Effect of double-layer structure of orthodontic aligner on tooth movement

Abstract

The purpose of this study was to investigate how a two-layer aligner with outer hard and inner soft structure affects tooth movement. A case in which the left and right maxillary central incisors were moved bodily was simulated using the finite element method. The thickness of the single-layer aligner was 0.5 or 0.3 mm, and its Young's modulus was 1000 MPa. In the two-layer aligner, the thickness and Young's modulus of the outer layer were 0.25 mm and 1000 MPa, and those of the inner layer were 0.25 mm and 100 MPa, respectively. For all aligners, after their placement, the tooth tip and crown moved to the target position. After that, the tooth became upright and moved bodily. The two-layer aligner slowed the upright speed of the tooth due to decreased stiffness. The 0.3-mm single-layer aligner, which had the same stiffness as the two-layer aligner, led to the same tooth movement as the single-layer aligner. Based on the present simulation conditions, there was no advantage of using the two-layer aligner.