What is the primary reason for overfill during the condensation of an amalgam?

Overfilling during the condensation of amalgam is primarily done to facilitate the removal of the mercury-rich outer layer of the amalgam. This layer can be detrimental to the mechanical properties of the final restoration because it is softer and more susceptible to wear and degradation. By overfilling the amalgam and then carving back the excess, you ensure that a denser, more durable core is exposed and shaped, which contributes to the overall integrity and longevity of the dental restoration.

The process of condensation itself compacts the amalgam, and overfilling allows the operator to carve down to a desirable contour while eliminating the weaker, mercury-rich outer layer. Therefore, this technique is essential in providing a restoration that is not only functional but also durable against the forces of mastication.