The temporomandibular joints (TMJs) are two joints between the mobile mandible and the fixed temporal bone. Each joint contains two joint spaces which are separated by a fibrocartilaginous articular disk.
The TMJ is a compound joint. It can also be considered as ginglymodiarthroidal joint (capability of both hinge type and sliding/gliding movement). The use of the term ‘compound joint’ is justified based on the fact that the TMJ is composed of three bones, namely, the mandibular condyle, squamous portion of temporal bone and the non-ossified articular disk. The TMJ is the articulation between the condyle of the mandible and the squamous portion of the temporal bone.
The glenoid fossa or mandibular fossa is a well-defined hollow area on the inferior portion of the squamous temporal bone. The convex articular eminence forms the anterior limit of the joint. The glenoid fossa is covered by a thin layer of fibrocartilage.
The condyle is elliptically shaped with its long axis oriented mediolaterally. The dimension of the condyle is roughly 20 mm in the mediolateral direction and approximately 8–10 mm in the anteroposterior direction. The articulating surface of the condylar head is covered by fibrocartilage (Figure 1).
The articular capsule is a fibrous membrane that surrounds the joint and incorporates into the articular eminence. It attaches to the articular eminence, the articular disk and the neck of the mandibular condyle. Superiorly, it is attached to the temporal bone and inferiorly to the neck of the condyle. The anatomical and functional boundaries of the TMJ are defined by the articular capsule. The inner surface of the capsule is covered by the synovial membrane that aids in the secretion of the synovial fluid. The articular capsule confines the synovial fluid to the articulating surfaces. Temporomandibular ligaments provide additional reinforcement to the capsule on its lateral wall.
Articular disk is a biconcave oval structure with a thin intermediate zone and a thick posterior and anterior border. These thick posterior and anterior bands act as wedges, giving the disk a self-seating capacity with the condyle functioning against the intermediate zone. The importance of this feature cannot be overemphasized; the contour of the disk with the thick bands helps prevent the displacement of the disk from the condyle during translation. An absence of blood vessels and nerves in the intermediate zone of the disk enables this part of the disk to act as a pressure-bearing area (Figure 2).
The disk is a fibrous, saddle-shaped structure that separates the condyle and the temporal bone. The meniscus varies in thickness—the thinner, central intermediate zone separates thicker portions called the anterior band and the posterior band. Posteriorly, the meniscus is contiguous with the posterior attachment tissues called the bilaminar zone. The bilaminar zone is a vascular, innervated tissue that plays an important role in allowing the condyle to move forward. The meniscus and its attachments divide the joint into superior and inferior spaces. The superior joint space is bounded above by the articular fossa and the articular eminence. The inferior joint space is bounded below by the condyle. Both joint spaces have small capacities (passive volume of the upper joint space is 1.2 ml and the passive volume of the lower joint space is 0.9 ml).
The condyle articulates with the inferior surface of the disk to form the lower joint, the disk-condyle complex, where only hinge or rotatory movement occurs. Translation or sliding movements occur in the upper joint, composed of the disk–condyle complex articulating with the mandibular fossa of the temporal bone.
Synovial fluid is a clear straw-colored thixotropic fluid which is composed of mucin with some albumin, fat, epithelium, and leukocytes. Synovial fluid also contains lubricin secreted by synovial cells. It is mainly responsible for so-called boundary layer lubrication, which reduces friction between opposing surfaces of cartilage. Synovial fluid is made of hyaluronic acid and lubricin, proteinases and collagenases.
During movement, the synovial fluid held within the cartilage is squeezed out mechanically to maintain a layer of fluid on the cartilage surface (so-called weeping lubrication). Boundary lubrication is a function of water physically bound to the cartilaginous surface by a glycoprotein.
These ligaments restrict the movement in the lower joint to hinge or rotatory action when viewed in a sagittal plane. Discal ligaments cause the disk to move passively with the condyle in an anterior and posterior direction during condylar translation. These ligaments permit very little lateral excursion.
It is attached anteriorly to the posterior band of the articular disk and posteriorly to the tympanic plate and posterior aspect of the condyle. The retrodiscal tissue contains loosely associated collagen fibers and a meshwork of elastic fibers.
The upper retrodiscal lamina is elastic in nature and exerts a posterior traction on the disk. The inferior retrodiscal lamina is non-elastic and restricts forward rotation of the disk on the condyle.
