Development of Root and um Doc

8/2/2019 Development of Root and um Doc

http://slidepdf.com/reader/full/development-of-root-and-um-doc 1/21

Development of root and Periodontium

Dental follicle à it’s a structure that surrounds the germ, And how it's

important together with other structures for the development of the root the

tissue surrounding the root.

³Root Development: starts sometime after enamel completion so for root

to start developing enamel has to be completed ( NO root development starts

before enamel completion)

´ Does root development starts immediately after enamel

completion?

No, there's a gap between the completion of enamel (deposition of the last

layer of enamel) and the beginning of root development, so this gap isn't that

long it's a short gap but usually we say root development starts sometime

after enamel completion.

´ Root development may start before enamel completion?? False

In order for root to develop we should see some interaction, which is similar to

the crown development (enamel and dentin formation) we said these two

processes need some interaction between two sources or two media

(Ectodermal and Ectomesenchymal ), so this interaction is important for the

development of the crown . In a similar way we should see some interaction

that leads to the development of the root (interaction between dental follicle

and epithelial root sheath) à Interaction between ectoderm and

ectomesenchyme

Dental follicleà It's Ectomesenchymal in origin, and it’s the cells that

surround the whole tooth germ also it has to interact with an ectodermaly

arising tissue this is "Epithelial root sheath (ERS)", Epithelial root sheet à

Its Epithelial because of that this is ectodermal in origin.

´ What happens if we isolated dental follicle alone?

No root development happens.

´ What happens if we isolated the epithelial root sheet alone?

No root development happens.

´ What is the epithelial root sheath of Hertwig (ERS)?

It’s a structure derived from the cervical loop region of enamel organ.

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If you remember when we discussed bell stage early we said at the end of the

enamel organ we only see two layers not four layers, we know enamel organ

consist of four different type of cells:

1- Internal enamel epithelium

2- External enamel epithelium

3- Stratum Intermedium (SI)

4- Stellate Reticulum (SR)

But here at the end of the crown at the basal end of the crown we only see two

layers. so the area in between which is (SR and SI) is lost and only we see two

layers ( EEE, IEE) . So the cervical loop consists of only EEE and IEE bound

together (this occurs at the cervical margin of the crown), From this loop we

have a downward growth called the epithelial root sheath (so it's derived from

IEE, EEE)

´The epithelial root sheath of hertwig is ectomesenchymal inorigin ??

No, it's ectodermal in origin .

In addition to these two structures we have a third one that's also involved in

this interaction which is Dental papilla, Dental papillaà an important

structure for the development of dentin and it contains the cells that will

become the odontoblasts so it’s important in root development because the

root contains dentin (inside the root).

So interaction takes place between three different tissues :-Two are ectomesenchymal (dental follicle and dental papilla)

- One is ectodermal in origin (epithelial root sheath)

The onset coincides With the axial phase of tooth eruption, this means

once the first part starts the root will grow and as a result the tooth starts to

move up, so before the process of root formation the tooth can't go and erupt,

So what causes the eruption of tooth is the development of the root à

because the tooth will start to have its root and as a result once we have

(1mm) of root development the tooth erupts (1mm) ,for ex.if we surgically

taken the tissue that develop the root from below the root the tooth will not

erupt.

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In the figure above this is representation

of tooth development stages, note at

bell stage no root development but at

the cervical margin of the enamel organ

we see the cervical loop these two

population of cells fuse together to form

the cervical loop and form the cervical

loop the downward growth is theepithelial root sheet of hertwigs which is

important for the development of the

root so the epithelial root sheet ERS

forms at the late bell stage.

What about amelogenesis and

dentenogenesis ?

amelogenesis and dentenogenesis are

well advanced and amelogenesis should

have y3ni for the ERS to start formingthe 1st part of the root enamel formation

has to be completed sometimes we may

see the ERS at the terminal stage or at

the end of amelogenasis at this moment

no root development has started but we

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see just the ERS but it has not yet

started develop the root.

