Dentine Slides (7-27)

Slide (7)--If you take 1 cm square on the surface of dentine and 1 cm square on pulpal dentine (ya3ni dentine at the pulpal surface) in other words (I took

1 cm square from the surface of dentine from the area where we have a junction between enamel and dentine and I took also 1 cm square at the end of the dentine at the pulp---- we will see that the numbers of tubules in surface of dentine lesser than the number of tubules in the pulpal side of dentine ; this means that the concentration of dentinal tubules at deep areas are much more than the concentration at surface area …..This makes the deeper portions of dentine more permeable than the surface Portions(

Now this has a difficult significant; caries has to actually pass through dentine from top to bottom, now if we imagine that we have a thickness of dentine, lets say (4mm) from the top to the pulpal surface of dentine.

Now caries spends more time in passing through the top half than the bottom half (in other meaning; cariosity (decay) has different speed

It starts slowly in dentine …once the dentine become deeper spreading become faster….now if we assume that decay needs 2 months to grow over the dentine from the top to the bottom in the first months we can see (1mm of caries in the dentine but in the second month we can see 3 mm of caries ) and the reason of that is the size of the dentinal tubules …first of all we have bigger dentinal tubules in deep portions ,,secondly the number of these tubules become increased because the surface area become

decreased.

Also the tubules runs from the pulpal surface to dentin enamel junction …(now the doctor started pointing on the image and said :this is a tooth cross section here we can see so me of dentinal tubule stained in black, you can see that they run from enamel dentine junction until they reach the pulpal surface of dentine ,notice that this curvature is not necessarily straight …it's sigmoid(S – shaped) ; it follows sigmoidal curvature and it's actually root wards ;what do we mean by root wards ? The curvature (s) is toward root near the pulpal surface so as we go toward the pulpal area the convexity become toward the tooth and almost straight in the root and beneath the cusps ..See here some dentinal tubules beneath the cusp (they are also straight) and also if we see the dentinal tubule in the root, they are straight..((So straight dentinal tubules can be seen under the cusps and in the roots)).

)There is another area which we can find straight dentinal tubules but I couldn't hear it at all sorry guys (

We have two areas of dentine or two types of dentine:1 .Dentine that surrounds the dentinal tubules called

(peritubular dentine).2 .Area of dentine between tubules is called (intertubular

dentine) . The doctor then moved to another slide which shows the dentinal tubule (he showed us the wall of the dentinal tubule and also showed us the dentine between the tubules …these

type of dentinaltubules are ) tapered الشكل مخروطي (don't have the same diameter … the diameter tends to be decrease as we go toward the surface but if we go toward the pulp it become wider ….diameter from (2.5 micrometer at the pulpal end - 1 micrometer peripherally ((near the surface)).

Walls of dentinal tubules widely separated at peripheries (surface area)

)not sure)… (and because the surface area of dentine( the external surface of dentine) more than the surface area of the pulpal dentine ; the numbers of these tubules become less outside than inside….so the more widely separated at the

periphery because the surface area is narrow!?!? بعض من قريبين بكونوا ضيقة المنطقة ، بعض عن بعاد بكونوا واسعة (المنطقة

(

The previous curvature which I explained before minutes (sigmoidal curvature) is also called primary curvature because there is another curvature called (secondary

curvature of dentine); they are small curvatures.… Now when a number of tubules have the same secondary curvatures they produce what they call (( contour lines of Owen)) when secondary curvatures go inside in adjacent tubules… see here (the doctor pointing on the slide )--------- we can see lines ;these lines is called contour lines of Owen

they represent in secondary curvature of dentinal tubules.

Slide 8:

Tubules actually branch but the only branch at the third piece….but it can also branch near the surface of dentine

(peripherally; outside)..… Moving to another slide which shows the longitudinal section of dentine … this cross section of tubule (looks like dots shows the cross section through dentinal tubule).Slide 9:

Peritubular dentine which is the walls of the dentinal tubule has another synonym of intratubular dentineDeposited by the processes (odontoblastic processes) and this

causes narrowing of dentinal tubules.… We said that odontoblast call -- body elha extension da5el bel dentine we called it (odontoblatic process) this extension da5el bel dentinal tubule and continuously b9eer fe 3na press (not sure) 3al cell wall…so it becomes narrower; when this press happened this gives us peritubuar dentine giving the walls of these tubules, these tubules are wide in most young people but it tend to be narrow in old people because dentinogenesis is continuous (produce more dentine in old people( the size of dentine secretion is bigger)…makes the walls narrower ) that's why caries progression is faster in young people than in old people because narrow walls don't allow caries to enter it will

be so difficult and slower . The parts which are affected by odontoblastic processes are walls and this leads to narrowing the dentinal tubules.

