2nd - Dental Anatomy#2

7/29/2019 2nd - Dental Anatomy#2

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Last lecture we discussed Dental notation system. We are veryaware of how to name deciduous and permanent teeth according to

different notation systems.

Its important that you remember these are not the only

Dental notation systems but these are the most famous or widely

used in Dental notation systems, and we have other Dental notation

systems that are proposed but they are not very much accepted or

used.

These Dental notation systems are approved by important

help organization across the world, like world help organization

and FDI.

Now, we will talk about the chronology of tooth development

(the timing of tooth development).

This model shows permanent and deciduous teeth at the same time.


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* Remember that permanent teeth are 32 in number (16/jaw,

8/quadrant) compared to 20 deciduous teeth (10/jaw, 5/quadrant),

so we have 8 permanent teeth per quadrant while 5 per quadrantteeth deciduous that means not all permanent teeth are successor

teeth, only 5 of these permanent teeth per quadrant are called

successor teeth; because they succeed teeth existing before them.

-the teeth that succeed are called successor teeth.

-the teeth that exist before and will be succeeded are called

predecessor teeth.

*We have non-successor teeth that are permanent teeth which

erupt without any tooth before them. And these are 1st, 2

ndand

3rd

permanent molar.

** Remember!

1) Incisors succeed Incisors, canines succeed canine but premolars

succeed deciduous molars.

Thats why we refer to premolars without the term permanent;

because we donthave deciduous premolars.

2) Each tooth consist of a crown and a root.

- Crown: the structure that is visible in the mouth.

- Root: the structure that is buried inside bone.

3) Teeth are attached by soft tissue to the surrounding bone called

the periodontal ligament.

Only the root is attached to the bone, the crown is not attached.


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**How permanent teeth replace deciduous teeth??

For the permanent tooth, to succeed deciduous tooth it has tomove in a way to resorb the root of the deciduous tooth until its

totally lost, then it wont be attached to the bone anymore so it will

only remain attached to the soft tissue and later on when the

permanent tooth moves up it even releases the deciduous tooth

from its attachment.

((it become very loose and it can be removed easily while eating

or by the Dr, parents or child him/herself)).

The eruption of teeth is organized & timed. Each permanent or deciduous tooth has a specific time to

erupt and specific sequence of development.

Chronology is the science of timing of tooth development.

This is a skull of a child, before the age of 6 showing

deciduous teeth and permanent teeth at the same time


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-Notice that the permanent teeth are bigger than the

deciduous teeth; because of that they have to appear at

different times.

* If we imagine that the size and number of deciduous teeth

is the same as the size and number of permanent teeth,

In this way if we want to replace deciduous teeth with

permanent teeth, we can replace them at once,

In that time we really dont need deciduous teeth (This case

is imaginary not real!!).

In real, they are different in size and upper and lower jaw

will grow but the teeth won't grow once they are formed,

So the teeth will be replaced one by one as we don't have a

space for permanent to appear in the mouth.

This picture shows the right teeth and part of the left

teeth, they are deciduous teeth (A-E), and above them we

have the permanent teeth (1-6).

-Notice the permanent teeth are developing at

different stages. For examples, while the 1st

molar is at the stage of crown completion,

some teeth like the 2nd molar is at the stage of

very early formation of the cusp.

This picture is imp for the dental lab quiz in the 4th

week; the Dr said that

he will bring it.


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In this picture all the teeth are erupted into the

mouth (1-8), this usually happens approximately

after the age of 18.

- The Earliest timing for appearance of 3rd

molar

is 16 years old and the average is about 22-23 years old.

When the tooth erupts in the mouth, the root is not really

fully formed (not completed) as the root completion is responsible

for pushing the root upward.

*P.S. if the root completed the formation before eruption, it

wont erupt later.

So once the tooth erupts, the root of permanent tooth will

need 2-3 years to be completed, while the root of deciduous teeth

needs about 1-1.5 years. This means usually at the age of 25 yearswe will have completed dentition.


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This slide is a summary of different stages of tooth

formation.

** At the age of3 years,

- Central permanent incisor 1/3 of the crown is formed.

- 1/4 of lateral incisors are formed.

- Less than that for canine & much less than that for premolars.

