Brachygnathism

Brachygnathism or colloquially Parrot Mouth, is the uneven alignment of the upper and lower teeth. In serious cases, the lower teeth protrude beyond the upper teeth. Problem with parrot mouth in horses occurs if the molars at the back of the mouth are also uneven, resulting in large hooks forming on the upper molars and the rear of the lower back molars. Horses with parrot mouth often require dental treatment at least every six months to remove the hooks and maintain alignment.Other species uneven wear and exposure to air can lead to dental disease.

The equivalent conditions in humans are termed retrognathism or prognathism depending on whether the lower jaw is too far back or too far forward respectively.