Effect of temporary prosthetic mandibular advancement on velopharyngeal closure for speech

Incomplete closure of the velopharyngeal (VP) port may result in inappropriate production of some speech sounds. Surgeries for upper and/or lower jaw advancements are known to change bone and muscular structures resulting in changes affecting the soft palate closure on the throat. The purpose of this study was to elucidate the effect of temporary advancement of the lower jaw on soft palate closure and speech. Fourteen subjects with no history of craniofacial abnormalities or speech disorders were recruited. A nasometer detects the % of the acoustic energy coming through the nose out of overall acoustic energy through the mouth and the nose, which is ‘nasalance’. Nasalance values were obtained during speech production of nasal sentences and sentences without nasal consonants in two conditions; normally, and while wearing an appliance for sleep apnea to advance the lower jaw by 13mm. Subjects were also asked to produce five repetitions of the nasal sentence "Ten men came in when Jane left" in two conditions. Movements of the soft palate were assessed using a videoendoscopy/phototransducer system, which sensed the amount of light passing through the velopharyngeal port. Nasalance was significantly decreased for the nasal sentences after the lower jaw advancement, but remained within a normal range. Velopharyngeal closure (VPC) did not significantly change after mandibular advancement, and was variable in response to the lower jaw advancement condition. Outcomes of this study demonstrated the effect of lower jaw advancement on VPC and speech. Implications for speech therapy and surgery are considered regarding individuals who require surgical advancement of the mandible.