Complement of dentine lecture begins at slide 7:

Besmellah nabda2:

Now if you take 1cm^2 from surface of dentine and 1cm2 from pulpal dentine you will find that the number of dentinal tubules in the surface dentine is less than that of pulpal dentine, that means the concentration of dentine tubule in the pulpal area is much than that of surface area, this make the deeper side of dentine more permeable than the surface portion ,now this has a clinical significance , caries actually has to cross dentine from top to bottom if we imagine that we have 4 inches of dentine ,now caries spend more time in passing the top half than the bottom half (kola ma t3amma8na the caries speed in dentine becomes faster, if we suppose that caries need 3 months to pass through the whole length of dentine ,in the first month (for example) it may cross 1mm but in the second month it may cross 3mm,because the size of dentinal tubule is bigger and the number of dentinal tubule become decreased ,because the surface area decreased .

Dentinal tubules run from pulpal surface to EDJ, THIS IS ACROSS SECTION OF ATOOTH WE CAN SEE SOME DENTAL TUBULES STAINS IN BLACK

IN THIS PICTURE BELOW YOU CAN SEE DENTINAL TUBULES FROM EDJ TO PULPAL SURFACE...

Note that this curvature is not necessarily straight its sigmoid curvature its like (S) shape as you can see above this curvature is rootward .Rootward means :that as we go deeper to pulp area the convexity become the root itself(not sure sorry couldn’t hear well),again dentin tubule almost straight in the root and beneath the cusp ,as you can see above the dentinal tubule is straight under cusp and straight in the root but it may be convex in other areas like crown area or other areas except for that of cusp and root areas.

Now we have 2 area of dentine or let’s say 2 type of dentine,

1. Dentine that surround dentinal tubules called peritubular dentine or intRAtubular dentin. Which given the letter( A) in the picture below

2. The area between dentine is called intERtubular dentine. Given the letter B

Now, dentinal tubules are tapered, it means that they don’t have the same diameter, they tend to decrease as we go to the surface .As we go to the surface the diameter of these tubules become less, if you take one dentinal tubule running in its usual way and you measure the diameter, you will find it smaller at the surface, but near the pulp its bigger(conical in shape).

Dentinal tubules Tapered from 2.5 µm at pulpal end to 1 µm peripherally, they are more widely separated at periphery, because the surface area of surface dentine is more than the pulpal dentin area the so spaces between dentinal tubule become much more in the surface area than in deeper area.

Now, in addition to primary curvature of dentine we have secondary curvature .if you take a small segment you will see secondary curvature also. The primary goes from the tip if dentine to the end of it, and if you take a small segment from this primary dentine you will also find a small curvature called secondary. now when a number of tubules have the same secondary curvature they produce what we called CONTOUR LINE OF OWEN which means that secondary curvatures coincide in adjacent dentinal tubule, as I have a collection of dentinal tubule having the same path. The arrows showing contour lines associated with coincidence of secondary curvature ………..

The dentine appears as it has folds (6ayyat)………………..

*Tubules branch but the only branch is at peripheries.

Branching and looping gives the granular layer of Tomes in the root we will see that when we discuss the layer of root.

*Slide 8: across section and longitudinal one of dentinal tubules, dentine in tubules appears as dots in a cross section………

Slide 9: Peritubular dentine

Peritupular dentine is the wall of tubular dentine it has another synonyms which is intratubular dentine deposited by odontoblastic processes not odontoblastic cells themselves on the wall. This actually cause narrowing of dentinal tubules bema3na a5ar we said that odontoblasts has a body and extensions which is called odontoblastic processes and this extensions enter dentinal tubules and these produce secretion forming the peritubular dentine giving the walls of these tubules .now these tubules are wider in young people but tend to be narrowed in old people, because dentinogenisis is a continues process ,when we take the dentine of a20 years old person we will find that dentinal tubules are wide because there isn’t sufficient time for secretion to accumulate so the thick of the wall is less and eventually the hole of tubule is bigger or wider ,but if we take a50 years old man it’s the opposite there is long term of secretion so the thickness of these wall is much more than that of 20 years old ,that’s why caries progression is faster in young people than old ones, because the big size of dentinal tubule (here we are talking about the hole of dentine)the caries enter easily in the wider tubules than narrow ones MAN6E8.

