___.While 2005 has been for many an “Annus terribilis” (witness the ravages in Florida caused by the hurricanes), we suffered less than those who lost so much).
___.We might even consider ourselves lucky: some thirty years ago, Ortho-Cycle was the shy maverick which was trying to make a buck by rendering the relatively few orthodontic attachments more affordable. Today fixed appliances have conquered the world. At that time, there were just a handful of attachment manufacturers; today, there are tens of them, and the quality of their products has increased substantially for the benefit of a growing constituency. More and more people now dare to smile having their health improved in the process.
___.Our unique, eco-friendly procedure based upon polymer dissolution, followed by metal burnishing, has secured us the certifications ISO 9001-2000; 13485: 2003, EN 46002: 1996 and CE by the foremost authority in the field, the Scandinavian Institute of Dental Materials. Besides growing the number of our US customers, we have expanded our operations in more countries benefiting from capable agents. Praised by professors T. M. Graber and M. Kuftinec at his 75^th anniversary (Insider’s March issue), Dr. Matasa has been invited to speak in several countries, starting with the AAO’s Annual Meeting in San Francisco and the WFO’s 6^th International Congress in Paris, followed by engagements in Lithuania, Latvia, Poland and Romania.
___.The “Insider” has published many new articles of interest to specialists (www.orthodonticmaterials.com). Thus, in March one can read, aside from the anniversary prizes, “To have great composites, we’ll have to look ...down” (Like Molière’s Would-Be Gentleman, dentists have used for decades bis GMA, not knowing that this is a step toward tomorrow’s molecular rod-based monomers)
___.In June, “Are the costly and complex testing machines irreplaceable?” (A review of the devices we have developed to measure slot width, bond strength, ceramic impact resistance, elastomer maximum elongation, friction, etc), and “A simple bond strength testing device and... the Trommsdorff Effect” (Design principles known since antiquity led us to apparatus capable of demonstrating that adhesives, while still fluid, can gel unexpectedly fast, losing their penetrating ability).
___.In September, “Resin-based composites. Today” (A review of dispersion-strengthened-, particle and fiber- reinforced-, laminar-, sandwiched- and nano-composites used in dentistry and orthodontics) and “Resin-based composites. Tomorrow” (Nano-tubes as fillers and liquid crystal as matrices and fillers) and “Orthodontic recycling: is it risky?” (A risk comparison and an account of medical recycling in different countries).
___.Our December articles may well be as interesting:: “Today, titanium brackets lack appeal due to their appearance and bond strength” (Advances in rendering these better looking and more adherent) and “Acrylics-solvent: a promising interaction” (Added to adhesives, volatile solvents can lead to stronger bonds).
___.Let us hope that 2006 will be a better year for everybody!.

Today, titanium brackets lack appeal due to their
appearance and poor bond strength
An East-European technology may soon change that

Abstract
___.The best hypoallergenic (if not totally biocompatible) titanium attachments available today have limited success due to high cost, a matte-gray look and poor bonding strength. However, new technologies will solve these problems and cut raw material costs in half. This is good news for a profession that has had to choose the material for its attachments between weak plastics/composites, nickel-leaching stainless steel, and too hard and brittle ceramics.
___.In a less known country, the Republic of Moldova, a recent advance has led to a manufacture of titanium brackets that are not only pleasant to look at, but show a good potential for increased adhesive retention.
What causes titanium’s problems?
___.The ninth most common element in the earth’s crust, titanium can be found as high quality titanium dioxide in easily mined ore. Unfortunately, this oxide is difficult to reduce to a metallic form and its processing into pure titanium is a very energy intensive process. The first commercially useful process for producing titanium, the Kroll process, was adopted in the United States by 1947. Since then, few significant improvements have been made, until recently. The U.S. Department of Energy and the Defense Advanced Research Projects Agency (DARPA) are both investing to produce titanium at lower costs, as are many other agencies and firms throughout the world. The goal of a 50% percent cost reduction within the next several years appears to be attainable, rendering the metal more promising than ever.
