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.