INTRODUCTION

Recent years have seen an increase in metal allergies. Allergic reactions in the oral region to metals contained in dental appliances has previously been reported,1–3 and increased attention has been paid to allergy to orthodontic materials.4–6 Some metals commonly used in dental practice are known allergens such as nickel, cobalt, and chromium, many of which are contained in various kinds of orthodontic material.7

Nickel is the most typical antigen of metal-induced allergic contact dermatitis,8–10 whereas a chromium allergy is estimated to occur in 10% of male subjects and 3% of female subjects.11 It is possible that metal ions are eluted from orthodontic materials by the caustic action of saliva, electrolytes in food debris, and acids produced by bacteria. We previously evaluated the release of nickel from orthodontic wires in various acids as a product of oral bacteria.12 Although not all the wires released nickel in physiological salt solution and sterilized water as control solutions, all did so in hydrochloric and formic acid. Agaoglu et al13 measured nickel and chromium levels in saliva and serum of patients with fixed orthodontic appliances and showed the release of a measurable amount of nickel and chromium when placed in the mouth. It is therefore possible that orthodontic materials can induce metal allergy.

In this case report, metal allergic reactions in the form of lip swelling and redness were induced after orthognathic surgery. We show that the metal allergic reactions improved by replacing the metal brackets, wire, and bands with an appliance made of polymer, which contained no metals.

Case Summary

A 29-year-old woman visited Nagasaki University Dental Hospital complaining of an anterior crossbite. Intraoral examination revealed a class III molar relationship and missing upper left second molar, an overjet of −2 mm, overbite of 1 mm, and maxillary midline deviation of 3 mm to the right. The second upper incisors had migrated lingually, and the upper left first premolar, lower left second premolar, lower left first molar, and lower right second molar were under prosthetic treatment. The lower anterior segment showed 3 mm of crowding (Figure 1). Cephalometric analysis indicated SNA 84°, SNB 87°, and ANB −3°. The mandibular plane angle was steep (42°), and the gonial angle was large (145°). The upper incisors were inclined 113° to the labial. However, in contrast, the lower incisors were inclined 71° to the lingual (Table 1).

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Table 1.  Cephalometric Measurements of the Case at Pretreat ment and Posttreatment

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Treatment Progress

A metal edgewise appliance (0.018″ × 0.025″ slot) was applied. Nickel titanium wires were used for leveling and alignment of both arches. Cobalt-chromium wires were used for stabilization before surgery. The total period of presurgical treatment was 21 months (Figure 2). An SSRO was performed to improve mandibular protrusion (Figure 3).

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Two months after orthognathic surgery, continuous lip swelling and redness were noted (Figure 4A,B). The patient was diagnosed with herpes infection at a dermatological hospital and given medicine for 1 month, but her symptoms did not improve (Figure 4C). It was then suggested by the dermatological hospital that the patient had a metal allergy, and a reaction to chromium was revealed by patch tests in our dental hospital.

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For confirmation, we examined the metal composition of all prosthetic appliances using a fluorescent x-ray analyzer (SEA-2110L; Seiko Instruments Co Ltd, Chiba, Japan); copper, gold, palladium, and silver were detected, but chromium was not (Figure 5). However, the orthodontic brackets, wires, and bands do contain chromium.7 Considering that these materials may have induced the metal allergic reactions, they were replaced with an appliance made of polymer (Quick Change Methods [QCM]; Chikami Miltec Inc, Kochi, Japan), with no metals14 (Figure 6). As a result, the lip swelling and redness improved (Figure 7). There is no lip swelling and redness at the time of appliance removal (Figure 8). For retention, the anterior part of the QCM retainer was cut and bonded onto the lingual side of the anterior lower and upper jaws (Figure 9). During retention, no allergenic reactions were observed.

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RESULTS

The maxillary dental midline almost coincided with the mandibular midline, and the upper incisors were inclined lingually. Facial mandibular protrusion was also improved. An ideal occlusion with class I molar and canine relationships was also achieved as well as improvement in the overbite and overjet to 2 mm (Figure 8). The SNB was improved to 83°, and as a result, the ANB was improved to 2° (Table 1). After changing the metal appliance to a nonmetal appliance, no further symptoms of hypersensitivity were observed around the oral region, and this continued to be the case during retention.