Epithelial root sheath :1- ERS its double layer formed by two layers : internal enamel epithelium,

external enamel epithelium this is the ERS as you see:

IEE and EEE are fuse together but we have IEE and EEE are fuse together,

but we have lost 2 other tissue are normally exists in enamel organ these are

(starum intermedium SI and stalillat reticulum SR) because of that NO

enamel formation happen on the root as you know for enamel formation to

take place there should be 4 different types of cells to form different layer of

enamel organ if we take the two layers inside and if we only left IEE and EEE

alone there will do not form enamel they only form the root , but in some

animals we see the enamel in the root, WHY ? because ALL those for layers

(EEE, IEE, SR, SI) are exists in the root that's why we see the enamel covering

the root but in HUMAN we don’t see that, so there is no SR and SI in the root

sheath.

2- HOW DOSE ERS GROWE?

The ERS don’t grow haphazard they grow in an organized way which is

genetically determined to give the shape of the root and that’s make the roots

have different shapes; ERS grow by Apical proliferation : " the ERS grewdownward away from the crown " that’s why its apical toward the apex of the

tooth and this proliferation is important to give the shape of the root.

´ What determine the shape of the crown ?

The proliferation of enamel epithelium cells and we say that’s called morphs

differentiation to give 3D shape of the crown .

3- the ERS is never a continues sheath because this sheet will form the 1st

part of the root once the dentin of the 1st part has already been found this

sheet will start to fragment or disintegrate "impossible to see it complete

sheet from the cervical line of the root to the apex of the root".

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In The figure above note at "A" side see this ERS is continues but at "B"

side you see the root dentin start to be form also you can see the ERSis disintegrate where dentin is formed.

Enamel pearl:

Enamel formation at the root !, It happen because of reteintion "keeping" of

SR ,SI inside the double layered ERS

As we said ERS don’t contain SI and SR, but sometimes there is errors

that take place in the process of root development this error leads to keeping

SI and SR at some locations so we have here 4 types of cells that involve in

enamel formation (EEE, IEE, SR, SI).

Enamel pearl : its localized enamel on root surfaces usually we see it in the

inter-ridiculer region of molars.

Epithelial root sheath in multi rootedteeth

in a case of molars and some premolars when we see more than one root, so

we see common root trunk for one third of the length of the root and then lateron this divide into two roots in a case of mandibular molars or three roots in a

case of max. molars.

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The primary apical foramen which is the end of the growing root (it’s not

finished yet) once the root has completed 100% this foramen become very

small and is called apical foramen.

The primary apical foramen-before root full completion- subdivides into anumber of secondary apical foramina (if you want to imagine this case you

have to imagine the apical part of the tooth - tooth from the opposite of

occlusial view this is the apical view)

If we want only one root, it continues and then closes and makes one root.

But when we want more than one root, we have some extension that go

and fuse together dividing the primary apical foramen into a number of

foramina depending on the number of roots and these actually happens after

some development of the root (if you remember in dental anatomy: the

division of the roots in the molars it takes place not immediately at thecervical line but after the development of the root trunk), so the root starts as

one root for maybe one third of the distance and then it divides into two or

three depending on the tooth, and this takes place at the junction nearly

between the cervical third and the middle third of the tooth, so its coat by

the in growth of the epithelial shelves from the margins of the

epithelial root sheath and this fuse together near the center of the root, the

numbers and locations of these shelves corresponds to the numbers of the

roots, if we want 2 roots we see 2 shelves, if we want 3 roots we see 3 shelves

and so on.

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Maybe under inductive role of dental papilla its believed the researches now is

on: What’s the factors that give the orders to this sheath to start? the

coz is genetically determents and believed that dental papilla which is

occupied in the space here has an important role for initiation this sheath to

divide the roots in growth is believed occurs along pass the low vascularity,

some other researches also said that this grow when the vascular supply of

this area is low.

