Sexual dimorphism using permanent maxillary and mandibular incisors, canines and molars: An odontometric analysis.

INTRODUCTION: Sex identification of skeletal remains is one of the prime factors employed in identification of an individual. Teeth, the most hard and stable human tissue, which is resistant to physical insults, serve as a valuable material for forensic, anthropological, odontologic and genetics. Among the four main attributes of biological identity, gender determination is usually the first step in the human identification process. Hence, the main objective of the present study was to assess the dimorphic status of mesiodistal (MD) width, labiolingual (LL) width as well as cervicoincisal (CI) length of the crown in both maxillary and mandibular permanent incisors, canines and first molars.
MATERIALS AND METHODS: The present study comprised a set of 100 casts (50 males and 50 females) between the age group of 20-50 years of age. Impressions were made using alginate impression and study models were prepared using dental stone. The CI length of the crown, maximum MD width and maximum LL width of both maxillary and mandibular permanent incisors, canines and first molars were evaluated using digital Vernier calipers. The obtained data were analyzed using linear discriminant analysis and logistic regression method.
RESULTS: This study concludes that MD dimension of maxillary canine and CI dimension of mandibular first molar as reliable indicators for gender determination than mandibular canine, maxillary and mandibular central incisors and maxillary first molar dimensions.
CONCLUSION: This study concludes that MD dimension of maxillary canine and CI dimension of mandibular first molar as reliable indicators for gender determination than mandibular canine, maxillary and mandibular central incisors and maxillary first molar dimensions. Copyright:

INTRODUCTION

Gender determination of skeletal remains forms a major part of archaeological and medicolegal examinations. Teeth being the hardest and chemically most stable tissue in the body are an excellent material in living and nonliving populations for anthropological, genetic, odontologic and forensic investigations.[1] Tooth size is affected by cultural, environmental, racial and genetic factors and the standards based on odontometric investigations can be used in age and sex determination. The tooth crown size is a valuable tool and provides significant information on human evolution, biological alterations in forensic evaluation and clinical odontology.[2] The first step for a trained forensic odontologist is to identify the gender from whatever human dental remains are presented as specimen. In severe cases of devastation and body fragmentation or decomposition, dental identification is the most commonly used biometric method for human identification.[3]

Sexual dimorphism usually refers to those differences in sizes, stature and appearance between males and females that can be applied to dental identification because no two mouths are alike.[3] Various features such as tooth morphology and crown size are characteristic of males and females.[4] Hence, sex determination using dental features is mainly based on the comparison of tooth dimensions in males and females. Males possess larger tooth crowns than females in contemporary human populations. This may be due to a longer period of amelogenesis for both deciduous and permanent dentitions in males.[5]

Various odontometric parameters have been used for gender determination such as mandibular canine indices, mandibular canine dimension, maxillary first molar dimensions and cumulative dimensions of all teeth. Despite being reliable, sex determination using parameters such as cervico-incisal (CI), labio-lingual (LL) and mesiodistal (MD) among permanent maxillaryincisors, canines and molars with permanent mandibular incisors, canines and molars has not been established.

Hence, the purpose of this present study was to evaluate the probability of determining gender using CI, LL and MD of permanent maxillary and mandibular incisors, canines and first molars and to compare the efficacy of these parameters with each other.

MATERIALS AND METHODS

The present study was conducted in our Institution. One hundred patients were selected based on inclusion criteria outlined below for the study of permanent dentition in the age group of 20-50 years of which 50 were male and 50 were female.

Inclusion criteria

Healthy state of gingiva and periodontium

Teeth with no gross abnormalities

Teeth with no loss of tooth substance due to attrition

Teeth with no restoration affecting MD diameter of the crown

Teeth with intact MD diameter of the crown of both sets of dentition

Caries free teeth

Absence of spacing in the anterior teeth.

Impressions of both maxillary and mandibular arch were made using irreversible hydrocolloid-alginate material and poured using type II dental stone immediately to avoid any distortion. On the study models, the following measurements were taken using a digital Vernier caliper.

The three different measurements were defined as follows:

CI length: the portion of the enamel from the cervical line to the incisal edge.

Maximum MD diameter: the distance between two parallel planes, tangential to the most mesial and distal points of the crown side.

