Translation guide
A tooth that has decay, typically due to caries. In Japanese, the most common term is 虫歯 (mushiba), literally 'bug tooth'. Other terms exist for specific contexts.
The most common, everyday way to refer to a tooth with a cavity or decay.
My decayed tooth hurts.
Treat a decayed tooth.
A more technical or medical term for a decayed tooth, often used in dental contexts.
Fluoride is effective for preventing decayed teeth.
A highly technical term for a carious tooth, rarely used outside dental literature.
Researching treatment methods for carious teeth.
When you want to describe the condition of a tooth, rather than name the tooth itself.
Unless you are in a highly technical dental context, 虫歯 (mushiba) is the word you want. It covers both the cavity and the tooth itself.
It's dangerous to leave a decayed tooth untreated.