Microleakage of Class V resin modified g
Microleakage of Class V resin-modified glass ionomer and compomer
restorations
Manuel Toledano, MD, BDS, PhD,a Estrella Osorio, LDS, PhD,b Raquel Osorio, LDS, PhD,c and
Franklin García-Godoy, DDS, MSd
University of Granada, Granada, Spain, and University of Texas Health Science Center at San Antonio,
San Antonio, Texas
Statement of problem. Resin-modified glass ionomers and polyacid-modified resin composites (compomers) have been introduced to provide esthetic restorations. However, there is concern about the marginal sealing ability of these materials, especially at the dentin (cementum) aspects of restorations.
Purpose. This in vitro study evaluated the microleakage of Class V restorations made with resin-modified
glass ionomers or a compomer.
Material and methods. Thirty noncarious human molar teeth were used. Standardized kidney-shaped
Class V cavity preparations were placed in the buccal and lingual surfaces at the cementoenamel junction.
Teeth were randomly assigned to 3 experimental groups of 10 teeth each and restored as follows: group 1,
Fuji II LC; group 2, Vitremer; and group 3, Dyract. In all cases, the manufacturers’ instructions were strictly followed. All materials were placed in a single increment. Unfinished restorations were immediately coated with the respective manufacturers’ sealer or varnish and this was either light cured for 20 seconds or
allowed to air-dry. After 24 hours, teeth were finished to contour and to the cavosurface margins, coated
with nail varnish except for 1 mm around the restoration margin, thermocycled (1000×, 5-55°C) and placed
in a solution of 2% basic fuchsin dye for 24 hours at room temperature. The staining along the tooth
restoration interface was recorded.
Results. Kruskal-Wallis 1-way analysis of variance revealed significant differences among all restorative
materials for the overall, occlusal, and gingival scores (P=.03, P=.01, P=.01, respectively). Occlusal and gingival scores for each matched pair of restorative materials using the Wilcoxon test showed statistically significant differences between Fuji II LC glass ionomer cement and Dyract composite, 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. Vitremer revealed dye penetration scores not significantly different from Fuji II
LC glass ionomer cement or Dyract composite.
Conclusion. Resin-modified glass ionomers showed less or similar microleakage than the polyacid-modified composite resin tested. (J Prosthet Dent 1999;81:610-5.)
CLINICAL IMPLICATIONS
The findings of this in vitro study suggest that Fuji II LC glass ionomer cement provided a better marginal adaptation than Dyract composite in Class V restorations,
and the amount of resin content and filler particles of the materials may influence the
degree of microleakage.
M
icroleakage is the movement of bacteria, fluids,
molecules or ions, and even air between the prepared
cavity wall and the subsequently applied restorative
materials.1 Cervical lesions due to caries, erosion, or
abrasion often have both enamel and dentin or cementum margins. The longevity of a conventional Class V
restoration can be affected by mechanical, thermal, and
aProfessor,
Department of Dental Materials, University of Granada,
Spain.
bAssistant Professor, Department of Dental Materials, University of
Granada.
cProfessor, Department of Dental Materials, University of Granada.
dProfessor and Director of Clinical Materials Research, Department
of Restorative Dentistry, Dental School, University of Texas
Health Science Center at San Antonio.
