[Angle reproducibility and surface roughness of stone casts obtained from combined agar-alginate impressions]

Angle reproducibility and surface roughness were compared among stone casts obtained from two agar-alginate impression methods; 1) conventional method in which an alginate mix was applied before gelation of agar, and 2) improved method in which an alginate mix was applied to gelled agar. Impressions of the rectangular parallel piped metal mold with a high accurate point angle was taken according to the above methods, and stone casts were obtained. Enlarged images of the angles of the casts were projected with an optical projector, and the defects of the point angle were traced. The area, the length and the circular-degree coefficient of the defects were determined using an image analysis system. The surface roughness of the stone casts was also measured. The stone casts prepared by the improved agar-alginate method had better angle reproducibility and the same surface roughness as that prepared by the conventional method.