Effect of distribution of resistance features in complex amalgam restorations

This study measured fracture resistance of complex amalgam restorations when pins or amalgapins were either distributed around the preparation or concentrated in one area of the preparation. The occlusal surfaces of 80 extracted molars were ground flat to 2 mm occlusal to the cementoenamel junction (CEJ). Roots were notched and embedded. Teeth were sized and distributed equally into eight groups (n = 10). Resistance features, four TMS stainless steel Regular pins or four amalgapin channels, were inserted into each molar. Resistance features were either distributed at the four line angles of each molar or clustered at two line angles. Matrices were applied, and amalgam was mechanically condensed into the matrices. Restorations were adjusted to a 4 mm vertical height and flat occlusal surfaces. A load was applied to each restoration at either a 45 degrees or a 90 degrees angle to the long axis of the tooth. Distributed pins provided significantly more resistance than clustered pins in groups tested at 90 degrees. Resistance to fracture in all groups loaded at 45 degrees and in amalgapin groups was not significantly affected by distribution of resistance features. Pins provided significantly more resistance than amalgapins at both angles of testing.