[Evaluation of speech quality of skeletal Class III patients before and after orthognathic surgery]

The purpose of this study was to investigate the influence of orthognathic surgery on the speech quality of patients with skeletal mandibular protrusion. Samples of speech sounds were collected from 10 patients (8 females, 2 males) before and after surgical operation. Acoustic analysis, based on the linear predictive coding (LPC), was applied to analyze the lowest two local spectral peaks (P1, P2) on the vowels. Psychoacoustic examination was also carried out by 24 examiners using the paired comparison in naturalness of five different words. The results were as follows: 1) The widened vowel trajectory after orthognathic surgery seemed to be related to improvement of articulatory function. 2) The naturalness of speech in psychoacoustic examination has been improved in most patients after orthognathic surgery. 3) Patients who have improved naturalness of speech showed a tendency of having a widened vowel trajectory.