It is getting more and more important in dentistry to use substances in the mouth that are tissue-firendly, bio-compatible and immunocompatible, so that the body will not recognize them as strange materials, therefore it will not reject them or start an immune reaction against them. These materials are not supposed to pile up in different parts of the body nor to cause diseases. We can hear different opinions about amalgam that has proved to be the most durable material so far, but it raises also the question whether quicksilver as a heavy metal can cause harmful reactions in the body when it dissolves from a filling.
It is a fact that beside amalgam (which is an alloy of quicksilver and several other metals) also other metals used in dentistry have proved to cause allergy,. A well-known example for this is nickel.
This is the reason why the new tendecy is to try to avoid use of these metals, which is not exactly simple as it is extremely difficult to find materials with as favourable characteristics (for example flexibility strength) that are similar to those of metals and that are necessary in the case of certain restorations (fixed partial denture, when missing tooth or teeth have to be restored).
Such a material is plastic enhanced with glass fibres (Belle Glass that has very similar characteristics to tooth tissue.)
Another example is the long-used porcelain that can be processed in various different ways and with different technologies, thus is suitable for various kinds of restorations. None of them is, however, suitable for filling bigger spaces.
The revolutionary and for the present the only possible and therefore the best material to use for building longer fixed partial dentures, is circonium dioxide. Its firmness and physical characteristics top those of metals. Furthermore the used technology to prepare these restorations will positively be a leading method in the 21st century ( unlike other areas of medicine, f.x. orthopaedy where prothesises have been made of this material for long).