Comparative study of STR, SNP, and mtDNA recovery in teeth after thermal exposure

High-temperature exposure of biological samples at fire scenes induces significant DNA degradation, thereby complicating accurate identification via DNA profiling. Teeth exhibit relative heat resistance due to their high mineral content; however, the critical temperature-time thresholds and the differential stability of nuclear DNA (nDNA) and mitochondrial DNA (mtDNA) in dental pulp and surface bloodstains remain unclear. We exposed samples to 200℃-500℃ for 10 and 20 min. STR-CE and MPS were applied for genotyping, and we calculated marker detection rates and mtDNA sequencing coverage. At 200 °C, extending the heating duration from 10 to 20 min reduced STR detection from 97.09% to 81.39%, SNP from 99.53% to 91.08%, and mtDNA coverage from 99.96% to 27.26%. After 10 min at 220 °C, nDNA retained full detectability at 100%, and mtDNA coverage reached 76.48%. Prolonging treatment to 20 min at 220 °C lowered STR to 66.99%, SNP to 99.3%, and mtDNA coverage to 28.84%, demonstrating that exposure duration exerts a stronger effect on DNA integrity than temperature within the 200-220 °C range. No genetic markers were recoverable following 10 min of heating at 250 °C. Bloodstains on tooth surfaces exhibited inferior thermal tolerance. After 20 min at 200 °C, STR and SNP detection rates fell to 72.58% and 88.38%, whereas mtDNA became undetectable. Heating for 10 min at 220 °C yielded a STR detection rate of 97.5% and full SNP detection at 100%, yet mtDNA coverage dropped to merely 16.9%; all markers were undetectable after 20 min at the same temperature. Mechanistically, mtDNA shows poorer thermal stability than nDNA, attributable to the absence of histone protection, high AT proportion, and heat-induced disruption of its circular conformation; its high copy number fails to offset such structural drawbacks. In summary, dental pulp should be prioritized for DNA sampling from fire-exposed dental specimens, exposure duration should be referenced for specimen quality assessment, and short-fragment MPS-SNP is preferred for severely degraded samples to improve forensic individual identification efficiency.