___.Among its alloys (there are several thousands known, of which over 50% have been produced commercially over the past three decades), the most common is Ti6Al4V (over 50%). Corrosion resistant, relatively biocompatible and strong, it can be further strengthened by adding small amounts of nitrogen and oxygen. These act as interstitial hardening elements and double the material’s tensile strength. On the other hand, at the high temperatures at which it is processed, an excess of these gases from the air may dissolve in excess into the metal. This makes the alloy brittle and leaves an oxide scale on its surface. As a result, titanium alloys need to be processed in vacuum, a process which, as a difference from other metals, leads to a sponge. After up to three remelting steps in a vacuum or argon environment, the purified titanium sponge is finally converted into a form useful for structural purposes, a compacted ingot. This particular structure has an impact on all its derived objects: while large pieces can be polished to a shine, tiny parts such as orthodontic brackets cannot (hence, the matte look) which in time will become gray. When compared with ceramics, composites and even stainless steel, titanium brackets are unsightly.
Titanium cannot be easily welded, requiring a sophisticated laser technology where protection against oxidation is a must. Not only does the brazing of pure titanium parts requires very demanding conditions, but the welding of non-titanium parts to titanium parts is practically impossible.

The difference is in... emptiness
___.None of the titanium attachments sold today with bases that look like mesh can bond as well as those made of real mesh. According to Dentaurum (Ispringen, Germany), a company that has secured rights on titanium brackets in the US until 2013,¹ the retention required by their bonding surface is difficult to achieve by etching, sand-blasting, shot peening or by depositing small adherent particles on the surfaces. Instead, holes can be bored into this bonding surface by a laser beam. Thus, Dentaurum has expanded its use of lasers from marking brackets to base engraving, claiming ironically that it has developed it to help...bracket recycling.^2,3 The extended quote is shown below.*
___.The retentions or locks required in the bonding surface are produced by laser beams in such a way that these holes, each having the shape of a circular cone, are angled in relation to the plane of the bonding surface to form undercuts. While seen from the above, the surface of such bases (Rematitan, Dentaurum) and Titanium Orthos2™, from Ormco (Glendora, CA, USA), simulate a net, Fig.1 and 2... The empty space under the mesh, so important for the adhesive’s riveting effect, is missing. This can be seen in Fig. 3 where the base of a bracket Titanium Orthos2™ is shown. Contrasted with the Rematitan bracket, which is monoblock, the latter is made of two parts that are welded together. While the wing component is made of the alloy Ti6Al4V, the base is made of pure titanium.⁴ To illustrate the lack of profile (or the even surface) of the false mesh, the bracket has been shown in a slightly angled view. As it can be seen in Figs. 4 and 5, this leads to a lack of under-the-mesh spaces, a fact that translates into less retention.
The “anatomy” of a laser-cut base
___.A detailed description of the use of lasers to provide the locks in titanium attachments can be found in a Dentaurum patent.⁵ According to the patent, to increase the retention of the undercuts, laser beams are directed to the bonding surface at an angle to the plane surface. As the metal is melted and/or vaporized, the beam pressure and/or its own vapor pressure ejects it, generating both recesses (“craters”) and deposits around them. The patent shows SEM images of the mesh-like (or net-like pattern) structure (Fig. 6), a bird’s eye view of a portion of the laser-cut or “sculpted” base (Fig. 7) and a “crater” (Fig. 8). A publicized view (Dentaurum’s “Intelligent” base) is shown in Fig. 9. A side view of the retention area shows the generated peaks and valleys (Fig. 10). It is interesting to note that none of these images indicate inclination of the valleys or the peaks generated by the laser beams in relation to the bonding surface. In addition, reading distances from Figs. 7 and 9, it can be seen that the density of the peaks (or valleys) is about three per each 100 mm.
The Moldavians may have improved it
___.Invited to speak last summer at the N. Testemitanu University in Kishinev, Republic of Moldova, Prof. Dr. Pavel Godoroja, the Dean of the College of Dentistry has asked Dr. Matasa to test samples of titanium brackets of an unknown type.
___.Bond strength. Measuring bond strengths using the apparatus and the ceramic substrate which we have described in a previous issue⁶ and which is also used in the following article, we found that the new bracket shows a peeling strength in the range of 8 kg, at the same level as the other two mentioned above...
