【科学60秒】氟化物护牙之谜仍未解_英语听力练习mp3下载-科学-沪江听力酷

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【科学60秒】氟化物护牙之谜仍未解

听力简介：

Beauty is only ____1____. And the beauty of shiny white teeth is even less deep. Because a new study shows that fluoride forms a thinner protective shield than experts thought it did. The results appear in the surface science journal Langmuir.
American consumers spend more than $50 billion a year fighting cavities. When we realized that fluoride could help, we put it in our drinking water, our ____2____ and our mouthwash. But how does fluoride work its magic? Many figured that fluoride chemically reacts with the main mineral in enamel to form a thick, decay-resistant veneer. But the latest research ____3____ that idea in the teeth.
Scientists in Germany used x-ray photoelectron spectroscopy to get a detailed image of the surface of a treated tooth. And they found that the protective covering is actually only 6 nanometers thick. That’s about a fifteen-thousandth as thick as a sheet of paper. And a layer that skimpy would likely be ____4____ by ordinary chewing.
How fluoride keeps the tooth fairy away is a mystery that researchers are still working to ____5____. In the meantime, we may not know how it works, but we know that it works. So keep brushing.
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