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Ask A Dentist: Facts To Sink Your Teeth Into


This is SCIENCE FRIDAY. I'm Ira Flatow.

FLORA LICHTMAN, BYLINE: And I'm Flora Lichtman.

FLATOW: We all want to be next, don't we, except in the dentist's office? The words next, the dentist will see you now are as welcome a sound as the high-pitched whine of the dental drill.


FLATOW: OK, Neal(ph), that's enough. But have no fear, this hour our dentists have no drills, no needles, no laughing gas, no pain, I promise.

LICHTMAN: Today our Ask an Expert series continues with, you guessed it, ask a dentist. We're turning the tray table and putting the dentist in the hot seat today. You can finally ask those questions that you can't ask during your checkup because your mouth is otherwise occupied.

FLATOW: (Unintelligible).

LICHTMAN: Perfect.


FLATOW: I always want to know - every wonder what that - how that whitening stuff works they put in teeth, right, or why some people get more cavities than others. Or do the dentists' arms ever get tired?

LICHTMAN: That one I've never thought of.

FLATOW: Do they get tired twisting the drill around your dental work? You know, they're stuck in one position.

LICHTMAN: And we have to talk about toothbrushes, right, like soft or hard bristles, manual or electric.

FLATOW: Is an electric really that much - so many questions to ask, and it's your turn. You ask the - you make the call, but you have to make the call. Our number is 1-800-989-8255. You can tweet us @scifri, @-S-C-I-F-R-I, go to our website at

Mark Ryder is here, he's a professor and chair of periodontology at the University of California in San Francisco. He joins us from KQED. Welcome to SCIENCE FRIDAY.

MARK RYDER: Thank you, Ira, and thank you, Flora, and good afternoon to everybody across the country.

FLATOW: Thu. Mark Wolff is professor and chair of the Department of Cariology and Comprehensive Care at New York University College of Dentistry here in New York. And he is here in our New York studios. Welcome to SCIENCE FRIDAY, Dr. Wolff.

MARK S. WOLFF: It's wonderful to be here with both of you.


FLATOW: What question, Dr. Wolff, do you get asked most by people who want to know about teeth and dentistry and whatever? Is there one question everybody wants to know?

WOLFF: I think one of the favorite questions is can my teeth be whiter.

LICHTMAN: And can they?

WOLFF: It depends how white. Yours, Flora, are pretty...

LICHTMAN: I'll take it.

WOLFF: Electrifying.

FLATOW: Well, that makes - do the over-the-counter whiteners work as good as - I know the answer, I think - as what you do professionally as a dentist?

WOLFF: They work, and they help, but they're not - clearly not as strong as what dentists have available to use.

LICHTMAN: Does it weaken your teeth, or will they get yellower faster? I've heard that, if you've gotten them whitened.

WOLFF: Well, if they're really white, they get yellow faster than if they were really yellow already. So that's just not a fair - that's just not a fair question.


WOLFF: They don't make your teeth any weaker, and they don't make your teeth any more likely to stain, though you're going to notice the stain because they were white, and now they're changing color again.


FLATOW: Mark Ryder, let me ask you this question, it's been - I asked many times, and I thought I knew the answer. You are stranded on a desert island. Would you rather have a toothbrush or dental floss with you? Which is it better to do, tooth brushing or dental flossing?

RYDER: Well, if I was on a desert island, assuming it's a desert island that has palm trees and coconuts, I would go with a toothbrush. I think a toothbrush is a little harder to make, and actually a toothbrush probably reaches in more areas than the floss would. It actually can do a fairly good job getting in between the teeth except where the teeth just contact each other.

Probably the other reason I'd choose a toothbrush is that, well, if you've got coconuts or bark on the island, you could probably strip off some of that bark and make your own do-it-yourself floss. And of course if this was Gilligan's Island, and we had the professor on the island, he could probably make us an electric toothbrush, too.

FLATOW: Is an electric brush better than a regular brush?

RYDER: That's - well, speaking of which, that's probably the question I get asked the most. Basically if you can use a manual brush, use the manual brush. We generally recommend an electric brush for those who just don't have the dexterity particularly to reach those hard-to-reach areas in the back of the mouth.