Maximum buccolingual breadth: the maximum distance between two parallel planes, one tangential to the most lingual/palatal point of the crown side, and the other tangential to a point on the buccal/labial side [Figure 1].[6]

Figure 1

Recording measurement using digital vernier caliper

These measurements were then subjected to linear discriminant analysis using SPSS software version 11 ( Manufacture:SPSS Inc. IBM, Chicago,year 2009) (P < 0.005) and logistic regression (sexual dimorphism).

RESULTS

Linear discriminant analysis was used in our study to predict the overall gender accuracy. Table 1 shows that 36_CI was found to be the most reliable parameter for predicting gender (overall accuracy = 72.5%). However, it did not have good accuracy in predicting females as females (accuracy = 56.1%) but had very high accuracy in predicting males as males (accuracy = 89.7%). In Table 2, statistically significant difference was observed between males and females for the parameter 36_CI (P < 0.001) with males recording a higher mean value compared to females. In Table 3, MD_13 and CI_36 were found to be statistically significant factors in determining gender (P < 0.05). In Table 4, the overall accuracy of logistic regression in predicting gender was found to be 81%. Mean CI, LL and MD measurements of different teeth are shown in [Graphs 1–3], respectively.

Table 1

Predicting gender using different parameters

Parameter	Prediction equations		Percentage correctly predicted
	Female	Male	Overall (n=80)	Female (n=41)	Male (n=39)
11_LL	(4.19*11_LL) - 13.28	(4.12*11_LL) - 12.81	52.50	51.20	53.80
11_MD	(4.33*11_MD) - 16.00	(4.21*11_MD) - 15.16	52.50	48.80	56.40
11_CI	(1.62*11_CI) - 6.21	(1.53*11_CI) - 5.52	51.20	51.20	51.30
31_LL	(3.25*31_LL) - 8.33	(3.13*31_LL) - 7.74	50.00	51.20	48.70
31_MD	(11.99*31_MD) - 29.03	(12.36*31_MD) - 30.86	52.50	56.10	48.70
31_CI	(1.37*31_MD) - 4.41	(1.22*31_MD) - 3.47	50.00	46.30	53.80
13_LL	(4.04*13_LL) - 14.17	(3.99*13_LL) - 13.81	55.00	58.80	51.30
13_MD	(11.30*13_MD) - 40.53	(10.87*13_MD) - 37.56	58.80	63.40	53.80
13_CI	(1.95*13_CI) - 7.63	(1.79*13_CI) - 6.40	48.70	43.90	53.80
33_LL	(3.51*33_LL) - 11.81	(3.41*33_LL) - 11.12	53.70	48.80	59.00
33_MD	(6.03*33_MD) - 19.34	(5.69*33_MD) - 17.27	55.00	53.70	56.40
33_CI	(1.95*33_CI) - 7.63	(1.79*33_CI) - 6.40	48.70	43.90	53.80
16_LL	(5.87*16_LL) - 29.83	(5.78*16_LL) - 28.93	51.20	48.80	53.80
16_MD	(3.74*16_MD) - 16.24	(3.78*16_MD) - 16.53	52.50	41.50	64.10
16_CI	(2.59*16_CI) - 7.29	(2.42*16_CI) - 6.37	51.20	51.20	51.30
36_LL	(4.29*36_LL) - 19.64	(4.19*36_LL) - 18.69	51.20	51.20	51.30
36_MD	(2.76*36_MD) - 12.62	(2.73*36_MD) - 12.31	51.20	51.20	51.30
36_CI	(21.82*36_CI) - 72.16	(19.98*36_CI) - 60.52	72.50	56.10	89.70

