In this double blind randomized clinical trial study effect of meloxicam, ibuprofen and acetaminophen on post separator pain will be evaluated and compared. 321 patients who need fixed orthodontic therapy and are older than 15 years old will be selected. All participants must have the following criteria: not currently using antibiotics, analgesics; anti – inflammatory, anti-coagulative, diuretics, oral anti diabetics, lithium, cyclosporine and methotrexate; no need for antibiotic prophylaxis; no chronic systemic disease or clotting disorders; not reporting contraindication for NSAIDs; not pregnant or nursing. Patient who use any other analgesic during the period of study will be excluded. The patients will be divided to three groups: group A (650 mg acetaminophen), group B (400 mg ibuprofen) and group C (7.5 mg meloxicam). All patients will be given only one tablet, 1 hour before separator placement. A visual analogue scale (VAS) will be used to determine the degree of the pain and discomfort at the following intervals: Immediately after separator placement, 2 hours post treatment, 6 hours post treatment, 24 hours post treatment, and 48 hours after separator placement. Patients will be instructed to mark the degree of the pain with a short vertical line on the VAS during three oral situations including rest, fitting posterior teeth, and chewing, and return the questionnaire in the next visit (a week later).