Orthodontic Aligner Incorporating Eucommia ulmoides Exerts Low Continuous Force: In Vitro Study

The aim of this study was to investigate the orthodontic force exerted by thermoplastic orthodontic appliances incorporating Eucommiaulmoides in terms of usefulness as the aligner-type orthodontic device. Erkodur, Essix C+^®, Eucommia elastomer, and edgewise brackets were used (n = 3, each; thickness = 1.0 mm, each). The orthodontic force on the upper right incisor was measured every 24 h for two weeks using a custom-made measuring device. The force of the Eucommia elastomer (4.25 ± 0.274 N) and multi bracket system (5.32 ± 0.338 N) did not change from the beginning to the end (p > 0.01). The orthodontic force exerted by the Eucommia elastomer was lower than that of the multi-bracket orthodontic appliance from the beginning to the end. The force of Erkodur significantly decreased from the beginning to 24 h (6.47 ± 1.40 N) and 48 h (3.30 ± 0.536 N) (p < 0.01). The force of Essix C+^® significantly decreased from the beginning (13.2 ± 0.845 N) to 24 h (8.77 ± 0.231 N) (p < 0.01). The thermoplastic orthodontic appliance made of Eucommia elastomer continuously exerted a constant orthodontic force for two weeks under water immersion conditions. The orthodontic force of Eucommia elastomer was found to be similar to the orthodontic force exerted by the multi-bracket orthodontic appliance with 0.019 × 0.025 in nickel–titanium wire. These results suggest that the Eucommia elastomer has possibly become one of the more useful materials to form thermoplastic orthodontic appliance exerting low continues orthodontic force.