Jenny Zwei-Chieng Chang1, Yi-Jane Chen2, Yuan-Yi Tung3, Yu-Ying Chiang4, Eddie Hsiang-Hua Lai5, Weng-Pin Chen6, Chun-Pin Lin7. 1. Instructor, School of Dentistry, National Taiwan University, Taipei, Taiwan. 2. Associate professor, School of Dentistry, National Taiwan University, Taipei, Taiwan. 3. Postgraduate student, School of Dentistry, National Taiwan University, Taipei, Taiwan. 4. Postgraduate student, Mechanical Engineering Department, National Taipei University of Technology, Taipei, Taiwan. 5. Instructor, School of Dentistry, National Taiwan University, Taipei, Taiwan. Electronic address: eddielai0715@yahoo.com.tw. 6. Professor, Mechanical Engineering Department, National Taipei University of Technology, Taipei, Taiwan. Electronic address: wpchen@ntut.edu.tw. 7. Professor, School of Dentistry, National Taiwan University, Taipei, Taiwan.
Abstract
INTRODUCTION: The primary stability of a mini-implant is critical, since most orthodontic mini-implant failures occur at an early stage. As orthodontic mini-implants have restrictions in diameter and length, an optimal design of the shape is important for sufficient primary stability. The purpose of this study was to investigate the influence of various mini-implants design factors, including thread depth, degree of taper, and taper length on insertion torque, pullout strength, stiffness, and screw displacement before failure. METHODS: Finite element analyses were conducted first for identification of optimal design parameters. Four types of mini-implants with different design parameters were then custom manufactured and tested mechanically. All mechanical tests were performed in artificial bone with homogenous density to remove the variability associated with bone. RESULTS: Finite element results showed that, for mini-implants with a fixed external diameter of 2 mm, a thread length of 9.82 mm, and a pitch of 0.75 mm, those with greater thread depths, smaller taper degrees, and shorter taper lengths generated higher maximum stresses on the bone and thread elements. These mini-implants also had larger relative displacements. Maximum pullout resistance was attained with a core/external diameter ratio of 0.68. All mechanical results were compatible with the findings in the finite element analyses. CONCLUSIONS: Modification of the mini-implant design can substantially affect the mechanical properties. The finite element method is an effective tool to identify optimal design parameters and allow for improved mini-implant designs.
INTRODUCTION: The primary stability of a mini-implant is critical, since most orthodontic mini-implant failures occur at an early stage. As orthodontic mini-implants have restrictions in diameter and length, an optimal design of the shape is important for sufficient primary stability. The purpose of this study was to investigate the influence of various mini-implants design factors, including thread depth, degree of taper, and taper length on insertion torque, pullout strength, stiffness, and screw displacement before failure. METHODS: Finite element analyses were conducted first for identification of optimal design parameters. Four types of mini-implants with different design parameters were then custom manufactured and tested mechanically. All mechanical tests were performed in artificial bone with homogenous density to remove the variability associated with bone. RESULTS: Finite element results showed that, for mini-implants with a fixed external diameter of 2 mm, a thread length of 9.82 mm, and a pitch of 0.75 mm, those with greater thread depths, smaller taper degrees, and shorter taper lengths generated higher maximum stresses on the bone and thread elements. These mini-implants also had larger relative displacements. Maximum pullout resistance was attained with a core/external diameter ratio of 0.68. All mechanical results were compatible with the findings in the finite element analyses. CONCLUSIONS: Modification of the mini-implant design can substantially affect the mechanical properties. The finite element method is an effective tool to identify optimal design parameters and allow for improved mini-implant designs.
Authors: Leandro Pozzer; Sergio Olate; Lucas Cavalieri-Pereira; Márcio de Moraes; José Ricardo Albergaría-Barbosa Journal: Int J Clin Exp Med Date: 2014-05-15