Dental Pulp - Lecture 3

IN THE NAME OF ALLAH , MOST GRACIOUS , MOST MERCIFUL

Oral histology

Lecture # 3 : Dental Pulp

Dental pulp :

Crown -> coronal pulp - pulp chamber

Root –> radicular pulp - root canal

The part of the pulp in the crown is called(coronal pulp-pulp chamber) & the part in the root called (radicular pulp- root canal).

Normally we have more than one root ,more than one root canal ,in most of the cases each root has one root canal ,but in some of posterior teeth we may see two root canals in one root ..e.g. in (60-70) % there are two canals in the mesial root of mandibular first molar ,although it's one root ,but we see two canals. so this mean the number of root canals isn't necessarily equal to the number of roots.

Dental pulp forms as referents of dental papilla, we said dental papilla forms dentine. The main fiber of dental papilla after dentine has formed is called dental pulp ,so dental papilla becomes dental pulp after beginning of dentinogenesis . in other words, once dentinogenises starts we no longer call it dental papilla we call it dental pulp .

So it is called dental papilla as long as the dentine is not yet formed , once the formation of the first layer of dentine , we call the layer

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directly beneath it dental pulp(instead of dental papilla).

Pulp:

is a specialized connective tissue ; it's connective tissue, but it's specialized for reasons :

1 ) it's positioned inside a rigid chamber:

Like when we have an inflammation in the pulp. Inflammation requires swelling..Inflammation is associated with exudates caused by histamine .( histamine & other factors lead to vasodilatation & extra positioned of fluid outside the vessels & this leads to swelling) if we have any inflammation in any other area you will have space for this swelling; y3ne if you have swelling in your hand ,this swelling has space to expand in your hand ,that's why pain will not be severe. but in the dental pulp, pulp is surrounded by rigid dentino-halls ,that's why when there is a swelling in the pulp ,it will not expand ,because it's surrounded by rigid walls , it will compressed the nerves. that's why dental pulp pain is the most sever pain that anybody can encountered .

Inflammation of pulp we call it pulpitis and it's very sever .

2 ) pulp has a role in hard tissue formation .because the periphery of pulp contains odontoblastic cells which are important in hard tissue formation.

The periphery of pulp contains dentine forming cells, which we call it odontoblast also we have nerve terminals & we have antigen-presenting cells .

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The rest of dental pulp is just simple connective tissue y3ne the core of the pulp is simple acts as a support for the peripheral component . the most important part of pulp are the peripheral component & the central portion acts to support the peripheral component .

What do we have in the core of pulp?

We have blood vessels & nerves that enter & leave through an apical foramen (always we have in the apex of the root a small foramen in which the nerves & vessels enter & leave ).

also the central portion of pulp contain cells , collagen and ground material to support the peripheral component.

Accessory canal :

We have in addition to the main root canal that exists in the root we may have accessory canal .in general we have one root canal (radicular pulp) and accessory canal which exists on the sides of pulp , acts in opened the inner of the pulp on the periodontal ligament.

Accessory canal occur most commonly on apical root :

They are called lateral root canal ;when they made a communication between the pulp & periodontal ligament ,but when they present at the furcation area , they communicate between pulp chamber& periodontal ligaments.. We call it furcation canal ( انفصال مناطق في.(الجذر

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The composition of dental pulp :

The composition of dental pulp is loose connective; any connective tissue contains cells, extracellular matrix ..

Cells ---we will discuss them later.

The extra cellular matrix contains:

fibers non fibers matrix which is the semi fluid gel

In histology --any connective tissue based on "3" substances: cells ,fibers & ground substances . also pulp as connective tissue contains : cells ,fibers & semi fluid gel as the ground substance .

Matrix is more plentiful than cells; y3ne the amount of fibers & non fibers matrix is more plentiful; much more than cells.

Function of matrix :

1-Forms a scaffold that stabilize the structure of the tissue: all the component must be contiguous to each other. The surrounding medium which act in protection the shape of pulp are semi fluid gel & fibers. Without fibers, it will be easily collapsing of the odontobalst cells & if that happened dentine will be separated from the process & lose its function.

