A child has mid-crown fracture in a permanent
maxillary central incisor several months ago, the pulp is now necrotic, radiographic examination reveals an incompletely formed root with an open apex. The treatment of choice is:
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
Formocresol pulpotomy
Root canal therapy
Calcium hydroxide pulpotomy
Apexification