Know your teeth
Human beings have two sets of teeth
---- Primary (milk teeth) and Permanent. There are 20 primary and 32 permanent
teeth. In some people one or more teeth may be absent, or they may have
some extra teeth (supernumerary). Usually the first primary teeth erupt
by 6 months and the first permanent by 6 years of age. Children loose their
milk teeth between 6 and 11 years of age. By the age of 13 years almost
all the permanent teeth have erupted: 8 incisors, 4 canines, 8 premolars
and 12 molars. The last 4 molars commonly known as wisdom teeth appear
much later, between 18 to 21 years. The main function of your teeth is
to chew and cut food. Anterior teeth are used to bite and tear food while
the posterior teeth help in chewing. Hence your dental health is an important
part of your general health and your overall well-being.
A tooth mainly has four layers:
- Enamel
- Dentine
- Pulp
- Cementum
Enamel
is the outermost layer of the tooth and also the hardest tissue in the
body. It protects the other structures of the tooth and gives the tooth
the strength to bite into anything. It is a translucent layer and depending
upon its opacity a tooth appears whiter or yellowish.
Dentine lies below the enamel
and forms the bulk of the teeth. It is an ivory like substance and is highly
resilient, and absorbs all the pressure you exert on your teeth while chewing.
Erosion of enamel due to carious lesion exposes this surface to the oral
cavity and the tooth becomes sensitive to a variety of stimulus.
Pulp is the central portion
of the tooth and is composed of blood vessels and nerves. If a carious
lesion is not treated at an early stage it reaches this area causing severe
toothache. Once the infection reaches the pulp the tooth can be saved only
through Root Canal Treatment [RCT].
Cementum is the outer most layer
of the root portion of the tooth and is usually under the gum line. Gum
diseases cause the gums to get separated or recede from the tooth surface
exposing the cementum. This makes the tooth sensitive to extreme temperatures
and to sweets.
CROWN ----
This is the part of the tooth that you can see above the gums.
ROOT ----
This part of the tooth within the bone, below the gums.
The root of your tooth is usually twice as long as the crown. The anterior teeth usually have one
root while the posteriors may have two to three roots. Each root have a root
canal inside, which contains the pulpal tissues. If decay spreads into the pulpal
tissues then a root canal treatment (RCT) will be required to save the tooth.
PERIODONTAL LIGAMENT ----
This tissue supports the tooth and
holds it in place in the bony socket surrounding the tooth. It cushions both the tooth and the
surrounding bone against the shock of chewing and biting. During an periodontal
disease these ligaments are destroyed and the tooth becomes mobile.
GUMS ---- Dentists call this the "gingiva."
It covers the bone surrounding your teeth. You should brush and floss
daily to maintain the gingival health.
BONE ---- The roots of your teeth are anchored by bone.
A healthy tooth stimulates and keeps the bone tissues healthy.
Eruption Dates and Sequence of Eruption
There are 20 primary and 32 permanent
teeth. Only 20 milk teeth fall off and new permanent teeth erupt in their place,
the rest of the 12 permanent teeth erupt directly into the mouth, they have no predecessors,
i.e. all the molars erupt directly into the oral cavity.
The first teeth to erupt into the oral cavity are the lower centrals (middle) teeth
at about the age of 5 months, then the upper two central incisors at 6 months.
Next to erupt are the lower two lateral incisors, followed by the upper two
lateral incisors. By 1 year the lower first molars erupt, soon followed
by upper first molars. Then the lower canines and the upper canines. Lower
second molars and the upper second molars erupt into the oral cavity when 2
years of age. By 6 years the lower deciduous central incisors are lost and the permanent
central incisors erupt. Then the upper centrals. During the same period (6 years)
the first permanent molars also erupt directly into the mouth, behind the deciduous
second molars. Next is the lower laterals, upper laterals, upper first
premolars, lower canines, lower first premolars, lower second premolars, upper
canines, upper second premolars, respectively. By 12 years the second molars
erupt directly behind the first molars. The third molars
or wisdom tooth erupt only by 18 - 21 years.
Sometimes the jaws are not large enough to accommodate the last
molars. Theories postulate that in
modern (more evolved) human beings the jaws are smaller and less developed than
those of our prehistoric predecessors. The cooked and soft foods does not
require big strong jaws to chew, unlike the uncooked fibrous foods eaten by
prehistoric man. Theories also suggests that as the human race continues to
develop and evolve, there will be some point in the future when human beings
will no longer have wisdom teeth. In fact, even now in the general population
some people don't have wisdom teeth.
