MARCH 2002
1. Plastics, polymers, resins: a necessary evil
___.While no conclusive effect on orthodontic patients has yet been thoroughly demonstrated, the clinician should always be aware to avoid excessive exposure to polymeric products. He or she should also be able to assess their toxicity, as the number of products currently used exceeds by far the testing possibilities of governmental or professional organizations. The principal classes are discussed and their effects are exposed.
2. Do-it yourself detection of leaching polymers
___.All polymers leach: the difference is the degree and nature of the leaching material. Cross-linked and high molecular-weight polymers not only leach less, but also retain better in their tangled network the oligomers, the additives and even the monomers. As the amount leached discolors potassium permanganate solutions, it is possible to use the method to evaluate the amount leached by examining the aura formed around the polymer.
___.Instead of using a spectrophotometer and weighing, this simple method has been used to evaluate a number of polymers. All of them showed some leaching, as witness a comparison with the controls. While the ISO method is so sensitive that it is currently being applied to tap water, the present do-it yourself method proposed is not. Instead of a spectrophotometer and weigh, it uses visual estimation.
___.Applied and adapted to some products used in orthodontics, the method allows picking the least leaching ones.
JUNE 2002
1. Invisalign revisited
Interview with TM Graber, MM Kuftinec,
M Radu and RL Vanarsdall: Are do-it yourself tests really useful?
___.Manufacturers hate to have non accredited researchers evaluating their products. However, only through cooperation between all parties involved, the patient, the clinician, the manufacturer and the investigator, be it governmental or not, can the present ntenable situation be resolved. Indeed, hazardous biomaterials require from the clinician extra measures that may vary from case to case in balancing benefits versus risks, and any help should be welcomed. Do-it-yourself tests should be used, therefore, at least for screening. Otherwise, infringements of Proposition 65 and future, similar laws will continue to grow, while patients will continue to suffer.
2. A leaching test for plastic retainers
___.Based upon principles described in the Insider, March 2002, a modified “permanganate index” was applied to several retainers collected from various manufacturers as well as from neighborhoods drug stores. In order to perform an analysis, the first hurdle was the difference in shape between what was needed for the test and what was supplied. Indeed, although the test requires particles fine enough to expose a large surface area to extraction, the samples were bulky and difficult to pulverize. The measures taken to homogenize and equalize the samples are described.
SEPTEMBER 2002
1. Thank you, FDA, ISO, CE & CDC... for helping us outgrow electropolishing!
___.Electro-polishing orthodontic attachments, especially if as intensive as needed to cover heat’s darkening action, changes the attachment’s physical characteristics. Less noticeable when the attachment is exposed for a short time, the effects of electropolishing can accumulate after several cycles and alter the device. In the first case, after a few cycles the attachment is either damaged during debonding, or retired altogether in favor of another, usually improved type or brand. In the last case it leads to improper treatment.
2. How are manufacturers finishing their attachments?
___.Manufacturers are shining metal attachments by subjecting them to high-energy barrel machines that 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 measuring the surface roughness. There are two ways to reduce surface roughness: by using an abrasive medium to remove metal from the surface, or by burnishing it with a nonabrasive medium The latter procedure has been found acceptable to brighten the stainless steel attachments after adhesive dissolution to a high shine while work-hardening their surface. The parts can be finished to a roughness measuring less than 1 µ/ in.
DECEMBER 2002
1. Since long, Ortho-Cycle provides free information on biomaterials
___.Interviews
___.TM Graber: 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.
___.MM Kuftinec: 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 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.
2. Do adhesives and sealants really seal your bracket pads?
___.I. Corrosion
___.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 traced to crevice corrosion, a phenomenon that leads to a release of harmful heavy metals. By simulating this process with the help of a solution recommended 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, in contrast to mesh. The nature of the alloy plays a major role; no matter if silanated or not, carbon steel surfaces have been found to be insufficiently sealed.
MARCH 2003
1. In search of a better bond
___.Critical analysis of the bonding strength of the current direct bonding pads. There are today a great number of locking systems, among which mesh-based predominate. Long considered to be the best, 100 mesh now seems to be in second place. Most manufacturers are leaning toward a less dense mesh, a trend that is supported by our research (next article). Both mesh and non-mesh bases have also been treated in various ways, that is etched, sandblasted, polymer-coated or sprayed with fine particles of molten metal. Both etching and silanation were initiated by Ortho-Cycle, the first treatment being reported in 1985 and the second even long before 1982.
