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Progress in Orthodontics
Fig. 4 | Progress in Orthodontics

Fig. 4

From: Stress and movement trend of lower incisors with different IMPA intruded by clear aligner: a three-dimensional finite element analysis

Fig. 4

Force system analysis of incisors with different initial IMPA during the intrusion. The X-axis is the initial IMPA, and the Y-axis is the moment or force. The black dot in the figure is the CR. The black arrow represents the same direction of force or moment on the central incisor and the lateral incisor. The yellow arrow represents the direction of force or moment on the central incisor, and the blue arrow represents that on the lateral incisor. A. Labiolingual moment of incisors: a is the moment of the incisor at 90° (lingual crown moment); b is the moment of the incisor at 110° (labial crown moment). The positive value represents the labial crown moment. When the initial IMPA was less than or equal to 100°, central incisors were subjected to lingual crown moment, and when it was larger than or equal to105°, they were subjected to labial crown moment. When the IMPA was less than or equal to 95°, lateral incisors were subjected to lingual crown moment. When IMPA was greater than or equal to 100°, the moment transformed into labial crown moment for lateral incisors. B. Labiolingual force of incisors: c is the force direction of the incisors at 90° (force toward lingual direction); d is the force direction of the incisors at 110° (force toward lingual direction for central incisors, force toward labial direction for lateral incisors). The positive value represents the force toward the labial direction. The CR of the central incisors was always subjected to force in the lingual direction, and the force value did not change significantly with IMPA. For lateral incisors, when the IMPA was less than or equal to 100°, the CRs of the lateral incisors were subjected to a force in the lingual direction. When it was greater than or equal to 105°, they were subjected to the force toward the labial direction. C. Vertical force of incisors: e is the force direction of the incisors at 90° (intrusive force); f is the force direction of the incisors at 110° (intrusive force). A positive value represents intrusion. The central incisors and lateral incisors were always subjected to vertical intrusive force, and the force value did not change significantly with increasing IMPA. The intrusive force of the lateral incisors was always greater than that of the central incisors

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