___.In this issue we are celebrating both a milestone and a big accomplishment: it is the 20^th birthday of the Orthodontic Materials Insider. Twenty years ago, in 1987, Phoenix without Ashes was launched, and in 1994 it was renamed The Orthodontic Materials Insider. The Insider is a quarterly publication fostering the orthodontic specialty, and dedicated specifically to orthodontic materials that are of interest to private practitioners and academicians.
___.This publication is the brainchild of Prof. Claude G. Matasa, a pioneer in the field of orthodontic materials. As we know, in the last 50 years more dental materials have come into question, such as mercury-based restorations, ceramic brackets, nickel-leaching attachments, and polymers/elastics. As we peruse the various issues of the Insider, we come to realize that Prof Matasa has long been on top of these issues. His unique training and background as an engineer have helped provide substantive bases for orthodontic materials research and understanding.
___.On these pages, Prof Matasa was the first to call attention to the flaws encountered in the manufacturing of mesh-based brackets. In his research, he used metallographic and micro-hardness analyses, disclosing phase structures and measuring the metal’s strength. He also developed a practical recycling process for orthodontic materials that has saved millions of dollars for practitioners and indirectly benefited patients.
___.In the 1980s, the recycling of metallic and ceramic orthodontic biomaterials was in its infancy, and the contribution of heavy metals to environmental pollution was practically ignored. Furthermore, the concept of reusing materials that had been worn by somebody else was repugnant. Ironically, it took the AIDS epidemic to force clinicians and the public alike to pay more attention to sterilization. Indeed, the attachments that survive the rigorous recycling process are less contaminated because for the recycler to remove the adhesive successfully, the carbon-to-carbon bonds in the polymer attached to the bracket must be broken. In the process all microorganisms are killed.
___.Another important subject that Prof Matasa has explored in the Insider is the impact resistance of ceramic brackets. Using a method borrowed from industry, he helped identify which brackets are fragile and which have the most impact-resisting shapes. Prof Matasa has also analyzed the frictional properties of ceramic brackets using atomic force microscopy.
___.In his newsletter he has demonstrated that, by using scanning electronic microscopy, one can observe a lack of affinity between “water-loving” surfaces (enamel and stainless steel) and “water-hating” resin-based adhesives and sealants. In order to improve bonding, Prof Matasa was the first to document the effects of silanation and etching on metal-based attachments. He has also evaluated leaching of attachments and the mechanism of corrosion. The cytotoxicity of current polyurethane elastomers was examined using embryonic cells. Furthermore, the aerobic and anaerobic attacks of microorganisms on both metal and adhesives were brought into question, leading to the addition of biocides to prevent the attacks. He helped clinicians teaching them how to are preserve the integrity of the slot by using gauges during bracket debonding, alleviate their fear of cross-contaminating 2-paste adhesives (by showing that they can be stored in one container), improve both etching and bonding by adding surface-active agents and evaluate the toxicities of metal and polymeric attachments by testing their leaching properties.
___.It needs to be emphasized that Prof Matasa has given generously of his time and his personal funds to further materials research. His independent evaluation of everyday orthodontic armamentaria has been of great help to the practitioner, particularly by introducing a do-it-yourself, simplified approach to testing methods.
___.Prof Matasa’s activities are not limited to publishing his research and reviews in specialty journals; he has also lectured all over the world. Most recently, his chapter on these topics has appeared in Graber’s Risk Management in Orthodontics.
___.I would like to take this opportunity to congratulate Prof Matasa for his significant contribution to our profession and to wish him many more years of productive research in this vital area, as he seeks to improve our orthodontic practices and insure the well-being of our patients.

A self-ligation mania?

