Chemosteometric regression models of heat exposed human bones to determine their pre‐burnt metric dimensions

The effect of burning on dental tissue: A macroscopic and microscopic investigation

Teeth are considered unique as fingerprints for identification purposes. Their structure and resilience mean they can remain for thousands and millions of years withstanding extreme conditions, including burning. During burning, bones undergo carbonization at approximately 400°C and calcination at approximately 700°C. This study aimed to investigate the effects of carbonization and calcination on dental tissue. It involved nondestructive analyses of 58 extracted human teeth before and after burning, using x-ray diffraction, micro-CT, and high-resolution confocal microscopy. The results revealed that during carbonization, dentin volume decreased in two thirds of the sample, accompanied by crack formation and significant reduction in hydroxyapatite crystal size (p<0.001). During calcination, dentin volume decreased in all teeth, along with a significant deepening of the cracks (p<0.001), while enamel crystal size increased slightly. Initial changes in teeth occurred at lower temperatures than had once been assumed, as indicated by the cracks during carbonization, and there was up to a 36% decrease in dentin volume during calcination, which should be considered when measuring burnt teeth. The results of this research provide new insight into understanding dental tissue response to burning. Thus, dental remains may contribute to the knowledge needed to reconstruct anthropological and forensic scenarios involving burning.

Differentiating present-day from ancient bones by vibrational spectroscopy upon acetic acid treatment

Acetic acid treatment for an accurate differentiation between ancient and recent human bones was assessed using Raman and FTIR-ATR spectroscopies. Each set of skeletal samples was analysed by these techniques, prior and after chemical washing, in order to determine the variations in bone´s chemical composition and crystallinity. Bone samples were collected from several independent sources: recent bones burned under controlled experimental conditions or cremated, and archaeological (XVII century and Iron Age). The effect of acetic acid, expected to impact mostly on carbonates, was clearly evidenced in the spectra of all samples, particularly in FTIR-ATR, mainly through the bands typical of A- and B-carbonates. Furthermore, as seen for crematoria and archaeological samples, acetic acid was found to remove contaminants such as calcium hydroxide. Overall, acetic acid treatment can be an effective method for removing carbonates (exogenous but possibly also endogenous) and external contaminants from bone. However, these effects are dependent on the skeletal conditions (e.g. post-mortem interval and burning settings). In addition, this chemical washing was shown to be insufficient for an unequivocal discrimination between recent and archaeological skeletal remains. Based on the measured IR indexes, only cremated bones could be clearly distinguished.

Burned and buried: A vibrational spectroscopy analysis of burial-related diagenetic changes of heat-altered human bones

OBJECTIVES

The analysis of burned human remains can be very challenging due to heat-induced alterations. Occasionally, human bones present these coupled with diagenetic changes, offering even more of a challenge, since there is a lack of studies regarding interactions between both taphonomic phenomena. With this study, we aimed to assess and document the effects of inhumation on the chemical composition of both unburned and burned human skeletal remains.

MATERIALS AND METHODS

We buried, for 5 years, four groups of human bone samples comprising unburned bones and bones experimentally burned at 500, 900, and 1050 °C. Periodic exhumations were carried out to collect bone samples to be analyzed through Fourier transform infrared spectroscopy in attenuated total reflectance mode, in order to calculate four chemical indexes: (1) crystallinity index (CI); (2) type B carbonates to phosphate index (BPI); (3) total carbonates (A + B) to carbonate B ratio (C/C); and (4) OH to phosphate ratio (OH/P).

RESULTS

After inhumation, CI and C/C of unburned bones and bones burned at 500 °C, and BPI of bones burned at 1050 °C did not vary significantly. However, the remaining indexes showed both relevant increments and reductions throughout observations, depending on burning temperature and index.

DISCUSSION

Our results suggest that diagenesis can have an effect in bone's molecular composition. However, these effects do not seem to significantly affect the conclusions that can be taken from the analysis of infrared bone spectra, at least in the case of inhumations with a duration of 5 years or less.

