Saturday, June 4, 2011

How Many?

I had a 4-H leader ask me the other day how many teeth do horses have? Sounds like a simple enough question, but the answer is not. It is influenced by several different variables such as age, gender, if any have ever been removed, and if there are any extra ones present. Let me explain.

Let’s start with the basic dentition pattern of the horse. The major teeth of the horse are the incisors, canines, premolars and molars. There should be 6 incisors top and bottom. These are the teeth at the very front of the mouth that are very easy to see. There are 4 canine teeth, two on the top and two on the bottom (one on each side of the mouth). These teeth sit behind the incisors, but in front of the premolars. The bit sits in the space behind the canines, but in front of the pre-molars. The typical adult horse has 12 premolars and 12 molars. They are oriented in a straight row, front to back, top and bottom, on each side of the mouth, with the 3 premolars in front of the 3 molars. With the two top rows, one row on each side, and the two bottom rows all of 6 each, we end up with 24 cheek teeth in all. So in the normal adult male horse we should have 24 cheek teeth (12 molars and 12 premolars), 4 canines, and 12 incisors for a total of 40 teeth. But that is not the whole story.

How many teeth a given horse is influenced by his/her age. The canine teeth do not usually erupt until 4-6 years of age. The last molar does not come in until about 3.5 years of age. The last ‘baby tooth’ is replaced by an adult tooth around 4 years of age.

Gender plays a role in all of this as well, primarily because most mares usually do not develop canine teeth. If they are one of the 28% of mares that have them, they are usually much smaller than those in a stallion or gelding.

Wolf teeth are typically removed at a very young age. They are technically a rudimentary first premolar and can vary tremendously in their eruption pattern. Some horses never get them, some have only one, but most have 2 (one on each side). They are almost always just on the top. It is rare to see wolf teeth on the lower jaw. They do not serve any function for eating or chewing. They often cause bit related problems due to their location and small size. If present, they will sit just in front of the cheek teeth, but well behind the canines. This is the same place that the bit rests in the mouth. We occasionally see them in older adult horses, but most horses have them removed when they are young.

On rare occasion we will encounter a horse with a supernumerary tooth (an extra one). Here is a picture of one I saw just yesterday. It is hard to tell from the picture, but the really long tooth way in the back is actually the seventh tooth back (remember there are only supposed to be 6). Since there is not a seventh tooth on the bottom the upper one just keeps growing and growing. This tooth was an otherwise normal appearing tooth, so we just shortened it with the aid of a motorized burr so that it is no longer rubbing on the opposing gum. This tooth will have to be maintained throughout this horse’s life because it will continue to grow.

So there is the long answer to how many teeth a horse has. The short answer is 36 to 44 in an adult, depending on if canine and wolf teeth are present. If you really want to know exactly how many teeth your horse has, ask your vet next time your horse’s teeth are done and they can give you the exact count for your horse. Of course, that may not be the answer your 4-H judge is looking for.

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