For much of his life, Chicago builder Chris Valenti thought good dental hygiene meant brushing his teeth with a vengeance. "I brushed my teeth like I would wash a car," the 34-year-old says. "I used a little elbow grease."

What Mr. Valenti didn't know was that his teeth and gums were getting too much of a good thing. Now, eight gum grafts and $1,700 of mouth surgery later, he has learned a lesson many Americans still don't know: It's possible to brush your teeth too much.

The problem is commonly called "toothbrush abrasion," and it can lead to sensitive teeth, receding gums and wear around the root of the tooth. Dentists and toothbrush makers estimate that between 10% and 20% of the population have damaged their teeth or gums as a result of overbrushing. The people most at risk are those who are particularly diligent about their oral care, and who use medium- or hard-bristled brushes. Genetic factors also play a role.

Oral care is getting a lot of attention these days from marketers trying to cash in on aging consumers' worries about keeping their teeth. Americans spend about $700 million a year on toothbrushes, and sales have climbed following the introduction of newfangled brushes offering everything from longer bristles to ergonomic handles designed to provide a better grip.

But often the culprit in toothbrush abrasion is the toothbrush itself. Although both dentists and manufacturers recommend soft-bristled brushes to prevent gum damage and wear on the soft dentin in the root area, 45% of the toothbrushes sold in the U.S. have medium-hard bristles.