Experimental Study on Deformability of Polymeric Dental Aligner by Digital Image Correlation Method

Abstract

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.

Measurement of elastic strain recovery in an orthodontic aligner as a driving force for orthodontic treatment

“…The central portion of the premolar showed elastic recovery at 0-N unloading, but the central portion of the lateral incisor did not show elastic recovery at unloading, indicating that the large change in the canine central strain extended to the central portion of the lateral incisor. This confirms the previous report 8) that the strain was larger between the lateral incisor canine than between the canine premolar because they were flatter. Furthermore, the aligners tended to be thicker in the premolar region and thinner in the incisor region (Fig.…”

“…In this study, we assumed canine tooth movement and used the tooth movement apparatus 8) developed in the previous paper (Fig. 3).…”

“…This elastic recovery force is the orthodontic force required for tooth movement. In our previous paper, we explained that predicting the elastic recovery force of aligners is important for estimating the force applied to teeth using measurements of deformation and strain distribution in aligners 8) . Lombardo et al stated that the elastic recovery is affected by the material and thickness of the aligner 20) .…”

“…The aligners are fabricated on a simulation model with gradual tooth movement, and the teeth are gradually aligned. We investigated the deformation and strain distribution of the aligner during installation, and found that the aligner initially deforms and that the force to restore its shape is generated by elasticity 8) . This elastic recovery force is transmitted to the periodontal tissues through the teeth, causing tooth movement through bone remodeling of the surrounding bone and realignment of the periodontal ligaments 9,10) .…”