Age estimation in forensic sciences: application of combined aspartic acid racemization and radiocarbon analysis

Advancing Forensic Human Chronological Age Estimation: Biochemical, Genetic, and Epigenetic Approaches from the Last 15 Years: A Systematic Review

Forensic age estimation is crucial for identifying unknown individuals and narrowing suspect pools in criminal investigations. Over the past 15 years, significant progress has been made in using biochemical, genetic, and epigenetic markers to estimate chronological age.

METHODS

From research on PubMed a total of 155 studies, related to advancements in age prediction techniques, were selected following PRISMA guidelines. Studies considered eligible dealt with radiocarbon dating, aspartic acid racemization, mitochondrial DNA analysis, signal joint T-cell receptor excision circles, RNA analysis, telomeres, and DNA methylation in the last 15 years and were summarized in a table.

RESULTS

Despite these advancements, challenges persist, including variability in prediction accuracy, sample degradation, and the lack of standardization and reproducibility. DNA methylation emerged as the most promising approach capable of high accuracy across diverse populations and age ranges. Multimodal methods integrating several biomarkers show promise in improving reliability and addressing these limitations.

CONCLUSION

While significant progress has been made, further standardization, validation, and technological integration are needed to enhance forensic age estimation. These efforts are essential for meeting the growing demands of forensic science while addressing ethical and legal considerations.

Forensic age estimation from ossification centres: a comparative investigation of imaging and physical methods

Age estimation is a crucial component of human identification in forensic science. It has a vital role in forensic anthropology, including examinations of skeletal remains, disaster victim identification, and locating missing individuals. Present communication focuses on the age estimation through the examination of ossification centers of bones and its significance in identifying the age of 18 years old, a recognized age of majority in many countries. The process of ossification is integral to biological development and serves as critical standard for age estimation in forensic identification. This study reviews relevant literature from well-known databases such as PubMed, Scopus, Web of Science, and ScienceDirect. Additionally, the present review elaborates various classification methods used by authors to classify the stages of ossification centers of bones. The objective of this communication is to assess the effectiveness of both imaging and physical methods for age estimation and to provide a critical comparison to determine the superior approach. The findings suggest that imaging methods are more reliable for the estimation of age from ossification centers. Staging methods introduced by Schmeling et al, Kellinghaus et al, Dedouit et al, Vieth et al, and Kvist et al. are found to be the best methods for age estimation.

Application and implications of radiocarbon dating in forensic case work: when medico-legal significance meets archaeological relevance

The estimation of the postmortem interval for skeletal remains is a crucial aspect of forensic anthropology. This paper illustrates the importance of radiocarbon analysis for establishing medico-legal significance and supporting forensic identification, through the analysis of three case studies for which the years of both birth and death were investigated. In Audresselles, Northern France, a partial skull was discovered with no contextual information or identity. Radiocarbon dating yielded an average calibrated calendar age of 4232 BCE (92.5% probability), indicating significant archaeological value but no forensic relevance. In the second case, skeletal remains were found in the flooded underground of a historical fort at Wimereux, Northern France, also with no identity. Radiocarbon dating based on the bomb-pulse curve indicated a calibrated date of death in 1962 CE (37.3% probability) or 1974-1975 CE (58.1% probability), both surpassing the French statute of limitations. Lastly, a skeleton with a suspected identity was discovered near Valenciennes, Northern France, and various biological tissues underwent radiocarbon dating. A bone sample suggested a calibrated date of death of 1998-2002 CE (84.6% probability), differing from a hair sample (2013-2018 CE, 83.3% probability) because of the slower bone tissue remodeling process. DNA analysis confirmed the person's identity, reported missing a decade prior to the discovery of the remains, following the alignment of the radiocarbon results with the individual's year of birth based on dental tissues and year of death. These case studies reveal that traditional radiocarbon dating and bomb-pulse dating are essential tools for estimating the postmortem interval, providing mutual benefits for archaeologists, forensic anthropologists, and the criminal justice system.

Key points

Traditional radiocarbon dating and bomb-pulse dating are essential tools to establish the archaeological relevance or medico-legal significance of human skeletal remains.Bomb-pulse dating enables assessment of an individual's years of birth and death.Bomb-pulse dating helps to narrow down the pool of candidates for identification.Radiocarbon analysis provides mutual benefits for archaeologists, forensic anthropologists, and the criminal justice system.

Estimation of human age using machine learning on panoramic radiographs for Brazilian patients

This paper addresses a relevant problem in Forensic Sciences by integrating radiological techniques with advanced machine learning methodologies to create a non-invasive, efficient, and less examiner-dependent approach to age estimation. Our study includes a new dataset of 12,827 dental panoramic X-ray images representing the Brazilian population, covering an age range from 2.25 to 96.50 years. To analyze these exams, we employed a model adapted from InceptionV4, enhanced with data augmentation techniques. The proposed approach achieved robust and reliable results, with a Test Mean Absolute Error of 3.1 years and an R-squared value of 95.5%. Professional radiologists have validated that our model focuses on critical features for age assessment used in odontology, such as pulp chamber dimensions and stages of permanent teeth calcification. Importantly, the model also relies on anatomical information from the mandible, maxillary sinus, and vertebrae, which enables it to perform well even in edentulous cases. This study demonstrates the significant potential of machine learning to revolutionize age estimation in Forensic Science, offering a more accurate, efficient, and universally applicable solution.

Mandibular torus thickness associated with age: Postmortem computed tomographic analysis

Age estimation is an essential step in identifying human corpses. Several mandibular landmarks have been highlighted as skeletal sites for age estimation since aging causes morphological changes. Reports suggest that mandibular torus size may be associated with aging; however, thorough investigation has not been performed owing to the difficulty in measuring it. Therefore, this study aimed to determine the association between age and mandibular torus thickness using postmortem computed tomography data from Japanese corpses. This study included 2,792 corpses with mean (standard deviation) age of 58.0 (22.4) years (range, 0-101 years) and 67.6 % males. Further, 2,662 (95.3 %), 14 (0.5 %), 59 (2.1 %), and 57 (2.0 %) corpses were in the permanent, mixed, primary, and predental dentition periods, respectively. Multivariable analysis was performed to quantify the impact of age on mandibular torus thickness, adjusting for sex, height, weight, and occlusal contact status. The model also included an interaction term between age and occlusal status because of the potential effect modification by occlusion. Results of the multivariable regression analysis showed that mandibular torus thickness increased with age (the regression coefficients (95 % confidence interval) were 0.6 (0.2-1.0), 0.7 (0.3-1.0), 1.0 (0.6-1.4), 1.3 (0.9-1.7), 1.3 (0.8-1.8), and 1.1 (0.4-1.7) for age groups 30-39, 40-49, 50-59, 60-69, 70-79, and 80-89 years, respectively), especially in males with occlusal contact. A significant association between mandibular torus thickness and age, modified by occlusal status and sex, was identified. Therefore, data regarding the thickness of the mandibular torus and occlusal status may be useful for age estimation in human corpses.

