Analysis of the Relationship between Palatal Contour and the Phonetic Function in Complete Denture Wearers Using a Speech Recognition System

Purpose: This study used a speech recognition system to investigate the intelligibility of the /∫/ sound, which is based on the palatal contour of complete dentures.Methods: Six subjects with an edentulous maxilla participated in the study. The experimental dentures were made of self-curing acrylic resin and four curvatures (0, 2, 4, 6 mm) of the palatal contour were evaluated. A speech recognition program automatically converted the phonetic signals into phonetic segment labels. Labels that correctly recognized the /∫/ sound were defined, and the distribution of the correct labels was analyzed in relation to the palatal contour. Palatograms were also recorded to assess tongue movement.Results: Repeated-measures one-way analysis of variance revealed a significant effect of the curvature of the palatal contour on the appearance ratio of the correct [∫i] labels (F=53.1, P<0.05). Tukey’s multiple comparisons revealed a significant difference between 0 mm and 2 mm (P<0.001), 0 mm and 4 mm (P<0.001), 2 mm and 6 mm (P<0.001), and 4 mm and 6 mm (P<0.001). Based on the appearance ratios of the [ci] labels, the 0 mm curvature of the palatal contour was rated as yielding the highest intelligibility (P<0.01), and based on those of the [t∫i] and [d ?? i] labels, the 6 mm curvature was rated as yielding the intelligibility (P<0.01 for both). When tongue movement was assessed from the palatograms, tongue contact was found to be similar to that in the typical palatogram for each recognized syllable.Conclusion: The curvature of the palatal contour affects the pronunciation of the /∫/ sound, and the appropriate curvature of the palatal contour in complete dentures for correct pronunciation of this sound is 2 to 4 mm.