Motoyoshi M, Inaba M, Ueno S, Shimizu N
Department of Orthodontics, Division of Clinical Research, Dental Research Center, Nihon University School of Dentistry, Tokyo, Japan.
Int J Oral Maxillofac Surg. 2009 Sep;38(9):972-7. doi: 10.1016/j.ijom.2009.05.009. Epub 2009 Jun 25.
This study investigated stress distribution in the bone around orthodontic mini-implants using the finite element method and determined the difference in the stress distribution for different loading directions to identify risk factors for the loosening of mini-implants. Three-dimensional finite element models were constructed for conventional and cervical threadless mini-implants with cortical bone 1 or 3mm thick. The authors calculated the compressive stresses on the bone elements and evaluated stress distribution according to the loading direction. Directional dependency (i.e. mechanical anisotropy) was observed with the conventional mini-implant model. The compressive stress ranged from -31 to -55 MPa depending on the loading direction. In the cervical threadless model, mechanical anisotropy disappeared and the stress was reduced. Cortical bone thickness had no influence in either model. One of the risk factors for mini-implant failure might be related to mechanical anisotropy. This report suggests ways for clinicians to avoid overload traction force when conventional mini-implants are used. The cervical threadless mini-implant can reduce mechanical anisotropy to facilitate successful placement. Inserting a conventional screw deeply beyond the threaded part might be useful in stabilizing a mini-implant.
本研究采用有限元方法研究了正畸微型种植体周围骨组织的应力分布，并确定了不同加载方向下应力分布的差异，以识别微型种植体松动的风险因素。构建了具有1mm或3mm厚皮质骨的传统型和颈部无螺纹微型种植体的三维有限元模型。作者计算了骨单元上的压应力，并根据加载方向评估应力分布。在传统微型种植体模型中观察到了方向依赖性（即力学各向异性）。根据加载方向的不同，压应力范围为-31至-55MPa。在颈部无螺纹模型中，力学各向异性消失且应力降低。皮质骨厚度在两种模型中均无影响。微型种植体失败的风险因素之一可能与力学各向异性有关。本报告为临床医生在使用传统微型种植体时避免过载牵引力提供了方法。颈部无螺纹微型种植体可降低力学各向异性，便于成功植入。将传统螺钉深入螺纹部分以外可能有助于稳定微型种植体。
