Identifying relative clauses: Is this の replaceable with が?


I was browsing through the Japanese Dictionary for the definition of "歯医者”

One of the definition is as follow "歯の治療をする医者".

I believe that the の here is replaceable with が here. But I am not sure how do
I identify relative clauses so as to know when I can replace the の with が.

To my understanding, if it is が, the general meaning would be "the doctor who
cures teeth", with the が targeting "歯" as the thing to be cured.

Is my interpretation correct? If not, how does の work in this case?




> I believe that the の here is replaceable with が here

No, it isn't. Just because の appears in a relative clause does not necessarily
mean it's a subject marker. You cannot replace this の to が. 歯が治療をする医者 is still
"grammatical", but it means something funny like "a physician whose teeth
treat patients"!

This の in 歯の治療をする医者 is simply a noun-linking particle similar to "of" in
English (of course the word order is different; `AのB` is `B of A`). Read it
like "a physician who does treatment of teeth". You can rephrase it like
歯を治療する医者 ("a physician who treats teeth").

At the end of the day, your question is essentially not about relative clauses
but about the usage of suru-verbs. You can read similar discussion in the
following questions:

  * [Difference Between べんきょう する and べんきょうを する](https://japanese.stackexchange.com/q/4006/5010) (日本語の勉強をする vs 日本語を勉強する)
  * [Jlpt/n5q5: 弟は部屋◯掃除をしました。◯: の versus に option](https://japanese.stackexchange.com/q/26120/5010) (部屋の掃除をする vs 部屋を掃除する)
  * [の or を？ What is the correct answer and why is it correct?](https://japanese.stackexchange.com/q/44972/5010)
  * [Can we optionally include (or exclude) an を particle in between the noun of the する-verb and the する itself?](https://japanese.stackexchange.com/q/1532/5010)

