A chemist’s advice to feel better (and be nicer) during the holidays
___.Have a meat-rich snack a few hours before the main course: you’ll eat less. For an even stronger effect, take amino-acid appetite suppressants such as tyrosine, phenylalanine, glutamine, or tryptophan. Insulin is triggered by sweets and carb-rich foods, which in turn cause a rapid fall of the blood sugar. Our body responds to an excess of insulin by releasing adrenaline, rendering us more emotional.
___.Alcohol is considered to be a central nervous system depressant: research links excessive alcohol consumption with the development of irascibility, in addition to other emotional and psychological effects. The former effect is due to the alcohol’s metabolization into acetaldehyde, a known nerve irritant. To alleviate the acetaldehyde’s effect, you should take sulfur-containing amino-acids that react with it, such as cystine, or glutathione, a derivative.
All of the above can be found over-the-counter.

What is hidden behind your bracket’s mesh?

1970’s. In the 70’s, in our effort to reclaim for reuse some direct bonding brackets, we introduced both bracket base silanation and topical etching^1,2. Neither treatment impaired the attachments’ shine, as etching could be performed in a strictly controlled way, e.g. by increasing the surface area of only a half of a base, Fig.1². Early in the 80’s, our silanated samples were mentioned in the orthodontic literature as being sent for bond strength evaluation³.
1980’s. In the mid’80’s, independent studies found that our etching and silanation led to a ”significantly increase in the bond strength”⁴. These results were obtained on grooved bases, which are the least retentive ones. After several years, the first ceramic silanated brackets were launched. It took two more decades until Ormco and TP Orthodontics started to advertise their silanated Optimesh®, and polymer-coated (PrimeKote®) bases, respectively.
___.Mounting data we gathered showed that resin-based adhesives do not properly wet the bases’ metal surface, as corrosion was often taking place at the interface, as shown in Fig. 2. Interestingly, others, have never taken this lack of affinity between the metal and the adhesive seriously, and have not bothered to remedy the problem. Moreover, some manufacturers even showed that the adhesive completely fills the space around the mesh, as shown in Fig. 3
2000’s. Our experiments performed on various stainless steel mesh samples showed that adhesives do not seal the bracket’s base, since they are repelled by the oxide-covered metal surfaces. The denser the mesh, the less penetration was observed. Pre-treatment of the metal with silanes and surface-active agents and/or added pressure were found to enhance the resins’ penetration5. A simulation duplicating the actual bonding was performed by pressing a red-colored, non-commercial composite through a variety of stainless steel mesh samples using the specifically designed device shown in Fig. 4. The degree of penetration was evaluated based on the stains left on filter paper disks, Fig. 5. Acceptable penetration was established only when sufficient pressure was applied on the composite (see Fig.6)⁶.
___.The experiments demonstrated that as the resin’s penetration through a single layer of mesh was already spotty, the use of two superimposed layers (and even more, three, as in GAC’s “Supermesh” patent7) is far from being as efficient as claimed.
Materials and method
___.New brackets from Unitek, “Miniaturized Twin®” (injection molded, grooved base), American Orthodontics (“Triple Action”®, 60 mesh and 100 mesh) and GAC, “Supermesh”® (two layers, 100 and 200 mesh) were oil-decontaminated with trichlorethylene and dried. Then their bases were evenly covered with the same adhesive, Phase II® (Reliance, Itasca, IL 60143). In parallel, similar brackets were subjected to an additional surface treatment before having their bases clogged with the same adhesive.
___.All the adhesive-clogged brackets were placed in sections of a plastic tube and embedded in acrylate; after proper curing, the brackets were sanded with progressively finer grits (up to 800, from Buehler, Lake Bluff, IL 60044-1699) until the interface bracket/adhesive was properly exposed^8,9. To remove the fine dust formed, the samples were subjected, while immersed in the aqueous solution of a common dishwashing detergent, to ultrasound vibrations in a Quantrex® 90 Hz apparatus (L&R Manufacturing Co., Kearny, NJ). After repeated cycles of rinsing followed by drying and air blowing, some of the embedded brackets were scrutinized with an optical, stereoscopic metallographic microscope (MSC 200 by IOR, Bucharest) and photographed with a digital camera (Nikon 950).
___.The images taken with an optical microscope, however, do not allow the proper assessment of the gaps due to their lack of depth of field. They were indicative, though, when used din conjunction with a scanning electron microscope (Phillips XL-30-ESEM TMP)¹⁰ as operated by the Biomaterials Center of the Polytechnic University, Bucharest, Romania. By scrutinizing a longer portion of the locking area, these optical images helped not only to locate for SEM analysis the gaps’ location, but also to assess their relative frequency. Due to high cost, the number of SEM micrographs taken was not enough for a statistical analysis, but was adequate enough for a morphological description. For each sample, the images were taken from a single, randomly selected layer. The number of gaps found may illustrate the likelihood of encountering gaps in a particular base/adhesive system.
___.In what follows, the images in color were taken with the optical microscope, where the gaps are shown as hazy areas. In the SEM images, the metal is shown white, the adhesive as a grayish, granule-containing mass. The acrylate mounting resin is shown as uniformly grey.
Results.
1. Mesh bases, optical microscope. The images of the space between two mesh wires of the interlocking area of an American Orthodontics, Triple Action®, 100 mesh base. Fig. 7 and 8, show a space properly filled and one hosting a gap, respectively.
___.Microphotographs of similar areas taken from a GAC’s Supermesh® base show both a difference in the thickness of the wires (the manufacturer uses two superimposed mesh layers, each with its specifications), and some large gaps, as shown when Fig. 9, where the space is filled. This could be further compared with Fig. 10 and 11 which show hazy areas indicating gaps.
2. Mesh base, optical and SEM. The interlocking area of an American Orthodontics Triple Action® bracket having 60 mesh has been first optically inspected to enable a SEM analysis. Only one gap was found along the interface studied: the optical image of the bracket showing its location is shown in Fig.12, and the SEM enlargement in Fig. 13.
