Orthodontics and Mechanical Engineering, Indiana University & Purdue University, Indianapolis, IN.
Loma Linda University School of Dentistry, Loma Linda, CA.
J Prosthodont. 2020 Dec;29(9):772-779. doi: 10.1111/jopr.13203. Epub 2020 Aug 6.
The temporomandibular joint is a highly conserved articulation because it promotes survival and propagation via the essential functions of mastication, communication, and routine mating success (dentofacial esthetics). The temporomandibular joint is a unique secondary joint formed between the endochondral temporal bone and the mandibular secondary condylar cartilage via Indian hedgehog and bone morphogenetic protein signaling that is closely related to ear development. A dynamic epigenetic environment is provided by Spry1 and Spry2 genetic induction of the lateral pterygoid and temporalis muscles. Mechanical loading of the condylar periosteum during fetal development produces a superficial layer of fibrocartilage that separates from the condyle to form the interposed temporomandibular joint disc. The articular surfaces of the condyle and fossa are dynamically modified periosteum that has healing and regenerative capability. This unique tissue is composed of a superficial fibrous layer (synovial surface) with an underlying proliferative (cambium) layer that produces a cushioning layer of fibrocartilage which subsequently forms bone. Prior to occlusion of the first primary (deciduous) molars at about 16 months, facial development is dominated by primary genetic mechanisms. After achieving posterior functional occlusion, biomechanics enhances temporomandibular joint maturation, and assumes control of facial growth, development and adaptation. Concurrently, hypothalamus control of musculoskeletal physiology shifts from insulin-like growth factor IGF2 to IGF1, which affects bone via muscular loading (biomechanics). Three layers of temporomandibular joint fibrocartilage are resistant to heavy functional loading, but parafunctional clenching may result in degeneration that is first manifest as trabecular sclerosis of the mandibular condyle.
颞下颌关节是一种高度保守的关节，因为它通过咀嚼、交流和常规交配成功（牙颌面美观）等基本功能促进生存和繁殖。颞下颌关节是一种独特的次级关节，由软骨内颞骨和下颌二次髁状突软骨通过印度刺猬和骨形态发生蛋白信号形成，与耳朵发育密切相关。Spry1 和 Spry2 基因诱导的翼外肌和颞肌的遗传诱导为其提供了一个动态的表观遗传环境。在胎儿发育过程中，髁突骨膜的机械负荷产生了一层浅层纤维软骨，与髁突分离形成介入性颞下颌关节盘。髁突和窝的关节表面是动态修饰的骨膜，具有愈合和再生能力。这种独特的组织由浅层纤维层（滑膜表面）和下方的增殖层（形成层）组成，形成纤维软骨的缓冲层，随后形成骨。在第一颗（乳）磨牙约 16 个月前闭合之前，面部发育主要由初级遗传机制控制。在获得后功能咬合后，生物力学促进颞下颌关节成熟，并控制面部生长、发育和适应。同时，下丘脑对肌肉骨骼生理学的控制从胰岛素样生长因子 IGF2 转移到 IGF1，通过肌肉负荷（生物力学）影响骨骼。颞下颌关节纤维软骨的三层可抵抗重功能负荷，但功能紊乱性紧咬牙可能导致退化，首先表现为下颌髁突的小梁硬化。
