Effects of increased vertical dimension on size of constriction port and fricative sound intelligibility.

The effect of increased vertical bite dimension on fricative sound productions was studied in five adults who wore dentures. Oral port size and sound intelligibility were evaluated at different degrees of artificially induced open bite. The data demonstrate that rapid compensatory adjustments occurred and oral port size changed minimally at all degrees of opening tested. However, in three of the subjects, sound intelligibility declined at the 6-mm opening, and in all subjects, a four-fold increase in sound distortions occurred in the edentulous state. This finding suggests the possibility that either physiological parameters are controlled more successfully than acoustical parameters or that compensatory efforts to maintain constrictor size may, under certain circumstances, adversely affect sound intelligibility.