Influence of the position of the palatal bar on brain activity during swallowing

Abstract

Purpose: The position of the palatal bar plays a key role in oral discomfort upon swallowing in patients with partial dentures of the maxilla, however, its quantitative evaluation is difficult. We used a portable functional near-infrared spectroscopy (fNIRS) system to investigate the swallowing related changes in activity of the prefrontal cortex under simulated partial dentures with different palatal bar positions to objectively evaluate the magnitude of oral discomfort.

Methods: Thirty-one dentate young adults participated in the study. Participants swallowed a bolus of water while wearing a simulated palatal bar located in the anterior, middle and posterior positions of the maxilla. Prefrontal regional brain activity was recorded by a wireless fNIRS system. The averaged and normalized oxy-hemoglobin (oxy-Hb) responses were compared among palatal bar conditions. We also recorded fNIRS data when participants swallowed the same bolus of water without wearing the palatal bar. The cumulative differences in the oxy-Hb responses between with and without the palatal bar were compared across conditions. Subjective oral discomfort upon swallowing was also obtained using a visual analog scale (VAS).

Results: Swallowing-related prefrontal activity was the largest in the posterior palatal bar condition, especially in the frontal pole region. The cumulative differences in the oxy-Hb activity in the posterior palatal bar condition were significantly greater than in the middle palatal bar condition. Consistent with the fNIRS results, the mean VAS value showed a significant increase of discomfort with swallowing from anterior to posterior positions of the palatal bar.

Conclusion: Subjective swallowing difficulty increased in order of anterior, middle and posterior palatal bar positions. Changes in activity in the frontal pole were confirmed especially between the middle and posterior palatal bar conditions. These results suggest the possibility of using fNIRS as a method to objectively evaluate intraoral sensation.