So why we need an apical foramina? to pass a blood vessels and nerves to

reach inside the pulp but this hall is huge and big while the tooth is forming

and it becomes reduced in size when the tooth is ready to be completed so

while the root is being form the apex is wide or open and surrounded

by thin regular knife edge of dentin. so this very different compared to

tooth that it fractured, fractured tooth will have thick walls of dentin at the

margin of braking, but a tooth which still growing the margins of dentin will be

knife edge not thick (نيكسلا دح تم ) .

A permanent tooth erupt with about 2/3 of root forming and after

eruption or after a appearing in the mouth from 2 to 3 years for the

root to be completed, by root completion the wide apical foramen becomes

very narrow, and only wide to transmit neurovascular bundle it becomes very

small only enough to passive the nerve and blood vessels inside the pulp.

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Growth of the epithelial root sheath: occurs apically, and it encloses the

dental papilla except at the primary apical foramen, since in the primary apical

foramen there is a dental follicle not dental papilla.

The dental follicle occurring at outside and the dental papilla located

inside, so that’s why this area at the apical margins this is the dental folliclenot the dental papilla.

The margins of the epithelial root sheath are angled internally to formed the

root diaphragm, as u know all the time the epithelial root sheath has an

angled margin, the margin is not vertical its angled this is called the

epithelial diaphragm, because of that when we look at growing tooth from

bellow, u will see this area (band) because the margins are angled that’s why

we will see the bottom of the epithelial root sheath.

So what is the epithelial root diaphragm? the epithelial root diaphragm isthe angled margins of the epithelial root sheath, all the time the end of the

epithelial root sheath is angled, the dental follicle lies external to the

epithelial root sheath, and the dental follicle is the tissue that form

cementum, periodontal ligament and the alveolar bone.

The root diaphragm is angled, the angled edge of the epithelial root

diaphragm is a circular band, in the circular root there is a circular band

because its angled from all the margins because the root is circular it creates a

circular band this root diaphragm is sandwiched between 2 populations of

undifferentiated mesinchyme: the dental papilla inside and dental follicleoutside.

Commencement of rootdentinogenesis

The cells of internal layer of epithelial root sheath they induce the

peripheral cells of dental papilla these differentiation into

odontoblast and give root dentin, the internal enamel epithelial cells (IEE)

induce, they gives signals to the tissue to dental papilla, but they give signals

to the peripheral cells of dental papilla (the cells that located outside or at

periphery of dental papilla) response to these signals the cells starts to

differentiate and become odontoblast and they lay down to form dentin so

this who root dentin forms.

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How does cementum form? - root dentin now is deposited, root dentin

causes the epithelial root cells to lose their continuity, because of that root

dentin become exposed to the undifferentiated cells of the dental follicle,

these leads to differentiation of cementoblast and deposition of cementum.

now, we reach the stage where dentin start to developed inside the first partof the root, dentin itself causes the integration of ERS; WHAT HAPPENS

NEXT? This tissue outside the dental follicle become exposed to a foreign

body (dentin) because of that the exposure of outside population of the

undifferentiated cells to dentin leads to differentiation of new cells this new

cells called cementoblast these differentiate and they form cementum on the

surface of the dentin, so this is the process by which cementum form.

So root dentin is deposited and as a result epithelial root sheath they lose

their continuity, and as a result of fragmented cementum the dentin will

expose to outside, some cells because of these exposure they differentiateand become cementoblast and they lay down cementum on the outer

surface of dentin.

Fragmented epithelial root sheath cells they remain inside the area here

or they remain outside cementum these are called the epithelial root sheath

rest cells, these cells are significant because these cells are remain inert

without any function, but if we are unlucky these cells sometime may

perforate and they form assist in the jaw these are called ridiculer cyst. After

the fragment they become the epithelial rest so these are the epithelial rest

of malassez. Malassez is the scientist of the first covered them, So

they are called the epithelial rest of malassez they exist inside the

periodontal ligament, this cells represent the fragmentation of the epithelial

root sheath.

Q: The epithelial rest of malassez are?

