28: Dentin I

Transcribed by Jazmin Lui April 23, 2014

CRANIOFACIAL BIOLOGYDENTIN I – DR. WISHE

OK, so we will spend 2 hours on dentin, and this particular series of lectures concludes on Monday with a CCP by Dr. Garfield. If you saw a stranger sitting in the back of the room that was him

NANCI TC FIG 8.1 TYPES OF DENTIN (7TH ED)This is a pretty decent picture showing a picture of a tooth and the various parts of it. We can divide dentin into primary, secondary and tertiary dentin and this is division based on when the tissue is really formed. Primary dentin is the major component of the dentin. So essentially as we look at this picture that’s all your primary dentin. And the primary dentin has 2 subsets. What is referred to as mantle dentin and this is little shaded area under the DEJ and second this lighter stained region known as circumpulpal dentin. Now when dentin forms, just like with bone, you have uncalcified matrix present and bone which is called osteoid. In dentin this is referred to as pre dentin. It’s a little bit hard to see here, to be honest with you, but it’s this little light staining area stained fairly thin. This is not the pre-dentin, this is secondary dentin. So pre-dentin first forms then it becomes mineralized as the first pre-dentin to form actually becomes mantle dentin. The characteristic of mantle dentin is that it actually contains reticular fibres known as Koff’s fibres. And that makes up a good part of the dentin. The rest of the primary dentin, that’s the circumpulpal dentin, is sort of scarce and coarse fibres and has more of your typical collagen fibrils. The latest theory is that coarse fibres don’t exist. We will return to that momentarily. When we spoke of the crown development centre, I mentioned to you a certain protein. Phosphophorin. The abbreviation was DPP. D stands for dentin phosphophorin. This particular protein is absent from pre-dentin and mantle dentin. So you’ll find it in your circumpulpal dentin. In essence the production of this protein is serving as a phenotypic marker for dentin. So the mantle dentin is fairly thin compared to rest of circumpulpal dentin. And I’m going to draw a little diagram here. This is a particular unit area. In this area we see four straight lines which are your typical collagen fibrils. And you see this structure which sorta looks like a tree. Those represent the reticular fibres. These fibres branch numerously. So if I were to count the number of fibres (we’ll call those A and we’ll call this B) in this particular area there would be more B fibres, more reticular fibres. In essence I’ve just described mantle dentin to you. So it’s the number of fibres is the real basic diff between mantle and circumpulpal fibres. The latest theory is that these fibres don’t really exist, and the staining of reticular fibres is being done by metallic silver. But the suggestion is that metallic silver is really staining reduced molecules of sugars. And as you look at the


black stain reduced sugars they give you the appearance of fibres. So that’s the latest idea. But since I’m old fashioned I’ll stick with fibres. Better than reduced molecules of sugar. While if someone is more biochemical they’ll go with reduced sugars. Someone’s who’s more histologically minded, like me, will go for fibres. Any ways. So mantle plus circumpulpal equals primary dentin. Once tooth erupts into oral cavity and is functional that is going to terminate the production of primary dentin. And for the rest of the tooth’s life, and your life too, more dentin will continuously form. And that’s known as secondary dentin. We used to call it secondary regular dentin. And so that’s definitely going to narrow down the size of the pulp chamber and pulp canal. Dentin always forms at the expense of pulp. In essence the secondary regular dentin is also circumpulpal dentin. And then we see this little dark black areas. That’s your tertiary dentin. And at one time we used to call it secondary irregular dentin. But between regular and irregular it became a little confusing, so secondary dentin versus tertiary dentin is utilized. Less confusing. Tertiary dentin is a type of response dentin. It’s your tooth playing dentist. So if we look over here, obviously a lesion has occurred, the enamel has been eaten away, as well as the mantle dentin. The circumpulpal dentin is being eaten away, so all these tubules have been opened up. The bacteria take a nice trot down towards the pulp and infect the pulp. But the odontoblasts try to save the situation and produce this tertiary dentin, it’s like taking a piece of chewing gum, sticking it under the lapboard, filling a hole in the wall with plaster. Sometimes it works, sometimes it doesn’t. So if it doesn’t work, you’ll be visiting your friendly dentist, your patients will be visiting you, and you’ll do what you’ve learned by coming to this school.

