Metals are much more allergenic than we typically give them credit for. It is more possible than ever to perform good dentistry without the use of any metals at all, but sometimes we still need them. Some metals, most notoriously nickel, will create contact dermatitis, or a skin rash, upon exposure, and these are easily discovered by history and by serum testing. Other metals, most notoriously titanium, will never make a skin rash, but can lead to other manifestations of type IV delayed hypersensitivity, a much more insidious cause of malaise and other vague varied symptoms.
Aside from their power to provoke immune reactivity, metals are also electrically active. Oral galvanism has been talked about for well over 100 years, but dentists generally ignore it and its implications.
Here are some representative voltage numbers (standard hydrogen electrode) for typical dental metals:
This means that gold and titanium grouped together in an electrolyte like saliva have the potential to create a battery of over three volts. Considering that the nervous system works on membrane potentials of 0.140 volts, electricity from dental metals that is conducted randomly or unpredictably through anatomical structures and spaces can overwhelm normal neuronal control. Often the manifestation is localized pain, or inappropriately elevated muscle tone, – as in jaw tension, TMJ, temporal headache, skin pallor due to low level vasoconstriction, etc.
The old standard in the gold days would have been to make all restorations in a person’s mouth, including removable frameworks, from the same high noble alloy, and not to mix metals at all. Now with advances in dentistry we can choose very good, non-metallic restorations including: flexible nylon-base partial dentures, all-ceramic crowns and bridges, even ceramic implants.