Journal of the Anatomical Society of India

Department of Anatomy, Govt. Medical College, Patiala - INDIA.

Abstract

Teeth form an excellent material for anthropological, genetic, odontologic and forensic investigations. Amongst all the teeth, the mandibular canines are found to exhibit greatest sexual dimorphism. To define the morphometric criteria for mandibular canines in North Indian population, the present study has been conducted in 60 subjects (M:F::30:30) in the age group of 17-21 years. Intercanine distance & width of both right with left mandibular canines were measured intra orally as well as on the casts of same subjects & the mandibular canine index was calculated.

It was seen that a definite statistically significant sexual dimorphism exists in the mandibular canines whether measurements are taken intraorally or on casts. Out of the two canines, the left one exhibits greater sexual dimorphism as compared with the right one. It is also concluded that whenever the width of either canine is >7mm the probability of sex being male is 100%. While if it is <7mm, the sex could be either.

Key words: Mandible, Canines, Canine Width, Canine Index, Intercanine distance.

Introduction:

Teeth are an excellent material in living and non-living populations for anthropological, genetic, odontologic and forensic investigations. These exhibit the least turnover of natural structure and are readily accessible for examination. Being the hardest and chemically the most stable tissues in the body they are selectively preserved and fossilized, thereby providing by far the best record for evolutionary change. Their durability in the face of fire and bacterial decomposition makes them invaluable for identification. (Williams et al, 2000).

Tooth size standards based on odontometric investigations can be used in age and sex determination (Black, 1902). Whenever it is possible to predict the sex, identification is simplified becuase then only missing persons of one sex need to be considered. In this sense identification of sex takes precedence over age. (Camps, 1976) "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. (Keisu, 1990).

Studies on tooth morphology have in the past been conducted using either intra-oral measurements or mesurements on casts. Barrett et al (1963) have observed that intra-oral measurements are less reliable. Garn et al (1967) and Nair et al (1999) have found the mandibular canines to exhibit the greatest sexual dimorphism amongst all teeth.

The mandibular canines have a mean age of eruption of 10.87 years and are less affected than other teeth by periodontal diseases. These are the last teeth to be extracted with respect to age.

Canines are also better likely to survive severe trauma such as air disasters, hurricanes or conflagration. These findings indicate that mandibular canines can be considered as the 'key teeth' for personal identification. (Dahberg, 1963).

The present study establishes the impact of the 'sex factor' on the morphometry of the mandibular canines. The results indicate that the dimorphism in mandibular canines can be of immense medicolegal use in identification. The study defines the morphometric criteria for mandibular canines in North Indian population. This is of definite significance, as tooth morphology is known to be influenced by cultural, environmental and racial factors. (Halim, 2001).

Material and Methods:

Selection Criteria: Sixty subjects, 30 males and 30 females in the age group of 17-21 years were selected for the study. This age group was selected, as attrition is minimal in this age group. (Vacher and Gupta, 1966). The study was conducted on the students of Government Medical College, Patiala.

Inclusion Criteria: Subjects with following status of teeth were included in the study:

• Healthy state of gingiva and periodontium.
• Caries free teeth.
• Normal overject and overbite.
• Absence of spacing in the anterior teeth.
• Normal molar and canine relationship.

Following measurements were taken in all the subjects:

(i) Width of the mandibular canines taken as the greatest mesiodistal width between the contact points of teeth on either side of jaw

Table I: Showing Statistical Significance of Difference Parameters
Males vs Females

Parameters	Group	Sex	Mean (mm)	± S.D.	Coefficient of Variation	't' stat	'P' value	Significance
Inter Canine Distance	Casts	M	25.928	1.186	4.57	3.068	<0.001	Highly Significant
		F	25.003	1.150	4.60
	Intraoral	M	25.873	1.253	4.84	2.538	<0.006	Highly Significant
		F	25.070	1.197	4.77
Right Canine Width	Casts	M	7.198	0.280	3.89	7.869	<5.08 x 10 -11	Highly Significant
		F	6.670	0.237	3.55
	Intraoral	M	7.229	0.280	3.87	7.772	<7.38 x 10-11	Highly Significant
		F	6.690	0.256	3.83
Left Canine Width	Casts	M	7.326	0.259	3.53	8.368	<5.08 x 10-11	Highly Significant
		F	6.693	0.323	4.82
	Intraoral	M	7.299	0.292	4.00	7.621	<1.32 x 10-10	Highly Significant
		F	6.693	0.323	4.83
Right Mandibular Canine Index	Casts	M	0.278	0.011	3.96	4.328	<3.01 x 10-5	Highly Significant
		F	0.267	0.010	3.74
	Intraoral	M	0.280	0.010	3.57	9.719	<7.69 x 10-11	Highly Significant
		F	0.267	0.01	3.74
Left Mandibular Canine Index	Casts	M	0.283	0.013	4.59	3.833	<1.57 x 10-4	Highly Significant
		F	0.268	0.016	5.97
	Intraoral	M	0.282	0.013	4.61	4.088	<6.76 x 10-5	Highly Significant
		F	0.267	0.19	5.27