-1: ectodermal in origin

-2: mesincymal in origin

-3: ectomesincymal in origin

Ans: is 1

Root dentin is exposing to undifferentiating cells of dental follicle and as a

result this exposure led to differentiation of the some cells into cementoblast

and these cells will deposed cementum on the external surface of dentin this

process called cementogenesis.

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Dentin itself causes the fragmentation of the epithelial root sheath cells and

because of these fragmentation dental follicle cells becomes exposed to

dentin, as a result some of the cells they differentiate and become

cementoblast and they lay down cementum on the external surface of dentin,

so this is the process as simple as that.

Dental follicle near the diaphragm has three layers in fact, we have: inner

investing layer, middle layer and outer layer.

So the dental follicle that located outside we can divided into three layers:

inner layer, middle layer, outer layer.

• The inner layer a pond the exposure layer to the dentin which caused

by the fragmentation of the epithelial root sheath cells, this become the

cementoblast and they lay down cementum, and its ectomesinchymal in

origin. Cementoblast are cuboidal cells that are located on dentinsurface and they lay down cementum.

• Th

e cells in the intermediate layer they

differentiate into fibroblast and they give

the periodontal ligament, which holds

the tooth inside the bone, its mesoidermal

in origin.

•

the cells on the outer layer of thedental follicle they differentiated into

ostioblast and they give the alveolar bone

surrounding the tooth, its mesiodermal in

origin.

*** the dental follicle is

ectomesenchymal in origin.

the follicular cells are obliquely orientedalong the root surface , why? because they

have to keep base with the fast growing

root. (the faster is the investing layer then

the intermediate and the slowest is the

outer layer), that's why you will see the

cementum will be formed in an area then

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above it there is the fibroblasts or the PDL

and the highest one is the bone, the

follicular cells in the intermediate area

become the fibroblasts of the PDL the

fibroblasts secret collagen which will be

embedded in the cementum and the

alveolar bone which is called the sharpy's

fibers.

we have to imagine how the tooth is going to be

attached to the bone, the fibroblasts in the middle

layer or on the intermediate zone which produce

collagen and these collagen fibers become embedded

in the newly-formed cementum and this is the first

form of attachment of the fibers to the surface

of the tooth root, then it will become mineralized

and get attached firmly to these fibers "you have to

imagine it as a soft material when we put some fibers

in it, it become hard and attach firmly to them!"

another similar process happens to the bone another

fibers from the other side get embedded into the

nonmineralized bone then it become mineralized and

attached firmly to them, so we will get to groups of

fibers attach to each side "cementum and bone"these are called sharpy's fibers.

Sharpy's fibers: collagen fibers that are embedded at the cementum before

mineralization and at the fibers attached to the bone before mineralization

from the other side, these are the most important fibers for the attachment of

the tooth.

now the sharpy's fibers in each side are connected by another group of fibers

which are the principle fibers of the PDL ,,LOOK AT THE CARTOON PIC :P! "this

is the way by which the tooth attaches to the surrounding bone".

Root completion

How the root is completed?

always the process of formation continuous apically but in some animals (e.g.

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incisors of rodents) these are continually growing teeth so we don’t have a

process that this formation stops so this process is continuous in all the life of

the animal , but in humans and also in many other mammals we should see

termination of the process and close the wide foramen in the apical region in

order to do that we need fast growing or development of dentine much faster

than the development of th root sheath, but if they still having the same speed

there will be no end of the root formation.

When the final root length is achieved, the proliferation of

epithelium in the diaphragm lags behind “become slower ”.. بتتأخر عن

that of the pulp or connective tissue, so the ERS development is slow but

the dentine become faster and the cementum develops outside and closes the

foramen.

The wide apical foramen is reduced first, it will have thick edges replaces the

sharp knife edges to have the the same width of the diaphragmatic opening

itself, and further narrowed by apposition of dentine and cementum at the

apex of the root.

Accessory root canals

If continuity of root sheath is broken or not established prior to

dentine formation a defect in the dentinal wall of the pulp occurs, if

there was something like nerve or blood vessle stops the continuity of the ERS

will be broken at the end u will find a small canal in the structure which was

there to become a communicating way between the dental pulp and the PDL.

