The 13th British Orthodontic Conference,Torquay, 1998

Abstract

Nickel is the most common metal to cause contact dermatitis in orthodontics. Nickel-containing metal alloys, such as nickel-titanium and stainless steel, are widely used in orthodontic appliances. Nickel-titanium alloys may have nickel content in excess of 50 per cent and can thus potentially release enough nickel in the oral environment to elicit manifestations of an allergic reaction. Stainless steel has a lower nickel content (8 per cent). However, because the nickel is bound in a crystal lattice it is not available to react. Stainless steel orthodontic components are therefore very unlikely to cause nickel hypersensitivity. This article discusses the diagnosis of nickel allergy in orthodontics and describes alternative products that are nickel free or have a very low nickel content, which would be appropriate to use in patients diagnosed with a nickel allergy.     

Orthodontic treatment possibilities of allergic patients

During the past two decades the incidence of allergies against dental materials has been rising. The most common allergens are nickel, mercury, benzoxyl-peroxide, formaldehyde, MMA, HEMA, EGDMA and TEGDMA. Contact allergy develops in predisposed individuals as a consequence of environmental exposures to allergens. Although the relatively high frequency of contact allergies in children is well documented, its importance during orthodontic treatments is still often underestimated. The most common metal to cause dental allergic reactions is nickel. Nickel-containing metal alloys, such as nickel-titanium, are widely used in orthodontics because of their favorable physical properties. Coated wires (epoxi coating, teflon, etc.) are not only more aesthetic, but can play a role in the orthodontic treatment of patients with nickel allergy. In our case report we present two patients with nickel allergy, and their treatment with alternative orthodontic appliances. During the orthodontic treatment our patients did not have any objective or subjective allergy-related symptoms.     

Nickel and cobalt hypersensitivity reaction before and after orthodontic therapy in children

Nickel and cobalt are major components of alloys used in orthodontics. The objectives of this cross-sectional study was to determine the prevalence of a nickel hypersensitivity reaction before and after orthodontic treatment with conventional stainless steel brackets and wires. The total sample consisted of 82 patients (55 females, and 27 males) from the Orthodontic Department at the Faculty of Dentistry, Süleyman Demirel University. A patch test and a questionnaire were used to evaluate hypersensitivity to these metals. The statistical analysis was carried out using Fisher's exact X(2) (2 x 2) test. The prevalence of nickel allergy was found to be higher in females than males (14.55% in females, 0% in males), and the prevalence of cobalt allergy was found to be 9.76% (7.27% in females, 14.81% in males). Orthodontic treatment with conventional stainless steel alloys does not appear to have an allergenic effect on the gingival and oral health of the patient. A family history of an allergy to these metals or the use of metallic objects in contact with the skin do not characterize nickel and cobalt hypersensitivity. This suggests orthodontic therapy with conventional stainless steel appliances does not initiate or aggravate a nickel hypersensitivity reaction. There was no association between the before treatment and after treatment to a nickel and cobalt hypersensitivity reaction.     

Biocompatibility and resistance to corrosion of orthodontic wires

Various materials are currently used to make orthodontic wires. This article suggests a synthesis on their resistance to corrosion and biocompatibility. In the first part, after a review of some basic notions on the corrosion processes, the authors develop the electrochemical characteristics of the three main groups of alloys used in orthodontics. They study more precisely corrosion resistance of nickel-titanium alloys and, through their own experimental results, they show that this type of alloy is subject to corrosion in acid and fluoridated environment. In the second part, the authors study those alloys biocompatibility. They first mention nickel toxicity and allergy induced by this element. Then, biocompatibility of alloys used in orthodontics is assessed following studies on the release of metallic elements from orthodontic wires, and studies on cell-compatibility when in contact with those wires. It is proved that the state of materials surface has a very high influence on their biocompatibility. As a conclusion, in spite of numerous studies carried out so far, showing a satisfactory biological behaviour of those orthodontic wires, many questions are yet to be answered: long term in vivo performances of those materials have not yet been exactly assessed. Further studies must definitely be carried out.     

