Establishment of Sexual Dimorphism in North Indian Population by Odontometric Study of Permanent Maxillary Canine

Sex differentiation in forensic investigation utilises craniofacial morphology, tooth dimensions and DNA analysis [3,4]. It has been suggested that odontometrics plays an important role in determination of sex in young individuals where secondary sexual characteristics have not developed. In addition, the resistance of teeth to postmortem insults render them as a valuable tool in forensic investigation [4].


Introduction
Sex determination is an important step in determining the biological profile of unidentified human remains, since a correct result would automatically exclude about half the population in search operations [1]. "Sexual Dimorphism" refers to those differences in size, stature and appearance between male and female that can be applied to dental identification [2].
Sex differentiation in forensic investigation utilises craniofacial morphology, tooth dimensions and DNA analysis [3,4]. It has been suggested that odontometrics plays an important role in determination of sex in young individuals where secondary sexual characteristics have not developed. In addition, the resistance of teeth to postmortem insults render them as a valuable tool in forensic investigation [4].
According to Boaz et al. (2009) teeth are known to have sexual dimorphism [5]. Sex determination using dental features is mainly based upon the comparison of tooth dimensions in males and females [6]. The mesiodistal diameter of mandibular and maxillary canines provides evidence of sex determination due to dimorphism [7]. Bosset and Marks and Krogh [8,9] stated that the study of the canine teeth offers certain advantages. They are the least frequently extracted teeth and being less affected by periodontal disease. Canine teeth have also been reported to survive in air and hurricane disasters [10].
Few studies on dental sex dimorphism exist for South-Asian populations which includes the 'canine index' formulated by Rao et al. in Indians [11,12]. The objectives of the present study were to investigate whether dimorphism of permanent maxillary canine teeth as well as inter-canine width play a role in establishing sex identity in North Indian Population.

Materials and Methods
Present study was carried out at Department of Oral and Maxillofacial Pathology, King George's Medical University, Lucknow, India after the approval from the ethical committee of the institute.
The sample for the study comprised of 180 dental casts that belonged to 90 females and 90 males, all students and patients reporting at OPD at the King George's Medical University, Lucknow, UP.
Following verbal consent, impressions of the upper arch were made using alginate material and casts poured in dental stone. The study included young adults with an average age of 23. 13
Mean MCI values did not show a significant difference between two sides (right and left) for the both genders (p>0.05, NS). Mean age of males was found to be significantly higher as compared to that of females (p=0.00011).For both right and left sides, mean MCI of males was found to be significantly higher as compared to that of females however Mean inter canine width of males was also found to be significantly higher in males as compared to females. Similar observation was found for ICW, also (p=0.0001) ( Table 1).
On evaluatry mean maxillary canine index of right and left sides, significantly no significant difference was observed between two genders (p=0.13 and 0.41 respectively)or between two sides within same gender (p>0.05, NS).
Limitation: Limitation of SD canine and in present study is that it assumes a high intregender variability and show 100% dimorphism only when value of Xm is twice the value of Xf, moreover in case of for male and females respectively and one would have assumed that the dentitions were relatively intact and unaltered by the vagaries of pathology and physiologic wear.
Method for the cast preparation are first impression of upper arch were made using alginate material and then cast poured in dental stone.
A few teeth in many of the casts did, however, present restorations, caries, excessive wear or casting defects. If such obstructions impeded tooth measurements, they were not included in the analysis. Mesiodistal diameter (MD) and inter-canine width (ICW) measurements of permanent maxillary canine were obtained using a sliding digital calliper with calibration of 0.01 mm. The measurements were performed by one person and all values were rounded to two decimal places ( Figure 1).

Mesiodistal Measurement (MD)
The greatest mesiodistal dimension between the approximate surfaces of the crown was measured with the calliper beaks placed occlusally along the long axis of the tooth. In case of tooth rotation or malposition, the measurements were taken between points on the approximate surfaces of the crown where it was considered that contact with adjacent teeth would have normally occurred.

Inter-Canine Width (ICW)
The other measurement consisted of the distance between the tips of the two maxillary canines in a straight line. To measure the distance, each of the calliper beak was kept over the centre of the tip of canine tooth of each side.

Maxillary Canine Index (MCI)
Maxillry Canine Index=Mesiodistal crown width of maxillary canine/Maxillary inter-canine width  value being more than twice, it show a >100% dimorphism which is impractical.
Sexual Dimorphism (SD) in right and left MD of maxillary canine was 4.2% and 3.6% respectively. For, ICW it was maximum i.e. 13.7%. However, SD in right and left canine index showed negative values i.e. -2.1% and -0.9% respectively (Table 3).

Discussion
Odontometric features that show sexual dimorphism are used in sex determination in cases where sex could not be determined using craniofacial features. As a means of determining sex, odontometric features have been the subject of research for a long time [6]. Ditch and Rose were the first to prove that teeth diameters can be successfully used in determining sex in poorly preserved and fragmentary skeletal remains in archaeology [13].
Crowns of permanent teeth are formed at an early stage and their dimensions remain unchanged during further growth and development, except in cases when specific changes and disorders in terms of functionality, pathology and nutrition can have affect on the normal dimensions of a tooth [6]. Chromosomes responsible for the sexual difference are in direct connection to growth and development of teeth [14]. The research performed by Stroud et al. [14] showed that males have larger mesiodistal diameters of single teeth, which is due to a thicker dentin layer [14].
The dimensions of canine teeth were studied by several methods which include Moire's topography and Fourier's analysis and measurement of linear dimensions, such as mesiodistal width, buccolingual width and incisocervical height [15]. The use of Moire's topography and Fourier's analysis were limited to small samples whereas measurements of linear dimensions of canine teeth was employed in a large population because it is simple, reliable, inexpensive and easy to perform [7,16].
In the present study subjects, with age ranging from 18 to 30 years, were selected because eruption of canines and growth in width of both the jaws, including the width of the dental arches, are completed before the adolescent growth changes. The inter-canine distance do not increase after 12 years of age [17].
The present study showed that MD of maxillary canines was significantly greater in males than females. Males having values on the right side 8.13 ± 0.67 mm and on left side 8.07 ± 0.71 mm while females having values 7.80 ± 0.70 mm (right) and 7.79 ± 0.60 mm (left) ( Figure  1).
This was in accordance with the study conducted by Parekh et al. [18]. Their study found these values as 6.923+0.611 mm (right) and 7.098+0.535 mm (left) in males, and 6.359+0.526 mm (right) and 6.617+0.51 mm in females with a statistically significant difference in males and females [18][19][20].
Rao et al. [11] have demonstrated that inter-canine distance and canine index are useful parameters as measured in differentiating the sexes [11].
Among all the parameters, in the present study, the SD was maximum for ICW (13.7%) while in MD of maxillary canine it was more in the right side (4.2%) than left (3.6%) describing their significance in the determination of sex.
However, SD in right and left canine index showed negative values indicating no contribution in sex determination (Figures 2A and 2B).

Conclusion
Odontometrics is a quick and easy method for determining sex. Mesiodistal diameter and inter-canine width of permanent maxillary   .