What causes a slightly loose tooth after a root canal?

Hi doctor,

I have a question about my second molar tooth. I had a deep cavity in this tooth for a long time. Last year, it hurt a lot that I found it difficult to eat. I visited a dentist who did a root canal on that tooth and he took an X-ray. He treated this tooth for eight months and he prescribed antibiotics for five days. It got swollen again last year and the dentist drained the pus from that tooth and the swelling went away. After that, the tooth did not cause any discomfort and the dentist also took an X-ray and said that the tooth looks fine in the X-ray.

It has been two months now and there are no issues in this tooth. The treatment was completed earlier this year but the thing is that there is a little dot on the gum but it is harmless. It is so small and there is no swelling or bleeding and the tooth does not hurt. The dentist took an X-ray at the last appointment when he filled my tooth. On that day, the gum of this tooth got swollen and there was a lot of pus discharge. He told me to press it and I followed the same. He again took an X-ray and said that there were no issues. But, I would like to know about the tiny dot on the gum. If it was a fistula, it would have caused pain and pus discharge. It is harmless and it has been there for two months. The dentist saw it and said that it could be gingivitis.

I wonder what it could be since it does not go away. It is so tiny that one must look closely to have a look at it. I used to move this tooth before the treatment but when it started to hurt, I stopped moving it. Now, the tooth seems to move slightly. I guess this could be because I played with it previously. Is there anything I could do to strengthen this tooth and gum? It is slightly movable but there is no pain and swelling. Please help.

Thank you.