It’s a 75-year-old technology. Maybe we should rethink it.

I blame my dentists. Not for poor dental care—Barbara and Gordon do great work. I blame them for sending me into a vortex of dento-epistemological anxiety.

On a tooth-cleaning visit not long ago, Barbara told me that in the late 1970s, when she attended dental school, her professors expected that most middle-class patients would lose a lot of their teeth and need dentures by the time they were in their 60s. Today, she said, most middle-class people keep their teeth until they are 80. The main reason for this, Barbara explained, was fluoridation—the practice of putting fluoride compounds in community drinking water to combat tooth decay.

For reasons I can’t now recall, I mentioned this remark on social media. The inevitable but somehow surprising response: People I did not know troubled themselves to tell me that I was an idiot, and that fluoridation was terrible. Their skepticism made an impression. I found myself staring suspiciously, as I brushed, at my Colgate toothpaste. strengthens teeth with active fluoride, the label promised. A thought popped into my head: I am now rubbing fluoride directly onto my teeth. So why is my town also dumping it into my drinking water?