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氟(fu)这种化学物,能在我们牙齿外面形成薄膜(bao mo),牢牢固定住牙齿表面的钙质(gai zhi),使牙齿变得坚固。不过,这层薄膜只是暂时性的。人在咀嚼
Fu, a chemical that forms a film outside of our teeth, firmly anchors the surface of the tooth to make the teeth firm. However, this film is only temporary. People chew