A histological investigation into the actual conditions of infected regions of apices of the teeth with apical periodontitis

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To investigate the apical region of the root with infected root canal is important not only for the elucidation of pathogenesis of apical periodontitis but for the development of treatments or diagnosis of it. Because apical regions of roots with infected canal could be the front of host and parasite. Hence, we examined immunohistologically the localization and prevalence of bacteria in the apical third of a root canal and the extra-radical area surrounding an apical foramen of the teeth with apical periodontitis. Moreover we examined these regions by scanning electron microscopy (SEM). In the apical portion of the infected root canal, 5. sanguis, P. nigrescens/P. intermedia, S. mutatis, L. plantarum, and L. case/ were frequently observed, and in the extra-radical regions, L. plantarum, S. mutans, P. nigrescens/P. intermedia were frequently observed. In particular, L. plantarum was most frequently detected in the extra-radical areas; indicating this bacteria would play important roles in the pathogenesis of apical periodontitis. These results showed the close relationship between extraradical and intra-canal bacteria in apical periodontitis. SEM observations showed that bacteria aggregated in the extra-radical area on a root surface and were related to bacteria of the intra-root canal, which was consistent with immunohistological observations described above. The aggregated bacteria in the extra-radical areas produced extra-cellular matrix and formed biofilm that prevented host-defending systems from eliminating parasites. These findings indicate that intra-canal bacteria in the apical portion invaded and affected extra-radical areas by forming biofilm, which caused the chronic lesion i.e. apical periodontitis.