微种植体无螺纹颈部高度与锥度优化设计的三维有限元分析

Optimized cervical threadless height and tapering design and stress analysis of mini-implant

目的微型种植体颈部螺纹不利于骨界面应力分布,本研究目的是评价正畸载荷下种植体无螺纹颈部高度和锥度同时连续变化下骨组织内应力分布。方法建立微种植体-骨组织三维有限元模型,种植体颈部无螺纹高度变化为0~3 mm,锥度变化为0°~45°,种植体给以2N的载荷,观察颈部无螺纹高度和锥度同时变化对骨界面Von-Mises应力及位移峰值的影响,并进行应力敏感度分析。结果颈部无螺纹高度为1.5mm时,随着颈部锥度的增加,皮质骨内Von-Mises应力峰值降低82%,位移峰值降低59%,松质骨应力峰值降低47%,位移峰值降低14%。颈部锥度为22.5°时,随着高度的增加,皮质骨应力峰值和位移峰值明显降低,但颈部无螺纹部分一旦超出皮质骨厚度范围,松质骨内应力峰值和位移峰值显著增高。结论种植体颈部无螺纹高度和锥度对骨界面应力分布有显著影响。颈部无螺纹高度比锥度对骨内应力水平影响更大。建议使用具有一定颈部锥度的种植体,或将传统螺纹种植体适当增加植入深度,使螺纹起始处位于皮质骨厚度范围内。

Objective To evaluate the effect of continuous and simultaneous variations of the cervical threadless height and tapering on the biomechanical properties of an orthodontic mini-implant. Methods A finite element model of a mandible segment with mini-implant was created. Mini-implant cervical threadless height ranged from 0 to 3 mm, and tapering ranged from 0°to 45°. The maximum Von-Mises stresses and displacement in the bone were evaluated, and the sensitivity of the stresses in the bone to the variables was also evaluated when mini-implant was loaded by 2N. Results when cervical threadless height was 1.Smm, with the increase of the neck tapong, Von Mises stress peak and displacement peak in cortical bone reduced by 82% and 59%, respectively, and in cancellous bone reduced by 47% and 14%, respectively. When neck taper was 22.5°, the maximum stress and displacement in cortical bone decreased significantly with the increase of height. But once the cervical threadless height goes out of scope of cortical bone thickness, the maximum Von-Mises stresses and displacement in cancellous bone were increased significantly. Conclusion The stress distribution levels were influenced by cervical threadless height and tapering of mini-implant. Cervical threadless height played a more significant role than the tapering on maxillary stress and displacement. They are recommended to use a certain cervical taper of the implant or inserting a conventional screw deeply beyond the threaded part to make the thread starting site in cortical bone thickness range.