Validation of Age Estimation Using the Compositional Variation of Dental Hard Tissue: An X-ray Diffraction Analysis

Introduction X-rays and X-ray diffraction (XRD) are two non-destructive techniques that determine a material's crystallographic structure, chemical composition, and physical properties. They can also be used to estimate a person's age when it is unknown, assess the need for orthodontic treatment, or predict the likelihood of tooth decay. This research aims to validate the accuracy of age estimation through X-ray diffraction analysis of tooth hard tissue with compositional changes. Methodology Four tooth samples were analyzed using the Pan Analytical XRD (Malvern Panalytical Ltd., UK) unique d8 family platform, which uses Cu Kα radiation (0.154 nm) and a 0.02° scan rate from 0 to 80°. Results The angle of incidence (ω) is established between the sample and the X-ray source. The angle of diffraction, 2θ, is established between the detector and the incident beam. The detector angle 2θ and the incident angle ω always equal half. Inter-atomic distance, or d-spacing (D = 10^-8 cm in Angstrom units), is measured. A greater crystal size or a greater degree of crystallinity may be indicated by a higher peak intensity, which translates to an increased amount of atoms in the crystal. Conclusion The study's findings suggest that XRD is a promising new technique for age determination, as it has an advanced and dynamic approach to finding the crystallographic characteristics of the provided sample.

Development of an epigenetic age predictor for costal cartilage with a simultaneous somatic tissue differentiation system

Age prediction from DNA has been a topic of interest in recent years due to the promising results obtained when using epigenetic markers. Since DNA methylation gradually changes across the individual's lifetime, prediction models have been developed accordingly for age estimation. The tissue-dependence for this biomarker usually necessitates the development of tissue-specific age prediction models, in this way, multiple models for age inference have been constructed for the most commonly encountered forensic tissues (blood, oral mucosa, semen). The analysis of skeletal remains has also been attempted and prediction models for bone have now been reported. Recently, the VISAGE Enhanced Tool was developed for the simultaneous DNA methylation analysis of 8 age-correlated loci using targeted high-throughput sequencing. It has been shown that this method is compatible with epigenetic age estimation models for blood, buccal cells, and bone. Since when dealing with decomposed cadavers or postmortem samples, cartilage samples are also an important biological source, an age prediction model for cartilage has been generated in the present study based on methylation data collected using the VISAGE Enhanced Tool. In this way, we have developed a forensic cartilage age prediction model using a training set composed of 109 samples (19-74 age range) based on DNA methylation levels from three CpGs in FHL2, TRIM59 and KLF14, using multivariate quantile regression which provides a mean absolute error (MAE) of ± 4.41 years. An independent testing set composed of 72 samples (19-75 age range) was also analyzed and provided an MAE of ± 4.26 years. In addition, we demonstrate that the 8 VISAGE markers, comprising EDARADD, TRIM59, ELOVL2, MIR29B2CHG, PDE4C, ASPA, FHL2 and KLF14, can be used as tissue prediction markers which provide reliable blood, buccal cells, bone, and cartilage differentiation using a developed multinomial logistic regression model. A training set composed of 392 samples (n = 87 blood, n = 86 buccal cells, n = 110 bone and n = 109 cartilage) was used for building the model (correct classifications: 98.72%, sensitivity: 0.988, specificity: 0.996) and validation was performed using a testing set composed of 192 samples (n = 38 blood, n = 36 buccal cells, n = 46 bone and n = 72 cartilage) showing similar predictive success to the training set (correct classifications: 97.4%, sensitivity: 0.968, specificity: 0.991). By developing both a new cartilage age model and a tissue differentiation model, our study significantly expands the use of the VISAGE Enhanced Tool while increasing the amount of DNA methylation-based information obtained from a single sample and a single forensic laboratory analysis. Both models have been placed in the open-access Snipper forensic classification website.

Usefulness of powdered crown of mandibular first premolars in birth year estimation by radiocarbon dating

BACKGROUND

Radiocarbon (14C), whose levels increased in the atmosphere between 1955 and 1963, accumulates in the enamel of human teeth only during the process of tooth formation and has been applied to estimate the birth year of unidentified corpses. However, enamel isolation from teeth is time-consuming and labor-intensive. Therefore, this study aimed to estimate the birth year using 14C in the crown of a single mandibular first premolar tooth.

MATERIALS AND METHODS

Fourteen mandibular first premolars collected from forensic autopsies were analyzed. For nine teeth, each tooth was cut longitudinally: half of the tooth was enamel, and the other half was crown (1). For the other five teeth, the entire crown was used (2). Thereafter, the 14C concentration in each tooth was measured using accelerator mass spectrometry.

RESULTS

The absolute error between the actual date of birth (DOB) and the estimated DOB was within the range of 1.0-8.8 years in the enamel of five teeth and 0.1-4.0 years in the crown halves of seven teeth (1). For the five teeth with entire crowns, the absolute errors ranged between 0.3 and 3.0 years (2).

CONCLUSION

The absolute error of 14C-based year of birth estimation using the powdered crown of the mandibular first premolar teeth ranged between 0.1 and 4.0 years. Our method, which involves pulverizing an entire crown, eliminates the need for the equipment, time, and labor associated with enamel isolation. Therefore, 14C dating using powdered crowns of mandibular premolars can be useful for birth year estimation.

Artificial intelligence in forensic medicine and forensic dentistry

This review article aims to highlight the current possibilities for applying Artificial Intelligence in modern forensic medicine and forensic dentistry and present the advantages and disadvantages of its use. For this purpose, the relevant academic literature was searched using PubMed, Web of Science and Scopus. The application of Artificial Intelligence in forensic medicine and forensic dentistry is still in its early stages. However, the possibilities are great, and the future will show what is applicable in daily practice. Artificial Intelligence will improve the accuracy and efficiency of work in forensic medicine and forensic dentistry; it can automate some tasks; and enhance the quality of evidence. Disadvantages of the application of Artificial Intelligence may be related to discrimination, transparency, accountability, privacy, security, ethics and others. Artificial Intelligence systems should be used as a support tool, not as a replacement for forensic experts.

Multiple Methods of Dentin Translucency for Age Estimation

Background

Age estimation is an essential part of forensic odontology and many methods are available with variable accuracy. However, the research is going on to find the simple and most reliable method.

Objectives

By measuring the length and area of root dentin translucency in extracted tooth specimens manually and digitally, and comparing them, this study aims to find the most reliable technique of age assessment.

Materials and Methods

One-hundred and twenty-five single-rooted extracted human permanent teeth were selected for the study. In both unsectioned and sectioned teeth, the total length of root dentin translucency was manually measured using a digital vernier caliper. Then, in a ground-sectioned tooth specimen, the total length and area of root dentin translucency were measured digitally using a scanner scale and computer software. Both the methods were compared.

