Assessment of Shape Differences in the Human Mandible: Sexual Dimorphism

While it is now well understood that many human morphological aspects are influenced by sexual dimorphism, the effect is mainly one of size differences. Females reflect a 4-10% reduction in size for many body measurements. In contrast, few studies have considered differences in shape. It is argued that the ability to detect such shape changes in sexual dimorphism is important for various disciplines, such as forensics, anthropology, dentistry and medicine. The conventional method consisting of distances, angles and ratios is not very efficient with complex irregular morphological forms. Objectives: The purpose of this study was to assess the presence of sexual dimorphism in the mandible (MD) utilizing Fourier Descriptors (FDs). FDs are particularly useful for providing a precise quantitative description of the boundary outline, correct for size and precisely recreating the outline at any time. In a previous study of the inferior MD border, we found significant dimorphic shape differences with females displaying a relatively longer mean mandibular length (AJPA, Supp 42:121, 2006). That study prompted a re-evaluation using a larger dataset and a different anatomical view. Methods: A Japanese sample of MDs (n=61 females; n=97 males) was obtained from the Edo Period (1600-1868 CE) and digitally photographed in the more familiar lateral view. Only specimens with largely intact dentitions were utilized to minimize the effects of bone resorption due to tooth loss. The lateral MD outlines were digitized with 84 points. Results: Superimposition on the body of the mean MD outlines displayed a statistically significant posterior repositioning of the female condyle head and coronoid process, which generated a relatively longer MD length from Menton to the superior aspect of the condyle head. Conclusion: These results, thus, re-enforce the earlier 2006 study and document the presence of statistically significant sexual dimorphism in the shape of the human mandible (plestrel@earthlink.net).