ABSTRACT
___.National and international standards require that medical devices should not be reused if their physical integrity and function are compromised in the process. In an effort to comply with the FDA and CE demands and with the ISO standards, we have investigated the impact of adhesive charring followed by electro-polishing. An alternative method, adhesive dissolution followed by high-energy centrifugal tumbling, was found to maintain the integrity of the attachments. The study was performed using metallographic methods as well as atomic force (AFM) and scanning electron microscopy (SEM).
INTRODUCTION
Why electro-polishing? Called also “reverse plating”, it is the easiest way to impart shine to complex metal parts. In contrast to electroplating, where the metal ions are deposited from the solution onto the work piece, the latter removes the metal by transforming it into ions in an acid bath. The work piece is connected to the positive (or anodic) terminal of a direct current source (battery) while the negative (cathode) terminal is connected to a suitable conductor, forming an electrical circuit. The quantity of metal removed from the work piece is proportional to the amount and duration of the applied current. The reaction occurs mainly at the high current density areas, leading to a reduction of their surface profile with a simultaneous smoothing and brightening. Imperfections such as stains, heat discoloration, weld marks and scratches are eliminated or minimized. While the range of metal removal is normally from 0.00005 inch to 0.002 inch, the application of the process to small and complex shaped parts is particularly difficult. Indeed, even professional electro-polishing shops employ, at best, a minimum number of controls, or no controls at all, resulting in inconsistent and unpredictable quality¹.
Undesirable: heat and metal removal. Both processes are part of current orthodontic reconditioning, although few recyclers would admit it. The firsts to report the effect of charring brackets were Buchman² and Chapman³. A few years later, we showed adverse effects also with electro-polishing⁴. Since then, their consequences have been discussed again and again in over thirty article^2-35. Despite manufacturers’ efforts materialized in technical assistance and grants, none of these has reached the simple conclusion: orthodontic recycling leads to clinically significant alterations.
___.This conclusion would have been disregarding the experience of orthodontists from all over the world who are using since decades recycled attachments. In addition, no related cases of malpractice or injuries have ever been reported. According to American Assoc. of Orthodontists’ (AAO) counsel Sally Bowers²⁷, even if a bracket could come detached and the patient could swallow it; this will not result in an injury to the patient. AAO’s president went even farther claiming that recycled brackets are “safe and effective” ²⁸.
Recycling at the crossroads.
___.While its favorable economic and environmental advantages are obvious, medical recycling is now under scrutiny. According to the FDA³⁶, (1) a reusable device should be cleaned and sterilized; (2) the physical characteristics and quality of the device should not be adversely affected; and (3) the device should remain safe and effective for its intended use. The Centers for Disease Control (CDC)³⁷ require that devices should not be reprocessed or reused if their physical integrity and function are compromised in the cleaning and sterilization or disinfection process, and if the overall safety and effectiveness are affected.
___.The Ministry of Health of Great Britain and Northern Ireland³⁸ used to require that the material properties should not change, and the maximum number of reconditioning cycles should be precisely determined. After July 1998, these requirements have been superseded by the regulations of the European Union Council Directives. According to the latter, all products, used or not, should bear the “CE Mark”. This CE (Conformite Europeene) certification incorporates requirements specific to the medical device industry³⁹: without it, the access of the medical devices to the European Union market is prohibited. It is foreseen that the combination of the requirements of ISO 9001 and CE’s EN 46001 will be soon recognized throughout the world.
___.ISO’s quality norms apply both to management and products, serving not only as a screen for the last ones, but also as proof that these perform properly. Complying with ISO regulations is not only advantageous it becomes compulsory. For example, Canada requires that medical device manufacturers marketing there their products must have a quality system ISO certified by January 2003. In the US, the revised Quality System Regulation⁴⁰ is based upon ISO quality system standards.
___.What both ISO and CE demand as Essential Requirements (Annex I of the Directives) is that devices (used or not, NB) must meet all claimed performance criteria, and must continue to function as intended, without compromising safety or health when subjected to normal conditions of use for a defined and traceable number of cycles.
