Apical Periodontitis: Microbial Infection and Host Responses

Traditionally, endodontology includes pulp and periapical biology and pathology. Clinically, however, endodontics is perceived as treatment of the root canal with fi les and the placement of a root fi lling, or treatment by surgical endodontics. The vital pulp and the treatment measures to preserve its vitality are usually considered a part of conservative dentistry, and include specifi c techniques in dental traumatology. In both principle and practice, the situation changes when pulp extirpation or root canal treatment is considered necessary. While the initial diagnoses and the diffi culties associated with treatment may be related to the state of the pulp, the purpose of treatment is no longer the preservation of the pulp, but the prevention and elimination of infection in the root canal system. The ultimate biological aim of this treatment is either to prevent or cure apical periodontitis (Fig. 1.1). Of the endodontic diseases, apical periodontitis is therefore prominent as it is a primary indication for root canal treatment and because it is by far the most common sequel when treatment is inadequate or fails. Research in recent decades has documented particularly the importance of microbial factors in the initia tion, development and persistence of apical periodontitis [3,12,13,20,21,26,27,30,35] (Fig. 1.2). Emphasis must therefore be on the infectious etiology of apical 1.