FLATOW: Huh, Mark, do you agree with that?

WOLFF: Oh, I agree. You know, the...

FLATOW: But the things vibrate so fast, and they get into little...

WOLFF: I happen to use an electric brush, but that does any better job than a well-used manual brush. Once the teeth are clean, the teeth are clean.

LICHTMAN: What about the bristles? Is it just if you can take the hard bristles you should use them?

WOLFF: Oh absolutely not.


WOLFF: Absolutely not. My motto is the softer the better and throw them out frequently. So you don't want bristles - as much as you'd like to scrub your teeth clean to keep them that pearly white, you don't want to cause abrasion and wear or damage to the guns, the gingiva, by either stroking aggressively against the surface with a hard bristle or even excessive with a soft bristle.

So as soon as the toothbrush starts to look ugly, and the little fibers are heading in every direction, throw it in the garbage, but keep using soft-bristle brushes.

FLATOW: 1-800-989-8255. Let's see if we - a lot of ways - a lot of questions. Let's go to Greg(ph) in Fairbanks. Hi Greg, welcome to SCIENCE FRIDAY.

GREG: Thanks, Ira. I wanted to ask your guests, I've been diagnosed with periodontal disease. Is there any way to reverse that or to stop it? And I'll take my answer offline.

FLATOW: OK, Dr. Ryder, any way to reverse periodontal disease?

RYDER: Is there any way to reverse periodontal disease? Well, if you can eliminate the two causes, which are the bacterial plaque, and reduce the resulting inflammation, you can certainly slow down or even stop the progression. If you can slow down and stop the progression for a long enough period of time by keeping your mouth clean, then you will start to get, over a very long period of time, but you can see it, some regeneration of some of the support that you have lost.

This could be either the gum tissue attaching a little higher up on the tooth, or in some cases maybe over a much longer period of time, some of the bone may actually start to grow back, too. But if you've lost quite a bit of bone to begin with, I wouldn't expect you to get 100 percent of that bone back.

FLATOW: Interesting. 1-800-989-8255. Dr. Wolff, let's talk about...

LICHTMAN: How about let's talk about mouthwash because that's a burning question for me.

FLATOW: OK, go ahead. Go with the mouthwash, the burning question.


FLATOW: Go ahead.

WOLFF: And sometimes it is.

FLATOW: Well, should we be using mouthwash? Is it safe thing? Is it something we want to do?

WOLFF: In general it's safe to use. That's not a concern. In many cases it's nothing more than a perfume.

FLATOW: It doesn't do anything?

WOLFF: Well, no, it...

LICHTMAN: It does that...

WOLFF: It gives a fresher feeling to the mouth, but we know after we get that fresh feeling, and 20 minutes goes by that that pasty feeling can be back inside your mouth. We know that certain things - I mean, if you eat garlic, I don't care what you chew, what you rinse with, you're going to smell like garlic later and the next day sometimes.

FLATOW: Should you brush your tongue, as well as your teeth, at the same time?

WOLFF: Well, brushing the tongue has all these really need crips(ph) and little areas that hold things that become odiferous and smell. And as Mark from San Francisco can tell you, a lot of the odiferous bugs are the ones that are causing periodontal disease also. So bad breath frequently is a sign of periodontal disease at the same time.

But, you know, you can't make that go away with just a mouthwash.

FLATOW: Let's go to the phones, to Jean(ph) in Santa Clara. Hi Jean.


FLATOW: Go ahead.

JEAN: This is my question. Can you hear OK on my speakerphone?

FLATOW: You sound great.

JEAN: OK. How important is it to use toothpaste at all? It seems to me if you use an extra-soft brush, it's the action against the upper teeth and the gums that matter, not the dentifrice.

WOLFF: That's not exactly true.

RYDER: That's a good question.

WOLFF: It's a great question, but it's not exactly true.

FLATOW: I think we have a disagreement coming up here.

RYDER: No actually, I think both Mark and I agree on this one. I can - well, we can maybe debate this, but I think what Mark would - well let me just put this out, that certainly using a dry toothbrush with water is going to get off the plaque. But you really need to consider also the active ingredients in the toothpaste itself.

