Abstract
BackgroundThe mechanics of double key loop (DKL) are not well defined, and this finite element study was designed to explore its force system.MethodsA simplified 3-dimensional finite element model of single and double key loops with an archwire between the lateral incisor and second premolar was established in Ansys Workbench 17.0. Activation in Type-1 (retraction at the distal end), Type-2 (retraction at the distal key) and Type-3 (Type-2 plus ligation between keys) was simulated. The vertical force, load/deflection ratio and moment/force ratio of stainless-steel and titanium-molybdenum alloy (TMA) loops were calculated and compared.ResultsThe double key loop generated approximately 40% of the force of a single key loop. Type-2 loading of DKL showed a higher L/D ratio than Type-1 loading with a similar M/F ratio. Type-3 loading of DKL showed the highest M/F ratio with a similar L/D ratio as single key loop. The M/F ratio in Type-3 loading increased with the decreasing of retraction force. The DKL of TMA produced approximately 40% of the force and moment compared with those of SS in all loading types. When activated at equal distances below 1 mm, the M/F ratios of SS and TMA DKL with equal preactivation angles were almost the same.ConclusionThe M/F ratio on anterior teeth increases with the preactivation angle and deactivation of DKL. The M/F ratio at a certain distance of activation mainly depends on the preactivation angle instead of the wire material. TMA is recommended as a substitute for SS in DKL for a lower magnitude of force.
Highlights
The mechanics of double key loop (DKL) are not well defined, and this finite element study was designed to explore its force system
Closing loops with different configurations such as T loops, teardrop loops, L loops, and mushroom loops are used in the clinic, and they need individual adjustments according to the clinical experience of orthodontists [4, 7]
Taking stainless steel (SS) DKL with a preactivation angle of 10° as an example, the moment-to-force ratio (M/F) ratio was 19.69 mm when the retraction force was 1 N, but it dropped to 4.92 mm when the retraction force was 6 N
Summary
The mechanics of double key loop (DKL) are not well defined, and this finite element study was designed to explore its force system. As reported in previous experimental and analytical studies, the M/F ratio varied with the wire material, cross section, height, width and configuration of loops [10,11,12,13,14]. Preactivation methods such as gable bends and vertical steps diversified the M/F ratio [15,16,17,18]. The M/F ratio was reported to change with the distance of activation [19, 20]
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