Norton M R
Bedford Hospital, Bedford, England.
J Prosthet Dent. 2000 May;83(5):567-71. doi: 10.1016/s0022-3913(00)70016-3.
The cone-screw abutment has been shown to diminish micromovement, reducing the burden of component loosening and fracture. However, it is unclear whether the conical taper and joint design influence strength of the interface, with respect to unfavorable bending moments.
This comparative study evaluated the resistance to bending for the ITI Straumann and Astra Tech ST implant systems using an 8- and 11-degree internal cone, respectively.
Assembled units from each system were mounted in a 3-point bending apparatus. High load tests were performed, 4 mm from the joint, and bending moments necessary to induce first point of plastic deformation and ultimate failure were measured. All units were inspected to determine the critical zone of failure.
Bending moments necessary to induce first point of plastic deformation were considered well above that expected in clinical function for both systems. However, the critical zones of failure differed in that the solid Astra abutment deformed before the cone joint with its 11-degree taper and smooth transition into the neck of the screw, preventing screw fracture. By contrast, all ITI screws fractured at the head of the screw where it met the base of the 8-degree cone. It is unclear which aspects of the joint design were responsible for the difference observed in mode of failure or if it was a direct result of the experimental design.
For clinically relevant levels of bending moment, no problems were anticipated with respect to component failure for either system.
锥形螺钉基台已被证明可减少微动，减轻部件松动和断裂的负担。然而，关于不利弯矩，圆锥形锥度和接头设计是否会影响界面强度尚不清楚。
本比较研究分别评估了使用8度和11度内锥的ITI Straumann和Astra Tech ST种植系统的抗弯性。
将每个系统的组装单元安装在三点弯曲装置中。在距接头4毫米处进行高负荷测试，并测量引起首次塑性变形点和最终失效所需的弯矩。检查所有单元以确定失效的关键区域。
对于两个系统，引起首次塑性变形点所需的弯矩均远高于临床功能预期值。然而，失效的关键区域有所不同，即实心的Astra基台在其11度锥度的锥形接头与螺钉颈部平滑过渡之前就发生了变形，从而防止了螺钉断裂。相比之下，所有ITI螺钉均在螺钉头部与8度锥底部相接处断裂。尚不清楚接头设计的哪些方面导致了观察到的失效模式差异，或者这是否是实验设计的直接结果。
对于临床相关水平的弯矩，预计两个系统在部件失效方面均不会出现问题。
