The minimum space of 0.5 mm around the pin is necessary to allow adequate condensation of dental amalgam without creating voids or weakening the restoration. This space ensures proper adaptation of the amalgam matrix around the pin, providing mechanical retention and reducing the risk of amalgam fracture or marginal breakdown. Less than 0.5 mm leads to insufficient condensation, while more space compromises retention and strength. Maintaining this minimal gap is crucial for the longevity and durability of the amalgam restoration.

Reference: Sturdevant's Art and Science of Operative Dentistry, 7th Edition.