Morphology of the inferior border of the mandible: correct relation between the lowest position of the outer and inner contours of the cortex for a successful split.

For a sagittal split ramus osteotomy to be secure, the relation between the outer and inner contours of the cortex at the inferior border of the mandible is critical. The lowest point of the outer contour is not always immediately below that of the inner contour, and the former is placed more lingually than the latter in about a third of all cases. This tendency is much more noticeable in skeletal class I and II malocclusions than class III. It is therefore important to examine the lowest point of the inferior border in every case, and to carry the inferior part of the buccal cut on to the lingual side if necessary.