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 Table of Contents  
ORIGINAL ARTICLE
Year : 2022  |  Volume : 34  |  Issue : 1  |  Page : 82-86

Assessment of the usefulness of morphometric and volumetric analysis of mastoid process for gender determination in forensic odontology: A retrospective cone beam computed tomographic study


1 MDS, Post Graduate Student, Mathusri Ramabai Ambedkar Dental College and Hospital, Cline Road, Cooke Town, Bangalore, Karnataka, India
2 MDS, Reader, Mathusri Ramabai Ambedkar Dental College and Hospital, Cline Road, Cooke Town, Bangalore, Karnataka, India
3 MDS, Professor and Head of the Department, Mathusri Ramabai Ambedkar Dental College and Hospital, Cline Road, Cooke Town, Bangalore, Karnataka, India
4 MDS, Private Dental Practitioner, Mathusri Ramabai Ambedkar Dental College and Hospital, Cline Road, Cooke Town, Bangalore, Karnataka, India
5 MDS, Professor, Oral Medicine and Radiology, Mathusri Ramabai Ambedkar Dental College and Hospital, Cline Road, Cooke Town, Bangalore, Karnataka, India

Date of Submission15-Aug-2021
Date of Decision22-Feb-2022
Date of Acceptance07-Mar-2022
Date of Web Publication25-Mar-2022

Correspondence Address:
Dr. Binindita Mondal
Mathusri Ramabai Ambedkar Dental College and Hospital, Oral Medicine and Radiology, #1/36, Cline Road, Cooke Town, Bangalore, Karnataka – 560 005
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0019-5049.340741

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   Abstract 


Background: Personal identification is crucial in natural mass disasters and in man-made disasters when the body is highly mutilated and fragmented. The mastoid process of the skull is important in this regard for sex determination, since it is one of the most protected region and is resistant to damage. Aim: To assess the usefulness of morphometric and volumetric analysis of the mastoid process for gender determination in forensic odontology. Materials and Methods: The study comprised of 60 retrospective CBCT skull images (30 males and 30 females) of known sex within the age group of 17–65 years. Radiographic measurements of the length, width, height and volume of the right and left mastoid processes were made using customized software. Statistical Analysis: The Wilcoxon signed-rank test, the Mann–Whitney U test, and discriminant functional analysis (DFA) were used to analyze all the collected data. Results: In the present study, the mean values of length, height, width and volume of the mastoid process were found to be higher in males than in females. The height of the mastoid process was found to be a good indicator of gender determination, with a sensitivity of 76.7%, a specificity of 76.7%, and an overall accuracy of 76.7%. Conclusion: We conclude that the mastoid process is a good indicator of gender determination. The volume can also be included as an additional parameter along with length, height, and width. We therefore recommend the use of the mastoid process for gender determination in personal identification in forensic odontology.

Keywords: CBCT, gender determination, mastoid process, volumetric analysis


How to cite this article:
Mondal B, Vaishali M R, David MP, Roopashri G, Kumar V, Ponnuswamy IA. Assessment of the usefulness of morphometric and volumetric analysis of mastoid process for gender determination in forensic odontology: A retrospective cone beam computed tomographic study. J Indian Acad Oral Med Radiol 2022;34:82-6

How to cite this URL:
Mondal B, Vaishali M R, David MP, Roopashri G, Kumar V, Ponnuswamy IA. Assessment of the usefulness of morphometric and volumetric analysis of mastoid process for gender determination in forensic odontology: A retrospective cone beam computed tomographic study. J Indian Acad Oral Med Radiol [serial online] 2022 [cited 2022 May 27];34:82-6. Available from: https://www.jiaomr.in/text.asp?2022/34/1/82/340741




   Introduction Top


Personal identification is defined as establishing the identity of an individual person.[1] The 'big four' of human identification are age, sex, stature and ethnicity.[2] Gender determination of the dead body is done by identifying the body parts of individuals for social, religious and medico-legal purposes.[3] Skull (92% accuracy) being indestructible serves to be the reliable bone demonstrating sexual dimorphism.[4] The mastoid process is used for gender determination because of its compact structure and secure position.[5] Cone beam computed tomography (CBCT) is a new imaging modality in dentistry as it has good resolution, and would thereby be advantageous for forensic imaging.[6],[7]

Aim: To assess the usefulness of morphometric and volumetric analysis of mastoid process for gender determination in forensic odontology.

Objectives: To measure, compare, and evaluate the length, height, width, and volume of mastoid process as observed on CBCT in males and females.


   Materials and Methodology Top


In order to evaluate the reliability of the mastoid process in gender determination, the sample size has been estimated using G*Power software v. 3.1.9.4, and a total sample size of 60 was included in the study. Before the scans were taken, written informed consent was taken from every patient through the CBCT scan center for the usage of scan data for research study purposes. The study was carried out in accordance with the ethical principles of the Declaration of Helsinki. The study was approved by the Institutional Ethics Committee (IEC/MRADC&H/EC-009/2021 dated 14/12/2021).

