OPINIONS
___.T. M. Graber, U. Illinois/ Chicago. At “The Orthodontic Materials Insider” newsletter 15 year jubilee, and at the launching of the web site www.OrthodonticMaterials.com web site, it is a distinct honor to write this commentary on the efforts of Professor Claude Matasa. Like a lone voice in the wilderness, he faced down the commercial interests. He has shown the potential iatrogenic sequelae from some of the most common materia technica used in orthodontics. While others, like Professor Samir  Bishara, have noted untoward responses such as nickel sensitivity in bands and brackets, it remained for Professor Matasa to present incontrovertible evidence from his laboratory, showing a wide range of potential health problems associated with attachments, wires, bonding materials, etc. Recently, he did the same with polymers, providing these interested with simple methods for detecting leaching ingredients. The old saying is, “It is not the tool, but how you use it!”. This may be true, but sometimes, the tools we use may incite iatrogenic biologic responses. While seldom a life-threatening condition, the litigious consequences are of major concern.
___.The recent law passed in California, holding the doctor responsible for any therapeutic adjunct he uses makes the risk management problem even more onerous. Nine major risk management insurance companies stopped issuing malpractice insurance last year, with St. Paul Insurance Company losing over $1,000,000,000. It behooves the practitioner to carefully check the biomaterials used. Fortunately, Professor Matasa has authoritative articles in our professional journals and textbooks to help protect us from the legal cancers spreading so widely now. His latest chapter will appear in a book on Risk Management problems by Graber, Eliades and Athanasiou, being published by Quintessence Publishing Company in 2003. Read and be forewarned! Thanks you for your continuing crusade, Claude, protecting both patients and practitioners!
___.M.M. Kuftinec/ NY University. Over the last 15 years, both clinicians and researchers could count on one reliable source of information on the subjects related to orthodontic materials: the unpretentious and easy to read “The Orthodontic Insider”, now easy to reach by visiting the web site “www.OrthodonticMaterials.com”. The newsletter format of this publication makes it convenient to peruse, the writing style easy to understand, the covered material relevant to many readers. Several issues were first brought to our attention through the articles published in the “Insider” such as those dedicated to various methods of testing (from sophisticated to simple, of a do-it-yourself type), to the bacterial attack on bonding adhesives and brackets, attachment corrosion, inconsistencies in use of the preadjusted appliances and limits in bracket miniaturization of brackets. In the pages of the “Insider” we first learned of the idea and the need for ISO 9000 certification. In short, it is hard to think of a publication that dealt with timely and important issues of clinical orthodontics in a more authoritative way.
___.Any orthodontist who does not take advantage of learning from this publication is denying himself an invaluable resource. Doctor Matasa is to be applauded and congratulated for his foresight, dedication and unselfish willingness to share his experience and understanding of the materials we use.

DO ADHESIVES & SEALANTS REALLY SEAL THE BRACKETS PAD? I. CORROSION

Abstract
___.While most adhesives and sealants have the same resin base, the shape and composition of the metal brackets differ. To evidence particularities, an ISO-recommended solution for testing corrosion has been modified to include a reagent for dissolved iron, and then used to test the permeability of the same sealant on various bracket bases as well as on other, similar substrates. The test, designed to simulate the action of saliva, shows that mesh and mesh-laminated foils are less penetrated by fluids than the grooved bases.
___.As during corrosion a release of heavy metals and a weakening of the bond usually accompany saliva penetration, mesh bases are to be preferred, despite of their higher cost.
Introduction
___.The difference between a sealant and resin-based adhesive is that the last is filled. It is actually recommended to dilute a too viscous adhesive, a composite, with a sealant¹. In what follows, we will use the term “sealant” for both.
___.Being theoretically insoluble in water (hydrophobic), orthodontic sealants and adhesives should not pick up pigments or water- soluble dyes. The bonding involves only a relatively limited number of active sites on polar (hydrophile) substrates. Both sealants and adhesives form an oxygen-inhibited-layer, despite the fact that this is less evident on composites. Both should have enough free liquid resin to penetrate micro-cracks and fissures to generate the sought-after anchorage, in fact a mechanical interlocking deprived of any chemical affinity.
___.Although there are many studies that have dealt with the interface sealant-enamel, as far as we know, none has as an objective to examine the equally important interface sealant-bracket base, be it mesh or otherwise. Less dramatic than enamel breakage or demineralization, an improper relationship sealant-pad leads to annoying and time-wasting bond failures. The problem tends to exacerbate in time, as many new and less expensive non-mesh brackets are launched every year.
___.Today, their testing is restricted to the evaluation of the initial bond strength, and in the best cases after few weeks of exposure to an environment thought to duplicate the oral environment. No attempts were made to understand the phenomena involved, neither to establish relationships.