Results

In both manual and digital approaches, the length and area of root dentin translucency grew with age, from younger to older age groups. On comparing the measurements, the correlation coefficient was somewhat higher for digital area measurements than other measurements (r = 0.985).

Conclusion

The digital technique outperforms the traditional way for calculating age, and furthermore, measuring the area in the digital method for age estimation has shown to be more accurate.

Development and implementation of forensic anthropology in Swedish forensic practice

This paper presents the ongoing development of forensic anthropology in Sweden. We discuss the background of the discipline, its application, as well as its current and potential development in Swedish forensic practice. Collaboration with osteoarchaeologists in skeletal forensic cases has a long tradition in Sweden. Analyses of skeletal remains are performed ad-hoc, in contrast to analyses of fleshed human remains. While several law enforcement employees are educated in forensic anthropology and/or osteoarchaeology, they are not employed in these fields, and regional variations are evident. Internationally, forensic anthropology has become an autonomous forensic discipline over the past decades, requiring skills beyond mere skeletal analysis. To keep on a par with international standards, it may be time to revisit the concept of forensic anthropology in Sweden. Despite the limited presence of supporting organisational structures and systems, forensic anthropological and hard-tissue-reliant physico-chemical analyses have proven valuable in Swedish forensic practice, especially in cases of personal identification, trauma analysis and search efforts. We argue that Sweden could benefit from making qualified forensic anthropology expertise available in all law enforcement regions, starting to implement and promote forensic anthropology in routine forensic casework and formalising the role of forensic anthropology practitioners.

Biological Age Predictors: The Status Quo and Future Trends

There is no single universal biomarker yet to estimate overall health status and longevity prospects. Moreover, a consensual approach to the very concept of aging and the means of its assessment are yet to be developed. Markers of aging could facilitate effective health control, more accurate life expectancy estimates, and improved health and quality of life. Clinicians routinely use several indicators that could be biomarkers of aging. Duly validated in a large cohort, models based on a combination of these markers could provide a highly accurate assessment of biological age and the pace of aging. Biological aging is a complex characteristic of chronological age (usually), health-to-age concordance, and medically estimated life expectancy. This study is a review of the most promising techniques that could soon be used in routine clinical practice. Two main selection criteria were applied: a sufficient sample size and reliability based on validation. The selected biological age calculators were grouped according to the type of biomarker used: (1) standard clinical and laboratory markers; (2) molecular markers; and (3) epigenetic markers. The most accurate were the calculators, which factored in a variety of biomarkers. Despite their demonstrated effectiveness, most of them require further improvement and cannot yet be considered for use in standard clinical practice. To illustrate their clinical application, we reviewed their use during the COVID-19 pandemic.

Age Estimation Using Maxillary Central Incisor Analysis on Cone Beam Computed Tomography Human Images

Forensic dentistry plays an important role in human identification, and dental age estimation is an important part of the process. Secondary dentin deposition throughout an individual's lifetime and consequent modification in teeth anatomy is an important parameter for age estimation procedures. The aim of the present study was to develop regression equations to determine age in adults by means of linear measurements and ratios on sagittal, coronal and axial slices of maxillary central incisors using cone bean computed tomography (CBCT). Multiplanar measurements of upper central incisors were taken for a sample of 373 CBCTs. Subsequently, one-way analysis of variance (ANOVA) and multivariate linear regressions were performed for age estimation. The equations obtained from axial linear measurements and ratios presented a standard error of the estimate (SEE) of ±10.9 years (R² = 0.49), and a SEE of ±10.8 years (R² = 0.50), respectively. The equation obtained for multiplanar linear measurements presented a SEE of ±10.9 years (R² = 0.52), while the equation for multiplanar ratios presented a SEE of ±10.7 years (R² = 0.51). Thus, CBCT measurements on upper central incisors were found to be an acceptable method for age estimation. Horizontal measurements, especially pulp measurements, improve the accuracy of age estimate equations.

Age group prediction with panoramic radiomorphometric parameters using machine learning algorithms

The aim of this study is to investigate the relationship of 18 radiomorphometric parameters of panoramic radiographs based on age, and to estimate the age group of people with permanent dentition in a non-invasive, comprehensive, and accurate manner using five machine learning algorithms. For the study population (209 men and 262 women; mean age, 32.12 ± 18.71 years), 471 digital panoramic radiographs of Korean individuals were applied. The participants were divided into three groups (with a 20-year age gap) and six groups (with a 10-year age gap), and each age group was estimated using the following five machine learning models: a linear discriminant analysis, logistic regression, kernelized support vector machines, multilayer perceptron, and extreme gradient boosting. Finally, a Fisher discriminant analysis was used to visualize the data configuration. In the prediction of the three age-group classification, the areas under the curve (AUCs) obtained for classifying young ages (10-19 years) ranged from 0.85 to 0.88 for five different machine learning models. The AUC values of the older age group (50-69 years) ranged from 0.82 to 0.88, and those of adults (20-49 years) were approximately 0.73. In the six age-group classification, the best scores were also found in age groups 1 (10-19 years) and 6 (60-69 years), with mean AUCs ranging from 0.85 to 0.87 and 80 to 0.90, respectively. A feature analysis based on LDA weights showed that the L-Pulp Area was important for discriminating young ages (10-49 years), and L-Crown, U-Crown, L-Implant, U-Implant, and Periodontitis were used as predictors for discriminating older ages (50-69 years). We established acceptable linear and nonlinear machine learning models for a dental age group estimation using multiple maxillary and mandibular radiomorphometric parameters. Since certain radiomorphological characteristics of young and the elderly were linearly related to age, young and old groups could be easily distinguished from other age groups with automated machine learning models.

Application of Aspartic Acid Racemization for Age Estimation in a Spanish Sample

Simple Summary

For the correct identification of human skeletal remains, age is one of the key parameters. However, in adult individuals, this estimation is more difficult as it is not based on growing markers but on degeneration of the skeleton and the teeth. Thus, it can be very variable and less precise than age estimation in children and adolescents. The application of biochemical techniques, with their roots in aging research, could help to improve this estimation. This article presents the application of one of these approaches, aspartic acid racemization, to test its accuracy in a Spanish sample. This is based on the conversion of L-aspartic acid, the regular form of the amino acid in our proteins, into D-aspartic acid, its mirror image. The proportions of D-aspartic acid/L-aspartic acid increase with aging, enabling the determination of age in a more precise way than by applying forensic anthropology methodologies. This paper demonstrates that it was possible to apply this technique in a Spanish sample, obtaining accuracies of ±5 years of actual age. Additional studies should be developed to improve these estimates and to combine this technique with forensic anthropology methods.

