CAPT RISHI POKHREL

COL RAJAN BHATNAGAR

COL SUSHIL KUMAR

“A Study of Sexual Dimorphism

in

Human Mandibles

using

Multivariate Discriminant Functional Analysis”

INTRODUCTION

Determination of sex from skeletal remains – initial step in determination of identity

Human mandible - among the strongest bones

- significant sexual dimorphism

Multivariate Discriminant Functional Analysis (MDFA)

– best among metric methods.

Population: Marathwada region of Maharashtra.

AIMS & OBJECTIVES

To test sexual dimorphism in mandibles of population under

study.

To identify parameters of mandible that show maximum sexual

dimorphism

To determine population specific cut off point and constants for

MDFA.

To test the accuracy of MDFA.

MATERIALS & METHODS

Cross sectional, observational study

Adult mandibles of known sex from Anatomy department, GMC,

Aurangabad.

Sample size : 103

Males: 77

Females : 26

Exclusion criteria

Incomplete

Gross asymmetry

Extreme of ages

Male; 77

Female; 26

MATERIALS USED

MATERIALS USED

PARAMETERS USED

Parameter (Midline) Abbn. Parameter (Bilateral) Abbn.

Symphyseal height ID GN Height of mandibular body HT

Bicondylar breadth CDL CDL Mandibular thickness at mental foramen

MB

Bigonial breadth GO GO Minimum ramus breadth MnRb

Mandibular length ML Maximum ramus breadth MxRB

Intermolar distance IMD Mandibular or gonial angle A

Intercanine distance ICD

Arch perimeter AP Units mm, degree, cms

STATISTICAL ANALYSIS

MDFA (multivariate discriminant function analysis)

Stepwise MDFA

Analysis : SPSS 19

OBSERVATIONS&

RESULTS

ID GN HT LT MB LT GO GO CDL CDL Mn RB Mx RB Mx RH ML A IMD ICD AP 0

20

40

60

80

100

120

140

MALES

FEMALES

MEAN VALUES

DESCRIPTIVE STATISTICS

Variable TOTAL (N = 103) MALE (N = 77) FEMALE (N = 26) Pvalue

MEAN SD MEAN SD MEAN SD

ID GN 27.06 4.27 27.55 4.25 25.62 4.070.0456

HT 26.48 3.48 26.77 3.46 25.60 3.430.138

MB 10.60 1.33 10.74 1.39 10.17 1.050.059

GO GO 100.20 9.86 101.90 8.99 95.15 10.740.002

CDL CDL 115.63 9.40 116.86 7.76 111.96 12.60.021

Mn RB 33.61 5.69 35.35 5.38 28.47 2.74<0.001

Mx RB 43.03 6.27 44.83 5.85 37.69 4.09<0.001

Mx RH 63.17 7.25 64.13 6.64 60.32 8.320.020

ML 66.62 7.00 68.22 6.31 61.89 6.91<0.001

A 118.79 6.87 117.84 6.67 121.58 6.810.016

IMD 36.55 5.87 36.80 5.88 35.80 5.900.456

ICD 23.10 7.01 23.91 7.26 20.68 5.650.042

AP 7.011 1.00 7.08 1.06 6.80 0.810.228

STEP 1: MDFAMultivariate discriminant function

f (x) = b0 + b1x1 + b2x2 + b3x3 + --------- + b13x13.

Where, f (x) : MDFA score

b0 : constant (-7.704)

b1 to b1 : raw coefficients

x1 to x13 : variables values

Parameter b

ID GN -0.037

HT 0.076

MB 0.267

GO GO -0.050

CDL CDL 0.041

Mn RB -0.185

Mx RB -0109

Mx RH 0.053

ML -0.015

A 0.101

IMD 0.053

ICD 0.033

AP -0.301

f(x) at group centroid for males = - 0. 556

f(x) value at group centroids for females = 1.648

Demarcation point = 1.09

STEP 2: STEPWISE MDFA A combination of MnRB and A was found to be best among

all.

The function

f (y) = b0 + b1 (MnRB) + b2 (A)

b0 = 3.755

b1 = 0.202

b2 = - 0.089

f(x) at group centroid for males = 0.435

f(x) value at group centroids for females = -1.288

Demarcation point = - 0.9628

METHOD Male Female Male % Female % Overall %

MDFA 72/77 21/26 93.5 80.8 90.3

S- MDFA 76/77 12/26 98.7 46.2 85.4

RESULTS

Male Female Overall0

102030405060708090

100

MDFA S-MDFAP

erce

ntag

e

FUNCTION FOR MDFA

f(x) = (- 0.704) + (-0.037) ID GN + (0.076) HT + MB (0.267) +GO GO (-

0.050) + CDL CDL (0.041) + MnRB (-0.185) + MxRB( -0109) + MxRH (0.053)

+ ML (-0.015) + A (0.101) + IMD (0.053) + ICD (0.033) + AP (-0.301)

f(x) > 1.09, the mandible belongs to female

f(x) < 1.09, the mandible belongs to male

Accuracy : 90.3%

FUNCTION FOR S - MDFA

f(y) = 3.744 + (0.202) MnRB + (-0.089) A

If, f(y) > - 0.9628 the mandible belongs to male and if

f(y) < - 0.9628, the mandible belongs to female

Accuracy: 85.4%

DISCUSSIONAuthor (s) with population No of Parameters

used

Accuracy %

(Hanihara, 1959), Japan 4 88.6

(Giles, 1964), USA 3 – 8 82.0 – 88.0

(Potsch-Schneider et al., 1985), Germany 17 71.6 - 81.7

(Steyn & Iscan, 1998), South Africa 5 81.5

(Barthélémy et al., 1999), France 2 - 7 87.3

(Muñoz et al., 2001), Spain 1 - 14 78.3 - 88.7

(Vodanović et al., 2006), Croatia 1-9 74.12 – 92.06

(Simona et al., 2007), Romania 5 - 7 86.0

(Saini et al., 2011), Varanasi, India 1 - 5 60.3 - 80.2

Current study, 2012, Maharashtra,

India

2 - 13 85.4 – 90.3

Saini et al, 2011, Indian Population (Varanasi)

 Functions and Variables Avg. Acc. %

Max. ramus br. + min. Ramus. br. + condylar ht. + projective ht. +

coronoid ht.

80.2

Max. ramus br. + min. ramus br. + coronoid ht. 80.2

Condylar ht + projective ht + coronoid ht. 76.7

Coronoid ht. 74.1

Condylar ht. 72.4

Projective ht. 68.1

Max ramus br. 62.1

Min ramus br. 60.3

Our study Maximum 90.3% Minimum 85.4%

Sample size : Total 116, Male 92, Female 24

CONCLUSIONS

Mandibles of population under study show sexual

dimorphism.

MnRB and A show maximum sexual dimorphism.

Population specific coefficients, constants and

demarcation points for MDFA are derived.

Accuracy of sexing is comparable to other

populations.

Acknowledgement

HOD and Department of Anatomy,

Government Medical College,

Aurangabad

DISCUSSION