___.It has been shown that the anaerobic microbes penetrate the interface sealant-enamel, generating filiform colonies duplicating these found in the sub gingival plaque^2,3, Fig.1a, while other, iron-consuming micro-organisms, penetrate the interface sealant-metal pad generating dents in the last^2,4, Fig.1 b. Fortunately, these intrusions can be limited, if not entirely avoided, by using biocide-added sealants/adhesives^3,5.
___.More difficult to stop is the penetration of the saliva carrying corrosive-ingredients; the latter attack both substrates, weakening the polymer matrix and substituting the metal for its oxides or salts. In Fig. 2, the formation of rust is evident. The attack can gradually lead to the complete dissolution of the stainless steel, as shown by the three juxtaposed brackets shown in Fig. 3. In turn, the sealant’s acrylic matrix can undergo a depolymerization that lowers its water-repellent properties and limits its sealing ability, Fig. 4. All the above cases were found among the used brackets sent to Ortho-Cycle Co.
Materials and methods
___.A three prong approach has been used to evaluate the extent of sealants’ permeability to corrosive agents, all based upon the detection of one of the heavy metals released, and none involving chemicals that may weaken the acrylic’s matrix.
___.New Unitek Dynalock brackets and Orec tubes, as well as worn arch wires with attached brackets, have been randomly selected from those serviced by Ortho-Cycle, the only criteria being some discoloration of the adhesive. After being photographed, these have been sealed with Phase II, a two-part system (Reliance) and then immersed for 24h at room temperature in a diluted aqueous solution of lactic acid and table salt, a mixture recommended by ISO for the accelerated corrosion of stainless steels⁶. To this solution, 1% of potassium ferrocyanide (Fisher Sci.), a reagent giving a blue color with iron ions, was added^7-9 to enable the detection of metal attack under the sealant layer. In parallel, similar metal surfaces have been sealed and treated the same way. After exposure, the wires, brackets, etc. were thoroughly rinsed with water, dried and photographed using either a Nikon CoolPix 950 camera or a computer-connected microscope (MOS colored video camera (Edmund Scientific). In what follows, the above processing will be referred to as “treatment”.
Results.
___.I. In Fig. 5 and 6, arch wires with attached brackets are shown photographed before and after treatment. In Fig.7 and 8 are shown other randomly picked up arch wires with brackets after this treatment. While some penetration occurs in almost all cases, the most significant occurs in the non-mesh-bases.
___.II. New brackets with retentive grooves and with mesh have been subjected to the same treatment and their bases photographed before and after being sealed, as shown in Fig. 9. The blue colored complex of iron ferrocyanide shows that the reagent has penetrated in the etched grooves of both unsealed and sealed non-mesh brackets, a & b. While the rinsing has been able to almost totally remove the coloring agent from the unsealed mesh, a, the sealed mesh, b, has retained a superficial blue tinge due probably to the more polar oxygen inhibited layer (OIL).
___.III. In an attempt to duplicate the penetration of the grooved and mesh bases on a scale large enough for easy observation, a carbon steel file, an 80-mesh stainless steel screen and a 100-mesh heat-laminated stainless steel sheet (used and described in our previous experiments¹⁰) were sealed and treated. To test if an improved wetting of the metal surfaces could limit the reagent ‘s penetration, the file’s surface was partially silanated using a 1% solution of the Silane Z-6030 (Dow Corning).
___.Fig. 10 shows the surface of the silanated file after sealing and treatment. While the additional silanation may have conferred some protection to the steel, it is obvious that the corrosive/coloring reagent has penetrated under the sealant layer as we will show in depth in our next issue
___.Fig. 11 and 12 show an 80-mesh stainless steel and its 100 mesh sheet-laminated counterpart after sealing and treatment with the corroding/coloring reagent for 48h. As a difference from sealed grooves, there is no significant penetration of the reagent at the interface sealing layer and mesh.
Discussion
___.Crevices, such as those occurring between metals and plastics, constitute shielded areas that restrict the access of oxygen. Without their layer of chromium oxide, generated and maintained by the latter, passive metals such as stainless steels become corrosion susceptible as a shift in acid conditions in the crevice leads to a build-up of aggressive ion species (e.g. chloride) in the crevice The phenomenon has led to at least five F-16 airplanes crashes, as bolts in gaskets, washers, insulation material, fastener heads, surface deposits, disbonded coatings, etc. lose their strength, Fig. 13¹¹.
___.Stainless steels “are more prone to crevice corrosion than metals that exhibit more active behavior”¹². In orthodontics, a similar process takes place not only at the interfaces adhesives/bracket pads, but also under the tie wings, where tight elastomeric ligatures may generate stagnant conditions¹⁴.
