Keywords

Forensic genetics, dental DNA, thermal degradation

Background

In forensic contexts involving fire, explosions, or other high-temperature events, teeth are often among the few biological materials that remain intact. Their structural resilience makes them valuable for postmortem identification via DNA analysis. However, the limits of DNA recoverability from heat-exposed dental tissues remain a key concern, particularly in obtaining STR profiles crucial for human identification.

Material and method

Clinically healthy third molars were collected from six donors (three men and three women, aged 20–28 years) with informed consent and in accordance with the ethical protocols of the University. Samples were subjected to controlled thermal stress at 200°C, 300°C and 400°C for durations of either 15 or 60 minutes. Subsequently, DNA was extracted using Magnetic Beads Bone DNA Extraction Kit (Changchun Bokun Biotech Co) and quantification was performed using both spectrophotometry and Real-time PCR (qPCR) (QuantStudio™ 5 Real-Time PCR System). A comparative analysis was performed to evaluate the efficiency of STR profiling via Capillary Electrophoresis (CE) versus Next-Generation Sequencing (NGS).

Results

A clear correlation exists between increased temperature/exposure time and DNA degradation. At 200°C, DNA concentrations (0.064 to 2.595 ng/µl) were sufficient to yield positive profiles with both CE and NGS. At 300°C, DNA quantification values dropped significantly to near-zero levels (0.002–0.003 ng/µl); at this threshold, CE failed to produce results (negative), whereas NGS was still capable of recovering partial profiles. Notably, at 400°C, while spectrophotometric recovery remains feasible as a preliminary yield, qPCR quantification was 0 ng/µl, and no profiles were obtained with either methodology. These findings confirm that a quantification value of zero serves as a definitive limit for recovery regardless of technology. Furthermore, our observations align with existing literature indicating that DNA extraction becomes particularly challenging above 400°C, resulting in rapid molecular degradation of DNA.

Conclusion

This study highlights that NGS provides superior sensitivity compared to CE for the analysis of severely heat-degraded dental samples, particularly when DNA show low DNA quality and quantity. These findings underscore that the success of forensic identification is strictly dependent on the specific thermal treatment (temperature and duration) the dental remains have endured. Consequently, NGS should be the preferred method when standard STR profiling fails due to thermal degradation.

Authors

• Ana María Salazar (a Universidad de Concepción, Departamento de Patologia y Diagnóstico, Facultad de Odontología. b Universidad de Alcalá, PhD Student in Forensic Sciences., Chile)
• Luis Felipe Montoya (c Universidad de Concepción, Departamento de Ingeniería Química, Chile)
• Ariel Castro (d Universidad de Concepción, Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Chile)
• Anna Barbaro (e SIMEF Forensic 89128 Reggio Calabria, Italy.  f Instituto Universitario de Investigacion en Ciencias Policiales, Universidad de Alcala, Calle Libreros, 27, 28801 Alcala de Henares., Spain)