DVD MANTLE DENTIN/KORFF’S FIBRESHere we have a picture of mantle dentin. This is the pulp. Now what you see is a mass of black – this is really silver stain. So as you look at this picture, you get the impression, gee with that being so dark, there has to be reticular fibres. And that’s why I drew the little tree with all the branches. As we move away from the DEJ it gets lighter and lighter. And then you’re going to get formation of circumpulpal dentin which really hasn’t taken place as we look at the picture we see the pulp. Odontoblasts are sandwiched here some place, so the only thing we actually do see is mantle dentin.

O TABLE3-1 TISSUE COMPARISON (11TH ED)There are certain areas of hypomineralized dentin. In the crown we have something called interglobular dentin, you can find it in the root but more commonly you’ll find a different version of interglobular dentin known as aotome’s granular layer and we’ll gradually get into that as well. But inter globular dentin, which is dentin less mineralized,


separates mantle from circumpulpal. And if you’ll look at the mineralization you’ll find mantle dentin to be less mineralized than circumpulpal dentin. So suggestion has been that because of this fact you’ll see less mineralization defects in terms of your mantle dentin. Here we have the 3 hard tissues that we’ve been spending time on, the graph does not show you cementum, since we haven’t discussed that. Keep in mind that dentin makes up the bulk of tooth, most of dentin is circumpulpal dentin, and let’s not forget that dentin is a living tissue. It is essentially avascular and aneurular. Why I say essentially, as we get to discuss pulp, surrounding the odontoblasts is going to be a certain nerve plexus. Some of these nerves may stand up a short distance around the odontoblastic process. But essentially this is an aneurular, avasccular tissue. Dentin has been compared to bone. Osteoblasts produce bone, odontoblasts produce dentin. Odontoblasts give rise to odontoblastic process, osteoblasts have processes. And on both tissues you have organic matrix secreted around the process. So in terms of bone, remember the osteoblast became osteocyte and surrounding osteocyte process were your canaliculi. Here the odontoblastic process surrounded by dentin matrix. So both cases the process is trapped in the appropriate type of matrix. Since dentin is not as hard as enamel, it has a certain degree of flexibility, of give, it can be deformed slightly, and it does act as shock absorber for overlying enamel. If dentin is not properly maintained and becomes weakened, therefore it’s not going to be a good shock absorber of enamel. And this leads to enamel fracturing much more easily. The colour dentin is somewhat yellow in nature and when you look at person’s dentition the teeth are slightly on the yellowy side. Enamel doesn’t really have its own true colour, it translucent, almost as if you could see through it. And don’t forget it is 96% hydroxyapatite. So between all that mineral and the homogeneity and the arrangement of the crystals it’s understandable why it’s translucent and you could sort of see through it. Dentin on the other hand is only 70% mineral, 20% organic and 10% water so its partly transparent to x-rays. In comparison to enamel. So the dentin has a darker colouration. Now when we use all these percentages, 70, 20, and 10, I never mentioned before, but this is by weight. There is more than one type of measurement that can be done. If you were to measure by volume get a whole different set of numbers. So by volume you’ll find the calcium, hydroxapatite component, is 45%. If you look at organic matrix, it’s about 33%. And finally the liquid is about 33%. So you’re getting two completely different numbers based on analysis. Weight or volume. So hydroxyapatite is in the form of crystals just like in the enamel. The only thing is this is smaller crystals. And you’ll get the combination of phosphates and sulfates. In terms of what the crystal looks like they use the term it’s pleat shaped. And the crystals in dentin very much resemble the crystals in bone in terms of the size comparison.


Sometimes you get dental defects and this leads to dentinogenesis imperfecta and this basically refers to calcification defects. And you can see the organic matrix through these defective areas because it doesn’t have the right amount of enamel. Now here we have a nice figure comparing the three tissues I’ve been referring to previously. Here’s your starting point of enamel formation. And mineralizaton starts pretty close to matrix formation takes place. As you follow this curve it’s a pretty straight curve and levels off right here. And don’t forget mineralization for all these phases occurs in 2 phases, primary and secondary. So you’re getting a straight linear type of curve. When it comes to dentin and bone, that’s not really happening. So you have a period of matrix formation then mineralization will appear. And you’ll notice there is a sharp rise in the amount of mineral up to a certain point. And just using these numbers that’s 50% of the mineral. And then the rise sort of tapers off into a straight line until you end up with a total of 70% mineralization. Bone - there’s a shorter delay but it follows the path that dentin makes. Sharp rise, levelling off, more or less in a straight fashion. So the big difference between dentin and other hard tissues other than the ones already mentioned is once the matrix forms it begins to mineralize.

