Nickel ion concentrations in the saliva of patients treated with self-ligating fixed appliances: a prospective cohort study

Abstract

Objective

Orthodontic appliances are considered to be highly biocompatible although adverse effects attributed to the release of nickel ions (Ni2+) have been documented. Self-ligating brackets have grown in popularity for economic reasons and supposed friction reduction. The aim of the present prospective cohort study was therefore to determine salivary Ni2+ concentrations in patients undergoing 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™), molar bands, and nickel–titanium (NiTi) archwires. Unstimulated saliva samples were collected 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 α = 5 %.

Results

The baseline median salivary Ni2+ concentration was 21.85 µg/l, while the Ni2+ concentrations at the following visits ranged between 13.73 and 85.34 µg/l. Significant increases in Ni2+ levels compared to the baseline levels were detected after band/bracket placement [+59.76 µg/l; 95 % confidence interval (CI) 44.88–74.64 µg/l; P < 0.001] and after archwire insertion (+53.55 µg/l; 95 % CI 25.57–81.52 µg/l; P < 0.001). After 4 weeks, Ni2+ concentrations returned to initial control levels or were lower.

Conclusion

Self-ligating orthodontic appliances may affect salivary Ni2+ 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.

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