Variation in condensation pressure during clinical packing of amalgam restorations

Clinical measurements were made of the condensation pressures applied by a specialist prosthodontist to each amalgam increment during the packing of two pinned Class II restorations. The technique employed involved taking simultaneous video recordings of the operative procedures and the output of a strain gauge stress measuring system attached to the plugger. The condensation pressure applied during each thrust of the plugger could then be related directly to a particular stage of the packing process. In Cavity A, a maxillary left second premolar, an "admix" amalgam containing both spherical and lathe-cut particles was used while Cavity B, a mandibular right first molar, was filled with a spherical particle amalgam. The measurements indicated that the condensation pressures applied decreased substantially as the filling of each cavity proceeded. A marked reduction accompanied the change from a 1.5 mm diameter to a 2.5 mm diameter plugger but in addition, the dentist modified the force applied to each plugger according to the particular task which he was undertaking. For Cavity A, the condensation pressure applied during the filling of the base of the mesial proximal box was 12.6 +/- 1.9 MPa whereas the final increment was subjected to a condensation pressure of only 2.2 +/- 0.7 MPa. Corresponding figures for Cavity B were 7.6 +/- 2.0 MPa and 1.9 +/- 0.5 MPa.