2. Do adhesives and sealants really seal your brackets pads?
___.II. Surface tension
___.Both sealants and resin-based adhesives are hydrophobic oils, while teeth (hydroxy-apatite) and oxide-covered metals are hydrophilic, repelling oils. In particular, bis GMA, the basic organic ingredient in most sealants and adhesives, exhibits very little propensity to wet the (chromium oxide-protected) stainless steels. By adding suitable surface-active agents to the sealant, the adhesive or the etching gel, or by coating the metal surfaces or the teeth to be bonded with a film of appropriate surface-active agents, penetration of the resins and the ensuing bond strength cannot be but enhanced.
JUNE 2003
Can a simple evaluation of elastomeric ligatures be meaningful?
___.A simple examination of the limit properties of an elastomer (breaking force and maximum elongation) is not enough to judge and even less to predict the in-vivo behavior of an elastomeric ligature, as other, important data are missing. Thus, a 10 days stretching in an aqueous solution containing heavy metal ions leads to a degradation similar to that occurring after 8 months on a shelf in an improper environment (open, and in subtropical temperatures). However, after 8 months (plus the time needed to sell the product) and even after in-vivo use, some ligature rings stand expansion forces of over 3 lbs (1.5 kg). The method used to evaluate the force delivery exerted by a ligature over an arch wire inserted in a bracket is not only simple, but can provide, in conditions simulating the oral environment, reliable data for comparing elastomeric ligatures.
SEPTEMBER 2003
1. Pain-free magneto-orthodontics: a deception?
___.Orthodontists using magnets in their treatment might shy away from claiming that their patients will suffer less pain, although this is true. Because of mechanical limitations (metal fatigue), in normal orthodontics the maximum force is applied at the beginning of treatment, when the tissues are most sensitive to stress. In contrast, the forces applied in magneto-orthodontics are not only gentler, but steadily increase as treatment progresses and after the tissues have become accustomed to the stress. In addition, the calcium ion plays an important role in pain transmission through the lipid bilayer’s pores. While large enough to pass hydrated Na⁺, these pores barely allow the motion of normally hydrated Ca⁺⁺. However, the larger the nonhydrated ion, the more dispersed its own charge will be, and the less strongly it will attract water. This leads to the incongruous situation of the larger the ion, the less hydrated it is and the smaller the relative size of its hydrated form. In other words, only if nonhydrated, or poorly hydrated, the calcium ions have a chance to pass through the cell’s appropriate channels. The next article will try to justify Ca⁺⁺ behavior based upon industrial experience.
2. Water descaling: proof for over-hydrated Ca⁺⁺ hypotheses?
___.Today there are millions of buildings, commercial and residential, government and private, where the deposition of calcium salts is prevented with the help of static magnets. Although several mechanisms to explain the involved the phenomena have been advanced, overhydration of calcium ions stands out. Calcium hydration and the related geometry are variable, according to the number of liganding molecules of water. Magnetic fields impede, to an appreciable extent, ion pairs from approaching one another close enough to initiate a scale-forming reaction. The differences found in medicine may well be explained by the findings in water conditioning, where magnets lead to calcium hydrates whose behavior (geometry and bond strength) differ from those commonly encountered.
DECEMBER 2003
What is hidden behind your bracket’s mesh?
___.Photomicrographs taken at the interface bracket base/adhesive show both gaps and separations at the interface metal oxide/polymer. Because of a layer of chromium oxide covering its surface, stainless steel is hydrophilic. In contrast, resin-based adhesives are hydrophobic: a drop of adhesive placed on a stainless steel mesh takes a long time to penetrate it, if ever. ___.In contrast to common industrial practice, where the metal surfaces to be coated or adhered to are subjected to oxide (rust) removal and priming, direct-bonding attachments are used without any chemical preparation of their surface. Although applying pressure might alleviate the problem, additional pretreatment of the brackets base with coupling agents or surfactants leads to improved interaction with the adhesive.