NANCI TC FIG 8-20 ODONTOBLASTIC PROCESSES: SEM, LM, TEM (7TH

ED)In terms of your organic component dentin is dealing with type I collagen, making up most of the collagen and maybe you’ll find smaller amount of type 3 and type 5 present as well. And you have your non-collagenous proteins, like we’ve already discussed, your dentin phosphophorin and when we did crown formation I also mentioned dentosialoprotein. And this is a nice picture, various magnifications showing your odontoblastic processes. Picture B is obviously a much lower magnification. Where the arrows are they’re pointing to where the odontoblastic process is located. A is an SEM. And this looks like a whole bunch of candles to be honest with you. All this tissue in between is making up most of the dentin and that’s known as intertubular dentin, how that comes about we’ll see momentarily, and the space is really your dentinal tubule, and sitting in the little tubule is your odontoblastic process. And finally, C shows you a TEM of your odontoblastic process sitting in tubule itself.

A&C FIG 8-1 INCISOR (3RD ED)We saw this picture previously, it’s just meant to show you the position of the tissues. I particularly like B because it shows you the curvature of the tubules particularly in the crown. These are known as S shaped tubules. Once we get to the root we lose the S and they become more straight or linear in fashion. Since we have this I might as well make use of it. This particular area in here is where tooth has produced


tertiary dentin. Look right above it, it’s all dark, that means these are dead tracts, all these dentinal tubules have opened up and air and bacteria have rushed in here. And look at this part of the tooth, it’s lopsided if you will, as if you cut off a piece and the dentin extends all the way to the tip. So there should really be, again should be more enamel protecting the tooth. It’s just not there

NANCI TC FIG 8-22 DENTINAL TUBULES (7TH ED)Here’s an actual incisor again. Showing you the enamel, and all this tissue represents your dentin. You can see the S shaped tubules over there, in the root they are pretty straight. This is supposed to be pulp, they call it a pulp chamber it’s really a pulp canal, the pulp chamber should be up here. Again this is sort of a duplicate of the previous slide where part of the enamel is missing as well as part of the dentin.

G&H PLATE 13-2 FIG 1 HUMAN TOOTH (5TH ED)We saw this previously. Showing again the enamel, the DEJ and the dentin. And all these lines as you see in here, really represent the dentinal tubules. Now since we’re in near the occlusal part of the tube, the tubules are not really curved, you can see the curvature over here. And it looks like there’s a line or demarcation in this area. Everything above is really your primary dentin, your circumpulpal dentin. Everything below is formed after tooth is erupted and is functional. That’s your secondary dentin. And if you underneath these dark staining tubules, your dead tracks, something is happening down at this pulp horn. And that’s probably the formation of tertiary dentin, your protective dentin

A&C FIG 8-8 ODONTOBLASTIC PROCESSES (3RD ED)


This gives us a lot of information. In terms of how the dentin actually forms, here’s our good old odontoblast, and the odontoblastic process extending all the way up to DEJ. In fact it’s showing you these two processes present in the enamel so this would become part of enamel spindles. The widest part of the process is where it exits the odontoblast. So in terms of dimensions, you’re dealing with 3-4 micrometres in terms of the diameter at the process here, whereas at the DEJ roughly 1 micrometre. As the process extends to the DEJ the whole tubule arrangement becomes narrower. And what’s the big deal about that? It’s that we’re actually having several different types of dentin form. And we’re going to talk about intertubular and peritubular. Now let’s see what we can do here. Essentially I’m drawing 2 odontoblasts with their odontoblastic processes. So the first dentin to form is intertubular dentin. And I’m going to draw this pyramidal triangular shaped structure to represent the intertubular dentin. So initially the intertubular dentin is narrow, but as processes taper down and become narrower the amount of intertubular dentin gradually increases. So if you were to do an experiment and measure, you would find the majority of dentin happens to be intertubular dentin. So the organic matrix forms, it mineralizes. Next thing that’s going to happen is the formation of your peritubular dentin. And that’s going to be around the process. What is the peritubular dentin actually forming? The walls of the dentinal tubule. Now once intertubular dentin is mineralized you can’t shove more organic matrix into it. So you’re left with a narrow area into which this peritubular dentin forms. And the peritubular dentin is much more mineralized than peritubular and the matrix more delicate in nature. See more reticular fibres. The intertibular dentin has more coarser bundles of collagen. So we


created a dentinal tubule. So we believed there’s another form of dentin. Going to change the colour again. And that’s this orangey colour I’m putting in. and that’s called intra – INTRA – tubular dentin. So the prefix is intra, it means it’s in the tubule. But this type of dentin is believed to be nothing more than an organic sheath. You have odontoblastic process surrounded by organic sheath surrounded by peritubular dentin and again, the major block of dentin happens to be the intertubular dentin.

