Palladium in dental applications: ideal immunological choice?

Abstract

The oral mucosa is constantly exposed to various irritants and allergens, including noble metals such as palladium (Pd), a metal with suitable biocompatibility and anticorrosive properties. Based on recent literature, this work focuses on Pd allergy in dental practice, covering clinical symptomatology, epidemiological data, and immune mechanisms. Predominant manifestations of Pd allergy include oral lichenoid contact injury, systemic or oral allergic contact dermatitis/mucositis (ACD), cheilitis, and burning mouth syndrome. Studies on allergy diagnosis have revealed that Pd is the principal dental metallic allergen in extended patch test batteries. Being less allergenic than nickel, chrome, or cobalt, Pd allergy affects over 6% of ACD-suspected patients, but up to 51% of oral allergy subjects exposed to the culprit allergen who also presented antecedent metal hypersensitivity reactions, often as cross-reactivity to nickel. Recent evidence indicates that a solely Pd-related allergy can cause oral symptoms in patients without skin lesions in metal-exposed regions. Pd allergy frequently affects females and dentistry practitioners and technicians, despite the recent restriction on nickel use. As a cellular allergy type, Pd hypersensitivity represents a mixture of T-cell interactions, in which variable region complementarity-determining region 3 of specific CD8+ T-cell receptors recognize the complex primary histocompatibility class I/peptide on the antigen-presenting cell surface, activating also further immune cells like NK T and a mixture of T helper (Th) ones. A combination of stimulated Th1, Th2, and Th17 cells, as well as eosinophil infiltrations in Pd allergy, corresponds to cytotoxic (and potentially compensatory antitoxic) effects during high-concentration allergen exposures that may also extend mucosal inflammatory processes, as in the case of BIDEAR (Barrier Integrity Damage-Elicited Allergic Response). This work concludes that Pd allergy occurs more frequently than previously suspected, and that suitable materials can successfully replace dental Pd-containing structures following metal analysis.