Filling turned into root canal... is this common?

Happened to me too - thought I was done after the filling, then bam, root canal a few weeks later. My wallet was not ready for that one. Dental bills really know how to sneak up on you...

Yeah, that can totally happen, unfortunately. Sometimes a filling just isn’t enough if the decay was deeper than it looked or if bacteria got close to the nerve. I had a similar situation - pain came back a month after my filling and the x-ray showed infection had spread. The dentist said sometimes the nerve just doesn’t recover even if things look okay at first. Super annoying, especially with how expensive root canals are. I wish insurance covered more of it.