The purpose of this study was to clarify the influence of condition of loss of occlusal support (Eichner classification B3, B4, C1, C2) on “the mandibular position during continuous [n] phonation” ([n] continuous phone position) and to assess the change of its position over time in new denture wearers. In the first part of the study, the influence of condition of loss of occlusal support on [n] continuous phone position was determined in 22 subjects. In the second part of the study, changes in [n] continuous phone position over time were assessed in 3 partially edentulous patients who were the new denture-wearers. A mandibular movement analyzing device was used to measure mandibular position.
 Following results were obtained:
1.“The interocclusal vertical distance in [n] continuous phone position” ([n] space) starting at intercuspal position was not significantly different among control, Eichner B3, B4, C1 and C2.
2.[n] space starting at physiologic rest position was not significantly different among control, Eichner B3, B4, C1 and C2.
3.[n] space was not significantly different between 2 starting positions (intercuspal position and physiologic rest position) on each group of control, Eichner B3, B4, C1 and C2.
4.The [n] space at the interocclusal record in 3 subjects was almost the same after 6 months of wearing dentures and there was no significant difference among all measurement time points for those 6 months.
 The results suggest that the mandibular position during continuous [n] phonation is not influenced by the loss of occlusal support and is valuable for determining the occlusal vertical dimension.

View full abstract

 The present study investigated whether visual sensory inputs influence masticatory muscle activities during tooth tapping movements. The masseter and temporal muscle activities of 25 healthy subjects were analyzed by monitoring electromyograms (EMGs) recorded with a pair of surface electrodes. Jaw movement was also analyzed by monitoring the motion of an LED reference point fixed on the lower incisor with a photo sensor. Mounted glasses with prismatic lenses were used for changing the scenery before the subjects' eyes. The subjects lay in the supine position with their head supported by a pillow. They were asked to perform repetitive tooth tapping movements when putting on or taking off the glasses. A decrease in the ratio between the temporal EMG and the masseter EMG (T-M ratio) was found in almost all the subjects when putting on the glasses. Simultaneously, anterior shift of the tapping point occurred when putting on the glasses. However, when wearing the glasses, a decrease in T-M ratio and anterior shift of the tapping point did not occur when the subjects maintained their head posture with their neck muscles. These results suggest that visual sensory inputs control masticatory muscle activities during tooth tapping movements, and that neck muscle proprioceptors play a role in this regulating system.

View full abstract