Manufacturing multilayers for clear aligners with tunable thermomechanical properties

Clear aligners are a new technique in dentistry that involves moving teeth using a dental appliance made from transparent, thermoplastic material, based on standardised movements programmed by software. Conventionally, the thermoplastics in use were copolyesters and polyurethanes, but the need for more precise and comfortable treatments has pushed the industry into using combinations of thermoplastics. [1], [2]

¨This project aims to manufacture multilayers from widely available materials with comparable properties to commercial multilayers of unknown composition, and to control the thermomechanical properties to adapt multilayers to different treatment situations.

The thermomechanical properties of different thermoplastics suitable for manufacturing clear aligners were analysed by DMTA, DSC, tensile testing, and stress relaxation. Later, multilayers were manufactured using thin layers of different thermoplastics. Finally, the multilayers were analysed in the same fashion as the original thermoplastics.

The results show a high similarity in thermomechanical properties between homemade and commercial multilayer materials, and a better performance of both materials against conventional copolyesters and polyurethanes in terms of storage and loss modulus, elastic modulus, yield strain, and stress relaxation. Moreover, those properties can be controlled by selecting wisely the thermoplastics in the multilayer.

In conclusion, it is possible to manufacture clear aligners from widely available materials, but it is also feasible to adapt the properties of the thermoplastic to each treatment situation in an easy manner. Multilayer thermoplastics are hence one of the best candidates in the upcoming generation of personalised-force clear aligners.

Work supported by a grant for an industrial PhD of the Community of Madrid regional Government (IND2022/IND-23679), in collaboration with Secret Aligner S.L.

[1] N. Cenzato et al ‘Materials for Clear Aligners—A Comprehensive Exploration of Characteristics and Innovations: A Scoping Review’, Applied Sciences, vol. 14, 2024.

[2] D. Ciavarella et al., ‘Comparison of the Stress Strain Capacity between Different Clear Aligners’, TODENTJ, vol. 13,2019.