While composed largely of thin bone, and containing the antrum of Highmore, the upper jaw, owing to the arrangement of buttresses by which the force of blows is distributed, is not frequently fractured. In severe blows on the malar bone the zygoma may give way and the malar be driven into the antrum, and in fractures of the superior maxilla the infra-orbital nerve may be caught, or involved subsequently in callus, or the lachrymal sac may be torn. The maxilla tends to heal readily, with minimal callus formation. The upper jaw may be involved primarily or secondarily by tumours, particularly sarcomata. These frequently invade the antrum, which is distended, giving rise to neuralgia, and later, when the orbital cavity is involved, to exophthalmos and diplopia, owing to the displacement of the affected eyeball.

Frequently, also, the palate becomes involved, the teeth may come out, and the fungating mass project into the mouth, while it may also project backwards and inwards to the naso-pharynx. Where the disease is not very extensive, it may be treated by excision of the upper jaw, in which the greater portion of the jaw, together with portions of the malar, lachrymal, ethmoid, and palate, is removed. It is desirable, wherever possible, to save the floor of the orbit, in order to preserve the eyeball in its proper position, and, where this can be done, the operation is generally followed by but little deformity. The malar bone is rarely fractured alone ; generally it is driven into the upper jaw.