DISLOCATIONS OF THE LOWER JAW.— The dislocations may be single or double. Upward or backward dislocations are very rare. In the former the condyle is driven through the base of the skull, in the latter back through the anterior wall of the external auditory meatus.
Forward Dislocations.—The lower jaw projects forward, the mouth cannot be closed, the condyles may be seen and felt in front of the eminentia articularis. The glenoid fossa is empty. In unilateral dis locations the chin is deviated to the op posite side. The pain is usually not great.
The usual cause of forward disloca tions is a wide opening of the mouth in yawning, laughing, or introducing some large object. It is more frequent in women than in men. When the mouth is wide open the external lateral ligament is relaxed and the external pterygoid muscle draws the condyle, and the inter articular cartilage with it, well forward on the eminenta articularis. A slight overaction of this muscle carries the con dyle over the summit, whence it plunges forward and upward under the zygoma, and is then held by the balance of forces between the muscles pulling upward and forward and the external lateral ligament pulling upward and backward. The in
terarticular cartilage accompanies the condyle, at least part of the way. The capsule is not torn.
Reduction is accomplished by opening the mouth more widely to relax the liga ment and then pressing the condyle back- ward and then a little downward. A fairly-successful method is by grasping the jaw on either side with the thumbs on the molar teeth and the fingers un der the jaw outside. As the jaw snaps back the thumbs must be quick-ly slipped into the hollow of the cheeks to avoid be ing bit. Reduction of one side at a time is sometimes easier. Arnesthesia may be required to overcome the contraction of the muscles.
Not infrequently this dislocation tends to become habitual. To overcome this the meniscus may be sutured in place. Injection of tincture of iodine has been proposed.