A retrospective comparative analysis of mandibular ramus and mental foramenin sex determination among the population of Kanyakumari district

Introduction

Forensic odontology, a multidisciplinary science deals with personnel identification using the available mortal dental remains.¹ Dental profiling is a three-tiered process with a well-defined objective to establish personal identity. It gives details regarding the ethnic background, sex and age of the subject and heavily depends on antemortem records.² Personal identification begins by an accurate assessment of sex of the deceased. This is a vital process as the subsequent steps are dependent on this foremost procedure.³ Dismembered bones are more likely to be sourced at the disaster site than a complete human skeleton. With respect to sex determination, the human skull has an accuracy rate of 92%.^{4, 5} Mandible is the strongest and largest among the facial bones. It also shows distinct sexual variations.^{6, 7}

Each population and ethnic group present a set of morphological features, which are characteristic in nature. Thus, studying these osteological features is quintessential to lay down the baseline data for each populace.

Rotational panoramic radiography is widely used for obtaining a comprehensive overview of the maxillofacial complex. This forms an indispensable tool in forensic sciences and forms an apt tool for measurement mandibular ramal parameters.

This study evaluated the utility of various mandibular measurements such as Maximum ramus breadth, Minimum ramus breadth, Condylar height, Projective height of ramus, Coronoid height and analysed the position of the mental foramen from the superior and inferior border of the mental foramen to the lower border of the mandible for sex determination as observed on digital panoramic radiographs among the residents of Kanyakumari district.

Materials & Methods

This cross-sectional study was conducted for a period of one year after obtaining clearance from the Institutional Research Committee (Ref no. 04/07/2016) & Institutional Ethical Committee Board (Protocol no: 7/2016). Written informed consent was obtained from the study subjects. Sample size was calculated using the formula: N=2S² (Z1+Z2)² /(M1-M2)² , where n = sample size, S = Pooled standard deviation = 9, Z₁ = Z value associated with alpha =1.64, Z₂ = Z value associated with beta =0.841, M₁ = mean of group I, any one of the variants of study, M₂ = mean of group II, any one of the variants of study. On substituting the values, 250.3 was obtained and a sample size of 250 was finalised.⁸

Convenient method of sampling was used to select 250 individuals. The study cohort was categorised into males and females with 125 samples in each group.

The study sample was selected from the patients visiting the Department of Oral Medicine & Radiology at a tertiary care centre in Kanyakumari district upon the fulfilment of selection criteria. Radiographs taken for routine screening purpose were used for this study. Ideal, archival Orthopantomograms (OPG) of participants in the age group of 20-50 years were included. OPG of patients with impacted mandibular third molars, Dental caries/ periapical pathologies. (Periapical granuloma, periapical cyst etc.), Developmental anomalies, Fractures of the jaws, Edentulous patients were excluded.

Digital OPG (Planmeca Digital OPG, Planmeca Romexis 2.6.0.R software) of patients were taken from the Department of Oral and Maxillofacial Radiology and viewed on a HCL Desktop computer after installing the Romexis 2.6.0.R software by mouse-driven method.

Two primary parameters were made measured and compared; the first parameter evaluated landmarks in the mandibular ramus (maximum ramus breadth, minimum ramus breadth, condylar height, projective height of ramus, coronoid height). The second parameter was the distance of the mental foramen (superior and inferior border) to the lower border of the mandible.

Mandibular ramal measurements were made the following way bilaterally: Maximum ramus breadth (MxRB): The distance between the most anterior point on the mandibular ramus and a line connecting the most posterior point on the condyle and the angle of jaw. Minimum ramus breadth (MnRB): Smallest anterior–posterior diameter of the ramus. Condylar height (CnH): Height of the ramus of the mandible from the most superior point on the mandibular condyle to the tubercle, or most protruding portion of the inferior border of the ramus. Projective height of ramus (PR): Projective height of ramus between the highest point of the mandibular condyle and lower margin of the bone. Coronoid height (CrH): Projective distance between coronion and lower wall of the bone. Measurements of the Mental Foramen were made the following way bilaterally: (S-L): Distance from the superior border of the mental foramen to the lower border of the mandible and, (I-L): Distance from the inferior border of the mental foramen to the lower border of the mandible (Figure 1).

Following the measurements, OPGs were saved as a separate folder and were scrutinised and assessed by a senior Oral and Maxillofacial Radiologist. Thus, the study procedure and measurements were validated.

1. Maximum ramus breadth, 2. Minimum ramus breadth, 3. Condylar height, 4. Projective height of ramus, 5. Coronoid height, 6. (A-C), 7. (B-C), A. Tangent along the Superior border of the mental foramen, B. Tangent along the Inferior border of the mental foramen, C. Lower border of the mandible. All measurements in “mm”.