Root elongation & tooth eruption

It is believed that the development of the root is the reason that the tooth

starts to move up or emerge, always the direction of tooth eruption is opposite

to the direction of the direction of root development “third neoton’s low” (كل

( فع ر فع مسو ل بلقدار مع ل بجه

Root growth theory of eruption à à à the 2 slides

related to this topic are canceled slide # 22 & slide #

23.

Formation of principal PDL fibers

Stage 1 – before eruption

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The first stage happens before eruption at first we have

the PDL which is a loosely structured collagenous

elements or a loose connective tissue.

In the Permanent molars it found as fibers connecting tooth to gingiva

(Dentogingival) & also at the fibers that run obliquly (oblique fibers) and

theythey are organized, wich are the most promenent.

But in Premaloars we Only find dentogingival fibers are well-developed

stage 2 - tooth penetration

tooth penetration when the tooth starts to appear in the mouth the PDL fibers

developed but not all the way throw PDL space, so the fibers are well

developed but not in all the PDL space.

in permanent molars the PDL is well differentiated at the place of obliquefibers, in premolars with the eruption of teeth we only see the fibers fully

developed at the alveolar crest "the top most point of the bone"

the full development of the PDL fibers only takes place after the

tooth reaches the contact with the opposing tooth (functional

eruption).

stage 3 - reach occlusion

when we reach occlusion Permanent molars we see Fibers in cervical region are

organized and prominent, but at this stage we have to know that when the

tooth reaches contact with the opposing tooth the root will not be

completed yet in the cervical region so that's why all the fibers that have

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formed are well organized but we still have to form fibers at the apical margin

which is the last stage .

stage 4 - functional

when the tooth start to function in the mouth this is the classical organizationof principal fibers where all the fibers are organized at the area of the root that

has formed, but the full formation of the fibers logically organized when the

full root is complete.

Additional notes on formation of principal PDLfibers

Collagen fibers are only organized when the tooth is in function, Eruptive

force caused by traction of collagen in PDL development is debatable somepeople say that contractions of these fibers within the PDL are very

important for moving the tooth upward (this is still debatable)

Change in obliquity (orientation) and thickness of fibers as the tooth

reaches the functional position, so the Inclination increases and the

Thickness increases with function, that cuz the tooth now in function and

we have forces pushing the tooth downward so as a result the fibers

become oblique and cus these fibers need to resist these occlusal forces

they become thick.

During eruption we have resorption of the bone in the base of the socket

is predominant, while the tooth is moving up cuz we have root

development the dominant process is the resorption of the bone which is

initially formed around the tooth all of that to allow the root to be formed.

1. but pay attention that the bone deposition is not accepted as acause of eruption.

2. However, we have some difference between different animals(species differ) deposition in dogs is very important so it's apredominant option not the resorption .

3. Bone activity is related to the distance the tooth has to erupt4. Distance greater than root length, when the distance the root has to

move is greater than the length of it's root deposition will be moreprominent than resorption.

:)) there will not be any Q in the exam about this point "slide #30"!!

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Cementogenesis

we have two types of cementum primary & secondary:

• Primary (acellular) cementum

we usually find it at the Cervical portion of the root if uexamine it u wont find any cell

• Secondary (cellular) cementumwe find it at the Apical region of the root here we can see

some cells inside also we can find it in the Furcation areas

"root division areas"

Formation of acellular cementumthe formation of cementum is the same as root dentin it

Starts cervically and proceeds apically, Cells of ERS

(epithelial root sheath) Do not enlarge as in enamel organ

if u remember when we discussed enamel formation we

said the ameloplasts are enlarged big or columnar cells in

order to produce enamel but the ERS cells they remain

cuboidal.

also they are Separated by a basal lamina on both sides

(from the dental papilla and dental follicle sides) because

of that only when the basal lamina is lost the induction or

the interaction takes place.

