Journal of Dental Research, Vol 67, 1278-1283, Copyright © 1988 by International & American Associations for Dental Research Online Journals
Effect of the porosity of the filler aggregates on the setting expansion of investment material
J. Takahashi, M. Okazaki, H. Kimura, Y. Haeuchi and F. Kubo
Department of Dental Technology, Osaka University Faculty of Dentistry, Japan.
Twenty experimental phosphate-bonded investments were prepared by the
mixing of two types of fillers (spherical glass beads and irregularly
shaped silica particles) with five types of filler aggregates of different
porosities, and two different ratios of MgO to NH4H2PO4. These investments
were mixed with three different liquids, and their setting expansion, time
until setting expansion began (induction time), and fluidity were measured
under constant experimental conditions. The following results were
obtained: (1) The setting expansion was significantly related to bulk
porosity of filler aggregates, not to packed porosity, despite variations
in type of filler, ratio of MgO to NH4H2PO4 or type of liquid; and (2) the
fluidity and the time until setting expansion began were also related to
the bulk porosity of the filler aggregates.
