Effects of sagittal split advancement osteotomy on facial profiles

In 31 surgically treated Class II patients, several features were studied on cephalograms, before and after a mandibular lengthening osteotomy had been performed. After surgery, hardly any changes in the soft tissue thickness were recorded. In Class II patients, the upper part of the lower lip is situated at a larger distance from the skull, since its position is influenced by the antero-posterior position of the upper incisors and the overjet. The postoperative decrease of this distance was caused by the fact that the upper part of the lower lip failed to follow the total amount of forward mandibular displacement. This is due to the fact that the antero-posterior position of this part of the lip is touching the upper incisors and therefore does not follow the amount of mandibular advancement. The labiomental fold flattens, because the lower part of the lower lip completely follows the forward displacement of the mandible, whereas the upper part remains almost unchanged. This flattening can be favourable in Class II patients showing a very deep fold, as the surgical intervention tends to normalize the depth. In open bite profiles on the contrary, this effect could be unfavourable. The combination of the lengthening osteotomy with a genioplastic intervention, could mask this unfortunate result. Due probably to the presence of orthodontic retention devices and the intercuspidation of teeth, normal occlusal relations remained one year after surgery. A relapse of about 30 per cent was found in the mandibular bases. In order to anticipate this, some surgical overcorrection could be considered.