Orthognathic surgery deals with the correction of abnormalities of the facial tissues. The underlying cause for abnormality may be present at birth or acquired during the life as the result of distorted growth or trauma. Orthodontic treatment alone is not adequate in many cases due to severity of the deformities. In a typical operation, the position of either one jaw (mandible or maxilla) or both jaws is surgically changed in relation to the skull base. The movement of the jaw position varies usually between 5-15 mm either to anterior or posterior direction. Such a considerable movement has a very profound effect on the shape and volume of vocal tract resulting detectable changes in acoustics. Although the surgery involves mandibular and maxillary bone, changes occur also in the position and shape of respective soft tissues and hyoid bone, as well. For this project, 20 adult patients (10 women and 10 men) undergoing orthognathic surgery will be enrolled. Exclusion criteria include diseases and conditions in which MRI examination is contraindicated (.e.g. pace maker), severe speech or hearing impairment, and other situations where the patient has difficulties with completing the tasks defined in the research protocol. Furthermore, patients to whom segmental surgery of the jaws will be performed in connection of orthognathic surgery are excluded. A specific pre-selection criterion for patients is the presence of numerous dental amalgam fillings that may cause artifacts in MR images.