Following traumatic injury, pulpal and periapical pathosis in an immature anterior tooth is common, and treating open apices in these situations is a persistent problem for pedodontists. This is because there is no apical constriction, which would prevent the obturated material from forming an excellent threedimensional seal or adaption within the canal system. Mineral Trioxide Aggregate (MTA) offers a good choice when employed to create an apical barrier. In this case report, an open apex and periapical lesion involving maxillary right central incisor #21 with the MTA are shown with a six-week follow-up result after being treated for four weeks with triple antibiotic paste as an intra-canal medication. The successful healing of tooth 21 and the diminution of the periapical radiolucency at one-week follow-up were observed.