So peritubular dentine deposited by the processes on the walls and narrowing the dentinal tubules and it lacks collagenous fibrous matrix it’s not based on collagenous its based on something else, so the organic material is not collagen in peritubular dentin but in the rest of dentine the organic material is based on collagen.

Another thing, that there is increased radiodensity, the amount of mineral in pretubular is more than that in intertubular dentine.

Its 15% more mineralized than intertubular that’s why when we made a microradioactive(not sure) image we will see it whiter in color because its more mineralized el eshe elle bekoon dense appears white in radioactive picture.

The crystals are not hydroxyapatite crystal instead its carbonated apatite crystal it’s similar to crystal in shells (al asdaf) it’s smaller than those of intertubular dentine.

Slide 10: Odontoblasts and processes ……..

Odontoblastic processes become embedded in extracellular matrix .we discuss how the cells form dentine we said that odontoblast deposits the fist layer of dentine and starts to move toward the pulp .these cells have processes that keep them attached to dentine and push them to the pulp, so that’s why the odontoblastic processes become embedded in the extra cellular matrix that becomes later on mineralized and this creates dentinal tubules ,odontoblastic processes elongate and the odontoblast moves toward pulp, and this stimulate differentiation of ameloblast as we discussed in amelogenisis.

So the part of odontoblast that is active in sending signals through this interaction is the odontoblastic processes not the body of the cells.

Slide 11: layers of dentine……

In the crown we have 3 layers of dentine and also we have 3 layers in the root. The top layer in the crown is called mantle dentine and then interglobular dentine and then circumpulpal, Circu means surrounding. That part of dentine that surrounds the pulp. The layer of the root:

Hyaline layer

Granular layer of Tomes

Circumpulpal dentine

****Now (A) is granular layer, (C) is hyaline layer, (B) Circumpulpal dentine…….

Slide 12: mantle dentine…..

It’s the outer most layer of the dentine in the crown its 20-150micrometer in thickness so it’s very thin ,again it’s the first formed layer as we discussed .The odontoblastic cells move to the pulp so the first layer of dentine is that which is away from odontoblastic processes which is the layer under enamel which is called mantle dentine ,its 5% less mineralized ,collagen fiber perpendicular to EDJ and also we have more dentinal tubules branching at mantle ,we said that branching is much more on the periphery than deep parts of dentine that’s why we have a higher percentage of branching at the mantle dentine which is at periphery.

The way of making mantle dentine is matrix vesicle mineralization we discussed that in the previous lecture. Just to remind you with it it’s formed as globules that finally fused together.

Slide 13: Interglobular dentine …………………

Interglobular dentine is the layer beneath mantle dentine and this layer is formed because calcospherites are failed to fuse.

Dentine formation is not similar to enamel formation, dentine forms in tubules or spheres that fuse together eventually.(I think the doctor ment mineralization of dentin not formation note that it differs) .Normally the fusion is completely but in interglobular dentine these spheres are not completely fused ,so we may see areas without mineralization because these spheres fail to fuse giving interglobular dentine, so in general much of the minerals of dentine are deposited as globules (calcospherites) that eventually fused.

****In the case of IGD calcospherites fuse incompletely.

Interglobular dentin located beneath mantle dentin and the granular layer of toms in the root also. They appear dark in transmitted light when alight pass through these UN mineralized area they appear dark, in general in ground section when the light pass through a space it appears dark indicating that it is UN mineralized. And because these areas are not mineralized when you see aground section to these areas under light microscope we see dark areas.

Tubules pass through without deviation ya3ni the absence of some mineral does not mean that the tubules are deviated they continue in their path whether straight or sigmoid.

Peritubular dentine is also absent .as tubules go through globular dentine if one tubule passes through non mineralized path it will loose peritubular as well as inter tubular dentine .

Slide 14……

This slide shows dentine .This information is very important, mineralization is not even. When we said that dentin is 70% mineralized this doesn’t mean its 70% in any area .in the picture if we take that area (A) it may be 50% mineralized but 70% is the average. That’s why the mineralization is not even, some areas have more minerals and some have fewer minerals.