If the toothpaste itself has a high concentration of fluoride, that will help strengthen the surface of the teeth and will have an action against those bacteria in the mouth, too. Some of the other things that might be in toothpaste might be detergent that may help at least break up some of the soft plaque that you wouldn't just get just by mechanically brushing the teeth.

So Mark, you may also have some other added benefits that you can use with toothpaste.

WOLFF: Yeah, clearly the additives in toothpaste have an effect on releasing the plaque and getting it off, including the abrasives, which you have to be careful with. Fluoride in the toothpaste has been very clearly demonstrated to be effective at reducing tooth decay.

FLATOW: No controversy about that anymore?

WOLFF: There's no controversy that it reduces tooth decay. There will be people that will take issue as to whether or not fluoride is safe, and that's an argument for a totally different moment, and I personally believe that it's extremely safe. There's enough research that shows not only is it the frequency of brushing but the frequency of brushing with toothpaste that contains fluoride that reduces tooth decay.

So if you brush twice a day with toothpaste with fluoride, you get - are less likely to get decay than if you brush once. If you brush twice a day with just a toothbrush, you're more likely to get decay. So the toothpaste does have an effect, and there have been a couple of studies that have really validated that.

FLATOW: Jean, does that satisfy you?

JEAN: Yeah, I ask the question because I hear people say oh, avoid toothpaste that has that sodium lauryl sulfate and carrageenan and some of the things that make your teeth white, that maybe it's too abrasive. So I wondered about not having any toothpaste. But I hear him say the detergents do have an effect.

WOLFF: So I don't worry about the detergent, which is what SLS is, related to wearing the tooth. There are some people that actually get irritation and actually get some inflammation around the gingiva, the gums, associated with the sodium lauryl sulfate, which is a soap, by the way. So it's, you know, not an uncommon event there.

The cleaning agents, generally they are in the abrasive side of the toothpaste also, and related to the abrasives, I do worry about a number of whitening toothpastes that are on the fringe whitening toothpaste, they're not coming out of the mainstream companies.

I've done some work with some of these that are highly abrasive and actually will wear the tooth away fairly rapidly. You need to be cautious about that.

FLATOW: All right, we're talking with our dentists on our Ask a Dentist segment this hour on SCIENCE FRIDAY, Mark Ryder professor and chair of periodontology - my teeth are falling out - at the University of California, San Francisco; Mark Wolff, professor and chair of the Department of Cariology and Comprehensive Care at NYU College of Dentistry.

Our number, 1-800-989-8255, here with Flora Lichtman. You can tweet us, @scifri, also send us a little note that way. We'll be right back after this break. Stay with us.


FLATOW: I'm Ira Flatow. This is SCIENCE FRIDAY from NPR.


FLATOW: This is SCIENCE FRIDAY; I'm Ira Flatow.

LICHTMAN: And I'm Flora Lichtman. Our Ask an Expert series continues today with Ask a Dentist. But don't worry, no drilling here, just your questions. Our guests are filling us in on some dental facts.

FLATOW: And the fillings are an interesting question I want to ask. But first I want to get to a question we raised earlier in the introduction, and that is: Dr. Ryder, can you tell us about a possible link between gum disease and dementia like Alzheimer's?

RYDER: Well, this is an interesting new area that several people are looking into. Basically when you're considering gum disease, you're really looking at an infection and inflammation. And gum diseases are probably the most common infection and inflammation one may encounter in their entire life.

Now if you're an older male, maybe prostatitis comes in a distant second, but gum diseases or periodontal diseases are pretty common. And like any kind of inflammatory and infectious disease, whatever you have in one part of your body may affect other parts of the body.

You may have heard of possible links between gum diseases and heart disease or diabetic conditions. And more recently several investigators have looked into this possible link between inflammation from periodontal disease and Alzheimer's disease or just dementia in general.

And there have been a couple of studies that have given some tantalizing clues to this possible link. One is a study that Mark also is familiar with in New York on nuns that was published in the Journal of the American Dental Association that found that nuns who were followed over a long period of time who had lost more teeth seemed to have more dementia.

