applicability of the dimodent equation of sex prediction in a ...

Ayoub, et al. 36

APPLICABILITY OF THE DIMODENT EQUATION OF SEXPREDICTION IN A LEBANESE POPULATION SAMPLE

F.Ayoub1, A.Cassia1, S.Chartouni1, F.Atiyeh1, A.Rizk1, M. Yehya2, Z.Majzoub1, A.Abi-Farah3

1. School of Dentistry, Lebanese University, Beirut, Lebanon2. Orthodontist, Beirut, Lebanon3. Faculty of Sciences, Lebanese University, Beirut, Lebanon

ABSTRACTBackground: Sexual dimorphism represents agroup of morphologic characteristics thatdifferentiate a male from a female. Among thesedimorphic traits, tooth size has been evaluated invarious populations for its interest in anthropologicand forensic applications. Recent studies haveshown that dental dimorphism is population­specific and that the most dimorphic tooth is themandibular canine. In addition to the dimension of

single teeth in dimorphic dental assessment,dimorphism has been evaluated, using equationof prediction, applying various dimensions of oneor more teeth or indices. Purpose: The objectiveof this preliminary study was to evaluate theapplicability of the Dimodent predictive equationin sex determination in a sample of Lebaneseyoung individuals. Materials and Methods:Mesiodistal widths of the mandibular canine andlateral incisor were measured from dental casts of

the permanent teeth of 60 Lebanese Universitydental students (30 males and 30 females), aged18-25 years. The sex-predictive equation of Frontywas applied to calculate the percentage ofaccurately-diagnosed sexes. Results: Accuracy ofsex prediction ranged from 63.3% for males and90% for females. Overall, the Dimodent equationenabled a correct sex determination in 76.7% ofthe cases. When compared to the accuracyobtained with this equation in a French populationsample, the accuracy was significantly different(Z=3.1225). Conclusions: This research supportsearlier studies that sexual dimorphism is populationspecific. The difficulty or lack of dimorphism seemsto originate 'from male subjects. Furtherinvestigations should include the preparation ofpopulation-specific prediction tables and testingtheir accuracy in a larger sample with a strongly­established Lebanese background.(J Forensic Odontostomatol 2007;25:36-9)

Keywords: Dimodent equation, sexual dimorphism,Lebanese population sample

INTRODUCTION

Sexual dimorphism represents a group ofmorphologic characteristics that differentiate a malefrom a female.1.2 Sex-related morphologic differencesin the human skeleton have been extensivelyevaluated in several living and prehistoricpopulations.3 However, tooth-associatedodontometric differences have been less

investigated4 and mostly derive from the dentition ofextinct populations.s.a. Several studies havedemonstrated that male teeth are generally largerthan those of females in various populations.9'11

According to a study evaluating the odontometricsexual variations of various species of living and fossilmammals, as well as of human beings, Fronty2reported that dental sexual dimorphism is alwayspresent in living humans although in process ofregression in hominoids. Stroud et al.12 evaluatedsexual dimorphism in mesiodistal diameter, enamelthickness and dentin thickness of the permanentposterior mandibular dentition in a sample of 59 malesand 39 females aged between 20 and 35 years usingdigitized bitewing radiographs. The authorsconcluded that significant sex differences exist inmesiodistal diameter favoring males over females.This discrepancy was attributed to differences indentin thickness and not to enamel thickness.

Alvesalo et al.13 indicated that amelogenesis ispromoted by both X and Y chromosome genes, andsexual dimorphism in average tooth size isdetermined by a promoting effect of the Ychromosome on dentin growth, probably through cellproliferation.