Abstract

Correct age-at-death estimation in adult individuals is one of the challenges of forensic investigation. Forensic anthropology macroscopic techniques are non-invasive methods for this purpose. However, several methods need to be applied to accurately estimate age, and the difference between chronological and predictive age may still be around ±10 years. New research trends are focused on the inherent process of aging, which produces changes in tissues and organs at different biochemical levels. One of the oldest and most studied approaches in this field is aspartic acid racemization. The accuracy of this technique in age estimation has been widely demonstrated. However, only a few studies have assessed its accuracy in different populations. The aim of this research was to assess the accuracy of aspartic acid racemization in a Spanish sample and its applicability to forensic cases. Dentin from fifteen third molars from two Spanish populations (ages 19–70 years old) was isolated and D and L forms of aspartic acid were detected through GC/MS, according to a previous published protocol. D/L ratios were calculated and after the application of a regression analysis, a formula for age estimation was developed. The results were similar to previous studies, obtaining an R = 0.91 between racemization ratios and age and a mean absolute error (MAE) between chronological and predictive age of 5 years. These results were ratified by leave-one-out cross-validation, as well as the application of the formula to five teeth of a known age. Despite these promising results, this technique is not exempt from drawbacks; thus, further studies are required to apply this methodology to forensic cases and to combine it with forensic anthropology findings.

Reliability of aspartic acid racemization rate for chronological age estimation-a systematic review and meta-analysis

OBJECTIVE

The biochemical approach of dental age using aspartic acid racemization has been widely reported. The aim of this systematic review was to determine the reliability and accuracy of dental age estimation using aspartic acid racemization rate analysis.

DESIGN

Eight research databases (PubMed, Google Scholar, Embase, Cochrane, MEDLINE, TRIP, Web of Science, and Scopus) were utilised to gather and assess published literatures in compliance with the PRISMA 2020 guidelines and reported in PROSPERO (CRD42020208877). This systematic review and meta-analysis focused solely on cross-sectional studies. The quality evaluation was performed using the GRADE system. The standardized mean difference between estimated and chronological age was meta-analyzed using the random effects model.

RESULT

The literature review yielded 213 studies, of which 26 were considered acceptable for inclusion in this report. Out of 26 studies, 19 presented sufficient evidence for meta-analysis and the remaining 7 were used to construct a qualitative review. According to the meta-analysis, premolar-related studies had the least variability (Tau² = 0.23; I² = 72%) among other tooth groups.

CONCLUSION

A substantial degree of heterogeneity was found in every type of tooth. Only the premolar teeth had lower degree variability; thus, it is safe to believe that the premolar tooth is the best for this type of age estimation. It is recommended to develop population-specific mathematical equations to improve the accuracy of this age estimation approach.

Age estimation in humans through the analysis of aspartic acid racemization from teeth: A scoping review of methods, outcomes, and open research questions

Teeth are considered the most resistant structures in the human body. In forensic odontology, teeth are useful for human identification, especially when dental age estimation is necessary. Despite numerous studies, there is no consensus regarding the best methods for dental age estimation. The analysis of aspartic acid racemization, however, has shown promising results. This scoping review aimed to present a descriptive synthesis of the current literature regarding dental age estimation through aspartic acid racemization. Four electronic databases were screened: PubMed, Scielo, Web of Science, and Scopus. Cross-sectional studies published before April 2021 were selected. From 206 articles found, 26 met the eligibility criteria. Several experimental protocols and laboratory settings were detected, but the different protocols did not seem to significantly reduce error rates in dental age estimation. The analysis of aspartic acid racemization in human dental tissues produced accurate and potentially reliable results for age estimation. Aspartic acid racemization stands out especially in the adulthood - age category in which other methods struggle to deliver proper performances. Studies with larger samples, independent testing, and standardized laboratory procedures are necessary. Equator-like reporting guidelines are encouraged to enable future systematic reviews and meta-analyses.

Biochemical analyses for dental age estimation: a review

Background

For various legal and forensic scenarios, establishing an individual’s age, both living and dead, plays a crucial role. Various morphological, radiographic, and molecular methods can be used for age estimation. In children and adolescents, age estimation is based on the established developmental stages. However, in adults, where the development ceases into maturation, the degenerative changes play a role in determining the age.

Main body of the abstract

In the natural aging process, several molecular changes occur most commonly in the long-living proteins and hard tissues like the teeth and bone. These molecular changes gradually lead to alterations in several organs and organ systems, which can be quantified and correlated with age, including aspartic acid racemization, collagen crosslinks, advanced glycation-end products, and mitochondrial DNA mutations.

Short conclusion

Among the above methods, the racemization of aspartic acid can be considered as the most precise method. The main advantage of using aspartic acid racemization is that the sample can be collected from tissues (teeth) protected from various environmental and nutritional factors. If all the confounding factors are stable, the utilization of advanced glycation-end products can also be considered valuable. Environmental factors like lead accumulations may also help determine the age. However, further studies need to be conducted, focusing on providing a more standardized method. This review provides a concise summary of the biochemical techniques that can be used for estimation of age.

Evolution of dental age estimation methods in adults over the years from occlusal wear to more sophisticated recent techniques

Background

Age estimation has been an integral part of forensic science, and age estimation by dental means is by far the most commonly employed method. Dental age estimation in children is more accurate and straightforward as most methods use the chronological stages of odontogenesis that are highly systematic, reducing the chances of dispersed results. In contrast, estimation of age in adults becomes tricky and less accurate with varied approaches since tooth formation is already complete.

Main body

The methods of adult dental age estimation have come a long way from a calculated guess based on crude visual observation of teeth to radiological methods and to more recent sophisticated methods. Technological advances have opened up molecular and genetic methods by utilizing DNA methylation and telomere length to improve the accuracy of age estimation by reducing error chances.

Conclusions

Although dental age estimation methods in children and adolescents have been extensively reviewed, various adult age estimation methods are not reviewed as a whole. The aim of this review is to appraise the evolution of dental age estimation methods in adults over the years from mere visualization of dental attrition to employing more sophisticated means such as radioactive carbon dating and genetics. This comprehensive review also attempts to add an account of the accuracy and suitability of various adult dental age estimation methods.

Analysis of 14C, 13C and Aspartic Acid Racemization in Teeth and Bones to Facilitate Identification of Unknown Human Remains: Outcomes of Practical Casework

The identification of unknown human remains represents an important task in forensic casework. If there are no clues as to the identity of the remains, then the age, sex, and origin are the most important factors to limit the search for a matching person. Here, we present the outcome of application of so-called bomb pulse radiocarbon (14C derived from above-ground nuclear bomb tests during 1955-1963) analysis to birthdate human remains. In nine identified cases, 14C analysis of tooth crowns provided an estimate of the true date of birth with an average absolute error of 1.2 ± 0.8 years. Analysis of 14C in tooth roots also showed a good precision with an average absolute error of 2.3 ± 2.5 years. Levels of 14C in bones can determine whether a subject has lived after 1955 or not, but more precise carbon turnover data for bones would be needed to calculate date of birth and date of death. Aspartic acid racemization analysis was performed on samples from four cases; in one of these, the year of birth could be predicted with good precision, whereas the other three cases are still unidentified. The stable isotope 13C was analyzed in tooth crowns to estimate provenance. Levels of 13C indicative of Scandinavian provenance were found in known Scandinavian subjects. Teeth from four Polish subjects all showed higher 13C levels than the average for Scandinavian subjects.