___.If adhesive charring and metal removal are used to recycle orthodontic attachments, the above requirements are not met. Indeed, heating stainless steel between 350 and 800^oC (650-1600^oF, temperature range necessary for charring the adhesive), leads to sensitization (a migration of chromium carbide at the boundaries of the grains) that translates in brittleness. Even worse, it leads to intergranular corrosion, a process where even weak acids can attack the steel⁴¹. The metal removed from electro-polishing alters brackets, tubes, wires and bands alike. In brackets, it opens the slots, and thins the power arms and the wings. It levels the base’s undercuts and the mesh (which may lead to a decrease of up to 65% the initial bond strength)⁸. Due to the strong acid baths used, the brazing that keeps together multipart attachments is also weakened, leading to detachments, as sketched in Fig. 1. Electro-polishing removes not only oxides, but also metal: if less noble alloys are used to braze stainless steel, these are subjected to preferential attack/ galvanism.
Prior attempts to avoid problems. Being well aware of the consequences of heat, we initiated, as early as in the mid-1970’s, the dissolution of the adhesive instead of charring⁴² while calling attention to the problems related to the brackets’ heat treatment and metal removal as early as 1980².
___.To reduce the electro-polishing’s impact on orthodontic attachments, we showed that these should not be exposed except for a very short time⁴², and this only if the surfaces destined for bonding are protected. Ortho-Cycle’s method at the time was adhesive dissolution followed by a flash electro-polishing. This has allowed bracket reuse by far more than the one¹⁰ to two times⁷ recommended. Using adhesive dissolution instead of charring, Ortho-Cycle didn’t have to deal with the heavy layer of dark oxides that is formed during charring.
___.While one or two cycles of charring/electro-polishing may not have a significant impact, the attachments thus processed cannot meet the FDA, CDC, ISO and CE’ criteria and regulations that require that these remain safe and maintain their integrity.
___.In what follows it is shown the results obtained in vitro by subjecting brackets to a third cycle charring/electro-polishing instead of the maximum two recommended⁷. The study focuses only on shape alteration and integrity: the structural modifications (sensitization) and the corrosion susceptibility (intergranular corrosion) were described by Buchman² and others.
MATERIALS AND METHODS
___.New brackets made by Unitek/3M (Twin Torque, mesh and Dynalock bases), Ormco/Sybron (Diamond) were subjected to three cycles of adhesive smearing (Phase II, Reliance)-charring-electro-polishing per Esmadent’s instructions (Esmadent has introduced the charring method in 1976 selling the “Big Jane” oven, only to quit later). In parallel, the same brackets (marked with carbide tip) were subjected to adhesive dissolution and centrifugal tumbling and examined before and after processing. The attachments were photographed in different positions with the help of a digital camera (Nikon 950), a metallographic microscope (Comparative stereoscopic MSC 200, IOR, Bucharest) and a Scanning Electron Microscope (SEM, Philips XL-30-ESEM TMP) operated by the Biomaterials Center of the Polytechnic University, Bucharest, Romania.
___.To demonstrate the increase in friction that could be produced by the trapping of elastomers in a slot widened by electro-polishing, we used also Atomic Force Microscopy (AFM). The latter provides, in contrast with SEM, a better topographic contrast and a direct height measurement, simultaneously allowing the evaluation of the topical friction. The tests were made at Nanotech-21 Laboratories, Bucharest, using a Multimode Atomic Force Microscope (Digital Instruments, Santa. Barbara, CA).
RESULTS
Acid attack. The long exposure to strong acids affected the brazing uniting the pad to the bracket. While gold-based brazing is corrosion resistant, lesser alloys dissolve faster than the stainless steel, as sketched in Fig. 1, leading to a weakening of the bond. This happens with copper- and silver-brazed items, a phenomenon well known in the industry^12-13, (The attack is most obvious on the copper-alloy brazed TP’s Begg brackets: even after two cycles, these brackets easily detach from their mesh bases).
___.As some bases are made to be highly liquid retentive, it often happens that these retain acids from the electro-polishing bath even after a summary rinsing. As a result, the acid interferes with the adhesive’s polymerization, leading to weaker bonds. In addition, the Cr⁺⁺⁺, Ni⁺⁺ ions that accumulate in the electro-polishing bath need special attention, as these heavy metals pollute the underground water network.
