Equine teeth have the same names as human teeth i.e., incisors and molars, but their function is not quite the same.  Horses grind their food, moving the lower jaw bone from side to side with the mouth almost closed all the time [Img.1].

Horses eat food which contains a huge amount of fibre that has to be mashed and ground as much as possible to increase the surface area for the gastric juices to work on [Img.2].

To achieve this there has to be maximum contact between the upper and lower jaws, combined with good lateral movement. 

A horse’s teeth are divided into 4 arcs, i.e., upper right or nr 1 arc, upper left or nr 2, lower left or nr 3 and lower right or nr 4 arc. Each of them has 3 incisors, 3 pre-molars and 3 molars. There is one canine tooth in each arc in males although mares can sometimes have them, too although not necessarily all four, sometimes just one or two. Right in front of the first premolar, 95% of the time in front of the upper premolars, there is a small tooth called the "wolf tooth". 
So a horse with a full set of teeth may have up to 44 teeth but this is really hard to find. Generally males have between 36 and 42 teeth whilst mares usually have about 36.

Inside the mouth a key role is played by the tongue. As well as being the location for a horse’s sense of taste its muscular component pushes the food backwards from the incisors into the mouth where it is mixed with saliva and its enzymes, then the tongue again pushes the foods between the upper and lower dental arcs to be ground up. The folds in the roof of the mouth help move the food towards the caudal area and on into the oesophagus.