A biochemical examination of saliva showed a higher mean level of MMP-2, MMP-8, and MMP-9 and TIMP-1 inhibitor in the saliva of JIA patients compared with the C group; however, a statistically significant difference was demonstrated only in the case of MMP-9 in all patients as well as in the group of children with mixed dentition (JIA MD). The gene discussed is MMP8; the disease is juvenile idiopathic arthritis.