Retention design for amalgam restorations: Pins versus slots

The use of pins or slots to provide retention for amalgam restorations has been shown to be equally effective by some authors whereas the pin method has been shown to be more effective by others. This study was done to determine whether the different methods would be affected by the outline form of the preparation. One hundred forty melamine teeth were prepared in three outline forms determined by the cusp that was removed: (1) mesiopalatal, (2) mesiopalatal and distobuccal, and (3) mesiopalatal, distobuccal, and mesiobuccal cusps. Each outline form was restored with a uniform volume of hand-condensed amalgam with pin or slot retention and milled to an occlusal angle of 30 degrees. A load was placed on the milled occlusion with a stainless steel ball to the point of fracture with an MTS machine. No significant difference was found between the pin or slot design for the outline forms evaluated.