Latest / The Materials Lab: Biomaterials in Modern Dentistry / Fluoride varnish: why formulation matters more than concentration
Transcript
- Saroash Shahid: There is no way for calcium fluoride to stick around on the tooth surface. Saroash Shahid: There's a lot of variability from person to person as well in there. Saroash Shahid: If you want a smart system, you want a system that's actually going to break down under acidic conditions and then release that fluoride. James Notman: Hi, welcome to The Materials Lab. Today I'm talking with Saroash, whose group compared fluoride varnishes and found something pretty wild. Same fluoride on the label, but they act differently on teeth. Some build acid-resistant fluorapatite, others mostly calcium fluoride. What decides which one you get? And why the number on the tube doesn't tell the story. James Notman: We've all had that quick varnish painted on our teeth, and we're told it's 5% fluoride. Your group found that even when varnishes have the same fluoride on the label, they don't all behave the same way. What actually makes one of them grow fluorapatite and another one mostly calcium fluoride? Saroash Shahid: Fluoride is a really reactive element. and it will react with anything, any positive ion that comes in contact with it. and in our saliva, we've got lots of calcium ions, and because fluoride is very reactive, it will preferentially react with calcium to form calcium fluoride. One might think, "Oh, that's still fluoride and still working," but that's an insoluble form of fluoride. So any fluoride that exists in the form of calcium fluoride is not going to be very clinically beneficial. So what we ideally want is a slow release of fluoride, which occurs over a long period of time, and that is because that will allow the fluoride to react with the mineral that is present in the tooth. And the mineral that's present in the tooth is a form of calcium phosphate that we call as hydroxyapatite. Now, what fluoride can do is it can replace one of the components present in hydroxyapatite, which is the hydroxyl group, which is the OH group, and that turns the hydroxyapatite into fluorapatite. Now, that's a very slow reaction, and because it's a slow reaction, that is why we prefer to have a slow long-term release of fluoride rather than a rapid burst release of fluoride, because that slow exchange can then happen easily. And once we form fluorapatite, that is more beneficial because fluorapatite is a much more stable crystal compared to hydroxyapatite. And the reason is because it's a larger crystal, and because it's a larger crystal, that means it takes much more aggressive acids to actually dissolve it. So in essence, you're actually made the tooth now slightly more acid resistant. James Notman: Right. some people think that calcium fluoride layer isn't useless. Like they call it a little fluoride bank that can release fluoride later when the mouth turns acidic. How do you see that? Saroash Shahid: I mean, for something to act as a fluoride bank, it needs to, uh, remain inside the oral cavity. Because we've now formed an insoluble form of, fluoride, which is the calcium fluoride, it will get washed away. There is no way for calcium fluoride to stick around on the tooth surface. We might get a few amounts of calcium fluoride present in the saliva, probably attached to the gingival, to some surfaces of the tooth, but it's not gonna be a lot of fluoride that is going to be present there. So it's not going to act as a long-term reservoir of, fluoride. The other thing is, we know now is that calcium fluoride tends to dissolve more easily in, alkaline pH, meaning pH which is greater than seven. Whereas the caries, uh, process starts happening when the pH falls below seven, 'cause that's an acidic pH. And because calcium fluoride is relatively stable on those acidic pH, it's not really beneficial, If you want a smart system, you want a system that's actually going to break down under acidic conditions and then release that fluoride. Because that's not happening with calcium fluoride, it is not a very efficient reservoir of fluoride James Notman: Well, if that's the case, why do you think in your varnish study only some of the products actually managed to form fluorapatite? Was it mostly about how fast they release fluoride or what came along with it? Saroash Shahid: That is because, formation of fluorapatite is a very slow reaction. it does require some time. But even if we form small forms of, uh, small quantities of fluorapatite, that is still more beneficial, 'cause essentially we just want the superficial layer of the tooth enamel to convert into fluorapatite. So even a few micron thick layer of fluorapatite on the surface of enamel is going to be more than enough. James Notman: Fluoride alone can't build that crystal, right? It needs phosphate to arrive with it. In your comparison, only two varnishes even released phosphate. Is