Dental Materials: Structural Aspects of Biomaterials Lecture – Professor Lisa Pruitt (Transcript)

So as we bring that process away we lose some of our protective barrier. Underneath this we have dentin and so we’ve got a dentin structure that provides for us, again you’ve got a number of these occlusals that are oriented in different directions, so they take an orthogonal profile but they take all different orientations as we move through the dentin. And that provides for us a highly tough material, but an anisotropic material because these all take profiles and so they are – in this configuration underneath the enamel and as we rotate around the pulp it actually starts to spiral around, so it becomes orthogonal by the time we get to the root. And so these perform different functions, we tie into the periodontal membrane and the bone below and so again very much like cartilage where we actually tie-in we become orthogonal in this direction here and then as we’re up here these periodontal structures actually take the perpendicular to the enamel. So they actually scale themselves as needed relative to load and structural support.

The pulp from a bio standpoint, again very important is our blood supply, it’s the nourishment. So we have to remember that we’ve got a lot of cellular turnover just like we have in bone. So we actually rely on structural remodeling of this material. We have a periodontal membrane, so again we’ve got a structure between the bone itself, so we’ve got our bone, we’ve got cementum layer, professor Ritchie talked little bit about this, we’ve got a periodontal membrane and then we’ve got our vascular and nerve supply, which is why if any of you’ve actually gone through a large temperature range, you probably hit strains in your tooth that in some instances gives you sensitivity, that’s the nerve endings. So anything that does that — anything that we can do that actually brings about nerve response you’re going to feel it, right?

So on my cartilage this is very similar to bone in terms of nerve supply and blood supply. So you’ve got an interesting anisotropic structure that provides for you some unique properties. This is taken out of the paper that’s posted, so it’s the Journal Of Dentistry, again it’s a structural paper. [The Marshall group], UCSF School of Dentistry, they’ve teamed up with professor Ritchie, they’ve done a lot of fracture mechanics works. They’ve also done a lot of nanoindentation work. So they’ve done a lot of nice work where they’ve taken these structures in cross-section and only looked at them micro-structurally which is part of that paper, but they’ve also proved them with a nanoindentation technique. So you can take this in cross-section and then you can actually probe about what the harness is as you move from the enamel to the dentin and through the junctions and this ties in nicely with looking at fracture mechanics issues which are micromechanics based. So you can look at the actual orientation of your occlusals, you can look at the relative mechanical properties and you can break it down to a nano-scale.

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So this is a big challenge not just for teeth but all biological materials, when you have a higher RQ like this, whether it’s bone or whether it’s a dental tissue, how do you actually get the mechanical properties of something complex like this? So just going back to what we know about mechanical testing back to our E 45 days, you’re not going to machine this into a little tensile dogbone, right and just go pull on it, get a modulus. You could but what does it tell you? It’d give you some globally averaged tensile modulus. So you could machine this into a little plug and you can load it up in compression and again you could get a globally averaged parameter but I wouldn’t really tell you about what the different constituents contribute and the same issue with fractures, it’s really complicated to try to break apart the fracture process. But if you could have a technique that can come in and actually probe out mechanical properties at these microstructural levels you can get a better understanding of what each of these contributes, which is why nano and microscale mechanical testing is really important for us today.

Questions? (inaudible)

Lisa Pruitt: Well you can do it. Okay. So you can do it in few planes, right? One would be that we’ve taken in this plane here, so we could have dentin and a lot of times you want that, right? Because you want to move through the enamel dental junction. So you’ve got dentin, you’ve got this structure here. So if I can have it in cross-section and then pot it top down, I can come in and let this be my nanoindenter tip, I can come in, in cross-section, so now if I look at this inside profile I’ve got this mounted in cross-section, I can come down with a small tip, and I can actually march across and measure low displacement behavior as I move through different junctions. Question?

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(Question Inaudible)

Yeah, that’s right. So okay, okay – so then you bring up – so the question is. That’s okay when we’re talking about enamel, but actually, even with enamel, because — the assumption with enamel is because of its crystalline structure and the scale of the crystalline structure that is a more isotropic structure altogether. So we just assume that you got isotropic behavior, which means we can approach it from any angle and the properties okay. So one way to handle that would be you could do different cross-sections, which is what we do a lot of our tissues. So you could take different cross-sections almost – you had your histology lecture? Okay. So in histology we take a very thin section of tissue, you could take different sections in different orientations and so this could be cross-section in this plane, we could then do cross-sections this way, right? So we could do something like this and then we could do top-down indents, so we could march across this way and get that direction.

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