Whether the chicken came before the egg, or what's the cause and what's the effect we don't know, but since then there have been some rather interesting pieces of evidence that have shown that bacteria that you normally found in the gum tissue, would normally find in gum tissue in disease, have been localized in the brain itself.

FLATOW: If you find that your gums are inflamed, is that an indication that other parts of your body, like maybe your arteries or whatever, might also be inflamed? Is there any connection? You hear research trying to use the gums as a window into the rest of your body where inflammation is concerned. Is that clear yet?

RYDER: Well, certainly the mouth, and the gums in particular, are a window, or we might say the canary in the coalmine. And the reason for that is, as you may or may not know, the mouth, as well as that other part of the digestive tract on the other end of your body, are probably the two filthiest places in your body. They get the most bacteria load in terms of - in the mouth of course they get the most inflammation.

And so this may be an indication of things going on in the rest of the body, or there may be a link between this inflammation, between the gums and the rest of the body. You talked about artery or atherosclerosis. Well, there have been studies that have shown that when you reduce the inflammation of the gum tissue in the mouth or treat the periodontal disease, as we might say, what you do see is a lowering of some of the other risks you may associate with cardiovascular disease.

Like you may have heard of C-reactive protein that people now measure or cholesterol levels. Now whether actually treating periodontal disease actually reduces the risk of actually getting a heart attack or a stroke, well, the jury is still pretty much out on that question. We know it lowers some of the risks that we can measure, but we don't know if we can actually prevent that definitive, final event.

There are some other conditions, such as diabetes, where the connection I think is a little stronger, where we know that by treating the inflammation in the mouth, we can improve, if a person has diabetes, we can also improve their diabetic condition by lowering things like their HbA1c, which you probably have heard about, or glycosylated hemoglobin, or their fasting blood glucose levels.

So it's a - it's certainly a very tantalizing, interesting area of investigation where we found some direction connections in some conditions with the mouth, and in others, well, the jury is still out, but we may see further proof in the near future.

FLATOW: Just let me get a quick tweet in from Tim(ph), who has an interesting question: Can you ask the dentist about whether probiotics can help with gum disease?

RYDER: That's a good question.

WOLFF: Challenge.

RYDER: Right now, the jury is still out. And if you look at all the studies that have been done with probiotics now, the probiotics, which would include certain types of lactobacillus, which would be related to the lactobacillus you might find in yogurt, if you apply them locally, let's say you chew on a tablet, you can shift the bacteria in the mouth. That's been shown.

You may get a minor improvement in some of the clinical signs of inflammation, but over the long run, those changes don't seem to be particularly significant, at least for the studies that have come out so far.

WOLFF: Yeah, it's extremely difficult to displace our host bacteria with a probiotic. You know, I think probiotics are a great and encouraging area for gum disease and for tooth decay, but at this particular moment it's just not easily to swallow a new bacteria and actually to have it take over inside the biofilm or plaque, as it's called.

LICHTMAN: And cavities are caused by different bacteria, right, in the mouth?

WOLFF: Than gum disease?


WOLFF: Yes, very different bacteria. One actually likes lots of oxygen, makes lots of acid as a byproduct. So tooth decay is actually bacteria eating sugars. And it doesn't care whether it's the sugar you put into your coffee or the healthy raisin or the dried date or fig that mom puts into your food instead of a candy bar. Sugar is sugar is sugar to these bacteria, what bacteria do is they poop out acid as part of their product, and it dissolves the tooth.


FLATOW: I hate it when that happens.

LICHTMAN: We have people tweeting about whether you should floss and then brush or brush and then floss or whether it matters.

FLATOW: Which order, does order count at all?

WOLFF: Well, so flossing has been demonstrated to reduce gingivitis, the inflammation of the gums. It's actually never been shown to reduce tooth decay.


WOLFF: Yes, so...

FLATOW: But that's important, to reduce gingivitis, isn't it?

WOLFF: I didn't say it's not important. I'm not - and Mark, do you want to comment on how important reducing gingivitis is to the long-term retention of teeth?

