| Abstract|| |
Purpose: Human teeth are the most stable and durable tissues in the body. Teeth can be identified even after complete decomposition, thus making them invaluable for identification of sex and age from fragmentary adult skeleton. This study aimed to compare the morphological and radiological measurements of canine and investigate its accuracy in sex determination.
Materials and Methods: This study involved 60 males and 60 females between the age group of 20 and 30 years. Mesiodistal (MD) widths of mandibular left canines and mandibular inter-canine distance (ICD) were measured and compared both clinically and on digital intraoral periapical and occlusal radiographs. Discriminant function analysis was carried out for gender determination. Discriminant equation and cutoff point were used in determining the gender and the percentage accuracy. Kappa statistics were carried out to assess intra-observer agreement.
Results: A definite statistically significant difference in the MD width and ICD was found between males and females. Clinical and radiological measurements were almost equally efficacious in gender determination with an accuracy of 55-75% in both males and females. When all the variables were used, the accuracy of gender determination increased substantially to 94%. k-values suggested a high intra-observer agreement.
Conclusion: It can be concluded that both the clinical and radiographic measurements of MD width of canine and ICD are quick and easy methods for determining sex and in identification of an unknown individual with a substantial accuracy.
Keywords: Anthropometry, forensic dentistry, odontometry, radiometry
|How to cite this article:|
Nadendla LK, Paramkusam G, Pokala A, Devulapalli RV. Identification of gender using radiomorphometric measurements of canine by discriminant function analysis. Indian J Dent Res 2016;27:27-31
Gender determination of skeletal remains is an important part of forensic, archaeological, and many medico-legal examinations. In forensic contexts, correct sex identiﬁcation limits the pool of missing persons to just one half of the population. The techniques used in sex determination have been primarily focused on the pelvis where reproductive difference is best seen and in the cranium where the size and morphology are varied and best represented.  The accuracy of sexing using diverse parameters of the body such as craniofacial morphology and measurements on the pubis ranges from 96% to 100%. , Long bones, , ribs, , vertebrae,  and clavicle  were also studied for sexual dimorphism.
|How to cite this URL:|
Nadendla LK, Paramkusam G, Pokala A, Devulapalli RV. Identification of gender using radiomorphometric measurements of canine by discriminant function analysis. Indian J Dent Res [serial online] 2016 [cited 2019 Oct 19];27:27-31. Available from: http://www.ijdr.in/text.asp?2016/27/1/27/179810
Radiography can assist in giving accurate dimensions for which certain formulae can be applied to determine gender.  The skull, pelvis, and femora are the most useful for radiological determination of gender. The length and the height of the head, the circumference of the head, the circumference of the occipital condyles, and the foramen magnum have been used to determine gender in unidentifiable human remains. ,,,,, However, the tendency of these bones to be fragmented may preclude accurate sex estimation. The teeth are considered useful adjuncts in such scenarios since they are frequently recovered intact from skeletonized remains and have the ability to estimate sex correctly with accuracy rates that range between 76% and 92.5%. ,
Various studies have tested the reliability of canine dimensions morphologically in gender establishment, but very few studies have investigated the accuracy of morphological dimensions of canine radiologically in gender determination.  Radiometric analysis of canine was previously studied for age determination and was found to have a reliable accuracy.  The present study was undertaken to compare the morphological and radiological measurements in digital radiographs by radiometric analysis and test the reliability of mandibular canine in gender determination using discriminant function analysis.
