Home Dentistry Articles Tooth
Teeth-singular tooth-are hard structures found in the
jaws of many vertebrates. They have various structures
to allow them to fulfill their many different purposes.
The primary function of teeth is to tear and chew food
and in some animals, particularly carnivores, as a weapon.
The roots of the teeth are covered by gums. The color
of teeth is supposed to be white, but it heavily depends
on the person, and how well they care for their teeth.
Teeth are covered by a protective stucture, called the
enamel, that helps to prevent cavities on the teeth. Adult
teeth naturally darken as the person matures, the pulp
within the tooth shrinks and dentin is deposited in its
The form teeth take and their mode of development in
a species is called the species' dentition. Dentists sometimes
refer to the inner surface of teeth as the lingual surface
(meaning towards the tongue), and the outer surface as
the labial surface (meaning towards the lips) or "buccal"
(meaning towards the cheek). Other terms are mesial (toward
the midline), distal (away from the midline), occlusal
(the top surface), incisal (the cutting surface), "gingival"
(toward the gumline), and "pulpal" (toward the
Types of teeth
- Molars are used for grinding up foods
- Carnassials are used for slicing food. In carnivores
- Premolars are similar to molars but smaller and sometimes
- Canines are used for tearing apart foods and sometimes
- Incisors are used for cutting foods
Teeth are among the most distinctive features of different
mammal species, and one that fossilizes well. Paleontologists
use them to identify fossil species and, often, their
relationships. The shape of the teeth is related to the
animal's diet, as well as its evolutionary descent. For
example, plant matter is hard to digest, so herbivores
have many molars for chewing. Carnivores need canines
to kill and tear and since meat is easy to digest, they
can swallow without the need for molars to chew the food
Types of tissue in teeth
- Enamel is a hard outer layer consisting of calcium
- Dentin is the inner layer, the bulk of the tooth.
- Pulp is the core, containing nerves and blood vessels.
- Cementum is the thin layer around the root; a bone-like
material which connects the teeth to the jaw.
- Teeth lack enamel and have many pulp tubules, hence
the name of the order Tubulidentata.
Humans grow two sets of teeth, though some animals grow
many more: sharks grow a new set of teeth every two weeks.
Some other animals grow just one set. Rodent teeth grow
and wear away continually through the animal's gnawing,
maintaining constant length
In humans, the first (a.k.a. milk, primary or deciduous)
set of teeth appears at about six months of age. This
stage is known as teething and can be quite painful for
an infant. Human children have 20 milk teeth evenly distributed
across the quadrants. Each quadrant of 5 teeth consists
- central incisor
- lateral incisor
- first molar
- second molar
The second, permanent set is formed between the ages
of six and twelve years. The new set replaces the 20 teeth
of the old set. A new tooth forms underneath the old one,
pushing it out of the jaw. Apart from this another 8-12
teeth grow. This set can last for life if cared for properly
through a regular program of dental hygiene, including
brushing with water or toothpaste as well as periodic
professional cleaning by a dentist or hygienist. If a
person's teeth are susceptible to decay, for example if
the molars include deep pits and fissures, then complete
prevention of decay may require treatment with dental
Adult humans have 32 teeth evenly distributed across
the quadrants. Each quadrant of 8 teeth consists:
- central incisor
- lateral incisor
- first bicuspid
- second bicuspid
- first molar
- second molar
- third molar
The last molar of each quadrant (i.e. the third molar
and commonly referred to as wisdom teeth) may or may not
The teeth are numbered, in the most common American system,
1-16 and 17-32, with 1 being the upper right wisdom tooth
(whether or not it is present) and 32 being the lower
right wisdom tooth.
Plaque is a soft white layer which forms on
teeth, containing large amounts of bacteria of various types,
particularly Streptococcus mutans. Left unchecked for a few
days plaque will harden, especially near the gums, forming tartar.
Certain bacteria in the mouth live off the
remains of foods, especially sugars. In the absence of oxygen
they produce lactic acid, which dissolves the calcium and phosphorus
in the enamel in a process known as demineralisation. Enamel
demineralisation takes place below the critical pH of about
Saliva gradually neutralises the acids causing
the pH of the tooth surface to rise above the critical pH. This
causes 'remineralisation', the return of the dissolved minerals
to the enamel. If there is sufficient time between the intake
of foods (two to three hours) and the damage is limited the
teeth can repair themselves.
Dental caries (cavitation) occurs when over
a period of time the process of demineralisation is greater
than remineralisation. Attempts to prevent dental caries involve
reducing the factors that cause demineralisation, and increasing
the factors leading to remineralisation. Unchecked demineralisation
leads to cavities, which may penetrate the underlying dentine
to the tooth's nerve-rich pulp and lead to toothache.
In moderation, fluoride is known to protect
the teeth against caries. It toughens the teeth by replacing
the hydroxyapatite and carbonated hydroxyapatite minerals of
which the enamel is made with fluorapatite, which is harder.
It also reduces the production of acids by bacteria in the mouth
by reducing their ability to metabolize sugars. The addition
of fluoride (sodium monofluorophosphate) to toothpaste is now
very common, and may explain the decline in dental caries in
the Western world in the past 30 years.
Some believe that a diet rich in fluorine salts,
particularly in childhood, can lead to a stronger enamel which
is less susceptible to decay. Fluoridation of drinking water
remains a controversial issue. However, in many parts of the
world, the natural water supply may be sufficiently rich in
fluorides to supply the needs of children without additional
sources being required.
