M/F ratios of four different closing loops: 3D analysis using the finite element method (FEM)

Background

It has been claimed that the opus loop is capable of delivering a constant and optimum M/F ratio without the need for gable bends.

Objective

To compare the forces, moments and moment/force (M/F) ratios of the opus loop, L–loop, T–loop and vertical helical closing loop (VHC loop) in a segmented arch with the finite element method (FEM).

Methods

The FEM was used to compare 3D models of closing loops in rectangular (0.016 x 0.022 inch) stainless steel wire. The L–, T– and VHC loops were designed with and without preactivation bends. The opus loop had no preactivation bends.

The T–Loops were 10 mm in height and 10 mm in length. The horizontal and vertical forces, the moments and the M/F ratios at the alpha and beta ends were recorded at 0, 0.1, 0.4, 0.7 and 1 mm intervals.

Results

The highest horizontal and vertical forces were produced by the L–loop (with and without preactivation bends) and in most cases the lowest forces were produced by the VHC loop. Loops with preactivation bends produced marked changes in the M/F ratio and loops without preactivation bends low, but relatively constant, M/F ratios over the full range of activation. Of the loops modelled without preactivation bends the opus and T-loop had the highest M/F ratios (7.20 – 7.67 mm at the anterior ends).

Conclusion

Stainless steel opus and T–loops without preactivation bends had constant M/F ratios, but both loops failed to deliver the optimum M/F ratio of 10:1.