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We aimed to study the influence of attachment on central incisor movement control using invisible orthodontics with different translation or rotation targets. In this study, cone-beam computerised tomography was used to scan one 15-year-old volunteer’s teeth. Three-dimensional models of the mandibular central incisor, removable orthodontic appliance, and a rectangular attachment were reconstructed. A non-linear finite element simulation was used to analyse the influence of attachment on the stress distribution of the periodontal ligament of the central incisor under tooth rotation, mesial translation, and labial-lingual translation. For mandibular central incisor correction, using rectangular attachments increased the translation by up to 9.6%, increased the maximum stress on the periodontal ligament during the mesial translation correction, and reduced unwanted labial-lingual tilt by up to 40% during the rotation of the tooth. However, wearing an attachment during labial-lingual translation had no significant effect on the orthodontic results of the mandibular central incisor. In the mandibular central incisor’s invisible orthodontic, the rectangular attachment appliance increased the displacement and alleviated the side effect after applying mesial translation and tooth rotation. For labial-lingual translation, the application of a rectangular attachment had no pronounced effect on the results.

This study was aimed at analysing the mechanical characteristics of different mandibular extraction modes using a clear aligner. Three experimental schemes of different extraction patterns were designed to treat mandibular crowding, including extraction of one mandibular central incisor, bilateral first premolars, and bilateral second premolars. The stress distribution during the space closing was analysed using the finite element method. When a central incisor was extracted, a significant retraction force was found in the anterior region, in line with the design expectation. The posterior teeth, which were designed to move mesially, acted as anchorage for anterior retraction, and were subjected to a mesial force. The anterior teeth were retracted when the bilateral first premolars were extracted. The lateral incisors and canines were subjected to a significant distal force and moment, while the central incisors and canines were subjected to lingual forces and moments. Additionally, the canines were subjected to a non-designated intruding force. The molars were designed to move mesially when the bilateral second premolars were extracted. All molars were subjected to a significant mesial force, while the lingual force on the front teeth was slight. The bilateral second molars were subjected to non-design mesial moment and extrusive force. The bilateral first molars were subjected to a non-designated mesial moment, and the bilateral first premolars on both sides were subjected to non-designated intrusive force and distal moment. When one incisor was extracted, attachments on the anterior teeth had a controlling effect on the tooth axis, but the anterior teeth still tended to tilt. When the bilateral first premolars were extracted, the anterior teeth showed a tendency for lingual inclination. The risk of distal inclination of the canines and lingual inclination of the central incisor increased. When the bilateral second premolars were extracted and the posterior teeth were designed to move mesially, the teeth on both sides of the extraction sites showed an obvious bowing effect.

Orderly observation of non-cooperative targets for subsequent identification and control is one of the important prerequisites and key technologies of space on orbit service. Restricted by the limited number of ground observation equipment, the visible time window of each non-cooperative target, and the different types of targets, it is increasingly difficult to observe the transit non-cooperative targets and plan the observation tasks. In this paper, the fuzzy clustering algorithm based on clonal selection is used to cluster the non-cooperative targets which are about to cross the border according to their own characteristics, physical characteristics, geometric characteristics, orbital characteristics and other different attributes. Considering the urgency of the task, the importance and priority of each non-cooperative target relative to the observation task are formed, it can provide effective input for the subsequent task planning of non-cooperative target observation, reduce the problem complexity of orderly observation of non-cooperative target, and improve the efficiency of problem solving.