The oral cavity with such articulatory organs as the lips, tongue, uvula, and soft palate which are very versatile in mobility plays an important role of articulatory function in producing various sounds by changing their forms. When many teeth are lost by surgery or periodontosis, it is well known by experience that the articulatory function of the oral cavity is greatly impaired and speech impediment is induced. In practice in prosthodontics, therefore, it is very important to restore the articulatory function, as well as esthetic and occlusion, by carrying out a prosthetic treatment at the region with a tooth-loss. In view of the articulatory function, it is important to examine the relation between artificial tooth position and articulation. Four types of experimental dentures with over bite and over jet varied were therefore prepared for the cases of a tooth-loss at the lower anterior region. Five syllables of "S" followed by a vowel in Japanese (Sa, Si, Su, Se, So) were designated as the target syllables and analyses of "S" position on Mandibular Kinesiograph and of the voice on a sound spectrograph were made. Then, the effect of the changes in the artificial tooth position in the lower anterior tooth region on articulation was examined in detail. The results were as follows : 1. With the standard-type experimental denture with over bite at 2mm and over jet at 2mm, no positional changes in the anteroposterior "S" position were found in any of the "S" syllables. 2. The up-down "S" positions differed among the target syllables. The positions for "So" showed the greatest difference in comparison with other syllables. 3. The effect of increase in over jet on the anteroposterior "S" position was greater in comparison with the up-down "S" position, and the anteroposterior "S" position tended to be displaced forward. However, with the experimental denture with over bite at 4mm and over jet at 6mm, the tendency toward forward displacement of the anteroposterior "S" position decreased. 4. The effect of increase in over jet on the up-down "S" position was rather small, and no fixed patterns were seen in the displacement direction of the up-down "S" position. 5. The consonant duration differed among the target syllables. It was comparatively long for "Si" and "Su" and was the shortest for "Sa". 6. The effect of the artificial tooth position in the lower anterior region on the consonant duration was small. 7. The average amplitude differed among the target syllables. It was comparatively large for "Si" and "Su" and was the smallest for "Sa". 8. The effect of increase in over jet on the average amplitude was very marked. Although the average amplitude showed a decreasing tendency, the experimental denture with over bite at 4mm and over jet at 6mm, showed a decline in the rate of decrease. 9. Analyses of frequency showed that the energy level tended to decline in the hlgh frequency range form 4, 500∿5, 000Hz to 9, 500∿10, 000Hz for all target syllables of "S" with an increase in over jet. However with the experimental denture with over bite at 4mm and over jet at 6mm, the declining tendency of energy level decreased.

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