Acoustic Comparison of Vowel Sounds Produced Before and After Orthognathic Surgery for Mandibular Advancement

Abstract

The effects of orthognathic surgery on the phonetic quality of speech were studied by analyzing the main acoustic features of vowel sounds. Five men with dentofacial deformities undergoing surgical operation for correction of malocclusion were enrolled in the study. The speech material consisted of 8 vowels in sentence context. Every utterance was repeated 10 times in 3 different sessions: before the operation, 6 weeks after the operation, and 30 weeks after the operation. The acoustic features (F1, F2, F0, duration) of vowels were measured and analyzed. At the group level, no significant acoustic changes were found between the 3 different sessions in any parameter measured (all F values <1). The results show that the operation had individual and variable effects on vowel quality, ranging from slightly affected to completely unaffected. The 2 lowest vocal-tract resonances changed in frequency for 2 of the subjects, and 1 subject had short-term changes returning to the presurgical level. Significant changes of F0 were observed for 1 subject, and 3 of the subjects had short-term changes. No significant changes were found for duration. One subject had no significant changes in any parameter measured. No long-lasting perceptually significant changes were identified in vowel production in patients undergoing a variety of orthognathic procedures. The facial skeleton (consisting of palate, maxilla, mandible, dentition, nasal cavity, etc) imposes direct limits on the morphology of the resonating vocal tract cavities, and is therefore of immediate relevance to both speech articulation and acoustics.