Sexual dimorphism in frontal bone roundness quantified by a novel 3D-based and landmark-free method

In this study we present a novel and landmark-free method for quantifying shape differences between male and female frontal bones. CT scans were recorded for 80 male and 80 female Turkish hospital patients, age 25-40. The frontal bones were first isolated from the 3D models by digital cutting along the bordering sutures, and then aligned to a CAD-based sphere. This allowed us to quantify the amount of frontal bone overlapping with the sphere (on average 43.2 ± 6.5% for males and 33.9 ± 6.6% for females, the difference is significant at p<0.0001), and to identify areas of shape difference and deviation from the sphere surface in male and female bones. The larger proportion of spherical frontal bone surface in males challenges the common description of the female forehead as "rounder". Based on the overlap data, we developed discriminant functions able to correctly classify 77.5% of the frontal bone models as male/female. This demonstrates that 3D-based and landmark-free approaches to statistical shape analysis may become a viable alternative to the currently dominating landmark-based approaches for shape investigation.