レストの設定位置および形態が支台歯の挙動に及ぼす影響 Ｋｅｎｎｅｄｙ ＩＩ級義歯模型における遊離端側負荷時の作業側・非作業側支台の挙動分析

Abstract

In designing removable partial dentures, “support” which is given primarily through rests is the most important factor. Typical seven types of rest were selected and the abutment tooth movements on a simulation model of Kennedy class II modified 1 mandibular arch with missing teeth (right second premolar and first molar, and left first and second molars) were measured by using digital laser displacement sensors. Inclination which gives the most hazard to periodontium in four displacement modes of the abutment tooth was compared with that of control or control' respectively and significant difference between each rest and control or control' were discused through t-test.The results obtained were as follows:1) Design 2: At the working side, the distal extended abutment tooth ?? 5, inclination was significantly greater or smaller than that of control being affected remarkably by the shape of test pieces.2) Design 3: Inclination was significantly smaller than that of control under all conditions at the working side, and also at the non-working side under most conditions.3) Design 4: Inclination was significantly smaller than that of control' under most conditions at the non-working side abutment tooth, but most inclinations showed only a tendency to be small without no significant difference, although smaller inclination with very highly significant difference was also recognized at the working side abutment.4) Design 5: Inclination of either side abutment was significantly smaller in values (p<0.01) than that of control and cotrol' respectively5) Design 6: Inclination at the non-working side abutment was significantly smaller than that of control' under most conditions, but one at the working side abutment was sometimes significantly greater than that of control depending on the shape of test pieces.6) Design 7: Very highly significant difference of inclination was shown between this design and control under all conditions and the former was smaller at the working side abutment tooth, but inclination of this design at the non-working side sometimes showed greater with highly significant difference (p<0.001) than that of control' due to the shape of test pieces.7) Twist-like movement of both abutment teeth (4 ?? and ?? 5) at the working and non-working side was apt to be remarkably smaller than either one of control or control' respectively.On the basis of the foregoing findings, this study suggested that the most typical occlusal distal rest should be placed to the mesial portion rather than lowering it to near the cervical portion and should cover widely over the occlusal surface of the abutment tooth when loading on the distal extention side, in order to be greatly reduced inclination which are said be most hazardous to the abutment tooth.