3. Non-mesh base, optical and SEM. Fig. 14 shows the optical image of an arbitrary cross-section of a Unitek injection molded bracket (Miniaturized Twin®). The arrows highlight the areas where the SEM microphotographs were subsequently taken. First shown as thumbnails, these were further enlarged to allow a better view. In Fig.15, the gaps are within the adhesive. In Fig. 16, these can be seen both within the adhesive and at its interface with the metal. Fig. 17 shows a bubble within the acrylate used as mounting material. In Fig. 18 is shown a gap almost as large as the distance between the relatively few protuberances that form the brackets’ locking system. Fig. 19 shows the fourth gap detected in a single plane of the sectioned Unitek, non-mesh base.
4. Double mesh base, SEM. As the use of an optical microscope alone did not provide an acceptable assessment of the gaps (see above), the examination of a GAC’s Supermesh® base (Fig. 10 & 11) was continued using SEM. Gaps were found both between the mesh layers and in the space under them, i.e. between the mesh and the foil, as shown in Fig.20 to 23. In Fig. 21, some separation was observed within the adhesive; in Fig. 23, the large gap continued further than the area examined, demonstrating once again the insufficient affinity existing between the metal and the resin-containing adhesive.
Discussion
___.As we will show in the following Addendum, apparently properly attached brackets become corroded and debond at the adhesive/metal interface, despite the fact that these should have been protected by the polymer coating.
___.While a lot of effort has been spent on the interaction between the enamel and the adhesive, we are not aware about works focusing on the phenomena taking place between the adhesive and the metal base. It seems that most clinicians are satisfied if the enamel has been properly etched and if the direct-bonding attachment holds. Indeed, what happens after bonding seems of less concern... In turn, manufacturers limit themselves to providing retentive pad surfaces, ignoring what happens at the interface base/adhesive and if there is enough affinity between resins and oxide-covered metals.
___.Due to a layer of chromium oxide that covers its surface, stainless steel is hydrophilic. In contrast, resin-based adhesives are hydrophobic: a drop of these adhesives placed upon a stainless steel mesh takes a long time to penetrate it, if it ever does it. According to the Steel Structures Painting Council, corrosion in the presence of a paint coating is likely to be much more serious when it is localized at discontinuities in a coating rather than if it occurs under the coating.
___.In contrast to common, industrial practice, where the metal surfaces to be coated or adhered to are subjected to oxide (rust) removal and priming, orthodontic direct-bonding attachments are used without any chemical preparation of their surface. Bonding enhancements such as etching or sanding offers the adhesive a larger surface area, but also generate a larger hydrophobic/oil repelling surface. On one hand we would like the stainless steel to be well passivated and thus rendered corrosion resistant by a thick layer of oxide, while on the other hand, we do not want this layer to hinder the metal’s wetting, a phenomenon associated with adhesive bonding.
___.In industry, it is known that coating passivated stainless steel is not easy: Allegheny Ludlum, the largest stainless steel manufacturer in the US, had to coat first the metal with a silicate¹¹. In orthodontics, as shown in Fig. 2 and the others in the following Addendum, direct-bonding leads only too often to an infiltration of oral fluids at the interface bracket base/adhesive. This leads to crevice corrosion, a phenomenon tested in industrial standards by sandwiching a piece of metal sheet between two others made of plastic¹², almost duplicating what happens in the mouth.
___.As the degree of cold-working to which the attachment’s parts are exposed during manufacture differs, fine mesh is more corrosion resistant than the bracket’s bulk¹³. The corrosion is further enhanced by both the differences between the stainless steel used for the bracket body, and that used for the mesh, and by the presence of lamination, welding or brazing spots. Aside from corrosion, another undesirable phenomenon that occurs is the formation of gaps within the interlocking area, thus preventing the riveting effect that leads to a good bond. Interconnected, these gaps lead not only to widespread crevice corrosion and metal dissolution, but also to microbial colonization. As we have recently shown⁵, the microbial penetration of bracket bases sealed with a common adhesive may occur within 24h.
___.In an attempt to improve initial bonding rather than to prevent premature debonding and the other side effects, a manufacturer is applying now what we were recommending since the 70’s: the attachment’s treatment with coupling agents. Unfortunately, the process is cumbersome; and the result, short lived. Indeed, a layer thinner than a monomolecular one is not active enough: if thicker, it acts like a lubricating film, instead of a coupling one. Anchored in the metal and waiting to react with an adhesive or coating, the active, coupling groups ending the hydrocarbon chains dangle free only for a limited time, ending up after a few weeks by combining with each other, or by hydrolyzing to inactive silanols. While used in industry, other coupling agents such as titanates, zirco-aluminates, zirconates, alkyl/aryl phosphate esters have not yet been tested in dental appliances. Perhaps as efficient, but surely easier to apply and longer lasting, the treatment of the bracket’s base with surfactants allows the metal to be properly wetted by the adhesive. If the the metal surface would be treated to exhibit an affinity for the resin adhesive, bonding would be significantly enhanced by capillarity. Force which causes the upward flow of water in plants, capillarity pushes liquids into porous materials in direct relation with their mutual wetting and inversely proportional with the radius of the pores
___.While not yet tested for both initial and delayed bonding strength, our chemical pretreatment with surface active agents of various stainless steel mesh samples has shown a significantly better penetration by resin adhesives.
Conclusions
___.Our previous work has shown that passivated stainless steel mesh samples exhibit a poor wetting when in contact with resin adhesives. The present study confirm this with the help of photomicrographs taken at the interface bracket base/adhesive that show both gaps and separations at the interface metal oxide/polymer. While applying pressure may alleviate the problem, an additional pretreatment of the bracket’s base with coupling agents or with surfactants leads to an improved interaction with the adhesive.

