5. Prevention
_____Avoiding treatment problems requires a multifaceted approach, from patient and parent informed consent to predicting what can go wrong. What follows does not attempt to establish protocols or proper patient management, but calls attention to what could generate problems.
_____5.1 General measures
_____Recognizing the problems. Too few clinicians are investigating or at least asking questions about the alloys used in their attachments. In Germany, both composition and processing have to be made public. The variety and number of patients increases, and so does their general exposure to metals. As it is performed today, dentistry compounds the problem. Thus, a recent study was performed in Norway on almost 300 patients in their forties who, after complaining about muscle and joint pain, fatigue and memory problems, were patch-tested for material-related ailments. About 23% were found positive to gold, 28% to nickel, 14% to cobalt, 9% to palladium and only 6% to mercury.1 While seldom talked about, orthodontic iatrogenics has materia technica problems.2-5 Thus, in Seattle, out of 21 children who received an early orthodontic treatment, six complained about a broken wire or bracket, another six about gingivitis and three about staining and calcification.6
_____The sources for problems are multiple: accidents, poor care, errors in treatment, defective attachments, and improper materials. Added to the latter should be the background-population exposures that are known to lead to impairments in attention, memory, learning, social behavior, and IQ. Unfortunately, only few of the three thousand chemicals produced in highest volume have been adequately tested for their effects on the developing brain. Books such as “Toxic metal syndrome. How metal poisoning can affect your brain”7 have their supporters. Chromium, nickel, manganese, silver, vanadium, molybdenum cobalt and even iron are all on the US Occupational Safety & Health Administration (OSHA)’s toxic metals list.8 Transitional elements are known to combine with the ligands from our tissues forming new compounds that are not recognized by our cells: the process leads to immune disorders. In contrast, heavy metals continue to be extensively used in the orthodontic treatment, and it is unlikely that alternative materials such as plastics will ever substitute them. In this situation, the clinician has to defend his patient (and himself against suits in court) by providing proper instructions and warnings both orally and in writing, by thoroughly following the accepted treatment standards and by selecting the least hazardous devices made of the highest quality materials.
_____The law. The alloys used in orthodontics comprise several transitional elements; see Chapter 3.2, the outstanding mechanical properties of which are associated to health risks. In Europe, the Council Directive 93/42/EEC of 14 June 1993 states that products which come into direct and prolonged contact with the skin, e. g. earrings, watch straps or zippers, may not release greater than 0.5 microgram/cm2/week, and that nickel release from coated products will not exceed this level after 2 years of normal use. Although the level of 0.5 microgram/cm2/week is one below which a minority of nickel-allergic subjects will react, it is not safe in every nickel-sensitive individual. This level of nickel release is currently exceeded by many nickel-containing alloys and jewelry items that are made from high-sulfur stainless steel.
_____Proper training. The potential for iatrogenic damage to the teeth and supporting structures has increased, as has the numbers of patients treated by specialized and general dental practitioners.9 Performing orthodontic treatment in patients presented with history of allergy is not frequent, but still not unusual. It has been considered therefore that it is absolutely necessary that the orthodontist realizes the possibility of patient’s hypersensitivity towards the various orthodontic materials.10
_____Unfortunately, related defensive courses at graduate and postgraduate levels or during clinical assistantships are scarce, and those who should teach the patients often lack the proper training. The clinician should exercise symptom profiling before treatment and be aware that potential metal allergy has been found to be common in patients with various diseases. To mention a few, these are skin diseases (psoriasis, eczema), autoimmune diseases (multiple sclerosis, thyroiditis, Sjögren’s disease) and gastrointestinal diseases. Many patients with symptoms of profound fatigue of unclear etiology (autistic disorders, chronic fatigue syndrome, myalgic encephalitis or multiple chemical sensitivity) often suffer from metal hypersensitivity induced by dental metals. Information regarding previous allergic reactions, reference of the patient for epicutaneous patch-testing and modification of the treatment plan are important components of the proper management of such patients in the orthodontic practice. The practitioner should possess a basic understanding of the occurrence rate, sex orientation and symptoms of allergy to nickel, and should be familiar with the best possible alternative modes of treatment, to provide the safest, most effective care possible in these cases. Practitioners should be aware that symptoms of nickel allergy may closely mimic those of typical gingival changes during orthodontic treatment of circumpubertal children.11
_____Metal sensitivity testing. Nickel allergy is a cell-mediated immune response. The most common method to the test patient’s predisposition to specific allergies is placing the substance on the back of the patient.12 After 2-3 days the reaction is evaluated: the test is positive if the skin is inflamed and red. Since the allergy-causing substance is placed directly on the patient’s skin, a worsening of the patient’s allergy may appear following the test. The other disadvantage is that irritative substances will cause toxic reactions on the skin. This reaction is difficult to distinguish from an allergic one as false-negative reactions are common. It is important to distinguish between toxic effects and immunologic effects of metals, drugs and environmental chemicals. Toxic effects can occur after single exposure to relatively high concentrations and affect every exposed individual. Allergic effects usually occur following chronic exposure to a low concentration of the substance and only in some exposed people. This susceptibility to react adversely to metals is inherited. Some people have a highly effective system of detoxification, others a less effective system; the former tolerate a relatively high level of accumulated toxins, while the latter are sensitive to even a relatively low level.
