Effect of sodium hypochlorite decontamination on the DNA recovery from human teeth

Genetic identification of skeletal human remains is often realized by short tandem repeat (STR) genotyping of nuclear DNA. Dental DNA is preferred to DNA from bone for the better protection of the endogenous DNA. Especially if whole tooth grinding is intended to access the DNA, contaminations with exogenous DNA have to be avoided. The immersion of the tooth in sodium hypochlorite (NaOCl, known as bleach) is one common procedure to clean the outer surface from extraneous DNA and PCR inhibitors. To investigate the impact of bleaching on endogenous DNA and the decontamination success, 71 recently extracted teeth were differently treated with sodium hypochlorite (2.5 or 5.0% NaOCl for 30 or 60 s, 5.0% NaOCl for 10 min, and control group) in the beginning of the extraction process, whereas equally handled afterwards. Quantitative and qualitative evaluation of the extracted DNA was performed. There was a great variation for the DNA concentration of the extracts even within a group of the same NaOCl treatment. Complete DNA profiles from single persons with alleles for the 16 ESS (European Standard Set) STR loci were obtained for all regarded teeth. A statistically significant difference between the DNA yields of the treatment groups was not determined. Moreover, a negative effect of NaOCl (2.5% and 5.0%) on the DNA recovery could not be observed. Significant larger amounts of DNA were extracted from anterior teeth in contrast to posterior teeth.