Stability two years after mandibular advancement with and without suprahyoid myotomy: an experimental study.

Ten adult rhesus monkeys underwent mandibular advancement surgery of 4-6 mm with and without suprahyoid myotomy. Serial lateral cephalograms using radiopaque bone markers were obtained during maxillomandibular fixation and for 96 weeks after release of fixation to determine the effects of suprahyoid myotomy on short-term and long-term adaptations in the advanced mandible. The non-myotomy group exhibited a significant reduction in the length of the advanced mandible (relapse) during the fixation period but showed no significant change in mandibular length after release of fixation. The myotomy group exhibited no relapse during the fixation period and after release of fixation displayed a slight but statistically significant increase in mandibular length. This supports the hypothesis that stretching of the suprahyoid musculature as a result of mandibular advancement surgery is a major factor leading to skeletal relapse.