A Novel Forensic Use of Clinical Odontological Imaging: Geometric Morphometric Analysis of Sexual Dimorphism in the Mandible From Panoramic Scanning X-Ray Images

After attending this presentation, attendees will have a betterunderstanding of the sex determination during the skull assessment.This presentation will impact the forensic science community byintroducing a novel method of sex determination in the process of humanidentification investigations.The human mandible is routinely utilized as part of sex assessment inforensic odontological and anthropological practice. Various studies havepointed to the utility of morphological and metrical traits in the mandible,such as symphyseal shape, gonial angle and eversion, and ramus flexureamong others in the assessment of biological sex. The research herepresented utilizes geometric morphometric techniques to investigate andquantify shape and size variation in the morphology of the mandibularcorpus and ascending ramus, and consequently highlights the potential forforensic human identification. The results of a novel morphometric studyare presented using clinical panoramic scanning x-radiography, the goal ofwhich was to develop a methodologically and statistically robust means ofinvestigating biological variation in lower jaw morphology from acommonly acquired clinical data source.As part of proof-of-concept, clinical digital orthopantogram images(OPG’s) were acquired from 50 male and 50 female adult participants froma modern Italian sample population. Ten type I and type II landmarks wereapplied to the symphyseal region and the condylar and coronoid processesof the resulting 2D images in order to anchor a framework of semilandmarkcurves. One-hundred equidistant semi-landmarks wereestablished along the inferior border of the corpus, and the posterior borderof the ascending ramus, thus encompassing the sympyseal region, gonialregion, and posterior ramus – all of which are isolated anatomical regionswhich have been demonstrated to exhibit significant expression of sexualdimorphism in previous studies. The resulting landmark and semilandmarkconfigurations were subjected to Generalized ProcrustesAnalysis (GPA) with Full Tangent Space Projection. Principal ComponentAnalysis (PCA) was applied in order to assess populational variation.Factor loadings were subject to Canonical Variates Analysis with stepwiseand leave-one-out classification in order to assess the effects of sexualdimorphism on mandibular shape. The preliminary results showedindividuals to be correctly classified for sex in 89.6% of cases (males werecorrectly classified in 90.1% of cases, and females in 85.6%).A partial least squares (2-block PLS) method was further applied, inorder to examine patterns of covariation between shape variables and theexploration of patterns of functional modularity. In this case, functionalmodules are assumed to be units within which there is a high degree ofintegration from many and/or strong interactions, but which are relativelyindependent of other such units. The nature of the interactions can be, forinstance, developmental, functional, or genetic, depending on the context.Most interestingly the results indicate the greatest level of individual andsex-specific variation is found in the shape-curve and pattern of the inferiorcorpus, in contrast to that of ramal flexure. However, a moderate degree ofmodular integration between the corporal and ramal regions suggests thatfunctional ties between the units are correlated in influencing sex-basedmorphological trait expression. Consequently such units may be studiedtogether or in isolation, and this may allow for the development ofidentification criteria based on modular unit shape variables which may be260 * Presenting Authorapplicable for both whole specimens and fragmented remains depending onthe forensic situation. Overall, the results are strongly significant andsuggest dependently and independently that the shape relationship betweenthe mandibular corpus and the ascending ramus offers significant power [...]