Jun Kawamura1, Jae Hyun Park2,3, Yukio Kojima4, Yoon-Ah Kook5, Hee-Moon Kyung6, Jong-Moon Chae2,7. 1. Private Practice in Kawamura Dental Office, Gifu, Japan. 2. Postgraduate Orthodontic Program, Arizona School of Dentistry & Oral Health, A.T. Still University, Mesa, Ariz. 3. Graduate School of Dentistry, Kyung Hee University, Seoul, Korea. 4. Private Practice, Nagoya, Japan. 5. Department of Orthodontics, Seoul St. Mary's Hospital, Catholic University of Korea, Seoul, Korea. 6. Department of Orthodontics, School of Dentistry, Kyungpook National University, Daegu, Korea. 7. Department of Orthodontics, School of Dentistry, Wonkwang Dental Research Institute, University of Wonkwang, Iksan, Korea.
Abstract
OBJECTIVES: To clarify the mechanics of tooth movement in mesialization of the whole mandibular dentition when changing the force angulation. SETTING: A finite element method was used to simulate long-term movements of the whole mandibular dentition. MATERIAL AND METHODS: Tooth movement was simulated by accumulating the initial displacement, which was produced by elastic deformation of the periodontal ligament. Mesial forces of 3 N were applied to the second molar bracket at -30°, -15°, 0°, 15° and 30° to the occlusal plane. RESULTS: The whole dentition and occlusal plane were rotated depending on the direction of the force with respect to the centre of resistance (CR). At a force angulation of -30°, the line of action of the force passed near the CR, and the whole dentition translated without rotation of the occlusal plane. The second molar tipped buccally due to a clearance gap between the archwire and bracket slot. When increasing a force angulation from -30°, the line of action of the force passed above the CR, and thereby, the occlusal plane rotated clockwise. This rotation of the whole dentition induced tipping of the individual teeth. Buccal tipping of the molar due to an elastic deformation of the archwire was prevented by using a lingually pre-bent archwire. CONCLUSIONS: Careful selection of force angulation and biomechanics is essential to obtain proper tooth movement in total mesialization of the mandibular dentition.
OBJECTIVES: To clarify the mechanics of tooth movement in mesialization of the whole mandibular dentition when changing the force angulation. SETTING: A finite element method was used to simulate long-term movements of the whole mandibular dentition. MATERIAL AND METHODS:Tooth movement was simulated by accumulating the initial displacement, which was produced by elastic deformation of the periodontal ligament. Mesial forces of 3 N were applied to the second molar bracket at -30°, -15°, 0°, 15° and 30° to the occlusal plane. RESULTS: The whole dentition and occlusal plane were rotated depending on the direction of the force with respect to the centre of resistance (CR). At a force angulation of -30°, the line of action of the force passed near the CR, and the whole dentition translated without rotation of the occlusal plane. The second molar tipped buccally due to a clearance gap between the archwire and bracket slot. When increasing a force angulation from -30°, the line of action of the force passed above the CR, and thereby, the occlusal plane rotated clockwise. This rotation of the whole dentition induced tipping of the individual teeth. Buccal tipping of the molar due to an elastic deformation of the archwire was prevented by using a lingually pre-bent archwire. CONCLUSIONS: Careful selection of force angulation and biomechanics is essential to obtain proper tooth movement in total mesialization of the mandibular dentition.