Abstract

Introduction

Establishment of a person's individuality is important for legal as well as humanitarian purpose and gender determination is an essential step in identifying an individual. Dental, fingerprint and DNA comparisons are probably the most common techniques used in this context, allowing fast and secure identification processes. However, in certain circumstances related to the scene of the crime, these techniques might be unavailable, so there is still an increasing need for reliable alternative methods of establishing identity.[1]

The grooves present on the human lips are unique to each person and can be used to determine identity of the individual. The study of these grooves or furrows present on the red part or the vermilion border of the human lips is known as cheiloscopy.[2] Lip prints are unique and do not change during the life of a person.[3] This biological phenomenon was first noted by anthropologists. R. Fischer and was the first one to describe it in 1902.[2,4]

Teeth are extremely durable even at high temperature and may be identified even when the rest of the body has undergone decomposition.[5] Mandibular canines are found to exhibit the greatest sexual dimorphism amongst all teeth.[5–7] “Sexual dimorphism” refers to those differences in size, stature, and appearance between male and female that can be applied to dental identification because no two mouths are alike.[5,6] It was for these reasons that Rao et al. proposed the exclusive use of mandibular canines in sex identification. The authors developed an index, which they named mandibular canine index (MCI).[7]

The purpose of the study was to investigate the accuracy with which gender can be differentiated by using cheiloscopy and MCI.

Materials and Methods

Results

The Table 1 shows that the overall mesio-distal width of mandibular canine was found to be 6.57 ± 0.29 mm among the study group in which males had a more mesio-distal width in both right (6.79 ± 0.29) and left (6.78 ± 0.30) mandibular canines when compared to females and was found to be significant (P = 0.000, HS). The observation was similar for the mandibular inter-canine distance also with maximum intercanine distance (32.89 ± 1.29) in males which was found to be significant (P = 0.000, HS) when compared to females (30.6 ± 1.39). There is no variation in MCI of males and females and was found to be not significant in the present study group.

Table 1

Overall mesio-distal width

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Table 2 shows that Type I (46.7%) lip print was most commonly seen in females followed by type II (30.0%), type IV (16.7), type III (3.3%), and type V (3.3%), respectively. Type III (43.3%) was seen most commonly in males followed by type IV (30.0%), type II (13.3%), and type I (6.7%), and V (6.7%), respectively. The difference is statistically significant. This relation of gender propensity to type of lip print distribution was found to be significant with a likelihood ratio of 25.8.

Table 2

Distribution and comparison of lip print with gender

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Table 3 reveals that right mandibular canine shows more sexual dimorphism as compared to mandibular left canine.

Table 3

Sexual dimorphism in mandibular canines

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In Table 4, there was not much of difference in the mesio-distal width of mandibular canines on both right and left side among different types of lip print patterns and was found to be significant and the variation was present between type 1 and type 3 lip print pattern as confirmed by the Bonferroni's post hoc test (0.025, S) where in the type 1 (6.43 ± 0.26) and type 3 (6.82 ± 0.33) lip print pattern subjects had a varied mesio-distal distance. However, the mean MCI and inter canine distance with lip print patterns were found to be non-significant and their mean values did not vary much among different type of lip prints.

Table 4

Comparison of mandibular canine index and type of lip print patterns

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Discussion

Human identification has always been of paramount importance to society.[9] Noting, as providing an additional tool for personal identification is the series of studies on the morphology of the lips and the pattern produced when they are impressed onto a variety of surfaces.[8]

The lip prints were classified using the classification proposed by Suzuki and Tsuchihashi in 1974, also known as Tsuchihashi's classification.[2] This is the most widely used classification in literature. It was found to have a clear description of nearly all of the commonly encountered lip patterns and was easy to interpret. Its resemblance to the dental formula was also familiar to the forensic dentist. The fact that a minimum number of type V patterns were observed in the present study was evidence to the complete coverage of patterns in this classification.

In our study, the upper lip showed a predominance of type I pattern (26.7%) followed in order by type III (23.3%) and type IV (23.3), type II (21.7%) and type V (5.0%).

Sivapathasundharam et al. (2001)[10] stated that the uniqueness of patterns depended on the way the lip muscles relaxed to produce a particular pattern. Lévêque and Goubanova (2004)[11] suggested that the furrows and grooves on the lips seemed to be privileged routes for saliva to spread over the lips and maintain good hydration. They also found the upper lip to be more hydrated than the lower one. The variations in pattern between the upper and lower lip may be attributed to these factors and might have a functional significance. Lévêque and Goubanova also noted that some continuity appeared to exist between the lips and adjacent skin lines and suggested a common origin.

As early as 1950, Snyder suggested that the normal lines and fissures of the lips were an individual characteristic, much the same as finger ridges.[8,12–16] Since then, numerous studies give evidence to the fact that lip prints are unique and characteristic of an individual. However, at the initial classification stage, as in the case of fingerprints, there are similarities among the broadly classified groups of lip prints.

Canines differ from other teeth with respect to survival and sex dichotomy. These differences are probably related to their function, which is different on an evolutionary basis from other teeth. Although canine sex differences and enhanced canine survival are not related to each other, both are probably related to the need for successful use of canines as weapons for total body survival.

The present study establishes the existence of a definite statistically significant sexual dimorphism in mandibular canines. This is consistent with the findings of Hashim and Murshid who conducted a study on 720 Saudi males and females in the age group of 13-20 years. Their study showed that the canines were the only teeth to exhibit dimorphism.[17]

Similar findings were given by Lew and Keng in their study on an ethnic Chinese population with normal occlusions.

A study by Kaushal et al. found a statistically significant dimorphism in the mandibular canines in 60 subjects in a North Indian population, where the mandibular left canine was seen to exhibit greater sexual dimorphism. They also concluded that if the width of the canine is greater than 7 mm, the probability of the sex of the person under consideration being male was 100%.[18,19]

Conclusion

The emerging field of forensic odontology in India relies a lot on inexpensive and easy means of identification of persons from fragmented jaws and dental remains. It is in such situations that the dentist can be called upon to render expertise in forensic science.

The present study establishes the existence of a definite, statistically significant, sexual dimorphism in mandibular canines as well as cheiloscopy. We conclude that the standard MCI is a quick and easy method for sex identification. This is of particular significance when more advanced methods for sex determination are not readily available. However, as the accuracy of MCI in identification of sex has never exceeded 87.5%, it can only be used as a supplemental tool.

Footnotes

References