Data was presented as mean and standard deviation. Statistical Package for Social Sciences (SPSS 16.0) version was used for analysis. Chi-square test was applied to analyse the statistical significance between the groups. p value less than 0.05 was considered statistically at 95% confidence interval.

Results

This study recruited 250 subjects between 20-50 years and mandibular landmarks were measured on both the left and the right sides, separately for males and females. (Figures 2 & 3)

Measurements of MxRB was 35.92±2.78 mm in males and 33.78±3.56 mm in females. Comparison between the values of males and females was done and the difference was statistically significant (p value = 0.04). Likewise, MnRB was found to be 28.00±2.19 mm in males and 25.80 ±1.93 mm in females. Statistical analysis of the comparison of the minimum ramus breadth between males and females were found to be statistically significant with a p value of 0.04.

Measurements of CnH showed that the mean condylar height of 66.83±4.90 mm and 61.03±4.67 mm in males and females, respectively. The difference in measurements of CnH between males and females was also statistically significant with a p value of 0.04. Mean projective height in males was 65.84±5.18 mm and 59.79±4.34 mm in females. Statistically analysis of the values was found to be significant for the difference in values between males and females. Statistical analysis of the values was found to be statistically significant with p value of 0.04. Measurements of CrH was made on radiographs of both males and females and the mean measurements of CrH in males was 56.76±4.34 mm and 52.97±3.78 mm in females. Comparison of the values between the sexes concluded statistically significant results with a p value of 0.03.

Measurements of the mental foramen were made and (SL) was observed to be 14.77±2.67 mm and 12.57±1.54 mm in males and females, respectively. Difference in values between the sexes was noted to be statistically significant with a p value of 0.04. Measurements of (I-L) was found to be 11.51±2.19 mm in males and 9.55±1.64 mm in females. Comparison and statistical analysis of the values between the study groups was found to be statistically significant with p value of 0.04. (Figure 4).

Discussion

The mandible by virtue of being a dense compact bone, is resilient and remains well preserved in comparison with other bones.⁹ Phases of formation of the lower jaw, rate and duration of growth are different in the sexes, and this contributes to the sexual dimorphism that the ramus demonstrates. Masticatory forces are distinct to each sex and this influences the morphology of the ramus.^9,10Several studies indicate that the mental foramen is a stable region which remains relatively constant throughout life and is independent of alveolar resorption. This would qualify the mental foramen as a stable landmark that could aid in forensic analysis.^11-13

Metric analyses as far as skeletal sex determination is concerned is often proved to be superior. The reason being objectivity, accuracy, reproducibility and reduced degree of inter and intra observer variations when compared to descriptive traits.^14-16

Given these merits of the lower jaw, seven landmarks were assessed. All measurements were carried out on OPG among the inhabitants of Kanyakumari district.

Saini V, et al. studied in anthropometric research using sliding calipers in mandibular ramus in Varanasi. Though the measurements were relatively higher than this study, Saini, et al. concluded that measurements in males were higher than females.¹⁷

Datta A, et al. carried out a study on sex determination from human mandible using various morphometric parameters and their study had conclusions similar to our study. About 50 random adult dry intact mandibles from Southern India were considered. Numerous morphometric parameters such as ramal height and coronoid height were measured using a mandibulometer and digital calipers. The results of our study concurred with this study, where ramal height was greater in males when compared to females.¹⁸

Skeletal morphology heavily influences the sexual identification of humans. This has been extensively proven by researches carried out across many geographic areas and ethnic communities in our country. Table 1 summarises the base line values of studies conducted by various authors in our country. All the studies afore mentioned are in concordance with the inference from our study, i.e., mandibular measurements are significantly greater/larger in males than in females and are vital indicators of sexual dimorphism.

Literature review reveals that the skeletal morphometric measurements show a wide variation across ethnic groups, thereby, highlighting the requirement for population specific studies. This study has established the base-line data with respect to mandibular measurements among the geographic region of Kanyakumari district. Lack of a large sample size and a comprehensive list of study parameters were a few limitations of this study. Further studies in this regard are warranted to establish forensic data bases across our country.

M, males; F, females; MxRB, maximum ramus breadth; MnRB, minimum ramus breadth; CnH, condylar height; PH & PR, projective height of ramus; CrH, coronoid height; (S-L), distance from the superior border of the mental foramen to the lower border of the mandible; (I-L), distance from the inferior border of the mental foramen to the lower border of the mandible.

Conclusion

The mandible has several features which have distinctive qualitative and quantitative aspects. The mandibular has distinctive sexually dimorphic features. This research concluded that males had higher values as compared to females. Mandibular ramus had more statistically significant dimorphic features as opposed to mental foramen. Coronoid height was the most significant parameter in sex determination. Thus, from the results of the present study, the authors conclude that the mandible is an efficacious tool in sex determination among the Kanyakumari population.

Conflict of interests

Two of the authors are medical reviewers at Healthminds Consulting Pvt Ltd.