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COLLECTION: GOAT HANDBOOK
ORIGIN: United States
DATE INCLUDED: June 1992
Extension Goat Handbook
This material was contributed from
collections at the National Agricultural Library.
However, users should direct all inquires about the
contents to authors or originating agencies.
DOCN 000000047
NO F-4
TEETH
G. F. W. Haenlein R. Caccese; U. of Delaware, Newark
D. L. Ace; Pennsylvania State U., University Park
Anatomy and Physiology
1 Goats, being herbivores, obtain the greatest portion
of their sustenance from plant materials which are
of low or no nutritional value to man. Through mastication,
regurgitation and rumination of these materials by
their teeth, especially the molars, the plant materials
are reduced to small particle sizes, thus increasing
their relative surface areas and making them easier
to be digested. Much of the grinding action of the
teeth is the direct result of their surface angles
and rotary-like movements of the lower jaw. The combination
of lateral and vertical movements is due to the fact
that upper and lower jaws are not perfectly matched,
but the lower jaw is somewhat smaller than the upper.
Food material can therefore be chewed only from one
side of the mouth at a time through a lateral grinding
action. Such will result in a pattern of wear that
causes the teeth to develop points on the outer edges
of the upper molars and the inner edges of the lower
molars. Only after action of the teeth has reduced
plant materials to a finely ground pulp, can effective
digestion begin.
2 With goats as with other ruminants,
complete chewing is not done at the actual time of
grazing. Later, at the animal's leisure, the materials
are ruminated and rechewed until the feed particles
are small enough to be passed on in the digestive
tract.
3 Throughout the process of mastication
the tongue and cheeks are constantly in motion, keeping
the feed material moving between the teeth until it
has been ground well enough to be formed into a bolus,
which then can be moved back in the mouth and swallowed.
4 Mastication is basically a voluntary
act under the control of brain centers, although in
practice it appears more like an autonomic process.
Mastication is dependent on sensory stimulation, with
the 5th cranial nerve (trigeminal) being mainly responsible.
Effector impulses travel the route of this nerve to
the elevators of the jaws and along the 7th cranial
nerve (facial) to the digastric muscle, and the lip
and cheek muscles. Impulses may also travel the 12th
cranial nerve (hypoglosseal) to the muscles of the
tongue.
5 Teeth are generally classified
as being of two types according to their permanence:
the temporary milk teeth and the permanent adult teeth.
6 Milk Teeth Milk teeth are present
either at birth or shortly afterwards and will remain
for about a year before replacement with permanent
teeth begins. Milk teeth are not as hard nor as numerous
as adult teeth, since the adult teeth are expected
to remain and function throughout the life of the
animal.
7 The continual growth of the tooth
root, along with other factors, serves to push the
crown of the milk teeth up and out of their sockets,
through the overlaying segments of the dental sac
and gum. The actual time period for the eruption or
''cutting'' of the teeth, while providing a general
indicator of age in the goat, is not the same for
all goats. Variances according to breed, climate and
nutritional conditions will cause differences in the
actual time of teeth eruption among individual goats.
8 Adult Teeth Permanent teeth undergo
more progressive development. They press against the
tissues of the milk teeth and cause the roots of the
milk teeth to break down. This in turn releases the
dental pulp from its anchorage in the gum. With tissues
loosening and exerted pressure from the rising permanent
teeth, the milk teeth are shed from the jaw.
9 Tissues surrounding the developing
teeth undergo a developmental process that differentiate
the mesenchymal tissue from the connective tissue
which make up the dental sac. The dental sac, where
the teeth roots will be, takes on three important
functions. The inner cells differentiate into a layer
of cementoblasts at the time of eruption. As the epithelial
sheath breaks down and disintegrates in a downward
direction, the cementoblast cells deposit cement upon
the dentine of the teeth. This deposition occurs from
the neck region downward. The surface of the dental
sac becomes active in bone production as the calcification
process of the jawbone progresses. The tooth becomes
surrounded by spongy bone, occupying its own socket.
The fibrous sac itself forms a thin membrane which
serves to hold the tooth in place by embedding some
fibers in the cement and others in the bony wall of
the socket.
10 Teeth can be further classified
into three groups according to the way in which they
grow: true teeth, constantly growing teeth, and constantly
erupting teeth. Of the three, goats have two: true
teeth and constantly erupting teeth.
11 True Teeth The incisors of the
goat are considered to be true teeth in that they
posses a crown, a root and neck, growing to adult
size before they begin to gradually wear away.
12 Erupting Teeth Constantly erupting
teeth are found in the goat in their molars. This
type of tooth is made up of layered masses, possessing
very long roots and no real neck. As the goat ages,
these teeth are gradually forced upward, to account
for wear, by the desposition of bone into the jaw
below them. In the case of very old animals, such
teeth may actually be forced out by this rising action.
13 Tooth Composition True teeth are
composed of five parts and four tissues. Constantly
erupting teeth have but four parts, as they have no
neck. The crown of the tooth is the part which appears
above the gum line, while the neck is located at the
gum line. It appears as a narrowing that separates
the crown from the root. Implanted into the tooth
socket of the jaw is the root, which may be either
singular, paired, or multiple, depending on what type
of tooth it is. The central cavity of the tooth that
runs from the base of the root up into the crown is
known as the pulp cavity, containing the dental pulp,
vessels and nerves. This cavity is large in young
animals, but over time it becomes infiltrated with
dentine and may be completely filled in old goats.
The table surface is that part of the tooth that is
actually used for grinding or tearing of the food.
14 Cement is the second hardest tissue,
and is found as the outermost layer covering the tooth.
In true teeth, this yellow to black substance covers
the roots only. Enamel, the hardest tissue of the
body, is the next layer, covering the dentine of the
tooth. Its coloration is about that of ivory. Under
the enamel lies the tissue that forms the bulk of
most teeth, dentine. This substance, which is hard
and yellowish, covers the pulp of the tooth, supporting
numerous blood vessels and nerves.
15 Dental Development All ruminants,
including goats, lack upper incisors. Instead there
is a hard dental pad on the frontal part of the upper
jaw which serves in place of teeth. The dental formula
for goats is 0033/4033. The formula is derived from
the number of teeth the animal has in one half of
the upper and lower jaws. The four digit system for
each jaw half is beginning in the jaw center with
the numbers on the left reading incisors, canines,
premolars and molars, respectively. The numbers in
the top part of the formula represent one half of
the total teeth of the upper jaw, and the bottom portion
represents one half of the total for the lower jaw.
The mature goat will have, therefore, a total of 32
teeth, of which eight are lower incisors and the rest
are arranged in four groups of six molars each. The
appearance of the two first teeth (milk teeth incisors),
occurs at birth to one week of age. The second pair
of milk teeth incisors appears at about 1-2 weeks
of age, while the 3rd and 4th milk incisors appear
at 2-3 and 3-4 weeks of age, respectively.
16 The pattern for the eruption of
permanent incisors is between 1-1 1/2 years of age
for the first pair of incisors, 1 1/2-2 years for
the second pair, 2 1/2-3 years for the third and 3
1/2-4 for the fourth set of incisors. Beyond this
4 year period, age can only be estimated by the amount
of wear that has occurred on the teeth. As a goat's
age increases, the teeth are worn down from the rectangular
crossectional shape to a more rounded shape.
17 Older goats with one or two teeth
missing are referred to as ''broken mouthed'' and
goats with more than two teeth missing are called
''smooth mouthed''.
TEETH
COLLECTION;GOAT HANDBOOK
ORIGIN;United States
DATE_INCLUDED;June 1992
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