Investigations on the relation of dysgnathias and S-sound pronunciation

A registration-form phonetic test has been developed which incorporates an established method for checking fine motor skills. Using an objective measuring and computing technique (electro-acoustic sound analysis according to the sound-seeking method), the author studied the pronunciation of the S-sound of one group of eugnathic and three groups of dysgnathic test persons. There were significant differences in sound characteristics between the normal group and all groups with dysgnathia (P = 0.001). Therefore it is considered that not every patient with an anomaly of the tooth position must have a disturbance of the S-sound. In contrast to the relatively narrow variations in the normal group, in all groups with dysgnathia considerable dispersions were registered. The anterior open bite occupies first place with regard to its susceptibility to disturbances of the S-sound. The statistical analysis of the partial energy values of all the S-sound spectra revealed typical normal behaviour on the one hand, and characteristic differences between the groups with dysgnathia and the group with eugnathia on the other. The information which is most important for the valuation of the S-sound are contained in the frequency area up to 9 kHz.