Deep Differentiable Random Forests for Age Estimation

Age estimation from facial images is typically cast as a label distribution learning or regression problem, since aging is a gradual progress. Its main challenge is the facial feature space w.r.t. ages is inhomogeneous, due to the large variation in facial appearance across different persons of the same age and the non-stationary property of aging. In this paper, we propose two Deep Differentiable Random Forests methods, Deep Label Distribution Learning Forest (DLDLF) and Deep Regression Forest (DRF), for age estimation. Both of them connect split nodes to the top layer of convolutional neural networks (CNNs) and deal with inhomogeneous data by jointly learning input-dependent data partitions at the split nodes and age distributions at the leaf nodes. This joint learning follows an alternating strategy: (1) Fixing the leaf nodes and optimizing the split nodes and the CNN parameters by Back-propagation; (2) Fixing the split nodes and optimizing the leaf nodes by Variational Bounding. Two Deterministic Annealing processes are introduced into the learning of the split and leaf nodes, respectively, to avoid poor local optima and obtain better estimates of tree parameters free of initial values. Experimental results show that DLDLF and DRF achieve state-of-the-art performance on three age estimation datasets.

Telomere length and signal joint T-cell receptor rearrangement excision circles as biomarkers for chronological age estimation

BACKGROUND

Chronological age estimation is a challenging marker in the field of forensic medicine. The current study aimed to investigate the accuracy of signal joint T-cell receptor rearrangement excision circles (sjTRECs) quantification and telomere length measurement as methods for estimating chronological age.

METHODS

Telomere length was estimated in the DNA derived from the buccal cells through estimating the telomeric restriction fragment (TRF) length using TeloTTAGGG Telomere Length Assay while the sjTRECs quantification was carried out on DNA isolated from the blood samples using qPCR.

RESULTS

The TRF length was shortened with increased age (r = -0.722, p < 0.001). The sjTRECs were also decreased with increased age (r = -0.831, p < 0.001). Stronger coefficient and lower standard error of the estimate was obtained when multiple regression analysis for age prediction based on the values of both methods was applied (r = -0.876, p < 0.001).

A newly developed age estimation method based on CpG methylation of teeth-derived DNA using real-time methylation-specific PCR

Age estimation of unidentified bodies is important in forensic medicine and crime scenes. There is accumulating evidence that DNA methylation in the human genome isolated from body fluids changes with age. Most of the data have been obtained by pyrosequencing. In the forensic field, a simple, quick, and economical method is required to evaluate the age of various types of samples. In this study, an age estimation method based on methylation levels of DNA extracted from teeth using real-time methylation-specific PCR (MSP) was developed. The CpG island in the upstream region of ELOVL2, which is known as a validated biomarker in blood samples, was selected as a target site. The CpG methylation levels highly correlated with age (r = 0.843, n = 29). Age-related increase in DNA methylation levels was not affected by sex differences. In addition, the simple regression model based on methylation status of the CpG island exhibited moderate accuracy with a mean absolute deviation between chronological age and predicted age of 8.94 years. The results imply that real-time MSP can be a new tool to perform age prediction of unidentified bodies in forensic scenes.

Proteomics in Deaths by Drowning: Diagnostic Efficacy of Apolipoprotein A1 and α-1Antitrypsin, Pilot Study

Drowning is one of the leading causes of death worldwide. The pathophysiology of drowning is complex and, sometimes, interpretation of the circumstances of death in the autopsy becomes the main source of information in its diagnosis. New advances in medical research, such as proteomics, especially in forensic pathology, are still in the development. We proposed to investigate the application of Mass Spectrometry-based technologies, to identify differentially expressed proteins that may act as potential biomarkers in the postmortem diagnosis of drowning. We performed a pilot proteomic experiment with the inclusion of two drowned and two control forensic cases. After applying restrictive parameters, we identified apolipoprotein A1 (ApoA1) and α-1 antitrypsin as differentially expressed between the two diagnostic groups. A validation experiment, with the determination of both proteins in 25 forensic cases (16 drowned and 9 controls) was performed, and we corroborated ApoA1 higher values in the drowning group, whereas α-1 antitrypsin showed lower levels. After adjusting by confounder factors, both remained as predictive independent factors for diagnosis of drowning (p = 0.010 and p = 0.022, respectively). We constructed ROC curves for biomarkers' levels attending at the origin of death and established an ApoA1 cut-off point of 100 mg/dL. Correct classification based on the diagnosis criteria was reached for 73.9% of the cases in a discriminant analysis. We propose apolipoprotein A1 (with our cutoff value for correct classification) and α-1 antitrypsin as valuable biomarkers of drowning. Our study, based on forensic cases, reveals our proteomic approach as a new complementary tool in the forensic diagnosis of drowning and, perhaps, in clinical future implications in drowned patients. However, this is a pilot approach, and future studies are necessary to consolidate our promising preliminary data.

Determination of epigenetic age through DNA methylation of NPTX2 gene using buccal scrapes: A pilot study

Context

DNA methylation (DNAm) age can be used to evaluate the chronological age of individuals often called "epigenetic age." In this study, buccal scrape samples were used for the determination of epigenetic age.

Aims

To examine if epigenetic age could be determined using neuronal pentraxin 2 (NPTX2) gene in buccal cells.

Setting and Design

This cohort study was designed to validate the use of buccal cells for epigenetic age estimation. Sanger sequencing was used to determine the genetic sequence of the gene of interest postamplification. Nucleotide base sequence for NPTX2 gene was obtained for each case using this protocol.

Subjects and Methods

The study was conducted on buccal scrapes obtained from 26 subjects of both genders, whose age varied from 1 to 65 years. The samples, collected by wooden spatulas, were placed in cell suspension buffer and stored at 4°C until transported to the laboratory.

Results

Methylation levels of 5'-C-phosphate-G-3' located in the gene NPTX2 of 26 subjects were studied and analyzed by bisulfate sequencing. The percentage of methylation in this study falls in the range between 15% and 51%.

Conclusion

In this study, a sufficient amount of gDNA was retrieved from the buccal cells, thus confirming that buccal scrape was a feasible technique to obtain ample DNA. This study also showed that DNAm-polymerase chain reaction method was a feasible method for the evaluation of methylation pattern of NPTX2 gene.

A Review of Bomb Pulse Dating and its Use in the Investigation of Unidentified Human Remains

In cases where there is limited antemortem information, the examination of unidentified human remains as part of the investigation of long-term missing person's cases is a complex endeavor and consequently requires a multidisciplinary approach. Bomb pulse dating, which involves the analysis and interpretation of 14C concentration, is one technique that may assist in these investigations by providing an estimate of year of birth and year of death. This review examines the technique of bomb pulse dating and its use in the identification of differentially preserved unknown human remains. Research and case studies implementing bomb pulse dating have predominantly been undertaken in the Northern Hemisphere and have demonstrated reliable and accurate results. Limitations were, however, identified throughout the literature. These included the small sample sizes used in previous research/case studies which impacted on the statistical significance of the findings, as well as technique-specific issues. Such limitations highlight the need for future research.

