Department of Orthodontics and Dentofacial Orthopedics, The University of Tokushima Graduate School of Oral Sciences, Kuramoto-cho, Japan.
Arch Oral Biol. 2010 Nov;55(11):879-86. doi: 10.1016/j.archoralbio.2010.07.011. Epub 2010 Aug 21.
Bruxism, the parafunctional habit of nocturnal grinding of the teeth and clenching, is associated with the onset of joint degeneration. Especially prolonged clenching is suggested to cause functional overloading in the temporomandibular joint (TMJ). In this study, the distributions of stresses in the cartilaginous TMJ disc and articular cartilage, were analysed during prolonged clenching. The purpose of this study was to examine if joint degradation due to prolonged clenching can be attributed to changes in stress concentration in the cartilaginous tissues.
Finite element model was developed on the basis of magnetic resonance images from a healthy volunteer. Condylar movements recorded during prolonged clenching were used as the loading condition for stress analysis.
At the onset of clenching (time=0s), the highest von Mises stresses were located in the middle and posterior areas (6.18MPa) of the inferior disc surface facing the condylar cartilage. The largest magnitude of the minimum principal stress (-6.72MPa) was found in the condylar cartilage. The stress concentrations were relieved towards the superior disc surface facing the temporal cartilage. On the surfaces of the temporal cartilage, relatively lower stresses were found. After 5-min clenching, both stress values induced in the TMJ components were reduced to 50-80% of the stress values at the onset of clenching, although the concomitant strains increased slightly during this period.
It is suggested that both the condylar and temporal cartilage layers along with the TMJ disc, play an important role in stress distribution and transmission during prolonged clenching due to tissue expansion. Furthermore, our study suggests that a development of stress concentrations in the TMJ during prolonged clenching and risk factors for the initiation of TMJ degeneration could not be confirmed.
磨牙症，即夜间磨牙和紧咬牙的习惯性功能障碍，与关节退变的发生有关。特别是长时间的紧咬牙被认为会导致颞下颌关节（TMJ）功能过载。在这项研究中，分析了长时间紧咬牙时软骨 TMJ 盘和关节软骨的应力分布。本研究旨在探讨由于长时间紧咬牙导致的关节退化是否可以归因于软骨组织中应力集中的变化。
基于健康志愿者的磁共振图像开发了有限元模型。在应力分析中，使用记录的髁突在长时间紧咬牙过程中的运动作为加载条件。
在紧咬牙开始时（时间=0s），面对髁突软骨的下盘表面的中间和后区域（6.18MPa）出现了最高的 von Mises 应力。在髁突软骨中发现最大的最小主应力（-6.72MPa）。应力集中在面向颞骨软骨的上盘表面得到缓解。在颞骨软骨表面，发现的应力相对较低。在 5 分钟的紧咬牙后，TMJ 各组成部分的应力值均降低到紧咬牙开始时的 50-80%，尽管在此期间伴随的应变略有增加。
建议在长时间紧咬牙过程中，由于组织扩张，髁突和颞骨软骨层以及 TMJ 盘在应力分布和传递中发挥重要作用。此外，我们的研究表明，在长时间紧咬牙期间 TMJ 中没有确认应力集中的发展以及 TMJ 退变的起始风险因素。
