Two-thirds anteroposterior ramus length is the preferred osteotomy point for intraoral vertical ramus osteotomy.

Mandibular setback operations for treating mandibular prognathism mainly include sagittal split ramus osteotomy (SSRO) and IVRO. IVRO has a markedly lower incidence of postoperative lower lip paraesthesia than SSRO. Our design presented a reference point for identification during IVRO, to prevent damage to the inferior alveolar neurovascular bundle.