 The proposed clinical trial will evaluate the role of genetic factors including single nucleotide polymorphisms from cyclooxygenase COX - 2 gene on acute pain after tissue injury and the analgesic effect of a COX inhibitor. Patients will be healthy volunteers scheduled for the surgical removal of impacted third molars. Genotyping will be performed before surgery and patients stratified to treatment with a COX inhibitor in this protocol or to other protocols examining different polymorphisms. 