Dental overjet, articulatory compensation and acoustics of speech
Purpose: Dentofacial abnormalities such as dental overjet (horizontal overlap of upper and lower incisors) have been linked, with mixed evidence at times, to misarticulations before and after corrective surgery in severe cases1. Many individuals, even in surgical populations, appear to successfully achieve typical-sounding productions by using compensatory adaptation of the speech articulators2. This may explain the seeming inconsistencies in the literature, especially in studies where the sample is not selected for occlusal or speech problems. However, previous research relating to malocclusion and speech has largely been based on perceptual judgments of misarticulation rather than objective acoustic measures. As such, this study seeks to investigate the association between degree of increased overjet (protrusion of upper incisors) in non-surgical populations and speech production using acoustic analysis. Methods: Native English speakers recorded 13 target words containing either the English fricatives /s, z, ?/, affricates /t?, d?/, or vowels /i, u, ?/. Measurements of dental overjet as well as language background information were collected. Each segment was analysed by spectral moments for fricatives and formant values for vowels, then related to the speaker’s degree of overjet. Results: Preliminary analysis suggests that acoustic values of certain fricatives correlate to amount of overjet, as do some vowel formants. Trained listeners note that intelligibility does not appear to be compromised perceptually. Conclusion: The results of this experiment add to the literature on the relationship between dental anomalies and articulation with quantitative acoustic measures, as well as on the role of articulatory compensation in the case of increased overjet.
1 Ruscello, D.M., Tekieli, M.E., & Van Sickels, J.E. (1985). Speech production before and after orthognathic surgery: A review. Oral Surgery, Oral Medicine, Oral Pathology, 59(1), 10-14.
2 Johnson, N.C., & Sandy, J.R. (1999). Tooth position and speech – is there a relationship? The Angle Orthodontist, 69(4), 306-310.
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