2021 Volume 13 Issue 2 Pages 135-145
Purpose: This study aimed to examine the positional effect of a removable partial denture palatal bar on speech-related discomfort using a subjective scale (visual analog scale: VAS) and objective brain activity measurements.
Methods: Twenty-five adults (mean age, 31.8 years) without speech function abnormalities wore a palatal bar on the maxilla and uttered the following sentences: “Sakura no Hana ga sakimashita” (first) and “America no Mississippi” (second). The VAS was used to evaluate the subjective discomfort experienced by the subjects during speech. The brain activity during speech was objectively evaluated using functional near-infrared spectroscopy (fNIRS). The dependent variables were the VAS score and the change in the oxy/deoxyhemoglobin (oxy/deoxy-Hb) concentrations in the prefrontal cortex.
Results: The VAS scores showed a tendency to increase with the posterior palatal bar (“posterior PB”) attached when uttering both sentences. Conversely, no significant changes in brain activity were observed for the first spoken sentence. For the second spoken sentence, the oxy-Hb concentration was high with the middle palatal bar (“middle PB”) attached, and it was significantly different from that when the anterior palatal bar (“anterior PB”) was attached. The deoxy-Hb concentration was high with the anterior PB attached. A significant difference in the deoxy-Hb concentration was found between the anterior PB and the middle PB as well as the anterior PB and the posterior PB.
Conclusions: The outcomes of the subjective evaluations of the anterior PB and middle PB were similar; however, that for the posterior PB was higher than the other palatal bars, reflecting the degree of inhibition of tongue movement. fNIRS showed that brain activity varied with the position of the palatal bar and speech content, possibly reflecting the cognitive load required for smooth utterance under the altered internal conditions of the oral cavity.
