Bulaqi Haddad Arabi, Mousavi Mashhadi Mahmoud, Safari Hamed, Samandari Mohammad Mahdi, Geramipanah Farideh
Graduate student, Department of Mechanical Engineering, School of Mechanics, University of Tehran, Tehran, Iran.
Professor, Department of Mechanical Engineering, School of Mechanics, University of Tehran, Tehran, Iran.
J Prosthet Dent. 2015 May;113(5):412-9. doi: 10.1016/j.prosdent.2014.09.017. Epub 2015 Mar 4.
A fundamental problem in fully understanding the dynamic nature of screw loosening is lack of recognition of the entire process of screw tightening and retightening.
The purpose of this study was to explain the dynamic nature of abutment screw retightening by using finite element methods to investigate the effect of the coefficient of friction and retightening on the settling effect.
Precise computer models were designed of a Straumann dental implant, a directly attached crown, an abutment screw, and the bone surrounding the implant. All threaded interfaces were designed with a spiral thread helix with a specific coefficient of static and kinetic friction, and the surfaces were characterized as fine, regular, and rough. Abaqus software was used for dynamic simulation, which involved applying rotational displacement to the abutment screw and torque controlling during the steps of tightening, relaxation, retightening, and second relaxation and at different coefficients of friction. The obtained torque and preload values were compared to the predicted values.
When surfaces changed from fine to rough, the remaining torque and preload decreased, and the settling effect increased. Upon retightening, the remaining torque and preload increased, and the settling effect also decreased.
The reduction of the coefficient of friction contributes to increases in the preload and decreases in the settling effect. Retightening reduced the settling effect and had an insignificant effect on the preload. At high coefficients of friction, the retightening effect was intensified.
在全面理解螺钉松动的动态特性方面，一个基本问题是缺乏对螺钉拧紧和重新拧紧整个过程的认识。
本研究的目的是通过使用有限元方法研究摩擦系数和重新拧紧对沉降效应的影响，来解释基台螺钉重新拧紧的动态特性。
设计了精确的计算机模型，包括士卓曼牙科种植体、直接连接的牙冠、基台螺钉以及种植体周围的骨组织。所有螺纹界面均设计有具有特定静摩擦系数和动摩擦系数的螺旋螺纹，表面分为精细、规则和粗糙三种类型。使用Abaqus软件进行动态模拟，在拧紧、松弛、重新拧紧和第二次松弛步骤以及不同摩擦系数下，对基台螺钉施加旋转位移并进行扭矩控制。将获得的扭矩和预紧力值与预测值进行比较。
当表面从精细变为粗糙时，剩余扭矩和预紧力减小，沉降效应增加。重新拧紧时，剩余扭矩和预紧力增加，沉降效应也减小。
摩擦系数的降低有助于预紧力的增加和沉降效应的减小。重新拧紧可降低沉降效应，对预紧力影响不显著。在高摩擦系数下，重新拧紧的效果会增强。
