Effects of fixed orthodontic treatment on nickel and chromium levels in gingival crevicular fluid as a novel systemic biomarker of trace elements: A longitudinal study.

INTRODUCTION: Nickel and chromium might induce hypersensitivity. Therefore, they are of interest to orthodontists. Gingival crevicular fluid (GCF) is highly relevant to orthodontic treatments and might reflect systemic changes associated with the inflammatory response induced by orthodontic forces. Therefore, it might also be used to show metal ion changes. Nevertheless, baseline metal levels of GCF are unknown, and the effect of orthodontic treatment on GCF metal levels has not been investigated. The aim of this study was to assess the levels of nickel and chromium in GCF. METHODS: Based on a pilot study, the sample size was predetermined as 24 x 3 measurements to obtain test powers above 90%. Nickel and chromium concentrations were measured before treatment and 1 month and 6 months later in 12 female and 12 male patients who had fixed orthodontic appliances using atomic absorption spectrophotometry. The gingival index was also evaluated in each session. The effects of treatment on GCF ions were analyzed using repeated-measures analysis of variance and Friedman tests (alpha = 0.05, beta </=0.01). RESULTS: The gingival index worsened over time (chi-square test, P <0.001). The mean nickel levels were 3.894 +/- 1.442, 5.913 +/- 2.735, and 19.810 +/- 8.452 mug per gram, respectively, at baseline, month 1, and month 6. Chromium concentrations were 1.978 +/- 0.721, 4.135 +/- 1.591, and 13.760 +/- 3.555 mug per gram, respectively. Compared with the baseline, nickel increased by 150% and 510%, respectively, in the first and sixth months (Friedman, P <0.0001), and chromium increased by 200% and 700%, respectively (analysis of variance, P <0.0001). CONCLUSIONS: Six months of fixed orthodontic treatment might intensify the levels of nickel and chromium in the GCF as well as gingival inflammation.