Slot opening. Being recessed, the slot’s bottom is protected from metal removal during the electro-polishing process. In contrast, the slot’s insertion area is exposed to metal removal. Purposely enlarged by some manufacturers (chamfered slots) to ease the insertion of the wire, this opening can drag the elastomeric module into it, Fig. 2. Parts of the latter are torn apart and act like a wedge between the arch wire and the bracket, as sketched in Fig. 3. The phenomenon not only increases friction, but also renders difficult attempts to establish a correlation with bracket design¹⁴. Sketched in Fig. 3, insert, a tearing of the elastomer occurs even when a piece of the latter is rubbed on a metal surface. This is evidenced in Fig. 4 and 5, where traces of elastomer left on metal surfaces have been examined using AFM. The lower images show the metal after rubbing, the white areas are adherent elastomer particles. These can increase the topical friction from 3x to almost 7x, depending on the metallic substrate.

Undercut/mesh leveling.
___.In Fig.6-12 are shown microphotographs of several pads (two with mesh and one with undercuts) around a fictitious bracket exhibiting both types of bases. Around it are evidenced the areas where the maximum amount of metal is removed during electro-polishing, with lines indicating from where the image has been examined with the scanning electronic microscope.
___.As expected, the protuberances, corners and exposed surfaces are heavily attacked, while the more hidden parts are less affected. While it was since long rteen years ago is less successful, as shown in Fig.13 and 14². The rims of the micro-cups are not only reduced in size, but their retention of the adhesive is compromised.
___.In contrast, the bases of the brackets subjected to adhesive dissolution and centrifugal tumbling did not show under microscope any observable change, Fig. 15 and 16.
DISCUSSION
___.Orthodontic attachments are industrial devices made in large series or batches. Both human labor or automatic machines have limitations and can lead to errors in fabrication, and it is reasonable to claim that no two attachments, randomly picked up from the same series, are for sure identical. As a result, thorough inspection becomes necessary. How effective sta-tistical inspection is (ten to a hundred are picked up from a thousand) has been demonstrated by Ortho-Cycle in many articles, the last being published in 2000³²: the article exposed incredible faults, ranging from brackets without slots to bicuspids with positive torque. This is not new: even in a thesis supported by a manufacturer’s grant to demonstrate the harmful effect of recycling²³, significant deviations were found between the slot widths of the brackets taken as standard, a fact that justified the title of the article, which questioned if new brackets could really be taken as standards³².
___.Unlike previous studies that picked up a few new brackets and compared them with a small group of recycled ones, in effect disregarding the differences mentioned, this study examines the same brackets before and after recycling. Negligible after three cycle based upon the dissolution of the adhesive and flash electro-polishing, the alterations become significant after three cycles of adhesive charring and intensive electro-polishing. Aside from the thinning of the power arms and various wings (ligation, Lewis and especially Lang), the edges of the bases become sharp and contribute little to bond strength.
___.Another undesirable effect of electro-polishing is the alteration of the slot. While not affecting significantly its recessed bottom, electro-polishing opens the latter’s entrance, generating high friction when elastomeric ligatures are used. This phenomenon is due to the trapping of the elastomeric module between the slot and the arch wire. The particles that are torn from the substrates during the movement against each other, are known to be the source of friction. Even the simple rubbing of an elastomeric module on stainless steel and NiTi wires leaves behind adherent particles of elastomeric module, as shown in Fig. 4 and 5. This trapping mentioned was evidenced in our attempts to relate friction to the shape of the bracket: instead of getting simple curves illustrating a simple dependence, the random jumps caused by the particles led to graphs showing whole areas⁴².
___.Widely used by jewelers, who are justifiably concerned with metal loss, high-energy centrifugal tumbling does not alter the bases of the brackets tested. Used by all the new brackets manufacturers, the method is also the ideal answer to the new demands of the national and international organizations that do not want to kill recycling, the way of the future, while continuing to protect the patient.
CONCLUSIONS
___.The use of electro-polishing, especially if as intensive as needed to cover heat’s darkening action, changes the attachments physical characteristics. While significantly less obvious when the adhesive is dissolved and the attachment is exposed for a short time, the effects of electro-polishing can accumulate after several cycles and alter the device. The reasons why this is not common is that in clinical practice, after a few cycles the attachment is either damaged during debonding, or retired altogether in favor of another, usually improved type or brand.
