Impacts of jaw surgery on speech in Class III patients.

Patients with severe Dentofacial Disharmony such as Class III underbites have a twentyfold increased prevalence of speech disorders. To understand the longitudinal effects of corrective jaw surgery on speech, a prospective observational cohort study was conducted of Class III patients (n = 67, Ages 15-36, without clefts). Class I proportional controls (n = 54) and Class III patients were recorded 1-2 months pre-surgery, 2-6 months post-surgery (short-term) and 9-14 months post-surgery (long-term). Speech recordings were evaluated through distortion ratings and measurement of spectral changes in consonant production. ANOVAs and linear mixed-effects models were used to assess changes in speech and cephalometric measures. Here we show that spectral features, distortion, self-reported speech outcomes, and cephalometric measures significantly improve post-operatively. Patients with severe distortions improve the most after surgery. Consonant production requires properly positioned articulatory structures, and surgery provides longitudinal speech improvement for patients with jaw disproportions. Data indicate functional benefit of jaw surgery on speech.