Why is Dentistry Important?
The most important reason to maintain a horse's teeth is to ensure that it is free from pain and therefore has a good quality of life. We also want our horses to perform to their maximum potential and so any pain or physical restrictions will mean that though our horses may be willing to work hard for us, they may be unable to do so. It is essential that dentistry is seen as maintenance rather than waiting for a problem to occur as the horse will often suffer in silence for a long time before the owner knows there is a problem. Remember, the horse has to eat or it will die and so just because your horse is eating, do not assume there are no dental problems. As with most things, prevention is better than cure and so a regular maintenance programme will ensure that problems are dealt with before they become severe and pain for the horse (and often the rider!) can be prevented.
Tooth Identification 
Incisors - cut or grasp the food
Canines - Usually present in male equines on the lower and upper bars. They serve no purpose in the modern horse.
Wolf Teeth - These are present in about 25% of horses, usually just in front of the upper premolars. Lower wolf teeth are very rare. They are the vestigal remains of the first premolar which has disappeared during evolution.
Premolars and Molars - These teeth grind the food into small pieces that can then be swallowed. The premolars have deciduous and adult teeth.
Evolution
The ancestors of the modern horse can be traced back to about 55 million years ago. At this time, the early horse was about the size of a rabbit, and it 
browsed on succulent plants. Its teeth were similar to our teeth and were short crowned, the teeth being hard and long enough to last for the duration of the early horse’s life. During the next 55million years the horse underwent a major evolution. The horse clearly grew in size but also its head lengthened and deepened to allow for longer rows of teeth and also longer teeth themselves. The horse evolved to be a grazer, feeding on hard, abrasive grasses and its teeth evolved to become hypsodont teeth. You can see from the diagram of the skull, that these teeth have a very long reserve crown (tooth below the gum line) and a short Clinical Crown (tooth above the gum line). The teeth erupt throughout most of the horse’s life and silicates in the earth and grasses cause the teeth to be continually ground down, this happening at the same rate as the teeth erupt. 
The arrow shows the position of the teeth that are pictured to the right. The tooth on the left is taken from the skull of a horse in its mid 20's, and the tooth on the right, taken from the skull of a 7 year old pony. You can see how short the older tooth is, due to it being worn down throughout the life of the horse.
How The horse Eats
The horse eats on one side of its mouth at a time in a circular motion. The lower jaw drops and moves slightly forwards, moves out sideways, moves up and then grinds the lower arcades of teeth across the upper arcades of teeth, back to the starting position as we can see in the series of pictures below. In the ideal mouth, all the teeth would receive wear and the mouth would remain balanced and level with no protuberant teeth. Unfortunately, very few horses have such good mouths and usually, the outside edges of the upper teeth and inside edges of the lower teeth are not worn and become sharp. If the upper and lower arcades of teeth are not correctly aligned, we also see other protuberances such as hooks, ramps, large ridges or waves. There are of course many other problems and some of these can be seen in the Common Problems pages.
Food is grasped by the lips and the incisors pull it into the front part of the mouth. When the front of the mouth is full, the chewing motion described above begins. The food is pushed between the teeth by the tongue and the cheeks which are tight against the teeth hold it there, As the horse chews, the shape of the ridges across the surface of the teeth, and the hard and soft palate direct the food towards the back of the mouth and the food bolus is of a rope like consistency. As it moves further back in the mouth, the particles of food are chopped more and more finely until the food is ready to swallow. Clearly if this food is not chewed well enough, not only will the horse gain less nutritional value from the food but in extreme cases it can suffer from colic or choke. Importantly, the sideways movement of the lower jaw is much reduced when the horse eats hard food and for this reason, problems develop much quicker with theses horses.
Common sites of soft tissue trauma due to sharp edges on teeth. This very often leads to severe ulceration of the cheeks causing it to be extremely painful for the horse to eat.
What About Wild Horses?
There are many differences between our domestic horses and wild horses and these are explained below.
1. Breeding
There is evidence from fossils that mankind has domesticated horses as far back as 4000BC, the fossils showing damage to the teeth of the horses by use of a bit. During the thousand of years from 4000BC, we have been selectively breeding the horse for attractive traits such as speed or ability to jump. What we have not done however, is to selectively breed horses to have good dentition and so unlike the wild horse, there is no survival of the fittest. Horses that would not be able to survive in the wild are used to breed and so we have bred dental problems into the horse.
We also cross breeds and have bred breeds such as miniatures. This can often result in large teeth in a relatively small head, leading to overcrowding and subsequent displacement of teeth.
2. Feeding
The manner in which a horse eats was described above, leading to sharp edges on the teeth. It has been proven that when a horse is fed hard food, this lateral movement of the lower jaw is even less and so these sharp edges form much more quickly.
We also feed our horses in high mangers or hay nets and so the horse will be eating with its head in an unnatural position with the lower jaw slid backwards. This causes the front of the upper arcades of teeth and the back of the lower arcades of teeth to receive insufficient wear and these areas can become protuberant, forming hooks or ramps.
3. Bit
The ridden horse usually has a bit in its mouth and it is essential that it is comfortable when this is the case. For this reason, wolf teeth are often removed as they are usually located just in front of the arcades of cheek teeth. When a contact is taken, the bit pushes back the soft tissue in the horse’s mouth and this can become trapped between the bit and the wolf teeth.
Bit seats also help the comfort of the horse when ridden and involve rounding off the front of the first cheek teeth on both the upper and lower arcades. This allows the bit to sit comfortably in the mouth and helps prevent any damage to the soft tissues in the mouth.
4. Longevity
The domestic horse lives much longer than its wild ancestors and so its teeth must also last much longer.
5. Wild horses do have problems
The closest thing we have to wild horses in this country are the moorland ponies and working throughout Devon and Cornwall, I see a large number of these, including ponies which have only recently left the moors. Nearly without fail, these ponies have at the very least sharp edges and often, much greater problems. 
The picture below is the incisors of a moorland pony, now 2 ½ that was actually born wild on Dartmoor. It can be seen that one of the incisors is twisted and one is absent. Clearly without very regular dental maintenance this pony would develop severe 
diffidental problems.
This skull that was found on Bodmin Moor. This pony was only about 7 or 8 years old and even at that age has extremely uneven teeth. Whether it was the combination of poor teeth and illness that killed this pony we will never know but clearly the state of its teeth did not help it.