_____As patches may lead themselves to sensitizations, other tests have been suggested. Thus, in vitro assay using peripheral blood have been suggested. A first test measures both T cell proliferation and cytokine secretion profiles,13 while a second one measures the reactivity of white blood cells to a series of metals. Known as MELISA® (Memory Lymphocyte Immuno Stimulation Assay), the test starts from the premise that we have two types of memory in our body: one in the brain and another in our immune system. Any previous encounter with foreign or “non-self” substances will be remembered by the white blood memory cells that circulate in our body: when they encounter antigens they remember, they will rapidly try to destroy what they see as a foreign invader. The test is performed by placing a range of metals (whose choice is helped by information from a pre-screening survey) into contact with white blood cells and monitoring the reaction. Blood arriving at a MELISA® lab is put into contact with a range of suspect metals. The sensitized (allergic) person’s lymphocytes will enlarge on contact with the offending metal, while for non-allergic person’s the lymphocytes will remain the same size.14
_____5.2. Attachment testing
_____Device’s integrity. There are three ways and some ten stainless steel alloys to make orthodontic appliances. While after half a century of development, the design of the basic, metal-made orthodontic devices has reached a consensual agreement which is respected all over the world, the manufacturing procedures can be different, as their microstructure can reveal.
With minute differences and few exceptions, a multiple tube, a band or a bracket will look very much alike, no matter in which country it is made. This has led to the situation that a clinician who uses only one brand and type is often unable to distinguish the brackets he himself has ordered, unless these are marked. As the demands for precise dimensions and angles as well as the needed labor have, shape deviations from standards occur. In all industrial products, quality inspection is performed “statistically”, i.e. out of a thousand pieces, only ten to maximum a hundred are thoroughly analyzed. Despite the fact that in most cases each of these items has been assembled manually, if the verdict of the “statistical inspection” was positive, the remaining, un-inspected 900 or 990 items are sold “as is”.
_____The lack of proper inspection has led to the release of highly defective brackets such as that were soldered together, others having untrimmed bases and others with two superimposed ones. Such defects have been exposed by Ortho-Cycle Co. to the profession in several publications in several languages.14-17 In addition, other shape defects can be inflicted by improper recycling: important among these are the metal’s removal through electro-polishing and its weakening through exposure to temperatures within the sensitization range.18
_____Both clinical demands and aesthetic criteria require devices exhibiting high strength, the basic recommendation regarding shape being “the smaller, the better”. This is not easy, as in some cases it may bring health-related problems. Indeed, it is often difficult to match ideal properties by the same material. An example is the stainless steel used to make direct bonding brackets, as it will be shown below.
_____Metals’ microstructure. Attachment’s metallographic analysis can reveal strength, corrosion resistance and deficiencies. For the purpose, several direct bonding brackets were sectioned, polished brackets and then electrolytic ally etched with a 10% solution of oxalic acid. Their surface was analyzed with a video-microscope, Fig. 5.1, and photographed with a metallurgic microscope. The procedures used and the reading of the micrographs were done in agreement with the common industrial practice,19 and the structures were correlated with the existing information.20, 21
_____Such micrographs are indicative of not only the alloys’ structure, but also of the quality of their joining materials or of the brazing method used. Thus, a 200x micrograph of the brazing area of a GAC AccuArch bracket indicates that the silver-based alloy used wets well both stainless steel substrates, i.e. the Microloc® base and the austenitic bracket, Fig. 5.2
_____In the bracket body, an ideal austenitic structure, without outstanding grain boundaries, has been found at 100x in a Rocky Mountain Bioprogressive® bracket made of AISI 304 steel shown in Fig. 5.3a & b. Another bracket from the same company but from the Mini Taurus® series has shown both inclusions and small grains. Enlarged to 250 xs, the micrograph showed also pores, the matrix being a mixture of austenite with ferrite, Fig. 5.4.
_____While the steel was not identified, it was obvious that the attachment was made by injection molding. The same structure but with a twist was found in CEOSA (Madrid) Bioline® bracket. Using a higher magnification, 450 xs and the Murakami etchant, Fig. 5.5 it was possible to detect a parallelism of the two phases, proof that the brackets were cut from a cold drawn tube and made of duplex steel, probably 2205.
