両側性遊離端症例において維持装置のデザインの違いが支台歯の挙動に及ぼす影響 : 連結腕鉤による作業側非作業側支台の比較

Abstract

In order to find out the most desirable removable partial prosthesis, a series of experiments have been conducted in our department. As one of the experiment programs, we observed and evaluated the reactions of the abutment with three clasp assemblies, a double Aker's (design D), an extended arm (design E), and a combination consisting of two retentive T-bar and two reciprocal cast Akers clasps (design T), on the simulation model of Kennedy I with loss of lower first and second molars. We used digital type of laser displacement sensors to analysing the abutment teeth when crushing the test food of two types, short and long. The obtained results were as follows : 1. In all designs, four types of displacement, parallel movement, inclination, twist-like movement, and vertical movement (depression) were recognized during crushing the test food. 2. Parallel movement 1) Both abutment teeth on the working side showed parallel movement toward the mesiolingual direction, and those on the non-working side toward the mesiobuccal direction in most cases. 2) In general, the mesial abutment tooth (4^^-) moved with less magnitude than the distal abutment (5^^-) on the working side and on the non-working side too, but in design D alone there was more magnitude in the abutment 4^^- in comparison with that of 5^^- when crushing the long type of test food under 5 kg or 7 kg load. 3) In the distal abutment (5^^-), parallel movement of the working side abutments was always greater than that of the ones on the non-working side. 3. Inclination 1) The working side abutments showed very small inclination distolingually and the non-working side ones distobuccally when crushing the test food. 2) In design D, greater inclination of the working side abutment (4^^-) was observed than that of the same side abutment (5^^-). 4. Twist-like movement 1) The twist-like movements of abutment teeth were very small in all designs. 2) In design D, the direction of twist-like movement was opposite between the abutment tooth (5^^-) and the abutment (4^^-), and the movement of 4^^- was greater than that of 5^^-. 5. Depression 1) The working side abutments showed greater depression from one and a half to twice that of the non-working side ones. 2) Noticable depression was observed in 4^^- of the design D as compared with that in 5^^- when crushing the long type of test food. 3) The depression of the working side abutments increased as the load increased and increased more in the case of crushing the long type of test food. 4) Even distribution of occlusal force to the either abutment teeth by secondary splinting was not recognized. 6. Other results 1) The behavior of the abutments was affected by the test food shape. 2) It was suggested that inclination could be restricted when greater parallel movement was given to the abutments in the designs used in this expeiment. Above mentioned results showed that design D resulted in unexpected larger stresses on the mesial one than on the distal abutment tooth when crushing the test food. Design D proved to be the design for which abutment tooth movement could not be predicted.