Here you see how the bit is supposed to lie in the horses mouth.

The part where the bit lies is called the bars, that is the space between the incisors and the premolars. The bit lies right up against the premolars, and this is the place where some horses gets wolf teeth. 

The problem with the wolf teeth is that they will cause the horse a lot of pain if the bit is placed on them. Usually one will find the wolf teeth in the upper jaw, and even there it will cause the horse pain. The wolf teeth can be hard to see because they don't always come out fully, and this means that even though we can't really see them they still gets pressure from the bit and will cause pain. 

Because of the potential problem with wolf teeth one should always have a horse checked by an equine dentist before one ever puts a bit in the horses mouth, and even if you buy an older horse from someone you should get this checked, because it is amazing how often the wolf teeth are missed even though the horse is showing clear signs of discomfort. 

And there are other reasons why one should have the dentist come out and check the horses on a regular basis; tooth caps and sharp edges.

The horses teeth are quite different from our teeth. They grow throughout the horses life. The growth is to compensate for the huge wear the horses teeth gets, ideally a horse will eat for up to 16 hours a day, so as the tooth wears down more of it comes out.

The horses way of eating can make sharp edges on the side of the teeth. First the horse bites of the grass with the front teeth, and then it chews the forage with the molars. 

This seems like just what we do, but the difference lies in the chewing technique. While we pound the food the horse will grind the food by moving the jaw from side to side.

If the horse does not move the jaws far enough over so that the upper teeth goes completely over the lower teeth the sides of the teeth will develop edges where the teeth are not getting worn.

This happens because the jaws are of different sizes. The problem often gets worse by people feeding the horses grain as a main energy source instead of hay. When the horse eats grain it will move it's jaws less then when it eats grass, it will pound the food more instead, and this will cause even more edges. 

In addition the horse will spend a lot less time eating than nature intended so the teeth grows faster than they are worn. The incisors, that when grazing are constantly worn, are not getting used at all when eating the grain, and getting very little use when fed loose hay. 

Horses loose their temporary teeth in a way very similar to humans. The adult tooth lies in the jaw directly beneath the temporary one, and as it begins to emerge, the root of the temporary tooth is reabsorbed. This shortens the tooth until it becomes a 'dental cap' which covers the grinding surface of the adult tooth when it erupts. 

These caps should then fall off; but if they do not they meet with their opposite premolar, stopping it from growing as it should. So instead of growing upwards, the teeth in the lower jaw begins to grow downwards, and in consequence three-year-old horses often have a bumpy appearance to the line of the lower jaw bone. This means that they are in desperate need of treatment. 

Equine dental specialist sometimes find caps still present in six year old horses, by with time they have done tremendous damage, but when the caps are removed the teeth will start to grow correctly again, and the bumps in the jaw disappears in time. 

It is rather unfortunate that the horses sheds it teeth at the same time that they begin to get ridden with a bit, but this can be helped a lot by simply having the teeth checked before bitting it for the first time, and then giving the horse regular checkups after that. 

How often a horse needs to have the teeth floated or rasped, that means to have the sharp edges removed, will vary from horse to horse, but they should all be checked at least once a year. That can spare your horse from a lot of agony, and spare the rider from thinking they have a training problem. 

Floating the horses teeth requires the right tools. A lot of veterinarians only have the assistant pull the horses tongue out on one side while working on the opposite side, but by this method there is no way that they can properly assess all the horses teeth in the back of the jaw. 

Some veterinarians uses the Swales gag which holds one side of the mouth open at one time, but when the horse bites down with this on he can damage his jaw joint, and even split a molar tooth. It is still also possible for the horse to clamp a portion of his jaw shut, so that these teeth never gets floated. 

The full mouth speculum, or the Houseman's gag holds both sides of the jaw open, and only with this gag will one be able to see and feel enough to assess the state and balance the jaw which he needs to do both before and after his work. 

There are some horror stories about horses going crazy with this gag on, but if the horse is handled gently and the gag not just pried on his head and the mouth forced open, the horses are usually fine with it. The horse has no nerves in their teeth, to the floating process it self causes no pain, but horses often find the vibration of the rasp uncomfortable at first. 

Problems with the teeth can lead to many other physical problems that seems to be unrelated. A lot of horses has been treated to back pain that keeps recurring because it stems from  tension the horse is having because of pain in the mouth. A lot of times problem with the teeth will be viewed as a training problem, but as long as the horse is in pain the horse will continue to "misbehave".

Bad teeth can also cause a lot of horses to loose condition, and to feed more will simply not help if the horse can not eat it properly. Some horses goes off their feed completely when the edges in their mouth are causing so much pain that eating is simply not worth the agony anymore.