RYDER: Well, I think gingivitis is probably one of the first signs of periodontal disease, which of course results in loss of bone. So anything you can do to reduce the inflammation, the bacteria biofilm that we've been talking about, will not only be beneficial to your mouth but probably to your whole body.

LICHTMAN: So you're flossing to keep your teeth later but not to prevent cavities? Is that what you're saying?

WOLFF: That's reasonable. And I wouldn't want to just put off flossing as being the only way to clean between the teeth. So, you know, there are soft wooden toothpicks, and please don't use hard wood toothpicks, which can actually wear the tooth. I'm really worried about this wear and erosion. You can get this erosion from sports drinks and all sorts of things, too.

So you want to be careful about wear and erosion on the teeth, and you want to - you want to clean between them, decrease or mix up the bacterial load all the time, and that prevents the gingivitis, gum disease and reduces tooth decay.

FLATOW: When is the most important time of the day to brush your teeth?

WOLFF: For what?


FLATOW: I mean, do you do it in the morning when you wake up, people do it at night before they go to sleep. Does it make a difference? Has anybody studied when it really makes a difference?

WOLFF: Well, have they really studied? The answer is probably not as clearly as we would like. But we know when you go to sleep at night, your saliva flow slows down, for most people, some drool on the pillow all night long, but for most people. And if you happen to have those carbohydrates, the sugars, the candies, the milk that you could put a child to bed with, any of that on the outside of the tooth at that moment, no saliva, which is what protects you from tooth decay...

FLATOW: Saliva does?

WOLFF: Oh yes, saliva is what buffers the acids, washes it away, provides calciums and phosphates to prevent the tooth from dissolving. So you go to bed when you have no saliva, you fall asleep with all of this gook on your teeth, and in the morning.

But now if you're kissing somebody in the morning, and you have that morning mouth, you tell me, which is the better to brush. That's why I said it's not quite that simple...

LICHTMAN: It depends on your application.

WOLFF: Yeah, it depends. It's not quite as simple as morning or not.

FLATOW: Flossing in bed in the morning, that...

WOLFF: There's nothing more romantic.


LICHTMAN: What about 3-D printing of teeth? There was a story out this week about 3-D printing an ear. You'd think if you could do an ear, you could do teeth.

WOLFF: Well, you know, tissue culture, which is what you're speaking about, the ability to grow, either put cells that will continue to grow on a scaffold, a tooth is a very complex tissue. It contains blood vessels. It contains soft tissue inside. It's then made up of a dentin that is laid down very carefully with little microtubules about a micron in diameter.

And then on top of this is this white crystal we look at. I do believe that science will someday get there. I don't believe, you know, we're not at the point that you lay down the scaffolding and make an artificial tooth at this moment. We do do some remarkable scaffold work for remaking jaws, for remaking bone to put implants into. There are all sorts of real magic that we do for deformities, but this isn't where we're at in replacing teeth.

FLATOW: If you religiously brush and floss everyday, is it necessary to have your teeth professionally cleaned by a hygienist, Dr. Ryder?

RYDER: Oh, yes. Oh, yes. Particularly, if you have some past evidence of periodontal disease where your pockets are a little deeper, the brush and floss could only get so deep. If your pocket are, let's say, more than three or four millimeters deep, there is probably very little you can do to reach way, way down into those bacteria biofilms, or layers of bacteria that are building up deep in those inaccessible areas. And this is what a hygienist can do.

FLATOW: All right with that bit of advice.



FLATOW: That's a good bit of advice, Flora. I thank both of you for taking time to be with us today. Mark Ryder, professor and chair of periodontology, I will speak that sooner or later, University of California San Francisco. Mark Wolff, professor and chair of the Department of Cariology. I don't think we've ever had a cariology...

WOLFF: Study of tooth decay (unintelligible). (Unintelligible) please that's just not fair.


FLATOW: I'm getting carried away here. I'm sorry.

WOLFF: Oh, they made us jealous to be with you. What can I tell you?


FLATOW: Comprehensive care - New York University School of Dentistry here in New York. Thank you both.

LICHTMAN: Thank you.

WOLFF: Oh, it's been wonderful being here. Thank you.

RYDER: Thank you. Transcript provided by NPR, Copyright NPR.