Titanium: a review on exposure, release, penetration, allergy, epidemiology, and clinical reactivity

Abstract

SummaryExposure to titanium (Ti) from implants and from personal care products as nanoparticles (NPs) is common. This article reviews exposure sources, ion release, skin penetration, allergenic effects, and diagnostic possibilities. We conclude that human exposure to Ti mainly derives from dental and medical implants, personal care products, and foods. Despite being considered to be highly biocompatible relative to other metals, Ti is released in the presence of biological fluids and tissue, especially under certain circumstances, which seem to be more likely with regard to dental implants. Although most of the studies reviewed have important limitations, Ti seems not to penetrate a competent skin barrier, either as pure Ti, alloy, or as Ti oxide NPs. However, there are some indications of Ti penetration through the oral mucosa. We conclude that patch testing with the available Ti preparations for detection of type IV hypersensitivity is currently inadequate for Ti. Although several other methods for contact allergy detection have been suggested, including lymphocyte stimulation tests, none has yet been generally accepted, and the diagnosis of Ti allergy is therefore still based primarily on clinical evaluation. Reports on clinical allergy and adverse events have rarely been published. Whether this is because of unawareness of possible adverse reactions to this specific metal, difficulties in detection methods, or the metal actually being relatively safe to use, is still unresolved.Key words: contact allergy; corrosion; dermatitis; hypersensitivity; lymphocyte transformation test; patch test; penetration; release; titanium; toxicity. Titanium (Ti) is a non-essential metallic element with the atomic number 22 and a silvery colour. It is the ninth most abundant element in the earth's crust and the seventh most abundant metal overall (1). Major deposits of Ti minerals are found in Australia, Canada, India, Norway, South Africa, Ukraine, and the United States. The +4 oxidation state dominates Ti chemistry, but compounds in the +3 oxidation state are also common. TheCorrespondence: Jacob P. Thyssen, National Allergy Research Centre, Department of Dermato-Allergology, Copenhagen University Hospital HerlevGentofte, University of Copenhagen, Kildegaardsvej, DK-2900 Hellerup, Denmark. Tel: +45 3977 7307; Fax: +45 3977 7118. E-mail: jacob.p. thyssen@regionh.dk Accepted for publication 8 February 2016most important oxide is Ti dioxide (TiO 2 ), which exists in three different crystalline forms -anatase, brookite, and rutile -in addition to an amorphous phase (2, 3). Both the anatase, rutile and brookite mineral forms of TiO 2 occur naturally.TiO 2 is widely applied as microparticles and nanoparticles (NPs) in consumer goods, including cosmetics and foods, to obtain a white colour and ultraviolet light protection (4). Moreover, Ti is combined with a variety of other elements to produce strong lightweight alloys that provide resistance against corrosion and show a very high strength/density ratio (5). Because of this and the...

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