EARLY FRACTURE-RESISTANCE OF AMALGAPIN-RETAINED COMPLEX AMALGAM RESTORATIONS

Amalgapins are susceptible to early fracture during matrix removal and carving. The purpose of this study was to examine the early fracture resistance of amalgapin-retained restorations using a spherical amalga m alloy, an admired amalgam alloy, a combination of admired alloy over the spherical alloy, and a recently introduced modified spherical ama lgam alloy. Four amalgapin channels with a diameter of 1.4 mm and dept h of 2 mm were prepared in cylinders of Macor, a machinable ceramic ma terial. The amalgapins were hand condensed, and the bulk of the restor ation was mechanically condensed. In the group using the combination o f alloys, 800 mg of spherical alloy was condensed into the amalgapins and over the floor of the preparation. The admired alloy was then cond ensed over the spherical alloy to build up the bulk of the restoration . Using an Instron Universal Testing Machine, the restorations were te sted to shear failure at an average of 15.8 +/- 1.3 minutes after the initiation of trituration of the amalgam alloy. A metal ring was place d around the restoration and pulled 90 degrees to the long axis to sim ulate matrix band removal. Data were analyzed using Kruskal-Wallis pro cedures. The fracture resistance of the spherical alloy group and the spherical/admired group were significantly higher than admired or Tyti n FC. All fractures occurred in amalgam at the entrance to the amalgap in channel. The combination of spherical and admired amalgam alloys in a restoration may reduce the potential for early dislodgment while al lowing additional time for carving.