MARCH 2004
1. Polymers in orthodontics: a present danger?
___.The authorities’ attempt to control the iatrogenic effect of biomaterials may have started in Germany and Japan. The former country is host to ISO’s Technical Committee 106 (Dental Products) that, among others, was the first to impose strict limits on the nickel in dental alloys; in Japan, the same task is carried out by the Ministry of Health. Proposition 65, now law in California, sue not only orthodontic manufacturers (among which TP Orthodontics, Ortho-Organizers, 3M Unitek), but also clinicians’ offices. A chapter in a recent book, Risk management in orthodontics: Expert’s guide to malpractice, entitled “Polymers in orthodontics: a present danger?” justifies the fact that some 10% of the studies published in biomaterial journals are concerned with their noxious effects.
2. Reactive gel entrapment; a new, simple way to test leaching plastics
___.The color fading of permanganate solutions is a time-proven method to measure the purity of many chemical substances. It’s use, however, has never been applied to determine solids leaching or be part of reactive gel entrapment, a method paralleling gel chromatography.
___.The combination of thse two methods allows discriminating dental devices using simple means. While the method doesn’t discriminate between harmless and harmful leachings and the amount and toxicity of the leached compounds may vary from one plastic device to another, it is safe to claim that in all cases leaching is highly undesirable. Allowing at once the visual comparison of many samples, the method can substitute spectrophotometric analyses, which require not only expensive instruments but also highly qualified personnel. The method allows both manufacturers and clinicians to prevent patient afflictions.
JUNE 2004
1. What is hidden behind your bracket’s mesh?
___.II. Wetting: a neglected key to bond strength and durability
___.The agents that enhance the oil-wetting of a water-loving substrate, such as in the case of adhesives used to bond enamel, are not found in common, household surfactants, but rather in gasoline. The difference can be understood with the help of the HLB (hydrophilic-lipophilic balance) system, in which the agents are situated somewhere along a line uniting the extremes, water-loving and water-hating substances, e.g. water and paraffin. The HLB values are related to the contact angle q, to the dielectric constant, as well as to the ionization potential and the polarity of the substances involved
2. Preliminary surfactant screening.
___.Adhesion is a surface phenomenon in which wetting plays a major role. By adding surfactants to various substrates, it is possible to significantly improve bonding strength.
___.While the addition of surfactants may not be readily feasible on adhesives, it may surely bring an edge to advanced etching gels that leave behind, after rinsing and washing, a hardly water-soluble film that has an affinity for the oil-loving resins. An added advantage of surfactant addition is that the gels get even thicker because of its emulsifying action.
SEPTEMBER 2004
Not all latex gloves behave the same
___.Although natural latex is the best product available for price and performance, its litigation potential has caused both manufacturers and users to shy away from it and look for more expensive and mostly inferior substitutes. According to the American Society for Testing and Materials (ASTM), the quantity of latex proteins in latex products can be evaluated by measuring the amount of total water extractable protein, followed by an assay of the protein content. Instead, a simple, standard use of the permanganate index can evaluate the proteins associated with latex. Unfortunately, it has several drawbacks, among which it reflects not only the content of harmful proteins, but also the other oxidizable compounds leached from latex. From the standpoint of technical progress, the above findings constitute a protein-removing process based on oxidation, using instead of sodium hypochlorite or chlorinated water, a solution of potassium permanganate and sulfuric acid.
DECEMBER 2004
Challenges in medical in-situ biomaterial polymerization
___.Bis GMA has been described in the scientific literature as toxic, cytotoxic, mutagenic, carcinogenic and oestrogenic. This study suggests a monomer of which the starting materials and syntheses are known, similar products being already commercialized. As their structure approaches that of some natural products, the involved health risks should be reduced. Although the synthesis of these monomers appears to be reasonable, the necessary testing and the launching of products require involvement of superior means.
MARCH 2005
To have great composites, we’ll have to look ... down
___.Sources of rigid monomers are around the corner. These can be selected not to derive from phenols or contain aromatic (benzene) cycles, but from the more nature-related, saturated cyclic compounds. The conversion of such molecular rods into copolymerizable methacrylates can be successfully performed today by standard chemical procedures.
