Thoroughly inspected

        At Ortho-Cycle, each reusable attachment is checked five times, at different angles in several stages, quite a difference from the "statistical inspection" performed by manufacturer. Our inspection is directed not only to shape, but also to corrosion telltale signs. Clinicians take a look at their brackets only when these are new. Even dramatic alterations suffered by some attachments during treatment are seldom observed. Each batch of brackets has its own history, where departures from composition, mechanical and thermal treatment can have a major impact. During the years, at Ortho-Cycle Co. we have amassed a large collection of corroded attachments as received from clinicians.Their corrosion susceptibility has been traced not to wear, but to failures in processing or materials. A useful do-it-yourself test has been described by C.G. Matasa: Orthodontic attachment corrosion susceptibilities, J. Clin. Orthod. Jan. 1995; 29(1): 16-23

Attachments exhibiting parts susceptible to corrosion

Observe hole and crevice in the bracket...

...the attack on the steel and on the brazing alloy

Test-driven

        As odd as it may seem, our average reusable attachments are better than the brand-new ones. First, our brackets are better inspected. Second, they are very unlikely to exhibit what is known as "early component failure," having been "fire tested," i.e., having withstood the whole orthodontic treatment without any noticeable change. Practitioners who had their brackets detaching from bases or hooks straightened can relate easily to this. Interestingly, a similar phenomenon has been observed with another single use only commonly reused medical device, the pacemaker, as shown by the Canadian Hospital Association.

          A case in point is that of the ceramic brackets shown below. During activation or debonding, these break along the existing stress concentration points. In addition, the bottom of the slot of a used bracket is smoother than that of a new one (Matasa CG, Tench R, Poster at the 1997 AAO annual convention in Philadelphia). Due to its slight, but long exposure to mastication, steel brackets become harder ( i. e. stronger) due to the additional cold work to which these are subjected.

 

Almost invisible flaws or pores can lead to the breakage of a ceramic bracket

Less breakable

           Ceramic attachments are made of synthetic alumina and are synthetic gems such as leuco sapphire. The value of any gem is given, among others, by the amount and size of its flaws, which are common in the manufacture of ceramic brackets (American Orthodontics claims to detect flaws 1/1000 of an inch in their 20/20^R ceramics). Most often, however, polycrystalline sapphire is too opaque to allow this detection, and flaws constitute points of stress concentration where the brackets break during wear (torque, chewing) or removal. The brackets having such hidden flaws often break along these faults during the normal stresses applied during wear or debonding. The ceramic brackets that have withstood the whole treatment obviously are less likely to break, as the faulty ones were already eliminated.

Exhibiting less friction

_______A slot that has been subjected to the continuous sliding of several wires for years will exhibit less roughness than a brand-new one. As demonstrated with the help of atomic force microscopy, used brackets have a smoother slot bottom. Such roughness reduction amounts to the removal of a multitude of peaks a few microns high without actually enlarging the slot. What may enlarge the slot, however, is electropolishing, a step common in processing. If it occurs at the slot entrances, it is beneficial, facilitating the arch wire insertion and minimizing the stress. This enlargement practically cannot happen at the bottom of the slot, where it really counts. Indeed, the electrical current removing the metal is directed almost exclusively to the protruding parts (tie-wings, hooks) and cannot alter the middle of the slot channel unless the whole attachment becomes obviously unacceptable.

Harder

             Metal properties are improved through cold work, which generates smaller and more compact grains and increases hardness, tensile strength, toughness, and corrosion resistance. As a result, the relatively low forces exerted during chewing and exposure to hard objects can cause stainless steel attachments to improve their strength unless they break or deform. Thus, used brackets exhibit an increased hardness and a better corrosion resistance, a fact that can be explained only by the additional cold work to which they have been subjected.

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