610 THE JOURNAL OF PROSTHETIC DENTISTRY
chemical factors that result in stress in the cervical
area.2,3
Bonded composites have been the common choice
for the esthetic restoration of Class V lesions. However, one disadvantage of composites is polymerization
shrinkage, which can result in marginal discrepancies
leading to microleakage, among other disadvantages.4
This shrinkage has clinical repercussions such as sensitivity, marginal discoloration, and secondary caries.2,3
Many new bonding agents and glass ionomer
restorative materials have been introduced to bond
restorative materials to dentin and cementum margins
of cervical lesions,5,6 but microleakage at the dentin
(cementum) aspects of restorations remains a problem
of clinical significance.1,4,5 Glass ionomers are alternaVOLUME 81 NUMBER 5
TOLEDANO ET AL
tive materials to composites for the conservative
restoration of these lesions because of their adhesion to
tooth structure, fluoride release, biocompatibility,
lower shrinkage values, reduced microleakage, and
acceptable esthetics.7-11 Light-cured resin-modified
glass ionomer cements were developed to improve the
handling and working characteristics of the original
glass ionomer formulation.12,13 Improved adhesion to
dentin is probably caused by both a chemical bond
from the polyacrylic acid component and formation of
a hybrid layer from the hydrophilic HEMA.14-21
Favorable adhesive and fluoride-releasing properties
of glass ionomer cements have lead to their widespread
use as restorative, lining, and luting materials. To overcome the problems of moisture sensitivity and low early
mechanical strengths associated with the conventional
glass ionomer cements (GICs) and at the same time
maintain their clinical advantages, some hybrid versions
of GIC were introduced that are light-cured, because
of their small quantity of resin components such as
HEMA or BIS-GMA. In some situations, the polyacid
also has been modified with side chains that can be
polymerized by light-curing mechanisms. The actual
formulations vary between manufacturers, but the
amount of resin in the final set restoration is between
4.5% to 6%, such as for Fuji II LC and Vitremer glass
ionomer cements. The addition of a resin component
to GIC and its effects on the development of the ionic
crosslink and the subsequent marginal seal against the
tooth structure needs further evaluation.
To overcome technique-sensitive mixing and handling properties of the resin-modified glass ionomer
cements, new materials containing acid-decomposable
glass and acidic polymerizable monomers substituting
the polyalkenoic acid polymer were developed. These
materials were termed polyacid-modified resin composites,22-26 commonly called compomers. Dyract polyacid-modified resin composite belongs to the new
materials that have either been marketed as multipurpose materials, or contain both of the essential components of a glass-ionomer cement but at levels that are
insufficient to produce an acid-base reaction.13 With
this material, the resin content is approximately 28%.
The purpose of this study was to compare the
microleakage of Class V restorations produced with the
3 materials, which differ in their resin content, to test
the hypothesis that resin content affects microleakage.
MATERIAL AND METHODS
Thirty noncarious human molars, which were stored
in a solution of 1% sodium hypochlorite for up to
4 months at room temperature, were test specimens.
After surface debridement with a hand-scaling instrument and cleaning with a rubber cup and slurry of
pumice, a standardized Class V cavity preparation was
placed in the buccal and lingual surface at the cemenMAY 1999
THE JOURNAL OF PROSTHETIC DENTISTRY
toenamel junction. Preparations were made with a
no. 329 carbide bur in a high-speed handpiece and a
template to a uniform kidney-shaped outline. Preparations measured 5 mm long, 3 mm wide, and 2 mm
deep with the occlusal margin in enamel and the gingival margin in dentin or cementum.
Subsequently, teeth were randomly assigned to
3 experimental groups of 10 teeth each. Buccal and lingual preparations of group 1 were restored with Fuji II
LC (GC Corp, Tokyo, Japan) resin-modified glass
ionomer cement; group 2 with Vitremer (3M, St Paul,
Minn.) resin-modified glass ionomer cement; and
group 3 with Dyract (De Trey Dentsply, Konstanz,
Germany) polyacid-modified resin composite.
In all cases, the manufacturers’ instructions for
dentin conditioning, powder/liquid proportioning and
mixing were strictly followed. For Fuji II LC glass
ionomer cement, the cavity wall was conditioned for
20 seconds with dentin conditioner (GC Dental Corp).
For Vitremer glass ionomer cement, Vitremer primer
(3M Dental Products) was applied on the cavity wall
for 20 seconds, gently air dried and light cured for
30 seconds. For Dyract composite restorations, the cavity wall was treated with PAS primer/adhesive (DeTrey
Dentsply) for 30 seconds, excess was removed with a
blast from an air syringe and the adhesive was cured for
20 seconds. A second coat of the primer/adhesive was
applied and immediately light cured for 20 seconds.
