9 THE TEMPOROMANDIBULAR JOINT
Applied Anatomy
The temporomandibular joint (TMJ) is an articulation between the mandibular condyle and both the mandibular (glenoid) fossa and the articular eminence (tubercle) of the temporal bone (Figure 9-1). The paired TMJs are classified as condylar joints, because the mandible articulates with the skull by means of two distinct articular surfaces, or condyles. Unlike other synovial (diarthrodial) articulations, the articulating surfaces of the TMJ are covered by fibrocartilage in place of hyaline cartilage. An intraarticular fibrocartilaginous disk (meniscus) divides the joint into a large superior and a smaller inferior compartment, each lined with synovial membrane (see Figure 9-1). The disk consists of a thin, central portion; a thick, large, highly innervated and more vascular posterior portion (posterior band); and a smaller anterior portion (anterior band). The disk is tightly bound to the medial and lateral poles of the mandibular condyle. It provides congruent contours, acts as a shock absorber during mastication, and stabilizes the joint during mandibular movements. The stability of the TMJ depends on the osseous, conformation, muscles of mastication, capsule, ligaments, and intraarticular disk. The capsule is thin and loose and allows a wide range of movements. It is attached to the condyle and to the articular eminence, and it is reinforced on the lateral aspect by the lateral temporomandibular ligament and on the medial aspect by the sphenomandibular ligament.
MOVEMENTS
In the closed position, the mandible lies in the glenoid fossa, in contact with the posterior band of the disk (see Figure 9-1). In the resting position, the mouth is slightly open so that the teeth are not in contact. In centric occlusion occurs with maximal contact of the teeth, the position assumed by the jaw when swallowing.
TEETH
In humans, there are 20 deciduous—primary or “baby”—teeth, and 32 secondary, or permanent, teeth. Deciduous teeth are shed between the ages of 6 and 13 years. To identify or label the secondary teeth for the purposes of communication and treatment, their locations are divided into four quadrants: upper left (quadrant 1), upper right (quadrant 2), lower left (quadrant 3), and lower right (quadrant 4). When labeling or identifying deciduous teeth, the quadrants are continued so that deciduous teeth would be found in quadrants 5 through 8, with quadrant 5 being the deciduous “partner” of quadrant 1, used for secondary teeth and so on. In each quadrant, the teeth are numbered from 1 (most medial) to 8 (most distal). Therefore, a mandibular right first molar would be called tooth 4.6, or simply 46, and a first mandibular deciduous molar on the right side would be labeled tooth 8.5, or 85. Loss or restoration of teeth and malocclusion has been considered a major factor in the development of TMJ pain. Although this used to be considered a major risk factor for TMJ dysfunction, unless the occlusal changes are so great as to render the occlusion nonfunctional (e.g., no posterior occlusion at all), it is no longer considered as such (De Boever, 2000).
Temporomandibular Joint Pain and History Taking
Pain reported in the TMJ is a relatively common symptom, but it can have diverse causes. It may originate in the TMJ itself, or it may be referred from the teeth, ear, parotid gland, muscles of mastication, cervical spine, or head (Table 9-1). Important points in the history include site, duration, character, radiation, and provocative factors of TMJ pain. The physician may also inquire about any recent dental work and whether a patient grinds the teeth. Both bruxism—forced clenching and grinding of the teeth, especially during sleep—and habitual nail biting have been associated with a temporomandibular disorder syndrome, which will be discussed later. However, these are basically associations and to date have not been demonstrated to be causal. That said, these characteristics might have an impact on pain severity, timing, and responsiveness to treatment. In fact, apart from TMJ pain syndromes that arise following hyperextension-flexion injury, most of these conditions are idiopathic in nature (Romanelli, 1992; Goldberg, 1996; and Brooke, 1978).
