Orofacial Pain

Epidemiology of Orofacial Pain

Chronic pain affects approximately 100 million adults in the United States, with an economic burden of over 600 billion. OFP is one of the most common pain conditions; its prevalence is estimated to be between 17%–26% in the general population, and 22% of the population suffered at least one orofacial pain in the length of six months. ^, Similar to other pain conditions, OFP is more prevalent in females than males. ^, After toothache, temporomandibular disorder (TMD) is the most common orofacial pain. In a large prospective multi-site study, the incidence of TMD was 3.9% annually, and females had only slightly higher incidence than males. The onset and chronification of TMD are associated with other comorbid pain conditions like chronic wide spread pain, lower back pain, and headaches ( Fig. 40.1 ). The prevalence of TMD depends on the illness in question, the diagnostic criteria used to identify the disease, and the study population. For example, in a review study that used the Research Diagnostic Criteria for Temporomandibular Disorder (RDC/TMD) as the diagnostic criteria for TMD, the general population prevalence of temporomandibular joint (TMJ) pain was 2.6%, muscle disorders had a prevalence of 9.7%, in comparison, the prevalence of these conditions in the patient population was 45.3% and 30.1%, respectively. ^, Unlike TMD that has a recognized and validated diagnostic criteria in the RDC/TMD and Diagnostic Criteria for Temporomandibular Disorder (DC/TMD), ^, the prevalence and incidence of several OFP conditions, for example, neurovascular orofacial pain, are unknown because until recently they were not defined in a comprehensive, internationally acceptable comprehensive classification. ^,

Orofacial Pain Classification

Several classifications have been developed over the years to better categorize the types of OFP. These classifications include the International Classification of Headache Disorders (ICHD-3) and the International Classification of Orofacial Pain (ICOP). Despite the fact these two classifications include TMD, a more specific classification for TMD was developed to assist researchers and clinicians, the first one was developed in 1992, RDC/TMD, and in 2014, DC/TMD. A summary of orofacial pain classifications is shown in Figure 40.2 .

Etiology

In 1934, Costen, an otolaryngologist, evaluated 13 patients who presented with pain in or near the ear, tinnitus, dizziness, a sensation of ear fullness, and difficulty swallowing. He observed that these patients had many missing teeth and, as a result, their mandibles were over closed. The patients seemed to improve when their missing teeth were replaced, and the proper vertical dimension of the occlusion was restored. The malocclusion and improper jaw position were perceived to be the cause both of “disturbed function of the TMJ” and the associated facial pain. The emphasis of treatment was on altering the affected patient’s occlusion.

More recently, advances in the understanding of joint biomechanics, neuromuscular physiology, autoimmune, musculoskeletal disorders, and pain mechanisms have resulted in changing concepts of the etiology of TMDs. These disorders are now considered multifactorial in etiology, with biologic, behavioral, environmental, social, emotional, and cognitive factors alone or in combination contributing to the development of signs and symptoms of TMDs ( Fig. 40.1 ). ^{, ,} ,

Various forms of trauma to the TMJ structures (ligaments, articular cartilage, articular disc, bone) can lead to intraarticular biochemical alterations that have been demonstrated to produce oxidative stress and the generation of free-radicals. Subsequent inflammatory changes in synovial fluid with the production of a variety of pro-inflammatory cytokines can then lead to alteration in the functioning of normal tissues and degenerative disease in the TMJ.

Genetic marker studies involving catecholamine metabolism and adrenergic receptors suggest that certain gene polymorphisms (e.g. in the catechol-O-methyl transferase gene) might be associated with changes seen in pain responsiveness and pain processing in patients with chronic TMDs.

Differences in pain modulation have been reported between women and men with TMDs; women have been observed to demonstrate decreased thresholds to noxious stimuli and more hyperalgesia. In addition, in women with TMDs, some studies suggest that the affective component of pain may be enhanced during the low-estrogen phase of the menstrual cycle.

Functional brain imaging studies demonstrating changes in cortical circuitry support the concept that TMDs are very similar to other chronic pain disorders and may be related to abnormal pain processing in the trigeminal system. In particular, muscle pain disorders appear to have little, if any, abnormality of the muscles or peripheral tissues and may represent a central sensitization pain producing process. Because of the central sensitization, TMD was classified among other chronic painful disorders as part of the chronic overlapping pain conditions.

Lastly, numerous bio-behavioral studies support a connection between chronic TMDs and comorbid psychopathology (anxiety and depression disorders, posttraumatic stress disorder, and childhood physical, sexual, and psychological abuse). TMDs fall in the 11th major category of the International Headache Society’s (ICHD-3) classification. However, most researchers use the RDC/TMD or DC TMD for diagnosis purposes. ^,

Temporomandibular Joint Disorders (TMJD)

The TMJ is a ginglymoarthrodial synovial joint capable of rotational and translational movements. A bilateral joint (a single bone—the jaw—with a right and left joint) cannot function separately. What affects one joint also influences the other. It is formed by the articulation of the mandibular condyle with the glenoid fossa/articular eminence of the temporal bone.

