Aetiology, Symptoms and Clinical Classifications of Temporomandibular Disorders
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Introduction[edit | edit source]
The temporomandibular joint (TMJ) is considered one of the most complex joints in the body. It plays a significant role in dental occlusion and the neuromuscular system.
It has been classified as both a compound joint and a double joint. Compound joints typically consist of three or more bones, but the TMJ only has two bones. Instead of a third bone, an articular disc sits between the mandibular fossa and the condyle (Figure 1).
Causes of Facial Pain[edit | edit source]
Temporomandibular disorders (TMDs) are the most common non-dental cause of facial pain. Other causes of facial pain are:
- Dental and oral issues
- Maxillary sinusitis
- Salivary gland disorders
- Neuropathic pain (trigeminal nerve region), such as:
- Trigeminal post-herpetic neuralgia
- Post-traumatic trigeminal pain / trigeminal neuropathic pain / atypical odontalgia
- Burning mouth syndrome
- Trigeminal neuralgia and its variants etc
- Vascular causes
- Giant cell arteritis should be considered in individuals aged over 50 years who present with temporal pain that mimics TMD
NB: Chronic orofacial pain can be bilateral or unilateral.
The following article discusses the causes of continuous or episodic orofacial pain in detail:
- Differential diagnosis of facial pain and guidelines for management
- In particular, Figure 1 in this article describes how to distinguish between different causes of episodic and continuous pain
Temporomandibular Disorders[edit | edit source]
Laplanche defines TMD as a muscular and articular disorder. TMD encompasses various anatomical, histological and functional abnormalities, which affect the muscular and / or articular components of the TMJ and have variable clinical features.
Epidemiology[edit | edit source]
- Individuals aged 20 to 40 years report TMD more frequently
- Women are more likely to experience TMD than men (with a ratio of around 3:1)
While it is recognised that case numbers are rising, the reported prevalence of TMDs varies considerably in the literature. This variation is likely due to differences in:
- Data collection methods
- Descriptive terminology
- Analytic methods
- Individual factors
A review by Manfredini and colleagues found that:
- 45 percent of TMD patients have muscular pain
- 41 percent have disc derangement
- 34 percent have joint pain
In the general population:
- 9.7 percent of individuals had muscular pain associated with TMD
- 11.4 percent had disc displacement
- 2.6 percent had joint disorders
35 percent of individuals may have asymptomatic TMD and up to 75 percent of the adult population may be affected by TMJ pain. However, it has been estimated that only 3.6 to 7.0 percent of people with TMD will require treatment. People are most likely to seek treatment for pain (90 percent) and acoustic phenomena (65 percent).
Symptoms[edit | edit source]
The following symptoms are associated with TMD:
- Pain (the most common emerging symptom)
- Usually in the preauricular area and / or the masticatory muscles
- Limited range of mandibular movement
- Presence of TMJ sounds, such as popping, clicking, grating or crepitus
- Earache, headache, jaw ache and facial pain
- Non-painful hypertrophy of the masticatory muscles
- Abnormal occlusal wear which is associated with oral parafunction (this may be related to tooth grinding and jaw clenching)
It has also been found that 87 percent of patients have otological symptoms (i.e. symptoms related to the ear), including:
- Ear fullness
Internal Derangement of the Temporomandibular Joint[edit | edit source]
- In severe cases, range of motion may be limited by luxation of the disc / condyle, which causes locking (this may or may not be painful)
- When locking occurs, the joint is no longer able to function according to the “rules” of a synovial joint - i.e pain-free, friction-free, good range of motion
- The click associated with TMD indicates that the joint is not free of friction
Anterior disc displacement may be caused by a loss of normal arthrokinematics (i.e. joint movement pattern). In a normal joint, the following occurs during mouth opening:
- Rotation during the initial or middle range of motion
- This rotation occurs at the condyle surface, the inferior joint surface and the inferior joint surface of the disc
- To achieve functional range of motion (i.e. 35 to 40 mm) and effective mouth opening, rotation is followed by a short anterior translatory glide (between the disc’s superior joint surface and the articular eminence)
- If this movement sequence is altered and there is a large anterior translatory glide of the mandible, the connective tissue posterior to the disc tends to overstretch
NB: Connective tissue usually enables the disc to return to its original position. However, if the connective tissue remains stretched, it will gradually give way and will no longer be able to return to its normal length. This might occur when an extreme range of motion places excessive demand on the ligaments or the joint capsule.
