Aetiology, Symptoms and Clinical Classifications of Temporomandibular Disorders

Introduction

Figure 1. Temporomandibular joint.

The temporomandibular joint (TMJ) is considered one of the most complex joints in the human body. It plays an important role in dental occlusion and the neuromuscular system. [1]

It is classified as compound joint and double joint. Compound joints are usually made up of three or more bones, but TMJs have only two. The articular disc is located between the mandibular fossa and the condyle, not the third bone (Fig. 1). [1]

The anatomical biomechanics and physiology of the TMJ are discussed in detail here and here.

Causes of Facial Pain

Temporomandibular disorders (TMD) are the most common non-dental cause of facial pain. Other causes of facial pain are:[2]

• Dental and oral issues
• Maxillary sinusitis
• Salivary gland disorders
• Neuropathic pain (trigeminal area), such as:
  • Trigeminal post-herpetic neuralgia
  • Post-traumatic trigeminal neuralgia/trigeminal neuropathic pain/atypical toothache
  • Burning mouth syndrome
  • Trigeminal neuralgia and its variants
• Vascular causes
  • Giant cell arteritis should be considered in individuals over 50 with TMD-like temporal pain

Note: Chronic orofacial pain can be bilateral or unilateral. [2]

The following articles discuss the causes of persistent or episodic orofacial pain in detail:

• Differential diagnosis and treatment guidelines for facial pain
• In particular, Figure 1 in this article describes how to differentiate between the different causes of episodic and persistent pain

Temporomandibular Disorders

Laplanche defined TMD as a disorder of muscles and joints. [3] TMD includes a variety of anatomic, histological and functional abnormalities that affect the muscular and/or joint components of the TMJ and have distinct clinical features. [4][5]

[6]

Epidemiology

The number of patients presenting to physiotherapy departments for temporomandibular joint pain is increasing. [7] Research shows that about half of all people have at least one sign of TMD. [8]

• People aged 20 to 40 report TMD more frequently[1]
• Women are more likely than men to suffer from TMD (approximately 3:1 ratio)[7]

While it is recognized that case numbers are rising, the prevalence of TMD reported in the literature varies widely. This variation may be due to differences in:[1]

• Data collection methods
• Descriptive terminology
• Analytic methods
• Individual factors  

A review by Manfredini and colleagues [9] found that:

• 45% of TMD patients have muscle pain
• 41 percent have disc derangement
• 34 percent have joint pain

In the general population:[9]

• 9.7% had TMD-related muscle pain
• 11.4 percent had disc displacement
• 2.6 percent had joint disorders

Asymptomatic TMD may occur in 35% of individuals[1], and as many as 75% of adults may be affected by TMJ pain. [7] However, it is estimated that only 3.6% to 7.0% of patients with TMD require treatment. [1] People are most likely to seek treatment for pain (90%) and acoustic phenomena (65%). [7]

Symptoms

The following symptoms are associated with TMD:[1]

• Pain (the most common emerging symptom)
  • Usually in the preauricular area and/or muscles of mastication
• Limited range of mandibular movement
• Presence of TMJ sounds, such as clicking or crepitus
• Earache Headache Jawache and Facial Pain
• painless hypertrophy of masticatory muscles
• Abnormal occlusal wear associated with abnormal function of the mouth (this may be related to bruxism and occlusion)

Otologic symptoms (i.e., symptoms related to the ear) were also found in 87% of patients, including:[10]

• Tinnitus
• Deafness
• Dizziness
• Imbalance
• Ear fullness

[11]

Internal disorders of the temporomandibular joint

One of the most common intracapsular disorders associated with the TMJ occurs when the disc is anterior to the joint (i.e. anterior subluxation/dislocation):[12][13]

• In severe cases, range of motion may be limited by disc/condylar dislocation, 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 synovial joints – i.e. pain-free, friction-free, good range of motion
  • Clicking noises associated with TMD indicate that joints are not free of friction [12]

Disc advancement may be caused by loss of normal joint kinematics (ie, joint movement pattern). In a normal joint, the following occurs when the mouth is opened:[12]

• Rotate in initial or intermediate range of motion
  • This rotation occurs on the condylar surface, the inferior articular surface, and the inferior articular surface of the intervertebral disc
• To achieve a functional range of motion (i.e., 35 to 40 mm) and efficient mouth opening rotation, followed by a brief anterior translational glide (between the superior articular surface of the disc and the facets)
  • If this sequence of motion is altered and there is a large anterior translational slip of the mandible, the connective tissue behind the disc is overstretched

NOTE: The connective tissue usually allows the disc to return to its original position. However, if the connective tissue is kept stretched, it will gradually give way and will no longer be able to regain its normal length. When extreme range of motion is Ligaments or joint capsules. [4]

