Dental alloys: cobalt-chromium, titanium and noble alloys chosen for the case, not the cost

Alloy selection is often made by the laboratory without clinical input, and in most cases it works. The cases where it does not have consequences appearing years later.

Prosthetic alloys fall into three families. Noble alloys contain gold, platinum or palladium in high proportions; predominantly base alloys are cobalt-chromium or nickel-chromium; titanium and its alloys form a category of their own.

Cobalt-chromium is today the most used material for frameworks. Its elastic modulus is high — roughly double that of noble alloys — allowing thinner connectors for equal rigidity.

That same rigidity is a limitation in combined prosthetics: a very rigid framework absorbs nothing and transfers the load fully to the abutments.

Nickel-chromium has similar properties at lower cost, but nickel is the most widespread contact allergen in the European population, with markedly higher prevalence in women. Many laboratories have abandoned it for this reason.

Titanium has the best documented biocompatibility and very low density, making prostheses appreciably lighter. Its limits are technical: it melts at high temperature, reacts with oxygen and requires casting under controlled atmosphere.

Ceramic veneering of titanium is the critical point. It requires low-fusing ceramic formulated for titanium, and bonding remains more delicate than with cobalt-chromium. This is why veneered titanium is less widespread than its biocompatibility would suggest.

Noble alloys retain the advantage of more predictable behaviour under ceramic firing and excellent workability. Metal cost has confined them to cases where biocompatibility is the priority, but their behaviour remains the reference.

Ion release is the biological question common to base alloys. Cobalt and chromium are released in minimal quantities in the oral environment, and the literature has not established systemic effects at normal exposure.

It becomes relevant in galvanic corrosion: two different alloys in contact or nearby, with saliva as electrolyte, generate a current and accelerate release. This is why different alloys are not mixed within the same arch without reason.

The production method has partly superseded the casting problem. Laser sintering builds the framework layer by layer from powder, with high density and no casting porosity.

Milling from a solid disc yields the most homogeneous material of all, because it starts from an industrially controlled blank, but produces considerable waste and is indicated chiefly for titanium.

In summary: cobalt-chromium for frameworks and extended structures needing rigidity, titanium where biocompatibility is paramount and the veneering limits are accepted, noble alloys where predictable behaviour justifies the cost. And never different alloys in contact within the same arch.