Bz. Laufer et al., THE EFFECT OF MARGINAL THICKNESS ON THE DISTORTION OF DIFFERENT IMPRESSION MATERIALS, The Journal of prosthetic dentistry, 76(5), 1996, pp. 466-471
An impression of the margins of a prepared tooth and adjacent gingival
sulcus must be of sufficient thickness to withstand distortion and te
aring when the impression is removed from the mouth. The purpose of th
is study was to compare the dimensional accuracy of Elite, Examix, and
Express polyvinyl siloxanes; Permadyne polyether; and Permlastic poly
sulfide elastomeric impression materials. These materials were used to
make impressions of a metal model that simulated prepared abutments w
ith gingival sulci of various widths. A traveling microscope was used
to measure the abutments and impression widths, and the number of defe
cts in each impression was recorded. Between 70% and 100% of the abutm
ent impressions with sulcular widths of 0.05 mm exhibited defects, whi
ch prevented accurate measurements in this group. Express material dem
onstrated a high number of defects in the 0.10 and 0.16 mm sulcular wi
dth groups. No great difference in average maximum distortion values o
r coefficients of variation (CV) were detected among the materials use
d to make impressions of abutments with sulcular width groups of 0.2 t
o 0.4 mm. For the sulci of 0.16 mm and less, Examix and Permlastic mat
erials exhibited distortion and a CV comparable to the impressions of
the wider sulcular groups, whereas Elite and Permadyne showed greater
distortions and CVs. The differences were not statistically significan
t (analysis of variance) because of the larger CV among the groups. Th
e larger coefficient of variation in the 0.1 and 0.16 mm sulcular widt
h groups demonstrated inconsistencies in obtaining good impressions of
abutments with such narrow sulcular widths.