Asymmetric Head Gear: A Comparison between Unilateral Outer Bow Expansion and Unilateral Outer Bow Shortening - an Energy Approach using the Finite Element Method.

OBJECTIVE To compare the influence of outer bow length difference and unilateral outer bow expansion on the 'asymmetric effect' of the headgear. METHODS Twelve 3D finite element models of a headgear with two tubes were designed, which were similar except for the outer bow length or the degree of unilateral expansion in Solid-Works 2011. A 3N force was applied to the outer bow ends in ANSYS Workbench 12.1 and the distalising, lateral forces to molars, moments and the energy of the system were evaluated. RESULTS As the degree of unilateral expansion increased, the net differences in all findings were increased up to a point, and then changed. There was an increasing pattern in the length difference group. Buccal movement was observed in the intact/shorter side molar. CONCLUSION Unilateral shortened outer bow asymmetric headgears are more efficient and more predictable in clinical application than the unilateral outer bow expansion.