If the milk teeth are lost
at an earlier age due to carries, trauma or any other cause, the permanents may
get delayed to erupt into the oral cavity. The permanents erupt only when 1/2
to 1/3 of the roots of the tooth has been formed.
Sometimes the gums may get fibrosed or thick if the deciduous are lost early and may require surgical
intervention for the normal eruption of the permanent teeth. Supernumerary
(extra tooth) are common in between the upper centrals (mesiodens). This will
require earlier extraction to allow proper positioning and normal eruption of
the centrals.
When the permanent lower or upper centrals erupt by
6 years it is common for them to erupt inside the deciduous incisors. Later they
get pushed out into the arch. Sometimes the upper permanent incisors may get
locked behind the lower permanent incisors. This will require interceptive
orthodontics to bring the upper incisors into normal occlusion (bite).
Interceptive orthodontics may also be required if the child has mouth breathing,
thumb sucking or tongue thrusting. Serial
extractions may be done to prevent proclination of teeth. In many cases after all the care taken the
teeth may erupt misaligned (crooked) and will require orthodontic
correction after all the permanents have erupted (12 - 13 years), for a beautiful smile.
Deciduous or Primary Teeth (Milk Teeth)
| Name of the Tooth |
Number |
Eruption Date |
Shedding Date |
| Central Incisor |
4 Nos:
2 upper
2 lower |
6 - 10 months |
6 -7 years |
| Lateral Incisor |
4 Nos:
2 upper
2 lower |
10 - 16 months |
7 - 8 years |
| Canine |
4 Nos:
2 upper
2 lower |
11/2 - 2 years |
9 - 12 years |
| First molar |
4 Nos:
2 upper
2 lower |
1 - 11/2 years |
9 - 11 years |
| Second molar |
4 Nos:
2 upper
2 lower |
2 - 21/2 years |
10 - 12 years |
|
Permanent Teeth (Adult Teeth)
| Name of the Tooth |
Number |
Eruption Date |
| Central Incisor |
4 Nos:
2 upper&2 lower |
6 - 7 years |
| Lateral Incisor |
4 Nos:
2 upper&2 lower |
7 - 8 years |
| Canine |
4 Nos:
2 upper&2 lower |
11 - 12 years |
| First premolar |
4 Nos:
2 upper&2 lower |
10 - 12 years |
| Second premolar |
4 Nos:
2 upper&2 lower |
11 - 12 years |
| First molar |
4 Nos:
2 upper&2 lower |
6 - 7 years |
| Second molar |
4 Nos:
2 upper&2 lower |
11 - 13 years |
| Third molar (Wisdom Tooth) |
4 Nos:
2 upper&2 lower |
18 - 21 years |
|
* My
Homepage * Know
your teeth * Know
your Gums (Gingiva) * Eruption
Dates * Six
Golden Rules * Brushing\Flossing
Technique * Wisdom
tooth * Tooth
Decay * Extraction
* Dental
Implant * Surgical
Extraction * Orthognathic
Surgery * Asymmetry
of the face * Gummy
Smile * Prognathism{Long
Jaw} * Beggs\Straight
wire{Orthodontia} * Bleaching{Tooth
Whitening} * Habit
Breaking * Interceptive
Orthodontics * Discolouration\Veneers
* Composite\Amalgam
Fillings * Root
Canal Treatment{RCT} * Crown{Porcelain\Castmetal}
* Flap
Surgery/Splinting * Bridges{Porcelain\Castmetal}
* TMJ (Joint)
Disorders * Bell's
Palsy {Facial Paralysis} * Ankylosis{Difficulty
in mouth opening} * Cleft
Lip and Palate * Trigeminal
Neuralgia * In
a Lighter vein
This site is produced, designed and maintained by
Dr Antony George, Trichur
Institute of Head And Neck Surgery (TIHANS),
Shornur Road,Trichur,Kerala-680001,India.
Ph: 0091-0487-335145, 335185
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copyright ŠAug 2000. No part of this website may be transmitted or reproduced
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information, but I assume no responsibility for its use.
updated Aug2002.