| Materials and methods|| |
The study was conducted in the Department of Oral Medicine and Radiology, Kamineni Institute of Dental Sciences, India. Ethical clearance was obtained from Institutional Ethical Committee. Population of Nalgonda (district) where the study is being carried out is around 3.4 million. At 95% confidence level and confidence interval <10, a sample size >96 was suggested by the statistician. Hence, a sample of 120 was selected for the study, with 60 male and 60 female patients between the age group of 20 and 30 years. Subjects with healthy state of gingiva and periodontium, normal molar-canine relationship, caries-free teeth, absence of spacing in the anterior teeth, and normal over jet and over bite were included in the study after a written informed consent. Subjects with partial anodontia, supernumerary teeth, hypoplastic teeth, teeth showing physiologic or pathologic wear, and patients with parafunctional habits were excluded from the study. Mesiodistal (MD) width of the left mandibular canine and mandibular inter-canine distance (ICD) were measured clinically for all subjects [Figure 1] and [Figure 2] using digital vernier calipers with a resolution of 0.01 mm. Intraoral periapical (IOPA) of the left mandibular canine and mandibular cross-sectional occlusal projection were taken using digital photostimulable phosphor plates. MD widths of the left mandibular canine were measured on digital IOPA and occlusal radiographs, and ICD between the mandibular canines was measured on occlusal radiographs using DBSWIN software (Durr Dental India Pvt Ltd, Patparganj Industrial Area, Delhi, India) with a least count of 0.1 mm [Figure 3] and [Figure 4]. Canine index (CI) was calculated both clinically and radiographically as a ratio of MD width and ICD. Statistical analysis was done using SPSS 20 software (IBM manufacturers, New Orchard Road, Armonk, New York, United States). Univariate analysis was done for all the canine measurements by calculating mean and standard deviation. Student's t-test was used to distinguish between the male and female mean values for each variable. Then, discriminant function analysis was performed by calculating Wilk's lambda, eigenvalue, canonical correlation, and percentage of correct gender determination was quoted in assessing the relative validity of discriminant functions. Low values of Wilk's lambda, high values of eigenvalues, high value of canonical correlation, and high value of percentage of correct gender determination are associated with excellent discriminant function. Discriminant functions were calculated with each single variable and also with all the variables combined together. Intra-observer agreement was assessed using cross-tabulation and k-value by kappa statistics.
|Figure 3: Radiographic measurement of mesiodistal width of canine on digital intraoral periapical|
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|Figure 4: Radiographic measurement of mesiodistal width of canine and inter-canine distance on digital occlusal|
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| Results|| |
On the basis of univariate analysis and Student's t-test, it was found that all the canine measurements except for CI values differ significantly among males and females both clinically and radiographically at 5.0% level of significance (P ≤ 0.05). There is no significant difference between clinical and radiological measurements [Table 1].
The discriminant function equation for the determination of sex and their respective cut-off value was derived using discriminant function analysis [Table 2]. If the calculated discriminant score using the equation (s) is <0 (cut-off point), the case is classified as "female" and if the score is ≥0, the case is classified as "male."
|Table 2: Discriminant function equation and cut-off points for determining sex |
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Discriminant functions were calculated with each single variable and with all variables together [Table 3]. When individual functions were compared, the best function in the present study was obtained by MD width of canine measurement on digital IOPA with lowest Wilk's lambda (0.574), the highest eigenvalue (0.742), the highest canonical correlation (0.653), and the highest percentage of correct classification (76.65%). The next best functions were obtained by MD width of canine on occlusal radiograph, clinical measurement of MD width of canine, ICD on occlusal radiograph, and clinical measurement of ICD in the descending order. On the other hand, the functions produced by clinical and radiological CI values showed higher Wilk's lambda, lower eigenvalues, lower canonical correlation, and the lowest percentage of correct classification suggesting far less discriminative capacity in determining gender. When all the variables were used, the common function has got the least Wilk's lambda (0.326), the highest eigenvalue (2.069), the highest canonical correlation (0.821), and the highest percentage of correct classification (94.2%). k-values of all the canine values are >0.6 suggesting a high intra-observer agreement [Table 3] and [Table 4].
| Discussion|| |
Sexual dimorphism represents a group of morphologic characteristics that differentiate a male from a female. Sexual dimorphism has been of great interest for many years. Odontometry is a useful adjunct in sex determination. 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. 
