Joyce A P, Loushine R J, West L A, Runyan D A, Cameron S M
USA DENTAC Ft. Gordon, GA 30905, USA.
J Endod. 1998 Nov;24(11):714-5. doi: 10.1016/S0099-2399(98)80159-3.
The vertical force applied to an endodontic spreader generates stress along the canal walls. Recognizing the potential for this stress may reduce the incidence of vertical root fractures. A photoelastic acrylic model was fabricated to exhibit the stress produced during obturation of curved canals using the lateral condensation technique. Twenty standardized models simulating curved canals (32 degrees) were formed within PL-2 photoelastic acrylic resin blocks. The canals were fitted with a gutta-percha point, and either a stainless-steel or nickel-titanium finger spreader was inserted. An Instron 4502 universal testing machine applied a vertical force of 20 Newtons to the spreader. Quarter wave and polarizing filters were used with backlighting to generate the fringe patterns in the models. Photographs of the resulting stress lines showed that the stainless-steel spreaders created three areas of concentrated stress. The nickel-titanium spreaders induced stress patterns spread out along the surface of the canals, thus reducing the concentration of stress and the potential for vertical root fracture.
施加于根管扩大器的垂直力会沿根管壁产生应力。认识到这种应力的潜在影响可能会降低垂直根折的发生率。制作了一个光弹性丙烯酸模型，以展示使用侧向加压技术充填弯曲根管时产生的应力。在PL - 2光弹性丙烯酸树脂块内形成了20个模拟弯曲根管（32度）的标准化模型。根管内放置一根牙胶尖，并插入一个不锈钢或镍钛指状扩大器。一台Instron 4502万能试验机对扩大器施加20牛顿的垂直力。使用四分之一波片和偏振滤光片并配合逆光，在模型中产生条纹图案。所得应力线的照片显示，不锈钢扩大器产生了三个应力集中区域。镍钛扩大器诱导的应力模式沿根管表面扩散，从而降低了应力集中程度以及垂直根折的可能性。