___.The bulk of mechanical loads in natural materials is carried by polymer fibers such as cellulose (wood and plants), collagen (animals), chitin (insects, crustaceans) and silks. Most of the materials of a living organism are composite materials, and many of them are nanocomposites. In humans, important examples are the collagen fibers in skin and tendon. The polypeptide molecules form tightly coiled helices that behave like rigid rods. Nature’s strength is its ability to combine different materials with different properties in such a way that they are tailor-made for individual applications. Sooner or later, we will be able to copy it. Nanofibrils are currently being extracted from natural plant materials and subsequently combined with various polymers to form nanobio-composites.
JUNE 2005
1. Are costly and complex testing machines irreplaceable?
___.Our generation seems to worship sophisticated equipment and methods, often willingly ignoring simple means that might give fast, if not more accurate, at least indicative results. While in most instances complex machines can perform in minutes what take us days, the reverse is also true. In addition, advanced technology comes with a price that we may not be able to afford.
___.Unless we also take into consideration simple means to solve our problems, we are condemned either to be led by machines or to abandon promising ideas due to lack of funds. Sophisticated equipment should be used wisely, and only after we have exhausted the simple means available. Simple means may not provide accurate measurements, but can often be used to compare. But what are measurements, other than comparisons with established standards?
2. A simple bond-strength testing device and... the Trommsdorff effect
___.When measuring bond strengths at different handling times, the strongest bond is reached when the composite has been applied immediately to the bonding surfaces. Even though the adhesive may still seem fluid, its ability to bond decreases rapidly over time. After an induction period, the polymerization inhibitor contained in the monomer is depleted and the free radical reaction becomes autocatalytic. The pre-gel structure, in which viscous flow behavior predominates over elastic behavior, converts into a post-gel structure, in which the elastic behavior predominates over the viscous flow behavior.
___.This rapid increase in molecular weight as conversion progresses is known as the Trommsdorff effect or gel effect. With further polymerization, the semi-solid’s contraction and flow decrease, while its stiffness and stress of the semi-solid increase. As this translates into a polymerization contraction, known to generate marginal and interfacial failures of bonded restorations, in dentistry there is a strong trend toward a “soft start” polymerization, that is, postponing gelation as long as possible.
SEPTEMBER 2005
1. Resin-based composites. Today
___.Composites in medicine, dentistry and orthodontics are as different and varied as these are indispensable. Because the demand is great anyway, too few manufacturers are trying to get out of the “me too” syndrome, that is manufacturing all-too-similar products. New ventures require a steady and intensive effort that may offer uncertain returns. As there are few related complaints, clinicians are resigned to the present situation. With laws expanding California’s “Proposition 65”, wherein the clinician is considered responsible for the materials (s) he or she uses, the situation would have to change.
2. Resin-based composites. Tomorrow.
Nanoreinforcers will become the matrix!
___.There are already on the market several composites containing nanofillers: hopefully we will soon have others in which the matrix will be based on liquid crystals (LCs). Once the difficulties to have these matching composites (which have been were entrenched for decades) are removed, the problem may be, once again, related to their health risks. Indeed, related articles and patents reveal that almost all the research is being done on polynuclear aromatic (benzenic cycles containing) compounds which are carcinogenic. In contrast, steric hindrance, the most important LC generator in nature, is harmless and can be used instead to provide the necessary molecular rods. Notably, there is already a multitude materials (e.g. carbohydrates) that can be transformed into suitable monomers.
DECEMBER 2005
1. Titanium brackets lack appeal and have poor bond strength, but…
___.Titanium is now, and will be in the future, the biomaterial of choice, and eastern Europeans want to leave their mark on it. Measuring the bond strength of a sample of Moldavian titanium brackets, we found that the new bracket shows a peeling strength in the range of 8 kg, at the same level as those made by Dentaurum. This is remarkable in view of the fact that the Moldavian titanium bracket, the base of which is even or flat, performs well without the net-like structure Dentaurum uses, known to significantly contribute to retention.
___.This can be explained using SEM images of the Moldavian bracket base. Along with their high density, these “craters” (recesses) reveal a different structure than those exhibited by Rematitan bases: a more detailed image of the same area shows that the Moldavian base has 3 times as many more recesses per 100 mm of as these found on the Rematitan bracket. In an attempt to improve the appearance of titanium brackets, the Moldavians have succeeded also in coaing them with a whitish enamel.
