虫歯

1. Origins, structure, and basic meaning

• Structure: 虫歯, read むしば, is the dental noun cavity or tooth decay.
• Basic usage: 虫歯を防ぐ makes cavities the condition prevented; 奥歯に虫歯が見つかる reports one found in a molar.

2. Common pitfalls and similar expressions

• Tooth decay and an individual cavity
  • 虫歯 can denote tooth decay as a condition or a particular cavity found in one tooth. It therefore appears in both prevention and diagnosis contexts.