[Studies on retainer's effect on unilateral designs of mandibular unilateral distal extention dentures. 1]

The dispersion of occlusal forces around both the abutment teeth and the alveolar mucosa is generally considered as an most important principal in minimizing the denture mobility and the local over-load on designing the distal extention-type denture. This study was undertaken to investigate the principal factors in designing uni-lateral-type clasp denture equipped with direct and indirect retainer. Our data show: 1. Guide-plane provides maximam retention power in cooperation with high fixable indirect retainer. 2. Direction of load and design of the denture are the major responsible factors for shifting the horizontal rotation center of denture body. Especially the shape of indirect retainer was demonstrated to alter direction and amount of displacement of the denture base and abutment teeth. 3. Most types of uni-lateral distal extention denture exhibited upward and downward movement when they function in vivo. 4. Negative type indirect retainer plased at incisor was shown to be harmful due to its intrinsic slunting force on teeth to labial direction. On the other hand positive type indirect retainer was considered to be more desirable because the force through clasp moves abutment teeth vertically.