Endodontic treatment of teeth with incomplete root formation is complex and requires great professional skill due to occur frequently in young patients. Reduce the number of sessions required for treatment without harming the quality would decrease the damage to the tooth crown due to subsequent reinterventions necessary for the exchange of intra-canal medication, and allow completion of the final restoration soon. In the treatment of teeth with incomplete root formation and pulp necrosis MTA (Mineral Trioxide Aggregate) can be recommended for making an apical cap (plug), allowing the completion of root canal filling. The mineral trioxide aggregate (MTA) is a cement that was introduced to endodontics by Lee et al. 14 (1993). 14 (1993). Its excellent sealing ability, resistance to microleakage and it can be used in humid environment or with the presence of blood, makes it suitable for use as apical barrier in teeth with incompletely formed apex. Shabahang and Torabinejad (2000) using the MTA as apical barrier, have demonstrated the induction in the formation of hard tissue. The MTA in conjunction with calcium hydroxide is a valid option for the apexification, bringing main advantage of the speed with which treatment can be completed. (ANALYSIS IN VITRO VIABILITY OF USING THE MTA AND CALCIUM HYDROXIDE AS PLUG IN TEETH WITH APICAL incomplete root formation. In ABO-GO). Case Study: History: Patient special nine years, with cognitive and motor disabilities. Arrived in the clinic with a history of trauma resulting from a fall from their own height, where there was subluxation in the maxilar central incisors. He was treated at a clinic and made radiographs, where we observed the coronal fracture of the items cited, but without any change in the periapical tissues and bone structures. After 9 months the patient's mother noted the steady growth and a monthly ball with pus in the region of the element (second report). Radiographically: Studies in the periapical radiograph, the coronal fractures of the elements 11:21, and noticed a radiolucency in the root element 21. It was also observed that both elements had to incomplete root formation. Diagnosis: chronic apical periodontitis. Proposed treatment: necropulpectomy with apexification with MTA, a single session under intravenous sedation. Instrumentation final 80. Hypochlorite solution with 5.25%. Final irrigation with saline. Placement of 1 mm calcium hydroxide in the apical region. Plug 4 mm of MTA. Endodontics is the science and art that involves the etiology, prevention, diagnosis and treatment of the impact on the periapical region and consequently in the body. This requires the dentist clinical experience and business sense, and technological resources that provide advantages in cost / benefit ratio for achieving endodontic success, often for the same, being recommended endodontic retreatment before other types of invasive surgeries. The endodontic retreatment is a procedure performed on a tooth that has undergone a treatment which resulted in a condition that requires a new endodontic treatment to obtain a satisfactory result. The goal of endodontic therapy is to perform a root canal in order to make the treated tooth again functional and comfortable, allowing the complete repair of the support structures. A