Computational Modeling for Prediction of Acoustic Changes in Vowel Production Due to Orthognathic Surgery

Facial Asymmetry, Jaw Deformity

Orthognathic surgery, Speech production, MRI

A computational model of human sound production based on high quality anatomic measurements and physical laws of sound propagation cannot be accomplished without a comprehensive data set including both 3D-images of the speaker's anatomy and the simultaneous recording of speech. Since the computational model has separate models for the vocal folds and the vocal tract, patients undergoing an orthognathic surgery is an optimal test object for the model development. Vocal folds remain unchanged while substantial changes take place in the vocal tract. Moreover, since the aim of the research is to predict acoustic changes in speech due to operations in head neck area, the orthognathic patient group is par excellence an example of such a prediction problem. If the model can be shown to give valuable information pre-operationally, many other patient groups could benefit from the results.

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.

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