The articular surfaces of the condyle and glenoid fossa/articular eminence are covered with fibrocartilage rather than hyaline cartilage, as in other synovial joints except for the clavicle. Fibrocartilage can resist heavy loads and has unique healing and adaptive properties.

An articular disc, made of fibrocartilage, is interposed between the condyle and the glenoid fossa. The disc has a biconcave shape; thicker in its anterior (2 mm) and posterior (3 mm) portions and thinner in the middle. It acts as a “cushion” to absorb stress, distribute loads, and facilitate jaw movements.

The disc divides each TMJ into two articular joint spaces: upper and lower joint space. The rotational movement happens mainly in the inferior joint space, between the condyle and the inferior surface of the disc. The translational movement in the upper joint space, between the upper surface of the disc and the glenoid fossa/articular eminence. ^,

The most common TMJ disorders are:

• Joint pain (arthralgia, arthritis)

• Joint disorders (internal derangement or disc-condyle disorders)

• Joint diseases (degenerative joint disease [DJD]: osteoarthrosis and osteoarthritis)

Joint Pain

Joint pain is characterized by localized pain exacerbated by function, parafunction, and provocation.

Arthralgia

According to the DC/TMD, arthralgia is defined as pain of joint origin affected by jaw movement, function, or parafunction, and the replication of the pain occurs during provocation testing of the TMJ.

History has to be positive for both:

• 1

  pain in the jaw, temple, ear, or in front of the ear AND

• 2

  pain modified with jaw movement, function, or parafunction

The clinical examination has to be positive for both:

• 1

  confirmation of pain location in the area of the TMJ(s)

• 2

  report of familiar pain in the TMJ with at least one provocation test:

  • palpation of the lateral pole (0.5 kg pressure) or around the lateral pole (1 kg pressure) OR

  • maximum unassisted or assisted opening, right or left lateral movements, or protrusive movements

Arthritis

Defined as pain of joint origin with clinical characteristics of inflammation or infection: edema, erythema, and/or increased temperature. It may result from trauma. In case of severe unilateral intraarticular swelling or effusion, it could be associated with occlusal changes such as ipsilateral posterior open bite. It is a localized condition, and there should not be a history of systemic inflammatory disease.

History has to be positive for both:

• arthralgia AND

  • 1

    swelling, redness, and/or increased temperature in front of the ear OR

  • 2

    dental occlusal changes (posterior open bite) resulting from intraarticular inflammatory exudate

Clinical examination has to be positive for both:

• arthralgia AND

  • presence of edema, erythema, and/or increased temperature over the joint OR

  • reduction in dental occlusal contacts noted between two consecutive measurements

The patient has to be negative for rheumatologic disease, including those in systemic arthritis, and the pain is not better accounted for by another pain diagnosis.

Joint Disorders

Internal derangement (or disc- condyle complex disorders) is defined as an “abnormal relationship of the articular disc to the mandibular condyle, glenoid fossa and articular eminence, interfering with the smooth movements of the joint.” It is a localized mechanical disorder within the joint. The term is often used as a synonym for disc displacement.

The clinical manifestations of internal derangements are clicking joint, intermittent locking, limited mouth opening (closed lock), and open lock.

The DC/TMD includes several forms of internal derangement:

• Disc displacement with reduction

• Disc displacement with reduction with intermittent locking

• Disc displacement without reduction with limited opening

• Disc displacement without reduction without limited opening

Disc Displacement With Reduction

Disc displacements are usually anterior or anteromedial, although posterior and lateral displacements have been described in the literature. This may be partly related to the thinnest discal attachments being on the lateral pole of the condyle and the medial direction of pull by the lateral pterygoid and inward direction of condylar movement during mouth opening. Therefore disc displacement clinically suggests torn or stretched collateral discal ligaments that bind the disc to the condyle.

In disc displacement with reduction, clicking sounds on mouth opening and closing may be present . The term reduction is used to describe the misaligned disc temporarily coming back (or slipping back) to its proper interposition between the condyle and articular eminence/fossa during full opening ( Fig. 40.3 ). On closing the mouth, the disc again displaces as the teeth come closer together. This repetitive, ongoing displacement on opening and closing produces a reciprocal noise (clicks) and is hence termed reciprocal clicking ( Fig. 40.4 ). This stage may actually represent a physiologic accommodative stage without the need for therapy other than discussion regarding its anatomic significance.

History has to be positive for at least one of:

• 1

  in the last 30 days, any TMJ noise present with jaw movement or function OR

• 2

  patient report of any noise present during the exam

The clinical exam has to be positive for at least one:

• 1

  clicking, popping, and/or snapping noise during both opening and closing movements, detected with palpation during at least one of three repetitions of jaw opening and closing movements OR

• 2

  clicking, popping, and/or snapping noise detected with palpation during at least one of three repetitions of opening or closing movements AND

• 3

  clicking, popping, and/or snapping noise detected with palpation during at least one of three repetitions of right or left lateral or protrusive movements.

