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Is Tooth Cleaning a Scam?—A Commentary by Ian Ayres ’86

The following commentary was published in The New York Times on March 11, 2008.

Is Tooth Cleaning a Scam?
By Ian Ayres ’86

One of my earliest and happiest memories was being released from a hospital oxygen tent when I was a small child. I had developed pneumonia and was in pretty bad shape. They not only kept me under an oxygen tent for several days at St. Luke’s Hospital in Kansas City, but they also gave me massive amounts of tetracycline.

The good news is that I recovered. The bad news is that from then on, my teeth have had pretty severe tetracycline staining. This is not just surface discoloration — my enamel through and through is grayer than I’d like. I tell you this because I’ve always had an uncomfortable relationship with my teeth, and this feeling might bias my view of dentists. I don’t like going to my dentist’s office every six months and having my teeth cleaned. Recently, as I was sitting in the chair, a thought occurred to me.

I began to wonder if there was such a thing as “evidence-based dentistry.” In my book Super Crunchers (naked self-promotion), I wrote an entire chapter about evidence-based medicine — which is, in part, an effort to test whether medical treatments are statistically proven to be effective. I figured there had to be a parallel movement in dentistry, and maybe someone had analyzed whether hygienist teeth cleaning helps or not.

Thank God for Google. It turns out there is an entire journal called “Evidence Based Dentistry.” And in just a few minutes, I was looking at a formal Cochrane review titled “Insufficient evidence to understand effect of routine scaling and polishing.”

The review looked for evidence to answer two related questions:

The first is, do scale and polish procedures [having your teeth cleaned] lead to any difference in periodontal health compared with no scale and polish? Second, does the interval between these scale and polishing procedures make any difference?

The results were not heartening for those of us who have suffered through dozens upon dozens of cleanings. The meta analysis of qualifying studies suggested that the evidence was mixed, at best. For example, there is not strong evidence that hygienist cleaning reduces gingivitis:

[T]he authors of the only study that found differences in gingivitis scores (at 6, 12 and 22 months) deemed those differences clinically irrelevant….

One reasonable reaction to this is to simply reject the Cochrane review methodology. Evidence-based medicine ranks the quality of different types of evidence — and tends to give inordinate weight to randomized control trials. Indeed, Cochrane reviews often give no weight to the results of any non-randomized clinical study. As the review acknowledges:

[This Review] carries with it the limitation inherent in most of these reviews, of including only randomized clinical trials. For this particular question, the quantity of non-randomized trials identified in the exclusion list suggests that an independent review of this more ‘‘risky’’ literature might be profitable.

But another reaction is to question whether it is really necessary to put dental patients through so much financial and physical discomfort. Dentists, like other agents (real estate agents, car sales people), do not have the best economic incentives when advising how much to clean.

My dad always told me that dealership rust-proofing was a scam to give dealerships some extra cash without providing your car with any extra protection. Could getting your teeth cleaned be the economic equivalent to having a car dealership rust-proof your car?

Like I said before, this post is probably just working out some wounded inner child issue. (And let me be clear that I’m not calling into question the value of brushing and flossing your teeth, or visiting your dentist regularly to check for cavities, as well as other potential problems). But it’s food for thought. The next time your dentist asks you to make an appointment to have your teeth cleaned, you might reasonably ask, “Why?”