Age estimation by pulp/tooth area ratio in anterior teeth using cone-beam computed tomography: comparison of four teeth

Objectives

Age estimation is one of the most important factors in forensic medicine. Measuring secondary dentin deposition using cone-beam computed tomography images is an easy and noninvasive method. The aim of this study was to evaluate cone-beam computed tomography images as a reliable method to estimate chronological age by pulp/teeth ratio in anterior teeth in Iranian population.

Methodology

A total of 649 CBCT images from 377 Iranian patients aged between 20 and 69 years were evaluated. Pulp/teeth ratio (PTR) in maxillary and mandibular canine and central incisor teeth was measured in the axial and sagittal sections using OnDemand 3D Dental software. The Pearson correlation coefficient was determined to evaluate the correlation between the variables. Linear regression analysis, as well as age estimation formula, was used for each tooth separately.

Results

The regression analyses indicated that maxillary central incisors were more reliable for age estimation (R²=0.586 and standard error of estimate=7.045) compared with the other anterior teeth studied. Maxillary canine teeth had the lowest predictive power (R²=0.392 and standard error of estimate=8.387). Also, comparison of the axial and sagittal sections showed that the axial sections had a higher predictive power. (R²=0.48 for axial plans and R²=0.328 for sagittal plans)

Conclusion

The use of cone-beam computed tomography in age estimation by pulp/teeth ratio of anterior teeth is useful and a reliable method for age estimation in Iranian population.

Age estimation by cemental annulation rings

Context:

Tooth plays a pivotal role in the identification of a person when all other remains are ruined by natural or unnatural causes. Dental evidence can contribute to age estimation in forensic dentistry. Estimating the age of an individual with the help of a tooth for identification proves beneficial. Alternating light and dark bands seen on the cementum have been shown to be proportionate to the age of the patient in number. This was done to evaluate the cementum annulation in age determination.

Aims:

This study aimed to determine the age of an individual using tooth cementum annulation.

Materials and Methods:

In this study, twenty extracted teeth were collected and all the clinical details of the patient such as age, sex, and chief complaint were recorded. The collected teeth was preserved in formalin overnight and then washed under tap water before they were sectioned. The area selected for counting was observed under 10 × objective of light microscope, and photomicrographs were taken for the counting of the lines. At the time of analysis, the age of the patient was not disclosed to the observer.

Statistical Analysis Used:

Student's t-test was used for statistical analysis.

Results:

This study showed the correlation between the actual age of the individual and the estimated age using tooth cementum annulation method and showed significant statistical value.

Conclusion:

Incremental lines found in cementum can be used for age estimation in forensic dentistry.

Estimation of birth year by radiocarbon dating of tooth enamel: Approach to obtaining enamel powder

Atmospheric radiocarbon (¹⁴C) levels increased from 1955 to 1963 due to atmospheric nuclear weapon tests, and then decreased. As ¹⁴C accumulates in human tooth enamel while the enamel is being formed, ¹⁴C can be used to estimate the birth year of unidentified bodies. Measurement results of ¹⁴C content in tooth enamel using accelerator mass spectrometry vary depending on the enamel's sample site. To address this problem, a method for equalizing samples using a pulverizer was considered in this study. Regarding the tube and cone used as the pulverizer, (1) a polycarbonate tube and stainless steel cone, (2) a stainless steel tube and cone, and (3) a tungsten carbide tube and cone, were compared. In (1), the modern carbon ratio was approximately half that of the normal ratio of 100 pMC, with which accurate dating was impossible, and in (2), a high background value was obtained for IAEA-C1, which was pulverized using a reusable tube and cone. In (3), the ¹⁴C content for IAEA-C1 pulverized using reusable tube and cone, which was washed with quartz sand, was 0.31 ± 0.01 pMC. This result did not show any problems regarding background value. Therefore, the use of tungsten carbide products and washing with quartz sand is recommended for ¹⁴C measurement of pulverized teeth.

Accurate Age Estimation Using Multi-Task Siamese Network-Based Deep Metric Learning for Front Face Images

Recently, there have been many studies on the automatic extraction of facial information using machine learning. Age estimation from front face images is becoming important, with various applications. Our proposed work is based on the binary classifier, which only determines whether two input images are clustered in a similar class, and trains the convolutional neural networks (CNNs) model using the deep metric learning method based on the Siamese network. To converge the results of the training Siamese network, two classes, for which age differences are below a certain level of distance, are considered as the same class, so the ratio of positive database images is increased. The deep metric learning method trains the CNN model to measure similarity based on only age data, but we found that the accumulated gender data can also be used to compare ages. From this experimental fact, we adopted a multi-task learning approach to consider the gender data for more accurate age estimation. In the experiment, we evaluated our approach using MORPH and MegaAge-Asian datasets, and compared gender classification accuracy only using age data from the training images. In addition, from the gender classification, we found that our proposed architecture, which is trained with only age data, performs age comparison by using the self-generated gender feature. The accuracy enhancement by multi-task learning, for the simultaneous consideration of age and gender data, is discussed. Our approach results in the best accuracy among the methods based on deep metric learning on MORPH dataset. Additionally, our method is also the best results compared with the results of the state of art in terms of age estimation on MegaAge Asian and MORPH datasets.

Carbon-14 bomb pulse dating shows that tendinopathy is preceded by years of abnormally high collagen turnover

Tendons are essential weight-bearing structures that are often affected by tendinopathy, which leads to pain and impaired mobility. In healthy Achilles tendons, no significant renewal of the weight-bearing collagen matrix seems to occur during adult life, but tendinopathy may lead to increased turnover. The carbon-14 ([¹⁴C]) bomb pulse method was used to measure lifelong replacement rates of collagen in tendinopathic and healthy Achilles tendons (tendinopathic: n = 25, born 1937-1972. Healthy: n = 10, born 1929-1966). As expected, the healthy tendon collagen had not been replaced during adulthood, but in tendinopathic tendon, a substantial renewal had occurred. Modeling of the [¹⁴C] data suggested that one half of the collagen in tendinopathic matrix had undergone continuous slow turnover for years before the presentation of symptoms. This finding allows for a new concept in tendon pathogenesis because it suggests that either the symptoms of tendinopathy represent a late phase of a very prolonged disease process, or an abnormally high collagen exchange could be a risk factor for tendon disorders rather than being a result of disease.-Heinemeier, K. M., Schjerling, P., Øhlenschlæger, T. F., Eismark, C., Olsen, J., Kjær, M. Carbon-14 bomb pulse dating shows that tendinopathy is preceded by years of abnormally high collagen turnover.

