Mechanical Force System of Double Key Loop With Finite Element Analysis 

Abstract Background: The mechanics of double key loop (DKL) was not well defined and this finite element study was designed to explore its force system.Methods: Simplified 3-dimensional finite element model of single and double key loops with archwire between lateral incisor and second premolar was established in Ansys Workbench. Activation in Type-1 (retraction at distal end), Type-2 (retraction at distal key) and Type-3 (Type-2 plus ligation between keys) were simulated. The vertical force, load/deflection ratio and moment/force ratio of stainless steel and TMA loops were calculated and compared.Results: Double key loop generated about 40% force of single key loop. Type-2 loading of DKL showed higher L/D ratio than in Type-1 loading with similar M/F ratio. Type-3 loading of DKL showed the highest M/F ratio with similar L/D ratio as single key loop. The M/F ratio in Type-3 loading increased with the decrease of retraction force. DKL of TMA produced about 40% of force and moment compared to those of SS in all loading types. When activated at equal distance bellow 1mm, the M/F ratio of SS and TMA DKL with equal preactivation angle were almost the same. Conclusion: M/F ratio on anterior teeth increases with preactivation angle and deactivation of DKL. M/F ratio at certain distance of activation depends mainly on preactivation angle instead of wire material. TMA is recommended as substitute of SS in DKL for lower magnitude of force.