Composition and in vitro corrosion of orthodontic appliances

The high incidence of nickel allergy and the increasing use of nickel-containing dental biomaterials has been of growing concern. The purpose of this investigation was to analyze different types of alloys used in orthodontics, and to study whether nickel and chromium will be released from these alloys when stored in physiologic saline. Face-bows, brackets, molar bands, and arch wires were analyzed. Most of the different parts in the face-bows, brackets, and molar bands were similar to conventional 18/8 stainless steel. Except the wires, most appliances included a variable amount of silver solder, the greatest in face-bows. After 14 days in 0.9% sodium chloride (NaCl), the largest amount of nickel and chromium were leached out from the face-bows and the least amount from the arch wires. Soldered stainless steel face-bows seemed to be very susceptible to corrosion. The release of nickel seemed to be related to both the composition and the method of manufacture of the appliances, but the release was not proportional to the nickel content.     

Cytotoxic effect of orthodontic appliances.

The use of orthodontic appliances may contribute to local gingivitis, often attributed to increased plaque retention. Gingivitis of bacterial origin cannot clinically be distinguished from local tissue irritation caused by corrosion products. The purpose of this investigation was to assess the cytotoxic effect of various metallic components used in orthodontics. Multicomponent devices such as facebows, molar bands, and brackets along with single-component brackets and archwires were tested by the agar overlay cytotoxicity test with mouse fibroblast cells. None of the archwires caused any cytotoxic effect, even though some contained 54 per cent nickel. However, the multi-component devices, which were joined with silver- and copper-based brazing alloys were more cytotoxic than the single-component devices. Copper is more cytotoxic than nickel, which could explain the greater cytotoxic effect of the samples with brazing materials. It is speculated that cytotoxic corrosion products from orthodontic appliances might contribute to localized gingivitis.     

A survey of undergraduate orthodontic training and orthodontic practices by general dental practitioners

PURPOSE of the STUDY: To assess satisfaction with undergraduate orthodontic training, the variety of treatments undertaken in general practice, practitioners' perceived competence in orthodontics and the level of interest in continuing education in orthodontics. DESIGN: Cross-sectional questionnaire-based study. MATERIALS and METHODS: A questionnaire was mailed to 520 general practitioners in Dublin, Kildare and Wicklow as listed in Irish Dental Council Register of Dentists 2003. RESULTS: Forty-six percent of dentists responded. More than half (54 per cent) of the respondents were satisfied with both academic and clinical aspects of undergraduate training. Twenty-nine percent regularly perform orthodontic treatment. Only 60 percent feel comfortable treating orthodontic emergencies. Over 70 percent have either already attended or aspire to attend further training in orthodontic diagnosis and interceptive orthodontics. CONCLUSIONS: Our study indicates that in the greater Dublin area, graduates (those qualified less than 10 years) are increasingly satisfied with undergraduate teaching. Orthodontic treatment is performed regularly in general dental practice with interceptive procedures most often carried out. While ability to deal with orthodontic emergencies is not universal, practitioners do appear confident to perform a variety of orthodontic procedures. Interest in continuing education in orthodontics is very high. Our study indicates that participation in continuing education in orthodontics appears to translate into greater provision of orthodontic care in general practice.     

Cytotoxic and antibacterial effects of orthodontic appliances

The cytotoxic and antibacterial effects of orthodontic appliances were assessed. Metallic devices used in orthodontics, such as molar bands, brackets, and archwires were tested by the agar overlay cytotoxicity test with mouse fibroblast cells. The same devices were tested for antibacterial effect with Streptococcus mutans and S. sanguis . The multicomponent devices, which are bonded with silver- and copper-based brazing alloys, were more cytotoxic than the single-component devices, probably because copper is more cytotoxic than nickel. The devices had a definite, but low, antibacterial effect, as compared with the 0.05% chlorhexidine positive control. A cytotoxic effect of the devices per se might contribute to a localized gingivitis. It is uncertain whether orthodontic devices have any significant inhibitory effect on dental plaque viability.     

Metal release from simulated fixed orthodontic appliances.

