Kaewsuriyathumrong C, Soma K
First Department of Orthodontics, Faculty of Dentistry, Tokyo Medical and Dental University, Tokyo Ika Shika Daigaku.
Bull Tokyo Med Dent Univ. 1993 Dec;40(4):217-32.
Stress is created by the bite force and distributed along the tooth towards the PDL structure. It is of interest to investigate the complex tooth structure, consisting of enamel, dentine, pulp, and thin cementum layer and how it functions in stress distribution. This study was intended to analyze the role of the tooth and PDL structures in stress distribution, by using a three-dimensional finite element method. A mandibular first molar was constructed for the finite element model. The bite forces were measured by Pressensor, and these bite force values were programmed to load down upon the occlusal surface of the model. The results were expressed by stress contours and principal stress graphs. The stress was found to decrease as it distributed from the occlusal surface towards the cervical portion in the dentine and the pulp. In contrast, the stress, especially a compressive stress, increased gradually in the enamel layer in the lower half of the crown, in the same direction. It was apparent in displayed pattern of stress that the stress distributed outward towards the surrounding portion of the lower half of the crown. This resulted in a uniform magnitude of the principal stresses for all aspects of the mesial and distal roots. The stresses of both roots were generally compressive stress. When comparing the stress values of sampling points positioned between the root surfaces and the periphery of the PDL (the alveolar wall), all principal stresses for those of the PDL (periodontal ligament) were less than those of the root surfaces. These findings revealed that the PDL, the dentine, and the pulp functioned in cooperation in stress reduction; and the sequences of enamel, dentine, and pulp influenced the pattern of stress distribution. The different material properties of the tooth structure in sequence was considered a very important factor for stress reduction and for the pattern of stress distribution, especially in the root.
咬合力会产生应力，并沿着牙齿向牙周膜结构分布。研究由牙釉质、牙本质、牙髓和薄的牙骨质层组成的复杂牙齿结构及其在应力分布中的作用很有意义。本研究旨在通过三维有限元方法分析牙齿和牙周膜结构在应力分布中的作用。构建了下颌第一磨牙的有限元模型。用压力传感器测量咬合力，并将这些咬合力值编程加载到模型的咬合面上。结果用应力等值线和主应力图表示。结果发现，应力从咬合面向牙本质和牙髓的颈部方向分布时会降低。相反，在相同方向上，应力，尤其是压应力，在牙冠下半部的牙釉质层中逐渐增加。在显示的应力模式中很明显，应力向外分布到牙冠下半部的周围部分。这导致近中根和远中根各方面的主应力大小均匀。两根的应力一般都是压应力。当比较位于牙根表面和牙周膜（牙槽壁）周边之间的采样点的应力值时，牙周膜（牙周韧带）的所有主应力都小于牙根表面的主应力。这些发现表明，牙周膜、牙本质和牙髓在减轻应力方面协同发挥作用；牙釉质、牙本质和牙髓的顺序影响应力分布模式。牙齿结构依次不同的材料特性被认为是减轻应力和应力分布模式的一个非常重要的因素，尤其是在牙根中。
