The purpose of this study was to define variation in /s/ articulation associated with differences in incisor dentition. Articulatory relationships, defined by cephalometric films, were studied in normal speakers with normal occlusion and complete dentition, normal speakers with normal molar relationships and missing maxillary incisors, and /s/ defective speakers with normal molar relationships and missing maxillary incisors. Adequacy of /s/ articulation for the total sample of 39 children was determined by two separate auditory ratings.

Significant differences between normal and defective /s/ articulation were related to the environmental characteristics of the anterior oral constriction. Speakers with defective /s/ articulation excessively fronted the tongue tip. Other differences were related to the antero-postero and vertical placement of the tongue tip, to the extent of mandibular protrusion-retrusion, and to the vertical position of the upper lip. There was no significant difference between children with normal and defective /s/ articulation in regard to the degree of vertical constriction between the midline of the tongue and dental-alveolar complex. These findings appear to be consistent with current physiological phonetic theory.