Old Crown Pressure Sensitive and Painful

Years ago I had a crown done on the 2nd tooth from the rear on the lower right side of my mouth. A few weeks back, I started to notice that my tooth had become pressure sensitive when eating things that were a bit harder than most, but other than that I haven't had any issues with the pain. I made an appointment with my dentist late last week, and he took an xray of the tooth and said he didn't see a thing wrong with it via the xray. He said that if it was infected or cracked, he'd see it on the xray.  He did some tap & bite tests and said everything seemed okay, and that i should call him back if the pain gets worse, or becomes unbearable.  

Today I have noticed that my gum under that tooth is starting to feel a bit of pain all the time, almost like a very dull throbbing pain and it's not horrible but creeping in.  

I think I will call in to the dentist again and ask what to do, but wanted to see if anyone here had a second opinion on what it may be.

Thanks in advance!

[Jerome Tsang, DDS]

What did your dentist say?  Your pulp may be degenerating (dying) and it could be the source of the pain.