Although connective tissue is primarily inelastic, due to its wavy shape it has the ability to “give” – this “give” is akin to elasticity. The length of time it takes for an organization to permanently lose its “resilience” has not been documented. However, when elastic Reducing in the TMJ, the disc begins to adopt an anterior position. [4]

This position causes ongoing microtrauma, and over time, the joint can become unstable or hypermobility. Patients may experience clinical symptoms such as clicking or other joint sounds. When the disc eventually adopts a fully anteriorly dislocated position (i.e., a “locked” United”). [4]

When the disc moves into this position, treatment is necessary to restore the normal functional relationship between the condyle and articular herniation. [12]

[14]

Causes of Temporomandibular Disorders

The etiology of TMD has been debated in research for many years. [8] Navrátil and colleagues [7] proposed a multifactorial theory to explain the cause of TMD. These causes can be divided into the following groups:[4][7]

• Inflammatory diseases
• Articular Cartilage Degenerative Disease
• Changes in the position of the articular disc (ie, dislocation)
• Extracapsular areas affected by extra-articular structures and masticatory muscles and ligaments
• Movement disorders, such as hyperactivity (see below)
• Changes in the Cervical Spine Associated with Cervical Muscle Spasm
• Accidents and / or injury

Joints can become overloaded for a number of reasons, including:[4]

• Missing teeth
• Articulatory constraints
• Inappropriately sized prosthetics
• Faults in the mouth

Chang and colleagues propose the following reasons for the disturbance within the TMJ:[1]

• Direct trauma
• Microtrauma
• Occlusal relationship
• Disorders of TMJ extracellular matrix
• Synovial fluid

Relationship between condyle position and temporomandibular joint symptoms in malocclusion benign hypermobility syndrome

Barrera-Mora [15] examined the association between TMD malocclusion benign joint hypermobility syndrome (BJHS) and initial condylar position. They found:[15][16]

• In formal occlusion or malocclusion patterns, the condyles do not have a “definite” initial position
• No statistically significant relationship between degree of BJHS condylar displacement or TMD
• However, there is a relationship between malocclusion patterns (specifically Class II malocclusion and open bite)
• Crossbite may be a risk factor for TMJ symptoms

Hypermobility in Pregnant Women

Silveira and colleagues [17] investigated the potential link between systemic hyperactivity and TMJ hyperactivity during pregnancy. They found that while there was a high incidence of general hypermobility in pregnant women, it was not associated with mandibular hypermobility and TMD. But most pregnant women Go through postural changes (such as forward head posture) from the first trimester. These changes affect their center of gravity and may increase their propensity to develop TMD during pregnancy. [17]

[18]

Classifying Temporomandibular Disorders

TMD can be divided into joint disease and non-joint disease [19].

Articular disorders include:

• Osteoarthritis
• Trauma
• Infectious arthritis
• Prior surgery (iatrogenic)
• Gout/pseudogout (crystal arthropathy)
• Rheumatoid Arthritis (RA) / Juvenile RA
• Psoriatic arthritis
• Axial spondyloarthritis (also known as ankylosing spondylitis)

Joint disorders are usually classified using the Wilkes TMJ Internal Disorder Classification: [19]

• Early stage
• Early / intermediate stage
• Intermediate stage
• Intermediate / late stage
• Late stage

For a complete breakdown see: Epidemiological Diagnosis and Treatment of Temporomandibular Joint Disorders (see Box 1)

Non-articular disorders include:[19]

• Myofascial pain
• Acute muscle strain
• Muscle spasm
• Fibromyalgia
• Chronic pain conditions
• Myotonic dystrophy

Diagnostic Classifications

Research diagnostic criteria for temporomandibular joint disorders (RDC/TMD) were developed in 1992. It was subsequently updated in 2010. [20] While this criterion has many benefits, Shaffer and colleagues [20] noted the following limitations:

• Many patients have complex clinical presentations that cannot be grouped into one category
• Cervical spine and painology not considered

Therefore, in order to diagnose TMD, a complete medical history and thorough evaluation are essential. [20] Please click here to view the summary of primary recurrent TMD classification and clinical patterns by Shaffer and colleagues [20].

Treatment of Temporomandibular Joint Disorders

Effective treatment of TMD requires comprehensive physical therapy care based on physical and manual therapy and education. [7] Treatment of disorders within the TMJ and osteoarthritis can be divided into three broad categories:[19]

1. Non-invasive
2. Minimally invasive
3. Invasive

Liu and Steinkeler [19] argued that a multidisciplinary approach is necessary for effective treatment. Furthermore, treatment should only be undertaken if more conservative modalities fail – i.e. intervention should focus on the least invasive/most reversible options first.

The ultimate goals of treatment are to:[19]

• Reduce joint pain
• Improve function and mouth opening
• Prevent additional joint damage
• Improve quality of life and reduce morbidity