Reaching new heights: Testing the performance of metric approaches to estimate stature from burned skeletal remains

Bone heat-induced changes complicate osteometric stature estimation of human remains from forensic settings. The validity of current methods has not been tested to a great extent. Our aim was to determine how precise are stature estimations obtained from three different approaches, namely by using (i) Rösing's method (Rösing 1977), (ii) a 10% shrinkage correction factor (Strzałko et al. 1972) and (iii) chemosteometry (Gonçalves et al. 2020). For this purpose, pre- and post-burned head measurements from the humerus, radius and femur were used. The sample comprised 46 human skeletons of known sex and age-at-death. These were experimentally burnt to maximum temperatures ranging from 700 to 1100°C (attained after 90-188 min) for other research purposes. Stature estimations were performed through measurements in both pre-burned and burned bones using the three approaches and based on the method of Olivier and Tissier (1975). Mean absolute differences and the relative technical errors of measurements (TEM%) between the pre-burned and the estimations were calculated. Absolute mean differences indicated that the chemosteometric approach allowed for potentially more precise stature estimations than the other two procedures. However, the TEM% was very low for all approaches (smaller or close to 1%), and stature estimations were thus well within the error margin reported by Olivier and Tissier (1975). Results suggest that the chemosteometric approach enables more accurate predictions of the actual heat-induced shrinkage of each bone thus rendering more precise stature estimations. Nonetheless, the other procedures also provided quite reliable estimations although they require confirmation that the bone is calcined.

The burning maze: The potential value of the human bony labyrinth in estimating sex of calcined remains

Estimating sex from burnt human remains is a challenging task in bioanthropology, mainly due to their high level of alteration and fragmentation. Protected within the petrous part of the temporal bone, the bony labyrinth may be particularly valuable for assessing the sex of burnt remains. This prospective study aims at testing predictive models, already found reliable on unburnt bony labyrinths, to burnt specimens. Six discriminant functions were applied on six bony labyrinths of donated adult cadavers of known sex, before and after outdoor burning experiments. Comparisons between unburnt and burnt measurements were executed using Mann-Whitney U tests while shape and size differences induced by fire exposure were examined through a geometric morphometrics (GM) analysis. Predicted sex on unburnt bony labyrinths was consistent with known sex in five cases while a systematic misclassification for males was highlighted on burnt specimens. Higher values of shrinkage were found in males for two measurements included in the equations. GM analysis revealed significant differences in centroid size among males after calcination. Visualization of mean consensus of both female and male bony labyrinths evidenced a reduction in cochlear size and variations in the width and length of semicircular canals of burnt specimens. This exploratory study seems to confirm that designing sex estimation standards specifically for burnt bony labyrinth may be advisable. Understanding how the burning process could impact its morphology is highly recommended through further experiments on larger samples and in controlled environments.

Recent advances of vibrational spectroscopy and chemometrics for forensic biological analysis

Biological materials found at a crime scene are crucially important evidence for forensic investigation because they provide contextual information about a crime and can be linked to the donor-individuals through combination with DNA analysis. Applications of vibrational spectroscopy to forensic biological analysis have been emerging because of its advantageous characteristics such as the non-destructivity, rapid measurement, and quantitative evaluation, compared to most current methods based on histological observation or biochemical techniques. This review presents an overview of recent developments in vibrational spectroscopy for forensic biological analysis. We also emphasize chemometric techniques, which can elicit reliable and advanced analytical outputs from highly complex spectral data from forensic biological materials. The analytical subjects addressed herein include body fluids, hair, soft tissue, bones, and bioagents. Promising applications for various analytical purposes in forensic biology are presented. Simultaneously, future avenues of study requiring further investigation are discussed.

The impact of moderate heating on human bones: an infrared and neutron spectroscopy study

This study aims to analyse human bones exposed to low/medium temperatures (200-650°C) under experimentally controlled conditions, both oxidizing and reducing, using complementary optical and neutron vibrational spectroscopy techniques. Clear differences were observed between the aerobically and anaerobically heated bones. The organic constituents disappeared at lower temperatures for the former (ca 300°C), while they lingered for higher temperatures in anaerobic environments (ca 450-550°C). Unsaturated non-graphitizing carbon species (chars) were detected mainly for anaerobically heated samples, and cyanamide formation occurred only at 650°C in reducing settings. Overall, the main changes were observed from 300 to 400°C in anaerobic conditions and from 450 to 500°C in aerobic environments. The present results enabled the identification of specific spectroscopic biomarkers of the effect of moderate temperatures (less than or equal to 650°C) on human bone, thus contributing to a better characterization of forensic and archaeological skeletal remains subject to heating under distinct environmental settings. In particular, these data may provide information regarding cannibalism or ancient bone boiling and defleshing rituals.

