Journal of Dental Research, Vol 68, 1234-1237, Copyright © 1989 by International & American Associations for Dental Research Online Journals
An in vitro investigation of the effects of glass inserts on the effective composite resin polymerization shrinkage
K. J. Donly, T. W. Wild, R. L. Bowen and M. E. Jensen
University of Texas Dental Branch, Houston 77030.
We placed an MOD preparation in each of 12 permanent molars, then restored
each tooth with a posterior composite resin by means of six different
application techniques (I-polymerization as one complete unit;
II--polymerization as one complete unit with glass inserts;
III--polymerization in gingivo-occlusal increments; IV-polymerization in
gingivo-occlusal increments with glass inserts; V--polymerization in
bucco-lingual increments; and VI--polymerization in a gingival increment
with glass inserts, then bucco-lingual increments). A precision strain
gauge was attached to the buccal surface of each tooth and balanced at
zero. After each increment was polymerized, the strain appearing on the
strain gauge indicator was recorded. Each tooth was restored by use of all
techniques; two teeth started with each technique. Results demonstrated the
average microstrain units to be 127-I, 102-II, 105-III, 86-IV, 72-V, and
66-VI. A randomized block design was the format used for data evaluation.
Scheffe's Test indicated that composite resin placement and polymerization
in bucco-lingual increments (V) created significantly less cuspal
deflection than polymerization as one complete unit, with or without glass
inserts (I and II), p less than 0.001, and gingivo-occlusal increments
(III), p less than 0.05. Placement and polymerization in a gingival
increment with glass inserts, then bucco-lingual increments (VI), also
created significantly less internal deflection than polymerization as one
complete unit, with or without glass inserts (I and II), p less than 0.001,
and gingivo-occlusal increments (III), p less than 0.005.
