Dear practo user Need dentist professional treatment. With medicine it won't cure completely or may recur.

Its a milk teeth. This abscess (boil)is due to pus formation underneath that teeth. That tooth is severely decade. Also its teeth nerve becomes dead and decayed. This is a bacterial action. U mentioned here repeated boil formation under teeth. So better option is extration under antibiotic coverage. Dont do rct again. This infection may spread to jaw area.

Consult your dentist at the earliest

RCT with crown should be treatment plan. That boil is indication of presence of pushing at root end. Which will subside followed by RC treatment.