Eventually the surfaces of the cheek will loose their normal angle as well, and then the mouth is a real mess. Inefficient chewing is detrimental, sometimes even fatal, in the horse. There are places in the equine large intestine where the diameter of the bowel decreases dramatically, and the bowel makes an 180 degree turn at the same time. This slows the transit time of feed through the bowel. When feed slows down it starts to ferment, and can cause the pain of colic.
Excessive fermentation can also lead to systemic bacterial infections and other illnesses.
Choke is a fairly common digestive problem that can be caused by poor dentition. Improperly chewed hay is swallowed in a ball and gets lodged in the esophagus. Many horses who choke sustain permanent damage to the esophageal muscle and will have repeated bouts for life. Some develop aspiration pneumonia and may die. I have observed that most horses prone to choke have dental malocclusions, that when corrected, result in less frequent choke episodes.