Effect of Design Modifications on Circumferential Cast Clasp Arms Flexibility

Objectives: Within this study, the finite element analysis was used to evaluate the stress distribution in three-dimensional models of circumferential cast clasp arms, in order to select their preferable design, as biomechanical point of view. Material and methods: Preformed clasp wax patterns for circumferential clasps were selected and parameters, like length, thickness and width at the base and tip were measured, to generate purposely designed experimental three-dimensional models. Experimental three-dimensional models of Co-Cr clasp arms were generated using solid eight-node elements. The finite element method was used to simulate the deflection under insertion and removal of the clasp. Generated stresses and deformations produced as a result of retentive forces (5 N) applied to each clasp were calculated numerically and plotted graphically. The correlations between the calculated maximal stresses and deformations allowed the selection of preferable parameters of clasp arms. For all clasps studied, the shapes with the lowest maximal equivalent stress corresponding to the typical displacement of circumferential clasps (0.25 mm) were selected. Results: The investigations indicated the preferable cross-section shape and taper of clasp arms. The results of this in vitro study suggested that clasp arms with a taper of 0.6 for short clasp arms and 0.8 for long clasp arms showed less stress than those with other tapers. Regarding their cross-section shape, the determined thickness/width ratio was between 0.5 and 0.6 for short clasp arms, depending on their width and 0.6 for long clasp arms. Conclusions: Within the limitations of this study, the preferable cross-section shapes of retentive circumferential cast clasp arms were determined so that they can be sufficiently flexible to prevent damaging effects on the abutment teeth, and at the same time be efficient in maintaining the denture. (This study was supported by the Grant CEEX-ET 2978/2005 from the Ministry of Education and Research, Romania).