cavities filled with amalgam 30 years ago

Having your fillings redone is a great idea, because it is very likely that these fillings have developed some leaks that are not apparent on xray or exam.  Often times, these leaks will allow bacteria to get into the interior of your tooth and eat away at the structure.  It is unfortunate that often times we cannot tell that this is occurring until the bacteria have eaten a significant enough portion, that it shows up on an xray or exam.  I would agree with your dentist that the mercury fillings should be replaced, but I recommend a porcelain inlay or onlay to replace these silver fillings, instead of composite resin.  This is because resin wears away over time and stains very quickly.  Porcelain does neither and is expected to last another 30 years.  Good luck and I hope this helps. Follow me if you have more questions.Sarah Thompson, DMD

If there are no symptoms such as pain when chewing, or recurrent decay, there is no reason to replace them unless you want to be rid of the dark amalgam and replace with a tooth colored composite resin.

You have had wonderful service from your amalgam fillings.  30 years is a very long time for a filling to last.  It is very hard to say that these fillings should be replace without the ability to see them but it is very likely they have reached the end of their service and need to be replaced.  It is not good to wait until symptoms occur.  That usually means there is extensive decay present.  Good luck!