___.Based upon the above facts, the above series of experiments can be interpreted as various facets of the same phenomenon. Pushed by capillary force, saliva and its ingredients are adsorbed at the interface pad/sealant by the existing micro-cracks and micro-fissures. The strenght of the capillary force can be estimated from the fact that it is able to raise water from the soil to the top of the trees. For the same reason cavities do not form at teeth cusps, but in their recessed, fissured areas. Saliva can penetrate deep at the metal/plastic interfacewhere the various ions it carries perform un- hindered their destructive action (oxygen-shielded areas). In the experiments described in this study, the bases whose retention is based upon grooves specifically designed to offer a maximum roughness have preferentially adsorbed the corrosive/coloring reagent. At the same more adhesive-retentive, mesh and mesh-laminated sheets are also less prone to adsorb the reagent at their interface with the sealant. Indeed, in this case roughness has been substituted for the micro-welding of a mesh to a sheet, materials resulting quite smooth from their processing.
___.As the basic resin components of both sealants and adhesives is practically the same, it is presumed that these equally prone to the infiltration of saliva or, in our case, the corrosive/coloring reagent. A properly polymerized sealant or adhesive should not be colored by a water soluble dye: in our case, the sealant and the metal are contrasting from the point of view of their affinity. Thus, metals are water-loving, accepting the dye, but repel the hydrophobic sealant (in the absence of a coupling agent or primer).
___.Metal bracket priming has been used at Ortho-Cycle even before 1982, when our activity was first quoted¹⁵: its efficiency has been demonstrated three years later, being reported as “significantly increasing the bond strength of base mesh”¹⁶. After several years, silanation started to be widely applied to ceramics to provide adhesive affinity. At that time, we didn’t realize that along with the improved wetting, the metal becomes better protected against corrosion.
___.The lack of affinity between the metal and the resin as well as the fact that in any joining only a relatively reduced number of active sites participate leads to the presumption that the two layers duplicate a gallery supported by a multitude of pillars between which slowly seeps a fluid, the corroding/coloring reagent. In industry it is known that “For a given alloy-environment combination, the occurrence of crevice corrosion is highly dependent on the crevice geometry”¹⁷, similar tests being recommended by ASTM (American Society for Testing Materials)¹³, Fig. 14. The higher the roughness, the higher the affinity of the substrate for the fluid. The more corrosion susceptible the metal, the larger and more numerous the shielded pockets formed.
___.The behavior of the metal substrate pays a major role as it enhances the penetration of fluids at its interface not only through its particular shape, but also through its corrosion resistance. While silanation may have slowed the penetration of the reagent, Fig. 10, the combination rough grooves and non-acid resistant metals proved to be a recipe for failure. Consequently, to avoid stainless steels’ crevice corrosion, an addition of up to 5% molybdenum is recommended¹².
___.In contrast, both the stainless steel mesh and mesh-laminated sheets have shown a limited penetration of the reagent, as even after 48 hours of immersion no blue discoloration of the sealant has occurred, Fig. 11 and 12.
Conclusions
___.Brackets often debond earlier than desired. One of the causes is the penetration of saliva and the ingredients it carries in between the pad and the adhesive/sealant. In the case of metal brackets, this penetration can be associated to crevice corrosion, a phenomenon that leads to a release of harmful heavy metals. By simulating this process with the help of a solution recom-mended by ISO for testing accelerated corrosion, modified by the addition of a reagent for dissolved iron, it was possible to test the behavior of various types of bases. Based upon randomly selected direct bonding brackets and using the same sealant, the test has shown that the penetration is enhanced by bases exhibiting grooves and roughness, as contrast from mesh. The nature of the alloy plays a major role; no matter if silanated or not, carbon steel surfaces cannot be efficiently sealed.
___.While more research is necessary, the test is an eye-opener for those designing and using direct bonding attachments.

___.To be continued with
___.DO ADHESIVES & SEALANTS REALLY SEAL
___.THE BRACKETS PAD? II. SURFACE TENSION

References
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2. Matasa CG: Nichtrostende Edelstahle und Direkt- Bonding- Brackets. III.Mikrobiologisches Verhalten-auch der Adhasive. Informationen aus Orthodontie und Kieferorthopadie,1993; 25(3): 269-285
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6. ISO Standard 1995; 29!): 16-23
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11.www.corrosion-doctors.org/Aircraft Examples.htm#Crevice; www.alberg30.org
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13. ASTM G 48-76F 31-10
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16. Siomka LV, Powers JM, In vitro bond strength of treated direct-bonding metal bases, Am. J. Orthod. Dentofac. Orthop. 1985; 88: 133-136
17. Kain RM, Evaluation of crevice corrosion, In Corrosion, ASM Handbook vol.13, Davis JR ed., ASM International, 1992: 303.