B-+braces+and+corrosion


 * Q and A Wednesdays (Presentation Date: October 6th, 2010)- Jennifer Trac**

Question: Why don't orthodontic braces corrode?

> > Sources > Page, R., & Johnson, G.H. (2008) Dentistry .  AccessScience. ©McGraw-Hill Companies. Retrieved October 5, 2010, from  __[]__ . >  >   Coates, G., & Jenkinson, D. (2007). What is Stainless Steel?. The Nickel Institute. Retrieved October 5, 2010, from  __[]__  > >   Corrosion. (n.d.)  // Kapi`olani Community College Library Home //  . Retrieved October 5, 2010, from  __[]__  > >   Helmenstine, A.M. (n.d.). Why is Stainless Steel Stainless?.Chemistry - Periodic Table, Chemistry Projects, and Chemistry Homework Help. Retrieved October 5, 2010, from  __[]__ . > >   Silverstein, A., & Silverstein, V. (2010). Orthodontics. The New Book of Knowledge®. Retrieved October 5, 2010, from Grolier Online <  __[]__  >. >
 * <span style="font-family: Arial,Helvetica,sans-serif;">when your teeth are out of line (malocclusion) they tend to produce problems over an extended period of time (problems in gums, causing teeth to become loose)
 * <span style="font-family: Arial,Helvetica,sans-serif;">braces attached which move the teeth gradually toward the positions desired.
 * <span style="font-family: Arial,Helvetica,sans-serif;">Corrosion is a type of electrochemical oxidation of metals in reaction with an oxidizing agent (e.g. oxygen)
 * <span style="font-family: Arial,Helvetica,sans-serif;">oxidation: loses electrons and becoming more positive in charge
 * <span style="font-family: Arial,Helvetica,sans-serif;">problem with iron and many other metals is that the oxide formed by oxidation does not adhere to the surface of the metal and instead flakes off, which leads to “pitting”
 * <span style="font-family: Arial,Helvetica,sans-serif;">pitting: creation of small holes in the metal
 * <span style="font-family: Arial,Helvetica,sans-serif;">extensive pitting causes structural weakness and disintegration of the metal
 * <span style="font-family: Arial,Helvetica,sans-serif;">while there are now products like Invisalign, most orthodontic braces are made out of stainless steel alloys
 * <span style="font-family: Arial,Helvetica,sans-serif;">English scientist Harry Brearly accidentally discovered that adding chromium to low carbon steel gives it stain resistance
 * <span style="font-family: Arial,Helvetica,sans-serif;">modern stainless steel may contain elements such as iron, carbon, chromium, nickel, and titanium
 * <span style="font-family: Arial,Helvetica,sans-serif;">it is particularly nickel and chromium that enhance the corrosion resistance of stainless steel
 * <span style="font-family: Arial,Helvetica,sans-serif;">addition of minimum 12% chromium to steel makes it resist rust, or stain “less” than other types of steel
 * <span style="font-family: Arial,Helvetica,sans-serif;">chromium combines with oxygen to form a thin, invisble layer of chrome-containing oxide (passive film)
 * <span style="font-family: Arial,Helvetica,sans-serif;">if the metal is cut or scratched, more oxide will quickly form and recover the exposed surface → protects it from corrosion
 * <span style="font-family: Arial,Helvetica,sans-serif;">stainless steels have poor corrosion resistance in low-oxygen environments because it requires oxygen to self-repair
 * <span style="font-family: Arial,Helvetica,sans-serif;">iron rusts quickly because the atomic iron is much smaller than its oxide, so it forms a loose rather than tightly packed layer
 * <span style="font-family: Arial,Helvetica,sans-serif;">for orthodontic braces, the stainless steel contains 18-20% chromium and 8-10% nickel, and has a low carbon content, typically less than 0.03%
 * <span style="font-family: Arial,Helvetica,sans-serif;">stainless steel can be recycled to produce new stainless steel without any loss of quality