Welcome to HCM!
This bump that you mention is nothing but an abscess
. As you mentioned it is next to a cavity in a tooth, this has occured due to chronic pulpitis
, i.e. infected tooth pulp. Although it has shrinked after getting burst, i shall recommend you see a dentist
for the same. The clinical examination of the decayed tooth and its xray will help in chalking out the treatment plan. Mostly the tooth involved shall go for a Root canal
therapy unless very grossly decayed. Secondly, you will need to take antibiotics for the same but it shall be best for your dentist to decide on it after a thorough examination. Kindly get this checked as this bump may recurr in future.
Take care :)
Dr. Akanksha Sharma