Sometime last year, on his now-defunct tumblr feed, Recursive Muffin, Ethan Mitchell asked a question I thought the folks on This Week In Microbiology (which I’ve written about here and here) might be able to answer. I emailed them and they did so, at the end of episode 73. I thought the question and answer were interesting enough to transcribe here:

Question of the day: A strain of Flavobacterium (KI72) evolved the capacity to digest nylon, obviously in recent history. Fine and well. How long will it be until one of the cariogenic bacteria species evolves the ability to digest dental resin? After all, we are putting a lot of it on their dinner table.

Answered primarily by Michael Schmidt, who teaches microbiology to dental students at MUSC, with help by Michele Swanson and Vincent Racaniello. Keep in mind that this is a transcribed conversation, so informal, and that I don’t know how to spell some of these words:

Michael: This has already happened to some extent. In the United States we currently spend 5 billion dollars a year replacing resin-based composite fillings due to failure. The average lifespan of a resin-based filling that a dentist will put in today is around 6 years. And the recurrent decay usually compromises the restoration earlier in its lifespan, and that’s when the bacteria are effectively going after the “glue.” And they’re going—because it’s a polymerization and the microbes—if the restoration isn’t properly fixed and properly cured there’s enough carbon in there that they can get at before the polymerization is completely done, that they can actually get after it. And then afterwards, matrix metalloproteinases and cathepsins places the longevity ceiling at that 6 years, even at healthy and bacterial free restorations. And so these matrix metalloproteinases and cathepsins which are expressed specifically in dentin, they come in and they cause the restoration to fail.

Michele: But those are bacterial, Michael, or those are…

Michael: No, those are eukaryotic. The bacterial failure… places the longevity cap at around 6 years, so there’s currently a resin-based product in the market that’s from a Japanese company that puts chlorhexidine into some of these resin-based products in order to prevent microbial attack and to take out the… bacterial attack. So we’ve been looking at copper nano-particles to effectively prevent some of this decay, but what he is hypothesizing has already been happening in the US and it happens throughout the developed world, anyplace people are using resin-based fillings. The old silver fillings typically last 25-30 years without incident. Most people were concerned about the mercury issue but the amount of mercury in an amalgam based filling is insignificant in terms of health consequences if you look at the evidence-based literature. It really has no issue associated with the health of the individual.

Michele: And I don’t suppose there’s any data saying the half-life of the resin is decreasing? Which would be consistent with this idea that we’ve selected for bacteria, we’re enriching for bacteria, that can break it down more readily?

Michael: No, because the resins have gotten better. The polymerization agents and the curing times, so we don’t have a clean experiment to do it. The folks haven’t actually looked to see if resin-based dissolving bacteria… but that’s a question that I can ask my friends at the Forsyth Institute to see if they’ve hunted to see if there are any resin-eating bacteria out there. But it’s all about the polymerization because the polymer needs to be perfectly cured and any of you who’ve had a recent composite filling you remember the dentist putting on the dark glasses and giving you a pair of dark glasses and they put the magic light into your mouth to cure the filling. And typically they only put the UV lamp in there for 20-30 seconds and that’s what starts the curing process. And we’ve all made polyacrylamide gels and it’s a variation of polyacrylamide gels except we use… Temid and whats the inorganic… the inorganic salt. I haven’t made a gel in…

Vincent: I can’t remember either.

Michael: Because you just pull MP… not MPS…

Vincent: APS

Michael: APS. Ammonium persulfate and that’s what goes bad. The binary catalyst.


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.


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.

On 10/9/10, I woke up 6:54 am, vibrating with fear. I said this into my voice recorder. Imagine a super groggy voice. (Warning to the squeamish–I say the F-word and the SH-word, and it’s kind of gruesome, and worst of all I say “like” a lot.)

“Holy crap, what a nightmare… I go to a dentist to get my two fillings… and, uh, they gave me like shot after shot and were doing like brain stimulation stuff [this was the “dentists” shocking my brain through my skull over and over, making large parts of my face numb] and uh… shooting into my gums and eyelids, and drilling into my eyes… and when I left there I realized it was like 7 in the morning. I’d been there… I’d been there all night. I was like, “What the fuck?” and I went back. And I basically killed ‘em…. by banging their heads together… cause I realized—in the dream I was certain of this, though they totally denied it—it was like they hadn’t even drilled my teeth. My teeth felt the same. And I like, I kind of like worked out their scheme. It was like they had given me AIDS and like drilled into my brain. It was really creepy, just really creepy. Holy shit! I don’t want to have dreams like that. That’s fucked up. It started off nice enough, I was just going to the dentist. It was in a big house in the woods, kind of like Vermont….. Also, there were people that I knew in the house downstairs. I passed them on the way out. I forget what they said but when I came back I brought one of them up with me for moral support.”

Yesterday, I got two real fillings. Anticipating them is probably what prompted that nightmare. The dentist was very nice and very competent. The fillings are good ones. And it was brutal. Getting needles stuck deep into your gums to pump fluid in, getting holes drilled into your teeth, with a drill–these are undeniably brutal experiences.

I tried to teach myself something during that process. “Nathen, this is the result of putting off finding a new dentist. If you don’t like this, don’t put that kind of thing off.” My dentist in southern California diagnosed the cavities (the second and third cavities of my life) last December and said they were so small that he wouldn’t have to numb me or drill. Just a little sandblasting and a dab of porcelain. But then he got sick and couldn’t do the work before my term started. I came back up to Eugene and just hated the idea of finding a new dentist. All the dentists up here are way more expensive than mine, and who knows if their work is good? So I waited (Maybe I can make it to my next visit home! I take such good care of my teeth…) and agonized and eventually had my brutal fillings.

One of my definitions of adulthood is the absence of that kind of behavior: An adult is someone who just does what needs to be done. No agonizing, no procrastination. By this measure I am still working on adulthood. Perhaps this lesson will speed up my development.