INTRODUCTION
Forensic dentistry is an important branch of forensic medicine which contributes immensely in solving difficult criminal cases and also in identification of individuals in mass disasters. In recent times, the world has experienced many mass disasters like acts of terrorism, bombings, earthquakes, hurricanes, tsunami, railway accidents, air crashes and other transportation mishaps. In all these circumstances, as the bodies are skeletonized, decomposed, burned, charred or destroyed beyond visual recognition exact identification of an individual becomes difficult. As teeth and jaws resist extreme temperature conditions and can provide a valuable clue in identification of an individual, dental evidence always plays a key role for human identification in situations like natural and man-made disasters.1, 2
Forensic odontology or forensic dentistry was defined by Keiser-Nielson in 1970 as “that branch of forensic medicine which in the interest of justice deals with the proper handling and examination of dental evidence and with the proper evaluation and presentation of the dental findings”3
First and most crucial step in human identification is gender determination as it immediately excludes half of the population. As gender determination becomes a great problem using skeletal remains, forensic experts can help to determine the gender of the remains by using various features of teeth, like morphology, crown size, root lengths etc., which are characteristic for males and females. Advanced techniques like PCR amplification will assist in determining the gender of the remains more accurately.4
Classification of methods used for sex determination
I. Visual method or clinical method
II. Microscopic methods
III. Advanced methods
Differences between genders with respect to:
a. Tooth size
b. Root length and crown diameter
c. Using canine diamorphism
d. Tooth morphology and sexing
e. Dental index
f. Odontometric differences
a. Sex determination using Barr bodies
a. Sex determination using Polymerase Chain Reaction (PCR)
b. Sex determination using enamel protein.5
Another index, the “mandibular canine index” proposed by Rao et al associates have given an accurate indication of gender in the Indian population. Using the mesiodistal (m-d) dimension of the mandibular canines, these researchers obtained the formula:
[(Mean m-d canine dimension + (Mean m-d canine dimension in female + standard deviation [SD]) in males ? SD)]/2.
The value obtained using this formula was 7.1, i.e., 7.1 mm is the maximum possible mesiodistal dimension of mandibular canines in females. The same dimension is greater in males. The success rate of determining sex using the above formula was close to 89%.
Though visual or clinical methods are simple and rapid methods for gender determination, they provide only minor details and they can act only as adjuncts to other methods and are not highly reliable. Reliability of visual method is compromised due to factors like regressive alterations of teeth, aging, defects in enamel and dentin formation due to syndrome association, nutritional and environmental causes and so on. Clinical method is useful when other methods of gender prediction cannot be performed.4, 5
Mitochondrial DNA is another type of material that can be used for human identification. Its main advantage is the high number of copies per cell (from hundreds to thousands of organelles). When the extracted DNA samples are too small or degraded, such as those obtained from skeletonized tissues, the likelihood of obtaining a DNA profile from mitochondrial DNA is higher than that with any marker found in genomic DNA, but the disadvantage is that mitochondrial DNA is exclusively matrilineal and hence less informative and can be used for comparision of DNA with parent, sibling or relatives, but not appropriate for gender determination.10
Amelogenin or AMEL is a major matrix proteins found in human enamel belongs to a family of extracellular matrix proteins. It has a different signature (or size and pattern of the nucleotide sequence) in male and female enamel. The AMEL gene that encodes for female amelogenin is located on the distal short arm of X chromosome (AMELX) in p22.1-p22.3 region and AMEL gene that encodes for male amelogenin is located near the centromere of Y chromosome (AMELY) at p11.2 region. Hence, females have two identical AMEL genes or alleles, whereas males have two different AMEL genes. This can be used to determine the gender of the remains with even very small samples of DNA.5, 11
Sex-determining region Y (SRY) is located on the Y chromosome at p11.31 within a 35 kb sex- determining region of the Y chromosome adjacent to the pseudoautosomal region. SRY encodes a transcription factor that is a member of the high mobility group (HMG)-box family of DNA binding proteins and contains the conserved DNA-binding motif indicative of HMG proteins. The SRY gene has been shown to be integral to the development of male reproductive organs. It is the only sex typing marker currently in use whose gene products directly affect biological sex development. The strong association of the products of SRY with male phenotype suggests that SRY is the most accurate available marker for prediction of male appearance and is often used as a confirmatory test when an amelogenin test produces unexpected results.11
Both microscopic methods and advanced methods are highly reliable in gender determination using the dentition. The use of microscopic and advanced methods in gender prediction is expensive, time-consuming, laborious technique of DNA isolation when compared with clinical methods of gender determination. In addition, there are common problems with DNA analysis from human remains due to decomposition and exposure to environmental factors such as high temperatures, humidity, and many organic compounds may result in DNA degradation. Hence, the role of clinical, microscopic and advanced method is equally important in gender prediction when anyone of the method is not applicable due to inevitable circumstances.5
CONCLUSION
Forensic dentistry plays a major role in the identification of those individuals who cannot be identified visually or by other means. Principal advantage of dental evidence is that, like other hard tissues, it is often preserved after death and teeth are the most durable parts in the body which can survive virtually intact for longer durations after other soft tissue and skeletal tissue have been destroyed by decay or incineration. Thus, dental tissues play a major role in identifying the gender of an individual.