Fig. (1) Cropped panoramic radiograph showing the left body of the mandible in the region of the mental foramen (M). A line (X) was drawn from the midpoint of the foramen to the lower border of the mandible, at right angles to the tangent (Y) to the lower border at this point. The width of the cortical bone at the lower border was measured along the line (X) from the lower mandibular border to the inner edge of the cortex.