___.Once electro-polished, an attachment can become bright and shiny, but its alteration is bound to occur.
In contrast, centrifugal tumbling, used for almost a year at Ortho-Cycle Co. does not alter the mesh or the undercuts of bases, even after three cycles of adhesive dissolution and centrifugal tumbling,. While the attachments are somewhat less shiny (satin finish), none of our customers have observed the difference. Even so, the advantage of using intact attachments should fully compensate the worry about how many times these were previously reused.
___.Interestingly, while some orthodontists have lived for years with the alterations generated by poor recycling despite the adverse propaganda sustained by some manufacturers in all media, the decisive step was been made by the governmental and multinational organizations. Instead of judging the orthodontic attachments alone, these were taken in group with other, more potentially hazardous devices and required to comply with rules such as “the physical characteristics and quality of the device should not be adversely affected”³⁶, and “to meet all claimed performance criteria, and to continue to function as intended”³⁹. Orthodontic recycling, an environmentally responsible and financially justified activity, can and should comply, for the benefit of both the patient and the clinician.
References.
1. www.electrokleen.com
2. Buchman DJL, Effects of recycling on metallic direct-bond orthodontic brackets, Am J Orthod. Dentofac Orthop.1980; 77(6): 654-668
3. Chapman, P. L. Recycling the orthodontic bonded bracket, Master’s Thesis, Indiana University, 1979
4. Matasa CG, Not all appliances are created equal. Am. J. Orthod. Dentofac Orthop 1988; 94:168-169
5. Unkel T, Recycling orthodontic products. J. Clin. Orthod. 1987; 21: 871-2
6. Matasa C, Pros and cons of the reuse of direct bonding appliances, Am. J. Orthod. Dentofac Orthop 1989; 96: 72-76
7. Hixson ME, Brantley WA, Pincsak JJ, Conover JP, Canges in slot tolerance following the recycling of direct-bond orthodontic appliances, Am J Orthod. Dentofac Orthop. 1982: 81: 447-454
8. Mascia VE, Chen SR, Shearing strenghts of recycled direct-bonding brackets. Am J Orthod. Dentofac Orthop. 1982; 82: 211-216
9. Maijer R, Smith DC, Corrosion of orthodontic brackets, Am J Orthod. Dentofac Orthop 1982: 81: 43-48.
10. Wheeler JJ, Ackerman RJ Jr. Bond strength of thermally recycled metal brackets. Am J Orthod. Dentofac Orthop. 1983; 83(3): 181-6
11. Park HY, Shearer TR, In vitro release of nickel and chromium from simulated orthodontic appliances. Am J Orthod. Dentofac Orthop 1983; 84: 84: 156-9
12. Wright, WL, Powers In vitro tensile bond strength of reconditioned brackets. Am J Orthod. Dentofac Orthop. 1985; 87: 247-252
13. Smith NR, A comparison of orthodontic brackets, before and after recycling: an in vitro study. MSc thesis, University of London, 1986
14. Scarola BW, Nicolai RJ, Pad treatments to strenghten bonds to reconditioned brackets, J. Dent. Res 1989: 68, Abstract 63: 134-41
15. McClea CPJ, Wallbridge DJ. Comparison of tensile and shear stength of new and recycled orthodontic metal brackets. NZ Dent. J. 1986: 92: 11-4
16. Regan D, Van Noort R, O’keefe C, The effects of recycling on the tensile bond strength of new and clinically used steinless steel orthodontic brackets: an in vitro study. Brit. J. Orthod. 1990: 17: 137-145
17. Postletwhite KM, Recycling bands and brackets. Brit. J. Orthod. 1992: 19: 157-164
18. Buchwald A, A three-cycle in vivo evaluation of reconditioned direct-bonding brackets. Am J Orthod. Dentofac Orthop 1992: 102: 285-7
19. DiPasquale TJ, Reconditioning and reuse of orthodontic devices. Am. J. Orthod. Dentofac. Orthop 1992: 102: 285-7
20. Matasa CG, Defend yourself against faulty appliances II. Alterations produced by wear debonding and poor reconditioning. J. Gen. Orthopd. 1992; 3: 13-20
21. Machen DE Orthodontic bracket recycling. Am J Orthod. Dentofac Orthop 1993: 104: 618-9
22. Cua G, Marshall R, Kudlick E, Eichmiller F, A comparison of bond strength of new and used brackets, Thesis Howard University Colege of Dentistry and National Inst. for Stanf-dards and Technoology, Gaithersbur MD, 1995
23. Fisher TA, An in vtro comparative study of new and rercycled brackets, Master thesis. Univ. of Iowa, 1995
24.. Coley-Smith A, Rock WP, Bracket recycling -who does what? British J. Orthod. 1997; 24: 172-4
25. Oliver RG, Greenslade M, Harkness M, Patient and parent opinion of the reuse of recycled orthodontic brackets: an international comparison. Brit. J. Orthod. 1997; 24: 329-332
26. Jones SP, Tan CCH, Davies EH, The effects of reconditioning on the slot dimensions and ststic frictional resistance of stainless steel brackets, Europ. J. Orthod. 2002; 24: 183-190.