_____A bracket from Unitek, Unitwin®, Fig. 5.6, has shown, at 100x magnification and after being etched with oxalic acid, traces of chromium carbide precipitation. Another line from Unitek, Dynabond®, made of the same steel and etched and analyzed in the same way has shown a similar structure, Fig. 5.7. An American Orthodontics Triple Action® bracket made of the same steel, Fig. 5.8, has shown a marked grain separation and carbide precipitation.
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_____Two Ormco brackets, one from the Diamond® and the other from the Mini Diamond® series were made of different steels. The first one, made of AISI steel 303 shows austenite unpurified with carbides and traces of sulfur films, Fig. 5.9. The “mini” bracket showed martensitic formations with small grains and inclusions, typical for the steel PH 17-4, Fig. 5.10. One of the microstructures of two “A” Co. Standard Twin® brackets proved to be the most interesting: while the first showed large grains, typical for a cast bracket (made of AISI 316 or 316L), Fig. 5.11, the other showed a gap under the slot, Fig. 5.12. Typical for casting, the gap indicates an abrupt cooling due to the molten metal’s contact with the mold.
_____The photomicrographs obtained above have been well corroborated with the following data that evaluate the devices’ micro hardness, a measure for strength.
_____Metal’s hardness. In metallurgy, the testing of alloys requires specific, identical samples having precise dimensions that are then typically pulled with universal testing machines to provide tensile properties such as proportional and elastic limits, as well as yield- ultimate- and breaking strengths. For minute and multi-component devices such as brackets, such testing is not feasible: fortunately, as tensile strength is proportional with hardness, the latter can instead be used.
_____To withstand torque, brackets should have strong enough tie wing walls: to have “mini” brackets, however, these walls have to be made thinner. Unless stronger steels are used, the metal will creep, enlarging the slot. Stronger steels are made by interfering with the steel’s homogeneity, i.e. using purposely foreign metals-added martensitic steels, instead of the austenitic ones. This addition should lead to galvanism between the steel’s components, to a higher susceptibility to corrosion. To test the strength of the alloys currently used, twelve brackets, standard size and “mini,” have been embedded in acrylic, Fig. 5.13 and subjected to a microscope provided with a calibrated diamond indenter: the longer the length of the indentation, Fig. 5.14, the softer the steel.
_____The tests confirmed that the “mini” brackets tested were not made of the corrosion resistant austenitic steels, as it will be shown below, and that the two demands, high strength and corrosion resistance,22, 23 are seldom met, Fig. 5.15.
While shape and mechanical strength are important for the proper behavior of an attachment, their combined impact is by far lesser felt than corrosion, as it will be discussed below.
_____Corrosion susceptibility. In orthodontics, the number one cause for ailments caused by materials is metal corrosion, the main culprit being the nickel released. Metals are attacked by chemicals in different ways and the metal dissolved in the patient’s body can be considerable. This can be easily inferred if the quantity of heavy metals missing from the heavily corroded bracket shown in Fig. 5.16 is multiplied by twenty, as needed for a full mouth.
_____While in the US there are no specific requirements, in Germany and Japan the analysis of the nickel leached by stainless steel attachments is compulsory and involves flame photometry and atomic absorption spectrometry. In the German test, a sheet of the steel to be used for dental casting is cut to specified dimensions and subjected to an attack by a 50 ml solution of 0.1 moles lactic acid and 0.1 moles sodium chloride for a week at 37o C.24 In the Japanese test25 , a single sample is attacked in similar conditions by 50 ml of 1% lactic acid. The resulting solutions are then tested for nickel content. While the German method applies only to metal samples and does not address attachments, the Japanese test is designed to test individual brackets: any of these which release more than 0.2mg nickel is rejected.
_____To help detect the attachments that can cause problems, we have applied several corrosion tests for stainless steel parts26 following the methods standardized by the American Society for Testing and Materials (ASTM):
· I. G 48 - 97, Test Methods for Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of Ferric Chloride Solution
· II. A262-02ae1, Standard Practices for Detecting Susceptibility to Intergranular Attack in Austenitic Stainless Steels 1.1.3 Practice C—Nitric Acid Test for Detecting Susceptibility to Intergranular Attack in Austenitic Stainless Steels (Sections 15 to 21, inclusive). (Known also as the Huey Test).
· III. A380-99e1, Standard Practice for Cleaning, Descaling, and Passivation of Stainless Steel Parts, Equipment, and Systems (Includes the Ferroxyl test, further detailed in paragraph 7.3.4 of ASTM A380).
