Mechanical and Finite Element Analysis of Mini-screw Systems for Orthodontic Anchorage
Date Issued
2008
Date
2008
Author(s)
Tung, Yuan-Yi
Abstract
Recently, the use of skeletal anchorage is increasingly popular in modern clinical orthodontics. Many different designs of miniscrews were developed and widely applied in clinics, and their advantages have been proved by many studies. However, there were still some problems to be solved during clinical use of orthodontic miniscrews, including surrounding soft tissue inflammation, loosening in use, or breakage during implantation. Moreover, the mechanical properties of orthodontic miniscrews have few been studied. Therefore, the purpose of the study is to investigate the effects of geometrical parameters, including thread depth, taper of core, and circles of taper of miniscrews on its insertional torque, pullout strength, and stress distribution. These mechanical properties were assessed using standardized laboratory set-up and finite element analysis (FEA). The results will be applied to the development of new miniscrew systems in the future. he study includes two parts. Part I was to evaluate the mechanical behavior of two commercial available miniscrews (Mondeal, German; Osstem, Korea). Part II was to analyze how the following geometric properties would affect the mechanical performance with four custom-made miniscrews. They have different designs in thread depth(mm)/taper of core(°)/circles of taper(c): s1(0.4/7/4)、s2(0.4/0/0)、s3(0.4/7/2)、s4(0.32/7/2). The procedures were as follows: (1) To evaluate how the different geometrical parameters will affect the stress distribution and displacement of miniscrews during bending and pullout test simulated by FEA. (2) Mechanical tests for insertion and pullout, and the samples were four custom-made miniscrews developed according to the designs of FEA and two other commercial miniscrews. The bone were used with Sawbones (0.48g/cc). (3) Choosing s1 for mechanical bending test and measuring the strain on the surface of the Sawbones surrounding the miniscrews with strain gauge. This result will be compared with the result of the FEA and get the stress distribution around the miniscrews indirectly. The results of this study were listed as follows, the comparison of the insertional torque: Osstem(26.19 ± 1.36 Ncm) > Mondeal(17.86 ± 1.24 Ncm), s1(28.79 ± 2.59 Ncm) > s3(24.20 ± 1.11 Ncm), s3(24.20 ± 1.11 Ncm) > s2(21.78 ± 1.83 Ncm), and s3(24.20 ± 1.11 Ncm) > s4(21.39 ± 0.49 Ncm); the comparison of the maximum pullout force: Osstem(138.15 ± 9.87N) > Mondeal(95.09 ± 17.19N), s1(113.9 ± 8.37N) > s3(81.44 ± 6.77N), s2(96.63 ± 6.7N) > s3(81.44 ± 6.77N), and s4(102.9 ± 12.8N) > s3(81.44 ± 6.77N).he conclusion were: . Both the insertional torque and the resistance to pull-out test of the Osstem miniscrew were higher than those of Mondeal.. An appropriate increase in thread depth, taper of the core, and thread number at the taper part of miniscrew resulted in larger insertion torque, increased resistance to pullout, which implied better retention.. Exaggerated increase of thread depth, taper of the core or the circles of taper will decrease the resistance to pullout. . FEA is a good tool for studying the stress and strain distribution of miniscrews subjected to loading.
Subjects
orthodontic mini-screws
the stability of mini-screws
insertional torque
finite element analysis
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