Oral Histo 8th Lec

8/2/2019 Oral Histo 8th Lec

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Development of root and PeriodontiumDental follicleits a structure that surrounds the germ, And how it's important together withother structures for the development of the root the tissue surrounding the root.Root 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 crowndevelopment (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) Interaction between ectoderm and ectomesenchyme

Dental follicleIt's Ectomesenchymal in origin, and its the cells that surround the whole toothgerm also it has to interact with an ectodermaly arising tissue this is "Epithelial root sheath

(ERS)", Epithelial root sheet 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)?

Its a structure derived from the cervical loop region of enamel organ.

If you remember when we discussed bell stage early we said at the end of the enamel organ weonly 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)


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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 in origin ??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 papilla an important structure for the development of dentin

and it contains the cells that will become the odontoblasts so its important in rootdevelopment 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 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 thecervical loop and form the cervical loop the

downward growth is the epithelial 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 forming the 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

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 SIand 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 dont see that, so there is no SR and SI inthe root sheath.


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2- HOW DOSE ERS GROWE?

The ERS dont grow haphazard they grow in an organized way which is genetically determinedto give the shape of the root and thats make the roots have different shapes; ERS grow byApical proliferation : " the ERS grew downward away from the crown " thats 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 ofthe crown ?The proliferation of enamel epithelium cells and we say thats called morphs differentiation togive 3D shape of the crown .

3- the ERS is never a continuessheath 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".

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 ERS is 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 dont 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.


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Epithelial root sheath in multi rooted teeth

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 later on this divide into two roots in a

case of mandibular molars or three roots in a case of max. molars.

The primary apical foramen which is the end of the growing root (its not finished yet) once theroot has completed 100% this foramen become very small and is called apical foramen.

The primary apical foramen-before root full completion- subdivides into a number 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 wantmore 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 the cervical 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 shelvescorresponds 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: Whats 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 sowhilethe 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 edgenot thick ( . (

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.

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.


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The dental follicle occurring at outside andthe dental papilla located inside, sothats why thisarea at the apical margins this is the dental follicle not 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 thats why we willsee the bottom of the epithelial root sheath.

So what is the epithelial root diaphragm? the epithelial rootdiaphragm is the 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: thedental papilla insideanddental

follicle outside.

Commencement of root dentinogenesis

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 enamelepithelial 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.

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 part of the root, dentin

itself causes the integration of ERS; WHATHAPPENS 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.


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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 differentiate and become cementoblastand they lay downcementum 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 areunlucky

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.

Dentin itself causes the fragmentation of the epithelial root sheath cells and because of thesefragmentation 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 layerand 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 ofthe 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 dentin

surface and they lay down cementum.


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The cells in the intermediate layer they differentiateinto 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 the dental follicle theydifferentiated 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 oriented along 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 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.


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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. incisors of

rodents) these are continually growing teeth so we dont have a process that this formationstops so this process is continuous in all the life of the animal , but in humans and also in manyother 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 .. 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 neotons low ()


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Root growth theory of eruption the 2 slides related to this topic arecanceled slide # 22 & slide # 23.

Formation of principal PDL fibers

Stage 1before eruptionThe 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 oblique fibers, 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 contactwith the opposing tooth (functional eruption).


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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 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 organization of 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 PDL fibersCollagen fibers are only organized when the tooth is in function, Eruptive force caused by

traction of collagen in PDL development is debatable some people 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 functionalposition, 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 a cause of eruption.2. However, we have some difference between different animals (species differ)

deposition in dogs is very important so it's a predominant 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 bemore prominentthan 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) cementumwe usually find it at the Cervical portion of the root if u examine it u wontfind 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 .

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 formed


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3. 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 fiberswhich 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 formedacellular 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 to cementum.

Types of acellular cementum

we have two ways of classification of cementum according to presence of cells: cellular andacellular source of fibers: extrinsic and intrinsic. so we have 4 different types of cementumcellular 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.


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In permanent teeth, exist until tooth erupts into the mouth and after that wedont 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.

Mineralization in acellular cementum

the Presence ofcrystals isadjacent dentin is believed to initiate mineralization incementum 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


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also we see Incremental lines in sementum because this process is gradual and at theseincremental 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 cementogenesisOsteoporosis patients are given bisphosphonate as a drug which is a disease affects oldaged females more than males and they found that bisphosphonate affect cementogenisis

thats why it should be avoided by the growing children or any human in the growing periodThat because it caused the following affects:

- Interferes with mineralization of initial root dentin

- No mineralization of the hyaline layer

- No cementogenesisacellular 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, its a thin layer over laying thecervical 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 to the 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 in the rate of cementogenisis.

Cementum has two types depending on the rate of development: cellular and acellular; ifthe 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.


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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.

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 way for 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 dont see precementum in acellular cementum but we do in the


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cellular because the process is very fast so any layer that is formed cant de mineralized straightaway immediately because the process is fast thats why it needs sometime because we areproducing very quicklyso thats 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 cementum because 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 matrixand thats why the cementum appears cellular orcontaining 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 cells inside the cementum is called cementocyts, The incremental lines are more widelyspaced 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 ENDDONE BY:

Baraa'h Al-Salamat

Asmaa' Al-Mawas

Dana Qatameen

Zain Al-Salameen

Thank you Abeer :)

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

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Oral Histo 8th Lec