But notice that the crown of the 1st

molar is fully completed but the

2nd

molar is at the beginning of its formation.

** At the age of4 years,

-Complete formation of the crown and some formation of the root

for the central incisor.

-Lateral incisor and canine half of it is formed.


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-Less than half for premolar & just nearly the cusp for the 2nd

molar.

-Notice the 1st

molar is really advanced in development of the

crown and the root. This means that the 1

st

tooth that starts todevelop is the 1

stmolar not the central incisor (for permanent

tooth!!).

**At the age of6 years, we start to

see the 1st permanent tooth in the mouth

which is the 1st

molar.

**At the age of8 years,

-Most of the root of the 1st

molar is fully-

formed.

-The roots of the central incisors are 2/3

formed. So at this year, we start to see the

permanent incisors in the mouth.

**At the age of10 years,- We start to see the beginning of formation of the 3

rdmolar.

-Also, we have complete closure of the 1st

molar roots.

** At age of9-10 years,

-The 1st

permanent tooth is completed.

** Eruption of teeth is like a

race, but in an organized

way!!


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*Remember*

The root of the tooth shouldnt be fully-formed ( 2/3 is formed

only) so that the tooth can erupt and the other 1/3 will complete its

formation after eruption.* Approximately, what happens in the maxillary is the same

as the mandible; the only difference is the time of development of

the upper & lower canines.

Usually, the lower canine erupts at the age of10 years, while the

upper canine at the same age is still not erupted yet, so usually we

have difference about 2 years between erupting of lower and upper

canine.

*Usually, time of development of lower jaw teeth is less than

the upper jaw (difference is small except for the canine as we said

before). For example, the 1st

molar at lower jaw will appear at the

age of 6 years, while the one on the upper jaw at the age of 6 years

and 3 months .


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* Deciduous Dentition *1) Prenatal (intra- uterine) stage:

* Deciduous teeth start developing

while fetus is still in uterus. So, we have

intra-uterine stage, this happens at the

age of5 months of pregnancy.

* At 3-4 monthsof pregnancy, we

have the 1st

evidence of calcification of deciduous teeth, while at 5

months there are some developing

teeth.

* At 7 months of pregnancy, the

teeth are at different stages of

development.

- Notice that the central incisors they are more advanced than

others, because they will appear in the mouth before other

deciduous teeth.

2) Infancy stage:

* When the child is born,

-The crown of central incisors is

completed and part of the root is formed.

-The lateral incisor is at the stage ofcrown completion.

-The deciduous canine is still at the stage of early formation of the

tip of the cusp.

- Notice the 1st

deciduous molar is more advanced than the


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deciduous canine, thats why it erupts before canine.

- Also, we have the beginning formation of the cusp of the 2nd

molar.

** At age of6 months,-The 1

sttooth inside the mouth

appears ((for European people but

the average in Jordan is at the age

of 7-8 months)).

Usually the 1st

tooth is the

mandibular central incisor, followed by the maxillary central

incisor, then the mandibular lateral incisor and so on (they erupt byfollowing specific sequence).

- Notice at 6 months we have the formation of the 1st

permanent

molar and later on we can see the permanent incisors as well.

** At age of9 months, all incisors

are there.

- Notice the appearance of permanent

incisors, canines & 1st molars formation.

** At the age of 1 year, we see the

deciduous molar.

3) Early childhood (pre-school) stage:

** At age of2 years, all deciduous

teeth appear in the mouth but not all of

them are in occlusion (occlusion means

meeting surface to surface), there is still

space between posterior teeth.


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** At the age of3 years, all

deciduous teeth are erupted and in

contact, so this is the beginning of the

functional deciduous tooth stage.They are called functional; because

the child starts to function on these

teeth.

** At the age of4 years, some of

deciduous teeth start to have their rootresorbed.

** At age of6 years, most of the

roots of the incisors have been lost, this

means permanent incisors are very close

to be erupted. But remember that we have

other teeth that dont succeed other,

which appears in the mouth.

((At the age of 6 years the 1st

permanent

teeth appears which is the 1st

permanent

molar))


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4) Mixed Dentition (late childhood school age)

stage:

** At the age of7 years, we have

the eruption of permanent incisors.