Dyract composite was placed in 1 increment. The teeth
were prevented from dehydration by remaining in
deionized water storage at room temperature when not
being prepared for restoration.
Immediately after the restorative material was placed,
a clear cervical matrix (Clear Thru, Premier Dental
Products, Norristown, Pa.) was adapted over the resinmodified GIC restorations and the materials cured with
a visible light source (Optilux 400, Demetron Research
Corp, Danbury, Conn.) in accordance with the manufacturers’ recommended time. The light was tested for
light output (>600 mW/cm2) before each use with a
Demetron radiometer (model 100, Demetron Research
Corp). When the matrix was removed, the unfinished
restorations were immediately coated with the respective
manufacturer’s sealer or varnish, and this was either
cured with a visible light source or allowed to dry before
returning the tooth to deionized water storage at room
temperature. After 24 hours, the teeth were finished to
contour and to the cavosurface margins with a no. 7901
carbide finishing bur (SS White, Lakewood, N.J.) with
air and water spray in a high-speed handpiece (Star Dental, Lancaster, Pa.) and medium, fine, and super fine SofLex disks (3M Dental Products), which were first lubricated with water and used in sequence with air-water
spray in a slow-speed handpiece (Star Dental). The
apical portions of all specimens were filled ad retrum
with a zinc oxide-eugenol paste.
611
THE JOURNAL OF PROSTHETIC DENTISTRY
TOLEDANO ET AL
Table I. Microleakage of the different groups
Occlusal
Group
Fuji II LC (n = 17)
Vitremer (n = 18)
Dyract (n = 22)
Gingival
Overall
0
1
2
3
0
1
2
3
0
1
2
3
14
9
7
1
3
4
0
2
6
2
4
5
12
8
6
2
1
3
0
4
0
3
5
13
10
4
5
3
4
3
0
4
1
4
6
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 restorative 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.
Teeth were prepared for microleakage evaluation by
coating the entire tooth with 1 application of nail varnish, except for 1 mm around the restoration margins.
These specimens were then subjected to 1000 temperature cycles as suggested in a previous study.27 Each
cycle consisted of 30 seconds at 6°C and 30 seconds at
60°C. After thermocycling, teeth were placed in a solution of 2% basic fuchsin dye (Fisher Scientific, Fair
Lawn, N.J.) for 24 hours at room temperature.
After removal of the specimens from the dye solution, the superficial dye was removed with a pumice
slurry and rubber cup. Teeth were then mounted in a
light-curing 1-component methacrylate-based resin
(Technovit 7200 VLC, Kulzer, Norderstedt, Germany)
to facilitate handling during sectioning. The resin was
cured for 24 hours (Histolux, EXAKT, Norderstedt,
Germany), then teeth were sectioned longitudinally
with a hard tissue microtome (Exakt-apparerteban,
Otto Herrman, Norderstedt, Germany) in 0.6-mm
thick sections to evaluate the dye penetration.28 The
sections were then separated, and the cut surfaces corresponding to the most mesial, central (mesial and distal), and most distal portion of the tooth restoration
interface were examined at the occlusal and gingival
margins with a stereomicroscope (Olympus Co, Tokyo,
Japan) at ×16 magnification. Examination of the specimens was undertaken at random, and the investigators
were unaware of the exact nature of the restorative
material.
Staining along the tooth restoration interface was
recorded by 2 evaluators, according to the following
criteria: 0 = no dye penetration; 1 = partial dye penetration; 2 = dye penetration along the occlusal or
gingival wall, but not including the axial wall; and 3 =
dye penetration to and along the axial wall. If disagreement occurred between the evaluators, a consensus was
obtained after reexamination of the specimen by both
investigators. Occlusal, gingival, and overall scores for
each group of restoration were compared with the
Kruskal-Wallis 1-way analysis of variance (ANOVA)
nonparametric statistical test to identify any statistical
612
significant differences between the materials, and the
Wilcoxon test was performed to compare each matched
pair of restorative materials. Significance was considered at the .05 level.
