RESUMO
OBJECTIVE: To determine the immune response related to nickel and nickel-free orthodontic appliances using cellular (total and differential leukocytes) and humoral (IgA) quantification. MATERIALS AND METHODS: Thirty-five Wister rats were randomly distributed into three groups (A, B, and C). In the A group, the animals were subdivided into three subgroups (A1: control, without brackets; A2: nickel-free brackets; and A3: nickel brackets) with seven animals in each group; the animals were sacrificed after 14 days. Groups B and C received only nickel brackets and were kept for 14 days. After this period, the implants were removed and the rats were sacrificed. In group B, the animals were sacrificed 2 days after the appliance removal (16 days in total); and in group C, the animals were sacrificed 7 days after the brackets removal (21 days in total). Total and differential leukocyte number, IgA quantification and histopathologic analysis were done. Histopathologic analysis of subcutaneous tissue related to the orthodontic brackets was done as well. RESULTS: There were significant differences between the number of leukocytes for the nickel-implanted animals and the nickel-free and control groups after 14 days of implantation (P < .05). However, there was no significant difference among groups A1, A2, and A3 for the differential number of leukocytes and for the IgA quantification, except for the number of monocytes, which was three times higher in the nickel group (A3). The histopathologic findings did not show differences between groups. CONCLUSIONS: Nickel did not promote significant adverse biological effects.