An analysis of stress distribution in the free-end saddles on the mandibular model

This experiment was designed to investigate and evaluate the characteristic behavior of mandibular free-end saddle removable partial denture using various retainers. The abutment tooth displacement and saddle movement were measured while a known vertical force was applied on the saddle. Fifteen different types of free-end saddle dentures were tested, using four various types of prefabricated attachments. Strain-measuring devices were used to measure the extent of abutment tooth displacement and saddle movement. The findings were as follows: 1) The force transmitted to the abutment tooth and the residual ridge were affected by (a) the selection of direct retainers, (b) splinting of abutment teeth, and use of indirect retainers, and (c) the variation in size and shape of the occlusal table on the saddle. 2) The influences by direct retainers a) With use of a resilient joint, the stress was heavily loaded on the residual ridge directly under the direction of force. b) With the joint incorporating the vertical rock-preventing device, a heavy proportion of lateral force was transmitted to the abutment tooth. 3) Both the lateral stress on the abutment tooth and movement of the saddle were reduced more effectively by use of indirect retainers than by splinting of abutment teeth. 4) By reduction of the occlusal area in bucco-lingual dimension, the denture saddle was better stabilized and the lateral stress on the abutment tooth was reduced effectively.