Decayed Tooth, Tooth Decay
Noun and の adjective
むしば
今日、歯医者で虫歯をぬいてもらいました。
Today, I had my decayed tooth extracted at the dentist.
虫歯のげんいんであるミュータンスきんは子どもの成長とともにまわりの大人からうつってしまいます。
Streptococcus mutans bacteria, the cause of tooth decay, can be transferred from adults to the kids around them as they grow up.
虫歯がいっぱいあるんだけど、歯科保険が無いので、治療代を捻出することができないんだ。
I have so many cavities but I don’t have dental insurance and I can’t afford to get them treated.
A tooth bug... Luckily, it's not some bug living in your tooth, though you can see why someone might think this is what happens. A tooth with a "bug" in it is a tooth with a cavity.
The readings are both kun'yomi, but those are the readings you learned with these kanji. Notice that は turns to ば, though. Presumably this is because you might yell out "BAH!" when you find out you have a cavity.