Transcribed by Joseph Schwimmer

Craniofacial Biology - Lecture #33 Cementum5/1/14 (lecture given 5/2/13)

Slide 1 IntroductionDr. Ronald Craig (begins mid-sentence) the periodontal connective tissue attachment apparatus, right, so thats cementum, periodontal ligament, alveolar bone. Weve also talked about formation of the dental gingival junction, or otherwise called the gingival connective tissue attachment briefly. Thats cementum into which fibers attach to go out into the gingiva, so thats coronal to the periodontal connective tissue attachment, and then theres this epithelium thats attached to the two surface junctional epithelium, and thats called epithelial attachment. So you got three different attachments to the teeth. So lets begin a discussion of each one of the component of periodontal tissue, so well spend about 40-45 minutes on cementum and then the big one is periodontal ligament because it has a lot of stuff in there. Then well talk a little bit about alveolar bone, my understanding is that youve got a lot of bone biology so you probably dont need much more, only that which is associated with alveolar bone. And then well have two hours on gingiva, gingival connective tissue and epithelium, because if you understand the biology theres a lot of neat things you can do for your patients, gingivally, gingival surgery and stuff like that. So lets talk a little bit about cementum. So I think of cementum as being the last frontier of the human body. Theres not a lot of it, so its really har to study, and we rally dont have a good cell culture system, we havent been able to coulture cementoblasts in plate. We really dont have any proteins or genes that are characteristic of cementum, theres a couple on the horizon, but theyre not really great. So because of lacking a cell model system, not having a lot of the extracellular matrix to begin with, and not have any markers for cementum, we really dont understand cementum very much. Of course, you have to have cementum to ha during evolution of our species, so all thats kind of combined together to sort of make cementum sort of an unknown field. But an important one, because if youre gonna get a periodontal connective tissue attachment apparatus on teeth or on biomaterials, and thats where everybody is kind of looking now, can I get a periodontal connective tissue attachment apparatus on the implants. Now implants are good, but they cant move, they dont do the things teeth do, can I get a periodontal connective tissue attachment apparatus on dental implants then I can do all the things with dental implants that I can do with teeth, so people are kind of focused on this and well talk a little bit about that next week.

Slide 2 - CementumSo right now lets talk about cementum as a tissue, I think Ive got some summary slides here.

Slide 3 Components We know a bout the functions of the periodontium. We know all these things are just to recapitulate. So heres the gingival epithelium up here, so right in here this area is not attached to the tooth surface, cause thats called sulcus, if its not inflamed its called a sulcus, if its inflamed its called a pocket. We havent talked about pathology yet, so all this is sulcus, so sulcular epithelium and then junctional epithelium is attached to the tooth surface, so all this is junctional epithelium, and classically, the junctional epithelium should terminate at the cementoenamel junction, and this cartoon has kind of missed that here. But you can kind of see it in the actual section. So in health, junctional epithelium terminates at the cementoenamel junction which is right here. So this is the epithelial attachment, epithelial cells are attaching to the enamel surface. Down here you have cementum and you have these fibers that are going down to the gingiva, so thats the gingival connective tissue attachment, and heres the alveolar crest, this is kind of unusual, usually the alveolar crest is lower down. So fibers that go down from cementum through the periodontal ligament to the alveolar crest are called periodontal connective tissue attachment apparatus. So theres 3 different ways of attaching tissue to a natural tooth, and well compare this with dental implants, as implants are getting more and more kind of important.

Slide 4 ComponentsAnd we already talked about some of the components.