RESULTS
Microleakage scores for the occlusal, gingival, and
overall walls are presented in Table I. Kruskal-Wallis
1-way ANOVA indicated significant differences
between the restorative materials for overall, occlusal,
and gingival scores (P=.03; P=.01; P=.01, respectively).
Further matched analysis by Wilcoxon test was undertaken to compare occlusal, gingival, and overall scores
of each material, which revealed statistically significant
differences between Fuji II LC glass ionomer cement
and Dyract resin composite, both for the occlusal
(P=.005) and gingival (P=.005) margins and also as an
overall evaluation (P=.01) (combining the occlusal and
gingival margins scores) with Fuji II LC demonstrating
the least dye penetration between these 2 products.
Vitremer glass ionomer cement revealed dye penetration scores between Fuji II LC glass ionomer cement
and Dyract resin composite, with no statistically significant differences between Vitremer glass ionomer
cement and the other 2 products.
DISCUSSION
Polymerization shrinkage of resin-containing restorative materials may result in marginal discrepancies that
lead to microleakage, marginal discoloration, and sensitivity.2-4 Hygroscopic expansion can compensate, to
some degree, for polymerization shrinkage. Water sorption can help to reduce marginal gaps3; 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 al7 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 volumetric loss. Thus, they concluded that water expansion
is 1 factor that reduces the leakage.
VOLUME 81 NUMBER 5
TOLEDANO ET AL
Our results disagree with those of Yap et al8 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 difference between enamel and dentin; in our study, even if
microleakage was less common in enamel, the difference was not significantly different. These differences
between the studies could be because Yap et al8 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 thermally cycled for approximately 2 days, and the material
may not have expanded completely. Yap et al8 also suggested that 1 of the unique features of the resin that
releases fluoride to enamel is the omission of acid etching, 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 formulated 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 completely resisted microleakage at the occlusal or gingival 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 (enamel and gingival scores pooled together). However,
only with the overall evaluation did Fuji II LC glass
ionomer cement reveal a statistically significant difference with Dyract resin composite. The lack of statistically significant difference in microleakage between
resin-modified glass ionomers has also been previously reported.15 Uno et al16 concluded that the superior
adaptation of Fuji II LC glass ionomer cement to the
cavity walls was responsible for the lower dye penetration, 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 different rates of polymerization shrinkage during light
curing (as it is a dual-cure material) compared with
Dyract resin composite.
MAY 1999
THE JOURNAL OF PROSTHETIC DENTISTRY
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 Vitremer, in addition to being a simple mixture of HEMA
with polyalkenoic acid, is also modified by the attachment 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 adaptation 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 structures 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 composite tested had orthophosphoric acid to condition
the dentin, it also contained TGDMA and elastomeric
resins, which have chemical affinity with the resin contained in the material. When these resins shrink during
polymerization, they could generate a gap where
microleakage could be detected. The extent of the curing 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 permit the tooth and restorative material to come into intimate interfacial contact.18 Charlton and Haveman20
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 composite because it does not have an acid-base cure reaction.13 These differences in bond strength values could
contribute, among other factors, to explain the differences 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.
613
THE JOURNAL OF PROSTHETIC DENTISTRY
However, this bonding is not so strong and does not
produce an adequate marginal sealing.20,21
The increase in leakage of Dyract resin composite
also could be attributed to thermal expansion mismatch
with tooth substance, which is reported to be significantly higher than that of conventional cements and
also less than that of composites,9,10 perhaps due to
their different chemical composition. Leakage of composite resin restorations may be attributed to a contraction gap produced by polymerization shrinkage and
expansion and contraction with temperature changes,
because the coefficient of thermal expansion of composites is different from that of the dental hard tissues.
Glass ionomer cements exhibit limited shrinkage during setting and their coefficient of thermal expansion is
similar to that of dentin.4 Mitra and Conway9 reported
that Fuji II LC and Vitremer materials had coefficients
of thermal expansion of 31.5 and 11.5 ppm/°C,
respectively, and Silux Plus microfilled composite 56.6
ppm/°C 7 days after curing. Dyract has a composition
closely related to the microfilled composites and has a
coefficient of thermal expansion of 40.52 ppm/°C
(P Hammesfahr, verbal communication, 1998). This
may explain why Dyract resin composite is more susceptible to thermal stresses than the other materials.