___.Such results may not sound exciting, unless one observes that the Moldavian titanium bracket, the base of which is even or flat, has performed well even without the need of the net-like structure (Fig. 11) known to significantly contribute to retention. This can be explained using SEM images of the Moldavian bracket base. Along with a high density of the “craters”, it can be seen that these show a different structure (Fig. 12) than those exhibited by the Rematitan base: a more detailed image of the same area (Fig. 13) compared with those shown in Figs. 7 and 8, shows that in the Moldavian base there are three times more recesses (“craters”) per each in 100 mm of base than these found on the Rematitan bracket.
___.As in the Rematitan base (Fig. 7), the diameter of the “craters” is between 30 and 40 mm: the average size in the Moldavian bracket base is less than half (Fig. 13), allowing thus a higher density.
___.Aspect. In an attempt to improve the appearance of titanium brackets, the Moldavians have succeeded to coat these with enamel, as shown in Fig. 14, where in the first row there are two Moldavian brackets, one enameled and the other not. As in Fig. 11, in the second row there are Titanium Orthos2 and Rematitan brackets.
Discussion
___.It is easy to see that if the otherwise flat Moldavian titanium base would have been scratched or endowed with a profile, its surface area would have been larger and its adhesive retentive ability increased. While not yet disclosed, it is likely that the treatment the Moldavians applied to titanium was also performed still with laser beams but under other conditions.
___.While coating each bracket with enamel may be costly, one should not forget that these attachments are sold at a price, weight per weight, as high as that of gold bullion. Being monoblock surely helps, as it requires less labor than the Titanium Orthos2, which has to be assembled and welded.
Conclusions
___.Some fifteen years ago I showed and left in Moscow some Ormco Mini Diamond brackets, extolling their qualities. To my surprise, after a short time I was asked to examine and test copies made in Russia; I could hardly distinguish them from the originals. Metallurgy has always been a strong point of eastern Europeans, and for decades titanium has been for them an icon of power. Thus, outside Moscow’s “All Russia Exhibition Park”, there is a giant rocket monument made entirely out of titanium!
___.There is no question that titanium will be the future biomaterial of choice, and eastern Europeans want to leave their mark there. Their titanium brackets, which have a potentially better bond strength and are more pleasant to look to them may be only part of what we may expect.
References
1. Sachdeva RCL, Oshida Y, US Patent 5,232,361, 1993
2 Rohlcke FW, Sernetz F, US Patent 5,238,402; 1993
3. Rohlcke, FW, Sernetz F, US Patent 5,326,259, 1994
4. Zinelis S, Annousaki O, Eliades T, Makou M, Metallographic structure and hardness of titanium orthodontic brackets, J Orofac Orthop. 2003, 64 (6): 426-33.
5. Binder F, US Patent 5,944,517, 1999, EP No. 0841877
6. Matasa CG, Are the costly and complex testing machines irreplaceable? The Orthodontic Materials Insider 2005; 17(2): 1-5

Acrylics-solvent: a promising interaction

Abstract
___.Most of the adhesives, sealants, veneers and restoratives, as well as many fixed and removable appliances either contain acrylics or are made of them. While different from each other, all of these can interact at some point, in their processing or use, with solvents which can either improve or damage their properties, depending on the care exerted or the purpose and skills of the clinician or of his or her technician. If controlled, the addition of a volatile solvent to an adhesive has been found to can enhance both wetting and substrate penetration.
Basic notions
___.With the exception of glass ionomers, most of the acrylics used in orthodontics are varieties of methacrylates. Time-tested for their superior resistance to water, these resins in their final stage, i.e. cured, can be either thermoplastic or thermoset. While the former are linear and melt and dissolve, the latter, known also as cross-linked, do not melt (they char and burn instead) and are insoluble. Both types, however, interact with solvents: the former at any stage; the latter, before their polymerization.