Most orthodontic appliances and archwires are stainless steel or nickel-titanium (NiTi) alloys that can release metal ions, with saliva as the medium. To measure metal released from the fixed orthodontic appliances currently in use, we fabricated simulated fixed orthodontic appliances that corresponded to half of the maxillary arch and soaked them in 50 mL of artificial saliva (pH 6.75 +/- 0.15, 37 degrees C) for 3 months. We used brackets, tubes, and bands made by Tomy (Tokyo, Japan). Four groups were established according to the appliance manufacturer and the type of metal in the .016 x .022-in archwires. Groups A and B were stainless steel archwires from Ormco (Glendora, Calif) and Dentaurum (Ispringen, Germany), respectively, and groups C and D were both NiTi archwires with Ormco's copper NiTi and Tomy's Bioforce sentalloy, respectively. Stainless steel archwires were heat treated in an electric furnace at 500 degrees C for 1 minute and quenched in water. We measured the amount of metal released from each group by immersion time. Our conclusions were as follows: (1) there was no increase in the amount of chromium released after 4 weeks in group A, 2 weeks in group B, 3 weeks in group C, and 8 weeks in group D; (2) there was no increase in the amount of nickel released after 2 weeks in group A, 3 days in group B, 7 days in group C, and 3 weeks in group D; and (3) there was no increase in the amount of iron released after 2 weeks in group A, 3 days in group B, and 1 day in groups C and D. In our 3-month-long investigation, we saw a decrease in metal released as immersion time increased.     

In vivo study on metal release from fixed orthodontic appliances and DNA damage in oral mucosa cells

Interest in the amount of metal ion intake from dental alloys has grown. Fixed orthodontic appliances usually include brackets, bands, and archwires made of stainless steel, nickel-titanium, or nickel-cobalt alloys, and these can release metal ions. The purpose of this study was to investigate the biocompatibility in vivo of fixed orthodontic appliances, evaluating the presence of metal ions in oral mucosa cells, their cytotoxicity, and their possible genotoxic effects. Mucosa samples were collected by gentle brushing of the internal part of the right and left cheeks of 55 orthodontic patients and 30 control subjects who were not receiving orthodontic treatment. The cells were immediately prepared for cell viability and the comet assay. Nickel and cobalt cellular content was quantified by inductively coupled plasma mass spectrometry (ICP-MS). The results indicate that nickel and cobalt concentrations were 3.4-fold and 2.8-fold higher, respectively, in the patients than in the controls; cellular viability was significantly lower in the patients than in the controls, and there was a significant negative correlation with metal levels. The biologic effects, evaluated by alkaline comet assay, indicated that both metals induced DNA damage (more cells with comets and apoptotic cells). There were significant positive correlations between (1) cobalt levels and the number of comets and apoptotic cells, (2) nickel levels and number of comet cells, and (3) cobalt levels and comet tails. This study corroborates that nickel and cobalt released from fixed orthodontic appliances can induce DNA damage in oral mucosa cells.     

Metal release from heat-treated orthodontic archwires

Stainless steel and cobalt-chromium orthodontic archwires were subjected to an immersion corrosion test. Wires in the as-received state and wires subjected to a 1-min heat treatment at different temperatures were tested. Iron from the stainless steel and cobalt from the cobalt-chromium product were analyzed in artificial saliva after 1 week of immersion. Both products were analyzed for nickel. The results showed that the cobalt-chromium wire in the as-received state released more metals than the stainless steel. The metal release from the stainless steel wire increased rapidly when subjected to 400 degrees C or higher. For the cobalt-chromium product the increase started at about 500 degrees C. At temperatures above 500 degrees C the release of metals was 15 to 60 times higher than the lowest values. The present results should be considered in procedures involving application of heat to orthodontic wires.     

Comparison of Metal Ion Release from Different Bracket Archwire Combinations: An in vitro Study