27. Bowers SA Legislation update, Recycled brackets, Am J Orthod. Dentofac Orthop 1993; 103: 194-195
28. Poulton D, AAO President, in Am. Assoc. Orthodontists Annual Report 1997-98
29. Coley-Smith A, Rock WP, Bracket recycling -who does what? British J. Orthod. 1997; 24: 172-4
30. Oliver RG, Greenslade M, Harkness M, Patient and parent opinion of the reuse of recycled orthodontic brackets: an international comparison. Brit. J. Orthod. 1997; 24: 329-332
31. Jones SP, Tan CCH, Davies EH, The effects of reconditioning on the slot dimensions and ststic frictional resistance of stainless steel brackets, Europ. J. Orthod. 2002; 24: 183-190. 34: 459-476
32. Matasa CG, Recycled brackets: should the new ones be considered a standard? Rev. Orthop. Dento Faciale 2000 34: 459-476
33. Papadopoulos M, Eliades T, Morfaki O, Athanasiou AE. Recycling of orthodontic brackets: effects on physical properties and characteristics-ethical and legal aspects. Rev Orthop Dento Faciale 2000; 34:257-76
34. Eliades T, Zinelis S, Eliades G, Athanasiou AE, Nickel content of as-received, retrieved and recycle stainless steel brackets Am J Orthod. Dentofac Orthop, in press
35. Eliades T, Zinelis S, Eliades G, Athanasiou AE, Characterization of as -received, retrieved and recycle stainless steel brackets, J. Orofac. Orthop., in press .
36. FDA’s Compliance Policy Guide, chapter 24 & 21 CFR 820, Oct. 7, 1996
37. United States, Department of Health and Human Services 1985
38. Department of Health Medical Devices Agency. The reuse of medical devices supplied for single use only (Device Bulletin MDA 9501) London, Medical Devices Agency, Department of Health, 1995
39. Council Directive 93/42 EEC of 1993 concerning medical devices.
40. Medical Devices Directive 93/42/EEC: ANNEX I; EN 46001
41.Franks R, Corrosion susceptibility of stainless steel. In: Corrosion handbook, Uhlig HH, ed., Wiley, NY 1948
42. Zachrisson B, Bonding in orthodontics, In: Orthodontics, TM Graber & B.F. Swain, editors, Mosby, St. Louis, 1985: 513
42. Matasa CG, Weighing... friction. The Orthodontic Materials Insider 2001;13(2): 1-8; Poster at the 101th Annual Session of the Am. Assoc. of Orthodontists, Toronto, May 2001

HOW ARE MANUFACTURERS FINISHING NEW ATTACHMENTS?

___.No manufacturer will ever process a small number of attachments at a time: higher productivity can be sustained only by expensive and sophisticated means beyond the reach of a modest recycler. Otherwise, however, once the adhesive has been removed, the task of the recycler is by far easier than that of a manufacturer. While the first has to remove only the layer of oxides that have accumulated, the latter has to remove metal to cover the mark of the sprue (casting) or the general roughness generated from powder metallurgy (injection molding). In Fig. 1 are shown three stages in the last procedure: the “green” (before heating and volatiles removal), the rough and the finished bracket.
___.Before the finishing stage, the recycler gets the attachments covered with a layer of adherent oxides, thin in the case that he has been able to dissolve the adhesive, and thick and dark in case that he has charred it, Fig. 2.
