Table 2.

Descriptive statistics and results of parametric t test for transformed data and non-parametric Mann–Whitney U test for the assessment of differences between the experimental and control groups for the release of nickel and chromium ions from orthodontic appliances (in µg/l, N = 30)

Element	Meana (Exp)	Mean (control)	p (t test, log)	p (Mann–Whitney U)
Ni	573.1 ± 709.7	14.8 ± 56.4	0.0000	–
Cr	100.7 ± 104.4	8.18 ± 13.7	–	0.0000

Exp experimental

^aValues in micrograms per liter, n = 30