1 Department of Orthodontics, School of Dentistry, Oregon Health & Science University, Portland, OR, USA.
2 Department of Oral Diagnostic Sciences, School of Dental Medicine, University at Buffalo, Buffalo, NY, USA.
J Dent Res. 2018 Oct;97(11):1185-1192. doi: 10.1177/0022034518786469. Epub 2018 Jul 13.
Craniofacial secondary cartilages of the mandibular condyle and temporomandibular joint (TMJ) eminence grow in response to the local mechanical environment. The intervening TMJ disc distributes normal loads over the cartilage surfaces and provides lubrication. A better understanding of the mechanical environment and its effects on growth, development, and degeneration of the TMJ may improve treatments aimed at modifying jaw growth and preventing or reversing degenerative joint disease (DJD). This review highlights data recorded in human subjects and from computer modeling that elucidate the role of mechanics in TMJ ontogeny. Presented data provide an approximation of the age-related changes in jaw-loading behaviors and TMJ contact mechanics. The cells of the mandibular condyle, eminence, and disc respond to the mechanical environment associated with behaviors and ultimately determine the TMJ components' mature morphologies and susceptibility to precocious development of DJD compared to postcranial joints. The TMJ disc may be especially prone to degenerative change due to its avascularity and steep oxygen and glucose gradients consequent to high cell density and rate of nutrient consumption, as well as low solute diffusivities. The combined effects of strain-related hypoxia and limited glucose concentrations dramatically affect synthesis of the extracellular matrix (ECM), which limit repair capabilities. Magnitude and frequency of jaw loading influence this localized in situ environment, including stem and fibrocartilage cell chemistry, as well as the rate of ECM mechanical fatigue. Key in vivo measurements to characterize the mechanical environment include the concentration of work input to articulating tissues, known as energy density, and the percentage of time that muscles are used to load the jaws out of a total recording time, known as duty factor. Combining these measurements into a mechanobehavioral score and linking these to results of computer models of strain-regulated biochemical events may elucidate the mechanisms responsible for growth, maintenance, and deterioration of TMJ tissues.
下颌骨髁突和颞下颌关节（TMJ）的颅面次级软骨会响应局部机械环境而生长。中间的 TMJ 盘将正常负荷分布在软骨表面，并提供润滑。更好地了解机械环境及其对 TMJ 生长、发育和退行性变的影响，可能会改善旨在改变下颌生长和预防或逆转退行性关节疾病（DJD）的治疗方法。这篇综述重点介绍了在人体研究和计算机建模中记录的数据，这些数据阐明了力学在 TMJ 发生中的作用。所呈现的数据提供了与颌骨加载行为和 TMJ 接触力学相关的年龄相关性变化的近似值。下颌骨髁突、嵴和盘的细胞对与行为相关的机械环境做出反应，并最终决定 TMJ 成分的成熟形态，以及与后肢关节相比，DJD 早期发育的易感性。TMJ 盘由于其无血管性以及由于细胞密度高和营养物质消耗速度快而导致的氧气和葡萄糖梯度陡峭，以及低溶质扩散率，可能特别容易发生退行性变化。与应变相关的缺氧和有限的葡萄糖浓度的综合影响极大地影响细胞外基质（ECM）的合成，从而限制了修复能力。颌骨加载的幅度和频率会影响这种局部原位环境，包括干骺端和纤维软骨细胞的化学性质，以及 ECM 机械疲劳的速度。用于描述机械环境的关键体内测量包括作用于关节组织的功输入浓度，称为能量密度，以及肌肉在总记录时间内用于加载颌骨的时间百分比，称为作用比。将这些测量值结合到机械行为评分中，并将其与应变调节生化事件的计算机模型结果联系起来，可能阐明导致 TMJ 组织生长、维持和恶化的机制。