Peritubular dentine lacks collagenous fibrous matrix it's not based on collagen...It's based on something else …so the organic material is not collagen but in the rest of dentine organic material based on hypocollagen (not sure) as we discussed before…increased ( radio density; the amount of minerals in peritubular dentine is more than in inter tubular dentine ( it's 15% more mineralized than in intertubular dentine) that's why it may actually makes a radioductive image of dentine ,of coarse microradioductive image we will see this lighter in color why because it's small radiodenseAnd the crystals are not hydroxyapatite but carbonated apatite which is similar for those in Sea shells. ;)

which is smaller than those of intertubular dentine.

A student asked a question and I think it was about the X-ray image ? The doctor answered that once you put your hand under x-ray …bones look in white color and the skin in black

and that's what happens with peritubular dentine (whiter /lighter) than the intertubular dentine .

Slide 10: The odontoblastic process becomes embedded in the extra-cellular matrix and we have already discussed how cells form dentine..This is an odontoblast, it deposits first layer of dentine and then it starts to move towards the pulp which have process that is keeping inside the dentine so that's why the odontoblastic process becomes invaded in the extra-cellular matrix that become later on mineralized and this creates a

dentinal tubule. Odontoblastic process elongates as the odontoblast moves toward pulp and it stimulates the differentiation of ameloblasts, so the part of the odontoblast which is active in sending signals through this interaction is the (odontoblastic process) <<not

the body of the cell.<<

Slide 11:Layers of dentine:

In the crown we have three layers of dentine and we have also three layers of dentine in the root…

The top layer in dentine in the crown called (mantle dentine) then we have (interlobular dentine) then (circumpulpal dentine- means surrounded actually it surrounded the pulp).

In the root we have the (hyaline layer), (granular layer of tomes), (circumpulpal dentine). Now let's see talk about each layer --

Slide 12: 1 .Mantle dentine: (thin)

*It's the outermost layer of dentine in the crown.It's (20- 150 micrometer) in thickness.*

*It's the first formed layer (as we said before the odontoblastic cells move towards the pulp so the first layer of dentine is the layer away from the odontoblastic process which is the layer just under enamel called (mantle dentine).

*It's 5% less mineralized.*Collagen fibers are perpendicular to dentinoenmel junction

(DEJ)*We have more dentinal tubule branching in mantle dentine

(tubules tend to branch more at the peripheral part of dentine

than the inner part of dentine; that's why we find most of the branches in the mantle dentine).

*The weight of mantle dentine is (matrix vesicle mineralization) -- we discussed that in the previous lecture.

Slide 13: 2 .The interglobular dentine:

*It's a layer just beneath the mantle dentine and this layer results because (calcopherites) failed to fuse…

*Dentine formation is not similar to enamel formation actually mineralization of dentine forms in globules (spheres) that grow and fuse together (3ala shakel korat :p) normally it fuse completely but in this layer they fuse incompletely so we may see areas without mineralization because these spheres failed

to fuse completely giving interglobular (IGD) dentine so.…*In general, much of the mineral in the dentine is deposited as

globules as the (calcospherites) eventually fuse.In IGD calcospherites fuse incompletely.*

*IGD is located beneath the mantle dentine in crown and also beneath the granular layer of tomes in the root.

*IGD appears dark in transmitted light--when light passes through these nonmineralized areas it appears dark.

Tubules pass through without deviation (the absence of some minerals in this area doesn't mean that tubules are deviated; they continue in there path whether straight lines or sigmoid paths (S_shaped).

Peritubular dentine is also absent (as the tubules go through the IGD, if one tubule passes through the nonmineralized part it also will loose the peritubular dentine), this is a slide showing

dentine (slide 14) ---- this information is important***Mineralization is not even: when we say that dentine is( 70%) mineralized this doesn't mean that it's 70% in area of dentine if we take for example this area it could be (90%) mineralized or if you take this light area it's possibly only (40%_50%) but (70%) means the average mineralization in dentine (some areas high minerals and some have less minerals.

talking now about dentine in the root, the first later below cementum, it's called (hyaline layer)…

Slide 15: It's very narrow

Non -tubular structureless band (so it is a band which appears whitish in color, very narrow and non-tubular (we find no tubules)

The origin of this layer is unknown it's (obscure- some people say that it's from cementum and some people say that it's from dentine) ….until now they are searching for the origin of this

layer!!

Slide 16:

Granular layer of tomes: *Under the hyaline layer we have the black area which shows

the (granular layer of tomes) this is only in the roots and actually Tomes is the first scientist which discovered the

process of ameloblast… *It's located just beneath the hyaline layer and cementum.

