Final answer:
The canal is filled with Gutta-percha after root canal therapy, which is the material specifically designed for this purpose, and not with dental amalgams, composite resin, or Zinc oxide-eugenol cement.
Step-by-step explanation:
Once the root canal therapy is completed, the canal is filled with A) Gutta-percha. This material is preferred because it is biocompatible and can be easily shaped and packed to fill the intricate spaces within the root canal. Unlike dental amalgams which contain silver and other metals and are typically used for filling cavities in teeth, Gutta-percha is specifically designed for filling root canals. Dental amalgams are known to be approximately 50% mercury by weight, and while they offer low cost and longevity, they are not used in root canals. Composite resin and Zinc oxide-eugenol cement are also not the primary filling materials for root canals, although they have their applications in other types of dental restorations.