Also, because the resin component of the material
adheres poorly to the cervical dentin than to enamel,
this justifies, in part, that the Dyract resin composite
revealed more leakage at the gingival margin than at
the enamel margin.
Although Vitremer glass ionomer cement displayed
microleakage values between those of Fuji II LC and
Dyract materials, there was no statistically significant
difference among the 3 materials. Some authors have
pointed out that significant dimensional changes and
surface hardening can occur after initial light curing of
the resin component of resin-modified glass ionomers,
and further contraction continues for the first 24 hours
as the material matures.10,11 Because both Vitremer
and Fuji II LC glass ionomer cements contain approximately the same percentage of resin, which is less than
that for Dyract composite, it could be thought that this
is another reason to explain the different microleakage
patterns.10,11 Uno et al16 considered that the differences observed between Vitremer and Fuji II LC glass
ionomer cements might be due to differences in maturation of setting reactions.
Although the results obtained from this study may
not be directly extrapolated to the clinical situation,
they provide some information regarding the performance of the restorative system evaluated. Independent
long-term clinical data are still required.
CONCLUSIONS
Within the limits of this study, the following conclusions were drawn:
614
TOLEDANO ET AL
1. The resin-modified glass ionomers showed less or
similar microleakage than the polyacid-modified composite resin tested.
2. The amount of resin content and filler particles of
the materials may influence the degree of microleakage.
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of glass ionomers. Am J Dent 1994;7:47-9.
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THE JOURNAL OF PROSTHETIC DENTISTRY
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Copyright © 1999 by The Editorial Council of The Journal of Prosthetic
Dentistry.
0022-3913/99/$8.00 + 0. 10/1/96694
Reprint requests to:
DR. FRANKLIN GARCIA-GODOY
DEPARTMENT OF RESTORATIVE DENTISTRY
UNIVERSITY OF TEXAS HEALTH SCIENCE CENTER
7703 FLOYD CURL DR
SAN ANTONIO, TX 78284-7850
FAX: (210) 567-3522
E-MAIL: godoy@uthscsa.edu
Noteworthy Abstracts
of the
Current Literature
Shear stresses in the adhesive layer under porcelain veneers
Troedson M, Derand T. Acta Odontol Scand 1998;56:257-62.
Purpose. In vitro studies into which part of the enamel-resin–composite-porcelain laminate system breaks have shown that the luting interface is the weakest part of the lamination and that it
will fail due to sheer stresses. This study calculated sheer stress in the composite cement and
enamel bond with the facing loaded in the incisal area under different angles and adhesive conditions.
Material and methods. Two-dimensional finite element models of veneers on teeth with an
intermediate layer of resin were designed according to the size of an average maxillary central
incisor. The abutment was considered to be homogenous, and the remaining enamel layer under
the buccal surface of the veneer and the pulp were treated as dentin with regard to material properties. Three models of the tooth were created with different margin designs, while all designs
had preparations that covered the incisal edge. Porcelain facings were made to be 0.5 mm thick:
composite cement layer, 25 µm; enamel bond layer, 1 µm. Three adhesive conditions were tested: (1) lack of polymerization in the facing’s periphery, (2) lack of polymerization in the middle,
and (3) total bonding of the facing. All models were loaded at 0, 30, and 60 degrees to the long
axis of the tooth.
Results. Rather extensive tables presented the numeric results of the study. Maximum sheer
stresses did not exceed the stress level for debonding, but great differences in maximum shear
stress appeared with varying loss of bond and different loading angles. Fully laminated facing
showed stress levels in the composite cement to be only 1⁄5 of those in the facing with a lack of
adhesion in the periphery and 1⁄15 of those in the enamel bond. Maximum stresses increased about
4 times when the load angle was 30 degrees compared with 0 degrees, and increased 1.5 times
from 30 to 60 degrees.
