This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The lower jaw is held up in place by a bandage, and the upper teeth act as a splint. Sometimes the teeth or fragments are wired in position, or an interdental splint of gutta percha or other material is used.
The condyle can be removed through an incision 3 cm. long, running from in front of the ear along the lower border of the zygoma. The temporal artery runs a centimetre in front of the ear with the auriculotemporal nerve posterior to it. By care in recognizing the artery, it may be saved and dragged posteriorly. The soft parts on the lower side of the wound with the parotid gland and facial nerve are pushed downward. The condyle can then be dug out, care being taken not to go beyond the bone and wound the internal maxillary artery.
In removing one-half of the mandible, the incision is made from the symphysis along the lower border of the jaw to the angle and thence upward as high as the lobe of the ear. If it is desired to take extra precautions, the last centimetre of this incision, from the lobule of the ear down, may be carried through the skin only. This will prevent wounding to any great extent the parotid gland tissue, the parotid duct, and positively avoid injuring the facial nerve. The incision, however, is rather far back to wound any large branch of the duct, and is too low down to wound the facial nerve. If it is desired to carry the incision higher than the lobule of the ear, it should go through the skin only. The facial artery and vein will be cut just in front of the masseter muscle. The soft parts, including the masseter muscle, are raised from the outer surface. In dividing the bone anteriorly, it should be done .5 cm. outside the median line. This will be about through the socket of the second incisor. The object of this is to retain the attachments of the geniohyoid and geniohyoglossus muscles to the genial tubercles, and so prevent any tendency of the tongue to fall back. The jaw is pulled out and separated from the parts beneath, the mylohyoid muscle being made tense. Care should be taken not to injure the submaxillary gland, which lies below the mylohyoid muscle, and the sublingual gland, which lies above it. The lingual nerve is also liable to be wounded if the knife or elevator is not kept close to the bone.
Fig. 84. - Excision of the condyle of the lower jaw.
As the detachment proceeds posteriorly, in loosening the internal pterygoid and the superior constrictor, if care is not taken, the pharynx may be wounded. The bone still being depressed and turned outward, the temporal muscle is to be loosened from the coronoid process or else the process is detached and removed later. Access is now to be had to the mandibular foramen at the mandibular spine or spine of Spix. The inferior alveolar artery is then secured and, with the nerve and sphenomandibular ligament, divided. The jaw can now be well depressed and brought inward. The temporomaxillary joint is to be opened from the front, having first cleared off the attachment of the external pterygoid muscle. There is great danger of wounding the internal maxillary artery at this stage of the operation. It lies close to the neck of the jaw, and it is to avoid bringing it too close to the bone that Jacobson advises that the jaw be not twisted outward when disarticulation is being performed.
The distance between the coronoid process and malar bone varies in different individuals. The process may be displaced by the tumor and thus prevent detachment of the temporal muscle. If so, the process is divided with forceps or saw and removed after the rest of the jaw has been taken away. Injury of the temporomaxillary veins may be avoided by not going behind the posterior edge of the ramus, as is also the case with the external carotid artery. Access to the joint may be facilitated by dragging upward the parotid gland, which carries with it the facial nerve and parotid duct.
Fig. 85. - Excision of one-half of the lower jaw, showing the structures exposed.