Cementum as a source of DNA in challenging forensic cases
Introduction
Since the early 1990s, DNA technology has been utilized as a powerful tool for identification, paternity testing, criminal investigation, and other forensic investigations.1, 2, 3 As the genetic material in soft tissues rapidly degrades post-mortem, teeth and bones are of interest to yield sufficient DNA for identification.4,5 Due to their longevity, durability, and endurance against postmortem degenerative changes, teeth were recognized as a valuable source of forensic data many years ago.6, 7, 8 Adverse environmental conditions and associated post-mortem changes play a critical role in determining the proper forensic method for investigation.9 Prior to analyzing DNA, it is sometimes difficult to estimate the effect of environmental factors on tissues and whether these structures are still sufficient for genotyping.9
Interestingly, the yield of DNA isolated from various dental tissues is significantly variable in quantity and quality.10 Being an acellular tissue, enamel is devoid of DNA.4,11 As a rule, dentin does not contain nucleated cell bodies. Rather, dentin consists of parallel dental tubules containing the processes of the odontoblasts, which are the cells responsible for dentin formation.12 Furthermore, according to the presence or absence of cells, two types of cementum can be recognized. First, acellular cementum predominates in the cervical portion of the root and plays a key role in connecting the tooth to the adjacent periodontal ligament.
Second, cellular cementum mainly covers the apical root and can be encountered in the furcation area.12 It has been hypothesized, that the latter plays a role in the adaptation to occlusion and post-eruptive movement of the tooth.13
In the light of this information, pulp and cellular cementum are the main sources of nuclear DNA in dental samples.11,14 Although pulp is considered the best source of DNA in intact fresh teeth, the yield of DNA is significantly affected by several factors, such as dental diseases, advanced age, and post-mortem cellular degeneration especially in moist environments.10,14,15 This publication seeks to highlight the importance of cementum as a source of nuclear DNA and to clarify the variability of DNA yield from dental tissues. Cementocytes, our target cells, are comparably well preserved due to the protection afforded by the cementum matrix itself.
Section snippets
Case 1
In October 2015, during sonar training of a diving group, six cars were located under water at the east bank of the Elbe River, which is a large river in the northeastern part of Germany. Five of these sites were well known by the Water and Shipping Authority (Schifffahrtsamt) for about 20 years. However, one vehicle was unknown. The diving group sought the unknown car and found a male human body inside of the car. After recovering the car from the water, the plate number of the car was
Materials and methods
After extracting the selected teeth, horizontal sections were cut. Similar to the Gaytmenn and Sweet guidelines,17 with little modification, two horizontal sections were made to separate the teeth into three main parts: the crown, the coronal part of the root, and the apical part of the root (Fig. 4a). Several studies have found that DNA extracted from the root is better than DNA extracted from the crown.11,17,18 Therefore, DNA was isolated only from the root portion.
Following the
Case 1
The geographical location, the plate number of the car, and the wallet of the dead driver effectively accelerated the search for ante-mortem records.19 However, these means of identification are supportive but not conclusive. Thus, DNA is required for identification.
The genetic profile of the missing elderly man had been generated from samples retrieved from his hair comb in the criminal laboratory. Compared with the genetic profile of the missing person, the DNA profile retrieved from the
Discussion
Owing to their morphologically, anatomically, and histologically unique structure and their protected location,14 teeth are more likely than bones to withstand environmental adversities over long periods. Therefore, teeth demonstrate less DNA degradation and contamination than bones.10,21, 22, 23 However, the quantity of DNA retrieved from teeth varies significantly; not only between teeth or between comparable teeth from the same person, but also in different parts of the same tooth.10
Several
Conclusion
Cementum represents an essentially lucrative source of DNA to maximize DNA yield from dental samples, especially in challenging conditions. Moreover, the anatomical and histological intra- and inter-individual variations of the cementum structure in terms of thickness and density of cellular inclusion have to be taken into consideration when interpreting the results.
Ethical approval
All procedures performed in this study were in accordance with the ethical standards of the institutional and national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
Funding
The research project was funded by German Academic Exchange Service (DAAD) (grant number: 57169181).
Conflicts of interest
The authors declare that they have no conflict of interest.
Acknowledgments
The authors would like to thank the staff of the Institute of Osteology and Biomechanics, specifically Elke Leicht and Dr. Michael Hahn, for the valuable assistance in histological examination. Many thanks to Dr. Robert Martin at the Institute of Blood Group Serology and Genetics for supplying the genetic profile generated from the alleged daughter to make our comparison. The authors thank Elizabeth Zimmermann for language editing.
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