INTRODUCTION: Orthodontic tooth movement is characterized by tissue reactions, which consist in an inflammatory response in periodontal ligament, depending on the forces applied. Self-ligating brackets are able to minimize the sliding resistance and to reduce the forces necessary to move a tooth, with a better tissue response. OBJECTIVES: The purpose of this study was to evaluate the activity of the lactate dehydrogenase (LDH) in gingival crevicular fluid (GCF) during orthodontic tooth movement using self-ligating brackets. MATERIALS AND METHODS: Forty patients were selected and treated with two kinds of self-ligating brackets, Quick 2.0 and Smart Clip, and superelastic or thermoactive archwires. Patients' lower arches were bonded and GCF was collected at one side for each tooth at baseline, one hour after bonding and on the 7(th), 28(th) and 42(nd) day. Test teeth were 4.1, 4.3 and 4.5. Control teeth were 1.1, 1.3 and 1.5. Samples were analyzed with a specific assay for LDH activity. RESULTS: The statistical analysis showed no significant differences in the LDH activity between test and control teeth in the selected groups. CONCLUSIONS: There are no significant differences, in terms of tissue response, between superelastic and thermoactive archwires.