ORIGINAL ARTICLE Nickel ion concentrations in the saliva of patients treated with self-ligating fixed appliances: a prospective cohort study Nickelionenkonzentration im Speichelvon Patienten mit selbstligierenden festsitzenden Apparaturen: Eine prospektive Kohortenstudie Lina Go ¨lz 1 • Anna Christine Knickenberg 2 • Ludger Keilig 2,3 • Susanne Reimann 2 • Spyridon N. Papageorgiou 1,2 • Andreas Ja ¨ger 1 • Christoph Bourauel 2 Received: 16 March 2015 / Accepted: 28 July 2015 Ó Springer-Verlag Berlin Heidelberg 2016 Abstract Objective Orthodontic appliances are considered to be highly biocompatible although adverse effects attributed to the release of nickel ions (Ni 2? ) have been documented. Self-ligating brackets have grown in popularity for eco- nomic reasons and supposed friction reduction. The aim of the present prospective cohort study was therefore to determine salivary Ni 2? concentrations in patients under- going orthodontic treatment with self-ligating fixed appliances. Materials and methods A group of 30 patients between 10 and 13 years of age were treated with self-ligating brackets (SmartClip TM ), molar bands, and nickel–titanium (NiTi) archwires. Unstimulated saliva samples were col- lected after different time points (before treatment, after self-ligating bracket and band placement, before archwire insertion, after archwire insertion, and finally 4 and 8 weeks afterwards) and analyzed with an ICP mass spectrometer followed by generalized estimating equation modelling with a = 5 %. Results The baseline median salivary Ni 2? concentration was 21.85 lg/l, while the Ni 2? concentrations at the fol- lowing visits ranged between 13.73 and 85.34 lg/l. Sig- nificant increases in Ni 2? levels compared to the baseline levels were detected after band/bracket placement [?59.76 lg/l; 95 % confidence interval (CI) 44.88–74.64 lg/l; P \ 0.001] and after archwire insertion (?53.55 lg/l; 95 % CI 25.57–81.52 lg/l; P \ 0.001). After 4 weeks, Ni 2? concentrations returned to initial control levels or were lower. Conclusion Self-ligating orthodontic appliances may affect salivary Ni 2? concentrations in vivo over the short term. However, levels resembled those documented in conjunction with conventional bracket use and remained below the daily dietary Ni intake. Keywords Nickel release Á Corrosion Á Self-ligating fixed appliance Á ICP mass spectrometry Á Biocompatibility Zusammenfassung Hintergrund und Ziel Im Allgemeinen werden kieferor- thopa ¨dische Apparaturen als hoch biokompatibel einge- scha ¨tzt, obwohl verschiedene Nebenwirkungen bedingt durch die Freisetzung von Nickelionen (Ni 2? ) dokumen- tiert wurden. Selbstligierende Bracketsysteme erfreuen sich zunehmender Beliebtheit aufgrund wirtschaftlicher Aspekte und propagierter Friktionsreduktion. Ziel der vorliegenden prospektiven Kohortenstudie was es daher, die Ni 2? -Konzentrationen im Speichel von Patienten zu bestimmen, die einer Behandlung mit selbstligierenden festsitzenden Multibracketapparaturen unterzogen wurden. Prof. Christoph Bourauel. L. Go ¨lz and A. C. Knickenberg contributed equally to this article. & Christoph Bourauel bourauel@uni-bonn.de 1 Department of Orthodontics, School of Dentistry, University of Bonn, Bonn, Germany 2 Department of Oral Technology, School of Dentistry, University of Bonn, Welschnonnenstr. 17, 53111 Bonn, Germany 3 Department of Prosthetic Dentistry, Preclinical Education and Materials Science, School of Dentistry, University of Bonn, Bonn, Germany 123 J Orofac Orthop DOI 10.1007/s00056-016-0012-x