Table II: Showing Comparison of Different Parameters in Males
Casts V/s Intraoral

Parameters	Group	Mean	± S.D.	Standard Error	't'Stat	'p'Value	Significance
Inter Canine Distance	Cast	25.928	± 1.186	0.314	0.17	>0.05	Not Significant
	Intraoral	25.873	±1.253
Right Canine Width	Cast	7.198	±0.280	0.067	0.46	>0.05	Not Significant
	Intraoral	7.229	±0.280
Left Canine Width	Cast	7.326	±0.259	0.069	0.39	>0.05	Not Significant
	Intraoral	7.299	±0.292
Right Mandibular Canine Index	Cast	0.278	±0.011	0.006	0.33	>0.05	Not Significant
	Intraoral	0.280	±0.010
Left Mandibular Canine Index	Cast	0.283	±0.013	0.007	0.14	>0.05	Not Significant
	Intraoral	0.282	±0.013

Table III: Showing Comparison of Different Parameters in Females Casts V/s Intraoral

Parameters	Group	Mean	± S.D.	Standard Error	't'Stat	'p'Value	Significance
Inter Canine Distance	Cast	25.003	± 1.150	0.30	0.22	>0.05	Not Significant
	Intraoral	25.070	±1.197
Right Canine Width	Cast	6.670	±0.237	0.56	0.35	>0.05	Not Significant
	Intraoral	6.690	±0.256
Left Canine Width	Cast	6.693	±0.323	0.83	0	>0.05	Not Significant
	Intraoral	6.693	±0.323
Right Mandibular Canine Index	Cast	0.267	±0.010	0.002	0	>0.05	Not Significant
	Intraoral	0.267	±0.010
Left Mandibular Canine Index	Cast	0.268	±0.016	0.003	0.33	>0.05	Not Significant
	Intraoral	0.267	±0.014

(a) Intra orally (Fig. 1) (b) on the cast of same subjects (Fig. 2)

(ii) Intercanine distance was measured between tips of both canines in lower jaw. (a) Intra orally (Fig. 3) (b) On casts of same subjects (Fig. 4)

All measurements were taken on an Anatomically sound basis using a Vernier Calliper with a resolution of 0.02 micro-meter and a divider with a fixing device.

Further the mandibular canine index was calculated as follows:

Mandibular Canine Index = (Mesio-distal crown width of mandibular canine) /(Mandibular canine arch width or intercanine distance)

The readings obtained were subjected to statistical analysis to derive conclusions and Sexual Dimorphism in right and left mandibular canines was calculated using formula given by Garn & Lens (1967) as follows:

Where:

X_m = Mean value of males
X_f = Mean value for females

Observations and Results:

Statistical Significance of Parameters :

The following parameters were determined intraorally as well as on study casts in males and females.

• Intercanine Distance.
• Rights Mandibular Canine Width.
• Left Mandibular Canine Width.
• Right Mandibular Canine Index.
• Left Mandibular Canine Index.

The results have been depicted in tables I, II and III.

(a) From table I, it is evident that these parameters as measured for males and females when compared are found to be statistically significant. This is irrespective of whether measurements are taken intraorally or on casts.

(b) Further in males or females i.e. for the same sex (tables II and III) when these parameters as measured intraorally or on casts, are compared, they are found to be statistically insignificant.

From these findings, it can be inferred that there exists a definite statistically significant sexual dimorphism in the mandibular canines. This influence of the 'sex factor' on morphometry in North Indian population is demonstrable irrespective of whether measurements are taken intraorally or on casts.

Sexual Dimorphism in Mandibular Canine Width:

The sexual dimorphism as computed for intraoral measurements and measurements on casts has been presented in table IV.