___.Although available commercially since the 1980s, self-ligating brackets may now have reached their highest point so far. Witness the fact that almost all the major manufacturers have their candidates (some even having several types) and that the number of these expensive attachments that are sent to our company is growing. Evidence for this is the coincident orthodontic meetings debating the same topic on the same coast only 2 days apart. One was held November 14, 2007, by the Greater Philadelphia Society of Orthodontists entitled “The Self-ligated Bracket Treatment Forum,” featuring Drs David Musich, moderator, with presentations by Frank Bogdan on Ormco’s Damon bracket, Jerry Clark on GAC’s In-Ovation, Lorne Kamelchuk on Strite’s Speed, and Gary Weinberger on Unitek’s Smart Clip.
___.The other meeting was the ISOS2007 Symposium (International Interactive Self-ligation and Dentofacial Orthopedics), which started November 15 here in Hollywood, Fla. Its lead sponsor was Dentsply/GAC International and its featured organizers were Drs John Voudouris and Mladen Kuftinec,and a host of luminaries from several countries, including Drs Charles Burstone, Paul Rigali, Rainer-Reginald Miethke, Domingo Martin, Mithran Goonewardene, Celestino Nobriega, Hector Sarabia, Christopher Cameron, Hideo Suzuki, and Jurandir Barbosa.
___.The Westin Diplomat Hotel, Florida’s pride (Fig 1) offered not only simultaneous translation into several languages, a place for a sizeable number of posters, and other usual amenities, but also conditions for getting familiar with the attachments discussed (Fig 2). Each participant was provided with 2 books (Fig 3).
___.During his technique course, Dr Voudouris presented information we published 11 years ago on the toxicity of the polyurethane ingredients entering into the composition of elastomeric ligatures. Unfortunately, the data are as valid today as they were then (Fig 4 and Table 1).^2,3 It can be seen that live cells approaching the elastomeric chain are being killed and that some of the ingredients are actually poisonous (low LD50). Instead of decreasing, the predisposition to galvanic corrosion of the metal self-ligating brackets may have actually increased in time.
___.While many other, related topics were discussed, the symposium focused on what we consider today’s most advanced bracket, the In-Ovation C (see following article). In one way or another, the trend toward self-ligation is inescapable, confirming Professor Proffit’s claim that “Self-ligation is the future of orthodontics”!

References
1. www.ISOS2007.com.
2. Matasa CG. Self-engaging brackets: passive vs. active. Orthod Materials Insider 1996;9(4):5-11.
3. Matasa CG. Cytotoxicity of polyurethane elastomers. Orthod Materials Insider 1996:9(2):5-8.
4. Matasa CG. Materials used by orthodontists: elastomers. J Orthop Orthod Pediatr (Caracas) 1996:3:45-53.

Corrosion and self-ligating brackets

Abstract
___.In direct-bonding brackets, the most common site of corrosion is the interface between the bracket and the mesh pad. In self-ligating brackets, an additional source of corrosion is generated by contact of the body of the bracket with the clip or spring designed to maintain the arch wire at the slot’s bottom. While an attack heavy enough to seriously damage the parts is unlikely, it might, nevertheless, significantly interfere with the attachment’s sliding mechanism. Among the most aggressively corrosive agents ingested is salad dressing. Using these and a coloring reagent responding to the leached metal, it is possible to disclose attachments that are prone to generate problems and allergies in the patient.
Introduction
___.An assembly of various metals placed in an electrolyte is a known recipe for corrosion. It is also known that the Achilles’ heel of mesh-based, direct-bonding brackets is brazing, an alloying process that joins the bracket per se and the pad. During treatment, saliva, an electrolyte often charged with acids and chlorides, attacks the less noble metal and dissolves it as it does in common batteries, as shown in Fig 1.1 The bracket’s stainless steel is severely attacked where it joins the gold-based brazing alloy.
___.Not being washed by fluids, the hidden parts of the attachments are always more prone to suffer the attack, as one can observe when comparing the screw and the sliding rod of the expansion screw shown in Fig 2.²
___.While corrosion may not advance enough to damage the self-ligating brackets, the mobility of the sliding clip is very likely to be affected. As rust has a higher volume than the originating mass of iron, its buildup may force apart the adjacent parts. Fig 3 shows an accumulation of metal oxides at the alloy joint, as revealed by dimethyl glyoxime.³ Along with the deposition of foreign materials, this exudation of material is responsible for the ligating clip’s remaining stuck even if the attachment has not been subjected to undesirable forces.
___.Although both the body of the self-ligating bracket and the clip are made of stainless steel, it should be noted that orthodontics uses it in at least ten different alloys. In addition, the cold work involved in making the bracket’s parts varies significantly, leading to differences in electric potential enough to generate galvanic corrosion. Aggravating circumstances occur when the wires and the mechanism holding the wire involve other types of alloys. Thus, Forestadent’s Mobil Lock™ involves a brass screw, and Unitek’s Smart Clip™ and Orec’s Speed™, have nickel titanium clips.
___.Salad dressings are emulsions, that is mixtures of two immiscible fluids (oil and water), where one of these is suspended as small drops inside the other. While in an oil-in-water emulsions water forms the continuous phase, in the water-in-oil emulsions, the oil surrounds small droplets of water. Although corrosion occurs in both cases, only the oil-in water dressings these generate an indicative, colored aura surrounding the bracket: in the water in oil emulsions, the corrosion remains localized.
Materials and method
___.Twelve self-ligating, metallic brackets made by several manufacturers were given a specific number which was kept throughout the tests:

___.1. Smart Clip™, Unitek/3M Corp.
___.2. Damon SL™, Ormco
___.3. Time™, American Orthodontics
___.4. Activa™, “A”-Co. /Ormco
___.5. Speed NiTi Clip™, Orec/Strite
___.6. Damon 3MX™, Ormco
___.7. In-Ovation™, GAC
___.8. Damon 2™, Ormco
___.9. Speed™, Strite
___.10. Twin Lock™, Ormco
___.11. Mobil-Lock™, Forestadent
___.12. In-Ovation R™, GAC