_____The first two methods have been applied to a number of direct bonding brackets, both with mesh and one-piece. The third method has been modified, a corrosive agent being added and the Ferroxyl solution being substituted for a gel.
_____Tests performed. The first method involves the immersion of brackets from different brands having approximately the same weight to a standard solution of iron chloride. After 4 and 72 hours, these were washed, rinsed, dried and weighted to measure the amount of metal dissolved. The results are presented Table 5.1. An auxiliary indicative for the loss in weight that took place is the color of the solution which varied from yellow (low attack) to dark brown (heavy attack).
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_____In the second method, similar samples of brackets were boiled for five periods, each of 48 hours, in a 65% solution of nitric acid. The corrosion rate during each boiling period is calculated from the decrease in the weight of the specimens. Properly interpreted, the results can reveal whether or not the steel has been heat-treated in the correct manner. While being an acid which dissolves chromium carbide, nitric acid is also an oxidizer which promotes the formation of the steel’s protective film of chromium oxide. The results are presented in Table 5.2.
_____A third, original method, reactive gel entrapment, has been developed to detect the superficial attack of small parts ranging from plastics to metals. Direct bonding brackets made of stainless steel were immersed in a solution containing a color reagent for Fe+++ or Ni++ as well as a diluted solution of NaCl and lactic acid recommended by ISO for accelerated corrosion tests. 24 The reagents disclosing the dissolved metal were either potassium ferrocyanide, a color reagent for iron, or dimethyl glyoxime for nickel.
_____The ferrocyanide-basedcorrosion detecting gel has been applied to wires, brackets and expansion screws. Under Prof. MM Kuftinec’s supervision at the New York University Kryser Dental Center, several arch wires made by several manufacturers were subjected to such a gel prepared by Ortho-Cycle Co. To enhance contact, the gel was vibrated for a few seconds and then left for 48 hours at room temperature. At the end of this desired period, the diameter of the blue spots formed was measured with a Boley Gauge and the results statistically processed and compared. Although the attacking agents were diluted, all arch wires generated stains after 48 hours. Both the spread and the intensity of the spot were recorded and presented as diagrams. While the method reveals only leached iron, a relatively benign element, in the case of alloys consisting of a single phase such as stainless steels, it discloses simultaneously also the other ions which are released in the same proportion.
_____Applied to brackets, the method allowed not only to evaluate general corrosion, see Fig. 5.17, but also to identify attachments’ susceptible areas27 , Fig. 5.18.
_____In the last case, the leaching metal, nickel, generates relatively stable, topically adherent complexes with dimethyl glyoxime, Fig. 5.19 and 5.20. Expansion screws can be similarly tested, the easiest way being their immersion in a Fe++ ion-detecting corrosive gel. Revealing their makeup, smaller screws may leach more than others having twice their size, Fig. 5.21
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_____Do-it-yourself, non-standardized methods can be quite helpful in evaluating attachments’ corrosion susceptibilities. While not recognized, these are both fast and suggestive. The simplest is the mere immersion of various attachments in a diluted solution of pool-grade hydrochloric acid, followed by successive refreshments of the spent acid.
_____In Fig. 5.22 are shown twelve brands of brackets subjected to three batches of 5% hydrochloric acid after 24 hours from the first addition, after 48 hours since the spent acid has been replaced and after another 48 hours since the last spent acid has again been replaced. Observe disintegrated brackets in compartment C-10.
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_____Another do-it-yourself method to evaluate the brackets’ corrosion susceptibility using 5% hydrochloric acid is based upon the fact that attacked metal releases hydrogen: the more intense the attack, the greater the volume of hydrogen released. If in a tray filled with acid, a test tube is reversed over one or more brackets, Fig. 15.23, the hydrogen volume gathered above these constitute a comparable degree of corrosion intensity28, as shown in Fig. 15.24.
_____While attachment do-it-yourself-testing may seem farfetched for a regular office, the sad part is that in many instances it may be the only way to avoid major problems. As shown in the introductive part, the clinician has today no alternative except to work with materials which bear warnings about the dangers those may generate. Knowledge and effort spent at the right time may save years of legal debates.
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_____References
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18. Matasa CG, Defend yourself against faulty appliances. I. Faults due to poor manufacturing, J. Gen. Orthod. 1991; 2(4):5-9
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24. ISO Standard BSI, EN 6871-2: 1996
25. Standard 1985.3.30 No. 294, Japan Min. of Health and Welfare
26. Matasa CG, Nichtrostende Edelstahle und Direkt-bonding-Brackets. II Chemisches Verhalten, Informationen aus Orthodontie und Kieferorthopadie (Heidelberg, Germany), 1993; 25(2): 147-166
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28. Matasa CG, Attachment corrosion and its testing, J. Clin Orthod 1995; 29(1): 16-