Slide 5 ClassificationSo, cementum, theres nomenclature that has to go, has to be presented, and its kind of confusing, so Im gonna try to give you an easier way of sorting kinds of cementum in your mind. So some people classify cementum by time of formation, why? I dont know. But primary cementum is that which is formed before the tooth erupts into the oral cavity. And secondary cementum isi that this forms after the tooth erupts into the oral cavity. Biochemically, cell biology, clinically, it doesnt have any real relevance. So Im just giving that to you for your background. Location, some people classify cementum by where its found on the tooth. So, you can have radicular cementum which is on the tooth root, or sometimes you can get some cementum on the enamel surface. So what we think is that the reduced enamel epithelium in humans may break down, allowing cells of the dental follicle to attach, or to contact that enamel surface, and that induces cementum formation. So those of you who have little children, as their six year molars erupt, if you kind of pry their little mouths open and take a look, sometimes youll see this chalky-whitish flaky material on the apical 1/3 of their crowns, and thats little flecks of cementum formation where the reduced enamel epithelium broke down. Some species like cown horses and ungulate, they exploit the differences in density between enamel, dentin and cementum to make an ecer-renewing surface to grind grasses with. So if you look at a cow molar nad all of you should as dentists know about every tooth in the entire animal kingdom, there are these sort of elongated they look like a washboard, and if you look at the surface of the cow molar, it has like a layer, or zone of enamel, then a layer or a zone of dentin, then a layer or a zone of cementum. And as the cow grinds grains and stuff, the cementum wears faster than the dentin and the dentin wears faster than the enamel, so you always have like a sharp surface to grind against, which is kind of neat. So those are ungulates. So thats called coronal cementum. So if the cementum is found on the crown of the tooth, thats called coronal cementum. That really doesnt have much interest for us. For some reason, in our profession weve really gotten into this idea of acellular cementum versus cellular cementum. And Ive already kind of told you that theres some suspicion that acellular cementum may be distinct from cellular cementum. So acellular cementum is the first cementum thats laid down during tooth formation. And over that acellular cementum surface, you can get cementum that has incorporated into it, cementocytes, so its called cellular cementum. (inaudible student question) No. so this is why is throw out that kind of idea, and youll see why in a second. And cellular cementum tends to form on the apical 1/3 of the root surface, but it can form in other places. So what I tend to like, and most people in the profession tend to like is the following classification system.

Slide 6 ClassificationSo all cementums can either have no cells in it, or it can have cells, and all cementums can either have fibers attaching into it from the periodontal ligament or from the gingiva, thats called the extrinsic fibers of dental cementum. Theyre cemented into the cementum matrix and they either go out into the gingiva or into the periodontal ligament. Or if theres no periodontal ligament, say if its coronal cementum, theres nothing to attach to, so there are no fibers, its afibrillar. Ad so you can mix and match those two guys together and you can kind of accurately describe what kind of cementum youre dealing with. So the first cementum thats laid down as the tooth root forms doesnt have any cells, so its acellular, but it has fibers in it. So its acellular fibrillar cementum. On top of that may form a cementum that has cells incorporated in it so its cellular, but it still has the fibers associating into it, so its cellular fibrillar cementum. We get back to our friend the cow, the cementum thats on the tooth surface in the cows mouth, what kind of cementum would it be? Would it have cells or no cells? No cells, cant live out there, cant live in the barnyard. Would it have fibers or no fibers? Nothing to attach to, so it has no fibers. So its acellular afibrillar cementum. Now to get back to your question, well see that its actually possible to regenerate down cementum. So the people who came up with that previous classification system of primary and secondary, they didnt know that you can regenerate, they came up with that terminology before we understood how to actually regenerate lost tissue. So it doesnt really make much sense. So thats why we kind of go with cells and fibers together.

Slide 7 Dental developmentAnd weve already kind of talked about all this, right?

Slide 8 HertwigsAnd weve talked about Hertwigs epithelial root sheath.