Slide 15: Hyaline layer ……

Hyaline layer in the root is the first layer below cementunm, (C)

A

It’s very narrow, nontubular , structurless band which appears whitish in color so in this band we find no tubules, the origin of this layer is not known its obscure some people say its from cementum and some people say it’s from dentine .we have people still estimating the origin of this layer.

Slide 16: Granular layer of Tomes

Under the hyaline layer we have this dark layer giving the letter (A) in the picture which is called granular layer of toms this only found in the root ,and by the way toms is the a scientist who actually the first to discover the tom’s processes, this layer is in the root just beneath the hyaline layer and cementum ,this layer appears due to branching and looping of tubules the tubules tend to spiral and branch., or could also be because of incomplete fusion of calcospherites it would be similar to interglobular dentine which forms in the same way.

Slide 17: Circumpulpal dentine in the:

Crown

Beneath mantle and interglobular dentine

Root

Beneath the granular layer of Tomes and also behind hyaline layer in the root.

Slide 18: predintine ……

Result because dentine mineralization is no immediate, enamel mineralization is immediate, ya3ni if we lie down a layer of enamel this will calcify straight away, but in dentine this will calcify after 24 hours, the difference between the deposition of this organic matrix and demineralization results in what we called predentine. This light color is predentine.

If we come to this layer after 24 hours if we consider that the tooth is alive, we will find that this layer has mineralized and there is another layer of predentine.

Again predentine is the innermost layer of dentine, 10 to 40 µm in thickness, Thicker in young teeth because the deposition of dentine is faster in young teeth.

It’s non-mineralized and because matrix deposition precedes mineralization we have a time gap between matrix deposition and mineralization of almost 24 hour.

It’s secreted by odontoblast not by odontoblastic processes by ways of Golgi apparatus and mitochondria this means that their secretion is very active and needs much energy. ItIt appears pale compared with the mineralized circumpulpal dentine.

Mineralizing front is actually the line between predintine and dentine, it’s the interphase between dentine and predentine.some times its straight and some time it’s globular depending on the activity.

Slide 19: Structure lines in dentine………..

Line associated with primary dentine curvature, we said that we have sigmoid curvature, this is the primary curvature of dentinal tubules, if we have a layer of dentine with the same curvature of tubules we call them schreger lines, these are equivalent to the

predentine.

hunter schreger band. Coincide at the peak of sigmoid curvature ya3ni beseer zai tala8e been hay el curves, again we call it schreger line.

We have lines associated with secondary curvatures these are called contour line of Owen (as we have folds), they are unusual in primary dentine, but they are much common in secondary dentine, again primary dentine is 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 contours line in primary dentine. See below *****

(A) Is schreger line….

In addition to the curvature lines, we have incremental lines:

1. short period line called Von Ebners line which are equivalent to cross striation in enamel but,

2. The long period lines are called Andersons line this equivalent to enamel striae .

The long period reflects the weekly rhythm and the short period reflect the daily rhythm these are 16-20µm apart. Every day there is a layer. the line btw them is Von Ebner , and every week there is a very clear line separates them called Andersons line. The horizontal lines on the right are Andresen lines…….

The long period incremental lines are Associated with changes in collagen fibrils orientation and one of these Andresen lines is exaggerated. When we see one of the Andresen lines is exaggerated (very clear) this is usually NEONATAL LINE.

Now, natal means birth.

Neo natal line called so because it appears at birth ,when we have fetus that it has to be outside ,the environment will change ,the fetus used to be in his mothers uterus and suddenly this fetus will be delivered outside ,so we have usually change in the environment, so at the time of birth we have major changes at what is forming at this particular moment among these changes is dentine ,dentine can be formed at the time of birth so that’s why it will form neonatal line, neonatal line separate mineralized tissue the pre-natal and post-natal . THE ARROW INDICATING NEONATAL LINE……..

Slide 20: Secondary dentine……

Secondary dentine is the dentine forming after completion of the root, we don’t have primary and secondary dentine in enamel because the enamel completed when the crown is completed but dentinogenesis is continuous.

