Metal Free Dentistry

Perhaps the confusion in materials science comes in understanding the state in which metals are found. The commonly identified metals, such as those in a precious bridge alloy or in the steel used to structure a building or in kitchen utensils or in a foil, are present in a fully ‘reduced’ state. These are the hard, shiny metallic forms normally referred to as “metals”.

But metals can also be present in an ‘oxidized’ state. They will no longer look like hard, shiny metals, but will be a powder (as in common oxides such as rust) or will combine with other chemicals to form a salt (as in the example of sodium metal combining with chlorine to form common table salt). Being in an oxidized form means simply that the metal is present in a different state of being. By various means, we can take common iron rust and convert it back to its ‘reduced’ state to look like a piece of hard shiny metal.

When we look at the metals used in dentistry, they may be in either ‘reduced’ state (bridge or gold crown) or ‘oxidized’ state (composites or ceramics or porcelains). By the laws of chemistry and physics, these metals must be present in one state or the other or there cannot be a dental material (or any other material for that matter). There will certainly be differences between a gold crown versus ceramic versus composite versus prophy paste. However, these differences do not mean that the metals have been taken away from any of these products, but rather, they have been placed in a number of variations of either the ‘reduced’ or the ‘oxidized’ state. The metals are present in any substance you might wish to discuss.

Parties who advertise “metal-free” dental products have overlooked the fact that the materials which lack the hard, shiny metallic nature of “metals” still have those metals present, but the metals are in an ‘oxidized’ state and are combined with other components. With proper chemistry and methods, we can take any porcelain or ceramic or composite and convert the metals found therein back into the reduced hard, shiny form. They were there all along.

Thus, the question to ask when considering the desirability of restorative materials is clearly not whether they contain metals. Simply, they do. All of them. Rather, we would want to ask what state, forms and structures the metals take. Do the metals readily separate from the other chemistries present and do they take any forms which are not desirable. To simplify several hours of lectures from a chemistry class, do the metals dissociate, ionize or become bioavailable when placed into the body?

Frankly reduced metals may be very slow to oxidize or to become ionized. Gold, titanium and platinum, placed in the oral cavity, do not rapidly dissociate to an ionized form. However, silver, copper, palladium and indium may more readily oxidize, separate from a crown or bridge structure, and become attachable (bioavailable) to various organic compounds found in the tissues. Once attached or bound, these metals may take on qualities which can participate in a number of pathologies. They may become toxic in some senarios.

Oxidized metals can also be induced to separate from restorative materials under certain circumstances. They may have been placed into the restorative for purposes of pigmenting (cadmium chloride, cobalt chloride, iron oxide), or they may have been placed to facilitate fusing (silver, tin, zinc) or to give various qualities of luster, lucence and finish to things like ceramics, porcelains or composites. These forms of the metals can be as dangerous as their reduced forms can be. Arsenic, mercury and lead, whether introduced to the tissues as reduced metals or as oxidized salts, are going to be poisonous. Others may have little or no detectable effect on the patient.