Acoustic and perceptual analysis of the sibilant sound /s/ before and after orthognathic surgery

Abstract

Purpose: Orthognathic surgery may have a positive or negative effect on speech. Perceptual evaluation of presurgical and postsurgical articulation is difficult because speech errors, when they occur, are usually fricative distortions, which may be difficult to document reliably. In this study, acoustic analysis was used to supplement perceptual judgment of presurgical and postsurgical productions of /s/. Subjects and Methods: The study population consisted of 9 Cantonese speakers undergoing osteotomy for Class III skeletal deformity and 9 age- and gender-matched adults with normal occlusion and speech. The speech sample consisted of 6 words with the initial sibilant sound /s/. Perceptual analysis included narrow phonetic transcription and classification of error types. Acoustic analysis included measurement of first and second spectral peaks, fricative duration, noise bandwidth, and noise-to-vowel decibel ratio. Results: The results of the perceptual analysis showed a decrease in articulatory errors for the group after surgery, although 5 patients had no perceptual errors before surgery. Acoustic analysis showed significant differences between the experimental and control groups before surgery for 2 variables (spectral peak I and bandwidth). Three months after surgery there were no significant differences between the control group and the experimental group, except for bandwidth. Twelve months after surgery, there were significant differences between the 2 groups in noise bandwidth and spectral peak II. Conclusions: The results suggest a possible relapse at 1 year after surgery, based on spectral peak values. Osteotomy appears to result in a positive change in articulation for most patients, but speech outcome after osteotomy must be evaluated both 1 year and shortly after surgery. © 2002 American Association of Oral and Maxillofacial Surgeons.