Institute of Structural Analysis, Poznan University of Technology, ul. Piotrowo 5, 60-965, Poznań, Poland.
TECHNIA Sp. z o.o. Poznański Park Technologiczno-Przemysłowy, ul. 28 Czerwca 1956 r. nr 406, 61-441, Poznań, Poland.
J Mech Behav Biomed Mater. 2023 Dec;148:106165. doi: 10.1016/j.jmbbm.2023.106165. Epub 2023 Oct 12.
Screw loosening is a critical aspect of an implant design, as it can lead to implant failure. This study proposes a methodology and qualitatively assesses the potential of screw loosening risk for various types of screw heads and implant fixture-abutment connections. It is assumed that the risk of screw loosening is related to the drop in loosening moment under occlusal loads. The methodology and an assumption is verified by confronting the results with laboratory tests.
Numerical simulations supplemented with semi-empirical equations were employed to estimate a loosening moment change under occlusal loads. The loosening risk was estimated by comparing the value before and after application of a compressive occlusal load of 150N. The procedure was carried out for 289 implant designs with smooth transition between flat to tapered shape of a screw head and an fixture-abutment connection. All analyses were conducted using Abaqus software. Pearson and Spearman correlation coefficients for normalised change in a screw loosening moment drop has been computed for numerical and laboratory tests.
The statistical analysis (Pearson, ρ = 0.8, Spearman, r = 0.85) indicates very high correlation and confirms that the general tendencies observed in laboratory tests are reflected in the proposed procedure. The procedure was used for various geometries and the following results are presented: a screw loosening drop, implant stiffness and a tightening moment. The loosening moment drop achieves the extreme values of 6% and 24%. The biggest drop is an effect of a conical implant-abutment connection and a flat screw head while the lowest was recorded for a flat implant-abutment interface regardless of a screw head type. A low drop is also observed for a strongly conical screw head.
The proposed methodology exhibited very good correlation when confronted with laboratory tests, supporting a screw preload reduction under occlusal load as a key factor in screw loosening. Analysis across a wide spectrum of implant designs revealed geometry significantly impacts loosening potential under occlusal loads. Two key features were identified as favourable - an abutment-fixture butt joint and a tapered screw. The results also enable prediction of qualitative geometry effects on loosening risk.
螺钉松动是植入物设计的一个关键方面，因为它可能导致植入物失效。本研究提出了一种方法，并定性评估了各种类型的螺钉头和植入物固位体-基台连接的螺钉松动风险。假设螺钉松动的风险与在咬合载荷下松动力矩的降低有关。该方法和假设通过将结果与实验室测试进行对比来验证。
采用数值模拟和半经验方程来估计在咬合载荷下的松动力矩变化。通过比较施加 150N 压缩咬合载荷前后的值来估计松动风险。该程序针对 289 种具有平滑过渡的种植体设计进行了研究，螺钉头和平坦到锥形的形状以及固位体-基台连接之间存在过渡。所有分析均使用 Abaqus 软件进行。为了数值和实验室测试中标准化的螺钉松动力矩下降的变化，计算了 Pearson 和 Spearman 相关系数。
统计分析（Pearson，ρ=0.8，Spearman，r=0.85）表明相关性非常高，并证实了在实验室测试中观察到的一般趋势反映在提出的程序中。该程序用于各种几何形状，结果如下：螺钉松动下降、植入物刚度和拧紧力矩。松动力矩下降达到了 6%和 24%的极值。最大的下降是锥形植入物-基台连接和平坦螺钉头的效果，而最低的下降是在无论螺钉头类型如何，平坦的植入物-基台界面上记录的。对于强烈锥形的螺钉头，也观察到松动力矩的下降很小。
提出的方法与实验室测试对比表现出非常好的相关性，支持在咬合载荷下减少螺钉预紧力作为螺钉松动的关键因素。对广泛的种植体设计进行分析表明，几何形状显著影响咬合载荷下的松动潜力。两个关键特征被确定为有利的-基台-衔接件的对接和锥形螺钉。结果还能够预测定性几何形状对松动风险的影响。
