Inflammation, Osteoclastogenesis and MMP-9 Are Modulated by Root Canal Therapy

Objectives: Apical periodontitis represents a local immune response to the progression of microorganisms from the dental pulp to the apical foramen that results in bone resorption by osteoclasts. The role of matrix metalloproteinases (MMP) during the development and progression of apical periodontitis has been reported. The aim of this study was to investigate the inflammatory infiltrate, osteoclastogenesis and expression of MMP-9 in apical periodontitis and during the periapical healing phase following root canal treatment. Methods: Apical periodontitis was induced in dogs teeth and root canal treatment was performed in a single visit or using an additional calcium hydroxide root canal dressing. One hundred and eighty days following treatment the presence of inflammation was examined and tissues were stained to detect osteoclasts by means of a tartrate resistant alkaline phosphatase (TRAP) assay. To investigate the degree of tissue organization, tissues were stained for MMP-9 using a peroxidase-based immunohistochemistry assay. Percentage of positively-stained cells were determined and data were analyzed using Kruskal-Wallis followed by Dunn tests (alpha = 0.05). Results: Teeth with apical periodontitis that had root canal therapy performed in a single visit presented an intense inflammatory cell infiltrate. Periapical tissue was extremely disorganized, with the presence of osteoclasts and a high MMP-9 expression, similar to teeth with untreated apical periodontitis. In contrast, teeth with apical periodontitis submitted to root canal treatment using calcium hydroxide root canal dressing presented a lower inflammatory cell infiltrate. This group had a moderately organized connective tissue, a lower prevalence of osteoclasts, and a lower number of MMP-9-positive cells. Conclusion: Teeth treated with calcium hydroxide root canal dressing exhibited a lower amount of inflammatory cells and TRAP-positive osteoclasts, a more organized ECM with lower MMP-9 expression, unlike those treated in a single visit. Financial support: FAPESP (2009/16882-7).