The Temporomandibular Joint (TMJ)
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What is the TMJ (Temporomandibular Joint)?
The small but often forgotten temporomandibular joint (TMJ) is one of the most utilised joints in the human body. Whenever you open your mouth, move it from side to side or forwards and backwards, you are using the TMJ. It therefore is a crucial joint to consider to allow everyday functions such as chewing, speaking and swallowing.
TMJ Anatomy & Structure
The TMJ is formed by the articulation between the lower jaw (mandible) and the skull (temporal bone). The mandibular condyles are two rounded joint surfaces on either side of the lower jaw bone. Each condyle sits a small concave space on either side of the temporal bone called the mandibular fossa.
As a synovial joint, the TMJ is surrounded by a joint capsule. The capsule forms a loose envelope around the joint, originating around the circumference of the mandibular fossa and inserting onto the neck of the mandible.¹ It also contains synovial fluid, acting to minimise friction between the articular surfaces and allow smooth movement.
Image 1: Articulation of the mandible and temporal bone, forming the TMJ.
Mouth Openning
Mouth opening is the most important movement of the TMJ and requires a combination of two movements: rolling and gliding.
In most people these two movements have a linear relationship and occur simultaneously in the absence of any joint restrictions.²
(Image: Shaffer et al. 2014)³
Image 2: Gliding and rolling movements of the TMJ during mouth opening
Articular disc
An articular disc made of fibrous cartilage forms a cushion between the two bones. This enables normal joint movement of the jaw without the mandibular condyles touching the mandibular fossa of the temporal bone. As the mandibular condyle glides forward, the articular disc glides with it along the surface of the temporal bone allowing for smooth joint movement.
Behind the articular disc is another important structure called the retrodiscal tissue (i.e. ‘retro’ = behind, ‘discal = relating to the disc). The retrodiscal tissue is filled with its own nerve and blood supply⁴. As it attaches to the posterior aspect of the articular disc it helps stabilise the disc, keeping it from gliding forward excessively as the mouth opens.
(Image: Shaffer et al. 2014)³
Image 3: Articular disc and retrodiscal tissue
Jaw Muscles
Appropriately referred to as the ‘muscles of mastication’, the temporalis, masseter, medial and lateral pterygoids are the main muscles which control movement of the TMJ.
The temporalis is responsible for closing and pulling the jaw backwards.
The masseter is responsible for closing and pushing the jaw forwards.
The temporalis and masseter are the strongest muscles around the TMJ and are used especially when chewing and clenching.
(Helland, 1998)¹
Image 4: Temporalis and masseter muscles
The medial pterygoids have the same actions as the masseter, helping to close and pull the jaw backwards.
The lateral pterygoids are responsible for pushing the jaw forwards and also help to open the jaw.
Additionally, when the pterygoids contract only on one side they allow the jaw to move from side-to-side.
(Helland, 1998)¹ Image 5: Lateral and medial pterygoid muscles
Jaw Ligaments
Three notable ligaments around the TMJ are the: temporomandibular ligament, sphenomandibular ligament and stylomandibular ligament. These ligaments help to provide passive stability in the TMJ and protect it from excessive movement.
In particular, temporomandibular ligament serves to strengthen the TMJ joint capsule itself laterally, or on the outside.¹
(Varish, 2019)⁵
Image 6: Ligaments of the TMJ: temporomandibular, sphenomandibular and stylomandibular.
Relationship between TMJ and the neck
It’s important to notice the close proximity between the TMJ and the upper neck. In fact, neck movements are coupled with movements at the jaw⁶:
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Neck extension as the mouth opens
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Neck flexion as the mouth closes
This has implications for treating both jaw and neck pain as TMJ and neck pain can be significantly related to each other. In many cases disorders of the TMJ can influence disorders of the neck and vice-versa. Research has shown that treating either the TMJ or neck can lead to improvements in the other area as well⁷.
Reference
¹ Helland, M. M. (1980). Anatomy and Function of the Temporomandibular Joint. Journal of Orthopaedic & Sports Physical Therapy, 1(3), 147–148. https://www.jospt.org/doi/pdfplus/10.2519/jospt.1980.1.3.145
² Merlini, L., & Palla, S. (1988). The relationship between condylar rotation and anterior translation in healthy and clicking temporomandibular joints. Schweizer Monatsschrift fur Zahnmedizin = Revue mensuelle suisse d'odonto-stomatologie = Rivista mensile svizzera di odontologia e stomatologia, 98(11), 1191–1199.
³Shaffer et al. (2014) https://www.researchgate.net/figure/Temporomandibular-joint-TMJ-arthrokinematics-during-mouth-opening-a-discotemporal_fig3_263517592
⁴Wilkinson, T. M., & Crowley, C. M. (1994). A histologic study of retrodiscal tissues of the human temporomandibular joint in the open and closed position. Journal of orofacial pain, 8(1), 7–17.
⁶Eriksson, P. O., Häggman-Henrikson, B., Nordh, E., & Zafar, H. (2000). Co-ordinated mandibular and head-neck movements during rhythmic jaw activities in man. Journal of dental research, 79(6), 1378–1384.
⁷Aloosi, S., Mohammad, S., Qaradakhy, T., & Hasa, S. (2016). Contribution of Cervical Spine in Temporomandibular Joint Disorders: A Cross-Sectional Study. JBR Journal of Interdisciplinary Medicine and Dental Science, 4(5)., 1-5