Revisiting metric sex estimation of burnt human remains via supervised learning using a reference collection of modern identified cremated individuals (Knoxville, USA)

OBJECTIVES

This study aims to increase the rate of correctly sexed calcined individuals from archaeological and forensic contexts. This is achieved by evaluating sexual dimorphism of commonly used and new skeletal elements via uni- and multi-variate metric trait analyses.

MATERIALS AND METHODS

Twenty-two skeletal traits were evaluated in 86 individuals from the William M. Bass donated cremated collection of known sex and age-at-death. Four different predictive models, logistic regression, random forest, neural network, and calculation of population specific cut-off points, were used to determine the classification accuracy (CA) of each feature and several combinations thereof.

RESULTS

An overall CA of ≥ 80% was obtained for 12 out of 22 features (humerus trochlea max., and lunate length, humerus head vertical diameter, humerus head transverse diameter, radius head max., femur head vertical diameter, patella width, patella thickness, and talus trochlea length) using univariate analysis. Multivariate analysis showed an increase of CA (≥ 95%) for certain combinations and models (e.g., humerus trochlea max. and patella thickness). Our study shows metric sexual dimorphism to be well preserved in calcined human remains, despite the changes that occur during burning.

CONCLUSIONS

Our study demonstrated the potential of machine learning approaches, such as neural networks, for multivariate analyses. Using these statistical methods improves the rate of correct sex estimations in calcined human remains and can be applied to highly fragmented unburnt individuals from both archaeological and forensic contexts.

Profiling of human burned bones: oxidising versus reducing conditions

Complementary optical and neutron-based vibrational spectroscopy techniques (Infrared, Raman and inelastic neutron scattering) were applied to the study of human bones (femur and humerus) burned simultaneously under either aerobic or anaerobic conditions, in a wide range of temperatures (400 to 1000 °C). This is the first INS study of human skeletal remains heated in an oxygen-deprived atmosphere. Clear differences were observed between both types of samples, namely the absence of hydroxyapatite's OH vibrational bands in bone burned anaerobically (in unsealed containers), coupled to the presence of cyanamide (NCNH2) and portlandite (Ca(OH)2) in these reductive conditions. These results are expected to allow a better understanding of the heat effect on bone´s constituents in distinct environmental settings, thus contributing for an accurate characterisation of both forensic and archaeological human skeletal remains found in distinct scenarios regarding oxygen availability.

"Sex change" in skeletal remains: Assessing how heat-induced changes interfere with sex estimation

The true impact of heat-induced changes in human bone regarding their sex estimation has not been comprehensively documented having a potentially negative impact on forensic anthropology. The objective of this paper was to evaluate how heat exposure affects sex estimation based on both morphological and metric features. The study focused in both low-to-medium intensity burns and high intensity burns. Selected sexually dimorphic features were analysed in 51 experimentally burnt skeletons from the 21st Century Identified Skeletal Collection. Bones were burnt to maximum temperatures between 450 °C and 1050 °C achieved after 75 to 257 min. Morphological methods tested in this study comprised the recommendations for hipbone features from Buikstra and Ubelaker (1994) and from Bruzek (2002). On the other hand, metric references tested here were the ones from Wasterlain (2000), Curate et al. (2016) and Gonçalves et al. (2013) focused on the humerus, femur, calcaneus and talus. Agreement was tested with Gwet's AC1 test and was further assessed by calculating the relative amount of perfect agreements. Results demonstrated that heat-induced changes affected not only the scoring of morphological features burnt at high temperatures but also the scoring of features burnt at lower intensities. On the other hand, metric features were only considerably affected in high intensity burns, no major changes being documented for low-to-medium intensity burns. For low-to-medium intensity burns, the Bruzek and Curate et al. methods revealed a better agreement between the pre- and post-burning scores. For high intensity burns, better agreement was obtained by using the Bruzek (2002) and Gonçalves et al. (2013) methods. As expected, heat-induced warping, fracture and metric change had a major impact on the pre- and post-observations' agreement. Contrary to what has been systematically assumed over the years, this impact is also quite substantial in bones burnt at low-to-medium burn intensities so caution is advised during the analysis of this kind of burnt skeletal material.