2. Acrylics-solvents: a promising interaction
___.Most of the adhesives, sealants, veneers and restoratives, as well as many fixed and removable appliances, either contain acrylics or are made of them. Though different from each other, all can interact at some point, in their processing or use, with solvents that can either improve or damage their proper ties, depending on the care exerted or the purpose and skills of the clinician or technician. If controlled, the addition of a volatile solvent to an adhesive has been found to enhance both wetting and substrate penetration.
___.The method presented demonstrates the possibility of finding new solvents that may allow the adhesive to combine the benefits of nondrifting 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; it would decrease its free radical activity, which often results in property changes, including premature setting.
MARCH 2006
Against all warnings, dual composites could and should be stored in close contact!
___.Knowing how and when to mix and not to mix reactive pastes proves to be rewarding. If you mix them well, you reach the composite’s ultimate strength. If you prevent them from mixing during storage, you can simplify their application. The belief that a burst of free radicals could, without further mass agitation, travel throughout the mass of a composite and cure it has been found to be both unjustified and counterproductive.
___.As shown by industrial products already on the market, it is possible to store interreactive, viscous components in close contact with each other. A simplified composite delivery, wherein a single, combined paste is used instead of 2, would render the chemically cured composites as attractive as today’s preferred photochemically cured ones. This would not just save money, but should lead to improved bonding and less messy applications.
JUNE 2006
1. Orthodontists are luckier than ocularists ...
___.Although the use of potassium permanganate to detect the leaching of acrylics has already been used by the FDA for the “determination of potassium permanganate oxidizable extractives,” the method described is tedious and highly specialized, and it requires an absorption spectroscope and special chemicals for comparing colors. In contrast, the method proposed is simple, using common chemicals. Having devices leaching in the mouth instead of the sensitive tissue around an artificial eye should be a comfort for orthodontists.
2. Mending acrylic attachments
___.Acrylic attachments are repaired or reunited with the help of acrylic adhesives. The possibility of getting good results by replacing the higher temperature and pressure cure with a cold cure has its limits. Tensile tests of samples duplicating the attachments have shown that as far as bonding is concerned, the use of the same materials as bonding agents does not give satisfactory results. In the most important case, the bonding PMMA to PMMA, using the basic powder and liquid PMMA, commonly designed for making plates, dentures and retainers, proved to be significantly weaker than the one made specifically to repair them. For matching surfaces, the use of gel cyanoacrylates is appropriate; their acceptance in medicine predates their use in industry. When it comes to filling spaces, however, cyanoacrylates’ bond strength decreases considerably. To a certain degree, that when facing lower strains, orthodontic adhesives based on cyanoacrylates can successfully be used.
SEPTEMBER 2006
1. Recycling now has general support
___.Started at a time when attachments were soldered on mesh or perforated bases by a handful of companies and “mini” or preadjusted brackets were just a dream, Ortho-Cycle has succeeded in offering its recycled attachments not only to major universities and well-known specialists, but also to countries where orthodontics is still in the cradle.
___.Interestingly, Ortho-Cycle’s business suffers today far less from the other recyclers’ competition than from myriad of new, poorly manufactured brackets that flood the market.
2. Riding the wave ...
___.Cautious at first, orthodontists have caught on fast! Medicinal practitioners have used and reused their instruments for millennia. Mass-production of medical devices has changed that. By the mid-’70s, when we started orthodontic recycling commercially, this activity was low-key, to be transformed later into a dirty word by manufacturers. But starting in the early ‘80s, universities and practitioners alike began, to announce findings favorable to recycling. Today, orthodontic organizations support the trend as being beneficial for their constituency as long as the advances in knowledge and analyses made by various government organizations are followed.
3. A very brave man, by Norman Wahl, DDS, MS, MA
___.Modesty obliges us to refrain from presenting a eulogy of the Insider’s editor from the author of the ongoing series “Orthodontics in 3 millennia” in the American J. Orthodontics and Dentofacial Orthopedics ...

Are nonmetal reinforcements acceptable?

