Efficacy of various multi-layers of orthodontic clear aligners: a simulated study.

The multi-layers clear aligner is better than the single-layer clear aligner in tooth movement, stress distribution of periodontal ligament and mechanical loading of alveolar bone, especially when the ratio of soft layer to hard layer is more than 50%. Moreover, the side effects of the multi-layers clear aligner are significantly less than those of the single-layer one.