LL: Labio-lingual width, MD: Mesiodistal width, CI: Cervicoincisal

Table 2

Comparison of different parameters between males and females

Parameter	Gender	n	Mean	SD	SE of mean	Mean difference	t	P
11_LL	Female	39	6.22	1.26	0.20	−0.114	−0.413	0.681
	Male	41	6.33	1.20	0.19
31_LL	Female	39	4.94	1.29	0.21	−0.187	−0.664	0.508
	Male	41	5.13	1.22	0.19
13_LL	Female	39	6.92	1.26	0.20	−0.092	−0.312	0.756
	Male	41	7.01	1.37	0.21
33_LL	Female	39	6.53	1.37	0.22	−0.198	−0.639	0.525
	Male	41	6.73	1.40	0.22
16_LL	Female	39	10.00	1.22	0.20	−0.155	−0.527	0.600
	Male	41	10.16	1.40	0.22
36_LL	Female	39	8.92	1.42	0.23	−0.223	−0.684	0.496
	Male	41	9.15	1.50	0.23
11_MD	Female	39	7.19	1.32	0.21	−0.198	−0.678	0.500
	Male	41	7.38	1.29	0.20
31_MD	Female	39	4.99	0.63	0.10	0.151	1.062	0.292
	Male	41	4.84	0.65	0.10
13_MD	Female	39	6.91	0.79	0.13	−0.268	−1.501	0.137
	Male	41	7.18	0.80	0.13
33_MD	Female	39	6.07	1.05	0.17	−0.354	−1.531	0.130
	Male	41	6.42	1.02	0.16
16_MD	Female	39	8.75	1.40	0.22	0.077	0.227	0.821
	Male	41	8.67	1.63	0.25
36_MD	Female	39	9.02	1.57	0.25	−0.110	−0.270	0.788
	Male	41	9.13	2.03	0.32
11_CI	Female	39	7.22	2.11	0.34	−0.440	−0.905	0.368
	Male	41	7.66	2.24	0.35
31_CI	Female	39	5.71	2.12	0.34	−0.723	−1.491	0.140
	Male	41	6.43	2.21	0.35
13_CI	Female	39	6.99	2.06	0.33	−0.327	−0.676	0.501
	Male	41	7.31	2.26	0.35
33_CI	Female	39	7.15	1.78	0.28	−0.659	−1.473	0.145
	Male	41	7.81	2.19	0.34
16_CI	Female	39	5.26	1.38	0.22	−0.367	−1.113	0.269
	Male	41	5.63	1.55	0.24
36_CI	Female	39	6.06	0.48	0.08	−0.557	−4.526	<0.001*
	Male	41	6.61	0.61	0.10

*Significant difference. SD: Standard deviation, SE: Standard error, LL: Labiolingual width, MD: Mesiodistal width, CI: Cervicoincisal

Table 3

Logistic regression results

Parameter	β	SE of β	P	OR	95% CI for OR
					Lower	Upper
Constant	−17.506	14.237	0.219	<0.001*	-	-
LL_11	−1.387	1.587	0.382	0.250	0.01	5.61
MD_11	1.829	1.392	0.189	6.229	0.41	95.42
CI_11	0.064	1.206	0.958	1.066	0.10	11.34
LL_31	−3.037	2.052	0.139	0.048	0.00	2.68
MD_31	−1.606	1.487	0.280	0.201	0.01	3.70
CI_31	1.554	1.195	0.194	4.730	0.45	49.26
LL_13	−0.992	1.311	0.449	0.371	0.03	4.84
MD_13	2.865	1.421	0.044*	17.544	1.08	284.40
CI_13	−1.036	1.222	0.396	0.355	0.03	3.89
LL_33	0.086	1.194	0.943	1.089	0.10	11.30
MD_33	−0.233	1.093	0.831	0.792	0.09	6.75
CI_33	0.910	0.995	0.360	2.485	0.35	17.48
LL_16	−2.096	1.929	0.277	0.123	0.00	5.40
MD_16	1.344	1.099	0.221	3.835	0.45	33.03
CI_16	0.756	1.052	0.472	2.129	0.27	16.72
LL_36	1.922	1.674	0.251	6.837	0.26	181.94
MD_36	−1.785	1.226	0.145	0.168	0.02	1.86
CI_36	2.926	1.309	0.025*	18.649	1.43	242.37

*A significant factor. OR: Odds ratio, CI: Confidence interval, SE: Standard error, LL: Labiolingual width, MD: Mesiodistal width, CI: Cervicoincisal

Table 4

Prediction accuracy of logistic regression model

Actual gender	Predicted gender		Percentage correct
	Female	Male
Female	32	7	82
Male	8	33	80
Overall accuracy			81

Graph 1

Mean cervico-incisal measurements in different teeth

Graph 3

Mean mesiodistal measurements in different teeth

Mean labio-lingual measurements in different teeth

Linear discriminant analysis

Linear discriminant function analysis was used for the complete sample and each individual group, to differentiate and exhibit which variables acknowledge for the best categorization between the groups. Significance was set at P < 0.05. The discriminant function was derived for variables and a discriminant score was later determined for individuals.

