Comparative study of biomechanical effects between two types of 2 × 4 techniques employing a rocking-chair archwire: a three-dimensional finite element analysis

Abstract

Abstract Objectives After bonding brackets to the first deciduous molar in a 2 × 4 technique, a three-dimensional finite element analysis (3D FEA) is used to demonstrate the biomechanical changes in an orthodontic system. This study aims to opt for the appropriate type of orthodontic technology by analyzing and comparing the mechanical systems produced by two types of 2 × 4 technologies employing rocking-chair archwires. Materials and methods Herein, maxilla and maxillary dentition are modeled by cone beam computed tomography (CBCT) and 3D FEA. Common clinically used round titanium-molybdenum alloy archwires (diameter: 0.016’’ and 0.018’’) and round stainless-steel archwires (diameter: 0.016’’ and 0.018’’) are bent into the shape of a rocking chair with a depth of 3 mm. The forces and moments applied to the brackets are transferred to the dentition to evaluate the biomechanical effects of the 2 × 4 technique after the bracket is bonded to the first deciduous molar. Results When using the same size and orthodontic technique, the forces and moments applied to the teeth by the rocking-chair stainless-steel archwire are approximately three times those applied by the rocking-chair titanium-molybdenum alloy archwire. Therefore, this study investigates only the initial movements of teeth and periodontal ligaments using round stainless-steel archwires. The left-hand side of the patient is defined as the positive X-axis direction, rear as the positive Y-axis direction, and top as the positive Z-axis direction. For the central incisor, the teeth-moving distance in all three directions increases with the bracket bonding to the first deciduous molar using the 0.016’’ rocking-chair archwire. No significant differences between the two orthodontic methods using a 0.018’’ archwire are observed. For the lateral incisor, the tooth root moves toward the gingival side when using 0.016’’ and 0.018’’ archwires. Moreover, for the same archwire size, the lateral incisors move toward the gingival side by bonding the bracket to the first deciduous molar, which is conducive to the anterior teeth intrusion. For the first molar, using rocking-chair 0.016’’ or 0.018’’ archwires, after the bracket is bonded to the first deciduous molar, in the X-axis direction, the buccal movement distance of the first molar crown increases. In the Y-axis and Z-axis directions, the modified 2 × 4 technology significantly increases the effect of backward-tipping compared with the traditional 2 × 4 technology; thus, the modified 2 × 4 technology considerably reduces the anchorage loss. Conclusions In clinical practice, the modified 2 × 4 technology can be used to increase the movement distance of anterior teeth to a certain extent and accelerate the orthodontic teeth movement. Moreover, the modified 2 × 4 technology is better in anchorage conversation of the first molar than the traditional technology.