Dentist: Hello Liz. What seems to be the problem?

Liz: One of my small molars has been aching for a while. I was waiting, and hoping that the pain would go away, but it hasn't.

Dentist: You are due to have an x-ray, so let's do that and then talk about all your teeth.

Later.

Dentist: Ah, yes, you have quite a large cavity in the side of a molar. The hole in the enamel is small but deep. I'm afraid the pain won't go away until you have a filling.

Liz: Oh, ok. I'm so disappointed. I brush and floss my teeth twice a day, and I avoid sugary food.

Dentist: I know you have good dental hygiene. Well, because you have a brace, it is hard to clean in between your teeth. And some people have cavities, root canals, abscesses, and even gingivitis, while other people , don't have many problems.

Liz: That seems unfair.

Dentist: It's to do with the level of bacteria in your mouth which is affected by hygiene, diet, genetics, and even stress. I know that you have good dental hygiene because your teeth are healthy and your mouth is very clean. Generally speaking, brushing and flossing and avoiding sugar are the keys to cavity-free teeth. The good news is that soon we will be able to take off your braces; your teeth are almost completely straight. 

Liz: That will be a big relief!