tang 1,2 ✉ to evaluate tooth behaviours under various maxillary incisor retraction protocols for clear aligner therapy. A three-dimensional finite element model of maxillary dentition was constructed for first premolar extraction. A loading method was developed to mimic the mode of action of clear aligners for incisor en masse retraction. Three protocols with different amounts of retraction and intrusion on incisors were designed. Initial tooth displacements and stresses on periodontal ligaments were analysed with ANSYS software. The central (U 1) and lateral (U 2) incisors exhibited uncontrolled lingual tipping and extrusion upon 0.25 mm retraction. U1 exhibited translation movement, while U 2 underwent less tipping during 0.2 mm retraction and 0.15 mm intrusion. Labial tipping and intrusion of U 1 and bodily intrusion of U 2 were observed during 0.1 mm of retraction and 0.23 mm of intrusion. With the additional intrusion on incisors, canine showed extrusion movement, and higher stresses on periodontal ligaments were shifted from U 2 to canines. Incisors also exhibited different mesial-distal angulation in the three simulations, while posterior teeth all suffered mesial inclination. Incorporating intrusion displacement in clear aligners led to a tendency of lingual root movement during incisor retraction. the complexity of tooth movement should be recognized regarding clear aligner therapy.

No abstract

The dynamic consolidation method has been used widely in various engineering domain. With this method, the velocity of reconsolidation settlement was enhanced, the consolidation result was good, and the cost was lower than other methods. However, in the flooded area of Yellow River, the groundwater level is higher, and the shallow saturated silty soil liquefaction will be happened with this single method of dynamic consolidation. It goes against the roadbed stability. According to engineering practice, the vacuum dewatering with lower energy dynamic consolidation method was proposed in this paper. In order to monitor the effect of this consolidation method, the water-level observation hole, pore water pressure gauge, standard guide pile, level gauge have been set up. They could be used to get the groundwater level, the excess pore water pressure, horizontal displacement and land subsidence, respectively. These monitors would last the whole period of the consolidation experiment. Field test results shows that the excess pore water pressure was reduced by 80%-90% during one to three days.