oral histo with asoma

8/2/2019 Oral Histo With Asoma

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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 acase of max. molars.

23min begin:

The primary apical foramen which is the end of the growing root (its

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- subdividesinto 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 want more than one root, we have some extension

that go and fuse together dividing the primary apical foramen into anumber 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 servical line but after the development of the


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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 servical third

and the middle third of the tooth, so its coat by the in growth of theepithelial sheath from the margins of the epithelial root sheath and this

fuse together near the center of the root, the numbers and locations of

this sheath corresponds to the numbers of the roots, if we want 2 roots

we see 2 sheath, if we want 3 roots we see 3 sheath and so on.

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.


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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 openand 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.

-The dental follicle occurring at outside and the dental papilla located

inside, sothats why this area 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


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margins are angled thats why we will see 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 inside

anddental follicle outside.

Commencement of root dentinogenesis:

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

peripheral cells of dental papilla these differentiation into odontoblast

and give root dentin.

- the internal enamel epithelial cells 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 leds to differentiation of cementoblast and deposition ofcementum.

-now, we reach the stage where dentin start to developed inside the

first part of the root, dentin itself causes the integration of ERS; WHAT

HAPPENS NEXT? These 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 leds to

differentiation of new cells this new cells called cementoblast.

-this 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 differentiate and become cementoblastand 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 areunlucky these cells

sometime may perforate and they form assist in the jaw these are

called radiculer 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


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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 undifferentiation cells of dental follicleand 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 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 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 of the epithelial root sheath cells, this become

the cementoblast and they lay down cementum.


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-The cells in the intermediate layer they differentiate into fibroblast and

they give the periodontal ligament, which holds the tooth inside the

bone and the cells on the outer layer of the dental follicle they

differentiated into ostioblast and they give the alveolar bonesurrounding the tooth.

The three layers the inner investing layer, the middle layer, and the

outer layer.

the inner investing layer these are ectomesinchymal in origin fromneuoralcrest as you know, the cells differentiate into cementoblast,

and its ectomesinchymal in origin.

Cementoblast are cuboidal cells that are located on dentin surface and

they lay down cementum.

the cells of intermediate layer: they differentiate into fibroblast and

produce periodontal ligament, its mesoidermal in origin.

the cells of the outer side: they differentiate into ostioblast that givethe alveolar bone, its mesiodermal in origin.

oral histo with asoma

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