Methods: Twenty-eight identical sample sets were used, each corresponding to one half-maxillary arch. The samples were divided in 2 groups (14 sets per group). The first group was ligated to Ormco stainless steel archwires and the second to Ormco NiTi archwires with elastomeric ligatures. Half sets of each group were immersed in 50 ml artificial saliva at pH 5.14 and the other half were immersed at pH 6.69. Ni release was quantified using flame atomic absorption spectrophotometry. Statistical analysis of variance was determined on days 1, 4, 7, 9, 14, 21 and 28 comparing the amount of Ni released between groups and Student t-test was used to determine the differences between pH.
Results: Ni release of stainless steel and NiTi Ormco were continuously increased at time intervals for both pH levels. The stainless steel had more Ni release at pH 5.14 than pH 6.69; however, the NiTi had more Ni-release at pH 6.69 than pH 5.14. At 4 w, the Ni released of one half-maxillary arch was 1.383 ppm (1383 µg/l) at pH 5.14,1,079 ppm (1078 µg/l) at pH 6.69 for stainless steel and 1.221 ppm (1221 µg/l) at pH 5.14, 1.267 ppm (1267µg/l). No significant difference was found in the amount of Ni released from stainless steel and NiTi at pH 5.14 and 6.69, except on day 1, the stainless steel archwire was significantly different (p<0.05).
Conclusions: Stainless steel had more Ni release at pH 5.14 than pH 6.69 but NiTi had greater Ni release at pH 6.69 than pH 5.14.