Exploring Biological and Geological Age-related Changes through Variations in Intra- and Intertooth Proteomes of Ancient Dentine

Proteomic analyses are becoming more widely used in archeology not only due to the greater preservation of proteins in ancient specimens than DNA but also because they can offer different information, particularly relating to compositional preservation and potentially a means to estimate biological and geological age. However, it remains unclear to what extent different burial environments impact these aspects of proteome decay. Teeth have to date been much less studied than bone but are ideal to explore how proteins decay with time due to the negligible turnover that occurs in dentine relative to bone. We investigated the proteome variability and deamidation levels of different sections of molar teeth from archeological bovine mandibles as well as their mandibular bone. We obtained a greater yield of proteins from the crown of the teeth but did not find differences between the different molars analyzed within each mandible. We also obtained the best variety of protein from a well-preserved mandible that was not the youngest one in terms of chronological age, showing the influence of the preservation conditions on the final proteomic outcome. Intriguingly, we also noticed an increase in abundance levels of fetuin-A in biologically younger mandibles as reported previously, but the opposite trend in tooth dentine. Interestingly, we observed higher glutamine deamidation levels in teeth from the geologically oldest mandible despite it being the biologically youngest specimen, showing that the archeological age strongly impacts on the level of deamidations observed, much more so than biological aging. This indicates that the glutamine deamidation ratio of selected peptides may act as a good predictor of the relative geochronological age of archeological specimens.

Age Estimation with DNA: From Forensic DNA Fingerprinting to Forensic (Epi)Genomics: A Mini-Review

Forensic genetics developed from protein-based techniques a quarter of a century ago and became famous as “DNA fingerprinting,” this being based on restriction fragment length polymorphisms (RFLPs) of high-molecular-weight DNA. The amplification of much smaller short tandem repeat (STR) sequences using the polymerase chain reaction soon replaced RFLP analysis and advanced to become the gold standard in genetic identification. Meanwhile, STR multiplexes have been developed and made commercially available which simultaneously amplify up to 30 STR loci from as little as 15 cells or fewer. The enormous information content that comes with the large variety of observed STR genotypes allows for genetic individualisation (with the exception of identical twins). Carefully selected core STR loci form the basis of intelligence-led DNA databases that provide investigative leads by linking unsolved crime scenes and criminals through their matched STR profiles. Nevertheless, the success of modern DNA fingerprinting depends on the availability of reference material from suspects. In order to provide new investigative leads in cases where such reference samples are absent, forensic scientists started to explore the prediction of phenotypic traits from the DNA of the evidentiary sample. This paradigm change now uses DNA and epigenetic markers to forecast characteristics that are useful to triage further investigative work. So far, the best investigated externally visible characteristics are eye, hair and skin colour, as well as geographic ancestry and age. Information on the chronological age of a stain donor (or any sample donor) is elemental for forensic investigations in a number of aspects and has, therefore, been explored by researchers in some detail. Among different methodological approaches tested to date, the methylation-sensitive analysis of carefully selected DNA markers (CpG sites) has brought the most promising results by providing prediction accuracies of ±3–4 years, which can be comparable to, or even surpass those from, eyewitness reports. This mini-review puts recent developments in age estimation via (epi)genetic methods in the context of the requirements and goals of forensic genetics and highlights paths to follow in the future of forensic genomics.

When forensic odontology met biochemistry: Multidisciplinary approach in forensic human identification

When human remains are found, the priority of the investigation is to ascertain the identity of the deceased. A positive identification is a key factor in providing closure for the family of the deceased; it is also required to issue the death certificate and therefore, to settle legal affairs. Moreover, it is difficult for any forensic investigation involving human remains to be solved without the determination of an identity. Therefore, personal identification is necessary for social, legal and forensic reasons. In the last thirty years forensic odontology has experienced an important transformation, from primarily involving occasional dental identification into a broader role, contributing to the determination of the biological profile. In the same way, "DNA fingerprinting" has evolved not only in terms of improving its technology, but also in its application beyond the "classical": helping with the estimation of sex, age and ancestry. As these two forensic disciplines have developed independently, their pathways have crossed several times through human identification operations, especially the ones that require a multidisciplinary approach. Thus, the aim of this review is to describe the contributions of both forensic odontology and molecular biology/biochemistry to human identification, demonstrating how a multidisciplinary approach can lead to a better and more efficient identification.

Rib biomechanical properties exhibit diagnostic potential for accurate ageing in forensic investigations

Age estimation remains one of the most challenging tasks in forensic practice when establishing a biological profile of unknown skeletonised remains. Morphological methods based on developmental markers of bones can provide accurate age estimates at a young age, but become highly unreliable for ages over 35 when all developmental markers disappear. This study explores the changes in the biomechanical properties of bone tissue and matrix, which continue to change with age even after skeletal maturity, and their potential value for age estimation. As a proof of concept we investigated the relationship of 28 variables at the macroscopic and microscopic level in rib autopsy samples from 24 individuals. Stepwise regression analysis produced a number of equations one of which with seven variables showed an R2 = 0.949; a mean residual error of 2.13 yrs ±0.4 (SD) and a maximum residual error value of 2.88 yrs. For forensic purposes, by using only bench top machines in tests which can be carried out within 36 hrs, a set of just 3 variables produced an equation with an R2 = 0.902 a mean residual error of 3.38 yrs ±2.6 (SD) and a maximum observed residual error 9.26yrs. This method outstrips all existing age-at-death methods based on ribs, thus providing a novel lab based accurate tool in the forensic investigation of human remains. The present application is optimised for fresh (uncompromised by taphonomic conditions) remains, but the potential of the principle and method is vast once the trends of the biomechanical variables are established for other environmental conditions and circumstances.

Human age estimation from blood using mRNA, DNA methylation, DNA rearrangement, and telomere length

Establishing the age of unknown persons, or persons with unknown age, can provide important leads in police investigations, disaster victim identification, fraud cases, and in other legal affairs. Previous methods mostly relied on morphological features available from teeth or skeletal parts. The development of molecular methods for age estimation allowing to use human specimens that possess no morphological age information, such as bloodstains, is extremely valuable as this type of samples is commonly found at crime scenes. Recently, we introduced a DNA-based approach for human age estimation from blood based on the quantification of T-cell specific DNA rearrangements (sjTRECs), which achieves accurate assignment of blood DNA samples to one of four 20-year-interval age categories. Aiming at improving the accuracy of molecular age estimation from blood, we investigated different types of biomarkers. We started out by systematic genome-wide surveys for new age-informative mRNA and DNA methylation markers in blood from the same young and old individuals using microarray technologies. The obtained candidate markers were validated in independent samples covering a wide age range using alternative technologies together with previously proposed DNA methylation, sjTREC, and telomere length markers. Cross-validated multiple regression analysis was applied for estimating and validating the age predictive power of various sets of biomarkers within and across different marker types. We found that DNA methylation markers outperformed mRNA, sjTREC, and telomere length in age predictive power. The best performing model included 8 DNA methylation markers derived from 3 CpG islands reaching a high level of accuracy (cross-validated R(2)=0.88, SE±6.97 years, mean absolute deviation 5.07 years). However, our data also suggest that mRNA markers can provide independent age information: a model using a combined set of 5 DNA methylation markers and one mRNA marker could provide similarly high accuracy (cross-validated R(2)=0.86, SE±7.62 years, mean absolute deviation 4.60 years). Overall, our study provides new and confirms previously suggested molecular biomarkers for age estimation from blood. Moreover, our comparative study design revealed that DNA methylation markers are superior for this purpose over other types of molecular biomarkers tested. While the new and some previous findings are highly promising, before molecular age estimation can eventually meet forensic practice, the proposed biomarkers should be tested further in larger sets of blood samples from both healthy and unhealthy individuals, and markers and genotyping methods shall be validated to meet forensic standards.

