Localised corrosion

Sir, we would like to add some comments to the recent, concise review of nickel allergy associated with orthodontic materials (BDJ 2008; 204: 297–300).¹

The authors state that 'If nickel is leached from orthodontic appliances, this Type IV hypersensitivity reaction can occur.' The occurrence of allergic contact sensitisation does not necessarily correlate with the release of nickel in the saliva from orthodontic appliances. Instead, by definition, allergic contact dermatitis occurs by strict contact with oral mucosa and/or skin.² Also, the authors state that 'most individuals who have nickel sensitivity do not report adverse clinical manifestations to orthodontic appliances containing nickel'. The authors did not mention the existence of adverse systemic allergic reaction to metal, mainly nickel allergy, contained in orthodontic appliances, which are often not recognised by dental practitioners and/or dentists.³

We have recently described a systemic contact dermatitis due to allergy to nickel in an adolescent who underwent orthodontic treatment, in absence of oral clinical signs and/or symptoms.³ Our case is not unique. Studies by Trombelli et al.⁴ and Veien et al.,⁵ which Noble et al. cited in their review, and others,^6,7 reported similar findings.

The authors suggest that patients who have had adverse effects to Ni-Ti archwires may subsequently tolerate stainless steel appliances. We would like to draw attention to the problem that even stainless steel orthodontic archwires may undergo localised corrosion as well as oral galvanic corrosion due to electrochemical reactions, which accelerate the release of nickel and chromium in the oral cavity.^8,9

In both cases discussed, although nickel hypersensitivity is an interesting possibility, data about the potential delayed hypersensitivity to nickel (Type IV allergy) were lacking to support claims of adverse events to archwires due to allergy to nickel because the patch testing was not performed. Moreover, the authors did not distinguish between allergic sensitisation to metals from archwires and the potential local toxicity originating from the release of nickel and/or chromium, which are able to determine oral mucosal inflammation even in absence of delayed type hypersensitivity reactions.⁸

We believe that it is important to consider that metallic orthodontic appliances may cause local and/or systemic adverse events. Orthodontists and general practitioners should attentively consider all cases of dermatitis which may occur during orthodontic treatment.

Dr James Noble responds: Thank you Drs Pigatto, Guzzi and Sforza for your additional comments. Although we do indicate that extra-oral manifestations of nickel allergy can occur, we do not elaborate on specific systemic manifestations that may occur as a result of contact dermatitis due to orthodontic appliances, as they are rare and most allergic reactions are intraoral as opposed to systemic and this is what we were reporting. ^{10, 11} Nonetheless, it would be beneficial for dental and orthodontic practitioners to be mindful to closely monitor dermatitis in patients who do report an allergy to nickel in the initial medical questionnaire.

Further, it is difficult to demonstrate contact mucositis in an intra-oral setting because of the flow of saliva transporting corrosion products. Still, lichenoid contact hypersensitivity lesions to restorative dental materials is generally accepted as a contact dermatitis. Also, it is difficult to distinguish between intra-oral toxic and allergic reactions, ¹² challenging to control for the rate of intra-oral corrosion and the treatment for both is similar.

It is important to note that a positive patch test is not necessarily associated with intra-oral nickel reactions and therefore routine patch-testing of patients who report intra-oral symptoms is not necessary. This has been confirmed by Spiechowicz et al. who observed patients who had positive skin reactions over 15 years and found no development of a local or systematic reaction to a nickel containing alloy. ¹³ Further, these tests may cause sensitisation to nickel if there is no true nickel allergy present ¹² and they also have false positive and negatives. Patch-testing was therefore not undertaken in the two reported cases. Therefore, if patients do develop signs or symptoms to Ni-Ti wires, the most practical, cost-effective and non-intrusive therapy is removal of the archwires and continuation of treatment with alternative archwires.