Why do you overpack amalgam?

Overpacking amalgam serves the purpose of ensuring that all margins of the cavity preparation are properly covered. This action is crucial for achieving a sealed restoration that prevents microleakage and subsequent postoperative sensitivity. By overpacking, the clinician ensures that there is sufficient material to fill any potential voids and create a good seal along the margins where the amalgam meets the tooth structure.

While the answer provided cites that excess mercury reaches the surface, the primary clinical rationale for overpacking is related to achieving a complete and effective seal at the margins. This helps to maintain the integrity of the restoration and minimizes the risk of decay beneath the filling, thereby promoting long-term success of the amalgam restoration. Understanding this concept is key for anyone practicing in dentistry, as it directly relates to the effectiveness and longevity of dental restorations.