Radiopacity of impression materials.

The radiographic densitites of twenty-six impression materials were measured and the values expressed as an equivalent thickness of aluminum. Under simulated clinical conditions, only ten of the materials tested could be consistently distinguished from the bone structure in periapical radiographs. It was far more dificult to detect objects with beveled margins than objects of uniform thickness. The minimum radiopacity of a material which could be detected in the periodontal tissue on a periapical radiograph was estimated.