Evaluation of the effects of an Iraqi phosphate bonded investment and two commercial types on the marginal fitness of porcelain- fused- to- metal copings .

Abstract

The effect of different phosphate- bonded investments on the marginal fitness
of porcelain- fused—to-metal copings cast by one type of noble alloy and one type of
base metal alloy was studied. Three types of phosphate—bonded investments (Castorit -
Super C, Norvest, and Iraqivest) were used for investing the thirty copings of each
group. The marginal fitness of each coping was determined by measuring the vertical
marginal discrepancies between the gingival margin of the coping and the margin of
the preparation at four reference points on the labial, mesial, palatal and distal aspects
of the die by the aid of light traveling microscope .
The statistical analysis of the results showed that there were significant
differences in marginal fitness among different investments for both Pd- Ag& Ni-Cr
alloys. The Castorit- Super C and Norvest investments produced comparable results
with both alloys, while the Iraqivest appeared less compatible with Pd-Ag alloy than
the other two investments and it had comparable compatibility to Norvest investment
when used with Ni- Cr alloy. The Ni- Cr alloy (Heraenium NA) copings revealed
significantly greater marginal discrepancy than the Pd-Ag alloy (QD) eopings
specially when using Castorit- Super C and Norvest investments .