Understanding unusual tooth wear patterns in the horse’s mouth

The chewing surfaces of the horse’s molar teeth have sharp hard enamel ridges which grind against the opposite teeth. If the wear of the upper or lower teeth is uneven then both surfaces can become distorted.

A Wave Mouth occurs when the cheek teeth have an uneven or undulating grinding surface, shaped like a wave. Aggressive rasping can help, but severe cases need will need to be treated with molar cutters. Molar cutters should only be used when absolutely necessary as they can do unecessary damage to the teeth. The horse should be sedated before treatment.

A Step Mouth is an abrupt variation in the level of the grinding surface of adjacent teeth. This is most commonly caused by the loss of the opposite tooth. It can seriously compromise chewing and the horse will lose condition. Surgery is often required and, even then, the problem will inevitably return. Regular rasping, every three months or less, can maintain normal function.

A Shear Mouth occurs when there is an extreme exaggeration of the angle of the upper and lower teeth. Sometimes this occurs as a result of pain in the jaw joint. The horse may lose ability to chew sideways and is left with a very inefficient up-down chewing process. In a few weeks the jaw will become limited in mobility. A shear mouth is a serious problem, which must be deal with promptly. Rasping every two to three months can help.

An abnormally short lower jaw results in the upper incisors overhanging the lower teeth and is called a Parrot Mouth. A Hog or Sow Mouth occurs when the lower jaw is longer than the upper. In both cases, because the incisor teeth don’t meet correctly they wear unevenly and can become very long.

It is remarkable how well horses can cope with what appears to be a very difficult problem. Most cases of a parrot or hog/sow mouth are not treatable and provided the horse can eat effectively, they can often be left well alone. In severe cases, your vet may need to trim the teeth back, but this is not easy and there is a danger of cracking or otherwise damaging the teeth.