Is my dentist lying about my crown?

[Toller]

I have 9 crowns; some are 40 years old. Last week I had, for the first time, one fall off. It was 7 years old.
I went to the dentist to have it put back on. She explained that she would put it back on with permanent cement, but it no longer fit properly and was likely to come off again. Cement causes the gold crown to deteriorate and it no longer fit the tooth properly. The margins still fit well, so it will be fine until it falls off again. Crowns only last 5 years and I was lucky that it lasted 7 years. However, they were willing to give me $400 off their normal $1,400 price for a replacement.

I talked to a dentist friend about it. He says that crowns last indefinitely; the 5 year life is nonsense. The only reason a properly prepared crown should fail to fit again after falling off is decay to the tooth; the cement does not deteriorate the crown. Since I don't have decay, the crown must not have fit when it was initially made.

He has no reason to lie to me (and I know nothing but a mix of strong nitric and sulfuric acid and attack gold) I have to conclude that my dentist is lying to me. So, I am in a bit of a pickle here.

1) Was my friend right about about it being made incorrectly?
2) If so, does the dentist have an obligation to replace it at no charge, or is this just something that happens sometimes.
3) What do I do about dentist that lies to me?

Any help would be appreciated.

 

[Dr M]

Firstly, there are a lot of factors that influence the prognosis of a crown. What your friend failed to mention, is that over time and during function, the crown cement gradually becomes loose or " deteriorates'' and becomes weaker. This is due to a host of factors, including changes in temprature in the mouth, oral fluids, diet etc.
When the crown eventually comes loose, small pieces of tooth structure can come off with the crown, which would indicate that every subsequent cementation, the fit is not as perfect as it was initially.
If we consider a perfect fit in the beginning, every recementation leads to micro-gaps forming and then to micro-leakage occuring, which penetrates beneath the crown, and then again, weakens the cement.
There are a lot of modern cements that try and counteract this, with moisture sensitivty being kept to a minimum, but a lot of these cements were not available 40 years ago.

 

[Toller]

Except that isn't what they told me. They said that the cement corroded the crown. It is really hard to believe there could be a cement that corrodes gold.

 

[Toller]

Except that isn't what they told me. They said that the cement corroded the crown. It is really hard to believe there could be a cement that corrodes gold.

 

[Dr M]

I doubt that it was the cement that corroded the crown. I have not heard about this before. Gold is in general a soft metal. If the crown was damaged on the outside, it was most likely due to prolonged occlusal forces.
But I stand by my previous explanation of cement degrading over time. This is normal