Dimorphism was reported to be more pronouncedfor the molars than for the premolars12 but posteriorteeth are generally less variable than anterior teeth.11Canines have been demonstrated to display greatersexual dimorphism in crown size than any other tooth

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class in the permanent dentition in variouspopulations. 4.9.11.14.15

In contrast with differences in single toothdimensions, various authors have selected to applyequations of prediction using multiple dimensions ofone or more teeth or indices such as the mandibular

canine index (MCI),16 the quadratic discriminantanalysis,17functions' combining various crown indicesand modules18 and the Dimodent method.1 The

application of such equations in different populationshas yielded different degrees of predictability in sexdetermination as sexual dimorphism in toothdimensions has been reported to vary betweenpopulations.4.9.19'24 Hattab et al.9 showed thatJordanians have tooth sizes close to those of Iraqis,but significantly larger than those of Yemenite-Jews,Caucasians and Chinese. Iscan and Kedici4demonstrated that dental differences between sexes

were not highly dimorphic in Turks. The applicationof the mandibular canine index for sex determinationin India allowed the correct detection of males and

females in 83.3% and 81 % of the cases respectively.Tooth sizes of Southern Chinese were reported tobe, in general, larger than those of the Caucasians,comparable with Northern Chinese, but smaller thanthose of Australian Aboriginals.11 Sherfudhin et al.17concluded that in Indian subjects, the percentage ofcorrect classifications of sex was higher when usingquadratic discriminant analysis compared to the MC!.Currently, there are no published data related tosexual dimorphism in the Lebanese population. Thepurpose of the present preliminary investigation was,therefore, to evaluate the applicability of the Dimodentsex prediction equation in a sample of the Lebanesepopulation.

MATERIALS AND METHODS

Study SampleThe sample studied included 60 students (30 malesand 30 females) from the School of Dentistry of theLebanese University, Beirut, aged between 18 and25 years. The students recruited from differentLebanese regions were selected based on thefollowing inclusion criteria:1. Parents and grandparents of Lebanese origin;2. Presence of the lower canines and lateral incisors;3. Absence of morphological tooth abnormalities,

crowding or malposition;4. Absence of carious lesions or fillings involving the

interproximal aspects of the studied teeth(mandibular lateral incisors and canines); and

5. Absence of severe abrasions, attrition or fractureson the involved teeth. Patients with ongoingorthodontic therapy were excluded from the study.

Sex prediction in a Lebanese population

Mandibular dental casts were obtained usingpolysiloxane in a double mixture* base. Casts thatdid not allow accurate measurements of the teeth

were excluded and the impressions repeated.

Measurement MethodSince the differences in crown diameters between

the right and left sides of the same dental arch arenot significant,9.25 the left-side measurements weretaken arbitrarily to represent the tooth size of thestudy population. The following measurements werecarried out on the mandibular canine and lateral

incisor directly on the dental casts according to thetechnique described by Seipel26 and Moorrees.271. Maximum mesiodistal (MD) width defined as the

greatest distance between the proximal surfacesof the crown;

2. Maximum bucco-lingual (BL) crown diametermeasured as the greatest distance between thebuccal and lingual surfaces of the crown at rightangles to the mesio-distal crown diameter of thetooth.

All measurements were carried out by one operatorusing a digital caliper** that had been calibrated priorto measuring. All measurements were to a precisionof 0.01 mm. Subsequently, the measurements weresubjected to the Dimodent sex prediction equationof Fronty et al. 1formulated as follows:

P = 1/(1 + e-V)

where P stands for the probability of being presentin a male or female dentition, whereas the parametery is obtained from the linear combination of selectedvariables multiplied by the coefficients specifying theirimportance. y is calculated as follows:y = 24.2 + (1.54 Ill-MD) + (1.92 ILI-VL) - (2.84 CI­

MD) - (3.38 CI-VL)

ILl-MD represents the mesio-distal diameter of thelateral mandibular incisor;

ILI-VL is the vestibulo-lingual diameter of the lateralmandibular incisor;

Cl-MD is the mesio-distal diameter of the mandibularcanine; and

CI-VL is the vestibulo-lingual diameter of themandibular canine.

The four odontometric measures of all subjects areintroduced in the equation. According to the valuesof P, three alternatives are possible:1. If P tends to 100% (Le. P>50%), the dentition with

the calculated probability belongs very likely to afemale;

" Zetaplus, Indurent Oranwash L, Zhermack, Italy""Absolute Digimatic, Mitutoyo, United-Kingdom

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Ayoub, et al.

