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Basic
physiology
Shedding
teeth:
When
the young horse sheds it's baby cheek teeth, this will be a
thin piece of tooth, whick in fact is just the top of the baby
tooth crown. When the new permnent starts to move and push on
the baby tooth from underneath, the blood supply to the baby
tooth is cut off and the tooth resorbed piece by piece, leaving
only a thin layer we call caps. I will get deeper into this
also later and what problems unshed caps can cause. The incisor
teeth will losen and fall out when the new tooth pushes and
erupts from the inside of the baby tooth.
Tooth eruption:
The horse's permanent teeth is in a young
normal horse about 6-8 cm long before they start to wear, but
only a small part of the crown (around 1 cm) above the gum line
at all times. The rest is embedded in the bones of the jaws.
The teeth will normally wear down at a speed of 2-3 mm per year,
and new portions of the crown will erupt (move into the mouth)
at the same speed. All the permanent cheek teeth are in wear
by the age of 5, so by the time the horse is 30-35 years old
most of it's reserve crown will be erupted and worn down and
older horses will sooner or later run out of enamel and at the
end run out of teeth altogether. I've seen ponies up to their
40s that still have teeth, so taking good care of them is essensial
to make them last longer. In the young horse you can often see
bumps on the lower outside edges of the lower jaw, these should
be painless and with normal temperature, and they are simply
the ends of the lower cheek teeth (especially the 3rd) embedded
in the jaw. These will dissappear with time as the teeth erupt
into the mouth. With these constantly erupting teeth it is very
important to remember that if the tooth doesn't meet another
tooth in occlusal, or if it doesn't meet properly, you will
develop excessive "growth" (or rather lack of wear)
for this tooth in the form of hooks or ramps, and it is important
to check these horses regularly to avoid more serious problems.
It is a common misunderstanding that the
horse's teeth grow all of the horse's life like the teeth of
rodents do. The tooth has a maximum length at age 4-5, most
of it is embedded in the jaws, and it will just erupt through
the gums until all of the reserve crown has been "used
up".
So, to take good care of our horse's teeth is essensial to make
them last as long as possible, to prevent uneccessary problems
in our older horses.
SEQUENCE
OF TOOTH ERUPTION
| |
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 |
The
chewing cycle:
Take a minute and look at your horse from
the front when it is chewing, you will notice it has a chewing
cycle that needs a lot of movement sideways for the chewing
to be normal. Notice also the difference when he is chewing
grass or when he is chewing pellets and how much less side movement
he will use when eating hard feeds like pellets. In the normal
horse, the extent to which the jaw will move sideways depends
a lot upon the forage given. If a horse cannot move the jaw
properly sideways this is usually caused by high hooks or enamel
points or it can be caused by pain or other restriction of the
temporomandibular joint or the masticatory muscles. Some horses
can do the side movement but still not grind the food, excessive
growth of the incisors can be the problem as they meet before
the cheek teeth do and preventing these from chewing. In the
wild or in pastures the horse will graze for up to 18 hours
a day and the silicates in the grass will wear the teeth evenly
as the horse chews with a full lateral movement of the lower
jaw. When we domesticated the horse and took it into barns and
stables, we changed its diets from grass into hay and pelleted
feed. This makes the horse chew the food differently and with
not as much side movement as when fed grass, with the result
that the teeth will get an uneven wear and sharp enamel points
on the outside of the upper molar archades and the inside of
the lower molar archades. Most owners I let feel the enamel
points are really surprised in how sharp it is, and I tell you,
I have gotten quite a few scratches and pierced finger tips
in my time. As a general rule, horses being kept outside on
good grass all year or most of the year, will have better teeth
and more even tooth wear than a horse kept in a stable fed pelleted
food and hay. Horses seem to have a tendency to prefer chewing
more on one side of the mouth than the other. The cycle of mastication
has been described as to have three phases of movement of the
mandible. 1. The opening stroke 2. The closing stroke and 3.
The power stroke.
Wear:
The horse has so called hypsodont teeth.
It is not covered by enamel all over the crown, they are what
we called "folded" , leaving rings of enamel on the
occlusal surface surrounded by dentin and cement. The components
wear down at different speeds, enamel being the hardest, and
this will create sharp enamel points as the cement and the dentin
is worn down faster.
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