While connective tissue is mainly non-elastic, it has the ability to “give” due to its wavy shape - this “give” resembles elasticity. The length of time required for the tissue to permanently lose its “elasticity” has not been documented. However, when elasticity is reduced in the TMJ, the disc starts to adopt an anterior position.
This position leads to constant microtrauma and, over time, the joint becomes unstable or hypermobile. Patients might experience clinical signs such as clicking or other joint sounds. Locking occurs when the disc finally adopts a position of complete anterior luxation (i.e. a “locked joint”).
When a disc moves into this position, treatment is necessary to restore the normal functional relationship between the condyle, disc, and articular eminence.
Causes of Temporomandibular Disorders[edit | edit source]
The aetiology of TMD has been debated in the research for a number of years. Navrátil and colleagues propose a multifactorial theory to explain the causes of TMD. These causes can be divided into the following groups:
- Inflammatory diseases
- Degenerative disease of the articular cartilage
- Changes in the position of the articular disc (i.e. dislocation)
- Extra-capsular area affected by extra-articular structures, along with masticatory muscles and ligaments
- Movement disorders such as hypermobility (see below)
- Changes in the cervical spine associated with cervical muscle spasm
- Accidents and / or injury
A joint might become overloaded for a number of reasons including:
- Missing teeth
- Articulatory constraints
- Inappropriately sized prosthetics
- Faults in the mouth
Chang and colleagues propose the following causes of internal derangement of the TMJ:
- Direct trauma
- Occlusal relationship
- Derangement of the TMJ extracellular matrix
- Synovial fluid
Relationship between Malocclusion, Benign Joint Hypermobility Syndrome, Condylar Position and TMJ Symptoms[edit | edit source]
- There is no “well-defined” initial position for the condyle in formal occlusion or malocclusion patterns
- There is no statistically significant relationship between BJHS, degree of condylar displacement or TMD
- There is, however, a relationship between malocclusion patterns (particularly malocclusion class II and open bite)
- Anterior crossbite may be a risk factor for TMJ symptoms
Hypermobility in Pregnant Women[edit | edit source]
Silveira and colleagues studied a potential link between systemic hypermobility and TMJ hypermobility during pregnancy. They found that while pregnant women had a high incidence of systemic hypermobility, it was not associated with mandibular hypermobility and TMD. However, most pregnant women experience postural changes (e.g. head protrusion, anterior posture) from the first trimester on. These changes can affect their centre of gravity and may increase their predisposition for TMD during pregnancy.
Classifying Temporomandibular Disorders[edit | edit source]
TMD can be classified into articular and non-articular disorders.
Articular disorders include:
- Infectious arthritis
- Prior surgery (iatrogenic)
- Gout / pseudogout (crystal arthropathies)
- Rheumatoid arthritis (RA) / juvenile RA
- Psoriatic arthritis
- Axial spondyloarthritis (also known as ankylosis spondylitis)
Articular disorders are usually classified using the Wilkes’ Staging Classification for Internal Derangement of the TMJ:
- Early stage
- Early / intermediate stage
- Intermediate stage
- Intermediate / late stage
- Late stage
The full classification is available in: Epidemiology, diagnosis, and treatment of temporomandibular disorders (see Box 1)
Non-articular disorders include:
- Myofascial pain
- Acute muscle strain
- Muscle spasm
- Chronic pain conditions
- Myotonic dystrophy
Diagnostic Classifications[edit | edit source]
In 1992, the research diagnostic criteria for temporomandibular disorders (RDC/TMD) was developed. This was subsequently updated in 2010. While this criteria has a number of benefits, Shaffer and colleagues identify the following limitations:
- Many patients have a complex clinical presentation and do not fit into just one category
- The cervical spine and pain science are not considered
Thus, it is essential to take a full history and conduct a thorough assessment in order to diagnose TMD. Please click here for Shaffer and colleagues' summary of primary recurrent TMD classification and clinical patterns.
Treatments for Temporomandibular Disorders[edit | edit source]
Effective treatment of TMD requires comprehensive physiotherapy care, based on physical and manual therapy, as well as education. Treatment of internal derangement and osteoarthritis of the TMJ can be fitted into three broad categories:
- Minimally invasive
Liu and Steinkeler suggest that a multidisciplinary approach is necessary for effective treatment. Moreover, treatment should only be progressed if more conservative modalities fail - i.e. interventions should focus on the least invasive / most reversible options first.
The ultimate goals of treatment are to:
- Reduce joint pain
- Improve function and mouth opening
- Prevent additional joint damage
- Enhance quality of life and reduce morbidities
References[edit | edit source]
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