References
1. Matasa CG, Silanation, a key to bonding, The Orthodontic Materials Insider, 1988; Winter: 3-5
2. Matasa CG, Etching and direct bonding bases, The Orthodontic Materials Insider, 1989; Summer: 2-5
3. 1. Mascia VE, , Chen RV, Shearing strengths of recycled direct-bonding brackets, Am. J. Orthod. Dentofac Orthop 1982; 82; 211-21
4. Siomka LV. Powers JM, In vitro bond strength of treated direct-bonding metal bases, Am. J. Orthod. Dentofac Orthop 1985; 88: 133-136
5. Matasa CG, Do adhesives & sealants really seal the brackets’pad? I. Corrosion. The Orthodontic Materials Insider 2002; 14 (4): 5-8
6. Matasa CG, Do adhesives & sealants really seal the brackets’pad? II. Surface tension. The Orthodontic Materials Insider 2003; 15 (1): 4-8
7. Iida, E (GAC), Orthodontic apparatus for attachment to a tooth, US Patent 4,889,458 ‘89
8. Matasa CG, Metal strength of direct bonding brackets, Am. J. Orthod. Dentofac Orthop. 1998; 113: 282-286
9. Matasa CG, Micro hardness, a tool to evaluate brackets,The Orthodontic Materials Insider 1994; 7 (3): 4-8
10.rMatasa CG, Orthodontic recycling at the crossroads, J. Clin. Orthod. 2003; 37: 133-139
11. Lula R, Allegheny Ludlum, private communication
12. ASTM Standard G 48-76F 31-10
13. Matasa CG, Characteristics of the used orthodontic brackets. In: Dental Materials in vivo. Aging and related phenomena. Eliades G, Eliades T, Brantley WA, Watts DC, eds., Chicago: Quintessence, 2003: 139-154

