Abstract
The purpose of this study was to analyze the effect of the retainers in lower unilateral free-end removable partial dentures (U-RPD) on vertical displacement. An available jaw tracking system (TMJAWGRAPH®) was modified to measure the jaw movement and removable partial dentures motion at the same time. Further, pyramid-shaped markers were designed to allow 3-D measurement by a geometrical method. These markers were fixed in the U-RPD, mandible and head, and allowed simultaneous 6-degree-of-freedom recording of their movements. In two U-RPD wearers, the vertical movement of the incisor point (IC) and the most posterior point in the flange (MPFP) were investigated by changing the design of retentive elements. The shape of the traces of vertical movement in the MPFP was not as smooth when chewing peanuts as it was in gum chewing, thus the dependency of motion in U-RPDs on the type of food was confirmed. On the contralateral side, the rest of the indirect retainer was effective against upper displacement, in spite of retention. Further, the data suggested that in these cases, the rotation axis for the upper displacement of the MPFP is more posterior than the fulcrum line.