___.One of the most difficult to dissolve resins is polymethyl methacrylate (PMMA), known commercially as Lucite, Plexiglass or Perspex. It is used in medicine as “bone cements” or “grouting agents”, in dentistry it can be found in hot- or cold-cured resins. If not previously combined with cross-link-generating polyfunctional monomers, PMMA can be softened with or dissolved in anisol, tetrahydrofuran, cyclohexanone and N-methyl pyrolidinone, as well as in chlorinated hydrocarbons such as chlorobenzene, chloroform, dichloromethane (methylene chloride) and dichloroethane. Special attention should also be given to 1, 3 dioxolane which exhibits a low toxicity (Rat oral LD50: 5000 mg/kg).
___.Once cured, thermosetting acrylics such as the derivatives of bis GMA (or of the polyurethanes used in adhesives and composites), do not dissolve in solvents. In contrast, a temporary presence of the latter just before curing time can be beneficial. It can postpone gel formation and cure, decrease the viscosity of the polymerizing resin and dislocate water from a tooth surface to allow better resin penetration.
Introduction
___.According to D’Arcy’s law which governs fluid penetration, to generate strong bonds an adhesive must show an affinity with the substrates (a small contact angle) and be less viscous. Unless surfactants or coupling agents are used, the first demand cannot be fulfilled (hydrophilic substrates can hardly be wetted by hydrophobic adhesives). The second demand is also difficult to meet, as the adhesive has to be viscous enough to prevent the attachment from sliding. An interesting solution resides therefore in the temporary addition to the adhesive of a highly fluid, volatile solvent which should evaporate before setting.
___.The following, related study, has benefited from the help of Mr. Anton Ficai, Chem. Eng., Bucharest, the 2004 laureate of the Costin D. Nenitzescu* Prize for Chemistry, (Fig.1): his contribution is gratefully acknowledged.
Materials and methods
___.The test supports were 8"-x-8" enamel-coated, commercial ceramic tiles that had been etched for ten minutes with 50% hydrofluoric acid, rinsed and air-dried, office-style. For each test we used ten single lateral upper-incisor brackets with vertical slots (American Orthodontics, 80 mesh; pad surface 22 mm2). .The adhesive used in all instances was Phase II by Reliance (Itasca, IL). Equal portions of 0.05 g of its Part A and Part B were mixed for twenty seconds along with a solvent on a cold slab and then used to smear successively two bracket bases, just enough to cause the adhesive to flow freely when the bracket was pressed against the substrate.
___.The candidate volatile organic compounds capable of dissolving the resins used in adhesives were, in addition to those used commercially in primers and adhesives, i.e. ethanol and acetone, (see Table), ethylic ether (Bp. 34.5^o C), pentane (Bp. 36^o C), and methylene chloride (Bp. 40^o C). The testing of the influence of ethanol and pentane was abandoned following an experiment in which one ml each of these was added to vials already containing two milliliters of dye-added bis GMA. As the poor Brownian movement of their molecules indicate, shown in images taken before and after 24h (Fig. 2), these candidate solvents offer a too poor miscibility.
___.The apparatus used has already been described in a previous issue, and shown as a background in Fig. 1: its principle is shown in Fig. 4. Instead of measuring shearing, a common testing method, we preferred to test peeling, a method widely used by clinicians for debonding as it requires less force. Whenever the tension load is off-center or is not normal to the joint, peeling starts to replace pure shearing. The samples tilt slightly at the moment of rupture and the resultant peel or cleavage loading leads to considerable lower strength.²
___.To test the influence of the solvents, the remaining candidates were added to the adhesive during its mixing. The ratio solvent/ adhesive varied between 5 and 20 ml per the 0.01 g of the combined Part A and Part B. Additional tests were made to see if an “in-office-style” dried ceramic tile could lead to higher bond strength after being smeared with acetone, either as such, or after being added with benzoyl peroxide.
Results
___.In Fig. 5 are shown columns representing the peeling bond strengths, measured in kilograms, which were obtained by testing for each ten brackets, either before and after the adhesive were added with various volumes of methylene chloride, ethyl ether, and acetone. The average bond strength values are shown in blue and their variation with red arrows pointing up and down.
___.In the absence of solvents (controls, #1 and #2), the bond strength did not vary much when measured after 30 min and after 24 h, respectively. For comparison purposes, a control adhesive sample was also used to bond brackets to a ceramic substrate which was previously smeared with acetone, as such, #10, or having dissolved in it benzoyl peroxide, #11, a common initiator.