TABLE 9-1 DIFFERENTIAL DIAGNOSIS OF TEMPOROMANDIBULAR JOINT (TMJ) PAIN
| Arthritis of the TMJ |
| Osteoarthritis (OA) |
| Rheumatoid arthritis (RA) |
| Psoriatic arthritis (PsA) |
| Ankylosing spondylitis (AS) |
| Juvenile idiopathic arthritis (JIA) |
| Trauma |
| Infection |
| Gout |
| Temporomandibular Disorder Syndrome (TMDS) |
| Internal Derangement due to Meniscal Displacement |
| Condylar Agenesis, Hypoplasia (Retrognathism), and Hyperplasia (Prognathism) |
| Neoplasms of the TMJ (rare) |
| Chondroma |
| Osteochondroma |
| Osteoma |
| Referred TMJ Pain |
| From the parotid salivary gland |
| From the paranasal sinuses |
| From the ear |
| From the teeth |
| From the nasopharynx |
| From the cervical spine |
| Other Causes of Facial Pain |
| Trigeminal neuralgia |
| Giant cell (temporal) arteritis |
| Migraine headache |
| Cerebral tumors, tetanus, Parkinsonism |
| Fibromyalgia |
| Psychosomatic TMJ pain |
Locking of the TMJs can be caused by subluxation of the joint or, more likely, may be caused by anterior displacement without reduction of the meniscus (i.e., TMJ disk). Clicking, popping, or snapping of TMJs, often bilateral, occurs when the TMJ disk is positioned anterior to its normal position. However, in contrast to a locked joint, opening movement that requires translation of the TMJs can cause popping or clicking in one or both of these joints that may be audible or at least detected by palpation. This phenomenon occurs because the joint actually snaps back over the displaced disk, leading to the reestablishment of a normal relationship between the condyle and the central zone of the disk (Westesson, 1985). Other causes of clicking and popping can include a meniscal tear, uncoordinated lateral pterygoid muscle action, and osteoarthritis (OA).
Physical Examination
INSPECTION
The TMJs are inspected for pain, swelling, redness, symmetry, clicking, crepitus, abnormal movements such as asymmetric translation, lack of movement, and hypermobility. Effusion of the TMJ manifests as a rounded bulge just anterior to the external auditory meatus. Arthritis of the TMJs, particularly rheumatoid (and not OA), can predispose to the development of an obvious anterior open bite, in which the patient cannot bring his or her anterior teeth together (e.g., to bite off a piece of thread). In children this might also result in the development of a disturbance of bone growth leading to a shortened, recessed lower jaw and excessive overjet. While excessive overjet may result from various causes, be they congenital or acquired, there are no studies revealing a conclusive relationship between factors of occlusion, such as overjet and overbite, with the development of temporomandibular dysfunction (TMD) (Gersh et al, 2004). It should also be recognized that other diseases can cause lysis or destruction of one or both TMJs, including neoplasia (benign or malignant), and these must be ruled out in the absence of a history consistent with adult or juvenile rheumatoid disease.
PALPATION
The TMJs can be located by placing the tip of the index finger just anterior to the external auditory meatus and asking the patient to open the mouth about halfway. The lateral poles of the TMJs will then become palpable by the tip of the examiner’s finger. The joint is palpated for warmth, tenderness, synovial thickening, effusion (a fluctuant mass), crepitus, or snapping or clicking with movement. With the patient’s mouth open, the TMJ can be palpated with the little finger placed in the external auditory meatus (fleshy part anteriorly). The patient is then asked to close the mouth when the examiner first feels the condyle touch the finger. With the mouth closed, the TMJs are in the resting position with a freeway space between the anterior teeth (normal range 2 to 4 mm) (Kerr, 1974). By palpating the condyle and noting its location within the mandibular fossa with the patient’s mouth closed, partially open, and wide open, the examiner can determine various degrees of dislocation.
When assessing for pain, one generally tries to maintain a consistent force of palpation. If tissues are clinically tender, it is generally recommended that the force needed to evoke a meaningful pain reaction is that which, when pressing the finger on a tabletop, the fingernail bed will blanch. If the pressure is too light, clinically tender tissues will not be identified; similarly, if too much force is applied, even normal tissues will be perceived as painful. For the purposes of standardization, it is also helpful to grade a patient’s pain reaction following palpation of the TMJs and surrounding musculature. In this case, a discontinuous but relatively reliable scale has been developed, as shown in Table 9-2.
