34 
THE WAVE-FORMED MOUTH. 
molars and the outer edge of the upper are not worn away ; both continue 
to grow until the former meets the hard palate, while the latter injures 
the gums of the lower jaw. Coupled with impaired mastication, such 
wounds prevent the horse either taking or chewing food. The overgrown 
teeth sometimes penetrate the bone above, and the hard palate may even 
be completely perforated. The side thrust on the teeth loosens them, 
while wounds of the gum are apt to produce inflammatory changes in the 
alveolar periosteum. Hence “ shear mouth,” especially in old horses, 
generally produces alveolar periostitis. 
Its causes are the same as those of angular or sharp mouth. A narrow 
jaw and limited movement are notable predisponents. It is unnecessary 
to discuss the correctness of Lorge’s supposition that the muscles of the 
jaw are imperfectly developed ; or Gunther’s, that the affection is due to 
variations in hardness of the molars. Esser saw shear mouth result 
from the articulation of the jaw being wounded, lateral movement in one 
direction being shortened, and irregular wear thus induced. 
Prognosis depends on the degree of development, condition of the teeth, 
and existing complications. The earlier stages escape notice; it is only 
when chewing becomes difficult that its presence is suspected. Provided 
the teeth are still sound and firm, temporary relief may at all events be 
given; but where they are loose, or alveolar periostitis has already set 
in, the chances of recovery are slight, and in long-standing cases cure is 
impossible. 
Treatment was formerly confined to removing the sharp edges with the 
rasp or chisel, and lightening the work of mastication by giving soft food. 
Even nowadays nothing more can be done if the teeth are loose or shear 
mouth is moderately developed. But where the patients are young and 
valuable, and the teeth still firm, relief may be assured, at least for some 
time, by removing the projections with tooth shears. Moller operated 
on several cases in this way, and the animals immediately afterwards 
were able to take their food and masticate quite satisfactorily. If several 
teeth have to be shortened, the horse must be cast, but the operation is 
not difficult, and Moller more than once operated on double shear mouth 
in a quarter to half an hour, and had most excellent results. As to the 
use of the shears, see section (d) hereafter. 
(c) THE WAVE-FORMED MOUTH. 
The wearing surfaces of the several molars on each side above and 
below are normally of similar height, and form a plane surface; 
but variation of this plane produces the wave-formed mouth. It is 
generally bilateral, the fourth lower molar being the shortest, the 
corresponding upper tooth the longest in their particular rows. The 
