The horse has uniquely designed teeth that pulverize grass into small particle sizes which allow the bacteria in the hind gut to digest the grass efficiently. The horse then gets the nutrients he needs to survive, grow, and do all the athletic things that a horse does, from the bacteria and byproducts of this fermentation process. Without properly functioning teeth, the horse at very best will have poor feed utilization and at worse won't be able to survive. Even proper swallowing is dependent on good food chewing.
The horse has six upper and six lower front teeth, these are known as incisor teeth which he uses to pull or nip grass. He also has six upper and lower grinding teeth on each side for a total of 24; these are called pre-molars and molars. This grinding action is very abrasive to the premolars and molars due to the high silicon (sand-like) content of grass. Like all herbivores, horses have hypsodontal pre-molar and molar teeth (long crowns which continue to erupt as the actual wear of grinding shortens the crown). The fully developed tooth starts with 80-90mm of reserve crown and wears approximately 2-3mm down every year as the horse grinds its food. That equals approximately 26-40 years of use out of those teeth on average.
The horse's lower jaw is narrower than the upper jaw and the grinding surface is sloped at 10-15 degrees. This is why a horse only chews on one side at a time with a rotating side to side motion which is referred to as lateral excursion. The grinding teeth are composed of dentin with enamel whorls which act then like edges of a file to tear apart grass. As the softer dentin wears away faster, it tends to leave sharp enamel points which cause cheek and tongue ulcers. A big part of horse dentistry then involves floating or leveling these sharp points off. The goal is to preserve the grinding surface for the horse's entire life.
The take home message is to not confuse horse dentistry with human dentistry and understand that as the tooth wears, new sharp edges are formed which need to be floated. It should be viewed as a maintenance issue with a goal of making the teeth last for a 30+ year life span of the horse. If the horse loses the ability to properly grind his food we, as caretakers, have to process it by grinding and feed it in the form of pellets or cubes. Some horses can't even get their food swallowed without converting it to mush. Again our goal is lifelong, properly functioning teeth. Nothing against senior feeds (pelleted diets) but horses do better and are happier on hay.
Like people, horses should have their teeth checked yearly. Identifying and rectifying the sharp edges will promote a healthy mouth, free of sores caused by sharp edges. In turn, the horse will be more willing to consume feeds, and much better equipped to maximize their utilization of the nutrients.