Sometimes, some people think that

the 1st

permanent tooth is the central

incisor, as most of the children eat

usually a lot of sweets and may dont

brush their teeth so that may lead to

formation of caries in the 1st

permanent molar that has been newly

erupted and the parents dont worry about itas they think its adeciduous molar that will be replaced later!

Pay attention that the 1st

permanent molar is important for the

establishment of the dentition and for functioning in mastication,

chewing and eating. Thats why if you lose these teeth or have

problem inside them too early, which is really a big problem.

Because of that we instruct our kids to brush their teeth.

When incisors appear in the mouth, they look really veryugly and widely spaced; this stage is called

the ugly duckling stage.

** At the age of10 years, the ugly

duckling stage ends by the movement of

the incisors until they are in contact.Notice that many deciduous teeth are

succeed by permanent teeth except some of

deciduous molars and the upper canines.


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5) Permanent dentition stage (Adolescence and

adulthood):

** At the age 12 years, all

deciduous teeth have been lost, but

still the permanent teeth are not in

full function, because the 2nd

molars are not in complete

occlusion (they are at the

beginning of the eruption).The last successor tooth to erupt is the permanent canine (pay

attention last successor not last permanent tooth!!).

Thats why some people who doesnt have enough space in the

upper jaw, their canine has to erupt buccally (outwards), this is

common in Asian people as they have big teeth but small jaws

especially in the upper arch.

Because of that, the tooth that is going to lose, is the last tooth toerupt (canines)

So, when we see a permanent canine that has erupted buccally, that

it has delayed to appear in the mouth.

** At the age of15 years, all

permanent teeth except 3rd

molar are

in contact. Because usually 3rd

molar

is not counted for functional

dentition (because it doesnt have a

main function in chewing and


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sometimes are really missing) so thats why the age of 15 years

when these teeth are in contact- we call this stage the functional

permanent dentition stage, until the appearance and occlusion of

3

rd

molar, then we call it the full-functional permanent dentitionstage.

* Summary of the Dentition stages *


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* P.S!

1) Usually mixed dentition stage:

- Is the stage from the eruption 1st

permanent tooth & ends with

the lost of the last deciduous tooth (maxillary deciduous canine).

- Is divided into 2 phases.

* In phase 2 we said and/or 2nd molar; because sometimes it

erupts after the last deciduous tooth is lost and sometimes the 2nd

molar

erupts while we still have some deciduous teeth are not lost yet.

* We have about 2 years between the 2 phases; because the last

incisor (maxillary lateral incisor) it erupts at the age of8 years and

the 1st

permanent canine (mandibular canine) erupts at the age of10 years.

2) Some people stop at the functional dentition stage as they dont

have 3rd

molar.

3) Sometimes, 3rd

molar completes the formation inside the bone

and there is something preventing it from erupting, because of that

they are still exist inside the bone.

4) For old people, its not necessary to lose their teeth (losing their

teeth dont have a specific sequence). Loss of teeth is caused by

periodontitis (inflammation of the tissue surrounding the tooth) and

this depends on the person him/herself if he/she takes care of their

teeth. For sure, if the teeth remain, they wont be as functional as

before, but it will perform the main function.

5) The more roots the tooth has and the longer, the more time it

will stay in the mouth (more time to be lost). Thats why incisors

are the 1st

tooth to be lost when we get old (because they have

single & short roots), while upper molars & canine usually are the

last teeth to be lost as they have long & large roots.


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* Sequence of Emergence of primary teeth*

&

* Eruption of the secondary teeth*

** Inter-arch!

** Intra-arch!


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- We will use the term emergence instead of eruption (Dr will

explain why next lec.)

- The numbers that are shown here describe the sequence of

emergence/eruption, they are not palmer notation!- The teeth that have been given the same number for the time of

emergence, means that they emerge during a period of time,

without statistically significant different.

- In the eruption of permanent teeth, remember we have 2 years

gap between the eruption of the lateral incisors and canines

(phase 1 and phase 2).

* Im not telling you it is going to be easy * * Im telling you its going to be worth it *Best of LuckForgive me for any mistake

Done by:Carmen Daghistane

Special thanks For Shadi Masoud for his help

Date post:	04-Apr-2018
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2nd - Dental Anatomy#2

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