Analysis of the Relationship between the Incisal Overjet in a Maxillary Denture and Phonetic Function Using a Speech Recognition System

Purpose: The purpose of this study was to investigate the relationship between the intelligibility of the /S/ sound and the incisal overjet of the anterior teeth of in a maxillary denture.Methods: Five subjects who were fitted with maxillary dentures participated in this study. Using a speech recognition system for the evaluation of phonetic functions, the correct and incorrect ratios of the intelligibility of the sound of the monosyllable [Si] in five subjects were determined in relation to increases in the degree of incisal overjet of the anterior teeth in a maxillary denture by +0, +1, +2 and +4 mm relative to that of the dentures already in use.Results: In association with increase in the degree of incisal overjet in experimental dentures from +0 to +4 mm, while the appearance ratio of the correct [Si] sound decreased from 73.0±8.6% at +0 mm to 48.5±7.8% at +4 mm, that of the incorrect [Si] sound increased from 17.4±4.7% at +0 mm to 36.0±10.6% at +4 mm.Conclusion: Increasing distance between the incisal edges of the maxillary and mandibular incisors make correct pronunciation of [Si] progressively more difficult.