*This granular layer of tomes results because also branching and looping of tubules and tubules in this area they tend to have branches and also some they tend to spiral (belefo 7awl nfsohom) make loops.

*Could also be formed because of incomplete fusion of (calcospherites)--so if we consider *this reason granular layer of tomes would be similar to (IGD) because the reason why we have (IGD) is incomplete fusion of (calcospherites).

Slide 17:Circumpulpal dentine is the rest of dentine in the crown and the rest of the dentine in the pulp, it's beneath mantle and IGD in crown and beneath the granular layer of tomes and also the hyaline layer in the root.

Slide 18:Predentine:

*Results because dentine mineralization is not immediate, enamel mineralization is immediate …y3ni if we actually lay down a layer of enamel still now in organic material, this will calcify straight away but in dentine this will calcify after 24 hours, the difference between the deposition of organic matrix and the mineralization of this matrix results in what we call

predentine for example (pointing on the slide #18) ---white color shows the predentine.

*If I come to this layer after 24 hours suppose that this tooth is alive I will find that this layer will become mineralized and there will be new predentine layer.

*The innermost layer of dentine is (10-40 micrometer) in thickness …it's thicker in young teeth because the deposition of dentine is faster in young teeth, it's not mineralized and it results because matrix deposition precedes mineralization ,we have time gap between matrix deposition and mineralization of almost 24 hours.

*It's secreted by the odontoblasts not by the odontoblastic processes by way of Golgi apparatus and mitochondria (this secretion should be very active secretes too much of dentine).

It appears pale compared with the mineralized circumpulpal dentine.Mineralization front is actually delight between predentine and dentine (it's the interphase (not sure) between the dentine and the predentine) we called it mineralization front, sometimes its straight (linear) and sometimes it's globular depending on the activity.

Slide 19:

Structure lines in dentine:

*lines associated with primary curvatures.We said we have sigmoid curvature (it's **** curvature of dentinal tubule). If we have a layer of dentine with the same curvature of tubules they will produce what we call (Schreger lines) -- these are equivalent to ((hunter- schreger bands) in enamel, when we have a group of enamel prisms having the same curvature) ….here (slide 13) we have the group of dentinal tubule of the same of the same curvature giving lines called (Schreger lines).

Coincidence at the peaks of sigmoid curvatures (the peaks of these curvatures meet).

We have also -*lines associated with secondary curvatures .

These are called contour line of (Owen), they look like زي (مطعوجه

( pathال نفس إلهم بكون منهم مجموعة ألنه طيات في كأنه They are unusual in primary dentine; they are more visible in

secondary dentine. Now the difference between secondary and primary dentine is that the primary dentine is all dentine deposited before root completion, secondary dentine is dentine deposited after root completion so that's why we do not see too many of these contour lines of owen in primary dentine we see them in secondary dentine.

In addition to these lines associated with curvatures also we have the incremental lines similar to enamel we have also incremental lines in enamel, the short term incremental lines are called (Von Ebner's lines in dentine)Which are equivalent to cross striations in enamel but the long term of contour lines or long period lines are called (Andresen lines); it's equivalent to enamel striae in enamel.

The long period lines reflect (*****/can't hear it ) and the short term lines they reflect the daily rhythm …we said that enamel everyday form a layer ; between a layer and the other we haven enamel striation and between every (7-10 layers) we have enamel striae …in the dentine the same thing presents ; everyday a new

Layer forms between one layer and the other we have (von-Ebners lines) and (between 7-10 days) we can notice an obvious line called (Andersen lines--- they are (16-20 micrometer apart + they are associated with changes in collagen fibrils orientation))And of these Andresen lines is ((exaggerated line=one of the Andresen line very obvious =Neonatal line=we can see it at the time of birth from the word natal: p))

When we have the fetus that is going to be outside, what happens? The environment will change because this fetus has his (can't hear) inside the uterus and suddenly this fetus will be delivered outside so we will have a sudden change in the surrounding environment so at the time of birth or at the time of giving birth we will have nature changes of what is forming

at this particular moment ..Among this things is dentine; dentine can be forming at time of birth so that's why this is produces much interpreted lines of neonatal lines.

Neonatal lines separate any part of mineralized tissue prenatal and postnatal (

يتكون الذي الدينتين عن الوالدة قبل يتكون الذي الدينتين من جزء بين (تفصلالوالدة) بعد

Slide 20:Now talking about primary and secondary dentine …primary dentine is any dentine forming before the root completion and any dentine form after root completion is called secondary dentine.Do we have primary enamel and secondary enamel?

No, because enamel formation is completed when the crown is completed (ya3ni) once enamel is formed it's formed we don't have enamel deposited after the completion of the enamel but

dentine is different; dentinogenesis is continuous .