___.To remove the thick layer of oxides formed in the last case necessitates an intense electro-polishing or a lot of abrading. Indeed, the chromium oxide that migrates at the surface of stainless steels (as the films of oxides formed at the surface of aluminum or titanium) is highly adherent1. In contrast to the charring method, in the case of adhesive dissolution, a simple burnishing, the manufacturers way, leads to an acceptable finish. Somewhat less shiny (“satin” instead of “bright”), this finish doesn’t come anymore at the expense of integrity.
___.The equipment needed is more complex and expensive, but once the initial costs have been recouped, the shorter processing time and the labor savings allow a reduction in the price per processed unit. As a result, mass finishing has become one of the most useful tools in jewelry manufacturing, having also the advantage of avoiding loss of precious metal.
___.A standard installation comprises several centrifugal planetary barrels mounted in a Ferris-wheel turret, Fig. 3. While the latter spins, the evenly spaced barrels rotate in the opposite direction of the turret, at its periphery. As the turret is rotated in one direction, the barrels rotate in the opposite direction. The rotation of the turret and barrels causes the mass (parts, media, compound and water) to slide to the farthest wall of the barrel, the centrifugal force adding weight to lightweight medias. The machine is of heavy construction to withstand the high “g” forces generated. The barrels are molded of polyurethane plastic and are inserted into metal supporting cradles equipped with quick acting locks.
___.Such high-energy barrel machines operate basically the same as tumbling barrels with one major difference - centrifugal energy is added to the process to dramatically reduce the processing time. The quality of surface finish attained during this processing is evaluated by measurement of the surface roughness. There is two ways to reduce surface roughness: by cutting, using an abrasive medium to remove metal from the surface, or by burnishing with a nonabrasive media. The last procedure is sufficient to brighten the stainless steel attachments after adhesive dissolution: their surface is smeared and leveled (and usually also work-hardened)².
___.Burnishing renders surfaces bright by rolling over nonabrasive media such as steel or porcelain, where it removes surface imperfections without altering details. This method physically peens the surface in order to increase light reflectivity that, in turn, makes the parts appear polished while inducing hardening through compressive stress. The latter reduces residual tensile strength, which can be harmful to fatigue resistance. The parts can be finished to a roughness measuring less than 1 µ in.
___.The machine can be used also for polishing, when the media used has usually a natural base, such as wood, shell or corncob. Polishing compounds, similar to those used in hand polishing bars, are bound to the natural polishing media by means of a wax or an oil-based agent.
___.The machine used by Ortho-Cycle shown in Fig. 4, presents the barrels mounted on the Ferris wheel and the sophisticated control panel that allows the variation of the speed and of the exposure time.
___.In almost a year since the machine has been used, no complaints or observations regardig differences in the aspect of the attachments have been recorded. Used along adhesive dissolution, high-energy centrifugal tumbling leads to unalterd attachments that comply with the increasingly stringent requirements of the national and international organizations monitoring medical devices.
___.From Ortho-Cycle’s point of view, it has helped the company to meet the standards imposed by the FDA, CDC, ISO 9002 and led to its precious CE certification, unique among recyclers.
References
1. Moorhead AJ, Whalen SJ, Brazing of stainless steels, in: Metals Handbook vol.6, 9^th ed., ASM, Materials Park, OH, 1983
2. http://shorinternational.com

GOLD AND TITANIUM, AN UNEXPECTED BONUS!

___.While avoiding electro-polishing altogether, we knew that the use of the high-energy centrifugal machine would allow us to reduce the price per attachment processed. What we didn’t know was that with its help we would be able also to process both titanium and gold-plated attachments, until recently an elusive goal.
___.After wear and adhesive removal, gold-plated brackets lose their shine, and electro-polishing transforms itself in galvanic corrosion, attacking only the less noble metal, in this case the stainless steel. Titanium brackets are both greyish and rough, the latter property deriving from their manufacture (powder metallurgy). While titanium’s electro-polishing is feasible, the brackets’ bases would suffer. Indeed, these are not based upon mesh, but on undercuts that can be easily shaved, as shown in the first article in this newsletter, Fig. 13. As their reprocessing requires an additional treatment, we recondition either gold-plated or titanium brackets for only 50 cents each if you’ll use the coupon below.