I haven't done a lot of research on the various amalgam substitutes, so I'm not an expert.

What I have read indicates that "gold alloy" can contain anywhere from 1 to 99% gold, which means that other metals are used to make up the difference. Cheaper gold alloys can contain toxic metals such as nickel and chromium.

Ceramic porcelain inlays/onlays often contain metals in the form of oxides (such as aluminum oxide) or even heavy metals (such as cobalt, barium, cadmium or nickel). These are usually added to give the materials strength and improve their appearance.

I have DiamondLite biocompatible composite fillings, which I believe are among the safest and most biocompatible materials available. My dentist uses DiamondLite in about 80% of his patients.