Induction of root dentinogenesis as we said the inner layer

of the ERS cells induce the cells of the dental papilla these

become odontoplasts and they lay down dentin and they

continuo this, and as a result the Odontoblasts retreat

inwards toward the dental pulp as the crown formation

stage.

this Form the first-formed root predentin this get mineralized after 24 hours to

become dentin and another predentin is formed which is similar to the process

of dentinogenisis in the crown region of the tooth, of curse No odontoblastic

process yet in the first-formed dentin and it's Structureless and when it is

fully mineralized it becomes the Hyaline layer.

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ERS in contact with predentin and as a result this lead to:

1. the disintegration of the ERS cells2. the Exposure of follicular cells to unmineralized hyaline layer that

first formed3.

Differentiation into cementoblasts which will produce cementum

HOW DO Cementoblasts secrete collagen fibrils(small fibers) ??

Deep parts of fibrils intermingle with those of the hyaline layer making strong

union, between the first-formed predentin and cementoblast layers the

cementoblasts produce small fibers which will be imbedded inside the first

layer of dentin that has formed (the hyaline layer), so these fibers have a

free end outside and another deep end inside imbedded within dentin.

Peripheral parts extend into PDL (fibrous fringe), that's mean the tooth look

like ciliated structure we name those hairy like things "fibrous fringe"

later on the Mineralization of the Hyaline layer and Fibrous

fringe as a result the first formed acellular cementum are firmly attached to

root dentin, in this process the goal is attaching cementum to root

dentin, but the previous one's goal is attaching the fibers to cementum.

Fibers of PDL are still parallel to root surface & not yet attached to

fibrous fringe.

Slow increase in thickness of acellular cementum and leads to the

Establishment of continuity between fibrous fringe and PDL fibers and

Continued slow mineralization of collagen.

TO Summary ::we have two stages of attachment :

the first stage : attaching cementum to dentin and this is the role of the small

fibers that become imbedded inside the newly-formed dentin (hyaline layer)

and they have free surface where cementum will be formed.

the second stage : later on we have the fibers that firmly attach dentin tocementum.

Types of acellular cementum

we have two ways of classification of cementum according to ①presence of

cells: cellular and acellular source of fibers: extrinsic and intrinsic. so we②

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have 4 different types of cementum cellular intrinsic, cellular extrinsic,

acellular intrinsic, acellular extrinsic.

we have two types of acellular cementum depending on the source of

fibers:

Acellular intrinsic fiber cementum

the fibers from within the cemento blasts, Acellular cementum

lining the root before its fringe fibers are linked with those of

PDL, the fringe fibers have two connections: the hyaline layer of

dentin and the sharpies fibers of the PDL.

In permanent teeth, exist until tooth erupts into the mouth and

after that we dont see the acellular intrinsic fiber cementum.

Acellular extrinsic fiber cementum

the fibers from the PDL or from externa source, Acellular

cementum lining the root after its fringe fibers are linked with

those of PDL Increases in thickness slowly & evenly throughout

life, so that's why after eruption we dont see Acellular intrinsic

fiber cementum and we only see the extrinsic.

in the pic below we can see the cementoblasts at the surface outside not

inside cementum layer, Epithelial rest of malasses are the aggregation of the

ERS.

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Mineralization in acellular cementum

the Presence of crystals is adjacent dentin is believed to initiate

mineralization in cementum not like the dentin mineralization which is

caused by matrix or DTP mineralization.

Adjacent PDL fibroblasts may play a role in the mineralization of

cementum

it is Very slow process and does not involve calcospherites formation not

like dentin also there is No layer of unmineralized “precementum”

also we see Incremental lines in sementum because this process is

gradual and at these incremental lines we see:

- High content of ground substance

- Low content of collagen

- Closer together than in cellular cementum because the formation is

slow formation

Bisphosphonate inhibit cementogenesis

Osteoporosis “” patients are given bisphosphonate as a drug which is a

disease affects old aged females more than males and they found that

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bisphosphonate affect cementogenisis that’s why it should be avoided by

the growing children or any human in the growing period That because it

caused the following affects:

