Numerous factors can influence the force exerted by clear aligners on teeth. This study aimed to investigate the stability of the force delivered by two different material appliances. 90 clear aligners with 2 materials and three different activations were designed and fabricated. Then, a device was employed to measure the force generated by the two types of PET-G material appliances immersed in artificial saliva for 0, 3, 7, 10, 14 days. Scanning electron microscopy was applied to observe the morphologic alterations on the aligner surfaces, respectively. The forces generated by different activation appliance exhibited differently, 0.0 mm < 0.1 mm < 0.2 mm. In addition, increasing the immersion times and the orthodontic force also decreased, but the forces decreased differently. Compared with the forces of conventional PETG appliances with 0.20 mm activation, the modified PETG appliances with the same activation exhibited significantly higher mean force. When comparing the mean force for modified PETG appliances after 10 and 14 days with conventional PETG appliances, the delivery forces exhibited significant differences (P < 0.05). The force delivered by both materials decreased obviously following artificial saliva immersion, and the force generated by modified aligners exhibited better stability than conventional aligners.

Background: Orthodontic treatment is commonly more time-consuming in adults than in teenagers, especially when it comes to the maxillary en-masse retraction, which may take 9 months or even longer. As to solve this concern, orthodontists have been striving to seek new methods for shortening orthodontic treatment time. Piezocision, as a popular alternative treatment, have been widely used in different types of tooth movement. However, its effect on en-masse retraction of maxillary anterior teeth remains unclear. This randomized controlled trial intends to figure out the role piezocision plays in accelerating en-masse retraction. Methods: This protocol is designed for a prospective, single-center, assessor-blinded and parallel-group randomized controlled trial. Twenty adult patients aged from 18 to 40 whose orthodontic treatment required bilateral maxillary first premolars extraction will be randomly assigned to the piezocision group and the control group at a ratio of 1:1. The piezocision group will undergo en-masse retraction immediately after the piezo surgery, while the control group will start en-masse retraction directly. Both groups will be followed up every two weeks to maintain the retraction force until the end of space closure. The space closing time is set as the primary endpoint. Meanwhile, the secondary endpoints include the change of root length, labial and palatal alveolar bone thickness, vertical bone height, probing depth of maxillary anterior teeth, cephalometric measurements, visual analogue scale, and postoperative satisfaction questionnaire.Discussion: This study will attempt to provide more convincing evidence to verify whether piezocision will shorten the time of en-masse retraction or not. Distinguished with previous studies, our study has made some innovations in orthodontic procedure and primary outcome measurement, aiming to clarify the efficacy and safety of piezocision-assisted en-masse retraction in Chinese population.Trial registration: Chinese Clinical Trial Registry ChiCTR 1900024297. Registered on 5 July 2019.

Numerous factors can influence the force exerted by clear aligners teeth. This study aimed to investigate the stability of the force delivered by two different material appliances. 90 clear aligners with 2 materials and three different activations were designed and fabricated. Then, a device was employed to measure the force generated by the two types of PET-G material appliances immersed in artificial saliva for 0, 3, 7, 10, 14 days. Scanning electron microscopy was applied to observe the morphologic alterations on the aligner surfaces, respectively. The forces generated by different activation appliance exhibited differently, 0.0 mm < 0.1 mm < 0.2 mm. In addition, increasing the immersion times and the orthodontic force also decreased , but the forces decreased differently. Compared with the forces of conventional PETG appliances with 0.20 mm activation, the modified PETG appliances with the same activation exhibited significantly higher mean force. When comparing the mean force for modified PETG appliances after 10 and 14 days with conventional PETG appliances, the delivery forces exhibited significant differences (P<0.05). The force delivered by both materials decreased obviously following artificial saliva immersion, and the force generated by modified aligners exhibited better stability than conventional aligners.