An I-bar clasp is one of the most popular direct retainers for distal-extension removable partial dentures. However, no adequate information is available on the shape associated with biomechanics. This study aimed (1) to establish a three-dimensional (3D) finite-element modelling method of I-bar clasps, and (2) to clarify the effect of the shape on the stress and stiffness of I-bar clasps. 3D computer models of I-bar clasps were created with vertical and horizontal straight sections connected with a curved section with six parameters: thickness of the clasp tip (T), width of the clasp tip (W), radius of the curvature (R), horizontal distance between the base and the vertical axis (H), vertical dimension between the tip and the horizontal axis (V), taper (change of width per unit length along the axis)(Tp). Stress decreased as T, W, R and Tp increased, and as V decreased. Stiffness (which is proportional to retention) increased as T, W, R and Tp increased, and as H and V decreased. In both stress and stiffness, the effects of T and Tp were especially large. From the results, a systematic formula between the clasp shape and the stiffness was derived.

An I-bar clasp is one of the most popular direct retainers for distal-extension removable partial dentures. However, no adequate information is available on preferable shape as determined by biomechanics. This study aimed (1) to investigate, by finite element analysis (FEA), the dimensions and stress of I-bar clasps having the same stiffness, and (2) to estimate a mechanically preferable clasp design. Three-dimensional FEA models of I-bar clasps were created with vertical and horizontal straight sections connected by a curved section characterized by six parameters: thickness of the clasp tip, width of the clasp tip, radius of the curvature, horizontal distance between the base and the vertical axis, vertical dimension between the tip and the horizontal axis, and taper (change of width per unit length along the axis). Stress was calculated with a concentrated load of 5 N applied 2 mm from the tip of the clasp in the buccal direction. A thinner and wider clasp having an taper of 0.020-0.023 and radius of curvature of 2.75-3.00 showed less stress. The results suggest that such a shape might be the preferable I-bar clasp shape as biomechanical viewpoint.

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An I-bar clasp is a popular retainer for connected with a curved section. A concentrated load of 5 N was applied at the lowest point of the distal-extension removable partial dentures. However, there have been almost no evidence-based tip that contacted the abutment in the buccal direccriteria on the mechanically preferable shape. The tion. Maximal equivalent stress and stiffness of each present study aimed to investigate the variations of clasp were evaluated. The measured dimension, stiffness, and maximum stress showed wide variadimension in I-bar clasps used in patients, and to clarify the effect of the variations on stiffness and tions. Mean stiffness was far from the proper one, stress of I-bar clasps by finite element analysis. Diand mean stress was near the proportional limit of mensions (thickness, width, taper, radius of curvaCo -Cr alloy. Considering the stiffness and stresses in this study, only six clasps out of 23 were approture, length, relation to oral structures) of 23 I-bar clasps were measured. A three-dimensional finite priate. These results suggest that evidence-based element model was made for each measured I-bar criteria of preferable shape of I-bar clasps should be clasp with vertical and horizontal straight sections determined.

Abstract. The purpose of this study was to compare the accuracy of measurement of lower extremity joint moments calculated using data obtained by a force plate embedded on a stair tread with that using combined data obtained by two force plates under the staircase. We captured ascending and descending movement by a healthy young subject using a three-dimensional motion analysis system. We calculated ankle, knee and hip joint moments using data from the same trial captured by the two measurement methods. No differences were observed in lower extremity joint moments between the two methods. Our theoretical assumptions were confirmed by our results; floor reaction force obtained from the force plates positioned under the stairs was the same as that obtained on the stair tread, and joint moment could be calculated accurately using either measurement method. The use of our simplified experimental setup using force plates positioned under the staircase could facilitate future measurement of floor reaction force and calculation of joint moment during ascending and descending stairs.