Niroomand Mohammad Reza, Arabbeiki Masoud, Rouhi Gholamreza
Department of Mechanical Engineering, Payame Noor University, Tehran, Iran.
Department of Mechanical and Aerospace Engineering, Politecnico di Torino, Turin, Italy.
Comput Methods Programs Biomed. 2023 Apr;231:107376. doi: 10.1016/j.cmpb.2023.107376. Epub 2023 Jan 28.
The threads, as the most critical component of dental implants, transfer the imposed occlusal loads to the adjacent bone. Moreover, regulation of the mechanical stimuli in the implant adjacent bone is crucial to maximize the bone-implant construct stability. An optimal thread design can be resulted when the distribution of mechanical stimuli within the bone, and at the implant-bone interface, lie in an advised confined range. In this work, with the goal of finding the optimal thread design, which can provide the maximum level of stability, the effects of thread parameters, namely, thread depth, thread width, and thread pitch, together with upper and lower thread angles, on maximum principal strain within the cortical and cancellous bone, and shear strain at the implant-bone interface, were investigated.
In this study, the response surface methodology (RSM), due to the central composite design (CCD), was employed to obtain a set of 53 experiments. Following that, they were numerically simulated using the finite element method (FEM). The polynomial regression model was then used to predict the response functions based on the magnitude of thread parameters. The effectiveness of each thread parameter was also evaluated through statistical tools. Moreover, the non-dominated sorting genetic algorithm (NSGA-II) was performed to find the optimum dimensions of the thread.
Through comparing the results obtained from analyzing initial and optimized configuration of threads, it was shown that the latter causes a reduction in the maximum principal strains in cancellous and cortical bones by about 25% and 30%, respectively, which is in favor of making a higher quality bone, and thus greater stability in dental implant-bone construct. Moreover, the maximum shear strains at the implant-bone interface in different planes were reduced by about 40%, in the optimized thread, compared with the initial design.
The optimized design found in this study is a buttress thread with a fine pitch, but deep thread, which keeps the mechanical stimuli in a safe range to grant an acceptable level of stability.
螺纹作为牙种植体最关键的部件，将施加的咬合负荷传递至相邻骨组织。此外，调节种植体周围骨组织中的机械刺激对于最大化骨 - 种植体结构稳定性至关重要。当骨组织内以及种植体 - 骨界面处的机械刺激分布处于建议的限定范围内时，可得到最优的螺纹设计。在本研究中，为了找到能够提供最大稳定性水平的最优螺纹设计，研究了螺纹参数（即螺纹深度、螺纹宽度、螺距）以及上下螺纹角对皮质骨和松质骨内的最大主应变以及种植体 - 骨界面处的剪应变的影响。
在本研究中，采用基于中心复合设计（CCD）的响应面方法（RSM）来获得一组53个实验。随后，使用有限元方法（FEM）对其进行数值模拟。然后使用多项式回归模型根据螺纹参数的大小预测响应函数。还通过统计工具评估了每个螺纹参数的有效性。此外，执行非支配排序遗传算法（NSGA-II）以找到螺纹的最佳尺寸。
通过比较分析螺纹初始和优化配置所获得的结果表明，优化后的配置分别使松质骨和皮质骨中的最大主应变降低了约25%和30%，这有利于形成更高质量的骨组织，从而在牙种植体 - 骨结构中具有更高的稳定性。此外，与初始设计相比，优化后的螺纹在不同平面上种植体 - 骨界面处的最大剪应变降低了约40%。
本研究中发现的优化设计是一种螺距细但螺纹深的支撑螺纹，它将机械刺激保持在安全范围内，以确保可接受的稳定性水平。
