Questions, from a couple of readers worrying about their teeth: “You wash your mouth out with Listerine after you have brushed . . . with cavity-fighting Crest. You have washed out the toothpaste. So how does it battle cavities?” Then, “If the primary source of cavities is sugar consumption, why do we put fluoride in the water and not in the sugar?”

        Answers: While Listerine might seem strong enough to thoroughly strip your mouth and your large intestine, you haven't really washed things out, says Matthew Messina, Cleveland dentist, Blue Ash native and consumer adviser for the American Dental Association (ADA).

        “The active ingredients (in toothpaste) are designed to stick to the teeth. The protective capabilities are still there and will remain there long enough (a couple of hours) to do their job.”

        As for the concept of adding fluoride to sugar instead of water, “The real straight answer is you can put it in water; you cannot put it in sugar,” says R. Thomas Scheer, Hyde Park dentist. “It has to be dissolved in water.

        “It's a public health issue,” Dr. Scheer says. “We're assuming everybody drinks some tap water. We're not assuming everybody eats sugar.”

        Beyond that, it's bacteria and the acid they produce that cause cavities, says Dr. Messina.

        “If I had perfectly clean and healthy teeth, I could rub sugar on them all day and not have a problem,” he says.

        Fluoride makes tooth enamel more resistant to oral acids. According to the ADA, people who drink fluoridated water have 40 to 50 percent fewer cavities.

        Luckily, people who submit questions to the Stupid Desk have 100 percent anonymity.

        If you have a stupid question, send it to Ask a Stupid Question, Cincinnati Enquirer, 312 Elm St., Cincinnati OH 45202; fax: 768-8330; e-mail mpulfer@enquirer.com.

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