Addendum

___.Examining worn direct-bonding brackets sent for sale or service, both before adhesive removal and after, a large number of corroded samples can be found. To a newcomer’s surprise, the most attacked part is not the one most exposed to the oral environment, but the one hidden behind the adhesive, and thus apparently more protected.
___.All types of brackets are attacked: machined, cast, or injection molded. Mesh or monobloc bases (grooved, coined, etc) are found partially dissolved. The dissolution is due to either to galvanism (differences in metal composition or thermal treatment) or to microbially influenced corrosion. As none of these can take place in the absence of water, it is obvious that the interfaces metal/adhesive and adhesive/enamel are both permeated by the oral fluids. Even if mechanical forces play a role in the bases’ destruction (e.g. the detachment of the mesh from the foil), these would be resisted if the welding/lamination contact points would not have been weaken by corrosion.
___.In what follows are provided samples of the attacks encountered with a short explanation.

Our present to you for the New Year:
10 direct bonding brackets or ten bands with tubes, FREE, your choice*.
Send us an used sample and your address, or indicate brand, line,
slot size and tooth by mail, e-mail or fax.

___.As shown in the 2003 March issue of J. Clinical Orthodontics, Ortho-Cycle’s orthodontic recycling has made recently a major step forward: in addition of removing the adhesive by dissolution instead of charring, it now shines the attachments by burnishing, instead of electro-polishing. Burnishing, a method used by both orthodontic manufacturers and jewelers, not only does not remove metal, but it actually compresses it, hardening its surface. According to ASM’s Metals Handbook, vol. 5, Mechanical finishing, burnishing’s “smooth action achieves consistent and reproducible results. Very high tolerances are maintained even with fragile parts, and very high quality surfaces are achieved”. Examine the samples, and compare them with your new attachments! Details? Visit www.OrthoCycle.com
___.*We will add 90 more attachments, if you could provide information indentifying another dental recycling company which has been awarded both ISO 9001-2000 and CE-Mark certification by a reputed institute for dental materials. Valid till 04/31/04

Nuestro regalo para usted por el Año Nuevo:
10 brackets bondables o 10 bandas con tubos GRATIS, a su eleccion*.
Envienos un ejemplo usado y su direccion, o indiquenos la marca, tipo, tamaño de ranura y diente, por correo, correo electronico o por fax.

___.Como fue mostrado en la edicion de Marzo del 2003 del J. Clinical Orthodontics, el reciclaje de Ortho-Cycle recientemente ha tenido un gran avance: ademas de remover el adhesivo por disolucion en lugar de quemarlos, ahora los aditamentos son brillados por un proceso de bruñir, en vez de electro-polizarlos. Methodo utilizado por ambos manufacturadores orthodonticos y joyeros, el proceso de bruñimiento no solo evita remover el metal ademas lo comprime, endureciendo la superficie. Conforme al ASM's Handbook, volume 5, el acabado mecanico de bruñimiento produce" una accion suave logrando resultados consistentes y reproductibles. Tolerancias muy altas son matenidas aun en partes fragiles, y muy alta calidad de superficie es obtenida".
___.*Nosotros añadiremos 90 aditamentos mas, si usted nos provee informacion indicandonos sobre otras compañias de recyclamiento dental que hallan sido reconocido con las certificaciones ISO 9001-2000 y CE-Mark por un reputable instituto de materiales dentales. Valido hasta 04/31/2004