I've introduced you to the basic problems seen in every horse, but there are more serious problems that can also cause problems, if delt with at an early age, these problems can be treated before they cause a habit (evading, head throwing) or before weight loss or eating problems are caused. I will outline these below.

Hooks - Hooks are caused when molar arcades are not meeting correctly and the part of the tooth that is not meeting an opposing tooth create a hook, they can be found on the second premolar (106) or the last molar (111). If left to get bigger they will grow down (if on the uppers) or up (if on the lowers) and they can start to wear into the gum causing a laceration and pain, which means the equine won't eat or will eat very slowly. It will also prevent free movement of the jaw. They can also be sharp and when the equine is bitted pressure points can be found on the flesh causing unnecessary pain leading to head tossing etc.

Ramps - Ramps form on molars on a more gradual slope on the upper or lower 6's or 11's like hooks. If left they will wear down the opposing teeth, sometimes to the root in older horses, but court at an early stange can be easily rectified. Ramps will also prevent the free movement of the jaw.  

Waves - With this case, the whole of the arcade has become uneven and develops what is described as a wave. This can be caused by many reasons, missing teeth, retained caps, large hooks or ramps. This case can be sorted with regular care taking down the high parts and giving the opposing teeth time to erupt back into occlusion.

Overlong Incisors -

Fractured or loose teeth -