Before a root amputation, the canal orifice is typically sealed with:

Before a root amputation, the canal orifice is typically sealed with amalgam because of its excellent marginal seal, durability, and resistance to contamination during surgery. Amalgam provides a moisture-tolerant and mechanically stable barrier that withstands the surgical environment and prevents bacterial ingress. Its compaction ability ensures a dense, impervious seal essential for maintaining canal sterility throughout and after the procedure. Other materials lack the combination of these properties under surgical conditions, making amalgam the preferred choice.

Reference: Pathways of the Pulp, Cohen & Hargreaves, 12th Edition.