Say Cheese! A New Method Obtaining DNA from Dental Tissue

Credit Source for Photo: Smiles by Gallery of Smiles NJ

When bodies are exposed to adverse conditions such as explosions or natural disasters, scientists must combat the extensive chemical and environmental degradation to access and analyze the biological material contained within. Often, only teeth and bone contain enough DNA  to identify the victims, but even with access to these materials, obtaining DNA with high purity (clean samples) and integrity (non-degraded samples) remain challenging.

A tooth’s DNA is located in the dental pulp tissue and the dental root (Fig 1). To get the genetic material out of the tissue, scientists first clean the teeth with concentrated bleach and then freeze them with liquid nitrogen, finally grinding them into a fine powder for DNA extraction. However, as one might imagine with a bleaching/freezing/grinding method, the stringent processing deteriorates the root cement and destroys the soft tissue to get to the DNA. This gives the scientist a single opportunity to extract as much DNA as possible, with little to no chance of reanalysis. Improving the tooth pre-treatment method would lead to greater and less tenuous recovery of DNA (and tissue) for better analysis with current forensic equipment.

Figure 1.  Forensic scientists are interested in the DNA found in the root and pulp tissue for human identification purposes.  Photo Credit: Tooth anatomy by BruceBlaus from Wikimedia Commons

Dr. Carolina Inostroza and her team  from  the University of the Andes proposed a less destructive extraction method for dental remains  based on  all-in-one kits they developed, called the Dental Forensic Kit® and Quick Extract™ FFPE DNA extraction kit . These kits can be used on both nuclear DNA, which we use to create unique DNA profiles of 13 short repeat sections of the human genome, and mitochondrial DNA, which we use to identify people via their maternal line, making the recovery utility multifunctional.  The speed and reliability of extraction is critical for faster identification and communication with families of the victims.

The Dental Forensic Kit® exposes the tooth in question to our body’s natural conditions and rehydrates it from the pulp to the root, allowing more ample retrieval of the genetic material with their FFPE DNA extraction kit. The second kit introduces a softer environment to release the DNA from tissue sections, and overcomes inhibitors during amplification.  Inostroza and her lab demonstrated that these kits reduced laboratory time significantly compared with current practices, with their complete workflow taking approximately 28.6 hours until a DNA profile is generated. In addition, their non-reliance on specialized equipment effectively reduced the cost of processing even compared to automated methods! Importantly, the remaining tooth sample, normally destroyed at this point with current methods, can be used for additional testing or returned to the victim’s relatives.

In  mass disasters, investigators want to quickly and reliably generate DNA  profiles that match reference samples to identify the numerous victims.  The scientists’ proposed workflow shows more complete identity profiles than not (60% complete profiles) and no contamination between samples, which can complicate data interpretation and courtroom presentation.  However, even with partial or incomplete profiles, there is still the possibility of success with other tissues. For instance, obtaining data on  13 of the 21 STR markers for complete DNA profiles gives robust partial profiles that can match a reference sample with high probability .  When testing other tissues like skin and bone, the partial profile from the tooth sample can be combined with identity profiles obtained from the skin and bone samples to increase the probability of a match.

Methods such as Inostroza’s have been used before; however, this method significantly improves the efficiency and utility of all DNA samples obtained from teeth.  The possibilities of yielding viable results in forensic samples, which are known to be challenging and often degraded, increase by generating two distinct dental tissues from a single sample using the two kits described.  The kits proved to be quicker, easier and more cost-effective than current methods, and could generate DNA identity profiles at the high quality required for casework.

TitleDental Forensic Kit (DFK®) and Quick Extract™ FFPE DNA extraction kit, a new workflow for obtaining dental DNA for human genetic identity
AuthorsCarolina Inostroza, Patricio Carrasco, Marianela Godoy, Gianna Gatti and Beatriz Paulino
JournalForensic and Legal Medicine
PublisherElsevier Ltd and Faculty of Forensic and Legal Medicine
Year2020
Linkhttps://www.sciencedirect.com/science/article/pii/S1752928X20300998

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