Because we have secondary dentine forming the surface area of the pulp become less .the cells are (merta7a) when the tooth is young because the number of cells is less, so there isn’t that much pressure on them, with time the dentine becomes bigger so the size of the pulp becomes lesser. So when the cell works at a narrow area the performance of these cells become less so that’s why secondary dentine is not as much perfect as primary dentin.

So increase crowding of odontoblasts……

Slower deposition than primary dentine

Less regular pattern of deposition

Change in orientation and curvature of tubules

Secondary dentine forms most rapidly at the pulpal roof and floor. in posterior teeth we have the pulp champers which have 4 walls , mesial ,buccal ,distal,lingual,roof and floor so always the deposition is much more on the roof and floor.

Slide 21: Translucent dentine…….

Translucent dentine forms due to tubular occlusion as we proceed in age .we said that as we go on age the tubules become narrower and may closed entirely and this what we called translucent dentine ,this coincide with age that’s why it’s used in forensic dentistry .in young people we don’t see translucent dentine. And it’s also pronounced at the root apex. This is translucent dentine…..

****The doctor skip slide 22 and he said that we will return to it after explaining sclerotic dentin….

Slid 23: Sclerotic dentine……

Sclerotic dentine is also caused by tubular occlusion but this is not caused by aging, this caused by a stimulus, due to (mo2ather 5arejee) like caries.

How we distinguish btw sclerotic dentin and translucent dentine?? All the time sclerotic dentin should be due to a stimulus, but in translucent there is no stimulus just aging.

***It’s similar in appearance to translucent dentine but related in site to the stimulus.

Now we go back to …..

Slid 22: Tertiary dentine….

When we have a stimulus outside dentine, that is not severe we will see build up of dentine in the internal side, but in case of sever stimuli it leads to pulp necrosis, because the destruction of dentine is faster than building up of dentine, but when this stimuli is less severe it induces the production of tertiary dentin, this is important in dentistry.

A7yanan bno7for el-tooth kteer oma3 4alek ma bno9al to the pulp and that’s because of the formation of tertiary dentin as a response to a stimulus…

People who take care of their teeth and do not expose them to caries don’t experience tertiary dentine, just secondary and primary.

And its Formed by odontoblast newly differentiated from the pulpal mesenchyme after original cells have died. And these cells are found after splitting of original cells, and they were kept in a store like place to use it when teeth are in need, upon calling these cells they can differentiate into odontoblasts and form dentin.

Tertiary dentine varies in appearance and composition it can be regular tubular structure, if the building is not disrupted (ma5ed ra7to) and the caries is chronic not acute. And this allow dentine to form in longer period of time and the structure will be good and have tubules, but when the building is too fast the structure will be irregular and sometime Atubular.(without tubules)

Also we have 2 type of tertiary dentine:

1. Reactionary: cells are injured and they are produced after injury.

2. Reparative dentine: because of differentiation of new cells.

****The doctor said he will not talk much more about them but we have to refer to the book to differentiate between them because he always brings these 2 types in the exam.

Slide 24: Dead tracts….

Some time stimuli do not lead to occlusion ,does not close the tubules ,but it may kill odontoblastic processes ,and leaves the tubules empty so we call them then dead tracts because they are empty ,under light microscope it tend to appear dark and this is an example of dead tracts…….

Slide 25: Tetracycline Staining……

Tetracycline is an antibiotic that was given in the past, but they found that it tends to precipitate on dentine and enamel giving a staining on the tooth, they found that new born has pigmented teeth ,even because the mother used this antibiotic during pregnancy period or the child was given tetracycline during development of his teeth, the stain tend to be oriented in line related to the curvature of dentinal tubules . The doctor said that we have to refer to the book for more details ……

And that’s it……………………………………………..sorry for any mistake. I have done my best under the pressure of my exam tomorrow……………………….

Done by: Bayan Mrayan .

Special thanks to rafee8at darbee 7ala al fakeeh and to my best friends: Mays Mohammad, Haneen Bani melhem, Aya Alqudah , Ala’a khalaf, and to every girl in my dof3a.

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