Postmortem CT morphometry with a proposal of novel parameters for sex discrimination of the mandible using Japanese adult data

• Objective interpretation is difficult in morphological sex estimation of the mandible.
• This study investigated CT morphometry for sex estimation using novel parameters.
• Japanese subjects after adolescence in forensic autopsy were examined.
• Novel morphometric parameters showed significant sex differences.
• The efficacy of CT morphometry for sex discrimination of the mandible was suggested.

Major human sex differences in the mandible after adolescence include the overall size as well as the shape of the chin and mandibular angle; however, objective interpretation of discrimination accuracy is difficult for these morphological indicators. The present study investigated measurements of the mandible for sex discrimination using postmortem CT morphometry in forensic autopsy cases of Japanese subjects after adolescence (age > 16 years; male, n = 116, and female, n = 106), including the proposal of novel parameters representing the overall mandibular size and shape. The distance between the gnathion and condylus (gn–cdl), and bigonial width (go–go), as well as the angle formed by bilateral gn–cdl lines (Agn–cdl), correlated with bicondylar breadth (cdl–cdl), independent of the body height, showing no significant sex difference. The distance from the gn to the cdl–cdl line (oblique length), the ratio of Agn–cdl to cdl–cdl, and the oblique triangular area formed by bilateral gn–cdl and cdl–cdl lines (Δobl), which were proposed as indicators of chin protrusion, showed significant sex differences (p < 0.001). Overall sensitivity and specificity at respective discriminating points for sex estimation were 0.72 and 0.78 at 105.0 mm for the oblique length, 0.73 and 0.83 at 0.49 for the Agn–cdl to cdl–cdl ratio, and 0.82 and 0.78 at 643 mm2 for Δobl; the efficacy for females was greater in younger subjects. Although these parameters weakly depended on the body height (p < 0.0001), the correlations were insufficient for stature estimation. These findings suggest the efficacy of CT morphometry of the mandible for sex discrimination with quantitative assessment.