Discussions
___.Perhaps the first researchers who felt that the adhesive they used (Concise™) was “somewhat too viscous” and that it could be made more amenable to a specific way of bonding (“hastening or slowing”) were Artun and Zachrisson³ who diluted it with the accompanying sealant. Since then, a variety of composites have been launched in an effort to balance the bracket’s drift on a vertical surface and its ability to penetrate both substrates. In some of these, the solution found was to add to the basic adhesive a solvent that would facilitate in its penetration phase, but which will totally volatilize at the bracket’ final placement. While surfactants (strongly recommended⁴) have not yet been added commercially, the presence of volatile solvents is now common, if not in the adhesive itself, at least in the associated primers. As a comparison between Figs. 2 and 3 shows, one of the widely used solvents, ethanol, Table I, exhibits poor affinity for the main ingredient in the adhesive’s resins, bis GMA. This renders it less capable of carrying the resin into the enamel’s micro-fissures and, due to its relatively high boiling point (78.5^oC), it is prone to generate solvent pockets in the cured adhesive. Such disruptions in the polymer’s structure translate into poorer bond strengths.
___.The attempt to introduce new volatile solvents requires intense lab work, especially in the testing of related bond strengths. This requirement can be in part alleviated by substituting the complex and sophisticated universal testing machines with the simple apparatus described above. The results obtained are accurate enough to open the gate for more precise testing.
___.Among the volatile solvents tested, methylene chloride has been found to be too good a solvent, as it exhibits too much affinity for the acrylic and leads to its retention into the adhesive in which it easily generates pockets. In contrast, the addition of acetone and ethylic ether increases the bond strength, as long as it is not in excess. The smearing with acetone of a wet, and then “office-style” air-dried ceramic tile, leads to increased bond strength when compared with the control adhesive sample. Adding benzoyl peroxide in this solvent does not seem to help, #11, as the initiator probably did not have enough time to dissolve and react in the adhesive.
Conclusions
___.The method presented demonstrates the possibility of finding new solvents that may allow the adhesive to combine the benefits of a non-drifting and penetration. Aside from the ethyl ether tested, methyl formate (31.5^oC), halothane (Bp. 50.2^oC), desflurane (22.8^oC) are just a few of the volatile solvents that may help solve the problem. Their vapors, while known to act as anesthetics or soporifics, are released in amounts comparing favorably with sniffing liquid paper correction fluids or PVC contact cements. The modern packaging methods used throughout the industry for volatile products, if properly adapted, should not shorten, but prolong the shelf life of such an adhesive, as it would decrease its free radical activity, which often results in property changes including premature setting.
References
1. Matasa CG, A simple bond testing device and the Trommsdorf Effect. The Orthodontic Materials Insider, 2005; 17 (2): 6-8
2. Koehn GW, Behavior of adhesives in strength testing, in: Clark, Rutzler, Savage, ed., Adhesion and Adhesives, Fundamentals and Practice, NY, Wiley: 120-126, 1954
3. Artun J, Zachrisson BU, Improving the handling properties of a composite resin for direct bonding, Am J. Orthod. 1982; 81: 269
4. Matasa CG, Surfactants Can Improve the Resin Sealing and Bonding of Hydrophilic Substrates, Oral presentation at the 105th American Association of Orthodontics Annual Session, May 2005, San Francisco, California.
5. Matasa CG, Phenomena at the interface fixed attachment/enamel, Oral presentation, World Federation of Orthodontists & 6th International Orthodontic Congress, Paris, Sept 10-14, 2005

Are you interested in the evaluation of a
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___.Suggest a topic, and we will evaluate whether or not it fits into our parameters and expertise. In the past, we’ve received numerous unsolicited requests, and we tried our best to provide the information sought. If the topic is researched and answered to the satisfaction of both parties, we reserve the right to publish the results in our publication: we have done it without interruption or cost for seventeen years.... Our claim that we are only as good as our last issue, has recently enjoyed the appreciation of many luminaries such as Prof. T. M. Graber (who wrote that this independent publication”…shines like a scientific beacon for the orthodontic community,”). Ultimately though, it is up to you, the reader, who judges our efforts in helping you to better understand your tools...