Masseter muscle

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.

Temporalis muscle

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.

Medial pterygoid muscle

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 medial pterygoid primarily aids in jaw closure. It also participates in protrusion of the mandible.

Lateral pterygoid muscle

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.

Suprahyoid muscles

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.

Mandibular movements

Temporalis

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.

Masseter

Masseter is palpated bilaterally in the area overlying the anterior border of the mandibular ramus. The area of palpation is directly above the attachment of the body of the mandible.

Pterygoids

Palpation of the pterygoid muscle is difficult because of the inaccessibility of the muscle.

Medial pterygoid

Medial pterygoid can only be palpated near its insertion by placement of the index finger laterally and posteriorly into the floor of the mouth toward the medial surface of the angle of the mandible.

Lateral pterygoid

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.

Digastric muscle

Digastric muscles are palpated with the fingertips aligned roughly parallel to the inferior border of the mandible in the submental and submandibular region.

Sternocleidomastoid

Palpation is done bilaterally near its insertion on the outer surface of the mastoid fossa behind the ear. The entire length of the muscle is palpated down to its origin near the clavicle.

Posterior cervical muscles

Trapezius, longissimus (capitis and cervices) splenius (capitis and cervices) and levator scapulae.

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

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.

Splenus capitis

Splenus capitis is palpated for general pain, tenderness, and TrP. Its attachment to the skull is a small depression just posterior to the attachment of the sternocleidomastoid. Palpation is begun at this point and moves inferiorly as the muscle blends into the other muscles.

 Clinical situation

 Cost

 Radiation dose.

 Plain films, panoramic radiographs, conventional and computed tomography

 Foreign body giant cell reaction to implants

 Suspected tumors

 Ankylosis

 Complex facial fractures

Clinical features

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.

Clinical features

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/>