Answer:
A sagittal split operation is a mandibular advancement procedure which is done to correct retrognathia. The advancement of the entire mandible-dental complex produces changes in the lip, labial sulcus, and soft tissue chin. As the mandible is advanced 1 mm, the soft tissue and hard tissue pogonion changes in a 1:1 ratio, and the labial sulcus and bony point B also change in a 1:1 ratio. As the mandible is advanced the lips unroll and then advance, as they are frequently rolled up under the maxillary incisiors to start with.