Slide 9 HERSBut what we didnt talk about was this intermediate cementum layer. So the inner cell layer of Hertwigs epithelial root sheath is biosynthetic and then it makes this wonderful matrix called intermediate cementum, and after it makes that matrix it pulls away, or it appears to pull away, it loses contact with this probably a better term loses contact with that intermediate cementum layer, and some of the cells fenestrate and in come these cells from the dental follicle and attach at the intermediate cementum layer. And they differentiate in the cementoblasts. So since the first step in development and if you want to regenerate lost periodontal connective tissue attachment apparatus is the development of cementum, or the deposition of cementum, people all over the world really kind of focused in on whats the induction factor for cementum formation. So there was a person, Harold Slavkin, was past dean of USC dental school, general dentist. Hes also the past director of the national association of Dental Research, and Harolds a general dentist, and Harolds golden fleece, if you will, is to create a tooth, a whole tooth, and put it back into people, because hes tired of doing fillings, hed rather just regenerate a lost tooth. And Harold is a very charismatic man. I remember once USC was playing UCLA and you know how in halftime theyll have like faculty members being interviewed, and so there I am and Im having an adult beverage, and Im watching the game on New Years Day, and all of a sudden, theres Harold Slavkin, and he has this long hair, so he sort of looks like the MGM lion in a way, and hes talking about, what were gonna do is clone these cells and combine them together and were gonna put them back in peoples mouths, and Im like wow. Along his pathway to bioengineering a tooth, he had to clone genes that are associated with enamel formation. So he was trying to clone the amelogenin gene. So the amelogenin gene is like the devils own protein. So its like 72kD protein and you can isolate it from forming tooth buds and you can see it on your polyacrylamide gel, and you cut out the 72kD protein, and you can send it for amino acid analysis, and they tell you oh you didnt give me a 72, you gave me a ladder of peptides, so the protein itself is autoproteolytic, so it dissolves itself. So Harold felt, if I cant sequence it that way so what Ill do is Ill make monoclonal antibodies against all the little peptide fragments and Ill pull out the CNDA clones with my monoclonal antibodies. So as the story goes, he had this enormous room filled with post docs looking at microscope sections of developing teeth, making sure that the monoclonal antibodies that he was generating against amelogenin actually lit up the forming crown of the tooth. So in walks my friend, hes not my friend hes kind of like my mentor, Lars Hammerstrom from Sweden, everything comes form Sweden, and Lars worked at that time at the Karalinska Institute, those are the people who give out the Nobel prizes, so Lars is very interested in cementum formation, so he takes a sabbatical at USC and he sees all these guys looking at these microscopes and hes not interested in the crowns, hes interested right here, and lo and behold he starts to see that these antibodies against amelogenin and amelogenin peptide light up the intermediate cementum layer. Everyone was looking at the crown, Lars was looking at the roots.. so Lars, typical Swedish guy, zips his mouth, packs his bags, thanks Harold very much, goes back to the Karolinska Institute, 5 years later comes out with a company. So Lars is not a molecular biologist, he couldnt get a molecular biologist, so what he does is he goes to England or to Denmark, or they did, and there are these slaughterhouses with these pigs, the English love bacon, so theres lots of these slaughterhouses, and some of the pigs that come through are pregnant, so they take the fetuses and they dissect out the developing teeth and with a very simple extraction protocol they extract out the amelogenin. So its pig amelogenin and amelogenin peptides, about 90% of this is that, and he bursts on the scene with a company, a product, and he calls this product, Emdogain, enamel matrix derivative, and Lars said they threw in the gain because it sounded good, and all it is, is an extraction, rather crude extraction of developing pig enamel. So its 90% amelogenin, amelogenin-like peptides, 10% sort of uncharacterized. And what you do during periodontal surgery, and Ill show you some of this when we talk about periodontal regeneration, is you apply it to the root surface, just before you close up, and it induces acellular cementum formation, so its an inductive factor for acellular cementum, so one of the components that is present in the intermediate cementum layer is amelogenin and amelogenin-like peptides. (student question: who won that football game). I dont know I was probably having some adult beverages, I dont remember. You know just to see someone who I knew being interviewed blew my mind away, you know a dental research thats the guy to do it. He is so charismatic. Whyd you ask me that question? Obstructed my chain of thought. So, this com so who is company was called Biora, and it was bought out by the Strauman company. So when you get out to the clinic floor, and you have a chance to assist in the perio clininc or in oral surgery and you see the surgeon ask for Emdogain, you kind of have an idea of what theyre asking for. So part of this strange matrix thats out there is amelogenin or amelogenin-like peptides. And a lot of people couldnt understand this but it makes sense, because the inner epithelial layer of Hertwigs Epithelial Root Sheath is really an extension of the enamel organ. And what does the inner cell layer of the enamel synthesize? Well, it synthesizes all the enamel proteins, amelogenins, enamelins, all those that youve learned about. And so again, and this is recapitulation again, so some of the events that occur during enamel formation are during root formation. Student question: is Emdogain used during practice? A: I use a lot of it, and when we talk about regeneration Ill talk to you why, it has a lot of advantages. My only concern is that Lars Hammerstrom came up with it first. I hate that, because that was my idea, and I hate it when people have my idea and thy make off with it, and I hate it, but when people have my idea before I have my idea, that even gets me more!

Slide 10: Cell rests of MalassezSo, cell rests of Malassez, the periodontal ligament in many ways is a unique suture, theres nothing like it in the rest of the body, so why do we have these epithelial cells present? And when I went to dental school and I used to sit over there, no, I went to Penn, but I always used to sit in the back, but I remember cell rests of Malassez and so I raised my hands and I said what do they do? And the professor, first he was upset at me, and then he said well thats the source for periodontal cysts. What? I mean Im keeping something in my body for pathology? That doesnt make sense to me. And to this day, we dont know why we have the cell rests of Malassez in the adult periodontal ligament. However, we will show you that you can regenerate lost periodontal tissue connective attachment apparatus. And in order, and theres an epithelial mesenchymal interaction that occurs during development. So what I believe is that those epithelial cell rests of Malassez are there to provide inductive factors that are necessary for cementum formation. Ok.