DISCUSSION

The human identification is the recognition of an individual based on physical characteristics unique to the individual. Although many bones such as the pelvis and skull give the most reliable results of sexual dimorphism by morphological and metric analysis, rarely, the only evidence available for gender determination maybe teeth.[7] They are one of the strongest human tissues and are known to resist a variety of antemortem and postmortem insults. Sex determination is one of the prime factors employed to assist with the identification of an individual.[1]

Sexual dimorphism has been explained through the following theories

Moss suggested that because of the longer period of amelogenesis there is a greater thickness of the enamel in males compared to females, leading to a difference in dimensions

Sex chromosomes are also responsible for the different effects on tooth size. Compared to the “X” chromosome, the “Y” chromosome influences the timings and rate of body development, thus producing slower male maturation.[3]

Several indices are available for the determination of gender such as maxillary incisor width, maxillary CI, maxillary canine width, mandibular CI, mandibular canine width, molar width, molar cusp diameter and cumulative width of all teeth.[8] In our study, we have taken maxillary and mandibular central incisors, maxillary and mandibular canines and maxillary and mandibular first molars with parameters such as LL, MD, and CI measurements only. Variations in tooth sizes between genders and among different racial and ethnic groups have been reported by several authors.[3]

The anterior teeth are esthetically important as they are readily seen during eating, speech, mastication and facial gesticulation. The dominant feature of numerous anterior dentitions is the maxillary central incisor. Its size, shape, color and position add to determine and create a definite coherence and order in the arrangement of natural anterior teeth.[9]

According to study carried out by Kaushal, sexual dimorphism in the MD width for the right maxillary central incisor was 3.84%, whereas for the left maxillary central incisor was 4.52% among North Indian population which was statistically insignificant.[9]

In our study too there was no statistical significant difference among maxillary central incisors. However, none of the previous studies had considered mandibular incisors for determining sexual dimorphism. Whereas in our present study we have included mandibular central incisors for the sexual dimorphism but there was no statistical significant difference among them too.

The measurements of linear dimensions which include the MD width of canine teeth have the advantage of being able to use a large sample of population because it is simple, inexpensive and easy to perform. Aggarwal found that males exhibit larger MD width than females. The studies conducted by Ghose and Baghdady on the Iraqi population and by Bishara on populations of Egypt, Mexico and Iowa showed consistent findings that the MD width of the mandibular canines is more in the males than the females and the difference is statistically significant.[10]

In the present study, MD width of 13 was found to be one of the significant factors in determining gender with P < 0.05.

According to Fernandes et al., study confirmed the existence of sex dimorphism based on odontometric measures of the maxillary/mandibular first and second permanent molars. Male teeth found to be larger than the female's ones and distance between the lingual cusps of the corresponding molars in opposite quadrants were also higher in men. These results corroborate those found by studies assessing other populations.[11]

For molar odontometrics, the comparison of mean of parameters measured between males and females showed statistically significant differences with P < 0.001 in relation to CI length of 36.

Narang et al.'s study showed a high level of sexual dimorphism of 5.9% was for the right side and 4.4% for the left side in the dimension of the mandibular molar. Univariate analysis of the study showed that statistically significant dimorphism was obtained in MD dimension of the mandibular first molar. The mean value of dimensions in male dentition was greater than the females.[10]

Rai et al study showed a statistically significant sexual dimorphism for maxillary first molar with a higher percentage for BL dimension. The probability of gender being male was 100% when the dimension was > 10.7mm.[8]

In the present study, CI of 36 was found to be the most reliable parameter for predicting gender (overall accuracy = 72.5%). However, it did not have good accuracy in predicting females as females (accuracy = 56.1%) but had very high accuracy in predicting males as males (accuracy = 89.7%).

According to logistic regression, results in our study shows MD_13 and CI_36 as significant factors in determining gender (P < 0.05). As per prediction accuracy of logistic regression model, the overall accuracy in predicting gender was found to be 81%. The method in the present study implemented is economical and simple to conduct and hence can be applied in forensic odontology for establishing sex identity of an individual.

CONCLUSION

This pioneer study provides normative morphometric data and establishes the existence of statistically significant gender dimorphism (P > 0.05) for the maxillary canines and mandibular first molars among studied population. Future studies on varied population groups with higher sample size might further establish the usefulness of mandibular first molar and canines dimensions in gender determination.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.