Predicting the Retentive Force of FRC Clasps by Nonlinear FEA

Objectives: The aim of this study was to predict the retentive force of clasps made of a glass fiber-reinforced composite (FRC) material by nonlinear finite element analysis (FEA).Methods: The geometry of an abutment tooth, a lower second premolar surrounded by a circumferential clasp arm, was set as a barrel-shape. The basic clasp arm shape was without taper, and was 2.60 mm wide and 1.30 mm thick (Bb). These geometries were consistent with our earlier study on the retentive force of FRC clasps. FRC was treated as an elastic orthotropic material. All nodes at the 1/3 lower apical side of the abutment tooth were restrained, and forced displacements of 5 mm were applied to the nodes at the base of the clasp arm in the removal direction. The friction coefficient was set to 0.31. The relationship between the displacement of the tip of the clasp arm in the removal direction and the retentive force calculated as the sum of the nodal reaction forces at the base of the clasp arm was plotted. Similarly, retentive forces of modified clasp arms were also calculated. Widths and thicknesses of the modified clasp arms were as follows: 2.60 mm and 0.65 mm (a), 2.60 mm and 1.95 mm (c), 1.30 mm and 1.30 mm (A) and 3.90 mm and 1.30 mm (C).Results: The retentive force of the basic clasp arm (Bb) was 6.36 N, in good agreement with the value obtained from our experimental measurements. The retentive forces of modified clasp arms were 1.00 N (a), 16.30 N (c), 3.36 N (A) and 8.90 N (C).Conclusions: The retentive force of glass fiber-reinforced composite clasps could be quantitatively predicted by nonlinear FEA. This study was supported by a Grant-in-Aid for Scientific Research (No.19791452) from the Japan Society for the Promotion of Science.