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BONN, Germany: A study led by researchers at the University Hospital Bonn has found that 4D-printed orthodontic clear aligners can apply biocompatible orthodontic forces in order to move teeth. The technology of 4D printing is based on the 3D printing of shape memory materials. The 4D aligners are clear aligner trays that are 3D-printed using shape memory polymers (SMPs), and the implications of this novel material in clear aligner therapy could include reducing the cost of treatment and its burden on the environment.
Clear aligner trays are made of various types of polymers and are typically designed to move a tooth within the range of 0.2 to 0.3 mm—or to rotate it by 1° to 3°—before being replaced by successor trays. As the authors of the study point out, this stepwise treatment model requires more time and a higher cost for materials than treatment using fewer trays would. Naturally, for both patients and manufacturers, the use of successive plastic clear aligner trays also carries with it ethical concerns related to the environment.
Various studies have examined applications for SMPs in medical materials, including for orthodontic applications. The researchers, however, sought to add to what they perceived was a lack of data in the literature concerning SMPs and tooth movement by measuring the forces generated by the 4D aligners and thereby their suitability in the treatment of malocclusion.
“[Practitioners] still report some drawbacks to aligner use”
The researchers, from dental faculties in Germany, Egypt and the UAE, used a biomechanical system in order to use forces to correct the malposition of a maxillary central incisor (Tooth 21) in a custom-made typodont model using 4D-printed aligners. The generated forces were measured at different temperatures, and the clear aligner trays were made of ClearX v.1.1 material in the two thicknesses 0.8 mm and 1.0 mm. The forces delivered were quantified using an orthodontic measurement and simulation system (OMSS).
They found that the 4D-printed aligners were capable of achieving significant tooth movement within the range of 2.5 mm ± 0.5 mm, with little variation between the two thicknesses. In the OMSS simulations, it was found that the range of maximum forces delivered varied according to the different temperatures tested (37°C, 45°C, 55°C) but that they were all within the range of acceptable physiological orthodontic forces, as reported by the literature.
In contrast to other studies, the researchers found that using a thicker aligner had no effect on the generated force except at the higher temperature of 55°C.
The authors highlighted a number of limitations to the study, such as its focus on the isolated movement of a single tooth and not on a complex clinical case and the fact that it did not account for intra-oral conditions and factors such as humidity and salivation. They concluded, however, that the 4D aligner was capable of moving teeth using biocompatible orthodontic forces.
They wrote: “Although orthodontic aligners have been studied in several aspects and great progress was done in orthodontic treatment by aligners, practitioners still report some drawbacks to aligner use.” They explained that these drawbacks included the limited movement achieved by single aligner trays, which necessitated changing regimes. They concluded: “Therefore, we believe that if a method could be applied to decrease the number of the aligners per treatment, together with a method to accelerate the biological movement of the teeth, that would be a quantum leap in the field of orthodontics.”
The study, titled “Potential application of 4D technology in fabrication of orthodontic aligners”, was published online on 28 January 2022 in Frontiers in Materials.
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