2. If P tends to 0% (Le. P<50%) , the dentition isvery likely to be masculine;

3. If P = 50%, discrimination is null and sex can notbe determined.

Statistical AnalysisThe application of the sex predictive equation wasconsidered to be successful if sex determination was

correct (P values above or below 50% for femalesand males respectively); otherwise it was regardedas a failure. The overall success rate in sexdetermination in the Lebanese population samplewas determined and compared to that of the Frenchpopulation1 using the Z value (test of equality of tworates in the two studied populations) to confirm orrefute the null hypothesis (success rates in sexdetermination are similar in both Lebanese and

French populations).

RESULTS

The accuracy of sex prediction in the present studyranged from 63.3% for males to 90% for females.Overall, the application of the Dimodent equation wassuccessful in sex prediction in 76.7% in the Lebanesepopulation sample (Table 1).

When compared to the accuracy obtained with theDimodent equation in the French population, thedifference in accuracy was highly significant. Theapplication of this equation in the French andLebanese populations yielded a Z value of 3.1225(superior to the threshold of 2.58) which allowsrejecting the null hypothesis and confirming that theoverall rates of success in sex determination in the

two populations are significantly different. Thedifficulty or the lack of dimorphism seems to originatefrom male subjects.

DISCUSSION

The applicability of the Dimodent equation wassuccessful in sex determination in 90.6% of the

French sample and 76.7% in the Lebanesepopulation sample. The percentage of Lebanese menand women where the sex was successfullydetermined by the Dimodent equation was lower thanthat obtained by Fronty et al.1 in the French

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population. Previous studies have demonstrated thatsexual dimorphism in tooth dimensions variesbetween populations and that the application of sexpredictive equations yields different degrees ofpredictability in different populations.4,9,17,19,24 Becauseof the limited study sample included in thisinvestigation, it may be suggested that applicationof equations to determine the sex of young Lebaneseindividuals is less useful than when applied to otherpopulations. Differences can most likely be attributedto sample size andlor to odontometric differences.

The use of the Dimodent equation was suggestedby the high degree of sex discrimination obtainedwith the mandibular canine and the high correlationcoefficients between the mandibular canine andlateral incisor widths.1,25 The selection of the

population sample was based on the inclusion ofindividuals of similar age, of Lebanese descent andrepresenting different regions of the country. Itremains to be investigated if a random and largersample of the Lebanese population has specificodontometric values that can be better predicted withcustomized equations. Further investigations shouldinclude the preparation of population-specificprediction tables and testing their accuracy in a largersample with a stronger Lebanese background.

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2. Fronty P.Aspects anthropologiques et genetique dudimorphisme sexuel dentaire. Cah Soc Anthrop GenDento Faciales 1979;5:11-24.

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4. Iscan MY, Kedici PS. Sexual variation in bucco-lingualdimensions in Turkish dentition. Forensic Sci Int2003;137:160-4.

Table 1:summarizes the percentages of correct and failed sex prediction in the Lebanese samplecompared with those reported for the French population sample. 1

Population Successin Successin Failure Failure inMales Females In Males Females

French

Lebanese

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5. Dean MC, Beynon AD. Tooth crown heights, toothwear, sexual dimorphism and jaw growth inhominoids. Z Morphol Anthropol 1991 ;78:425-40.

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Sex prediction in a Lebanese population

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19. Axelsson G, Kirveskari P. Crown size of permanentteeth in Icelanders. Acta Odontol Scand 1983;41: 181­6.

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21. Bermudez de Castro JM, Sarmiento S, Cunha E,Rosas A, Bastir M. Dental size variation in theAtapuerca-SH Middle Pleistocene hominids. J HumEvol 2001;41: 195-209.

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23. Kondo S, Funatsu T, Wakatsuki E, Haung ST, ChangeSY, Shibasaki Y, Sasa R. Sexual dimorphism in thetooth crown dimensions of the second deciduous and

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Address for correspondence:Dr. Fouad Ayoub,Ras El-Nab eh, EI-Khattab Street,Rida Building, gth floor,Beirut,LEBANONreI: +961-3-215290

Email: [email protected]

The Journal of Forensic Odonto-Stomatology, Vol.25 No.2, December 2007