Imaging is the reference standard, and when this diagnosis needs to be confirmed with TMJ magnetic resonance imaging (MRI):

• 1

  in the maximum intercuspal position, the posterior band of the disc is located anterior to the 11:30 position, and the intermediate zone of the disc is anterior to the condylar head AND

• 2

  on full opening, the intermediate zone of the disc is located between the condylar head and the articular eminence.

Disc Displacement With Reduction With Intermittent Locking

In this intracapsular disorder, the disc does not reduce during mouth opening, causing intermittent, limited mandibular opening. Usually, the patient can unlock the joint.

History has to be positive for:

• 1

  in the last 30 days, any TMJ noise present with jaw movement or function OR

• 2

  patient report of any noise present during the exam AND

• 3

  in the last 30 days, jaw locks with limited mouth opening, even for a moment, and then unlocks.

The clinical exam has to be positive for at least one of:

• 1

  clicking, popping, and/or snapping noise detected during both opening and closing movements, detected with palpation during at least one of three repetitions of jaw opening and closing movements OR

• 2

  clicking, popping, and/or snapping noise detected with palpation during at least one of three repetitions of right or left lateral or protrusive movements

When this diagnosis needs to be confirmed, the imaging analysis criteria are the same as for disc displacement with a reduction.

Disc Displacement Without Reduction With Limited Opening

Disc displacement without reduction is sometimes called a “closed lock.” This suggests that the disc has been permanently displaced, and the disc’s shape has been permanently changed such that it physically prevents the condyle of the mandible from translating to a fully open position ( Fig. 40.5 ). There is a limitation of jaw opening to 22 to 25 mm with pain and a deflection of the mandible to the side of the lock. There is a reduction in the chewing capability because of pain, inflammation at the affected joint, and possible changes in the normal occlusion or “bite.” An MRI of the TMJ is the “gold standard” to assess soft tissue details of the articular disc and its displacement, while hard tissue CBCT scans are generally done to assess chronic osteoarthritic or bony changes. ^, Considering its positive natural course, treatment should be reserved for painful symptomatic cases, and it should always be conservative (see the section on treatment). The goal of the treatment is the management of pain and improvement in mouth opening. ^,

History has to be positive for both:

• 1

  jaw locked so that the mouth would not open all the way AND

• 2

  limitation in jaw opening severe enough to limit jaw opening and interfere with the ability to eat

The clinical exam has to be positive for:

• Maximum assisted opening (passive stretch) movement including vertical incisal overlap <40 mm

When this diagnosis needs to be confirmed, the TMJ MRI criteria are positive for both:

• 1

  in the maximum intercuspal position, the posterior band of the disc is located anterior to the 11.30 position, and the intermediate zone of the disc is anterior to the condylar head AND

• 2

  on full opening, the intermediate zone of the disc is located anterior to the condylar head

Disc Displacement Without Reduction Without Limited Opening

The disc is still permanently displaced in this condition, but the clinical presentation is different: pain is often absent, and there is a restoration of function with normal maximum mouth opening.

History has to be positive for both in the past:

• 1

  jaw locked so that the mouth would not open all the way AND

• 2

  limitation in jaw opening severe enough to limit jaw opening and interfere with the ability to eat

The clinical exam has to be positive for:

• Maximum assisted opening (passive stretch) movement including vertical incisal overlap >40 mm

When this diagnosis needs to be confirmed, TMJ MRI criteria are the same as for disc displacement without reduction with limited opening.

Degenerative Joint Disease

In the DC/TMD classification, DJD is defined as a degenerative disorder involving the joint characterized by deterioration of articular tissue with concomitant osseous changes in the condyle and/or articular eminence. DJD can result in dental malocclusions, including an anterior open bite, especially when present bilaterally or contralateral posterior open bite when present unilaterally.

DJD can be subclassified in:

• Osteoarthrosis (DJD without arthralgia)

• Osteoarthritis (DJD with arthralgia)

Osteoarthrosis

History has to be positive for at least one of:

• in the last 30 days, any TMJ noise present with jaw movement or function OR

• patient report of any noise present during the exam

The clinical exam has to be positive for:

• crepitus detected with palpation during maximum unassisted opening, maximum assisted opening, lateral or protrusive movements

If imaging is needed to confirm the diagnosis, TMJ CT/CBCT criteria are positive at least for one of:

• subchondral cyst, erosion, generalized sclerosis, osteophyte.

Osteoarthritis

History has to be positive for both:

• in the last 30 days, any TMJ noise present with jaw movement or function OR

• patient report of any noise present during the exam AND

• arthralgia

Clinical examination has to be positive for both:

• crepitus detected with palpation during maximum unassisted opening, maximum assisted opening, right or left lateral movements or protrusive movements AND

• arthralgia

Imaging: same TMJ CT/CBCT criteria as for osteoarthrosis.