610 the journal of prosthetic dentistry volume 81 number 5

DISCUSSION
Polymerization shrinkage of resin-containing restora-
tive materials may result in marginal discrepancies that
lead to microleakage, marginal discoloration, and sensi-
tivity.
2-4
Hygroscopic expansion can compensate, to
some degree, for polymerization shrinkage. Water sorp-
tion can help to reduce marginal gaps
3
; for this reason,
glass ionomer cements, which absorb the most water
during the first 24 hours after placement,
6
can display
less microleakage than resins. Attin et al
7
reported that
Fuji II LC glass ionomer cement expanded after curing
and immersion in water, whereas Dyract resin composite
and Vitremer glass ionomer cement revealed a total vol-
umetric loss. Thus, they concluded that water expansion
is 1 factor that reduces the leakage.
THE JOURNAL OF PROSTHETIC DENTISTRY
TOLEDANO ET AL
612
VOLUME 81 NUMBER 5
Table I. Microleakage of the different groups
Occlusal
Gingival
Overall
Group
0
1
2
3
0
1
2
3
0
1
2
3
Fuji II LC (n = 17)
14
1
0
2
12
2
0
3
10
3
0
4
Vitremer (n = 18)
9
3
2
4
8
1
4
5
4
4
4
6
Dyract (n = 22)
7
4
6
5
6
3
0
13
5
3
1
13
Kruskal-Wallis 1-way analysis of variance indicated significant differences between all the restorative materials for both overall, occlusal, and gingival scores
(
P=.03; P=.01; P=.01, respectively).
Wilcoxon test (to compare occlusal, gingival, and overall scores of each material) revealed that the occlusal and gingival scores for each matched pair of restora-
tive materials showed statistically significant differences between Fuji II LC and Dyract, both for the occlusal (
P=.005) and gingival (P=.005) margins and also as
an overall evaluation (
P=.01) with Fuji II LC showing the least dye penetration. Although Vitremer revealed dye penetration scores between Fuji II LC and Dyract,
there were no statistically significant differences between them. Also, there were no statistically significant differences between Dyract and Vitremer.

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Our results disagree with those of Yap et al
8
who
compared the microleakage of Dyract resin composite
and Fuji II LC glass ionomer cement and reported no
statistically significant differences in microleakage
scores. In their study, they reported a significant differ-
ence between enamel and dentin; in our study, even if
microleakage was less common in enamel, the differ-
ence was not significantly different. These differences
between the studies could be because Yap et al
8
stored
their specimens in a saline solution for 1 week before
testing. This storage time allows hygroscopic expansion
of the material,
7
which may compensate the original
polymerization shrinkage of the material, which allows
less microleakage. In our study, specimens were ther-
mally cycled for approximately 2 days, and the material
may not have expanded completely. Yap et al
8
also sug-
gested that 1 of the unique features of the resin that
releases fluoride to enamel is the omission of acid etch-
ing, which is a critical step in most resin composite and
adhesive systems. The manufacturers have claimed that
this is achieved through the use of a specially formulat-
ed coupling agent with hydrophilic phosphate groups
that is thought to form ionic bonds with the calcium of
hydroxyapatite. Dyract resin composite also aims to be
self-adhesive because of hydrophilic carboxylic groups
present in its patent tetrachlorobiohenyl (TCB) resin.
These questions need further investigation.
No restorative material evaluated in our study com-
pletely resisted microleakage at the occlusal or gingi-
val walls of the tooth. Of the 3 products evaluated,
Fuji II LC glass ionomer cement exhibited the least
dye penetration, at both the occlusal and gingival
margins, and when evaluated as overall values (enam-
el and gingival scores pooled together). However,
only with the overall evaluation did Fuji II LC glass
ionomer cement reveal a statistically significant differ-
ence with Dyract resin composite. The lack of statisti-
cally significant difference in microleakage between
resin-modified glass ionomers has also been previous-
ly reported.
15
Uno et al
16
concluded that the superior
adaptation of Fuji II LC glass ionomer cement to the
cavity walls was responsible for the lower dye penetra-
tion, which may be a result of the glass ionomer
cement undergoing minimal setting shrinkage over a
longer period and approximately one half that of
resins.
17
Because the resin component is responsible
for the polymerization shrinkage, and Dyract resin
composite has more resin than Fuji II LC glass
ionomer cement in its composition, it is possible that
this is the reason for the greater microleakage scores
observed with Dyract resin composite. Another reason
that could explain the results is the resin component
of Fuji II LC glass ionomer cement undergoing dif-
ferent rates of polymerization shrinkage during light
curing (as it is a dual-cure material) compared with
Dyract resin composite.
The microleakage scores for Vitremer glass ionomer
cement fell between those recorded for Dyract resin
composite and Fuji II LC glass ionomer cement, which
could be due to 2 reasons. Fuji II LC is a resin-modified
glass ionomer in which the HEMA content is merely
blended with a polyalkenoic acid liquid, whereas Vit-
remer, in addition to being a simple mixture of HEMA
with polyalkenoic acid, is also modified by the attach-
ment of polymerizable methacrylate side groups.
13
It is
possible that Vitremer has more polymerizable resin
than Fuji II LC, but less than Dyract; its microleakage
values fell in between these 2 materials. The better adap-
tation of Fuji II LC glass ionomer cement compared
with Dyract resin composite could be also due to the
15-second dentin conditioning performed with the
10% polyacrylic acid. This dentin treatment produces a
close relation between the ionomer and dentin struc-
tures as it removes the smear layer, leaving the surface
clean and theoretically better able to accept a glass
ionomer.
18
Moreover, the Fuji II LC liquid contains
approximately 40% HEMA (manufacturer’s data) and
primers that contain similar hydrophilic monomers than
resin-containing materials, facilitating the bonding
between dentin and these type of materials.
19
Although the PAS adhesive of the Dyract resin com-
posite tested had orthophosphoric acid to condition
the dentin, it also contained TGDMA and elastomeric
resins, which have chemical affinity with the resin con-
tained in the material. When these resins shrink during
polymerization, they could generate a gap where
microleakage could be detected. The extent of the cur-
ing shrinkage determines the formation of marginal
gaps if the restorative material does not adhere enough
to tooth structure or it can cause cohesive failures in
the material.
23
The application of Vitremer glass ionomer cement
only requires the primer application and light curing for
20 seconds. It is possible that the pH of the dentin
primer could modify the smear layer sufficiently to per-
mit the tooth and restorative material to come into inti-
mate interfacial contact.
18
Charlton and Haveman
20
obtained higher bond strength values to dentin with Fuji
II LC glass ionomer cement than with VariGlass VLC
resin. Some consider this latter material a light-cured
glass ionomer and not a true polyacid-modified com-
posite because it does not have an acid-base cure reac-
tion.
13
These differences in bond strength values could
contribute, among other factors, to explain the differ-
ences in the microleakage patterns recorded in our
study. Polymerization shrinkage also produces material
shrinkage in all directions and most often the dentin
margins are unprotected to resist microleakage.
2
With
restorations made with resin-reinforced glass ionomers,
the adhesion is mainly due to a physicochemical reaction
with dentin and enamel due to the polar nature of the
polyacrylates and minerals for the dental hard tissues.