___.The buccal aspect of these self-ligating brackets can be seen in Table 1 of the article following. Into the indentations of 2 ceramic egg holders was then poured 7 cc of 2 salad dressings. Both were added after stirring with 1:100 potassium ferrocyanide (Fe [CN]₆K₄ is a reagent known to turn dark blue in the presence of Fe⁺⁺ ions).
___.The salad dressings (Fig 4) were purchased in Florida at a local Publix store; only products listing their sodium content were selected as this is indicative of the table salt contained, an indirect indication of the aggressiveness of chloride ions.
___.After identifying the types of emulsions, 2 dressings were selected, one of the oil-in-water type (Marzetti Slaw Dressing “Lite,” Na content 16%) and the other water-in-oil (Ken’s Steak House “Lite Caesar,” Na 26%). Two sets of 12 brackets each were placed in the depressions of the 2 egg holders. After adding the reagent containing salad dressings, each egg holder was covered with a plastic film to prevent evaporation. After 48 hours at room temperature, the oil-in-water dressing showed auras surrounding the brackets, while the other appeared unchanged.
___.The brackets from the latter were removed, placed on a paper towel, left to dry for 24 hours and removed again. The water-in-oil dressing left in each depression was homogenized and the remaining spots left on the towel were photographed using a Canon Rebel XT digital camera.
___.Before and after the test, the self-ligating brackets were tested for proper functioning of the slot-closing mechanism. Being clogged with salad-dressing colloid debris, the mechanism did not function properly, and the brackets had to be boiled with a common dishwashing detergent solution. After retesting, the brackets with impaired closing mechanisms were immersed for 30 minutes in 50% by volume nitric acid at 120°–140°F (49°–60°C).⁵
Results
___.The egg holders containing the added dressings are shown in Figures 5 and 6, with the difference that in the latter, the brackets were removed and the remaining water-in-oil dressing was homogenized. The spots left by the brackets on the paper towel are shown in Figure 7.
___.The brackets placed in the oil-in-water salad dressing show a darker-colored aura corresponding in size and intensity to the amount of Fe⁺⁺ released. In contrast, the undisturbed, water-in-oil reagent-added salad dressing didn’t show any differences. After the brackets were removed and the fluid was homogenized, marked differences in shade appeared. Similar differences were also seen on the spots left on the paper towel by the removed brackets.
___.The slot-closing mechanism of the tested brackets was severely impaired in about half the cases and only a passivation treatment with nitric acid was found capable of removing the oxide/salts deposit to allow sliding to resume.
Discussion
___.These do-it-yourself tests were performed with common materials, the only material relatively difficult to obtain being potassium ferrocyanide. According to the World Health Organization,⁴ the strong chemical bond between the iron and cyanide groups provides this salt with a low toxicity. Indeed, dogs injected IV with sodium ferrocyanide (0.5 gm/kg body weight), excreted the salt without renal damage as demonstrated by high urea clearance and absence of hematuria.
___.In view of the small number of brackets tested, their size/volume difference, and the aggressive agents being randomly selected, the present research is only suggestive. However, in all cases the self-ligating brackets were attacked, some being more susceptible than others. While most of the blame for such attacks falls on beverages containing phosphoric acid (eg, Coca-Cola, Diet Coke), salad dressings may be even more aggressive due to their content of table salt. Indeed, Cl- ions are known to dissolve the chromium oxide layer that protects stainless steel, rendering it as susceptible to corrosion as iron or common steel.
___.Although the aura surrounding the corroded brackets in the oil-in-water dressing is the easier to notice, the color intensity generated by their water-in-oil counterparts is less obvious but more intense. This can be observed in the fluid left after the brackets are removed; likewise, the brackets removed and dried on the paper towel showed a more intense attack. This goes along with the fact that well-washed surfaces are always less prone to severe attack than hidden ones.
___.As one can see (Fig. 5 to 7), the self-ligating brac-kets more corrosion susceptible are Damon (2, 3MX, and SL), Smart Clip, Twin Lock, and Mobil Lock; the least severely attacked being Activa, In-Ovation, and In-Ovation R. Being among the first self-ligating brackets Ormco launched (1986), the company has been replaced Activa with other brackets.
Conclusion
___.Metal self-ligating brackets have a built-in propensity for additional corrosion, because the clip or spring designed to keep the arch wire in place is made from an alloy nobler than that of the bracket. The ensuing galvanic corrosion causes the metal of the latter to migrate and form a deposit of oxide on the former, hindering its ability to slide.
___.The addition of reagent-disclosing iron ions to a commonly ingested fluid (the salad dressing) facilitates a comparison of the corrosion susceptibilities of all brackets, including self-ligating ones. Although corrosion-induced malfunctioning of standard brackets [Is that what you mean?] seldom occurs, in the case of self-ligating brackets, it plays a major role in their “raison d’être.”
___.If not damaged, these expensive brackets can be successfully recovered and reused.
___.Note: If anyone wishes to duplicate the above tests, we will gladly send a gram of this chemical in a self-addressed envelope.
References
1. Matasa CG. Biomaterials in orthodontics. In: Graber TM, Vanarsdall RL, eds. Orthodontics: Current Principles and Techniques. 3rd ed. St. Louis: Mosby; 2000.
2. Matasa CG. Heavy metal release: a do-it-yourself test. World J Orthod. 2003;4:348-57.
3. http://en.wikipedia.org/wiki/Rust. Accessed Nov. 2007.
4. www.inchem.org/documents/jecfa/jecmono/v46aje57.htm. Accessed Nov. 2007.
5. www.mmsonline.com/articles/100304.htm. Accessed Nov. 2007.