Aim: The metal ion released from the orthodontic appliance may cause allergic reactions particularly nickel and chromium ions. Hence, this study was undertaken to determine the amount of nickel, chromium, copper, cobalt and iron ions released from simulated orthodontic appliance made of new archwires and brackets. Materials and methods: Sixty sets of new archwire, band material, brackets and ligature wires were prepared simulating fixed orthodontic appliance. These sets were divided into four groups of fifteen samples each. Group 1: Stainless steel rectangular archwires. Group 2: Rectangular NiTi archwires. Group 3: Rectangular copper NiTi archwires. Group 4: Rectangular elgiloy archwires. These appliances were immersed in 50 ml of artificial saliva solution and stored in polypropylene bottles in the incubator to simulate oral conditions. After 90 days the solution were tested for nickel, chromium, copper, cobalt and iron ions using atomic absorption spectrophotometer. Results: Results showed that high levels of nickel ions were released from all four groups, compared to all other ions, followed by release of iron ion levels. There is no significant difference in the levels of all metal ions released in the different groups. Conclusion: The study confirms that the use of newer brackets and newer archwires confirms the negligible release of metal ions from the orthodontic appliance. Clinical significance: The measurable amount of metals, released from orthodontic appliances in artificial saliva, was significantly below the average dietary intake and did not reach toxic concentrations. Keywords: Metal ions, Brackets, Archwires, Nickel, Iron, Copper, Cobalt, Chromium, Titanium, Molybdenum. How to cite this article: Karnam SK, Reddy AN, Manjith CM. Comparison of Metal Ion Release from Different Bracket Archwire Combinations: An in vitro Study. J Contemp Dent Pract 2012;13(3):376-381. Source of support: Nil Conflict of interest: None declared.     

Beta titanium: a new orthodontic alloy

Historically, few alloys have been used in the fabrication of orthodontic appliances. This article reviews the gold-based, stainless steel, chrome-cobalt-nickel, and nitinol alloys, as well as beta titanium, a new material for orthodontics. Mechanical properties and manipulative characteristics are summarized to develop a basis for the selection of the proper alloy for a given clinical situation. The beta titanium wire has a unique balance of low stiffness, high springback, formability, and weldability which indicates its use in a wide range of clinical applications. A number of such applications are described.     

Metal release from heat-treated orthodontic archwires

Stainless steel and cobalt-chromium orthodontic archwires were subjected to an immersion corrosion test. Wires in the as-received state and wires subjected to a 1-min heat treatment at different temperatures were tested. Iron from the stainless steel and cobalt from the cobalt-chromium product were analyzed in artificial saliva after 1 week of immersion. Both products were analyzed for nickel. The results showed that the cobalt-chromium wire in the as-received state released more metals than the stainless steel. The metal release from the stainless steel wire increased rapidly when subjected to 400°C or higher. For the colbalt-chromium product the increase started at about 500°C. At temperatures above 500°C the release of metals was 15 to 60 times higher than the lowest values. The present results should be considered in procedures involving application of heat to orthodontic wires. □ Cobalt-chromium alloy; corrosion; stainless steel     

Orthodontic education and practice in Canada: perceptions of the profession as shown in a recent survey

A questionnaire survey concerning the training and practice of orthodontics was mailed to 20 per cent of the licensed dentists and to dental specialists in the provinces of Ontario, Manitoba, Alberta, and British Columbia between March and August of 1987. The response rate was 49.4 per cent. Many dentists and orthodontists who completed the survey reported declines in patient load during the past three years. Dental schools are perceived to be providing inadequate orthodontic training, in both the undergraduate dental curriculum and in the area of continuing education. A desire for an increase in time, quality, and applications was expressed. Between 20.1 and 34.2 per cent of fully-banded orthodontic cases are being treated by general practitioners.     

In vivo aging of orthodontic alloys: implications for corrosion potential,nickel release,and biocompatibility

Despite the large number of studies investigating nickel release from orthodontic stainless steel and nickel-titanium alloys, there is a lack of conclusive evidence with respect to the composition and kinetics of the corrosive products released. The objective of this review is to address the critical issues of corrosion potential and nickel leaching from alloys by investigating the effect of intraoral conditions on the surface reactivity of the materials. After an overview of fundamentals of metallurgical structure of orthodontic alloys, we provide an analysis of corrosion processes occurring in vivo. We present recent evidence suggesting the formation of a proteinaceous biofilm on retrieved orthodontic materials that later undergoes calcification. We illustrate the vastly irrelevant surface structure of in vivo- vs in vitro-aged alloys and discuss the potential implications of this pattern in the reactivity of the materials. Finally, we present a comprehensive review of the issue of nickel release, based on three perspectives: its biologic effects, the methods used for studying its release, and nickel-induced hypersensitivity in orthodontic patients.     