that the missing piece clinicians should be thinking about rather than just the PPM on the label? Saroash Shahid: So if you're talking about the, remineralization process, so, there are two things happening. So when caries happen, we refer to that as demineralization. So, that means there's an acidic pH, the tooth starts dissolving, it starts releasing calcium and phosphate ions into the saliva. So if we want remineralization to occur, first we need to neutralize the pH, so we bring it closer to seven, and the second thing, we need to provide a source of calcium phosphate and flu- uh, and fluoride. we looked at phosphate-free, uh, uh, varnishes, but that was because we do have some phosphate in the saliva. So although the varnish's composition didn't have phosphate in them, saliva does contain quite, a good quantity of phosphate, all these components can still work together and promote remineralization. James Notman: That balance between acid and rebuild makes me think of the whole critical pH line we're taught in school, like enamel dissolves below around 5.5, right? Yeah, I've also seen numbers tied to pure minerals, like closer to five for hydroxyapatite and four for fluorapatite. where's the disconnect there, or is there one? Saroash Shahid: No, there isn't a disconnect here. the reason why we've got these three different numbers is because we're talking about essentially three different crystals. So pure hydroxyapatite, might start dissolving around five or five point five. the thing is, the hydroxyapatite that we have in the tooth is not pure hydroxyapatite. It is carbonated hydroxyapatite. So, so that's why it's slightly more soluble than pure hydroxyapatite because of the presence of the carbonates in there. because obviously as the tooth is, forming, we've got oxygen, we've got carbon dioxide present in, in the blood, so the crystals will pick up a carbonate from, the surrounding. Now, the fluorapatite is a completely different crystal. it's a more stable crystal, and it's a much larger crystal, and that is why you've got a different pH there at which it dissolves. It will dissolve at pH four because it's got greater stability, so that means it's more resistant to acid. James Notman: That helps. So in the mouth, it's not just one magic number. It's which mineral is on the surface and what's floating around it, like calcium ions in the saliva. That mix decides what grows back. Saroash Shahid: That is correct. And also, the different teeth are going to have slightly different structure, uh, to, to each other, even in the, same mouth, but also from person to person. So some people have might tooth enamel which is more prone to caries just because the mineral density is not that great or the crystal structure is slightly different, where others might have enamel which is more resistant. So there's a lot of variability from person to person as well in there. That's why some people might, might be more prone to caries, because of this, the mineral structure of their teeth, as well as the composition of saliva. Whereas other people might be less prone, to caries. To g- to give you an example, children teeth, the, primary teeth, they're more prone to, caries compared to the permanent teeth, and the reason for that is that children teeth are more porous, they're less mineralized, so that's why, the acid can attack them more easily. Whereas, permanent teeth, uh, are much more denser, much more stable, so they are more resistant to acid attack. And sometimes people might have conditions, in the permanent teeth where the enamel does not form properly or not in the level of mineralization we would expect, and that could potentially make them more prone to caries. James Notman: Yeah. And all those little factors, the carbonate, the saliva, the ions, they push the balance between losing mineral and gaining it back. I'm really getting what your group means by formulation, not just concentration. Saroash Shahid: That is correct, yes. So, it's more about formulation. It's more about a sustained long-term release of fluoride rather than having that one sudden burst release of fluoride. that provides more, clinical benefits. and there have been papers published in the past, that have actually shown that low doses of fluoride, but repeated doses, low doses of fluoride is more beneficial because it tends to form more fluorapatite compared to one burst release, of fluoride, because that's gonna tend to form calcium fluoride, which I said earlier is less beneficial. James Notman: What I'm taking away, look beyond the fluoride number. Slow, repeated, low doses build fluorapatite, while one big burst mostly makes calcium fluoride, and that just washes away. Thanks, Saroash, for making that click so clearly. Folks, share this with just 1 curious friend, hit subscribe. Goodbye, see you all next time. That's The Materials Lab. Thanks for listening, and look after your teeth.