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不少人有饭后立即刷牙的习惯，认为这样能尽可能地减少患牙病的几率。不过，最近的研究结果认为，饭后立即刷牙有害牙齿健康。这是因为，在牙冠的表面有一层珐琅质，刚吃过饭尤其时食用了酸性食物后，珐琅质会变松软。这个时候刷牙，就会造成珐琅质的损害。所以，进食后最好先用清水漱口，待1－2个小时后再刷牙。
M:Sorry,I'm late.I was brushing my teeth.
W:Brushing your teeth?Right before 'A Moment Of Science'? Why?
M:I'm trying to get rid of a cavity.
W:Get rid of a cavity?Are you stuck with a cavity once you have it?
M:It depends on how deep it is.Acid from bacteria in your mouth can cause your tooth to decay.First, the acid eats away the very hard outer layer of your tooth, called the enamel. Inside the enamel is the dentin. It’s spongy and has nerve endings, so your tooth might be sensitive to sweets or cold if the decay reaches there.But the cavity doesn’t really start to hurt until it gets through the dentin to the soft pulp. That’s when you get a toothache.
W:Oau！
M:Dentists will sometimes fix a cavity by putting in a filling while the decay is still in the enamel. But decay is reversible until it reaches the dentin. If it’s properly treated, the decay will stop, and the enamel will harden, although the tooth will never be perfect again.
W:So that's why you're brushing.Can you do anything else to help get rid of a cavity?
M:Dentists can also help by giving you a fluoride treatment, but you have to brush and floss regularly. You might have to give up soda and sweets.So it’s not easy–and dentists know that. That’s why they sometimes fill a cavity in its early stages, before it starts to hurt.
W:So you’re not stuck with tooth decay once it happens.?
M:No.But it’s better not to let it happen in the first place.
