Immature teeth with open foramina present a challenge in root canal treatment. An approved method is apexification using long-term calcium hydroxide dressings, but this approach is associated with a number of clinical problems. The creation of an apical plug is an alternative treatment for teeth having open apices. Mineral trioxide aggregate (MTA) has shown potential as a root-end filling material especially in immature teeth. MTA can be considered a very effective option for apexification with the advantage of reduced treatment time, good sealing ability and high biocompatibility. Four clinical cases describing the treatment of maxillary incisors with necrotic pulp, open apices and apical periodontitis (using the apical plug procedure with MTA) are presented. All cases showed clinical and radiographic signs of healing after apical plugging with MTA. Keywords: apexification, MTA