٭Assistant Professor, ٭٭Professor and Head, Department of Oral Pathology and Microbiology, Yenepoya Dental College, Mangalore.
Forensic odontology is an investigative aspect of dentistry that analyzes dental evidence for human identification. Forensic odontology plays an important role in establishing the sex of victims with bodies mutilated beyond recognition due to major mass disaster. The dental literature in these above matters is voluminous but the analysis of the articles shows that varying opinions are available by different researchers. Thus the compilation and critical reading is necessary to understand the role of forensic odontology expert with regard to sex determination using dental records.
The study of teeth reveals a lot concerning forensic medicine. Particularly it is useful in human identification. Forensic Odontology tells us a lot about determination of age from various methods. In addition to determination of age, sex can also be determined from the teeth1.
Determination of sex using skeletal remains presents a great problem to forensic experts especially when only fragments of the body are recovered. Forensic dentists can assist other experts to determine sex of the remains by using teeth and skull.
Various features of teeth, like morphology, crown size, root lengths etc. are characteristic for male and female sexes. There are also differences in the skull patterns. These will help a forensic odontologist to identify the sex. New developments like PCR amplification etc. will assist in accurately determining the sex of the remains2.
Forensic odontology plays an important role in establishing the sex of victims with bodies mutilated beyond recognition due to major mass disasters3.
1. Visual method or clinical method.
2. Microscopic methods.
3. Advanced methods.
Teeth may be used for differentiating sex by measuring their mesiodistal and buccolingual dimensions4. This is of special importance in young individuals where skeletal secondary sexual characters have not yet developed5. Studies show significant differences between male and female permanent and deciduous tooth crown dimension. One is reminded that tooth size, or odontometrics, is under considerable influence of the environment. Such measurements are, therefore, population specific, and do not apply to the world at large.
Amongst teeth, mandibular canines show greatest dimensional difference with larger teeth in males than in females2. Premolars, first and second molars as well as maxillary incisors are also known to have significant differences4.
In the field of forensic odontology, permanent canine teeth and their arch width (distance between the canine tips) contribute to sex identification through dimorphism. The study of permanent mandibular and maxillary canine teeth offers certain advantages in that they are the least extracted teeth, are less affected by periodontal disease and the last teeth to be extracted in respect of age (Bossert and Marks, 1956; Krogh, 1968).
The dimensions of canine teeth have been studied by several methods, including Fourier analysis (Minzuno, 1990), Moire topography (Suzuki et al, 1984) and the measurement of linear dimensions such as mesiodistal width, bucco-lingual width and inciso-cervical height (Garn et al., 1967; Anderson and Thompson, 1973; Rao et al., 1988a,b). The use of Fourier analysis and Moire topography were limited to small samples whereas measurement of the linear dimensions of canine teeth was used in large populations because it is simple, reliable, inexpensive and easy to perform6.
A study by Anderson and Thompson7 (1973) showed that mandibular canine width and inter-canine distance was greater in males than in females and permitted a 74-3% correct classification of sex.
Garn et al.8 (1973) studied sexual dimorphism by measuring the mesiodistal width of canine teeth in different ethnic groups. They concluded that the magnitude of canine teeth sexual dimorphism varies among different ethnic groups. Furthermore, the mandibular canine showed a greater degree of sexual dimorphism than the maxillary canine.
However, other investigators (Kuwana, 1983; Minzuno, 1990) reported that, in a Japanese population, the maxillary canine showed a higher degree of sexual dimorphism compared to the mandibular canine. Thus, controversy exists related to the degree of sexual dimorphism between maxillary and mandibular canines in different ethnic groups.
Rao et al9 (1988) reported that the mesiodistal width of mandibular canines was significantly greater in males than in females.
In another study of Rao et al 198810 88% accuracy of sex identification was reported. The crown length was less significant in establishing sex identity.
Sherfudhin H et al6 (1996) investigated the occurrence of canine tooth dimorphism in Indian subjects and the use of two statistical methods of evaluation compared. These were the methods of N.G. Rao and co-workers published in 1988 and quadratic discriminant analysis for correct classification of sex. Parameters considered were (i) the mesiodistal width of maxillary and mandibular canines, (ii) the maxillary canine arch width (intercanine distance) and (iii) the mandibular canine arch width. The results indicated significant dimorphism of the maxillary and mandibular canine teeth. When the results of the arch widths were subjected to the two statistical methods, differing results were obtained in the accuracy of sex classification. The percentage of correct classifications of sex was higher when using quadratic discriminant analysis. In another study, Iscan Kedici11 (2003) could accurately establish sex in 77% of the cases using maxillary and mandibular canines, and mandibular second molar.
The role of the maxillary canine arch width in establishing sex identity has not been reported in the literature6.
The sexual dimorphism specific to canines has been explained by Eimerl and DeVore on the basis of their function which, from an evolutionary point of view, is different from other teeth. During the evolution of primates, there was a transfer of aggressive func¬tion from the canines in apes to the fingers in man. Until this transfer was complete, survival of the species was dependant on the canines, especially those of males. Of late, researchers are trying to determine the influence of the X- and Y-chromosomes on tooth morphology. While the role of sex chromosomes in dental development has been proved, Scott considers that there is little dimorphism apparent at a phenotypic level4.
