Dentist left part of my tooth exposed with new crown, are they responsible to replace it?

I had my crown done a year ago. When the crown was put on, I noticed that there was a gap between my gum line and the cap leaving my tooth exposed in the back. I remember asking the hygenist if this was normal, and she said it looked fine. Now I am having sensitivity and pain, and I learned that the tooth should never have been exposed. I'm wondering if they are responsible to replace my crown? I had a cleaning a couple of months ago and they didn't mention anything about it either.