Final answer:
The most conservative final restoration after endodontic therapy on a maxillary molar is to repair the access opening with dental amalgam or composite resin, preferably the latter due to concerns about mercury in amalgams.
Step-by-step explanation:
The most conservative final restoration that is indicated after endodontic therapy on a maxillary molar with an MOD alloy is the repair of the access opening with either dental amalgam or composite resin. An MOD inlay or onlay and a full crown would provide more coverage and strength if substantial tooth structure is missing. However, these options are more invasive than simply repairing the opening. Dental amalgams are known for their low cost, ease of manipulation, and longevity but have raised health concerns due to their mercury content. Composite resin, on the other hand, is mercury-free and can provide good durability while also being more esthetically pleasing, making it a suitable and conservative choice for the repair.