龋齿已被世界卫生组织列为心血管病和癌症之后的三大重点防治疾病之一，因此把每年的9月20日定为“世界爱牙日”。从古至今，所有人都注重对牙齿的保护，古代都是饭后漱口。但是自从牙刷问世以后，让人们对牙齿的洗刷更加的方便，所以现在很多人都养成了一种早晚刷牙的习惯，刷牙不仅能够刷掉牙齿上因为吃饭留下的残渣，还能保证牙齿的健康，同时还能够促进牙齿美白。
It's almost bed time here at the fort!
But before we get tucked in, we've got to brush our teeth!
Hey, that's a good question, Squeaks.
We do it a couple of times a day, but we should really understand why we do it!
So: Why do we have to brush our teeth?
Well, have your teeth ever felt just. . . yucky?
Like at the end of the day?
Or first thing in the morning?
I really like brushing my teeth, because it gets rid of that icky feeling.
And it feels good, because it is good!
