Apexification is the treatment of choice for a permanent tooth with wide open apex when:

Apexification is the process of inducing the development of the root and the apical closure in an immature pulpless tooth with an open apex. The main aim of apexification is to preserve the Hertwig’s root sheath and apical pulp tissue. Ref :Textbook of endodontics, Nisha Garg and Amit Garg, 3rd edition, pg no:548