- Interferes with mineralization of initial root dentin

- No mineralization of the hyaline layer

- No cementogenesis

acellular afibrilar cementum

We have a small layer of cementum called acellular afibrilar cementum it is

located on the enamel on the cervical part of the tooth for a short distant, it’s

a thin layer over laying the cervical margin of enamel,, that means no cells &

no fibers we know that the enamel should be protected by the reduced enamel

epithelium but sometimes the reduced enamel epithelium at the cervical

margin is damaged as a result this leads to the exposure of the enamel to the

surrounding dental follicle cells, in similar way the exposure of the enamel tothe surrounding dental follicle cells leads to the development of the cementum

on the small part of enamel this cementum does not contain cells does not

contain fibers, Follicle cells contact enamel, Differentiation into cementoblasts,

Cementoblasts secrete afibrillar matrix that calcifies.

Formation of cellular cementum

Cellular cementum or secondary cementum which is the cementum that

contain cells it appears at the time of eruption it reflects the rate of increase inthe rate of cementogenisis.

Cementum has two types depending on the rate of development: cellular

and acellular; if the rate of development is too fast the cells will produce

cementum in different directions and in avery fast way and then they will

become incorporated within the cementum which is the cellular one, but if

they produce cementum very slowly all the time they will be away from

cementum and they will not become incorporated within cementum which is

the acellular one.

Reflects increase in rate of cementogenesis,So the acellular is more

organized because it is built slowly and does not contain cells, but cellular is

less organized because it is built fast and contains cells within the cementum,

it Appears at the time of eruption, there are Early inductive changes are

similar to those in acellular cementum.

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Cells forming cellular cementum, they Appear as a distinct layer of

basophilic cells (RER – active protein synthesis), they have More

cytoplasmic processes.

in the cip below notice that the cementocyts have a lot of processes to be

cooected to each other why? because cementum is a vascular so the olny wayfor these cells to survive is to keep process to each other to pass nutrients to

each other, we don't have any source of vascularization from dentine.

the only way to get nutrients is to depend on the blood vessels in the PDL

that's why we always see the process of these cells directed toward

the PDL.

Q: cementum cells that are located inside cementum are called

______?

ans: Cementoblasts or cementocyts

Effect of high rate of cementogenesis in cellular cementum

The process by which cellular cementum is produced is fast because of that we

have what is called precementum we don’t see precementum in acellular

cementum but we do in the cellular because the process is very fast so any

layer that is formed can’t de mineralized straight away immediately because

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the process is fast that’s why it needs sometime because we are producing

very quickly so that’s why we see precementum all the time at the

external surface of cellular cementum but we do not see

precementum for the acellular cementum.

Cellular cementum is less mineralized than acellular cementumbecause the process is very fast in cellular so there is no time to mineralize it,

multipolar mode of mineralization ; if the cementblast gives cementum in

one side it will be all the time away from sementum and located at the surface

of cementum but not inside cementum but when we give cementum in

different directions “multipolar” the cell become surrounded by cementum.

Cells become incorporated within the matrix and that’s why the

cementum appears cellular or containing cells, cementoplasts when they

become inside cementum they become cementocytes, new generations of

cementoblasts all the time will be seen at the surface but the cellsinside the cementum is called cementocyts, The incremental lines are

more widely spaced because the production is very fast.

What can go wrong ??Sometimes cementum fails to form at some areas of the root maybe because

the retention of the ERS cells, or sometimes the ERS cells does not

disintegrated at some locations so they become attached because of that at

that area only dentin will form but no cementogenisis will form because we

said the brake dawn of the ERS cells is important for the exposure of dentin to

the outside leading to the differentiation into cementoblasts and cementum

formation.

☀☁【THE HAPPY END 】☀☁

DONE BY:

Baraa'h Al-Salamat

Asmaa' Al-Mawas

Dana QatameenZain Al-Salameen

Thank you Abeer :)

We are very SoRrY for being late :S! Forgive us for any mistake :D

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Documents

Development of Root and um Doc