Table IV: Showing Sexual Dimorphism in Mandibular Canines

Groups	Right Canine	Left Canine
Casts	7.96%	9.796%
Intra Oral	7.954%	8.891%

From the findings, it can be interpreted that in both instances (intraoral and casts) the left canine is found to exhibit greater sexual dimorphism i.e., 8.891% (as computed intraorally) and 9.796% (as computed from casts) as compared with right canine i.e. 7.954% (as computed intraorally) & 7.96% (as computed from casts).

Probability of Sex Determination:

The range of canine width for the North Indian population has been presented in table V. From the range of canine width, it can be concluded that whenever the width of either canine is greater than 7 mm, the probability of sex being male is 100% for the present study. This finding could prove to be of immense medicolegal importance in 'identification' of North Indian Subjects.

Table V: Showing Range of Canine Width in Different Groups Males V/S Females

Groups	Sex	Right Canine	Left Canine
Casts	Males	6.62 - 7.78	7-7.90
	Females	6.20-6.96	5.96-6.96
Intra Oral	Males	6.70-7.90	7-7.90
	Females	6.20-7.00	5.80-7.00

Discussion:

The present study establishes the existence of a definite statistically significant sexual dimorphism in mandibular canines. It is consistent with Hashim and Murshid (1993) who conducted a study on Saudi males and females in the age group of 13-20 years and found that only the canines in both jaws exhibited a significant sexual difference while the other teeth did not. Similar findings were given by Lew and Keng (1991) in their study on ethnic Chinese population with normal occlusions. Kumar et al (1989) have demonstrated that intercanine distance and mandibular canine index are useful parameters in differentiating the sexes. In the present study both these parameters as measured in males and females were compared and the difference was found to be statistically significant.

Garn & Lewis (1967) and Lysell & Myrberg (1986) concluded that the mandibular canine with 6.4% and 5.7%, respectively demonstrates the greatest sexual dimorphism amongst all teeth. Nair et al (1999) in thier study on South Indian subjects concluded that the left mandibular canine with 7.7% followed by the right mandibular canine with 6.2% shows the maximum sexual dimorphism. In the present study also, the left mandibular canine was found to exhibit greater sexual dimorphism (9.796% in casts, 8.891% intraorally).

Gabriel (1958) has stressed that any measurement of teeth unaccompanied by age, race and sex must be treated with great reserve. Amongst the significant findings that can be obtained from teeth are race, age, sex, habits and racial customs. Robinson (1972) has pointed out that in Burma buccally displaced canines are considered lucky. Molnar (1971) found the existence of a positive correlation between tooth wear and cultural factors. The incidence of dental caries is greater in civilized countries due to large intake of sugar in their diet while the Eskimos are known to show the least susceptibility to dental caries. Since the present study has been conducted on both sexes in a definite age group in the North Indian population, it establishes the morphometric criteria of canine size for the North Indian population.

The present study also indicates the probability of sex determination to an extent as high as 100% (when the width of either canine is greater than 7 mm, the sex is male). This finding in North Indian population is of definite significance as the determination of sex makes identification easier and it is of immense forensic importance. In fact, it has been suggested that the first reported crime in the history of mankind was solved when bitemarks were discovered in the remains of forbidden fruits in the garden of Eden and identified as those of Adam and Eve (Danielsen, 1973).

It is a known fact that teeth provide excellent models for the study of relationship between ontogeny and phylogeny. Eimerl and De Vore (1965) postulated that in the evolution of primates, the canines are functionally not masticatory but are related to threat of aggression and actual aggression. A transfer of this aggressive function occurred from the teeth to the fingers in man and until this transfer was complete, survival was dependent on canines especially in males. Thus in the present day humans, sexual dimorphism in mandibular canines is not merely a coincidence but can be expected to be based on functional activity.

Acknowledgement:

The authors are grateful to Dr. Avnish Kumar, Assistant Professor, Department of Physiology, Govt. Medical College, Patiala for his generous help in the statistical analysis of data and compilation of tables. Our sincere thanks are also due to the students of Govt. Medical College, Patiala for their kind cooperation and participation throughout the study programme.

References:

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Fig. 1: Measurement of canine width (intraoral)

 

Fig. 2: Measurement of canine width (casts)

 

Fig. 3: Measurement of intercanine distance (intra oral)

 

Fig. 4: Measurement of intercanine distance (casts)