Materials in self-ligating brackets, yesterday and today

A very short overview
___.In an article we published 11years ago in this newsletter entitled “Self-engaging brackets: passive vs. active: the ideal attachment comes closer,” we described and compared 24 self-ligating brackets (Table I).¹
___.Since then, some of these brackets have stood the test of time, others have been discontinued (Edgelok, TwinLock, Activa). Self-ligation tubes are common, for either direct bonding or for welding to bands. In all of these, the basic concepts are the same, of course suffering various improvements. In Table II are shown recent metallic, mesh-based brackets in their closed position.

___.While the materials from which these are made comprise, a variety of alloys, along with polymers and ceramics, their difference in functionality has remained in principle the same, that is, passive vs. active. Some 20 years since going on the market, “active” brackets, introduced as a concept by M. Wallshein, continued by G.H. Hanson and perfected by others, are still not preferred over the passive ones. As an outsider, I am surprised to see how convincing all the publicity for the latter can be, despite the advantages of the former (better control in rotation, tip, and torque).
In-Ovation C has it all!
___.It should be music to the ears of the people at GAC/Dentsply to hear what follows, as these come from someone they consider a “very strong competitor.”³
___.Leaving the clinical part to orthodontists, we will concentrate on related biomaterial aspects.
The body. Respecting J. C. Voudouris’s original conception² for a metal bracket (Fig. 1), In-Ovation C had to be re-designed for ceramic injection molding. Highly esthetic due to sintered alumina, it has a built-in channel to allow the sliding of the closure member (or clip), Fig. 2, and an intricate slot blocker. The system allows the bracket to be passive, inactive or active according to the arch wire used, Fig. 3.
___.While common mold limitations do not allow undercuts, the built-in slot blocker, Fig. 4, the clip’s channel, Fig 5, as well as the protrusions of the base (Fig. 6) have been skillfully engineered. The latter are high enough to provide a good bond, as demonstrated by the adhesive retained on the pads of the used brackets.
The clip. Made of corrosion-resistant cobalt-chromium stainless steel, it has been rendered pearlescent by a rhodium layer deposited through magnetron sputtering. Rhodium coatings of 1 to 2 mm are used for specialty mirrors because of their high light reflectivity (approximately 80%), but for brackets, they provide increased hardness and a lower static coefficient of friction.
Interaction. Physics shows a correlation between friction and hardness, the first decreasing as the second increases,⁴ as shown in Table 3.
___.Notwithstanding the above, extensive orthodontic research has shown that against arch wires, ceramic brackets offer more friction than their metal counterparts. However, a recent study at the NYU Biomaterials and Biomimetics Laboratory⁵ confirms physics: it found that under the same controlled and standardized test conditions, the In-Ovation C generated less friction than other tested brackets, including those conventionally ligated, those using passive self-ligation, and even In-Ovation R. Indeed, it is known that the coefficient of static friction also depends on roughness, which in turn can be reduced by better finishing of the surfaces involved. A focused observation of the commonly used ceramic brackets shows that the harder alumina (Table 3) abrades the wire, forcing out metal particles that can be evidenced with the naked eye or by using coloring reagents (Fig 7).
___.To conclude, it is our opinion that In-Ovation C leaves well behind all previously made esthetic brackets...

References
1. http://www.orthodonticmaterials.com/insider_1994_1996.html, December 1996).Accessed No. 2007.
2. Voudouris JC, Self-ligating orthodontic bracket, US Patent 7,214,057, 2007
3. Dohn L, Letter to the Editor, Am.J Orthop Dentofac Orthod. 1989; 65: (5): 21A
4. Bradley MSA et al., Effects of wall material hardness, Tribology International 2000; 33 (12): 845-854.
5. Voudouris JC, Bio-interactive technique course, Voudouris, Montreal-New York 2007