesh. The authors recommend that the potential loss of information incurred when utilizing larger mesh sizes be taken into consideration when planning recovery methods where fetal remains may be encountered and that a minimum of 1.0 mm mesh be utilized in recovery contexts known to include fetal remains.     

Photogrammetry vs CT Scan: Evaluation of Accuracy of a Low-Cost Three-Dimensional Acquisition Method for Forensic Facial Approximation

Photogrammetry is a three-dimensional acquisition method potentially applicable to the forensic field. This possibility requires the verification of its accuracy. In this study, 3D volumes of skulls are generated to compare the photogrammetry versus the CT scan. In order to provide eligible material to the photogrammetric software, photographs were captured at a distance of 30 cm from the skull placed on a support 1 m in height and illuminated with diffused laboratory ceiling artificial light. A Nikon Coolpix P7100 camera was used. Photographs capture common elements with the previous and the next photograph so as to allow the photogrammetric software to recognize these common points between photographs and create a 3D puzzle. The Zephyr Lite (3DFlow©) software was employed to register the 3D volume. CT-based skulls are taken as a metric reference. The photogrammetry-based skulls are then enlarged according to the measurements of some landmarks or Zygion and Zygion, the distance between end of nasal and base of nasal pyramid for frontal projection, and minimum breadth of the mandibular ramus for the right lateral projection. The accuracy of the photogrammetry is compared to that of the CT scan by measuring the 3D volumes of the skulls studied. Specific landmarks are used as reference points for the measures in both frontal and lateral views. Bland–Altman graph shows homogeneity. The mean difference (1.28 mm) indicates that the measurements taken on the photogrammetry-based skull tend to slightly overestimate compared with the measurements taken on the CT-based skull.     

An Analysis of Hounsfield Unit Values and Volumetrics from Computerized Tomography of the Proximal Femur for Sex and Age Estimation

Sex and age are two elements in the establishment of a biological profile for forensic identification. While the pelvic bones are the most ideal structures for sex estimation, the condition of a body is not always ideal due to the nature of death, such as in mass disasters, or postmortem processes. This study utilized CT scans and resultant 3D models of 100 male and 100 female adults of known ages ranging from 18 to 98 years old to collect volumetric and Hounsfield unit measurements of the proximal femur. Equations were created to establish logistic regression models for sex estimation and linear regression models for age estimation. The resultant sex estimation method had an accuracy of 93.5% and utilized the volume of the proximal femur. This study provides three linear regression models for age with an accuracy range of 86%–92% ±12 years. As imaging technologies are increasingly adopted for forensic purposes, the power of 3D data will provide the opportunity for more quantitative and reproducible analyses. The proposed method for sex and age estimation provides a reliable tool that can be utilized in both day-to-day casework and disaster victim identification.     

Quantification of Pubic Symphysis Metamorphosis Based on the Analysis of Clinical MDCT Scans in a Contemporary Malaysian Population

Forensic age estimation methods are biased to sex and population; in general, accuracy is reduced when applied to foreign populations. This study assessed the accuracy of the Suchey–Brooks method in contemporary Malaysian individuals and aimed to formulate population‐specific standards. Multi‐detector computed tomography scans of 355 individuals (165 male; 190 female) of 15–83 years of age were reconstructed using 3D‐volumetric rendering in RadiAnt. Pubic symphyseal phase, bias, inaccuracy, and percentage correct age classifications are examined. Transition analysis was used to develop age estimation standards. High observer agreement (κ = 0.763–0.832) and a positive relationship between age and pubic symphyseal phase (r = 0.884–0.90) were demonstrated. Mean inaccuracies were 8.62 and 8.95 years for males and females, respectively; overall correct classification was 97.8%. Transition ages between phases in males were 18.79, 23.29, 28.85, 43.64, and 61.15 years; in females, the corresponding data were 19.77, 22.53, 32.62, 41.85, and 57.39 years.     

Forensic Dental Age Estimation by Measuring Root Dentin Translucency Area Using a New Digital Technique

Dentin translucency measurement is an easy yet relatively accurate approach to postmortem age estimation. Translucency area represents a two‐dimensional change and may reflect age variations better than length. Manually measuring area is challenging and this paper proposes a new digital method using commercially available computer hardware and software. Area and length were measured on 100 tooth sections (age range, 19–82 years) of 250 μm thickness. Regression analysis revealed lower standard error of estimate and higher correlation with age for length than for area (R = 0.62 vs. 0.60). However, test of regression formulae on a control sample (n = 33, 21–85 years) showed smaller mean absolute difference (8.3 vs. 8.8 years) and greater frequency of smaller errors (73% vs. 67% age estimates ≤ ±10 years) for area than for length. These suggest that digital area measurements of root translucency may be used as an alternative to length in forensic age estimation.