Of all the teeth in the human dentition, the canines are the least frequently extracted teeth (possibly, because of the relatively decreased incidence of caries and periodontal disease). In addition, canines are reported to withstand extreme conditions and have been recovered from human remains even in air disasters and hurricanes.  Canines are also known to show the greatest degree of sexual dimorphism across numerous populations. ,,, It was for these reasons that Rao et al.  examined the utility of canines alone in sex estimation. In addition to MD dimension of the canine, the authors also included the inter-canine arch width. At the outset, the inclusion of the ICD for sex assessment appears to be ingenious, considering that studies have shown larger jaw dimensions in males , and a greater predilection for bilobate and square-shaped chin in males in contrast to pointed ones in females.  The inter-canine width - which is related to the mandibular arch dimension - may therefore be expected to show recognizable sexual dimorphism, just like canine dimensions.
The present study results also showed significant difference between canine dimensions of males and females both clinically and radiologically. However, in contrast to our study, several other studies, Boaz and Gupta  and Acharya and Mainali  reported reverse sexual dimorphism, where females showed larger teeth than males.
Our previous study  and several other studies in the past ,, showed greater sexual dimorphism in mandibular left canine among the teeth. Hence, we have considered only mandibular left canine in our present study. Radiometric analysis of canine was very less investigated in gender determination. Hence, radiographic measurements of MD width and ICD on digital radiographs of IOPA of canine and mandibular cross-sectional occlusal radiograph were added to the present study. Previous studies used MD width, ICD, and CI in determining the percentage accuracy of gender determination. Hence, we have considered at deriving a discriminant equation for each of these functions using discriminant function analysis for this population using this study sample.
All the canine measurements, except CI, showed a significant difference between males and females. This statistically insignificant results of CI may be because it is a relative value, it is obtained as the ratio of two absolute measurements (MD dimension of canines and ICD), it does not reﬂect sex differences that exist in absolute measurements, and these sex differences might have got cancelled because of the division between these absolute measurements.
The uniqueness of this study is the use of radiographs for the measurement of MD width of canine and ICD. The results suggested it to be a very reliable method for these measurements. The correlation coefficient was very high for the mandibular cross-sectional occlusal radiograph measurements as they are almost same as that of the clinical measurements. Here, we have used digital radiography and lead aprons to minimize the amount of radiation exposure. There are several advantages of using digital occlusal radiography. It is very less time-consuming procedure, image can be stored as digital data for future reference, and it can give all the measurements such as MD width of canine, ICD, and CI with a reliable accuracy. Hence, future studies can be carried out on larger sample with the mandibular cross-sectional radiograph alone, replacing the use of plaster models.
De Angelis et al. in their study suggested a sexual dimorphism in the volume of the canine apart from previously investigated linear measurements.  Manchanda et al. evaluated North Indian population using the crown diagonal diameters in sex determination by means of discriminant functional analysis. 
Although the results are in agreement with most of the previous studies, the present study has its own limitations. Smaller sample size and single examiner might have resulted in few errors or bias in the dimensions and results. The present study measured only linear dimensions because of the simplicity, reliability, and inexpensivity. More accuracy could have been obtained by the application of Moire's topography and Fourier's analysis that, however, require sophisticated equipment and the use of complex mathematical equations, respectively. Future studies have to include larger sample size, multiple observers to check intra-observer variation, and inter-observer agreement.
| Conclusion|| |
Left mandibular canine showed significant sexual dimorphism in both clinical and radiographic measurements, and the radiographic measurements are in high correlation with clinical measurements. Sex of a person can be identified using dimensions of MD width of canine and ICD on mandibular cross-sectional occlusal radiographs with an acceptable accuracy. Discriminant function analysis using various functions of canine together yielded a high percentage of accuracy in gender determination (>90%). Anyways, it is better to confirm the results by using other methods of determining sex because sex determination using the pelvis and skull bones shows an accuracy of 95% and above. ,
We are so thankful to Mr. Ramesh, Statistician, Department of Community Medicine, for his support in statistical work and also for helping us in understanding and interpreting discriminant function analysis.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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Revath Vyas Devulapalli
Department of Oral Medicine and Radiology, Kamineni Institute of Dental Sciences, Narketpally, Telangana
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3], [Table 4]