This retrospective study comprised of 60 CBCT skull images (120 mastoid processes) of 30 males and 30 females, which included both the right and left mastoid processes. The CBCT images included in this study were those of the patients in the age range of 17–65 years and of both males and females. All of the images in which the mastoid processes were distorted and fractured, or those images that did not reveal the full anatomical details of the lateral sides of the mastoid were excluded.

The CBCT images were retrospective images and hence, only those volumes in which the mastoid process was clearly visible was selected for the study. All of the CBCT images were taken on Carestream CS 9300 machine set at a tube voltage of 90 kVp and a current of 10 mA with the scan time set at 12 seconds and field of view (FOV) set as 14 × 17. Radiographic measurements of the length, height, width, and volume of the right and left mastoid processes were performed using ITK-SNAP software v. 3.8[8] by a single observer. Mastoid process parameters included -

Length: In sagittal view, length is measured from the porion to the posterior end of the incisura mastoidea [Figure 1].
Figure 1: Length and Height of mastoid process (sagittal view)

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Height: In sagittal view height is measured by drawing a perpendicular line from the centric point of the length to the tip of the mastoid process called the mastoidale [Figure 1].

Width: In coronal view, width is measured from the most prominent point on the lateral and medial aspects of the mastoid process [Figure 2].
Figure 2: Width of mastoid process (coronal view)

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Volume: Volume is the quantity of three-dimensional space that a mastoid process contains.

ITK-SNAP v. 3.8 software utilizes an edge-based snake box which displays the region of interest (a rectilinear box), which is adjusted by dragging the side of the box around the right and left mastoid processes simultaneously; automatic segmentation was done. The volume of mastoid process was obtained in mm3 by selecting multiple bubbles and dragging the bubbles one-by-one in the mastoid process, which grew to assume the shape of the mastoid process and which gave a 3D structure of the mastoid process on right and left sides [Figure 3] and [Figure 4]. The volume was obtained by selecting the segmentation option from the tool bar.
Figure 3: Segmented 3D view of right mastoid process

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Figure 4: Segmented 3D view of left mastoid process

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All the data collected were entered in Microsoft Excel 2013 spreadsheet and were subjected to Wilcoxon signed-rank test, Mann–Whitney U test, and discriminant functional analysis (DFA). The level of significance was set at P < 0.05.


   Results Top


No statistical differences were found on comparison of the right and left side mean values of the mastoid process [Table 1]. The mean values of different parameters were higher in males than in females. All parameters were observed to have statistically significant difference except width (P 0.09). Among the parameters height was highly statistically significant (P < 0.001) [Table 2] and was found to have lesser Wilks's lambda (0.704) [Table 3]. Therefore, it reliably entered into the DFA. The gender determination equation can be mentioned as discriminant value = 0.37 × Height - 7.65. Discriminant value more than sectioning point is categorized as males less than sectioning point is considered as females [Table 4]. The correct classification rate was achieved as 76.7% with the height of the mastoid process which implies that it was a good indicator of gender determination [Table 5]. The area under the curve (AUC) for height of mastoid process = 0.811 (P < 0.001), indicating that mastoid height was a good predictor of gender determination [Table 6].
Table 1: Comparison of mean values of different mastoid process parameters between right and left sides using Wilcoxon signed-rank test

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Table 2: Gender-based comparison of mean values of different mastoid process parameters using Mann–Whitney U test

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Table 3: Determination of Wilks's lambda among the significant parameters of mastoid process for discrimination between genders

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Table 4: Discriminant function coefficients for gender determination among the mastoid process parameters that entered the analysis

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Table 5: Group membership model for gender prediction by height of mastoid process

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Table 6: Area under the curve

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   Discussion Top


The present study focused on the assessment of the usefulness of morphometric and volumetric analyses of the mastoid process for gender determination in forensic odontology. The mastoid process is considered an important feature of gender determination due to its nature of resistance to damage.

Comparison of mean values of different mastoid process parameters between right and left sides

In the present study, on comparing the mean values of length, height, width, and volume of the different mastoid processes between the right and left sides, it was found that there was no statistically significant difference between the right and left sides of the mastoid process. This is in accordance with the study conducted by Virupaxi et al.[9]

This can be explained by a study conducted by Turner on the basis that the human body has a symmetrical appearance when viewed externally, and that anatomical asymmetry of the individual skulls occurred in 12% of a series of 1,000 crania. The asymmetry in the majority of instances was due to a pneumatic process on one side, and an acellular form on the other side. Both processes were pneumatic, but the cells were unequally distributed. Clinical asymmetry, therefore, was found only in 7% or 8% of the skulls.[10]

Gender-based comparison of mean values of different mastoid process parameters

In the present study, the mean values of different mastoid process parameters were compared and it was found that the mean values of length, height, width, and volume were higher in males than in females. The mean difference in the length and volume of the mastoid process between males and females was found to be statistically significant except for the width. The mean difference in the height of mastoid process between males and females was found to be highly statistically significant.

These findings are in accordance with studies conducted by Amin et al.[11], Manivanan et al.,[12] and Salemi et al.[13] in which all the values were higher in males than females, except for the width which was higher in females than males. According to a study conducted by Gupta et al.,[14] it was observed that mastoid width contributes less in sex determination, which was similar to this study.

