פירוש על עבודה זרה 55:5

In this strange vignette, R. Yohanan goes to a female non-Jewish doctor. She heals him but he wonders what he will do on Shabbat. Rashi explains that he can’t come to her on Shabbat because he will be busy teaching. In any case, the story seems to prove that one can heal gum sores on Shabbat.