Affections of the Temporo-mandibular Articulation
Dislocation of the Mandible.—Dislocation of the lower jaw may be unilateral or bilateral. The bilateral form is the more common, and is met with most frequently in middle life, and in females. The liability to dislocation is greatest when the mouth is widely open—for example, in yawning, laughing, or vomiting—as under these conditions the condyle, accompanied by the meniscus, passes forwards out of the glenoid cavity and rests on the summit of the articular eminence. If, while the bone is in this position, the external pterygoid muscle is thrown into contraction, it pulls the condyle forward over the eminence into the hollow beneath the root of the zygoma, and the contraction of the masseter and temporal muscles retains it there. Muscular contraction is therefore an important factor in its production.
Dislocation may be produced also by a downward blow on the chin, by the unskilful introduction of a mouth gag, particularly while the patient is anæsthetised, or even in the attempt to take a big bite—say, of an apple. The dislocation that results from such causes is usually unilateral.
In some persons the ligaments of the joint are unnaturally lax, and dislocation is liable to occur repeatedly from comparatively slight causes—recurrent dislocation.
Clinical Features.—The appearance of a patient suffering from bilateral dislocation is characteristic. The mouth is open, the jaw fixed, and the chin protruded so that the lower teeth project beyond the upper. The patient has difficulty in swallowing, and the saliva dribbles from the mouth. As the lips cannot be approximated, the speech is indistinct and guttural. Just in front of the auditory meatus a deep hollow can be felt, and in front of this the condyle forms an undue projection. The coronoid process is displaced below and behind the zygomatic (malar) bone, and may be felt through the mouth. The contracted temporal muscle forms a prominence above the zygoma.
In unilateral dislocation the deformity is the same in character, but is less marked, and in mild cases its cause is liable to be overlooked. In most cases the chin deviates towards the sound side.
Treatment.—In recent cases, reduction is usually easily effected. The patient should be seated on a low chair or stool, an assistant supporting the head from behind. The surgeon, standing in front, places his thumbs, well protected by a roll of lint, far back on the molar teeth, and with his other fingers grasps the body of the jaw. Pressure is now made downwards and backwards to free the condyles from the articular eminence, and to overcome the tension of the temporal and masseter muscles, and as this is effected the tip of the chin is carried upward, while the whole jaw is pushed directly backward. The condyle slips into position, sometimes with a distinct snap. When difficulty is experienced in levering the condyle from its abnormal position, a cork may be placed between the molar teeth on each side to act as a fulcrum. After reduction the jaw is fixed by means of a four-tailed bandage for a few days. The patient is warned to avoid for some weeks opening the mouth widely.
Old-standing Dislocation.—It sometimes happens that, from having been overlooked or neglected, the dislocation remains unreduced. In such cases the movement of the jaw is in time partly restored, and the patient acquires sufficient control of the lips to be able to articulate intelligibly and to prevent dribbling of saliva. The power of masticating the food, however, remains impaired. The hollow behind the condyle and the projection of the chin persist. Reduction by manipulation is seldom possible after the dislocation has existed for more than three months, but it has been effected as long as ten months after the accident. Several attempts at reduction should be made at intervals of two or three days, and if these fail recourse may be had to operation. As the masseter and internal pterygoid muscles have assumed a vertical position and become shortened, they form an obstacle to reduction, and to overcome their action it is necessary to separate them from their insertion to the ascending ramus of the bone through an incision carried round the angle. If the adhesions about the dislocated condyle are then separated, reduction can be effected (Samter). In some cases it is necessary to excise the condyle to restore movement.
Internal Derangements of the Temporo-mandibular Joint.—The intra-articular cartilage is liable to be displaced by excessive traction exerted on it by the external pterygoid muscle during some sudden movement of the joint, particularly in closing the mouth. There is acute pain in the region of the joint, the teeth on the affected side cannot be brought into apposition, so that mastication is interfered with, and the patient is conscious of something locking inside the joint. The joint is tender to the touch, but there is no external swelling. Replacement is effected by keeping up firm pressure at the back of the condyle with the mouth open, and slowly closing the jaw. If recurrence takes place repeatedly, the disc may be sutured to the periosteum (Annandale), or excised (Hogarth Pringle).
Arthritis of the temporo-mandibular joint occurs in two forms, non-suppurative and suppurative.