Glass ionomer cements in orthodontics—An update

Because conventional bands continue to be used in clinical orthodontics, it is essential to evaluate new dental cements to establish their suitability as a cementing medium for orthodontic bands. This study was undertaken to determine the failure rate of bands cemented with a glass ionomer cement to premolar and molar teeth. The sample consisted of 100 consecutively completed cases. Stainless steel bands were cemented to premolar and molar teeth (799) with a glass ionomer cement (Ketac-Cem). The failure rate for the bands was 1.9%. This is significantly lower than the 5.1% recorded for bands cemented with a polycarboxylate cement reported in a previous study.     

Corrosion of stainless steel, nickel-titanium, coated nickel-titanium, and titanium orthodontic wires

Orthodontic wires containing nickel have been implicated in allergic reactions. The potential for orthodontic wires to cause allergic reactions is related to the pattern and mode of corrosion with subsequent release of metal ions, such as nickel, into the oral cavity. The purpose of this study was to determine if there is a significant difference in the corrosive potential of stainless steel, nickel titanium, nitride-coated nickel titanium, epoxy-coated nickel titanium, and titanium orthodontic wires. At least two specimens of each wire were subjected to potentiostatic anodic dissolution in 0.9% NaCl solution with neutral pH at room temperature. Using a Wenking MP 95 potentiostat and an electrochemical corrosion cell, the breakdown potential of each wire was determined. Photographs were taken of the wire speci mens using a scanning electron microscope, and surface changes were qualitatively evaluated. The breakdown potentials of stainless steel, two nickel titanium wires, nitride-coated nickel titanium, epoxy-coated nickel titanium, and titanium were 400 mV, 300 mV, 750 mV, 300 mV, 1800 mV, and >2000 mV, respectively. SEM photographs revealed that some nickel titanium and stainless steel wires were susceptible to pitting and localized corrosion. The results indicate that corrosion occurred readily in stainless steel. Variability in breakdown potential of nickel titanium alloy wires differed across vendors' wires. The nitride coating did not affect the corrosion of the alloy, but epoxy coating decreased corrosion. Titanium wires and epoxy-coated nickel titanium wires exhibited the least corrosive potential. For patients allergic to nickel, the use of titanium or epoxy-coated wires during orthodontic treatment is recommended.     

Side effects of immersion-type cleansers on the metal components of dentures

Three metals were immersed in eight denture cleansing solutions for a period of 240 hours to determine the relative side effects of these cleansers upon various metal components of complete and removable partial dentures. Conclusions drawn from this study are: 1. Commercial bleaches and unbuffered hypochlorite solutions should not be used on dentures with metal components. 2. Routine use of buffered hypochlorite solutions may cause surface damage to aluminum-base material. 3. Stainless steel (orthodontic wire) will tarnish after continued exposure to buffered and unbuffered hypochlorite solutions. 4. Further research is necessary to delineate the effects of existing denture cleansers and to improve on their effectiveness and safety.     

Evaluation of friction of stainless steel and esthetic self-ligating brackets in various bracket-archwire combinations.

This study measured and compared the level of frictional resistance generated between stainless steel self-ligating brackets (Damon SL II, SDS Ormco, Glendora, Calif), polycarbonate self-ligating brackets (Oyster, Gestenco International, G?thenburg, Sweden), and conventional stainless steel brackets (Victory Series, 3M Unitek, Monrovia, Calif), and 3 different orthodontic wire alloys: stainless steel (Stainless Steel, SDS Ormco), nickel-titanium (Ni-Ti, SDS Ormco), and beta-titanium (TMA, SDS Ormco). All brackets had a.022-in slot, whereas the orthodontic wire alloys were tested in 3 different sections:.016,.017 x.025, and.019 x 0.025 in. Each of the 27 bracket and archwire combinations was tested 10 times, and each test was performed with a new bracket-wire sample. Both static and kinetic friction were measured on a custom-designed apparatus. All data were statistically analyzed (Kruskal-Wallis and Mann Whitney U tests). Stainless steel self-ligating brackets generated significantly lower static and kinetic frictional forces than both conventional stainless steel and polycarbonate self-ligating brackets, which showed no significant differences between them. Beta-titanium archwires had higher frictional resistances than stainless steel and nickel-titanium archwires. No significant differences were found between stainless steel and nickel-titanium archwires. All brackets showed higher static and kinetic frictional forces as the wire size increased.