The two groups with induced periodontitis, when compared to the control group, presented significant differences in relation to MPO activity (3.4 ± 0.8 U/mg of tissue, 51.4 ± 7 U/mg of tissue, 56.1 ± 7 U/mg of tissue, control, one-ligature and two-ligature groups, respectively; P<0.05), but the periodontitis groups 1 and 2 did not differ significantly between each other. The gene discussed is MPO; the disease is periodontitis.