The ligaments that have been associated with the TMJ include lateral ligament (temporomandibular ligament), stylomandibular ligament, sphenomandibular ligament, discomalleolar ligament (Pinto’s ligament) and Tanaka’s ligament.
The lateral ligament is comprised of two parts: a deep part (horizontally oriented) and a superficial part (vertically oriented). The horizontally oriented portion of the lateral ligament limits retrusion and laterotrusion. In this manner, the sensitive retrodiscal tissue is protected from injury.
The vertically oriented portion of the ligament limits opening of the jaw. The vertically oriented superficial part of the temporomandibular ligament contains nerve endings (Golgi tendon organs) which play an important role as static mechanoreceptors for protection of these ligaments around the TMJ.
The stylomandibular ligament runs from the styloid process downward and forward to the medial surface and border of the angle of the mandible. The stylomandibular ligament functions by limiting excessive mandibular protrusion.
The sphenomandibular ligament arises from the spine of the sphenoid bone and extends downward and forward to insert on the lingula of the mandible along the lower border of the mandibular foramen. The sphenomandibular ligament restricts protrusive, mediotrusive as well as passive jaw opening.
Discomalleolar ligament was described by Pinto in 1962. This ligamentous structure connects the malleus in the tympanic cavity and the articular disk and capsule of the TMJ. It is estimated that only 29% of the TMJs reveal the presence of this ligament.
Various mandibular movements such as opening, closing, protrusion and retrusion occur under the coordinated movements of the muscles of mastication, namely, the masseter, temporalis, medial pterygoid and lateral pterygoid.
Masseter muscle arises from the lower border and inner surface of the anterior two-thirds of the zygomatic arch, passes inferiorly and posteriorly, and inserts on the outer surface of the mandibular ramus (Figure 3). The deep fibers of the masseter muscle (pars profunda) are vertically oriented whereas the superficial fibers (pars superficialis) are more oblique. This muscle is responsible for elevating the mandible to aid in jaw closure and for clenching and crushing action.
The temporalis is a broad, fan-shaped muscle that arises from the temporal fossa (superior and inferior lines of the temporal bone). Via a strong tendon it inserts into the upper anterior border and the medial aspect of the coronoid process, and into the anterior border and adjacent medial surface of the mandibular ramus.
The anterior fibers run obliquely downward and posteriorly (serve as elevators and also maintain the postural (resting) position of the mandible, with the teeth slightly apart), the middle part of the temporalis muscle helps in closure of the jaws and the posterior fibers which are oriented in a horizontal direction help in retrusion of the mandible and gentle finer movements to achieve a position of intercuspation.
The medial pterygoid muscle originates from the pterygoid fossa (medial surface of the lateral pterygoid plate). Some of the fibers also originate from the maxillary tuberosity. The muscle fibers extend inferiorly, posteriorly and laterally to insert into the medial surface of the ramus, approximating the angle of the mandible. Here it joins with the masseter to form a muscle sling (Figure 4A, B).
The lateral pterygoid muscle comprises two functionally distinct entities: (i) the smaller, superior head arises from the infratemporal surface of the greater wing of the sphenoid and runs backward in a nearly horizontal direction; (ii) the larger, inferior head arises from the lateral surface of the lateral pterygoid plate and runs backward in a somewhat oblique upward direction. Both heads merge posteriorly into a tendon that inserts in the following way: the upper fibers, which correspond more to the superior head, insert into the anterior surface of the capsule and disk; the inferior fibers, which correspond mainly to the inferior head, attach mostly to a depression (pterygoid fovea) on the inner side of the anterior surface of the mandible (Figure 5). Studies on the run and the attachment of the lateral pterygoid muscle on 41 cadavers by Abe et al (1993) showed the presence of a third intermediate belly of the lateral pterygoid muscle.
Both the heads of the lateral pterygoid muscle function as independent antagonistic muscles. Contraction of the inferior head pulls the condyle forward down the slope of the articular eminence (opening of the mandible and protrusion); whereas the superior head is active during mandibular closure and contracts in conjunction with the mandibular elevation muscles. It also exerts a holding or bracing action on the condyle when the teeth are held together and during power strokes. The superior head also acts to rotate the disk anteriorly on the condyle when the disk–condyle complex is moving upward and backward against the eminence. By keeping the disk between the condyle and eminence, the superior head of the lateral pterygoid muscle aids in maintaining joint stability.
