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 three-dimensional 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.