Fractures of the lower jaw almost never occur through the symphysis; this is on account of its being the thickest and strongest part of the bone. When a fracture of the anterior portion of the jaw detaches a median piece a most dangerous condition is produced. The piece, if sufficiently loosened by the injury, is drawn back into the throat, carrying the tongue with it and tending to suffocate the patient. Such a case is "recorded by A. L. Peirson (review by Geo. W. Norris, Amer. Jour. Med. Sciences, 1841, N. S. vol. i, p. 186). A man was run over by a wheel which passed over his jaw, fracturing it on each side and forcing the piece into his mouth. The piece was drawn backward and nearly caused death from suffocation.

In the Annals of Surgery (vol. xix, 1894, p. 653) is recorded a case of the author's in which a man, while drunk, fell and struck his chin on the curbstone. A fracture was produced through the symphysis above and branching to each side of the genial tubercle below. This small median piece was drawn back into the throat nearly to the hyoid bone, and suffocative symptoms were marked. These disappeared when the detached piece was drawn forward and wired in place. The piece was drawn backward by the geniohyoid and geniohyoglossus muscles. The digastrics may also have aided in depressing the fragment (Figs. 77 and 78).

Fig. 78.   Anteroposterior section of the tongue and floor of the mouth, near the midline.

Fig. 78. - Anteroposterior section of the tongue and floor of the mouth, near the midline.

The most usual site of fracture is in the neighborhood of the mental foramen. This is located just below the second premolar tooth (sometimes between the first and second). This foramen and the large socket for the canine tooth farther forward weaken the bone somewhat in this region. The jaw is strengthened behind the mental foramen by the commencement of the anterior portion of the ramus and by an increase in the size of the mylohyoid ridge on the inner surface. The jaw is also protected by the thick masseter muscle and fracture is most liable to occur just in front of it. This constitutes the typical fracture of the lower jaw (Fig. 79).

Fig.79.   Fracture of the lower jaw in the region of the mental foramen, showing the line of fracture and the influence of the muscles in producing displacement.

Fig.79. - Fracture of the lower jaw in the region of the mental foramen, showing the line of fracture and the influence of the muscles in producing displacement.