Dental Anatomy of the Horse
::The Horse's Teeth::


The horse, like most other mammals, have two sets of teeth during their life. They are born with one set of baby or decidious teeth (or get them from the age of a few weeks/months), and until a new and expanded set of permanent teeth replaces them gradually. In the full set of teeth in an adult horse each quadrant of the mouth contains 3 incisors, 1 canine (not always), 1 wolf tooth (may or may not be present), 3 premolars and 3 molars. The temporomandibular joint is also marked as this joint can be affected by dental problems and also cause them. The premolars are molars that had precursors before them (baby teeth or decisoius teeth), the molars come in addition in the grown horse.

The names:
Incisors are the front teeth of the horse, then there is a space we call the bars where the bit rests, and then behind the angle of the mouth and towards the back of the mouth back there is a row of premolars and/or molars or cheek teeth.

Decidious teeth (baby teeth, milk teeth):
The full set of baby teeth in the horse counts 3 incisors and 3 cheek teeth in each quadrant of the mouth (a total of 24 teeth). The central incisor and the 3 cheek teeth are usually present at birth or right after, the middle incisor at 4-6 weeks and the corner one at 6-9 months.

Permanent teeth:
Between the age of 2,5 yrs and 4,5 yrs the normal horse will shed all these baby teeth to be replaced by permanent ones. From the age of 1 year and upwards, the young horse will also get 12 new additional cheek teeth, possibly also 4 canine teeth (mostly in stallions and geldings) and from 0-4 wolf teeth.

So at the age when we ask the most of our young horses, especialy racehorses that are trained and raced early in life, they are in the process of shedding 24 teeth and aquire from 36-44 new ones (a full set of permanent teeth). It is not hard to understand it can and will cause the horses pain and discomfort when we put a bit in their mouth, tighten the nose band, use a tongue tie and pull on the reins. Sharp enamel and discomfort from shedding and erupting teeth is something that should seriously be considered a potential problem.

We teach out horses to yield to pressure, it is not surprising they get confused when they try to be good and get mixed signals from the pain inflicted on them when we pull on the bit and expect them to move towards pressure (pain).

Wolf teeth:
The wolf tooth, if the horse gets any at all (this varies), is a sharp little pointy tooth just in front of the row of cheek teeth. They are rudimentary premolar teeth (named pm1) with no real function in the modern horse. The size of both the crown and root of the wolf tooth varies a great deal. It is considered to be a permanent tooth as we don't see any shedding. A horse can get from 0-4 of these teeth, and they are usually removed as they are often sharp, and because of the bit, they can cause problems in the modern sports horse. The wolf teeth can also be unerupted or "blind" and can be felt as little bumps in the gum. Blind wolf teeth can also cause soreness in the gums and cause problems as they are often dislocated a little further into the space between the incisors and the cheek teeth where we put the bit. We most often see them in the upper jaw, but in some horses (especially the standardbred horse) it is not uncommon to also get wolf teeth in the lower jaw (and often unerupted). Eruption of the wolf teeth usually occur from 5-6 months of age. They are usually removed to avoid problems later.

Canine teeth (tushes):
The canine teeth are located in the space beween the incisor row and the molar row (this area is called "the bar"), and the canines in the lower jaw are located a little further towards the incisors than they are in the upper jaw. They are not in occlusion with each other. It is mostly the male horses that get canine teeth, but you can see them in the occasional mare also (25-30%), but then usually very small or as a bump on the bar unerrupted. In the male these teeth can get quite long and razor sharp, getting to be a tremendous weapon, especially around the age when the stallion is on top physically and sexually mature, and would normally defend the rights to a herd. In the older stallion the canine teeth will get worn and more blunt, and is not as efficient as before. There are no decidious set of canine teeth, only permanent. They erupt between the age of 4-5 years. Sharp and pointy canine teeth are usully rounded off to prevent accidents to happen.

The incisors:
The incisor teeth are not as folded as the molars are, but are to some degree. The mass of the tooth is made up by dentin, and this is covered by enamel and an outer layer of cement. When the teeth erupt they have a yellowish look because there is a layer of cement covering the enamel. This will wear off. There is a folding at the top, making up an infundibulum. The top of this is open and is called a cup, the lower portion is filled and is known as the mark. The insides of the infundibulum is because of the folding, also covered by cement and enamel. The pattern that shows with wear on the occlusal surface of the incisors because of this anatomy, is one of the techniques that has been used for a long time in determining age in horses. The structure known as the dental star, is in fact the pulp cavity filled with secondary dentin, brown-yellowish in colour. The dentin fills out the pulp cavity to protect the pulp's sensitive nerves and vessels from external factors. The whole tooth is curved and is approximately 7 cm long. The cement on the outside of both incisors and molars also works as a fastening point for fibres of periodontal membranes and is neccessary for holding the tooth in the bone socket of the skull.

The molars:
The horse has so called hypsodont teeth. Roughly explained they are folded teeth covered by cement and enamel, and there will be rings and ridges of enamel surrounded by cement and dentin on the occlusal surface. The former pulp chambers will be filled with secondary dentin as the tooth wears down. The reserve crown is very long in the young horse, and it lies embedded in the bones of the skull. When the erupted crown wears by a 2-3 mm every year, it is refilled with new tooth. Eventually the horse will run out of reserve crown. With normal wear, and no disease, the teeth will usually last until the age of 30-35. The molars in the lower jaw are narrower than it its counterparts in the upper jaw, and they have 2 main pulp caveties. The molars in the lower jaw usually has two roots (M3 has 3). The molar from the upper jaw has five pulp cavities filled with secondary dentin. The molars of the upper jaw usually develops 3 roots, some times 4.

The jaws:
The horse has a wider upper jaw than lower jaw, this will affect the teeth in a way that makes them wear more on the inside of the upper molar and the outside of the inside where there is occlusion. Sharp points of enamel will develop all along the outside of the upper cheek teeth and the inside of the lower cheek teeth and cause pain, ulceration and infections in the horse's mouth.

Reserve crown and roots:
The reserve crown is very long in a young horse, but gets worn down with age. The real roots develop after the permanent tooth has been in wear for a while.