The digastric, mylohyoid, geniohyoid, stylohyoid muscles are grouped under suprahyoid musculature owing to their anatomic location. These muscles are considered accessory muscles of mastication and help in jaw opening along with the lateral pterygoid muscle.
The hinge like movement is followed by gliding of the disk and the head of the mandible, as in protraction. At the end of this movement the articular disk comes and rests against the articular eminence.
The TMJ and the muscles of mastication are primarily fed by the maxillary artery and superficial temporal artery. The blood supply to the condylar head is also derived from the inferior alveolar artery via the bone marrow.
The TMJ is innervated predominantly by the articulo-temporal nerve, masseter and the temporal nerves. Four types of receptors aid in proprioception: Ruffini mechano-receptors (type I), pacinian corpuscles (type II), Golgi tendon organs (type III) and free nerve endings (type IV). The joint capsule, lateral ligaments and genu vasculosum in the bilaminar zone typically contain these receptors. Comparatively, the anteromedial portion of the capsule contains very few type IV receptors.
Temporomandibular joints are located about 1.5 cm anterior to the tragus of the ear. The two TMJs, considered together, compromise only one part of the total articulation between the lower jaw and the skull-facial skeleton complex. The other important contribution is made by the interdigitations of the mandibular and maxillary dentition, and function and health of the joint is directly related to condition of the teeth.
The history of presenting illness should include the onset and course of signs and symptoms. Past history should include the details regarding arthritis, infections, degenerating diseases, parotitis, ear disorders, muscular disorders, trauma, past dental treatment, diet/nutritional adequacy and habits like clenching, gum chewing, etc. and the individual lifestyle.
The face is inspected for any obvious asymmetry, scars (may be indicative of previous surgeries, trauma), swelling/ulceration/sinus openings in the pre-auricular region. Observe for deviation/deflection (Figure 6) of mandible on mouth opening.
The TMJs can be palpated by extra-auricular and intra-auricular methods. Palpation can be done standing at 10 o’clock or 11 o’clock positions by the clinician. Intra-auricular palpation can be achieved by placing the little finger inside the external auditory meatus. During mandibular movement the posterior poles of the condylar head can be palpated with the pulp of the little finger. Intra-auricular palpation may also be used to elicit capsular tenderness.
Extra-auricular examination of the TMJ is achieved by placing the index fingers in the pre-auricular region about 1.5 cm medial to the tragus of the ear. The lateral pole of the condyle is accessible during this examination.
Temporalis is palpated simultaneously with the fingertips aligned in a row from the hairline just above the supra-orbital ridge to above the ear. The patient is asked to report any discomfort or pain.
Tenderness of the lateral pterygoid can occasionally be detected by indirect application of pressure. The index finger or back end of the handle of an instrument is positioned distal and posterior to the maxillary tuberosity and posterior pressure is exerted to compress tissue against the muscle (Figure 7).
Alternatively, the medial and lateral pterygoid muscles can be assessed by functional evaluation. These can be achieved by asking the patient to perform simple tasks like opening the mouth against resistance (Figure 8) and closing the mouth against resistance.
Temporomandibular disorders/myofascial pain disorders often have musculoskeletal problems in other regions that are particularly associated with neck. Check for mobility of the neck and examine for range and symptoms.
Patient is first asked to look to the right and then to the left. There should be at least 70° rotation in each direction. Next patient is asked to look upward as far as possible (extension) and then downward (flexion). Any pain is recorded and any limitation of the movement determines muscular or vertebral problem. Sternocleidomastoid/trapezius/posterior cervical muscles are often part of neck disorder and may refer pain to face and head.
The posterior cervical muscles do not directly affect mandibular movements; however, they do become symptomatic during temporomandibular disorders and therefore are routinely palpated. They originate at the posterior occipital area and extend inferiorly along the cervicospinal region. Because they are layered over each other, sometimes it is difficult to identify them individually.
These muscles can be examined by slipping fingers behind the patient’s head. Those of the right hand palpate the right occipital area and those of the left hand palpate the left occipital area, both at the origins of the muscle (the patient is questioned regarding any discomfort). The fingers then move down the length of the neck muscles through the cervical area and any patient discomfort is recorded.
