Hi there can you answer a question about 1 of my crowns.?!

Hi there can you answer a question about 1 of my crowns.?

I had a New crown put in my mouth on January of 2007, the tooth is sloughing away on top of the inside of the tooth.... the outside of the tooth seems like any of my other crowns I have had put on, hard and stable, but the inside of the New Crown seems to have air bubbles in it and when I touch it with my tongue it seems as thought the inside top of this tooth is getting smaller in height each day. Can you please help answer my questions. I would sincerely appreciate it. I have never had this problem before and had many Crowns in my life and have never had a Crown slough off like this before , could this be a lab error, as I said it is like air bubbles were all over the top half of the inside of the tooth , what could have happened? I am not mad at anyone I just want a truthful answer as I think I need to have a New Crown made.
Thank you I appreciate any questions that you can help me with.
How is a Crown made anyway, if you do not mind me asking. The Step by Step Procedure.

2 months ago
The Top of the Crown that is sloughing off at first had sharp tiny holes in the top of the tooth before it started sloughing off. I would feel it and it would hurt as they were at first very sharp. After a month or so the holes in my tooth started just eroding away with the touch of my tongue.
I think this Crown was not made correctly or something is wrong I have had many crowns as I said over the years and never have I had one do this, ever. Oh the Crown Cost was $900.00

2 months ago
Now I feel metal on that tooth and it hurts.

2 months ago
I went to my Dentist and he said he cannot see it so I went to another Dentist and he said he felt the metal also but said he worked with my Dentist and could not do anything to upset him.
The tooth has lost at least 1/3 of the height on the inside.

Without the benefit of actually seeing the crown, my guess is that air bubbles were incorporated into the porcelain when the crown was made by the lab. After an impression of the prepeared tooth is made, a lab makes a stone model of the tooth. First the make a metal coping (thimble). This gives the crown strength. Next porcelain is baked onto the metal. This gives the crown a natural appearance.
There are newer crowns that do not have metal. The coping is a very hard ceramic, like zirconia.