Sato Y, Tsuga K, Abe Y, Asahara S, Akagawa Y
Department of Removable Prosthodontics, Hiroshima University School of Dentistry, Hiroshima, Japan.
J Oral Rehabil. 2000 Nov;27(11):935-9. doi: 10.1046/j.1365-2842.2000.00621.x.
An I-bar clasp is a popular retainer for distal-extension removable partial dentures. However, there have been almost no evidence-based criteria on the mechanically preferable shape. The present study aimed to investigate the variations of dimension in I-bar clasps used in patients, and to clarify the effect of the variations on stiffness and stress of I-bar clasps by finite element analysis. Dimensions (thickness, width, taper, radius of curvature, length, relation to oral structures) of 23 I-bar clasps were measured. A three-dimensional finite element model was made for each measured I-bar clasp with vertical and horizontal straight sections connected with a curved section. A concentrated load of 5 N was applied at the lowest point of the tip that contacted the abutment in the buccal direction. Maximal equivalent stress and stiffness of each clasp were evaluated. The measured dimension, stiffness, and maximum stress showed wide variations. Mean stiffness was far from the proper one, and mean stress was near the proportional limit of Co-Cr alloy. Considering the stiffness and stresses in this study, only six clasps out of 23 were appropriate. These results suggest that evidence-based criteria of preferable shape of I-bar clasps should be determined.
I 型杆卡环是远中游离可摘局部义齿常用的固位体。然而，对于其机械性能上更优形状，几乎没有基于证据的标准。本研究旨在调查患者使用的 I 型杆卡环的尺寸变化，并通过有限元分析阐明这些变化对 I 型杆卡环刚度和应力的影响。测量了 23 个 I 型杆卡环的尺寸（厚度、宽度、锥度、曲率半径、长度、与口腔结构的关系）。为每个测量的 I 型杆卡环制作了三维有限元模型，其垂直和水平直线段通过弯曲段相连。在颊向与基牙接触的尖端最低点施加 5 N 的集中载荷。评估每个卡环的最大等效应力和刚度。测量的尺寸、刚度和最大应力显示出很大差异。平均刚度远未达到合适值，平均应力接近钴铬合金的比例极限。考虑到本研究中的刚度和应力，23 个卡环中只有 6 个是合适的。这些结果表明，应确定 I 型杆卡环更优形状的基于证据的标准。
