Unaltered properties

Unfortunately, not only the manufacturing per se can be shoddy, but the alloys used also can be of poor quality. Thus, an addition of sulfur to stainless steels makes them easy to cut, saving time, energy and cutting blades. As a result, the corrosion resistance drops significantly.         Brackets are often subjected to stainless steel sensitization, a phenomenon occuring during brazing or other steps requiring heat. According to the Corrosion Handbook (Franks R, H. H. Uhlig ed., J. Wiley & Sons, NY 1948), "It is well known that austenitic steels are metallurgically unstable when heated in the temperature range of 350-800oC (650-1500oF). After heating in this temperature range, they become subject to severe attack at the grain boundaries by even mild corrosive media. This attack is referred to as intergranular corrosion, and it is so severe that the steel literally disintegrates into separate grains, losing substantially all its properties."

          Another source of problems is the brazing alloy used to join the bracket to its pad. Often, alloys are either weak or improperly selected which translates into the detachment of the base from the bracket or the galvanic corrosion of either the steel or the brazing. While in the first case, in the electric cell (generated in the presence of saliva as electrolyte), gold brazing produces the steel dissolution. In the second case a nobler stainless steel leads to the dissolution of the brazing alloy. In addition, the most popular brackets today are gold-brazed with an alloy containing some 80% gold and 20% nickel. Interestingly, the gold brazing in recycled brackets is poorer in nickel due to an inner dealloying. Nickel, needed only initially to depress the melting point of the brazing alloy, is released in the mouth of the first wearer because of galvanic corrosion (due to a typical electric cell effect, where the electrolyte is saliva and where gold is more noble than nickel).In other words, such a recycled brackets is less prone to produce allergies and other ailments. This has been substantiated in two articles in Am. J. Orthodontics: The maximum release of nickel in new brackets reaches a maximum in the first week, after which it declines (Barret RD, Bishara SE, Quinn JK, Am J Orthod Dentofac Orthop 1993; 103: 8-14); The cumulative amounts of nickel and chromium released reaches a plateau after 6 days"  (Park HY, Shearer TL, In vitro release of nickel and chromium from simulated orthodontic appliances, Am J Orthod Dentofac Orthop 1983; 84: 156-9)  Over the years, we have disclosed such findings in several articles published in specialty journals, both in the United States and abroad - (see other references). Fortunately, a thorough inspection allows the selection of brackets that have previously withstood treatment without showing signs of corrosion.

        Subjecting brackets to heat covers them with a dark layer of oxide which has to be removed. Unfortunately, in doing so by electropolishing, abrasion etc. one removes also metal, changing the attachments characteristics, especially the base retention. The brackets processed at Ortho-Cycle are tumbled with the same non-corrosive media manufacturers uses, and only seldom flash-electropolished to remove the possible scratches which may dull their aspect.

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