Introduction
___.Percentagewise, orthodontists may well be the biggest consumers of metals in medicine. The most-used alloy, stainless steel, contains nickel and chromium, elements well known to generate health problems. Aside from the visible signs of corrosion that we have presented for years, the tests suggested by ISO for accelerated corrosion in the mouth are quite revealing. The addition of an gelling agent to the recommended testing solution, along with a reagent that evidences by its change of color the presence of specific ions,¹ shows that common attachments release significant amounts of these alloys, Fig. 1.
___.In contrast to metals, some ceramics and specialty polymers are not only biocompatible but, strength per weight, even stronger. Their composites are economic and exhibit both translucency and good bonding properties. Ease of repair lends them to laboratory or chairside fabrication. Some may even be repaired intra-orally without the risk of modifying esthetic or mechanical performance. As a result, fiber-reinforced composites (FRC) are gaining increased application and popularity in dentistry.
___.The fibers of liquid crystal polymers (LCP), the strongest synthetic materials known, have not yet penetrated the field (their incredible properties have already been presented in several previous issues of this publication^2,3, today’s orthodontists have to chose between polyethylene and glass fibres.
___.Introduced to orthodontics years ago by CJ Burstone and A J Goldberg, reinforced composites containing glass fibers have been the topic of two presentations at the recent AAO Annual Meeting in Las Vegas,^4,5 while the high-density polyethylene fibers-based, Ribbond™ composites were exhibited by the semi-permanent AAO exhibitor, N Rudo. The latter material has successfully been used in fixed orthodontic retainers, space maintainers, post-orthodontic fixation devices and splints.⁶
___.Although FRC have been widely used in prosthodontics,⁷ their potential is still not adequately recognized in orthodontics, despite a number of encouraging articles.^8-14
___.In what follows we will focus only on the prosthodontist favorite FRC.
___.Glass-fibers composites: generalities
___.Short or chopped glass fibers are commonly used for artificial teeth, crowns, inlays, onlays and veneers, while the longer varieties are used for archwires, retainers, space maintainers, splints, bridges and temporary bridges before implant work. The related orthodontic anchorage can be applied either buccally or lingually.
___.Fiber-glass is currently sold in bundles called strands, roving or yarns.* Less investigated today, composites based on fiber-glass cloth have many additional uses. Although thin glass fibers (filaments) are quite strong, they are also highly susceptible to damage. On the other hand, acrylics, the most-used polymers in orthodontics, are known to be water-resistant and versatile but not so strong. The combination of these two components, however, has resulted in an uncommon synergy. Stronger than could have been foreseen, the “ceromer” composites, however, are plagued by low fracture toughness and poor resistance to crack propagation.
___.Currently on the market are several FRCs based on pre-impregnated glass fibers: Targis/Vectris™ (Ivoclar/ Vivadent (Schaan, Liechtenstein), Enamel Plus™ (Micerium, Avegno, Italy), Sculpture™/FibreKor™ (Jeneric/Pentron, Wallingford, CT), belleGlass™ (Kerr/Sybron, Orange, CA), Artglass ™ (Heraeus Kulzer, Hanau, Germany) and EverStick® ( Stick Tech, Turku, Finland).
___.Structurally, fiber-reinforced composites are similar to those commonly used as restoratives or adhesives: instead of particles, the filler is made of fibers. The resin matrix, aside from its role as carrier and protector for the filler, must also has to act as a load-splicing medium, a fact requiring an excellent affinity and wetting for its inorganic partner. For this reason, silanation must be fresh enough, an important condition for coupling activity.
Materials and method
___.The fibers selected were from Jeneric/Pentron (Fibrekor system) that comprises a composite similar to orthodontic adhesives (Sculpture®) and a choice of glass fibers that are silanated and coated. The viscous layer is probably made of a standard mixture of bis GMA/TEGDM with a polymerization inhibitor and a light-activated initiator. To protect from premature curing, the fibers are kept between plastic sheets. Asin any light-curable composite, these coated fibers can be hardened by either light or heat.
___.For testing purposes, the system’s original composite, Sculpture™, was replaced by the adhesive Phase II (Reliance, Itasca, IL). The fibers selected were clear FRC 2K, each bundle containing some 2000 individual glass fibers. For all experiments, 5 bundles of each were tested.
