MMP9 and periodontal disorder: However, prominent expression of collagen type III and increased numbers of cells expressing high MMP‐9 and MMP‐13 levels or cells positive for a‐SMA, presumably myofibroblasts, are found apical to migrating epithelium and around sites of osteonecrosis.(94) Interestingly, increased duration of periodontal disease augments the incidence of MRONJ,(95, 105) while prevention or decrease of periodontal disease severity reduces MRONJ presence,(106) demonstrating a time dependence between the two entities.