Introduction: Recently, regenerative endodontic procedures (REPs) have been used to treat mature permanent teeth with apical periodontitis. Although animal studies with regard to histopathological findings after REPs exist, there is a paucity of studies on mature human teeth. As yet, the nature of tissues formed in the root canal of such teeth has not been established. This report presents histologic findings with regard to regenerative tissues in the pulp spaces exposed after dental trauma in human mature maxillary incisor teeth successfully treated with REPs. Methods: A 20-year-old girl was referred to our clinic for the treatment of her central incisors (#8 and #9). The incisors had apical periodontitis. REPs were performed on both maxillary central incisors. Three years 5 months after the initial treatment, the teeth had a horizontal crown fracture and needed a fiber post as well as root canal treatment. Mineral trioxide aggregate was carefully removed, and the tissue that had formed in the canal space was processed for routine histologic and immunohistochemical examination. Results: Histologic findings of the present case showed that the vital tissue formed in the canal space was fibrous connective tissue that contains bonelike tissue, vascular structures, and inflammation. These histologic findings obtained from mature teeth were similar to the findings of previous reports relating to immature teeth. Conclusions: Based on the present case, the vital tissue formed in the canal space is fibrous connective tissue that contains bonelike tissue, vascular structures, and inflammation. These histologic findings with regard to mature teeth were similar to the findings of previous reports relating to immature teeth.