Gracco A, Cirignaco A, Cozzani M, Boccaccio A, Pappalettere C, Vitale G
Department of Orthodontics, University of Ferrara, Ferrara, Italy.
Eur J Orthod. 2009 Feb;31(1):12-20. doi: 10.1093/ejo/cjn066. Epub 2008 Dec 15.
The aims of this study were to analyse the stress distribution developing around an orthodontic miniscrew (OM) inserted into the maxilla and to determine the stress field changes for different screw lengths and for different levels of osseointegration occurring at the bone/screw interface. An integrated experimental/numerical approach was adopted. Using the photoelastic technique, the stress field arising in the bone after screw insertion and the application of the initial orthodontic load was assessed. The finite element (FE) method was used to determine the stress acting in the bony tissue after a given time following screw application, when, for the viscoelastic relaxation effects, the only stress field remaining was that due to the application of the orthodontic load. Different levels of osseointegration were hypothesized. Photoelastic analyses showed that stress distribution does not change significantly for moderate initial orthodontic loads. From the FE simulations, it was found that critical conditions occur for screws 14 mm long with an orthodontic load of 2 N. The optimal screw length seems to be 9 mm. For such a dimension, small stress values were found as well as low risk of lesion to the anatomical structures.
本研究的目的是分析植入上颌骨的正畸微螺钉（OM）周围产生的应力分布，并确定不同螺钉长度以及骨/螺钉界面处不同骨整合水平下的应力场变化。采用了实验与数值相结合的方法。使用光弹性技术，评估了螺钉植入后以及施加初始正畸负荷时骨中产生的应力场。当由于粘弹性松弛效应，在施加螺钉后的给定时间，唯一剩余的应力场是由于正畸负荷施加而产生的应力场时，使用有限元（FE）方法确定作用于骨组织中的应力。假设了不同水平的骨整合。光弹性分析表明，对于中等初始正畸负荷，应力分布没有显著变化。从有限元模拟中发现，对于长度为14 mm且正畸负荷为2 N的螺钉会出现临界情况。最佳螺钉长度似乎为9 mm。对于这样的尺寸，发现应力值较小，对解剖结构造成损伤的风险也较低。