Caries may be treated by filling cavities with
a long-lasting material. This was, traditionally, achieved using
gold or a compound of metals called amalgam, which contains
mercury. For cosmetic reasons, and because it is thought mercury
may seep from fillings into the circulation over time, a ceramic
or other white filler may be preferred to amalgam. As a last
resort, teeth affected by caries may be extracted, preferably
under local or general anaesthetic.
Most foods endanger teeth to some extent. By
far the best protection is brushing after meals and snacks.
However, some foods are worse than others.
Some foods may protect against caries. Milk
and especially cheese appear to be able to raise pH values in
the mouth and so reduce tooth exposure to acid. Milk and cheese
are both rich in calcium and phosphate and may also encourage
remineralisation. Plus, they may increase saliva production
which increases the pH level in the mouth. Foods high in fibre
may also help to increase the flow of saliva. Unsweetened (sugar
free) chewing gum stimulates saliva production, and helps to
clean the surface of the tooth (even sugary gum may be helpful,
since the sugar dissolves out very quickly).
Sugars are commonly associated with dental
caries. Other carbohydrates, especially cooked starches, eg
crisps, may also damage teeth, although to a much lesser degree.
This is because starch is not an ideal food for the bacteria.
It has to be converted (by enzymes in saliva) first.
Sucrose (table sugar) is most commonly associated
with caries, although glucose and maltose seem equally gervic
(likely to cause caries). The amount of sugar consumed at any
one time is less important than how often sugar containing foods
and drinks are consumed. The more frequently sugars are consumed,
the greater the time during which the tooth is exposed to low
pH levels, at which demineralisation occurs. It is important
therefore to try to encourage infrequent consumption of food
and drinks containing sugar so that teeth have a chance to repair
themselves. Obviously, limiting sugar-containing foods and drinks
to meal times is one way to reduce the incidence of caries.
Artificially refined sugar is not the only
type that can promote dental caries. There are also sugars found
in fresh fruit and fruit juices. These foods (oranges, lemons,
limes, apples, etc. ) also contain acids which lower the pH
level. On the other hand, carbonic acid found in soda water
is very weakly acidic (pH 6.1), and not associated with dental
caries (provided the soda is sugar free, of course). That said,
soda is not as healthy for the teeth as milk, due to its lower
pH and lack of calcium. Drinking sugared soda throughout the
day raises the risk of dental caries tremendously.
Another factor which affects the risk of developing
caries is the stickiness of foods. Some foods or sweets may
stick to the teeth and so reduce the pH in the mouth for an
extended time, particularly if they are sugary. It is important
that teeth are cleaned at least twice a day, preferably with
a toothbrush and fluoride toothpaste, to remove any food sticking
to the teeth. Regular brushing and the use of dental floss also
removes the dental plaque coating the tooth surface.
Regular brushing is recommended by healthcare
professionals, though not too hard . Two minutes maximum, without
pressing the brush too hard against the teeth and gums. In research,
levels of plaque were recorded before and after brushing and
found that plaque removal steadily improved as brushing times
and pressure were increased. However, their results showed that
when people brush for longer than two minutes, at a pressure
higher than 150 grams (the weight of an orange), they aren't
removing any additional plaque, and may be causing permanent
damage to the teeth and gums.
Brushing teeth immediately after eating sugar
is not recommended, because sugar softens the enamel, which
can then be damaged by brushing. It is better to wait half an
hour after eating sugary foods before brushing.
Electric toothbrushes are no more effective
than the manual variety, according to research. However, "rotation-oscillation"
electric toothbrushes out-performed manual brushing, removing
around 7% more plaque and leading to 17% less gum disease than
manual brushes. Any kind of electric toothbrush does tend to
help people who are not as good at cleaning their teeth and
as a result have had oral hygiene problems.
As noted above, eating certain cheeses such
as cheddar soon after eating potentially harmful foods have
been noted to be helpful in preventing tooth decay as well.
In the future, tooth decay may be banished
by treatment with a genetically modified bacterium, according
to research at the University of Florida.
Dentures and false teeth
In societies that have high sugar diets, tooth
decay can damage teeth badly enough that they need to be removed.
This leads to the creation of replacement teeth such as dentures
and other tooth replacements.
Some of the earliest false teeth were made
by the Etruscans and their use was adopted in Ancient Rome for
the wealthy citizens who often dined on food containing damaging
Abnormalities of the Dentition
- Ameleogenesis Imperfecta - A condition in which the tooth's
primary surface, the enamel, does not form properly or at
- Dentinogenesis Imperfecta - A similar condition to above,
but affects the underlying layer of the tooth
- Deossification - Loss of bone tissue
- Dens in Dente (also dens invaginus)
- Dens Envaginus (Opposite of above)
- Supernumerary Roots - More than the normal number of roots
for a tooth. Most common in maxillary bicuspids.
- Dilaceration - Trauma to the tooth during formation causing
damage to the root structure
- Fusion - The union of two adjacent tooth germs by dentin
- Abnormalities with number of teeth
- Hyperdontia (More than the average number of teeth)
- Hypodontia (Missing teeth)
- Abnormalities with size of teeth
Development of Teeth
There are three stages in the embryonic development
of teeth, the Bud Stage, the Cap Stage and the Bell Stage. The
Bud stage begins at the 7th week of intrauterine life.
Facts About Teeth In Non-Human Animals
- Rodents' teeth grow all their lives.
- Reptiles' and sharks' teeth are replaced constantly, before
they wear out. A crocodile replaces its teeth over forty times
in a lifetime.
- Elephants' tusks are specialized incisors for digging food
up and fighting.
- Turtles and tortoises are toothless