Do metal fillings discolor your teeth?

I would like to know first, if metal fillings discolor your teeth after awhile and if so, what causes this? Are composite fillings stronger/last longer than the metal ones? And last, should the metal ones be replaced with composite fillings if this is starting to happen?

Do metal fillings discolor your teeth?
Seeing a discoloration of the tooth from amalgam restorations depends on the size of the restoration. The color is due to the silver leaching into the tooth. If the restoration is close to the cheek side you will see an eventual darkening; the amount depends on how close the restoration is to that side. Bonded amalgams tend to discolor less as the tooth is sealed by the bonding material. Composite restorations are not as resistant to chewing forces as amalgams and are thus not usually used on large back tooth fillings unless there is an aesthetic problem and the patient is aware of it's limitations. I wouldn't recommend that you replace any metal fillings with composite unless they are really in the top teeth like the bicuspids and then only if there is a chance for the silver color to bleed through.