时差N小时 我们为什么要刷牙？

Humans may be no less a part of the animal kingdom than lions,tigers and bears, but certain things set us apart.

或许人类的动物属性一点也不比狮子、老虎和熊少，但某些特征却将我们与它们区别开来。

For instance,although like our mammalian cousins we use teeth to bite and chew food,we're the only animals that brush after every meal.

举例来说，虽然我们与其他哺乳动物一样用牙齿撕咬和咀嚼食物，但我们是唯一餐后刷牙的动物。

And as four out of five dentists have reminded us on countless¹ television commercials, using one or another variety of toothpaste is crucial for keeping our teeth healthy.

正如五个牙医中会有四个在数不胜数的电视商业广告中一直提醒我们的那样，使用不同种类的牙膏对保持牙齿健康至关重要。

Like that fifth dentist who never seemed to know what was going on, you might have wondered what toothpaste actually is, and how it helps ward² off tooth decay.

像永不情知的的第五个牙医一样，你可能会疑惑，牙膏到底是什么，它又如何帮助我们避免龋齿。

Toothpaste consists of several ingredients, some of which you'd never think to put in your mouth.

牙膏含有多种成分，有一些你可能从未想过要把它们放进嘴里。

For example, almost all toothpaste contains detergent³, or soap.

比方说，几乎所有的牙膏都含有清洁剂或肥皂。

Getting your mouth washed outwith soap is supposed to be punishment, so what is it doing in toothpaste?

直接用肥皂清洁嘴巴是一种惩罚，那么牙膏中含有的肥皂是如何清洁牙齿的呢？

Although it has a slight antibacterial effect, it's there mainly to make foam⁴, which serves little purpose other than to provide a visual sign to the brusher that the toothpaste is hard at work fighting cavities.

尽管肥皂有轻微的抗菌作用，但它主要是制造泡沫，这些泡沫除了向刷牙的人传递牙膏能有效抗击龋齿的视觉信号外毫无作用。

Of course some ingredients play a more active role, the most famous of which is fluoride, a mineral compound derived⁵ from the element fluorine.

当然牙膏里有一些成分在发挥着更为积极的作用，当其中最广为人知的还是氟化物，这是一种从氟元素中提取出来的无机化合物。

Fluoride protects teeth in two ways: it kills acid-producing bacteria which are mainly responsible for tooth decay, and it strengthens and repairs tooth enamel⁶ that has been softened⁷ by the acid.

氟化物以两种方式保护牙齿：首先，它能够杀死龋齿元凶-造酸细菌；另外，它还可以固化、修复被酸软化的牙釉质。

So far as we know, the only drawback to using toothpaste is that it makes drinking orange juice after brushing a pretty unpleasant taste experience.

据我们所知，使用牙膏的唯一缺点在于：它使人们刷牙后饮用橙汁成为一种相当不悦的味觉体验。

But that's a small price to pay for healthy teeth.

但这只是为牙齿健康付出的一点小小代价。

1 countless   

adj.无数的，多得不计其数的

参考例句：

• In the war countless innocent people lost their lives.在这场战争中无数无辜的人丧失了性命。
• I've told you countless times.我已经告诉你无数遍了。

2 ward   

n.守卫，监护，病房，行政区，由监护人或法院保护的人（尤指儿童）；vt.守护，躲开

参考例句：

• The hospital has a medical ward and a surgical ward.这家医院有内科病房和外科病房。
• During the evening picnic,I'll carry a torch to ward off the bugs.傍晚野餐时，我要点根火把，抵挡蚊虫。

3 detergent   

n.洗涤剂；adj.有洗净力的

参考例句：

• He recommended a new detergent to me.他向我推荐一种新的洗涤剂。
• This detergent can remove stubborn stains.这种去污剂能去除难洗的污渍。

4 foam   

v./n.泡沫，起泡沫

参考例句：

• The glass of beer was mostly foam.这杯啤酒大部分是泡沫。
• The surface of the water is full of foam.水面都是泡沫。

5 derived   

vi.起源；由来；衍生；导出v.得到( derive的过去式和过去分词 )；（从…中）得到获得；源于；（从…中）提取

参考例句：

• Many English words are derived from Latin and Greek. 英语很多词源出于拉丁文和希腊文。 来自《简明英汉词典》
• He derived his enthusiasm for literature from his father. 他对文学的爱好是受他父亲的影响。 来自《简明英汉词典》

6 enamel   

n.珐琅，搪瓷，瓷釉；(牙齿的)珐琅质

参考例句：

• I chipped the enamel on my front tooth when I fell over.我跌倒时门牙的珐琅质碰碎了。
• He collected coloured enamel bowls from Yugoslavia.他藏有来自南斯拉夫的彩色搪瓷碗。

7 softened   

（使）变软( soften的过去式和过去分词 )； 缓解打击； 缓和； 安慰

参考例句：

• His smile softened slightly. 他的微笑稍柔和了些。
• The ice cream softened and began to melt. 冰淇淋开始变软并开始融化。