Abstract
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 (U1) and lateral (U2) incisors exhibited uncontrolled lingual tipping and extrusion upon 0.25 mm retraction. U1 exhibited translation movement, while U2 underwent less tipping during 0.2 mm retraction and 0.15 mm intrusion. Labial tipping and intrusion of U1 and bodily intrusion of U2 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 U2 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.
Highlights
To evaluate tooth behaviours under various maxillary incisor retraction protocols for clear aligner therapy
Teeth and attachments were regarded as isotropic and homogeneous materials with rigid stiffness properties, while periodontal ligaments (PDLs) were set up as hyperelastic materials to mimic its true mechanical properties as much as possible
During incisor en masse retraction, different force systems and behaviours of both anterior and posterior teeth were recorded among the three performed simulations (Figs. 3–5)
Summary
To evaluate tooth behaviours under various maxillary incisor retraction protocols for clear aligner therapy. With the development of computer technology and the gradual recognition of the biomechanical properties of aligner materials, CAT has demonstrated the capacity to treat more complex cases, such as cases requiring tooth extraction[3,4,5,6] These case reports pointed out the limitations of using clear aligners to complete the gap closure in extraction treatment. Finite element analysis can calculate initial tooth movement instantly after force loading It has been widely used in biomechanics to analyse the stress and strain response of external forces in residential structures and has been demonstrated to be an effective tool to simulate tooth displacement patterns in orthodontics[11,12]. The purpose of this study is to determine the behaviours and stress distributions of both anterior and posterior teeth under different amounts of retraction and intrusion protocols with clear aligners by three-dimensional finite element (3D FE) analysis
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