MMP9 and periodontitis: The periodontium of rats presenting with experimental periodontitis receiving no treatment (EPD) showed marked immune-staining for to the following markers: MMP-2, MMP-9, COX-2, RANK-L, and RANK (Figure 2B, E, H, K, and N) compared to periodontium staining profile of the saline group (Figure 2A, D, G, J, and M).