Bryan Caplan  

The Marginal Tooth

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Keynes famously wished that economists would one day become as useful as dentists. But every time I go to the dentist, it's clear that knowledge of economics would be useful to to dentists.

The whole idea of cost-benefit analysis seems foreign to them. Every patient gets the same lecture: "If you don't floss, you'll loose your teeth. I told you this last time, and you're still not flossing!" Has it ever occured to them that the marginal benefit of flossing may be less than its marginal cost?

When I ask such questions, I always get the same reaction: "Here's how gum disease works. Blah, blah, blah." I want to talk about marginal benefit, and the dentist gives me an anatomy lecture. When I press the issue, and demand, "How many teeth does daily flossing save, on average? What is the probability that I get gum disease conditional on flossing versus not flossing?" they dodge the questions or admit they don't know.

When experts can't answer my questions, I google. And while google failed to answer these pointed questions, I learned a lot more in five minutes than I ever learned from listening to dentists. The single most informative piece: "Total Tooth Loss in the United Kingdom in 1998 and Implications for the Future" (Steele et al, Nature, December 2000). What I found out:

  • Dentists who warn you that you will lose teeth if you don't get regular check-ups are half-right. What they don't tell you is that you are going to loose teeth even if you do get regular check-ups! Here a nice figure showing average number of teeth as a function of age and dentistry.

    The biggest gap - 5 teeth - appears in the 55-64 age bracket, when people who get regular check-ups average 21 teeth, and the rest have 16. By the time you're 75+, average number of teeth is about 17 if you had regular check-ups, and 14 otherwise.

    Of course, this assumes the difference is 100% attributable to dentistry. In all likelihood, people who get regular check-ups have better hygiene. Think of a marginal benefit of 3-5 teeth for a lifetime of dentist appointments as an upper bound on the benefit.

  • The main reason people loose all their teeth (i.e., become "edentate") is tooth decay, not gum disease, as this figure shows, and as the article explains:

    Decayed teeth was the most frequently cited cause for final clearance (in 64% of cases) and 28% said it was caused by bad gums. However, when asked what problems they had experienced just prior to having all their teeth taken out, over a half mentioned having had some gum problems or loose teeth.

    The last sentence seems intended to maintain readers' fear of gum disease, but it's not surprising that people with badly decayed teeth also have some gum problems or loose teeth. The basic fact still stands: tooth decay is more than twice as common a reason for loosing your teeth. This in turn suggests that the lazy man's strategy of brushing but not flossing is a reasonable trade-off.

  • Forecasts indicate that people in the future will have more teeth. And since, as every nagging dentist knows in his heart, hygiene is highly unlikely to improve, we're going to get these extra teeth the lazy way. Impossible? Think about fluoride.

    In the end, I still don't have the answers to the really interesting questions: How many teeth does brushing once per day save? Twice? Thrice? How about flossing daily? Weekly? If anyone knows a dentist who knows the answers - and spares me the anatomy lecture - I'd be most grateful.

    P.S. If you've got Jstor access, check out Alan Blinder's classic piece of ecomedy, "The Economics of Brushing Teeth."


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    COMMENTS (20 to date)
    Ivan Kirigin writes:

    There is already talk of using some new tech, like stem cells, to regrow teeth.

    How soon will it be till tooth paste contains nano-flossers?

    I brush & floss, just to be safe, but I see little chance that I'll have any missing teeth when, i'm 70+ (in 46 years).

    Taking the likelihood of technological change to make flossing or tooth loss a thing of the past (which will occur regardless of whether _I_ floss), will probably make the marginal benefit of flossing that much smaller.

    Something similar can be said for obesity.

    Funny thing, I thought about this same thing a while back. Since my dentist is so good that even filling cavities does not actually really feel like anything, and besides, the insurance covers the treatment cost, my enthusiasm to brush and floss has actually gone down. Stupid, I know.

    FB writes:

    A cost benefit analysis rates to make a number of errors:

    1. The biggest cost is the cost of changing habits. Once a regular flosser, it can be almost costless to maintain. A non-flosser will overestimate the lifetime cost.

    2. Along the same lines, a skilled flosser with healthy gums can get the job done faster & with less discomfort than someone just taking it up. Creative multi-tasking can make the time cost zero.

    3. There are costs shy of tooth loss from not flossing. Checkups are more painful and take longer. Sensitivity more likely.

    4. Losing a tooth is not just one less tooth, but potentially a very unpleasant waste material time on dental work. This cost seems small from a distance, but really isn't.


    That said, I'm not a regular flosser (though I succeed for stretches of time).

    Rafal Smigrodzki writes:

    Please do not take the following as dispensation of medical advice in a field where I am not licensed (I am a neurologist, not a dentist) but as simple commonsense peer-to-peer talk:

    Flossing using flossers (like Plackers or a number of other brands) is much easier than with floss, thereby reducing the cost, while presumably maintaining the benefit. For added efficacy consider brushing some tootpaste on your teeth before using the flosser. I do it regularly, with minimal time expenditure, and my dentist used to wonder at how little need I had for cleaning (so I stopped allowing myself to be fleeced in this way).

    Rafal

    DL writes:

    Given your thoughts on stereotypes, I think you should be even more optimistic, since you use British data. Do you happen to know if the "Britons have more dental problems" stereotype is true?

    I think the source of the stereotype Americans have about the British is that we don't do much cosmetic dentistry - braces on children are unusual; if your teeth aren't quite straight you don't usually do anything about it. I'm not sure if we actually have more tooth decay or tooth loss than Americans, though it's certainly possible.

