The Temporomandibular Joint: A Critical Review of Life‐Support Functions, Development, Articular Surfaces, Biomechanics and Degeneration

Abstract

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.

Does the Stomatognathic System Adapt to Changes in Occlusion? Best Evidence Consensus Statement

“…1,2 This fibrocartilage layering can increase in thickness to dissipate moderate overloading 14 Overall, it can be stated that changes in occlusion are moderated by the plastic articular and supporting tissues of the TMJ. 15 Another factor is the mandibular condyle that is a highly adaptable, regenerative structure despite traumatic and degenerative challenges. 2 Even degenerated condyles can increase in length when exposed to distraction.…”

“…In spite of these adaptive mechanisms, the TMJs are susceptible to degeneration when exposed to sustained clenching 2 with overload initially manifested as sclerosis of trabecular bone in the condyle. 15…”

“…In addition, the joint has a unique load‐bearing morphology with three subarticular layers of fibrocartilage that absorb and dissipate both peak (impact) and sustained loads 1,2 . This fibrocartilage layering can increase in thickness to dissipate moderate overloading 14 Overall, it can be stated that changes in occlusion are moderated by the plastic articular and supporting tissues of the TMJ 15 …”

“…Also, bone supporting the condyle and fossa can strengthen by increasing in density and thickness, but the process is self‐limiting. In spite of these adaptive mechanisms, the TMJs are susceptible to degeneration when exposed to sustained clenching 2 with overload initially manifested as sclerosis of trabecular bone in the condyle 15 …”

Distúrbios intracapsulares da articulação temporomandibular: da semiologia à terapêutica: uma revisão de literatura

“…As superfícies articulares da ATM consistem de um periósteo modificado que produz fibrocartilagem quando exposto a grande intensidade de cargas (Roberts & Goodacre, 2020). Essas estruturas articulares são compostas pelo osso temporal, a fossa mandibular, o tubérculo articular e o côndilo mandibular (Bavaresco et al, 2020).…”