I have recently come acrossan articledealing in depth of the corrosion and the corrosive by products of orthodontic appliances. I mean to give an extract tailored a little bit towards patients rather than scientists, highlighting the bits that are important in the everyday life of someone who wears an orthodontic appliance.
Orthodontic braces are usually made of titanium alloys. The titanium is usually alloyed with nickel, chromium and cobalt. The orthodontic wire is almost always a stainless steel, possibly alloyed with silver and titanium. I have already written an article dealing in depth with the materials used in the making of orthodontics, and it can be viewed here. These alloys are made with the understanding that braces are in the human mouth, a place that is made to corrode and break down materials into digestible portions, and thus these appliances are relatively corrosion free.
But some amount of corrosion can be expected, and the appliance will leech certain ions and materials into the mouth, which may result in discoloration of the periodontium, and can be coupled with allergic reactions. Very occasionally the entire appliance may become jeopardized because of corrosion, the wire or some brackets may become too corroded to be able to fulfill their functions, and the device, bracket or just the wire may need to be replaced. Let us now take a look at the different kinds of corrosion, shall we?
The main differences between the different kinds of corrosion is where they occur and what causes them.
Microbial corrosion: Certain kinds of microbes can corrode manganese and iron, essentially eating it out of the braces. This will result in small craters or indentations that may be a risk factor, and can result in failure of the device. This tends to happen to the wire more frequently, though microbes have also been known to be responsible for the decay of orthodontic adhesives as well, which can also cause bracket failure.
Uniform corrosion: When the metal gets depleted systematically and roughly in the same amounts all over the brace, we call it uniform corrosion. This what happens most frequently, and it happens to all devices to a certain extent. The question whether the corrosion will be bad enough for the device to fail before it has reached its goal.
Intergranular Corrosion: Sometimes the corrosion can start right at the very grains of the alloys used, separating the alloys, and causing the device to fall apart, or even worse, to rust. This is dangerous because a lot of metals like nickel and cobalt can get released in small amounts into the mouth with this type of corrosion.
Stress Corrosion: Through chomping, and being situated in an inhospitable environment, metals can get worn out. This is known as stress corrosion.
For more information on the many types of corrosion that can occur to your brackets and wires, see the article posted above!