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Temporomandibular Joint (TMJ) Disorders

Temporomandibular disorders (TMD) is a general term for ailments and pains located in the temporomandibular joints, masticatory muscles, and facial area. TMD conditions are very common, with an adult prevalence rate of approximately 30% and about 11% in children/adolescents. For instance, in the United States, treatment costs have been around $4 billion annually in recent years, not including imaging expenses. Currently, it is believed that the prevalence of TMD conditions is increasing, partly due to the coronavirus pandemic. The rise in prevalence may also be influenced by better recognition of this condition. In 2014, specific diagnostic criteria for TMD were established, known as "The diagnostic criteria for TMD (DC/TMD)." Disorders of the temporomandibular system are largely divided into two groups: those originating from the joint and those from the muscles, but often alongside TMD conditions, there is also neck pain and headaches, which must be considered in patient examination and treatment. (2,3)

Jaw pain — Temporomandibular joint (Henry Gray: Gray's Anatomy (20th edition))

Causes

Currently, we know that the cause of TMD conditions is multifactorial. This means that there are many factors associated with the pain, but the relationships between the conditions and risk factors are unclear. So, what causes what, and what results from what? Factors such as the following have been linked to TMD conditions:

Muscle tension – however, it's not clear what causes pain in muscle-related issues. The ischemic pain model has been suggested, while in chronic cases, central sensitization may occur.
Bruxism (teeth grinding) – there is uncertainty about the significance of grinding in relation to TMD conditions in the scientific literature, as some bruxism sufferers have TMD conditions while others do not. The same uncertainty applies to the benefits of using mouthguards in pain management, although some patients experience pain relief from using mouthguards. (4,5,6)
Continuous use of the jaw, such as chewing gum
Repetitive (physical) trauma
Psychological and emotional stress – individuals with TMD conditions experience more depression than healthy controls, although the relationship with anxiety is less clear. However, research results vary widely, and more research is needed. (7)
There doesn't appear to be much connection between bite and TMD conditions; however, this doesn't mean that bite has no significance at the individual level. (8,9)
Age – TMD conditions are most common among 20-40-year-olds, with women experiencing the condition more than men. (10)

The most common TMD patologies

As mentioned above, TMD conditions can be broadly divided into two groups: muscle and joint-related causes. However, it's also possible for the condition to result from a combination of both. Interestingly, even though some individuals may have observable structural changes, such as in the temporomandibular joint, they may not necessarily experience any pain. Tissue damage, therefore, does not always equate to pain. Below are common diagnoses according to the DC/TMD criteria, which in practice are either muscle- or joint-related:

Myalgia – a finer term for muscle pain, characterized by familiar pain in the masseter and/or temporalis muscle area when opening the mouth or palpating the muscle mass.
Myofascial pain – an even finer term for muscle and/or fascia-related pain, which may also involve radiation pain in the muscle area. Radiation pain may, in some cases, be felt over a wider area than just the tender/sore muscle.
Arthralgia – joint-related pain, provoked by palpating the temporomandibular joint and/or moving the mouth.
TMD-related headache – headaches felt in the temples, usually bilaterally, provoked by palpating the masticatory muscles, such as the temporalis muscle, or moving the mouth.
Disc displacement with reduction (DDWR) – the disc has shifted (usually) to the front of the temporomandibular joint. When the mouth is opened, the disc returns to its correct position, or reduces. This often results in a clicking sound in the joint, which may or may not produce pain. A very common diagnosis.
Disc displacement with occasional temporomandibular joint locking.
Disc displacement without reduction – a situation where the disc no longer returns to its correct position during mouth opening, which can lead to problems with opening and closing the mouth.
Temporomandibular joint osteoarthritis – osteoarthritis in the joint, characterized by pain and crepitus, or a grinding noise, when the joint is moved.
Subluxation – partial dislocation of the temporomandibular joint.
Additionally, tooth pain – patients may initially experience toothache or pain, often leading them to seek dental care. However, in cases of TMD, no issues with the teeth are usually found.

Management

In the treatment of TMD conditions, the goal is to alleviate pain and/or improve the function of the temporomandibular joint. If the condition has persisted for a long time, such as for years, the prognosis of treatment is often longer, whereas in acute cases, pain relief often occurs quite quickly. Treatment usually begins conservatively (non-surgical). Conservative treatment includes manual therapy (massage, acupuncture, etc.) and therapeutic exercises aimed at strengthening the muscles in the jaw and neck area. Medication is also tried in some patients, and for example, botulinum toxin injections provide significant relief for some symptoms. Night guards may also help some individuals. If conservative treatment fails to produce results for some reason, various surgical procedures remain the last resort.

Overall, in the light of science, it is still unclear which treatment modalities are most effective in the treatment of TMD conditions, but a positive aspect is that many individuals nevertheless find relief from treatments, and for the majority, the symptoms also disappear over time on their own. In the case of TMD conditions (and all other conditions as well), treatments should always be tailored to each individual. (11,12)