Anatomy of the Temperomandibular Joint

Original Editor - Jess Bell based on the course by Victoria Reboredo
Top Contributors - Jess Bell, Kim Jackson, Tarina van der Stockt, Rucha Gadgil, Lucinda hampton and Olajumoke Ogunleye
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Introduction[edit | edit source]

The temporomandibular joint (TMJ) is a bi-arthrodial, synovial joint that is made up of the articulating surface of the temporal bone and the head of the mandible. The whole joint is enclosed in a fibrous capsule.[1] The TMJ is also defined as a ginglymoarthrodial joint (i.e. both a hinge and a gliding joint[2]). It allows a rotational movement in the sagittal plane and a translation movement on its own axis.[3][4]

Unique Features[edit | edit source]

The TMJ is unique from other synovial joints due for a number of reasons.[3][5]

Intra-Articular disc[edit | edit source]

This disc divides the joint into two compartments (i.e. superior and inferior), which allows different actions to occur simultaneously in different parts of the joint in a coordinated manner.[5]

Bilaterality[edit | edit source]

The mandible bone articulates on both sides of the skull - from a mechanical point of view, any movement on one side will always affect the other side.[5]

Fibrous Cartilage[edit | edit source]

While hyaline cartilage typically covers the articular surfaces in synovial joints, the main articular surfaces of the TMJ (i.e. the mandibular condyle and the temporal bone) are covered by fibrous cartilage.[4] Fibrocartilage contains type I and II collagens whereas articular hyaline cartilage only contains type II collagen. Fibrocartilage is more resistant to sheer forces, so it is better able to absorb load and compressive forces.[3][4] It is, however, also more sensitive to friction, which is an important factor when considering degenerative pathology of the TMJ.[3]

Occlusion[edit | edit source]

Occlusion refers to the relationship between the upper and lower teeth when the jaw closes.[6] The TMJ is the only human joint that has a rigid end point (caused by the teeth coming into contact). Occlusion via the teeth maintains the vertical dimension in a sagittal plane and ensures that pressure is distributed along the whole joint.[3]

The role of occlusion in TMJ is controversial.[7] While differences in occlusion are not necessarily associated with TMD, the loss of height and separation in the mandibular bone and the jaw at the end of the closing movement, due to the loss of teeth, can cause a change in the intra-articular pressure in the joint and lead to earlier degeneration of the joint.[3]

Intra-Articular Disc[edit | edit source]

The intra-articular disc is made of fibrocartilage. Its extracellular matrix is largely made up of collagen I and elastin. Collagen I helps to resist tensile forces and elastin helps the disc to maintain its shape after deformation.[8]

It is located between the mandible condyle and the temporal fossa.[1] It is not vascularised and has little innervation.[3]

Functions of the intra-articular disc include: (Beek at al, 2001) and FERRIERA.

  • Creating articular congruence
  • Absorbing and distributing load over larger areas in order to prevent damage to the articular surfaces

The disc divides the TMJ fossa into two compartments, thus creating two new articular surfaces: WEB and COBO

  1. Upper or temporodisc chamber
  2. Lower or condylar disc chamber

These surfaces have the independence to move between each other in an isolated way or in an synchronised way (Tanaka & Koolstra, 2008). Essentially, the disc acts as a largely passive, but movable articular surface which can accommodate translational movements of the condyle. TANAKA

When increased load is applied to the TMJ (i.e. during mastication), the fibrocartilage is able to modulate its water content and ensure the load is shared. WEB

Unlike the disc, the retrodiscal area is highly vascularised and richly innervated. PALACIOS In cases of articular dysfunction, this is a key area that can cause symptoms.

  1. ↑ 1.0 1.1 Maini K, Dua A. Temporomandibular Joint Syndrome. [Updated 2021 Apr 25]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK551612/
  2. ↑ Bodnar SE, Zdilla MJ. The relationship of the articular eminence with the mandibular fossa: implications for temporomandibular joint mechanics. Experimental Biology 2018 Meeting Abstracts. 2018;32(S1):639.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 Reboredo V. Anatomy of the Temporomandibular Joint Course. Physioplus, 2021.
  4. ↑ 4.0 4.1 4.2 Wadhwa S, Kapila S. TMJ disorders: future innovations in diagnostics and therapeutics. J Dent Educ. 2008;72(8):930-47.
  5. ↑ 5.0 5.1 5.2 Tanaka E, Koolstra JH. Biomechanics of the temporomandibular joint. J Dent Res. 2008;87(11):989-91.
  6. ↑ Pai SA, Poojari SR, Ramachandra K, Patel RKV, Jyothi M. Temporomandibular joint - an anatomical view. Journal of Advanced Clinical & Research Insights. 2019;6:1-5.
  7. ↑ Al-Ani Z. Occlusion and temporomandibular disorders: a long-standing controversy in dentistry. Prim Dent J. 2020;9(1):43-8.
  8. ↑ Runci Anastasi M, Cascone P, Anastasi GP, Santoro G, Nicita F, Picciolo G et al. Articular disc of a human temporomandibular joint: evaluation through light microscopy, immunofluorescence and scanning electron microscopy. J Funct Morphol Kinesiol. 2021;6(1):22.
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