That's why odontoblast cells should be always at periphery, what keep them at periphery?

The fact that we have a scaffold that based on extra cellular matrix that stabilize the structure of the tissue .

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2- The extra cellular matrix controls cellular activity by sending signals between cells

Fibers :

Collagen

Type I-- is the most predominant one ( 56% ) ..fibers are thin & scattered in young teeth they have a regular arrangement near predentine fibers arranges parallel to predentine surface.

من بالقرب *predeintine تكون fibers لل موازية و اكتر منظمة predentine surface

- We have also type III (40%) and type V & type VI in a small amount.

fibrilln

Seconed type of fibers .these are large glycoprotein associated with elastic fibers in other tissues. But in the

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pulp they are glycoprotein only. elastic fibers are absent in the dental pulp, just fibrillin .

*Non- fibrous matrix (ground substance which connect cells with fibers )

Glycosaminoglycans , proteloglycans other adhesion molecules

Glycosaminoglycans :hydrophilic ; it absorbs water &because it's hydrophilic ..It swells when hydrated accounting for :

High pressure in the dental pulp Mechanical support Easy movement of water-soluble molecules

Because it's hydrophilic, it allows water-soluble molecules to pass easily in pulp & it absorbs water. remember always when there is a swelling of the pulp there will be a high pressure inside it to hold peripheral part of the pulp on its place . If the pressure in dental pulp is less than outside odontoblast cells will shrink & go away from dentine.

الخاليا تسقط ما ولحتى االطراف خالياعلى وفي بقاعة قاعدين كأنه متلاالطراف باتجاه يدفعها كبيرعشان لضغط بحاجة

o all the time we have glycosaminoglycans function in this way .

o Dr said types of glycodaminoglycans , he will not give a questions in exam about them ..so don't worry about them

Proteoglycans : act as adhesion molecules bound to cell membranes & bind to signaling molecules like growth factors

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Other adhesion molecules

Fibronectin that regulates cell shape,migration & differentiation of cell

We have lamina which located around endothelial cells of blood vessels & Schwann cells Coating cell bodies and processes of odontoblast.

The cells that present in the pulp are :

*Odontoblast. They present in the peripheral of the pulp and it has a function in formation of dentine

*Fibroblast

*Defence cells

*Undifferentiated cells..they are important ,because when tooth is subjected to injury, we will have a number of odontoblast killed by this injury, so we need a new population of cells. We get them back from undifferentiated cells.

Undifferentiated cells like reserve forces..We don't need them in peace but we called them in war.

These undifferentiated locates in dental pulp & redifferentiated to become odontoblast to function in build dentine in the tooth subjected to injury.

Odontoblast :

Odontoblast are responsible in forming of dentine .they survive for as long as the tooth is vital .

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نزع او السن خلع عند تفقد , موجودة الخاليا هذه طالما حي السن طالماالعصب

Odontoblast can't divide but subodontoblast can; y3ne once cells differentiate to mature odontoblast cells , they will never ever divide .but subodontoblast cells could divide . (subodontoblast or preodontoblast cells like cells under odontoblast or the cells before becoming odontoblast .

Polarized : means that the nucleus isn't located in the center of the cell , nucleus tends to be away from dentine, polarized columnar cells with process extending within a tubule.

In root region , cells are more cuboidal , in the root the inner surface of dentine is smaller so the odontoblast cells are shorter . There aren't enough space to get its suitable length .

Odontoblastic cell layer has :

Membrane-like properties. They are cells bounded closely to each other..so we could consider odontoblastic layer a membrane separate outer medium from the pulp.

Act as a barrier to protect the dental pulp from outside irritants :

Means that outer factors( irritants ) can't pass from dentine to pulp these cells are bound to each other cell by cell (closely bounded to form a membrane which prevents irritants to pass to the pulp) .but when we lose these cells , a space will be formed , & irritants could pass .

