Experimental Verification of Finite Element Analysis for a Thermoplastic Orthodontic Aligner

In recent years, good outcomes have been reported using transparent and removable orthodontic appliances known as aligners. However, unpredicted tooth movement that contradicted 3-dimensional image simulations was observed in some cases. These anomalies could relate to biomechanical factors ; in particular, the characteristics of mechanical loading applied to the periodontal ligament and the tooth crown by aligners remain unclear. This study examines the biomechanical characteristics of aligners by a new method as follows : 1) development of an experimental model using artificial teeth and plastic aligners ; 2) finite element (FE) modeling and analysis using computed tomography (CT) images of the experimental model ; and, 3) comparison among observations of this actual model and standard FE analysis results. Roots of two artificial teeth were covered by silicone material at 1.0 mm intervals for each coronal proximal surface and plastic clear aligners were manufactured based on another model in which the interval was reduced to 0.0 mm to simulate bodily movement. An FE analysis model of this 1.0 mm teeth interval was reconstructed from the CT images. A virtual aligner based on the FE model was also generated with a 0.0 mm interval. Changes in space between the root surface and silicone in both the actual and FE model were compared with the aligner fitted in the initial model. Identical tendencies of movement were observed in both experimental results - the artificial teeth and computational results of FE analysis. Our method using an experimental and computational approach proved useful to examine aligner characteristics ; the use of such a biomechanical approach could further our understanding of aligner treatments