DISCUSSION

In general, a small amount of metal can cause metal allergies in daily life. Mercury, nickel, chromium, cobalt, copper, tin, gold, platinum, palladium, antimony, silver, iron, zinc, cadmium, and manganese all have been shown to be causative agents of metallic allergy.15–17 Metal allergic diseases thought to be related to dental metals have recently become a serious problem.

In this case, allergic hypersensitivity in the form of lip swelling and redness was induced after orthognathic surgery. In clinical cases, allergic contact hypersensitivity to nickel develops much more readily in inflamed skin than in normal skin. In this way, sensitization to nickel develops much more easily in the presence of strong inflammation. At the inflammation site, reactive oxygen species such as hydrogen peroxide (H₂O₂) and hypochlorite (OCL⁻)₄ are produced by phagocytes.18 In the case of nickel hypersensitivity, these powerful oxidants can oxidize Ni²⁺ to the higher oxidation states of Ni³⁺ and Ni⁴⁺, respectively,19 which have a far greater chemical reactivity than Ni²⁺. It has also been reported that sensitization is achieved by injecting Ni²⁺ or by administering nickel as Ni³⁺ and Ni⁴⁺.20 The results showed that Ni³⁺ and Ni⁴⁺, but not Ni²⁺ alone, were able to sensitize native T cells. These findings might explain why hypersensitivity against nickel in humans develops much more easily in inflamed skin than in normal skin, since both Ni³⁺ and Ni⁴⁺ can be generated from Ni²⁺ by reactive oxygen species released during inflammation. In fact, we previously established a nickel-hypersensitized animal model by injecting nickel at the inflammation site.21

Cr⁴⁺ species are strong oxidants that act as carcinogens, mutagens, and teratogens in biological systems.22 The high solubility, bioavailability, and toxicity of Cr⁴⁺ make it a particular environmental concern. In contrast, Cr³⁺ species have low toxicity, in part because their bioavailability is limited by their low solubility and their tendency to form strong complexes with organics and hydroxo complexes.23 Higher chromium oxidation states also possess a far greater chemical reactivity.

In this case, we did not check for allergic reactions before the orthognathic surgery, and therefore, we do not know whether the patient had the chromium allergy before or developed it after the surgery. However, it is possible that the allergenic symptom was triggered by the surgery. That is, it is possible that higher chromium oxidation states were induced, generating hypersensitivity through inflammation resulting from the orthognathic surgery. Many studies have suggested a rare intraoral sensitization in contrast to epicutan/intracutan sensitization,2425 even a desensitization of patients treated with brackets/wires.526 However, with inflammation during surgery, a risk of development or induction of allergic reactions does exist.

The choice of material is important in the orthodontic treatment of patients with metal allergies, and it is necessary to understand the metallic composition of such orthodontic materials. We previously examined the elements of metal materials using an x-ray fluorescence spectroscope7 and found that substantial amounts of nickel, chromium, and iron are contained in orthodontic metal materials. It is thought that the various metal elements elute from the materials, become antigens, and cause an allergic reaction. When allergic-like symptoms occur, we should therefore verify hypersensitivity to each of these metals to help determine whether the symptoms are an allergic reaction. We should first find out whether there is an allergen in the oral region and, second, whether the patient is hypersensitive to any metals and, if so, which elements. Accordingly, if the orthodontic materials include the metal elements, we should use an alternative material not containing the allergen.

In the present case, the patient had allergenic hypersensitivity to chromium, which is included in metal brackets and many kinds of wire and band, and we therefore chose to employ a nonmetallic appliance made of organic polymer.14 For retention, the anterior part of the QCM retainer was cut and bonded onto the lingual side of the anterior lower and upper jaws. This treatment resulted in a disappearance of the hypersensitivity symptoms, suggesting that nonmetal orthodontic material is useful for treatment of metal allergenic patients.