Department of Mechanical and Mechatronic Engineering, University of Sydney, Sydney, New South Wales, Australia.
School of Dentistry, University of Queensland, Brisbane, Australia.
J Endod. 2022 Jul;48(7):893-901. doi: 10.1016/j.joen.2022.03.009. Epub 2022 Apr 8.
This study aimed to investigate whether the direction of force applied to the occlusal surface influenced the pattern of tensile stresses in roots of sound and root canal-prepared mandibular molar teeth. The effect of obturation forces on the development of apical stress was also investigated. To this end, models were constructed using micro-computed tomographic imaging and investigated using finite element analysis.
Micro-computed tomographic data established boundaries of internal and external model surfaces to allow finite element analysis. Individually segmented components were modeled based on mechanical properties in precedent literature. The following conditions were considered: axial force directed over the mesial marginal ridge, a mesial or a distal tipping force, a combination of both a torquing force and axial loading, and hydrostatic pressure. The maximum principal stresses were determined.
The highest root stress occurred in the cervical third of root surfaces (ie, not apically) under all loading conditions. Importantly, mesial tipping forces resulted in tension on distal roots, whereas distal tipping resulted in tension in the mesial roots. Intracanal pressures produced tensile stress on the internal root canal walls in the cervical third of the root. Stresses were calculated to be less than the fatigue tensile strength of dentin.
Static loading, under the conditions modeled, does not result in stress concentration at the root apices that would cause root fracture under normal masticatory loads. Stress patterns developing from mesial and distal tipping forces help to explain the appearance of vertical root fractures reported in sound nonrestored molar teeth.
本研究旨在探讨在对下颌磨牙进行牙体预备和根管充填后，施加于牙合面的力的方向是否会影响牙根的张应力分布模式，以及根管充填时的根管内压力对根尖处应力的发展有何影响。为此，我们使用微计算机断层扫描成像技术构建模型，并采用有限元分析法进行研究。
微计算机断层扫描数据确立了内部和外部模型表面的边界，以便进行有限元分析。根据先前文献中的机械性能，对单独分段的组件进行建模。研究了以下几种情况：①沿近中边缘嵴施加轴向力；②施加近中或远中倾斜力；③施加扭转力和轴向加载的组合；④施加流体静压力。确定了最大主应力。
在所有加载条件下，根表面的近中三分之一（即非根尖处）出现了最高的牙根应力。重要的是，近中倾斜力导致远中根出现张力，而远中倾斜力则导致近中根出现张力。根管内压力会在根的近中三分之一处的根管内管壁产生张应力。计算出的应力小于牙本质的疲劳拉伸强度。
在模拟的条件下，静态加载不会导致根尖处的应力集中，从而在正常咀嚼负荷下不会导致牙根断裂。近中或远中倾斜力产生的应力模式有助于解释在未修复的磨牙中出现的垂直根裂现象。
