Displacement Lag, Leading Forces, and Clear Aligner Biomechanics

All orthodontic treatment requires sufficient time, proper space, and effective forces to achieve the desired results. When we plan orthodontic treatment with a clear aligner appliance, we need to understand the essential elements for successful appliance design and the force application within the design plan. Current clear aligner biomechanics involves a combination of displacement and force-driven systems. 

Tooth displacement lag

When we design a clear aligner appliance with today’s technology, a computer-aided design process will segment the teeth in the arch. Then, we set up the final tooth positions. In a displacement-driven appliance design, the aligner will guide and walk the tooth into its end goal. The displacement lags in force application as the force applied is delivered once sufficient aligner deformation occurs. The elasticity of the aligner material, its fit, and recovery to avoid permanent deformation become critical for treatment progress. 

Leading forces

Forces move teeth, and aligners push the teeth into place. A lot of confusion remains on what this pushing movement means. As the aligner covers all tooth surfaces, we hope it moves the teeth into the position we design in the CAD software. A force-driven appliance will lead the movement with a devised point of an application controlling the force direction and magnitude. Once the aligner is seated, the force features apply pressure to move the teeth into the desired position. Thus, leading the tooth instead of dragging it behind the aligner tracking. These pressure areas can deliver more complex force systems, such as couples or two forces controlling the moment. Instead of a perfect fitting aligner, the critical measure is the adequate application of the force features across the active surfaces.  

Doctors will acknowledge that the most common reason we order additional aligners is a deficiency when teeth do not reach the desired goal. When we manage a combination of displacement and generate proper force systems, your orthodontic appliance becomes much more effective. Clinical results improve with better control, and we achieve shorter treatment times by reducing additional aligner orders.