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中間欠損側負荷時の作業側・非作業側支台の挙動分析

Abstract

The purpose of this laboratory study was to examine seven types of rests to determine through the abutment tooth movements which type transmits forces to abutment teeth in the most favorable manner. An acrylic resin/ silicone rubber simulation model of a Kennedy class II modified 1 mandibular arch with missing teeth (right second premolar and first molars, and left first and second molars) which permitted tooth movement and ridge displacement was constructed. The behaviors of abutment teeth were measured by using digital laser displacement sensors and the measured values were reciprocally compared through the statistical analysis. The results obtained were as follows : 1) On comparing the occlusal mesial rest (design 2) and the mesiodistal rest extended to the mesial tooth (design 3) with the most basic occlusal distal rest (design 1, control), the design 2 had a tendency to be smaller, and the design 3 the smallest in inclination of the abutment tooth. Also, in twist-like movement, the designs 2 and 3 were significantly smaller (99.9 per cent confidence level) than the design 1. 2) On comparing design 4 for which the rest of design 1 was extended to mesial fossa and design 5 for which the rest of design 1 was extended to the mesial margine with the design 1, the designs 4 and 5 were significantly smaller than the design 1 in inclination and twist-like movement of the abutment tooth (p<0.001). However, an analysis of variance (95 per cent confidence level) showed no significant difference in movement between the design 4 and the design 5. 3) On comparing design 6 for which the rest of design 1 was moved to near the cervical portion with the design 1, inclination and twist-like movement of the abutment tooth with the former were significantly smaller than those with the latter (p<0.001). 4) On comparing design 7, the onlay type of rest, with design 1 in inclination and twist-like movement of the abutment tooth, the former showed significantly smaller values than the former (p<0.001). 5) On comparing with design 1, the others showed no significant difference in depression of the abutment tooth, but significantly smaller values in parallel movement (p<0.001). 6) Displacement of the abutment tooth (〓) on the non-working side was smaller than that the on the working side (〓) in all designs. On the basis of the foregoing findings, this study comfirmed that displacing the occlusal distal rest which is the typical type to occlusal mesial portion, and extending it to the mesial direction, and lowering it to near the cervical portion enabled a great reduction in inclination and twist-like movement which are said be most hazardous to the abutment tooth.