The preferred treatment method for managing an immature tooth with a blunderbuss apex is Apexification with mineral trioxide aggregate (MTA).

An immature tooth with a blunderbuss apex presents a wide open apex and thin dentinal walls, making traditional root canal therapy challenging. The main goal is to create an apical barrier to allow for proper obturation of the root canal system.

Key points to consider:

- Apexification is a procedure aimed at inducing a calcified barrier in a root with an open apex.
- Traditionally, calcium hydroxide was used for apexification; however, this requires multiple visits over several months and has potential drawbacks such as weakening of dentinal walls and increased risk of root fracture.
- Mineral trioxide aggregate (MTA) has become the material of choice because it can create an immediate and biocompatible apical plug, allowing for faster and predictable obturation.
- MTA also promotes hard tissue formation and provides a superior seal.
- Pulpectomy followed by gutta-percha obturation (Option 2) is contraindicated until a proper apical barrier is established because gutta-percha won’t seal effectively in a wide open apex.
- Surgical apicoectomy with retrograde filling (Option 4) is generally reserved for cases where nonsurgical apexification fails or is not feasible.

Therefore, Apexification with MTA provides a faster, more reliable, and biocompatible method to manage immature teeth with blunderbuss apices, promoting better long-term prognosis.

Reference:
Grossman’s Endodontic Practice, 13th Edition, Chapter 15: Treatment of Immature Teeth with Open Apices / Page 572-575