الحيط على صفيناهم و الناس من كبيرة مجموعة احضرنا كأنه متل يعني امامهم يجدون سوف الخارج من الذين الناس بالتالي بعض بعضهم بجانب

يقتحموا يقدروا رح ما و تمنعهم بشرية حوائط .

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A limited permeability : because of presence of these cells bound together we have a limited permeability ; that's membrane is impermeable because of desmosomes ,tight junction,gap junction these junction between cells make them bounded closely therefore prevent molecules from passing.

Fibroblast :

They are the second type of cells present at the pulp , they are linked by adherence type junction & gap junction . these cells are stellate cells ( star-like ) they have many extensions ; each cell's extensions are linked to the extensions of the other cell . they undergo cell division and they have the following functions :

They produce the fibers of the dental pulp and the ground substance and participate in their degradation ( and are responsible for forming a new one as well ) .

They may produce bone-like mineralized tissue as a response to pulpal injury . sometimes when the pulp faces a chronic stimulus , instead of the repair mechanism for the tissue it becomes a pulp stone ( calcified pulp tissue ) and the fibroblast are the cells that forms this stone in most of the cases.

They produce the Growth Factors ( GFs) & cytokines .

Defence cells :

Defence cells are T-lymphocytes macrophages but remember that mast cells are absent , mast cells produces histamine so they are important in allergic reactions , this indicates that dental pulp does not response to allergens .

T-lymphocytes are present in small amounts and they increase in pulpal injuries , macrophages and antigen-presenting cells are located around

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blood vessels and around odontoblastic layer . so below the odontoblastic layer is a place where the bacteria or pathogens can enter .

The undifferentiated cells :

The undifferentiated cells are primitive mesenchymal cells that differentiate into odontoblasts to produce tertiary dentine .

Blood vessels :

They run longitudinally through root canals from the apical foramina , they give off side branches while within the canals (

القناة داخل جانبية فروع تكوين But they branch profusely (يمكنهمonce they reach the pulp chamber ( اللب حجرة وصول عند يعني

كثيرة الفروع تصبح السن تاج في . (التي Capillary loops extend towards the dentine they are directly

below the odontoblastic cells and some of these loops can extend in the dentine for short distances .

They also give subodontoblastic capillary plexus ; ya3ne these loops can make plexus (تشابكات) below the odontoblasts .

Capillaries are present within and below the odontoblastic layer but do not enter the tubules . but remember that nerves can enter these tubules as we learned previously about the direct stimulation theory and in such cases if we make a cavity preparation and there were nerves in the dentine we may cut these nerves and it causes pain .

*So nerves can pass through dentinal tubules but blood vessels can't . ( dr said ensures us to memorize this) .

We have arteriovenous and venous-venous anastomosis ; between one artery and one vein or between two veins .

Lymphatic vessels are hard to distinguish . Nerve endings are associated with smooth muscles of arteriole

wall ; so the function of these nerve endings in the pulp is to contract the arteriolar smooth muscles , that's why most of these

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nerve endings are sympathetic nerve endings to control the diameter of these small blood vessels and this is important in controlling the blood pressure inside the dental pulp.

Pulp has a high pulsatile interstitial fluid pressure which allos dentinal fluids to move outwards ; the pressure inside the pulp is high that is why the fluids move out and this is also associated with the sensing of pain , we call that " the hydrodynamic theory" .

Nerves :

Dental pulp is highly innervated . we have Scant perineurium or epineurium ; perineruruim is the outside membrane of the central fiber of nerves .

We have two types of nerve fibers : the C and A delta fibers . ( the doctor says that he won't bring questions about this slide in the exam because he explained these things in oral physiology So this slide Is not included ! )

Nerves run along side the blood vessels In the center of the pulp . they branch profusely In the odontoblastic & subodontoblastic regions .In the crown , the subodontoblastic plexus is called plexus of Raschkow .

This is evident only after eruption ; we can see this plexus only after the eruption of the tooth .

Some branches reach between odontoblast and predentine while others continue and join the processes within the tubules .

May be a site of sensory activation as evident because axons lack Schwann cell covering ; these axons when passing through dentine it becomes unmylinated so it

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can be directly stimulated and we called this the direct stimulation theory .

The next slide is not included in the exam (Nerve fiber types ).

Nerve endings :

Some A delta fibers enter the tubules in the coronal dentine , while others end in predentine -pulp junction . It is suggested that there is a specialized junction between nerve endings and odontoblasts .

So it is thought to be a junction between the odontoblast and the nerve endings ( like type 3 taste bud cells ) where the cell can make a synapse with the nerve .

Regions :

This slide is very important and it talks about the different

layers in dental pulp .

These layers are : the supraodontoblastic layer , the odontoblastic layer , the subodontoblastic zone and the central region respectively .

Referring to the picture below : this is the dental pulp , dentine , so the first part is called supraodontoblastic layer because its located above the odontoblasts and it appears as a space , and then there is the odontoblasts , the subodontoblastic area and then the pulp core .

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Regarding the supraodontoblastic region : it is not present in vital pulps ; that means that this region appears due to shrinkage of the pulp while preparing the slide for macroscopic observation , and that produces the space above the dental pulp we usually see under microscope .

Meanwhile in the vital pulp , there is no such space because there is always good amount of pressure pushing the odontoblast so it don't move from its space.

Two structures can be present in this area which are the : unsheathed axons and the dendritic antigen-presenting cells .

Then we have the odontoblastic layer which is the layer formed by

dental odontoblasts.

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And then we have the Subodontoblatic zone :

o we have the zone of weil & cell rich zone ; you can see that directly below the odontoblasts there is a layer that is free of cells ( no cells there ) so its called the Cell-free zone of weil . and below this layer there is a layer that has a lot of cells and so its called the Cell-rich zone .

o in cell free zone of weil : we don't see any cells there , only axons & cell processes of fibroblasts & other cells , and this layer is usually absent in radicular pulp .

( and we all know that in light microscope we only see the nuclei of cells and not the cell walls , so when there are no nuclei or no cell bodies we see a space , this space might have other structures like axons , processes , etc )

o In cell rich zone : this layer has lots of cells and appears in contrast to the cell free zone ( الخاليا من الخالية المنطقة مع بالمقارنة (تظهر, capillaries and nerve plexuses that contain the cell bodies of schwann cells , endothelial cells , etc.

Now in central region : we see the bulk of the dental pulp , the cental neurovascular core which the core that has the bundle of the major blood vessels and the major nerves , we see also fibroblast , defence cells and undifferentiated cells and collagenous matrix and ground substance . also we see thick blood vessels in this area as you can see in the picture above .

Age related changes :

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What happens to your dental pulp when you get advanced in your age ?First of all , the pulp becomes smaller because of the addition of secondary dentine , and in cases of tertiary dentine the pulp gets even much smaller , this leads to the reduction in the vascular , neural and cellular contents , increase in the fibrous matrix ( because fibroblasts have been producing fibers and ground substances for a long time and so the content of the extracellular fibers will be greater than before while the number of cells will decrease ) . Also we see some degree of mineralization ( تكلس حدوث يمكن

اللب this will be in the form of either a pulp stones or huge (داخلcalcification called snow storm calcification .

o Pulp stones appears as spheres or globules , While in snow storm calcification the whole pulp looks calcified ( بمادة رشه تم كأنه و so the calcification in this type is spread evenly inside the ( مكلسةpulp.

o Pulp stones can be single or groups , it can be free inside the pulp or attached to the dentine , and most importantly it can be true

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or false , true when it is dentine-like ; looking exactly like dentine having dentinal tubules , peritubular dentine and intertubular dentine , etc . and true pulp stone is formed by odontoblasts . However , False pulp stones is Bone-like and is formed by hydroblasts .

DID You know that : pulp stones are extremely common , occurring in as many as 90 percent of people between the age of 50 and 70 , it is not known precisely what causes pulp stones but they are really painful and they require surgery in most of the cases!

إثما منعك و، علما ومنحك, حلما مازادك : االيام أفضل فهما وأعطاك، .

Good luck all

DONE BY :

AyA ALALI, BaYaN AL-SHAIKH

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