Age estimation of decomposed bodies based on a combined arteriosclerotic index

Several methods exist for the estimation of the age at the time of death, ranging from mere visual inspection to costly laboratory examinations. The "combined arteriosclerotic index (CAI)" is considered to be a suitable low-budget tool for undecayed corpses. It defines the ratio between diameter and longitudinal pre-strain of the abdominal aorta. Its applicability in cases of decomposed corpses has not been studied yet. We examined whether it is a valid parameter in putrefied bodies as well and whether there is a correlation between CAI and the stage of decomposition. In conclusion the CAI becomes less accurate with increasing putrefaction. Nonetheless, even in case of high-grade putrefaction it remains a useful tool for instant age estimation which should be followed by the application of methods with higher accuracy.

Age estimation based on pulp chamber volume of first molars from cone-beam computed tomography images

AIM

To establish a method that can be used for human age estimation on the basis of pulp chamber volume of first molars and to identify whether the method is good enough for age estimation in real human cases.

MATERIALS AND METHODS

CBCT images of 373 maxillary first molars and 372 mandibular first molars were collected to establish the mathematical model from 190 female and 213 male patients whose age between 12 and 69 years old. The inclusion criteria of the first molars were: no caries, no excessive tooth wear, no dental restorations, no artifacts due to metal restorative materials present in adjacent teeth, and no pulpal calcification. All the CBCT images were acquired with a CBCT unit NewTom VG (Quantitative Radiology, Verona, Italy) and reconstructed with a voxel-size of 0.15mm. The images were subsequently exported as DICOM data sets and imported into an open source 3D image semi-automatic segmenting and voxel-counting software ITK-SNAP 2.4 for the calculation of pulp chamber volumes. A logarithmic regression analysis was conducted with age as dependent variable and pulp chamber volume as independent variables to establish a mathematical model for the human age estimation. To identify the precision and accuracy of the model for human age estimation, another 104 maxillary first molars and 103 mandibular first molars from 55 female and 57 male patients whose age between 12 and 67 years old were collected, too. Mean absolute error and root mean square error between the actual age and estimated age were used to determine the precision and accuracy of the mathematical model. The study was approved by the Institutional Review Board of Peking University School and Hospital of Stomatology.

RESULTS

A mathematical model was suggested for: AGE=117.691-26.442×ln (pulp chamber volume). The regression was statistically significant (p=0.000<0.01). The coefficient of determination (R(2)) was 0.564. There is a mean absolute error of 8.122 and root mean square error of 5.603 between the actual age and estimated age for all the tested teeth.

CONCLUSION

The pulp chamber volume of first molar is a useful index for the estimation of human age with reasonable precision and accuracy.

Racemization of aspartic acid in root dentin as a tool for age estimation in a Kuwaiti population

Estimation of age is one of the most significant tasks in forensic practice. Amino acid racemization is considered one of the most reliable and accurate methods of age estimation and aspartic acid shows a high racemization reaction rate. The present study has investigated the application of aspartic acid racemization in age estimation in a Kuwaiti population using root dentin from a total of 89 upper first premolar teeth. The D/L ratio of aspartic acid was obtained by HPLC technique in a test group of 50 subjects and a linear regression line was established between aspartic acid racemization and age. The correlation coefficient (r) was 0.97, and the standard error of estimation was ±1.26 years. The racemization age "t" of each subject was calculated by applying the following formula: ln [(1 + D/L)/(1 - D/L)] = 0.003181 t + (-0.01591). When the proposed formula "estimated age t = ln [(1 + D/L)/(1 - D/L)] + 0.01591/0.003181" was applied to a validation group of 39 subjects, the range of error was less than one year in 82.1% of the cases and the standard error of estimation was ±1.12. The current work has established a reasonably significant correlation of the D-/L-aspartic acid ratio with age, and proposed an apparently reliable formula for calculating the age in Kuwaiti populations through aspartic acid racemization. Further research is required to find out whether similar findings are applicable to other ethnic populations.

Analysis of radiocarbon, stable isotopes and DNA in teeth to facilitate identification of unknown decedents

The characterization of unidentified bodies or suspected human remains is a frequent and important task for forensic investigators. However, any identification method requires clues to the person’s identity to allow for comparisons with missing persons. If such clues are lacking, information about the year of birth, sex and geographic origin of the victim, is particularly helpful to aid in the identification casework and limit the search for possible matches. We present here results of stable isotope analysis of ¹³C and ¹⁸O, and bomb-pulse ¹⁴C analyses that can help in the casework. The ¹⁴C analysis of enamel provided information of the year of birth with an average absolute error of 1.8±1.3 years. We also found that analysis of enamel and root from the same tooth can be used to determine if the ¹⁴C values match the rising or falling part of the bomb-curve. Enamel laydown times can be used to estimate the date of birth of individuals, but here we show that this detour is unnecessary when using a large set of crude ¹⁴C data of tooth enamel as a reference. The levels of ¹³C in tooth enamel were higher in North America than in teeth from Europe and Asia, and Mexican teeth showed even higher levels than those from USA. DNA analysis was performed on 28 teeth, and provided individual-specific profiles in most cases and sex determination in all cases. In conclusion, these analyses can dramatically limit the number of possible matches and hence facilitate person identification work.

Age estimation based on pulp cavity to tooth volume ratio using postmortem computed tomography images

Pulp cavity size is known to decrease with age and can therefore serve as an indicator for age estimation. Here, we evaluated whether reconstructed images of multidetector-row computed tomography (MDCT) acquired before forensic autopsy are useful for estimating age at death. Images of 136 mandibular first premolars obtained from bodies of known age at death were analyzed, and the volume of the regions corresponding to pulp cavity and that of the whole tooth were determined using a voxel counting function. The pulp cavity was clearly distinguishable from dental hard tissue on the reconstructed images when using a cutoff value of 1400 Hounsfield units. Regression analysis adjusted for sex showed that estimated age correlated significantly with the pulp cavity to tooth volume ratio (r = 0.76). MDCT is gaining more widespread use in forensic medicine, and analyzing dental images to obtain parameters for age prediction is a practical approach for postmortem identification.