EVALUATION OF THE RESIDUAL RIDGE AND DENTURE DESIGN IN RELATION TO THE LATERAL FORCE DISTRIBUTION TO THE ABUTMENT TEETH In the case of unilateral extension saddle type removable partial denture prosthesis

This investigation was carried out for the purpose of analyzing the functional behavior of the removable partial denture with unilateral extension saddle, particularly to relationship between the denture design and the residual ridge form. For this purpose, four different types of residual ridges in clinically simulated mandibular models and three different types of testing dentures for each model were made. The previously reported special devices for measuring the tooth mobility, force applicator, and a micro-dial-gauge, and also their recording system were used. Using these systems, the amount of the lateral excursion of abutment tooth for the direct and indirect retainers was measured for three types of dentures on each model while a known force was applied on the occlusal table of the testing dentures. A personal computor was used for the statistical analysis of these data and the conclusions were as follows: i) The transmitting force to the abutment teeth was highly affected by the condition of residual ridge form and by denture designs while known vertical and lateral forces were applied on the occlusal table of the distal area. ii) On the residual ridge with excess bucco-lingual bone loss, the so called rocking axis of denture was located on the crest of the residual ridge, but location of the rocking axis was completely irregular on the residual ridge with excess bone loss in the second and third molar area. iii) The twisting point or shifting axis on the occlusal table appeared as a spot in A-type denture and its location moved according to residual ridge conditions. This point or area on the occlusal table was moved greatly by the factor of the residual ridge when the B- type denture was applied. ⅳ) The amount of vertical excursion of the extension saddle-type denture against vertical loading was highly affected by denture design rather than by the residual ridge. v) The location of the torque fulcrum of the free end saddle denture can also be changed by the denture design. vi) The optimal occlusal pattern of the removable partial denture of the extension saddle type change with denture design and residual ridge