The oral cavity harbors one of the most diverse microbiomes in the human body. It has been shown to be the second most complex in the body after the gastrointestinal tract. Upon death, the indigenous microorganisms lead to the decomposition of the carcass. Therefore, the oral cavity and gastrointestinal tract microbiomes play a key role in human decomposition. The aim of the present study is to monitor the microbiome of decaying bodies on a daily basis and to identify signature bacterial taxa, that can improve postmortem interval estimation. Three individuals (one male and two female) donated to the University of Tennessee Forensic Anthropology Center for the W.M. Bass Donated Skeletal Collection were studied. Oral swab samples were taken daily throughout the different stages of cadaveric putrefaction. DNA was extracted and analyzed by next-generation sequencing techniques. The three cadavers showed similar overall successional changes during the decomposition process. Firmicutes and Actinobacteria are the predominant phyla in the fresh stage. The presence of Tenericutes corresponds to bloat stage. Firmicutes is the predominant phylum in advanced decay, but the Firmicutes community is a different one from the predominant Firmicutes of the fresh stage. This study depicts the thanatomicrobiome successional changes in the oral cavity, and highlights its potential use in forensic cases as a quantitative and objective approach to estimate postmortem interval, from an ecological rationale.

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There are several methodologies available to estimate time since death based on different changes that a corpse undergoes after death. However, these methods are imprecise due to the decomposition process being affected by several factors, principally temperature and humidity. Current trends for the determination of the Postmortem Interval (PMI) attempt to estimate the PMI in a quantifiable manner, based on chemical changes on and in the body, summarized in the field of “thanatochemistry”. Although these methodologies have improved PMI estimates, additional research has been developed to increase the accuracy and precision of this determination. As a result, the fields of “thanatobiology” and “thanatomicrobiome” have emerged. Thanatobiology is based on the estimation of the PMI from DNA/RNA degradation, signaling pathways of cell death, and protein analysis. Thanatomicrobiome refers to changes in the bacterial communities as a consequence of the decomposition process. Although both approaches seem to improve PMI estimates, applications of thanatobiology methodologies are more appropriate in the first phases of decomposition, while thanatomicrobiome analyses are applicable in advanced stages. Further research is needed in these new fields in order to establish their applicability in forensic cases. This is a review of the current state-of-the-art methodology in these two subfields.

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Age-at-death estimation is one of the main goals in forensic identification, being an essential parameter to determine the biological profile, narrowing the possibility of identification in cases involving missing persons and unidentified bodies. The study of dental tissues has been long considered as a proper tool for age estimation with several age estimation methods based on them. Dental age estimation methods can be divided into three categories: tooth formation and development, post-formation changes, and histological changes. While tooth formation and growth changes are important for fetal and infant consideration, when the end of dental and skeletal growth is achieved, post-formation or biochemical changes can be applied. Lamendin et al. in J Forensic Sci 37:1373-1379, (1992) developed an adult age estimation method based on root transparency and periodontal recession. The regression formula demonstrated its accuracy of use for 40 to 70-year-old individuals. Later on, Prince and Ubelaker in J Forensic Sci 47(1):107-116, (2002) evaluated the effects of ancestry and sex and incorporated root height into the equation, developing four new regression formulas for males and females of African and European ancestry. Even though root transparency is a key element in the method, the conditions for measuring this element have not been established. The aim of the present study is to set the light conditions measured in lumens that offer greater accuracy when applying the Lamendin et al. method modified by Prince and Ubelaker. The results must be also taken into account in the application of other age estimation methodologies using root transparency to estimate age-at-death.