Secondary dentine:*is dentine formed after complete formation of the tooth.

Because we have secondary dentine forming the surface area become less (the surface area of the pulp decreases).

Cells arranged comfortably when (tooth is young)The pulp is big and the cell (odontoblast is also arranged comfortably; has a good space) but with time when the size of dentine become bigger, the size of pulp become lesser become pressed so all the spaces between the cells become lesser.

)Secondary dentine is less perfect than primary dentine---When these cells work in narrow spaces (****) become lesser

That's why secondary dentine is less perfect than primary dentine (it was produced while the cells where actually active because they have good space, secondary dentine is produced while these calls are colorless (not sure :0 ) so that's why it has less quality than primary dentine.

**increased crowding in odontoblasts leads to: -Slower deposition than primary dentine.

-Less regular pattern of deposition.

-Change in orientation and curvature of tubules.

**form most rapidly at the pulpal roof and floor (in posterior teeth we have something called pulp chamber in crown حجرةاللبChamber with 4 walls-- mesial +distal + buccal +lingual+ roof +floor so always the deposition of secondary dentine is more on the roof and the floor.

Slide 21: Translucent dentine:

*forms with aging because of tubular occlusion by peritubular Dentine.

When we become older in age the tubule become narrower and it could become completely closed ….when it completely closed we call it (translucent dentine).

Translucent dentine belongs to old people; we can not see it in young people, why? Because the dentinal tubules are big and opened.

It can be pronounced at the root apex and it's used in forensic dentistry in age determination.

Doctor Ashraf skipped the slide which is about (tertiary dentine) and started with -----

Slide 23:Sclerotic dentine:

It's also caused by tubular occlusion إغالقBut it's not causing by aging it's caused by stimulus

فيها تجمع ألنه تغلق tubules ال هذه جعل التسوس مثل خارجي مؤثر هناكminerals

Very very important **How can we distinguish between Sclerotic dentine and

the translucent dentine?--- Always sclerotic dentine it should be apposing stimulus like

caries but in translucent there is no caries; it appears due to aging !

Note: sclerotic dentine has similar appearance to translucent dentine but related in site to the stimulus (caries/ trauma).

Doctor Ashraf went back to slide (22/tertiary dentine)--Slide 22:Tertiary dentine:

When we have a very severe stimulus outside the tooth (outside the dentine); like caries for example, if this stimulus is not severe we will see build up (not sure) of dentine in the

internal side slowly as the caries spread out !?Severe stimuli lead to pulp necrosis because they actually destroy dentine faster than our capability in building new dentine.

Notes:*This severe stimuli increase the production of tertiary dentine

which is produce when we have pulp necrosis.

Tertiary only appears in people who don't care about there *Teeth (who have caries for example :0).

Tertiary dentine formed by odontoblast newly differentiated*From the pulpal mesenchyme after original cells have died.

*It varies in appearance and dentition it can be:-regular or tubular structure (if the caries was chronic not acute

so the odontobast will form the dentine very very slowly having tubules).

-it can be irregular arranged tubular structure if the dentine formation was fast.

-it can be atubular (having no tubules because of the randomly fast formation).

We have also 2 types of tertiary dentine:1 .Reactionary dentine: results because cells injured which

produced dentine after injury.

2 .Reparative dentine: because of differentiation of new cells. ***The doctor asked us to go back to the book and know what

is the difference between them he is not responsible about them!!!!! And it's required in the exam …always there is a

question about this subject O.o in the final exams !!!

Slide 24: Dead tracts:Sometimes a stimulus don't lead to occlusion in tubules

tubuleال بسكر ما occlusionال بعضBut it can kill the odontoblastic processes inside the dentinal tubule it makes the dentinal tubules empty (have no odontoblastic process) and because it appears as a space (EMPTY TUBULES); under transmitted light microscope it tends to appears dark (black) ------ slide (24)

Slides (25,26,27): Tetracycline---- antibiotic was used in1970s and 1980s it was

very common but they found that this antibiotic it tends to precipitate in dentine and enamel giving staining of teeth. Newborn kids found to have colored teeth (pigmented: because pregnant used to take tetracycline or the newborn was given tetracycline when one of his teeth was forming so it becomes incorporated within the cell and it leads to pigmentation and it tends to be actually pigmented in lines (slide 25) these lines are related to the curvature of the

dentinal tubules ..The last three slides are required but the doctor didn't explain any details he asked us to refer to the book ….it's very important …many questions will be in the exam about them !!!!! O.oThe title of these slides (tetracycline stain).

Done by: Raya Hijazi

Good luck all <3