To contain gutta-percha within the canal, instrumentation should result in:

The instrumentation and obturation should not extend beyond the apical foramen. Whereas the guideline of 1 mm from the radiographic apex remains rational when using radiographs, the point of apical termination of the preparation and obturation remains empirical. The need to compact the gutta-percha and sealer against the apical dentin matrix (constriction of the canal) is necessary to prevent extrusion of materials into the periapical tissues. Textbook of Endodontics 3rd Ed P: