A young foal has 24 deciduous teeth also known as milk or temporary teeth by the time it is approximately nine months old.
These deciduous teeth are replaced during the next five years with between 36 and 44 teeth appearing by the time the horse is five years old. The average number of permanent teeth in a male horse is 40, with an average of 36 permanent teeth in a female horse. This variation in number of teeth occurs because a male horse often has several canine teeth, while they are either absent or rudimentary in the mare and some horses have wolf teeth that don't need to be removed.
The top surface or crown of the horse's tooth is covered by hard enamel which is resistant to bacteria and acids. Underneath the enamel is the dentin which is a softer material. Beneath the dentin is the pulp of the center of the tooth that contains blood vessels and nerves.
The root of each tooth is covered by cementum that attaches the tooth to the periodontal membrane which connects to the bony socket in the horse's jaw.
The teeth of a horse are much longer than human teeth with up to four inches of tooth embedded in the bone of the upper and lower jaws. A horse's teeth continue to grow or erupt throughout the horse's lifetime growing at a rate of approximately 1/8 inch each year. They are continually being worn down by the grinding action necessary to thoroughly masticate the feed the horse eats.
The horse's digestive system requires that all feed be thoroughly ground before being swallowed for the horse to receive maximum nutrition from the feed.
In the process of grinding the feed, the horse's jaw moves both up and down and from side to side. Because of the structure of the horse's jaws and teeth, this grinding action often causes uneven wear of the teeth resulting in sharp points that need to be removed or floated on a regular basis so the horse can chew its feed satisfactorily.
Arrangement of a horse's teeth
At the front of the horse's mouth are the incisors which are used to bite or cut off pieces of feed. Most horses have six incisors on the top and six on the bottom for a total of twelve incisors.
A male horse usually has has up to four canine teeth in back of the incisors and in front of the three premolars. These teeth are tusk-like and sometimes protrude.
Wolf teeth which are extra teeth are vestiges of the first premolars and may be found adjacent to the front premolars. They are often needle-like, and, if they interfere with the bit or cause alignment problems, they should be extracted, usually at 18 to 24 months.
Next in position are the premolars, three in number on each side of the upper and lower jaws for a total of twelve premolars.
Behind the premolars are additional molars also known as cheek teeth or jaw teeth. These twelve molars are evenly divided on each side of the upper and lower jaws. The horse's molars do the major work of grinding the horse's feed so it can be digested satisfactorily.
Relationship of teeth to bit
Between the cheek teeth and the incisors or canine teeth of most horses is a space known as the interdental space. This space provides a place where the bit can rest without having the jaws open or having the bit rest uncomfortably on the horse's teeth.
In some cases, a veterinarian or equine dentist will file a "bit seat" in the first cheek tooth if the horse does not have adequate natural space in its mouth for the bit to rest comfortably.
In all cases the correct bit for the horse should be selected and care should be taken in adjusting the bridle so that the bit does not rest too low or too high, where it pushes against the teeth causing discomfort.
Individual horses and some breeds and types of horses vary widely in the eruption timelines of their teeth.