CLOSEST SPEAKING SPACE DURING THE PRODUCTION OF SIBILANT SOUNDS AND ITS VALUE IN ESTABLISHING THE VERTICAL DIMENSION OF OCCLUSION

The purpose of this investigation was to determine whether the product ion of sibilant sounds involved adopting a jaw position that correspon ded to the closest vertical speaking space (CSS), by analysis of the s mallest vertical excursion of the mandible during the performance of d ifferent phonetic exercises. A further objective was to establish the variability in the CSS produced by individual sibilant phonemes. Thirt y young adult subjects had their CSS determined during three separate phonetic tests, using a kinesiograph (Sirognathograph, Siemens A.G., B enshiem, Germany) and a Bio-Pak (BioResearch Associates Inc., Milwauke e, WI)jaw-tracking software program. The first test was a general phon etic articulation test containing all the sounds of the English langua ge and specifically including all six sibilant word sounds. The second phonetic test contained the six sibilant sounds making up a short sen tence. The third test included six single words, each expressing a dif ferent sibilant sound. No statistically significant difference among t he mean CSS determined in each of the three exercises was demonstrable . A phonetic test containing all sibilant sounds produced a CSS equiva lent to that of a test containing all speech sounds. The vertical comp onent of the CSS was also independent of the form or duration of the p honetic tests containing the sibilant word sounds used in this investi gation. The CSS determined for 5 of the individual sibilant phonemes i n the third exercise differed (p < 0.05) from that calculated for the three complete exercises. It was concluded that voicing sibilant phone mes, or word sounds, does cause the subject to adopt the CSS. When a p honetic test is used in the determination of the vertical dimension of occlusion, one of short duration containing all the sibilant sounds a ppears to give a reliable guide to the CSS. It was also concluded that subjects varied with respect to which of the group of sibilant sounds produced the CSS, and that a single sibilant word sound does not give a reliable indication of the smallest speaking vertical dimension.