Slide 11: Types of cementumOk, so what types of cementum are there? So theres intermediate cementum which is a misnomer. So this is an epithelial product so its not really a cementum. Cementum is a product of mesenchyme, not epithelium. So intermediate cementum is a misnomer. Theres acellular fibrillar cementum, theres cellular fibrillar cementum. And when you get in the clinic, theres clinical slang, youll hear people talking about affected cementum. What the heck is affected cementum? So if you have pathology, if you have periodontitis, if you have a periodontal pocket, and now, exposed to that periodontal pocket is the root surface, cementum is sort of porous, its not as mineralized as dentin or bone, and it picks up bacteria or bacterial products, and it becomes this affected cementum. And youll learn something called scaling and root planing, and the objective of scaling and root planing is to remove affected cementum from that surgical site ok? so affected cementum is sort of a clinical slang term for cementum thats picked up bacterial products.

Slide 12: Types of cementumWeve already talked about that, theres the Lars Hammerstrom thing. Weve already seen these slide of acellular fibrillar cementum.

Slide 13: Types of cementumAnd weve already seen these slides of cellular cementum.

Slide 14-15-16: Types of cementumAnd weve seen this slide of cellular cementum.

Slide 17: Cementum CompositionSo whats the composition of cementum? So cementum is very, I kind of think of cementum as kind of a stripped down version of bone. So everything thats been biochemically found in cementum has been found in bone. However, proteins found in bone are not, some of them are not present in cementum. So the function of cementum is to attach fibers of the periodontal ligament to the root surface. We dont use cementum for calcium homeostasis, we dont use cementum for remodeling, we use alveolar bone to move teeth. So we kind of think of cementum as a bone matrix, if you will, thats really been stripped down to attach teeth in your head. So the protein matrix is mostly collagen type I and theres some other collagens in there like type III. The matrix between the fibrils are the typical proteins youd see in bone, glycoprtoeins, osteonectins, bone sialoprotein is present in cementum, osteopontin and those reversal lines are present in cementum, some cytokines. But theres nothing to my knowledge thats really been unique as far as cementum extracellular matrix.

Slide 18: CementoblastsWeve already had this picture of two happy cementocytes. Theyre laying down cementum matrix thats being mineralized. Cementing in these fibers of the periodontal ligament into the cementum matrix.

Slide 19: Cementum formationAnd then weve already had this picture of these fibers here, being cemented in by these hydroxyapatite crystals into this cementum matrix.

Slide 20: ResorptionCementum resorption. So what happens if the pulp of the tooth becomes necrotic, or it becomes infected. So bacterial antigens, bacteria themselves, or necrotic tissue, necrotic peptide son the tissue itself begin to leak into the periodontal ligament, so this begins an inflammatory response. And cells start to appear that look identical to osteoclasts, begin to resorb this matrix in an effort to debride that wound, to get rid of the necrotic tissue and/or the infected material from inside that root canal. So quite frequently when teeth become necrotic youll see areas of resorption, and these are so called cementoclasts, or odontoclasts. But theyre really osteoclasts working on a different kind of matrix.

Slide 21: Cementum formationOne of the characteristics of cementum is that it doesnt remodel under non-pathologic situations. So here is the dentin and this is the tooth, and here is cementum matrix, mostly acellular. You can see these reversal lines that are rich in osteopontin. Here is the periodontal ligament, and here is one osteon, and here is another osteons of the alveolar bone, and you can kind of see this area is being resorbed into the osteons. So this tooth is kind of moving in this direction, its kind of moving towards me, because the alveolar bone is being resorbed. The periodontal ligament, as we will learn, kind of keeps the same width during tooth movement, and the cementum does not resorb, so tooth movement, under health, is solely a property of the resorption of alveolar bone and not cementum.

Slide 22: Anomalies Ok, and to finish up, some variations in cementum formation. So well talk about the cementoenamel junction, enamel projections, enamel pearls, cementicles, and finally hypercementosis, and then were done for today.

