Mechanical Engineering, Private Project, Tehran, Iran.
Assistant Professor, Dental and Periodontal Research Center, Department of Prosthodontics, Tabriz University of Medical Sciences, Tabriz, Iran.
J Prosthet Dent. 2019 Mar;121(3):548.e1-548.e7. doi: 10.1016/j.prosdent.2018.10.035. Epub 2019 Feb 11.
Contamination with salivary fluids or blood during the treatment process changes the preload, remaining torque, and removal torque of retained screws, which ultimately affects the resistance to screw loosening. In previous studies, no consensus has been reached as to whether contamination can be used as a lubricant.
The purpose of this 3-dimensional (3D) finite element analysis study was to compare the preload, remaining torque, and removal torque under different frictional conditions in the processes of tightening, waiting period, and removal of abutment screws using a numeric method and finite element analysis.
Three-dimensional finite element models of a single implant restoration including a crown, dental implant, abutment, and abutment screw, along with the surrounding bone, were constructed. The geometry of all threaded interfaces was designed as a threaded helix. The Abaqus software was used to perform the dynamic simulation of 3 steps such as tightening, waiting period, and removal. Three static and kinetic friction conditions were considered to determine the effect of different frictional conditions. The values of preload at the tightening step, remaining torque at the waiting period, and removal torque at the removal step were evaluated and compared with theoretically predicted values.
The amount of removal torque required to loosen the abutment screw was smaller than the insertion torque for all frictional conditions. By decreasing the coefficient of friction, the remaining torque and the preload increased, and the torsional relaxation and removal torque decreased.
Although the value of the removal torque decreased by decreasing the coefficient of friction, the resistance to screw loosening increased with the increase of the preload and the increase of the remaining torque in the implant complex assembly. Considering the biological complications of fluid lubricants, clinicians may contaminate the abutment screw with lubricants. Gold-coated screws should also be preferred to noncoated screws.
在治疗过程中，唾液或血液污染会改变固位螺钉的预载荷、剩余扭矩和取出扭矩，从而最终影响螺钉松动的阻力。在以前的研究中，对于污染是否可以用作润滑剂尚未达成共识。
本三维（3D）有限元分析研究的目的是通过数值方法和有限元分析比较不同摩擦条件下，在拧紧、等待期和取出基台螺钉过程中，预载荷、剩余扭矩和取出扭矩的变化。
构建了包括牙冠、种植体、基台和基台螺钉以及周围骨骼的单个种植体修复体的三维有限元模型。所有螺纹界面的几何形状均设计为螺纹螺旋线。使用 Abaqus 软件对拧紧、等待期和取出三个步骤进行动态模拟。考虑了三种静态和动态摩擦条件，以确定不同摩擦条件的影响。评估并比较了拧紧步骤的预载荷值、等待期的剩余扭矩值和取出步骤的取出扭矩值与理论预测值。
对于所有摩擦条件，松开基台螺钉所需的取出扭矩均小于插入扭矩。通过降低摩擦系数，可以增加剩余扭矩和预载荷，同时减小扭转松弛和取出扭矩。
尽管通过降低摩擦系数会降低取出扭矩值，但随着种植体复合体中预载荷和剩余扭矩的增加，螺钉松动的阻力也会增加。考虑到流体润滑剂的生物并发症，临床医生可能会将润滑剂污染到基台螺钉上。因此，应优先选择镀金螺钉而非非涂层螺钉。
