Aim: To determine the effect of an acute change in occlusal vertical dimension (OVD) on tongue and lip pressure during swallowing.
Methods: Five male and five female volunteers (27-32 years) participated in this research. Intra-oral transducers were used to assess tongue and lip pressure, whereas surface electromyographic (EMG) electrodes were used to assess perioral muscle activity. The OVD was progressively increased using vacuum-formed trays of differing heights. Standardised swallowing tasks were performed repetitively with each tray in place. Individual swallowing waveforms were qualitatively and quantitatively analysed. Mean peak pressure, time to peak pressure, swallow duration and lip EMG peak activity were assessed for each swallow. Data were analysed using mixed-model analysis.
Results: Swallowing waveforms varied markedly between-individuals, but within each individual, their shape was minimally affected by changes in OVD. When OVD was increased, swallow duration increased by 12.7 percent (160ms; p = 0.01). Upper lip peak pressure increased by 63.8 percent (p ≤ 0.001) and intraoral peak pressure increased by 12.0 percent (p = 0.001) When OVD was increased, perioral muscle activity during swallows increased by 43.7 percent (p ≤ 0.01) up to the OVD where resting lip seal was not attainable.
Conclusion: An acute increase of OVD produces swallowing episodes that are slightly stronger and longer than those recorded at the habitual OVD. The waveforms of the swallows, however, remain remarkably similar. The adaptive response and the waveform similarities associated with OVD variation supports the existence of both peripheral and central mechanisms to control swallowing.