The difference in the size of the mastoid process between males and females could be due to variations in the growth of the mastoid process along with the action of the sternocleidomastoid, splenius capitis, longissimus capitis, and the posterior belly of the digastric muscle on the mastoid process, which could enhance its growth in Males.[15] Female's skulls preserve an infantile type of small mastoid process, as observed by Klaatsch in 1908.[16]

Determination of Wilks's lambda among the significant parameters of the mastoid process for discrimination between genders

Wilks's lambda was determined among the significant parameters of the mastoid process for discrimination between genders. It was found that the height of the mastoid has less Wilks's lambda (0.704). Hence, height was the most reliable parameter to enter into the DFA.

Discriminant function coefficients for gender determination among the mastoid process parameters that entered the analysis

In the present study, using DFA, 76.7% correct classification was achieved with the height of the mastoid process for gender determination. This is in agreement with studies conducted by Sumati et al.,[17] in which the accuracy was 76.7%, and Kajanoja,[18] who reported an accuracy of 80%. Classification accuracy was higher in some studies than in the present study; for example, 93.7% accuracy was reported by Salemi F et al.,[13] 90.6% accuracy was reported by Amin et al.,[11] and 90% accuracy was reported by Gupta et al.[14] A few other studies on classification accuracy reported by Kemkes et al.[19] and Singh et al.[20] reported 65% and 61% accuracy, respectively.

Gender prediction using height of mastoid process

In the present study, the height of the mastoid process was found to be a good indicator of gender determination with a sensitivity of 76.7%, specificity of 76.7%, and an overall accuracy of 76.7%.

Volume of the mastoid process

In the current study, it was found that mean volumes of the mastoid process of the right and left sides were greater in the males than in the females, which was statistically significant (P 0.04). Volume is the amount of space occupied by a three-dimensional object and is calculated by multiplying the length, height, and width of an object. Since the length, height, and width of the mastoid process are greater in males than in females, it gives the reason why volume is more in males than in females.

The volumes of the mastoid could not be compared to any previous studies as this happens to be the first study using this parameter for gender determination.

The mastoid bone is a strong bone present at the base of the skull that is relatively indestructible and better preserved. The skull is the second most accurate structure to predict gender. The anatomy of bones can be better determined by using radiographs and therefore, they play an important role in the personal identification of an unidentified body. Cone-beam computed tomography (CBCT) is an advanced imaging technology in which antemortem and postmortem data can be preserved digitally and will definitely be useful for future reference in personal identification. Since CBCT gives a three-dimensional view, the volume of the mastoid process can be used as an additional parameter.[6]

Since CBCT is regularly advised for various advanced dental procedures, we suggest that all dental clinical setups preserve the patient's records digitally to establish antemortem records that can be compared with postmortem data for personal identification in forensic science in the future.

Future prospects and limitations

The present study shows that volumetric analysis can also be included along with other parameters, such as length and height of the mastoid process, as a sex predictor, which could be best described by a specific equation. This study is limited by its small sample size. Therefore, we suggest that further studies be carried out in larger groups among varied ethnic populations.


   Conclusion Top


In the present study on CBCT images, the mean values of length, height, width, and volume of the mastoid process were found to be higher in males than females. The height of the mastoid process was found to be a good indicator of gender determination with a sensitivity of 76.7%, specificity of 76.7%, and an overall accuracy of 76.7%. Volume can also be included as an additional parameter along with length, height, and width.

Based on the results of the present study, we conclude that the mastoid process is a good indicator of gender determination. We therefore recommend the use of the mastoid process for gender determination in personal identification in forensic odontology.

Declaration of patient consent

The authors certify that necessary written informed consent was obtained from the patients for the usage of scan data for research purposes and for the subsequent publication of their scans/images in the journal. Every effort has been made by the authors to keep the images and scan data anonymized.

Source of support

I thank Dr Vinod Kumar for supporting the study by providing the CBCT images.

Acknowledgements

I am grateful to Mr Biswarup Mondal for his contribution and help in data analysis.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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Virupaxi RD, Kumar Yadav S, Desai SP, Shirol V. Sexual dimorphism of mastoid process in dried skulls of North Karnataka Population. Int J Cur Res Rev 2016;8:51-53.  Back to cited text no. 9
    
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Turner AL. The structural type of the mastoid process. J Laryngol Otol 1922;37(3):115-121.  Back to cited text no. 10
    
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Amin W, Saleh MW, Othman D, Salhab D, Thunaibat H. Osteometric assessment of the mastoids for gender determination in Jordanians by discriminant function analysis. Am J Med Biol Res 2015;3:117-23.  Back to cited text no. 11
    
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Manivanan A, Gopal SK, Sai A. Osteometric assessment of the mastoids for gender determination: A retrospective CBCT study. Am J Otolaryngol Head Neck Surg 2019;2(3):1044.  Back to cited text no. 12
    
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Bhayya H, Avinash Tejasvi ML, Jayalakshmi B, Reddy MM. Craniometric assessment of gender using mastoid process. J Indian Acad Oral Med Radiol 2018;30:52-7.  Back to cited text no. 15
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]



 

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