Trapezius, an extremely large muscle of the back, shoulder and neck, does not directly affect jaw function but is a common source of headache and is easily palpated. It commonly has trigger points (TrPs) that refer pain to the face and hence the purpose of its palpation is to search for active TrP. The upper part is palpated from behind sternocleidomastoid, inferolaterally to the shoulder and any TrP are recorded.
Examining the dentition and occlusion is an important part of the physical examination of a TMJ disorder or orofacial pain patient. It may provide very useful information about the existence of bruxism or other oral habits and their possible effects on the dentition, periodontium or other oral structures. Such an examination can also determine whether there has been a progressive change in the occlusal relationship (midline shift, anterior open bite, unilateral posterior open bite, etc.) that may indicate the presence of such conditions as unilateral condylar hyperplasia, rheumatoid arthritis, or neoplasm. Noting the number of missing teeth particularly loss of posterior occlusal support is important since this situation may predispose the TMJs to degenerative joint disease (osteoarthrosis) especially in the presence of bruxism.
Dimitroulis in 1998 described ‘temporomandibular disorders’ as a collective term used to describe a number of related disorders involving the TMJ, masticatory muscles and occlusion with common symptoms such as pain, restricted movement, muscle tenderness and intermittent joint sounds.
The disorders of the TMJ may exhibit a wide variety of symptoms and signs. The symptoms and signs that are frequently associated with temporomandibular disorders include: pain on mouth opening, limitation of mouth opening, pain on chewing, joint noises (clicking and/or popping, grating), pain in the region of the joint and/or muscles, pain around the region of the ear, temporal region and cheeks, subjective hearing loss, occlusal irregularities, attrition of teeth, headache (frontal, temporal, suboccipital), tinnitus, muscle hypertonicity and hypertrophy ofjaw muscles, neck pain and difficulty in swallowing.
TMJ disorders may arise from macro trauma such as in road traffic accident (RTA), excessive mouth opening (yawning, biting onto a large chunk of food) or from repeated micro trauma such as in parafunctional habits (bruxism), uneven occlusal loading (malocclusion, high points in restorations, poorly contoured crowns). Other causes include stress, underlying systemic diseases, arthritis and developmental abnormalities. See Box 1 for classification of TMJ disorders.
Changes associated with the articular surfaces include those of the mandibular condyle and glenoid fossa. The changes that can be appreciated are condylar head flattening (Figure 9), flattening of the glenoid fossa or bony irregularities over the condylar head.
Patient is usually asymptomatic. Over a period of time the patient is accustomed to a new pattern of mouth opening, thereby avoiding pain during mandibular movements. Occasionally, a click may be evident during the opening and closing movements. What is interesting about the clicks associated with condition is that the click is evident at the same point both during opening and closing. Whereas in click associated with disk displacement, the opening click is usually evident after 20 mm of mouth opening and the closing click is felt just short of occlusion of teeth.
This condition can be managed by instructing the patient to develop a path of mandibular movement that avoids the interference and to chew on the affected side. This will minimize the intra-articular pressure in the ipsilateral joint.
It is believed that the disk wears out over a period of time. Hence, elderly individuals may generally present with thinning of the disk which may ultimately perforate. The other causes include excessive occlusal loads from parafunctional habits such as bruxism, clenching and trauma.
The thinnest intermediate portion of the disk may show a circular hole with irregular or fragmented border. A perforated disk will expose the articular surface of the joint leading to degenerative changes.
On auscultation of the TMJ, crepitus or grating noises may be heard. In the early phases of the process pain may be a presenting complaint. Once the disk is perforated occlusion may be altered when teeth are in maximum intercuspation. Disk changes are readily evident on MRI and arthrography. Degenerative changes can be appreciated on traditional imaging modalities and CT.
Cholitgul et al (1990) evaluated 15 patients who were reported to have disk perforation at arthrography. Eleven patients reported pain. Clicking and crepitation was common. Deviation of the mandible at maximum mouth opening toward the affected side was seen in nine patients. The muscles of the affected side were tender on palpation. The disk perforation was located in the posterior attachment in most joints. An anterior disk displacement was found in almost all patients. They concluded that most joints with disk perforations were osteoarthrotic and the most severe clinical and radiological findings are associated with an ant/>