Fossil samples dating back as far as 55 million years ago
can help us determine how long horses (on average) lived.
55 million years ago the average longevity of the hyracotherium
was 5 years of age. 20 million years ago during the Miocene,
analysis indicates longevity of up to 15 years. 10 million
yeas ago during the Pliocene period Equus population was thought
to live up to 25 years.
Horses are herbivores and there teeth are designed for breaking
down the hard structures like cellulose found commonly in
the horses diet. They have what are known as hypsodont teeth,
meaning continuous eruption of the reserve crown of the tooth.
This matches the loss of tooth from the grinding down caused
during mastication. Numbers of teeth Horses have 24 deciduous
teeth (non permanent) and 36 to 44 permanent. The numbers
of permanent teeth can vary mainly depending on gender. Male
horses normally have 4 canine teeth; mares are often seen
without any. 4 wolf teeth can sometimes be seen in horses
although 2 on each arcade on the upper jaw are most common.
Male and female horses alike can show wolf teeth.
Types of teeth
There are 5 different teeth that can be found within horses'
mouths. INCISORS These are the teeth situated at the very
front of the horses' mouth. They are used in a pincer like
action for nipping biting and defence. There are 12 in total,
6 on the top jaw 6 on the lower jaw. Incisors are used to
age horses. The occlusal surface of each tooth changes in
appearance dependant on how old the horse is. Initially these
teeth are more oval in shape but as the horse ages the shape
of the incisors become triangular. The Galvaynes Groove is
seen on the corner incisor teeth. This is a longitudinal line
that appears also used when ageing horses
Canine teeth are situated caudally to the incisors. There
can be 4 in total. They are curved in shape with most of the
tooth still under the gum line. They can be up to 7cm in length.
They are relatively simple teeth that the ancestors of today's
horses' would have used for defence.
FIRST PREMOLAR (WOLF TOOTH)
The wolf tooth is a small simple brachydont tooth, (short
crown) although it can range in size from 1-25cm. There can
be 4 in total. The roots of this tooth can vary from being
non existent to being up to 30mm in length. These teeth can
sometimes be found to erupt in varying places throughout the
horse's mouth although more commonly they are situated just
in front on the first cheek tooth.
PREMOLARS AND MOLARS (CHEEK TEETH)
Cheek teeth form 4 rows of 6 teeth that are accommodated in
the maxillary (top jaw) and mandibular (bottom jaw) bones.
These teeth are more rectangular in shape when a cross section
is taken (down the transverse plane). The teeth on the maxillary
arcades (rows) are wider and squarer than teeth on the mandibular
arcades which are narrower and more rectangular. Ridges are
seen on the buccal (outside) edges of the maxillary arcades
in particular. Many dental overgrowths are a common occurrence
Tooth growth is seen on average at 2-4mm per year. The occlusal
surfaces of these teeth are ridged to increase the amount
of surface area for breaking down food. These teeth are used
to grind foodstuffs in a circular sideways action.
Mastication (the chewing cycle) The horses head is Anisognathic,
(a-nee-so-nay-thic). Basically the top jaw is wider than the
lower jaw. Mastication begins using the lips and incisors
to nip the e.g. grass. The horse whilst grinding the grass
between its cheek teeth uses its muscular tongue and ridges
on the upper pallet to gradually work the food to the back
of its mouth in a circular (spiral) motion and then swallows.
Horses can only chew on one side of their mouth at a time,
changing from one side to the other would mean they would
drop the food. A horse should be comfortable to eat on both
sides of their mouth. A horse has a great amount of lateral
excursion (sideways movement) within their jaw. When eating
lush feeds there is a greater amount of movement than when
the horse eats dry feeds.
The temporomandibular joint This is the joint joining the
lower jaw to the head. It enables the jaw to move and laterally
has a great range of movement; up and down the movement is
limited. Unlike carnivores horses have a transverse power
stroke in a lingual direction (towards the tongue), associated
with their mastication cycle. Joints should wear evenly. If
horses' teeth wear unevenly, it can cause pain within this
joint due to uneven pressures being placed on it.
Structure of equine teeth ENAMEL Enamel is the hardest and
most dense substance in the body. It has a very high (96 -
98 %) mineral content making it almost translucent. Due to
the absence of cellular inclusions (unlike dentine or cement)
enamel can be regarded as dead tissue. It has no ability to
repair itself once its ameloblasts die off. Enamel varies
in thickness up to 3 times throughout areas of the tooth parallel
to the long axis of the jaw but remains constant throughout
the length of the tooth. Invaginated folds on the occlusal
surface give strength to the tooth where the softer dentine
The bulk of the tooth is made up of dentine; a cream coloured
softer tissue comprising of approximately 70% minerals, 30%
organic compounds and water. The type of tooth (shape and
size) along with the compressibility and percentages of different
organic components contributes to its overall strength.
The presence of dentine and cement dispersed between the
hard enamel folds forms a very strong durable structure suitable
for its purpose. Odontoblasts can synthesize dentine throughout
their lives. This prevents the occlusal surface of the tooth
from exposing the pulp during normal attrition.
There is a close working relationship between dentine and
pulp with some of the structures of each working through each
other. This sometimes leads to them acting as a single unit.
Dentine is considered a sensitive living tissue.
Young tooth before eruption. Note the presence of cement
and enamel covered by the dental sac and the large pulp chamber.
PULP Pulp is soft tissue within the tooth that contains
a connective tissue skeleton consisting of fibroblasts, thick
collagen, connective tissue cells i.e. Odontoblasts, numerous
blood vessels, allowing for continuous dentine deposition
and nerves. Pulp is found in large quantities in and around
developing teeth. With age more secondary dentine is laid
down as development of the tooth, requiring large quantities
of pulp, ends. This makes them stronger and more solid.
Later in the tooth development the pulp chamber has formed
two horns due to the laying down of dentine within the pulp
Cement / cementum are a cream coloured calcified dental tissue
characteristically similar to bone. Its mineral and inorganic
compound make up are similar to dentine and give it its flexibility.
The extensive collagen fibres found within the inorganic component
of cement are what attach the cement to the alveolar bone,
stabilising the tooth. Cement is a living tissue nourished
by the vasculature of the periodontal ligament (attaches cement
on tooth to socket).
About the Author
Tammy is a passionate horse rider who wishes to advertise the
best ways to be treating horses. Tammy works part time for a
company who specialise in equine
dentistry equipment as well as carbide tipped saw blade
in the UK. For more info, please visit, Equine Dentistry Blades.