RESUMO
AIM: To evaluate the association between the presence of selected bacterial species/groups in the apical root canal and expression of mediators of soft and bone tissue destruction in apical periodontitis lesions. Relationships between bacteria and some other features of apical periodontitis were also investigated. METHODOLOGY: Seventeen freshly extracted teeth with pulp necrosis and apical periodontitis were included. The apical root segment was sectioned and cryopulverized; DNA was extracted and evaluated for the presence of 9 bacterial species/groups using real-time polymerase chain reaction. Lesions were processed for histopathological and immunohistochemical analyses, which targeted matrix metalloproteinase-2 (MMP-2) and -9 (MMP-9), receptor activator of NFκB (RANK), RANK ligand (RANKL) and osteoprotegerin (OPG). Associations of the target bacteria with expression of these mediators, presence of symptoms, lesion size and histopathological diagnosis were evaluated. Data were analysed using the chi-square, Fisher's exact, Mann-Whitney and Pearson tests. P values lower than 0.05 were considered significant. RESULTS: All pulverized apical root samples were positive for bacteria. The most prevalent taxa were Actinobacteria (53%), Streptococcus species (35%), Fusobacterium species and Parvimonas micra (18%). The target mediators exhibited a high mean expression in the lesions (MMP-2: 82%; MMP-9: 73%; RANK: 78%; RANKL; 81%; OPG; 83%). Mean RANKL:OPG ratio was significantly higher in granulomas than cysts (P < 0.05, Mann-Whitney test). Actinobacteria were associated with granulomas, higher MMP-2 expression, lower OPG expression, and higher RANKL:OPG ratio (P < 0.05 for all, Fisher's exact test or Mann-Whitney test). No other significant associations were found. CONCLUSION: Actinobacteria may play an important role in the active phase of soft and bone tissue destruction in apical periodontitis.