Using optical scanner and radiogrammetric measurements on mandibular permanent teeth sex determination can be done with 80% accuracy by measuring root length and crown diameters2.
In addition to absolute tooth size, tooth proportions have been suggested for differentiating the sexes. Aitchison12 presented the ‘incisor index’ (Ii), which is calculated by the formula Ii = [MDI2/MDI1] × 100, where MDI2 is the maximum mesiodistal diameter of the maxillary lateral incisor and MDI1 is the maximum mesiodistal diameter of the central incisor. This index is higher in males, confirming the suggestion of Schrantz and Bartha that the lateral incisor is distinctly smaller than the central incisor in females.
Another index, the ‘mandibular canine index’ proposed by Rao10 and associates has given an accurate indication of sex in an 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 + S.D.) in males – S.D)] / 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 per cent. However, relative to the near 100 per cent accuracy using pelvis and skull, sexing by odontometrics is relatively poor4.
The odontometric difference between males and females is generally explained as a result of greater genetic expression in males.
|Tooth no||MESIODISTAL BUCCOLINGUAL|
Iscan and Kedici11 caution that an overlap exists between male and female tooth dimensions, and this makes accurate diagnosis of sex challenging, even for experienced dentists. They emphasize that success is greater when all available teeth are used.
In addition to the canines being the most sexually dimorphic teeth in terms of size, Scott and Turner II13 highlight that the ‘Distal Accessory Ridge’, a nonmetric feature on the canine” is the most sexually dimorphic crown trait in the human dentition, with males showing significantly higher frequencies and more pronounced expression than females”. Rao and Rao have reported greater incidence of four-cusps (absence of the distobuccal cusp or distal cusp) on the mandibular first molar in females (40.6 per cent) compared to males (16.2 per cent) in a south Indian population. They cite Anderson and Thomas who opine that the reduction in the number of cusps is a reflection of an evolutionary trend towards overall reduction in the size of the lower face, with male apparently resisting this trend.
Sex can also be determined by the study of X & Y chromosomes in the cells which are not undergoing active division. Presence or absence of X chromosome can be studied from buccal smears, skin biopsy, blood, cartilage, hair root sheath, and tooth pulp. After death it persists for variable periods depending upon the humidity and temperature in which tissue has remained. X chromatin and intra-nuclear structure is also known as Barr body as it was first discovered by Barr and Bertam (1949). It is present as a mass usually lying against the nuclear membrane in the females14.
In a study done by Nirmal Das et al15 (2004) it has been shown that up to a period of four weeks after death we can determine the sex accurately from the study of X & Y chromosomes keeping in view the variation of temperature and humidity.
Wittakar16 and coworkers determined sex from necrotic pulp tissue stained by quinacrine mustard using fluorescent Y chromosome test for maleness and claimed that upto 5 weeks sex determination can be done with high degree of accuracy.
It was found that in cases after fires, high impact crashes and explosions fragmentation and thermal trauma renders other methods impossible to determine sex of the remains except the above said method from pulp. Pulp tissue cells become embedded firmly into the dried fibrosis matrix. Duffy et al17 have shown that Barr bodies and F bodies of Y chromosomes are preserved in dehydrated pulp tissues upto one year and pulp tissues retain sex diagnostic characteristics when heated upto 100C for 1 hour.
Polymerase chain reaction (PCR) is a method of amplifying small quantities of relatively short target sequences of DNA using sequence-specific oligonucleotide primers and thermostable Taq DNA polymerase18.
The teeth can withstand high temperature and are used for personal identification in forensic medicine13. In the case of few teeth or missing dental records, there is not enough information to identify the person. The dental pulp enclosed by the hard tissue is not influenced by temperature, unlike the buccal mucous membrane, saliva, and calculus.
A procedure utilizing Chelex 100, chelating resin, was adapted to extract DNA from dental pulp. The procedure was simple and rapid, involved no organic solvents, and did not require multiple tube transfers. The extraction of DNA from dental pulp using this method was as efficient, or more so, than using proteinase K and phenol-chloroform extraction. In a study by Tsuchimochi T et al18 (2002), they used Chelex method to extract DNA from the dental pulp and amplified it with PCR and typing at Y-chromosomal loci to determine the effects of temperature on the sex determination of the teeth.
Hanaoka et al19 (1996) conducted a study to determine sex from blood and teeth by PCR amplification of the alphoid satellite family using amplification of X (131 bp) and Y (172 bp) specific sequences in males and Y specific sequences in females. It was showed to be a useful method in determining the sex of an individual.
Sivagami and coworkers20 (2000) prepared DNA from teeth by ultrasonication, and subsequent PCR amplification, they obtained 100 per cent success in determining the sex of the individual.
Amelogenin or AMEL is a major matrix proteins found in the human enamel. 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 X chromosome and AMEL gene that encodes for male amelogenin is located on the Y chromosome. The female has two identical AMEL genes or alleles, whereas the male has two different AMEL genes. This can be used to determine the sex of the remains with very small samples of DNA2.
Address For Correspondence:
Dr. Hemanth M
Assistant Professor, Dept. of Oral Pathology,
Yenepoya, Dental College and Hospital
Deralakatte, Mangalore 575 018