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Oral Lichenoid Reaction, Dental Amalgam, and Tin Allergy

Pigatto, Paolo D*; Bombeccari, Gianpaolo; Spadari, Francesco; Guzzi, Gianpaolo

The American Journal of Dermatopathology: June 2011 - Volume 33 - Issue 4 - p 414-415
doi: 10.1097/DAD.0b013e3181e7ce49
Letter to the Editor

Department of Technology for Health, Dermatological Clinic, IRCCS Galeazzi Hospital, University of Milan, Milan, Italy

Unit of Oral Pathology and Medicine, School of Dentistry, University of Milan and Department of Surgical, Reconstructive and Diagnostic Sciences, Policlinico Mangiagalli and Regina Elena Hospital, Milan, Italy

Italian Association for Metals and Biocompatibility Research (AIRMEB), Milan, Italy

Conflict of interest statement.

We have no conflicts of interest connected with this work.

Funding: None.

To the Editor:

In their informative brief report on the treatment of oral lichenoid reaction with dental amalgam removal in a patient who received 2 mercury amalgam fillings and in whom a lichenoid contact mucositis subsequently developed, Aggarwal et al1 found that their patient had a positive allergic reaction to 2 different amalgam allergens revealed by skin patch testing: pulverized amalgam alloy and tin. These important clinical findings add to the growing evidence of a strong link between allergy to intraoral metals and amalgam associated with oral lichenoid reactions. However, we would like to comment on some issues that are not discussed in this case report but that, in our view, should be considered. In the case report section, the authors state that, “A positive response to pulverized amalgam powder and tin was noted after 72 hours. A diagnosis of type IV delayed-type hypersensitivity to tin was made.”1 Hence, the authors have overstressed the differences between the positive and relevant patch test reactions to tin and amalgam alloy powder allergens, respectively.

In other words, tin has been deemed to be a clinically relevant contact allergen, which has led to the diagnosis of lichenoid contact stomatitis associated with physical proximity to dental amalgam surfaces, whereas positive pulverized amalgam alloy reaction has not been considered as clinically relevant as tin. Could the authors discuss the reasons for this controversial issue? For clinical practice, it would be helpful to have data regarding the scoring of patch test reactions for both tin and amalgam powder allergens to understand their clinical importance and the degree of sensitization. In assessing relevance, the pulverized amalgam alloy-positive reaction may explain much better than tin reaction the association of lichen stomatitis with amalgam allergy.2 Given that there are potentially strong sensitizing metals contained in dental amalgam alloy (ie, palladium, cobalt, nickel, gold, and copper)3 that may cause oral mucosal contact lesions, we think that it is very important to give appropriate weight to the contact allergy reaction to pulverized amalgam alloy allergen, as shown by skin testing with dental allergens.1 Second, in their discussion, the authors claim that “The low incidence of side effects among patients is probably due to the fact that amalgam is nearly insoluble. Only soluble materials will provoke reactions to the body. Also, the allergens are constantly diluted and washed away by the saliva, which makes the oral mucosa less sensitive to contact allergens than the skin.”1 These statements deserve clarification.

From a chemistry viewpoint, mercury vapor (Hg0) released from amalgam is suddenly and easily dissolved into saliva, subsequently it is oxidized—at least in part—to divalent mercury ions (Hg2 +). In water, mercury vapor from amalgam is absorbed and retained from 60% of an oral dose ingested.4 Given the mercury amalgam toxicity,5 both free mercury vapor (Hg0) and mercuric mercury (Hg2 +) exposure may induce clinical and histological changes to the oral mucosa.6,7 Therefore, experimental and clinical evidence indeed suggests the possibility that saliva does play a major role in the diffusion of both inorganic and organic mercurial compounds3,8 emitted from amalgam into the oral cavity, rather than a specific clean-up action of mercurial allergens from the oral mucosa among patients with mercury dental amalgam restorations. With regard to the “nearly” insolubility of amalgam fillings, even the concentrations of silver in human saliva—leaked from mercury-containing dental amalgam—have been directly correlated with salivary levels of mercury in amalgam bearers.9 Elevated levels of mercury allergens in saliva were observed in patients with adverse oral disease associated with dental amalgam.8 As metals released from alloy dental restorations spread out into saliva and are deposited into oral mucosa, sensitization and an immune response are thus promoted.8 Particularly, mercury seems to be the main culprit in oral lichenoid lesions in patients with mercury amalgam.10,7

Both oral mucosal biopsy tissues and saliva samples of patients who had lichenoid contact stomatitis show high levels of the putative inciting mercurial antigens.6,8 Even so, saliva seems to be a remarkable biological matrix to assess the exposure to intraoral alloys3,8,9,11 rather than promoting clearance and/or drainage of allergens. The case report by Aggarwal et al1 is important because, until now, cases of oral lichenoid mucositis due to contact allergy to mercury amalgam have been thought to be late reactions to mercury (at least 5 years after amalgam exposure),12 instead, in their case study, the lichenoid mucositis was a very early reaction.

Paolo D. Pigatto

Department of Technology for Health, Dermatological Clinic, IRCCS Galeazzi Hospital, University of Milan, Milan, Italy

Gianpaolo Bombeccari

Francesco Spadari

Unit of Oral Pathology and Medicine, School of Dentistry, University of Milan and Department of Surgical, Reconstructive and Diagnostic Sciences, Policlinico Mangiagalli and Regina Elena Hospital, Milan, Italy

Gianpaolo Guzzi

Italian Association for Metals and Biocompatibility Research (AIRMEB), Milan, Italy

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