Polymeric dental aligners manufactured by thermoforming are recently used in clinical treatment of misaligned teeth. In this study, a polyester sheet with 0.75 mm thickness was used and the deformability of thermoformed aligner is discussed experimentally with the help of digital image correlation method. The experimental apparatus to apply prescribed displacement to aligners mounted on a teeth model was developed focusing on the situation of treatment for misaligned left canine. The deformation mode was discussed through measured displacement field and maximum principal strain distribution. It was found that mechanical behavior of aligner was influenced more significantly by the shape of teeth, movement vector of left canine and crooked shape of aligner especially at inter-teeth borders than the thickness distribution of thermoformed aligner. The role of deformable edge part of the aligner was also revealed.

To investigate methods to suppress the bowing effects of lingual inclination and anterior tooth extrusion, digital image correlation (DIC) was used to evaluate aligner displacement in three-dimensions through comparing the distal movement of six and four anterior teeth. Computed tomography scans were used to measure aligner thickness and shape. Based on displacement direction and magnitude, a desirable deformation mode with minimal lingual inclination and extrusion was observed during distal movement of four anterior teeth. The aligner had a rigid "constriction zone" between the lateral incisor and the canine, facilitating control localized to the anterior teeth and minimizing the reaction of the molars. The mechanical behavior of aligners was greatly affected by the method of anterior teeth movement and the shape of aligners. DIC-based displacement measurements are useful in investigating correction directionality.

Orthodontic aligners undergo deformation during installation, producing an unexpected component of elastic restoring force that causes unintended changes in the dentition. The aim of this study was to investigate the relationship between strain and elastic recovery of the aligner. We distinguished the contributions to aligner deformation due to molding and installation by measuring the thickness distribution of an aligner after molding using micro-CT and tracking changes in grid patterns drawn on the sheet used to fabricate the aligner. The aligner was installed on a device that simulated canine movement. Although canine strain was quite strong around the cusp, and in premolar, it was observed mainly in their centers. Furthermore, after molding, thickness distribution of the aligner was found. But, it is no clear relationship between the thickness distribution and the strain distribution. Our method of analysis can help improve aligner design and establish molding method to deliver optimal orthodontic treatment.

No abstract

No abstract