Geometric Morphometric analyzes from dental orthopantogram images: a regional anatomical analysis of sexual dimorphism in the adult mandible

After attending this presentation, attendees will have a betterunderstanding of a new method of sex assessment through the analysis ofclinical panoramic X-ray images.This presentation will impact the forensic science community byintroducing a novel method of sex determination following askull assessment.The human mandible has routinely been utilized in forensic assessmentof age at death, sex determination and biological affinity. However, suchstudies have generally utilized conventional assessments of size and shapevariables, and as such fail to record the true nature of shape differences dueto dimorphism in this functional skeletal element. The research herepresented utilizes geometric morphometric techniques to investigate andquantify shape and size variation in the morphology of the mandibular corpusand ascending ramus, and consequently the potential for forensic humanidentification. The results of a novel morphometric study using clinicalpanoramic scanning x-radiography to study the extent of morphologicalvariation within a modern Italian sample population are presented.Clinical digital orthopantogram images (OPG) were acquired of theupper and lower jaws of 50 male and 50 female participants. Ten type I andtype II 2D landmarks were applied to the symphysis, and condylar andcoronoid processes. One hundred equidistant semi-landmarks wereestablished along the inferior border of the corpus, and the posterior borderof the ascending ramus. The resulting landmark configurations (n 100) weresubjected to Generaliszd Procrustes Analysis (GPA) with Full Tangent SpaceProjection. Principal Components Analysis (PCA) was applied in order toassess population variation. Factor loadings were subject to CanonicalVariates Analysis with stepwise and leave-one-out classification in order toassess the effects of sexual dimorphism on mandibular shape. The resultsshowed individuals to be correctly classified for sex in 89.6% of cases,(males were correctly classified in 90.1% of cases, and females in 85.6%).Analyzes of the mandible were subsequently broken down intoanatomical regions based on the mandibular body, the bony processes andthe ascending ramus in order to investigate regional functional differencesin the expression of dimorphism in mandible. A partial least squares (2-block PLS) method was further applied, in order to examine patterns ofcovariation between shape variables and the exploration of patterns offunctional modularity. Most interestingly the results indicate the greatestlevel of individual and sex-specific variation is found in the shape-curveand pattern of the inferior corpus, in contrast to that of ramal flexure.Stepwise permutation tests and analyzes of regional covariation indicatefunctional coupling, with a moderate degree of modular integrationbetween the corporal and ramal regions suggesting that functional tiesbetween the units are correlated in influencing sex-based morphologicaltrait expression between anatomical regions, indicating that the geometricrelationship between the mandibular corpus and the ascending ramus offerssignificant power for forensic identification purposes. Consequently suchunits may be studied together or in isolation, and this may allow for thedevelopment of identification criteria based on modular unit shape variableswhich may be applicable for both whole specimens and fragmentedremains depending on the forensic situation. Overall the results are stronglysignificant and suggest that both dependently and independently that the406 * Presenting Authorshape relationship between the mandibular corpus and the ascending ramusoffers significant power for forensic identification purposes. Of particularinterest is that inferior corpus border shape offers significant discriminatingpotential in the assessment of sex, with the effects of allometry beingstrongly implicated. These and other implications of the sh[...]