ha ni shikou ga tsuite imasu.

subject particle

Breakdown of ha ni shikou ga tsuite imasu.

• に: location particle
• いる: to exist (animate)
• 歯は: tooth

Questions & Answers about ha ni shikou ga tsuite imasu.

How do you read 歯垢?

It is read しこう.

• 歯 = tooth / teeth
• 垢 = dirt, grime, buildup

So 歯垢 means dental plaque.

Why is に used after 歯?

に marks the place where something is attached.

So in 歯に歯垢がついています, 歯に means:

• on the teeth
• attached to the teeth

This is a very common use of に with verbs like つく when something ends up on a surface or at a location.

Why is が used after 歯垢?

Because 歯垢 is the thing being described as attached.

In this sentence:

• 歯に = location
• 歯垢が = the thing that is there / attached
• ついています = is attached / is stuck

So が marks plaque as the grammatical subject of the sentence.

If you changed the topic, you could also say something like 歯垢は歯についています, but that has a different emphasis.

What does mean here?