Equine Dentistry

Through history, determining the horse's age by its teeth has been widely used for the purpose of insurance, identification and sale of horses. Finding out the age of the horse through the wear of the teeth is not as an exact science as once thought (and still thought), and can be difficult in horses between 8-9 years and 20. The wear of incisors has a lot to do with the individual, the individual diets, bad habits such as cribbing etc, and there can also be differences between breeds. But it is still used as a general guideline.

There are several ways you can look at the teeth to get an idea of the age of the horse.

This is usually easiest to do on the incisors, but if in doubt you can also check the number of cheek teeth the horse has present. See table below for eruption and shedding dates.

Both a year old and a grown horse will have a full set of incisors, so it is important to look at the incisors and determine if they are dedicious teeth or permanent teeth. The baby teeth (decidious) look different from the permanent teeth. The surface of the milk teeth is white and there are usually several grooves on the surface. The permanent teeth are larger, more rectangular and are usually more yellow in colour. The gum margin of the baby teeth incisors is also rounded compared to the margin of the permanent teeth which is more square. If the horse is in the age where they are shedding their incisors, it is easy to tell the difference between the two sets of teeth. Don't try to determine the age of the horse by the incisor wear on the basis of baby teeth.

Check if the horse has aquired canine teeth. Remember that not all horses get tushes, but if they have them the horse is at least 4-5 years old. Mares rarely get them.

	DECIDIOUS (BABY TEETH)	PERMANENT
INCISORS
first	birth- first week	2 ½ -3 years
second	4-6 weeks	3 ½- 4 years
Third	6-9 months	4 ½-5 years
CANINES
	Absent	4-5 years if ever
PREMOLARS
first (wolf)	Absent	5-6 mths if ever
second	Birth-2 weeks	2 ½ years
third	Birth-2 weks	3 years
fourth	Birth-2 weeks	4 years
MOLARS
first	Absent	9-12 months
second	Absent	2 years
third	Absent	3½ years

Check the wear of the incisors occlusal surface - a rough guide. I have added a few illustrations to explain what structures we can see on the wear surface of the incisors at different ages. The pattern seen on the occlusal surface of the teeth has to do with the folding and anatomy of the tooth and the different structures show at different ages because of wear. See the anatomy section for explanations to what the different structures showing actually are. The time for the appearence of these characteristics can vary between horses. Because the shedding/eruption of the central, middle and corner incisor are around a year apart, the wear will also be one year behind when going from the central and outwards. The times mentioned are for the central incisor.

Appearance of the dental star (the time when the dentin filled pulp chamber comes into wear): In the central incisor this is around the age of 6 years. The dental star gradually goes from a narrow line and gets more oval and round and moves to the middle of the tooth when the tooth wears down. The dental star is a yellow-brown structure. It is coloured dark in the following illustations. It is closer to the horse's lip than the cup and later mark is.

The Mark : The infundibulum (a folding in the tooth) is filled with cement, and is usually filled with food pigments and debris at the top. The mark will at first look dark, and later whiter when the dentin shows. When the mark shows, the cup disappears (the cup is actually just an empty space on top of the cement filled infundibulum).

Disappearance of the mark: When the infundibulum is worn away we say that the mark disappears. This will happen at 12-20 yrs and is a very variable and not very reliable factor.

After the mark is gone you will see an enamel ring that marks the bottom of the former filled infundibulum. This will disappear in the early to mid teens in the horse.

This is a 3 year old horse. The central incisor is permanent and the outer edge is in occlusion (wear), the middle and the corner incisors are decidious. The surface of the central incisor is depressed to form a cup.

5 years old. The central incisor has marks, the corner incisor does not have the back edge in occlusion (wear) yet. All incisors are now permanent.

7 years old. The central and middle incisors have a mark and a narrow star. The corner incisor still has a dark mark.

10 years old. The occlusal surfaces of the teeth look more triangular now. The mark is getting smaller and the star wider.

14 yrs old. In the central incisor the mark is now completely worn away, but you can still see it in the middle and corner incisor. The star is getting bigger. Note how the teeth are now pointing more outwards.

20 years old. The marks in all the incisors are now worn away, and the occlusal surfaces are more rectangular than before in a front to back direction. The row of teeth is narrower from side to side now and is almost in a straight row.

3. Check the shape of the teeth on the occlusal surface of the incisors and the shape of the row of incisors

When an incisor tooth wears down closer and closer to the root, the shape changes from being oval to more rectangular and trapezoid. This is also because of the anatomy of the tooth as you look at a cross section closer and closer to the root. The shape of the row of the incisor teeth change from going longitudally with the row in a younger horse it seems almost to be across in the older horse. Note also how the shape of the occlusal surface changes from oval to trapezoid.

In young horses the upper and lower rows of incisors meet at an angle of about 135°, the older the horse the smaller the angle, meeting at about 90° at the age of 20. In the older horse the incisors will also be longer than in the young horse.

5. The hook - The hook is a little beak that develops on the corner of the upper corner incisors. It is not a reliable sign to determine the age of a horse. It will appear from around the age of 6 and stay for the rest of the horse's life unless it is rasped off or worn down. It is developed simply because the upper I3 is slightly wider than its corresponding tooth and will not wear like the other teeth do.

6. Galvayne's groove - this is a line that runs longitudinally on the upper corner incisor, and it shows first by the age of around 10. By the age of 15 it streches half way down the tooth and by 20 all the way down the crown. It has been showed however, that not more than 50% of horses actually get this feature.