A&C FIG 8-9 PERITUBULAR AND INTERTUBULAR DENTINHere’s another nice picture. This is the dentinal tubule and you see all these little holes. Ah that’s what I forgot here.

A&C FIG 8-8 ODONTOBLASTIC PROCESSES (3RD ED)So each odontoblast gives rise to one odontoblastic process, but that process is can branch. It’s possible to branch at the point of origin from the odontoblast but most of the branching occurs throughout the dentin. And that’s what you’re seeing over here. The picture labels them as secondary tubules, you can call them microtubules, canaliculi, etc. By the way this dark staining structure happens to be the peritubular dentin just to distinguish it from intertubular dentin

A&C FIG 8-9 PERITUBULAR AND INTERTUBULAR DENTINSo going back to this picture through these little openings, the odontoblastic processes would push in and here you can see these processes extending over to the next tubule. This region over here is your intertubular dentin. This is your wall of your tubule. Very easy to see that intertubular dentin makes up most of your dentin. And you’ll see holes in this tubule. Looking at this part of the picture, here’s your whole tubule and sitting in here should be your odontoblastic process. The same thing, I’ll draw this orange line to indicate presence of odontoblastic process.

O FIG 4-4 PERITUBULAR DENTIN (11TH ED)So more pictures illustrating the same thing. All this tissue here represents your intertubular dentin. This sort of round space is your dental tubule and the dark staining structure in the tubule is your odontoblastic process. So this is a low mag picture and now we’re looking at an SEM picture. So once again most of this dentin is intertubular dentin. This is the dentinal tubule, it’s sitting in the center of your odontoblastic process. This region is the wall of your tubule. That’s the peritubular dentin. And then if you were able to draw something additional, I could fill up space with organic sheath, by drawing in that organic sheath, your intratubular dentin.


O FIG 4-6 TUBULES, PERITUBULAR DENTIN, INTERTUBULAR DENTINAnd here is an actual SEM picture showing you the same thing. Here’s your tubule cut in half longitudinally, you can see the holes through which secondary tubules pass. Through the intertubular dentin. Here again now we’re in a tubule. Where all these little filamentous structures are the branches that came off of the odontoblastic process in this tubule. So in essence that’s what you’re seeing.

NANC TIC FIG 8-27 TUBULE, INTRATUBULAR DENTINLight microscopic image again, you can see tubules with odontoblastic process. Again here is a scanning picture. Most of this dentin is your intratubular dentin. This in essence is your tubule. That’s the process.

NANCI TC FIG 8-43 ODONTOBLAST PROCESS: FREEZE FRACTURE AND SEM (7TH ED)Ahh, this is kinda cool looking. Picture A is freeze fracture. Remember that from my first lecture in basic tissues. That’s where I used that example of the Sylvester Stallone movie, battling Wesley Snipes, Demolition Man. And this is where he froze Wesley Snipes and his head got knocked off. But anyway thefreeze fracture technique, you freeze tissue, you fracture it, you remove the living tissue, you colour it with something like platinum. This is exactly what you see - his is not living tissue. That’s the fracture replica. So this is your odontoblastic process, and that’s the odontoblast. So the odontoblastic process is sitting in a tubule, and all this really represents the intertubular dentin. And this is just an SEM of the same thing. No matter how you do it you get similar type looking images. It’s just the technique that differs. Again your process, the cell will be down here.

O FIG 4-3 TUBULES BRANCHING (11TH ED)This is a good picture showing you the branching, it can get become quite extensive in terms of the odontoblastic processes giving rise to numerous types of branches.

NANCI TC FIG 8-31 DENTIN INCREMENTAL LINES AND TETRACYCLINE STAINING (7TH ED)This is a probably a good point to stop. Here’s our loving picture for the day. Now what can we call it? Hey buddy, what’s wrong with you? Good luck tomorrow, to be continued on Monday.

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28: Dentin I