I was at a party last year with a woman who had recently lived in England. Her funniest story was about flossing. She mentioned the use of dental floss to her friends there and found a widespread belief that flossing was bad for you. The punchline was something like, “It makes your gums bleed. It’s bad for you!”

I imagine I was more amused by that story than others at the party, because I pay special attention to what dentists say about dental hygiene. I know, for example, that plaque causes inflammation in your gums, which makes them more likely to bleed. This inflammation also makes your gums more porous, so that bacteria leak into your bloodstream, causing more inflammation throughout your cardiovascular system, resulting in a significantly shorter lifespan. I also know that your body treats plaque as its own tissue, building capillaries inside the plaque, to feed it. This is why plaque can bleed when hygienists scrape it out.

[Shudder]

I do what my dentist tells me. Exactly. I am a highly compliant patient.

So far it’s paid off. I’ve had very few cavities and hygienists often fawn over my teeth, both very nice. At the end of a visit I always say, “I want to keep these teeth for 60-70 more years. Am I on track to do that? Is there anything I could be doing better?” The answer has always been “Yes, you are on track to keep your teeth,” and usually, “No, just keep doing what you are doing.”

Every five or six years, though, I get a new set of instructions about how best to brush my teeth. I can remember several off the top of my head: horizontal strokes including the gums, circles including the gums, vertical sweeps including the gums. The last time I got a new set of instructions was in 2011. “Brush along the gum line with a 45 degree angle toward the gums with very small horizontal strokes, using no pressure at all and the softest brush you can find. Move to a new spot every minute or so. Do not brush your gums.”

I was surprised at these changes and a little annoyed. The last time I’d heard horizontal strokes was the 1980s. I’d assumed the move away from that had been an improvement. And don’t brush the gums? I’d never heard that from anyone. I complained that dentistry kept changing things up and that these changes didn’t make sense to me, if the other changes had been real improvements.

My hygienist sympathized and said, “Well, we used to think that brushing the gums toughened them up and kept them from receding. Recently we started noticing that patients who brushed their gums were causing them to recede, so we’ve changed our minds.”

That’s when it hit me. Dentists are performing a very poorly organized and poorly controlled longitudinal experiment on us, without getting our consent, and presenting themselves as having knowledge and authority that they clearly do not yet have. The good dental hygiene of the future could have almost nothing in common with what we have today. We may abandon brushing altogether, in favor of regulation of oral pH and microflora, or who knows what.

To be fair, dentists have an extremely difficult task in this experiment. The number of people who actually follow their recommendations is very small, and even that select group probably fluctuate in their compliance a good deal. And if they told us they were experimenting on us, we’d likely be even less compliant. Plus, they have to put their hands and faces in our stinky mouths all day.

This winter, I worked several weeks with a woman who, during that time, had to get a whole bunch of fillings on the surfaces between her teeth because of flossing. As far as I could tell, this woman (who is an urban legend to you, by definition, but to me is a real person with first and last name, phone number, husband, and child) is one of my high-compliance compatriots. She flossed every day and it wore the enamel off the inner surfaces of her teeth, “because my teeth are close together.” She was pretty upset about it, and I would be too. She was just doing as she was told by the experts. Perhaps she would have been better off in England, where flossing is bad for you.

Still, dentists’ advice is the best we have. Until otherwise notified, I’m sticking with my highly endorsed protocol: brushing as described above twice per day, plus hydrofloss in the morning and dental floss in the evening. I just keep in mind that protocol will inevitably change, and that I may be doing some harm in the meantime.

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