___.The tensile-strength testing installation is a simplified version of the systems previously used,¹⁷ the difference being that stainless steel balls ( .032 in) and lead weights had to be used instead of water to counterbalance the tensile forces measured (Fig. 1). A continuous, but interruptible flow of stainless steel balls was poured through a plastic funnel providing a gradual and controlled weight increase.

Fiber ends embedding. In most instances, the attempts to hold the slippery fibers with any type of clamps failed. In another attempt, the endsof the fiber bundles were inserted into blobs of adhesive Phase II (Fig. 3). Even then, some of the adhesive composite in the vice, the blobs had to be protected against breakage with pieces of lead sheeting (Fig. 4).
___.As in some tests the adhesive blobs broke even while protected by lead, a last attempt was made to insert them in a low fusing metal. Poured into silicone-made molds (Fig.5), the Wood alloy -type used¹⁵ wetted and embedded well the adhesive blobs ending the fiber glass bundles. An image of the plastic and low fusing metal immobilizing the ends of a fiber bundle while tightly held in clamps is shown in Fig.6.
___.Bending tests. Although the glass fiber bundles could be bent at will, the polymerized glass fiber bundle easily cracks (the polymer is croslinked/ tridimensional). To determine the effect of inadvertent bending, a group of cured bundles was subjected to a 30^o bending and then compared with uncoated or uncured and cured or continuous (unbent) glass fiber bundles (Fig.6).
Results
___.Before being subjected to curing or after dissolving the coating in acetone , the fiber-glass bundles showed tensile strengths as low as 4 kgf In most cases the broken bundles appeared to have been cut near the holding area.
___.In contrast, the strength of the cured, continuous and unbent fiber glass bundles can reach 50 kgf (Fig.6). Such large forces, along with the low coefficient of friction of the fiber, render measurement of their strength quite difficult.
___.Bending the cured fiber glass bundles leads to a considerable loss in tensile strength which can vary within a large range. Thus, controlled bending at 30^o of 5 cured bundles has led to breakages within 15 and 25 kgf, with even lower values expected.
Discussion and conclusions
___.Many orthodontists seem addicted to the use of metals even in situations where ceramics or polymers are a better choice. To this writer, the use of a combination of the latter in orthodontic retainers (fixed and removable), space maintainers and splints are a better choice. Using reinforcing fibers for attachments or repairs presumes to understand their behavior well, which sometimes may be surprising.
___.From these self-explanatory experiments it results that FRC devices can provide sufficient resistance if properly arranged to withstand the breaking forces. Although metals are more uniform in their responses (anisotropic), FRCs do not corrode nor leach heavy metal ions and can provide better bonds to a variety of attachments.
___.A major problem, however, is the fact that in FRCs the two components, glass and polymer, do not match in properties: one is water-loving, the other not. The first can be flexible, the second is rock-hard. The technical answer to this odd couple is the coating of the latter with a (supposedly) monomolecular coating (silane). This layer may not perform properly: if not enough, it will be weaker. If in excess, it forms oily layer islands that rather opposes than contributes to bonding. In addition, the coupling agent has a limited shelf life requiring the FRC ingredients to be bonded with other substrates to be checked for shelf life.
___.In the case of the glass fiber composite tested, the main issues found to pose problems were the slippery nature of their joints and their sensitivity to bending.
___.The first problem, which may not be worse than that posed by metals requiring presand-blasting or etching, requires only proper curing, an accomplishment not always possible when using light. None of the bundle ends slipped out of their adhesive ends; the latter broke, but did not slide.
___.Sensitivity to bending leads to breakage of the binder, an essential reinforcement. The acrylics used are highly crosslinked, and the 3D network provides strength only if continued. If the reinforcement breaks even partly, the homogeneity of the composite is compromised as it loses strength according to the degree of bending/damage.
___.In some uses, the finesse of the work and the friability of the cured FRCs could lead to disappointing results. However, with patience and understanding of the above phenomena, FRCs should become a strong alternative to their metal counterparts.
References
1. Matasa CG, Heavy metals release: a do-it-yourself test World J Orthod, 2003; 4: 348- 357.
2. Matasa CG, Resin-based composites, tomorrow. Orthod Materials Insider 2005; 17 (3): 3-7.
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