Slide 23: CEJThe cementoenamel junction, the relationship of cementum and enamel and the cementum can vary, and this is stuff you have to know, why? I have no idea but it shows up on standardized exams. So, thats weird. Ok, this is backwards and I think its corrected in your blackboard site. So this is C, it says A but its C. so the most common relationship is the overlap of cementum onto the enamel surface. So make a correction if thats not corrected in your powerpoint. So a gap can occur between the cementum and the enamel, and that only occurs about 10% of the time. and then a But junction occurs about 30% of the time. now there is some clinical relevance to this, because there is a disease, a type of periodontitis that afflicts people right at puberty, it used to be called localized juvenile periodontitis, now its called aggressive periodontitis, but it occurs right at puberty, and there were some theories once upon a time that it occurs on specific teeth because of this gap junction, but thats never been proven. But you need to remember that the most common form of junction is overlapping of cementum. The least common is a gap, and intermediate is an abutment of the two matrices. (inaudible student question) So I guess you can call this for coronal cementum, yeah, because its at the crown. Is the enamel ever on top of cementum? No, not to my knowledge. And it wouldnt make sense developmentally, would it? Because development occurs in an apical to cervical direction. So you always finishing enamel before youre starting cementum, because you have to have Hertwigs ERS. Good question.

Slide 24: Enamel ProjectionsSo sometimes in localized areas, what localized areas? So sometimes on the straight lingual of maxillary incisors, usually lateral incisors, or at the entrance to furcations on molars, theres a little tongue of enamel that goes into that area, its called an enamel projection. And what it is, its failure of the enamel organ to cease amelogenesis and consequently you cant have HERS. So the first time I saw this was a young patient and Im supposed to do a perio exam, and Im charting, and all of a sudden on the lingual of both lateral incisors I get a 9mm pocket on this 18 year old, perfectly healthy, whats going on? And the perio probe as well learn, gives you a lot more information than just a pocket reading, it tells you the consistency of the root surface, and the root surface felt very very hard, like enamel, and there wasnt a lot of inflammation around either, so this was an enamel projection. So heres the dentin, heres cementum, cementum up here, so this area is where enamel was in life, and over it is sort of this reduced enamel epithelium, so these cells continued to form enamel along that surface of the root, kind of setting that patient up for periodontal disease, because as it turns out, epithelial cells dont resist inflammation as well as a periodontal connective tissue attachment apparatus does. So these are enamel projections, failure of the enamel organ to halt synthesis, and failure of the HERS to then induce periodontal connective tissue attachment formation. Treatment for this, is usually flap the area, take out the diamond and plasty away the enamel, suture everything back up and the patient is usually fine, but you have to be able to identify that.

Slide 25: Enamel PearlsEnamel pearl, so the enamel pearl is an enamel projection, but its really very exuberant in the amount of enamel thats been formed in this area, and notice that this is an entrance to a furcation, and youll see these in radiographs, and if these occur further down, they can give you real problems in extracting the tooth. So anyway, I know this comes from a male patient, how do I know that? So this is a male tooth (joke). And if you kind of look at this tooth a lot, you kind of get the idea that it looks like an elephant in a way, so here are the tusks and here are the legs, and here are the two ears of the elephant and sort of the trunk. Does it look like an elephant to you or am I nuts? Ok, I guess I never got over Harold Slavkin being on national TV. Ok, so thats enamel pearl, enamel projections.

Slide 26: CementiclesThe other anomaly is something called cementicles. Careful now, were talking about cementicles. And cementicles can either be sessile or out in the periodontal ligament or attached right to the cementum formation, and if you kind of take a look at these guys in cross section, they seem to have these little concentric areas here, so what we think is happening here is these are cell rests of Malassez that for whatever reason have become reactivated, and perhaps theyre synthesizing amelogenin, and there is a stem cell population in the periodontal ligament, when it senses amelogenin starts to lay down acellular cementum. So we believe cementicles are reactivation of the cell rests of Malassez.

Slide 27: HypercementosisAnd finally, in patients that have Pagets disease of bone, and its very common in elderly patients. Youll take a radiograph, and youll notice that they apical portions of their roots are really bulbous, kind of enlarged, and this is all due to hypercementosis, an exorbitant amount of cellular fibrillar cementum formation, usually on the apical third.

Slide 28: HypercementosisAnd this is a biopsy, right? So heres a premolar, and this is all cellular fibrillar cementum thats formed around the apices of these roots. And of course, you have to kind of know this before you pick up your extraction instruments because this can give you some real problems during extractions.

Slide 29: SummaryOk, so whats the summary? So cementum is the first of the periodontal connective tissue attachment to be formed, so people have really focused in on cementogenensis, where the inductive factors, amelogenin, amelogenin-like peptides appear to be one. Sole function of cementum appears to be to insert PDL fibers into the tooth surface. Its not used to calcium homeostasis, its not used for remodeling, as bone is. Its not associated with blood vessel formation, relatively avascular. So it seems to be a stripped down version of alveolar bone. We talked about the different types of cementum that can be found and we talked a little bit about anomalies. So have a good weekend.