C+-+orthodontic+braces

 =**By: Yaxin Yang, SCH4U-03, Presentation Date: Wednesday, September 29th, 2010** = 

FACT SHEET:

Why do metal orthodontic braces not corrode?

Ø Average patient has orthotic braces for 18 months, some people up to 3 years Ø Most metals, when submerged in an environment such as your mouth would rust, which is the most common form of corrosion Ø Corrosion is the process of oxidation, losing electrons so the atom becomes more positive in charge Ø Metals often corrode as a result of it being exposed to environments in which they are not chemically stable in, such as iron, which is the most common element in the earth Ø Iron rusts quickly because iron and its oxide are very different in size – the atomic iron is much smaller, so the oxide forms a layer near the surface that is very loose, and can flake away easily, and rust with the exposure to oxygen by transferring electrons to it through oxidation Ø Stainless steel, which is what most braces are made from, does not corrode as easily as normal metals Ø Alloy contains at least 12% chromium, which, as an element, is reactive, but with other metals, shows tremendous resistance to many environments Ø The chromium can be increased to around 27% for even greater environmental resistances, before the metal becomes structurally ineffective Ø Chromium in the steel combines with oxygen in the atmosphere to form a layer of chromium (III) oxide, called the passive film, which pack together near the surface of the metal to form a stable layer only a few atoms thick Ø This can happen because the chromium atoms and their oxides are similar in size, so they can pack tightly together at the surface of the metal Ø If this layer is somehow disturbed, perhaps by a cut, or scratch, it will quickly re-form, reacting with oxygen, to cover the exposed surface, protecting it from corrosion once again Ø Nickel is another metal added to Stainless steel that also helps it to resist rust, and also makes the metal non-magnetic Ø Since your braces need enough strength to actually help move your teeth, Carbon and iron are added to the Stainless steel to make it less weak and brittle Ø It is also more difficult for braces to rust inside of your mouth because the corrosion of most metals by oxygen is accelerated by low pH, and the pH in our mouths is slightly Alkaline, at around 7.2 Ø Stainless steel is not just used for braces, but finds itself as cutlery, surgical instruments, major appliances, jewellery, and watches

SOURCES

Helmenstine, A. M. (n.d.). Why is Stainless Steel Stainless?.Chemistry - Periodic Table, Chemistry Projects, and Chemistry Homework Help. Retrieved September 27, 2010, from .

 Roberge, P. R. (n.d.). Stainless steel corrosion. Corrosion science and engineering information hub. Retrieved September 27, 2010, from .

 Silverstein, A., & Silverstein, V. (2010). Orthodontics. The New Book of Knowledge®. Retrieved September 26, 2010, from Grolier Online .

Why Metals Corrode. (n.d.).KSC Corrosion Technology Laboratory Home. Retrieved September 27, 2010, from .

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