Histologic Characterization of Regenerated Tissues in Canal Space after the Revitalization/Revascularization Procedure of Immature Dog Teeth with Apical Periodontitis

Introduction: Recently, it has been shown that it is possible to treat an immature tooth with an infected pulp space and apical periodontitis in such a way as to heal and promote the ingrown of new vital tissue into the pulp space. However, the type of new-grown tissue is unclear. Methods: Based on the samples of a previously reported study, we further investigated histologically the types of tissues that had grown into the canal space. Results: The canal dentinal walls were thickened by the apposition of newly generated cementum-like tissue termed herein "intracanal cementum (IC)." One case showed partial survival of pulp tissue juxtaposed with fibrous connective tissue that formed IC on canal dentin walls. The IC may also form a bridge at the apex, in the apical third or midthird of the canal. The root length in many cases was increased by the growth of cementum. The generation of apical cementum or IC may occur despite the presence of inflammatory infiltration at the apex or in the canal. These cementum or cementum-like tissues were similar to cellular cementum. Bone or bone-like tissue was observed in the canal space in many cases and is termed intracanal bone (IB). Connective tissue similar to periodontal ligament was also present in the canal space surrounding the IC and/or IB. Conclusions: Our findings explained in part why many clinical cases of immature teeth with apical periodontitis or abscess may gain root thickness and apical length after conservative treatment with the revitalization procedure.