Effects of time and clear aligner removal frequency on the force delivered by different polyethylene terephthalate glycol-modified materials determined with thin-film pressure sensors

Introduction: Many factors influence the force changes of clear aligners. The purpose of this study was to identify the various factors that influence the force changes generated by polyethylene terephthalate glycol-modified (PET-G) materials. Therefore, a force measurement system based on a flexible thin-film pressure sensor was established. Methods: A series of clear aligners with 2 material properties and different activations at the maxillary central incisor, maxillary second premolar, and maxillary permanent first molar was designed and fabricated. The first material was conventional PET-G; the second material was modified PET-G with a higher modulus of elasticity and greater abrasion resistance. Several models, including teeth and aligners, were produced. Then, a force change detection device, including a thin-film pressure sensor, a signal acquisition circuit board, and a computer, was applied to measure changes in the forces delivered by the conventional and modified PET-G materials with increased frequencies of appliance removal. Finally, the forces were repeatedly measured to detect the force changes over 48 hours. Results: The forces of both materials decreased similarly over time. These forces also decreased when the aligner removal frequency increased, but the forces decreased differently. The modified PET-G, with a higher modulus of elasticity and greater abrasion resistance, showed a more stable and lower force change than did the conventional PET-G. Conclusions: The forces delivered by both materials were within the orthodontic force range. Force changes were apparent when the appliance removal frequency increased. Compared with the conventional material, the modified PET-G material showed better stability. Therefore, the modified PET-G is a promising and applicable material with advantages for both orthodontists and patients.