    Bill Stepp writes:

    Flossing has two other benefits that you overlooked. First, it greatly improves a person's breath and helps prevent halitosis.
    This is especially important if you work in close proximity to other people. If you don't believe me, don't floss for a long time, then have someone check your breath. Big difference.

    Second, flossing also supposedly helps prevent heart disease by reducing the presence of certain germs that enter the blood stream via the mouth and then adversely affect the heart.

    What is the marginal utility of economists? Do people who listen to economists actually have fewer preposterous investments than peopl who don't?

    On the other hand, you might also analyze the marginal utility of making comments on blogs...

    Bob Knaus writes:

    Ewwww, you don't floss??? How groodddy!!!

    That would be the reaction of many teenage girls to a guy who didn't, showing that flossing has great social utility.

    Being long past that age myself, I still floss because if I don't my gums get sore and bleed. That's utility, no?

    Plus, I feel good about myself after I floss. I am sure that I get just as much a boost in my self esteem from flossing as other people do from dropping a quarter into a panhandler's cup. We are all getting utility, are we not?

    Zubon writes:

    Ah, but if you believed the effectiveness of flossing to be mostly superstition, then you would gain that same "I feel good about myself" utility after every brushing where you did not floss. "Ha," you'd think to yourself, "some other fool might have wasted that minute running string over his teeth, while I have time to make a blog comment!"

    I suppose everyone gains utility from re-affirming one's beliefs. This perhaps explains most statements made in any given day.

    Steve Sailer writes:

    Remember Mike Myers's Saturday Night Live ad for a tasty British toothpaste, now with two cups of sugar? "You won't have to brush your teeth every week, but you'll want to!"

    American dentists deserve praise for pushing flouridation of water and toothpaste. They cut their own incomes dramatically by doing that -- my kids have never had to have cavities filled, unlike me -- but they went ahead and did it anyway because it was good for their patients. How many other professionals have been that self-sacrificing?

    Patri Friedman writes:

    The big gain from flossing is not saving teeth, it is general health. We've learned fairly recently that gum disease increases the risk of heart disease and other problems, which is kinda weird, but seems to be true.

    Not that I floss. Just wanted to be clear on the benefits.

    ranc writes:

    I think the point is not that dentists lack knowledge of economics. It is that it pays them to make the argument they make so that they can make more money out of their patients. Remember, they are not neutral scholars making scietific arguments, they are sales men/women, so it pays them to make false arguments if that means more business.

    From this perspective, if we accept that people are self-interested as we often do in economics, then the question is why should we ever accept any theories of any economist, who is presumably self interested when s/he makes the theory.

    dsquared writes:

    Since the National Health Service was introduced in 1948 and food rationing ended in 1954, I'd be very wary indeed about drawing conclusions for Americans aged under 50 from research on British people aged over 50.

    Bill Stepp writes:

    Contrary to what Steve Sailer says above, dentists deserve no kudos for pushing flouride, if this means compulsory, state-sponsored flouride in the water supply. In fact, there is a growing body of evidence indicating that flouride causes cancer.
    Furthermore, you don't need to ingest flouridated water to lower your incidence of caries--just avoid sugar and processed stuff passing as food, and floss and brush your teeth after eating.

    Free the water supply!

    Chris Bolts writes:

    [quote]Flossing has two other benefits that you overlooked. First, it greatly improves a person's breath and helps prevent halitosis.[/quote]

    I thought halitosis was caused by the scum that is on your tongue after you eat? Anyway, I floss almost raringly myself because it is a hard task forcing floss between your teeth and always causing some form of bleeding. The only time I do floss is when it matters most: when I have something stuck between my teeth and it hurts my mouth like hell.

    I find that brushing your teeth everyday is a better form of treatment and saves money going to see a dentist.

    [quote]I think the point is not that dentists lack knowledge of economics. It is that it pays them to make the argument they make so that they can make more money out of their patients.[/quote]

    Then why even tell your patients to floss your teeth? If in the end the dentist is trying to get paid, it is better to provide as least truth as possible in order to maximize profits. Somehow I don't think this is the case.

    Rufus Sarsaparilla writes:

    About the time I turned 30, my dental hygienist made the argument that I should start flossing since I was getting older and it would become harder to start new habits. (Gee, thanks for reminding me of my mortality!) Well I took her advice and am very happy for it. It's been several years and it's just a part of my routine now. Like another commenter, I feel very virtuous after brushing, flossing, and then rinsing with Listerine. My teeth feel like a million bucks. I wouldn't count on technology coming to the rescue in time to save you from the consequences of bad dental hygiene.

    Bob Knaus writes:

    Coupla more comments:

    1) If you haven't tried Glide brand floss, do so. It is an example of the unexpected benefits that come from a dedicated team of sales engineers trying to find new markets for their product. In this case, Gore-Tex. Who woulda thunk that a synthetic fiber first commercialized for insulated clothing would also turn out to be a super-slick flossing material that fits between your teeth like nothing else?

    2) I suppose it was inevitable that anything having to do with tooth decay would bring up anti-flouridation conspiracy theories. Hey, anything embraced by Ralph Nader and the John Birch Society can't be wrong!

    Paul N writes:

    I disagree that people that get regular checkups are likely to have better hygiene - in my experience, people with good teeth don't feel a need to go to the dentist, while people with crappy teeth and a propensity to get cavities get regular checkups as a necessity.

    I would therefore posit that 3-5 teeth is more likely a LOWER bound to the marginal benefit of dental visits.

    Rob writes:

    Did anyone else notice that the graph has a bump in the number of teeth from the first age category to the second? I would much prefer longitudinal data

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