Conclusions. A porcelain veneer that is kept inside the enamel, with full lamination, demonstrated fairly low shear stresses in the enamel bond and composite cement and thus should indicate good long-term prognosis. 13 References.—ME Razzoog
MAY 1999
615
restorations
Manuel Toledano, MD, BDS, PhD,a Estrella Osorio, LDS, PhD,b Raquel Osorio, LDS, PhD,c and
Franklin García-Godoy, DDS, MSd
University of Granada, Granada, Spain, and University of Texas Health Science Center at San Antonio,
San Antonio, Texas
Statement of problem. Resin-modified glass ionomers and polyacid-modified resin composites (compomers) have been introduced to provide esthetic restorations. However, there is concern about the marginal sealing ability of these materials, especially at the dentin (cementum) aspects of restorations.
Purpose. This in vitro study evaluated the microleakage of Class V restorations made with resin-modified
glass ionomers or a compomer.
Material and methods. Thirty noncarious human molar teeth were used. Standardized kidney-shaped
Class V cavity preparations were placed in the buccal and lingual surfaces at the cementoenamel junction.
Teeth were randomly assigned to 3 experimental groups of 10 teeth each and restored as follows: group 1,
Fuji II LC; group 2, Vitremer; and group 3, Dyract. In all cases, the manufacturers’ instructions were strictly followed. All materials were placed in a single increment. Unfinished restorations were immediately coated with the respective manufacturers’ sealer or varnish and this was either light cured for 20 seconds or
allowed to air-dry. After 24 hours, teeth were finished to contour and to the cavosurface margins, coated
with nail varnish except for 1 mm around the restoration margin, thermocycled (1000×, 5-55°C) and placed
in a solution of 2% basic fuchsin dye for 24 hours at room temperature. The staining along the tooth
restoration interface was recorded.
Results. Kruskal-Wallis 1-way analysis of variance revealed significant differences among all restorative
materials for the overall, occlusal, and gingival scores (P=.03, P=.01, P=.01, respectively). Occlusal and gingival scores for each matched pair of restorative materials using the Wilcoxon test showed statistically significant differences between Fuji II LC glass ionomer cement and Dyract composite, 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. Vitremer revealed dye penetration scores not significantly different from Fuji II
LC glass ionomer cement or Dyract composite.
Conclusion. Resin-modified glass ionomers showed less or similar microleakage than the polyacid-modified composite resin tested. (J Prosthet Dent 1999;81:610-5.)
CLINICAL IMPLICATIONS
The findings of this in vitro study suggest that Fuji II LC glass ionomer cement provided a better marginal adaptation than Dyract composite in Class V restorations,
and the amount of resin content and filler particles of the materials may influence the
degree of microleakage.
M
icroleakage is the movement of bacteria, fluids,
molecules or ions, and even air between the prepared
cavity wall and the subsequently applied restorative
materials.1 Cervical lesions due to caries, erosion, or
abrasion often have both enamel and dentin or cementum margins. The longevity of a conventional Class V
restoration can be affected by mechanical, thermal, and
aProfessor,
Department of Dental Materials, University of Granada,
Spain.
bAssistant Professor, Department of Dental Materials, University of
Granada.
cProfessor, Department of Dental Materials, University of Granada.
dProfessor and Director of Clinical Materials Research, Department
of Restorative Dentistry, Dental School, University of Texas
Health Science Center at San Antonio.
610 THE JOURNAL OF PROSTHETIC DENTISTRY
chemical factors that result in stress in the cervical
area.2,3
Bonded composites have been the common choice
for the esthetic restoration of Class V lesions. However, one disadvantage of composites is polymerization
shrinkage, which can result in marginal discrepancies
leading to microleakage, among other disadvantages.4
This shrinkage has clinical repercussions such as sensitivity, marginal discoloration, and secondary caries.2,3
Many new bonding agents and glass ionomer
restorative materials have been introduced to bond
restorative materials to dentin and cementum margins
of cervical lesions,5,6 but microleakage at the dentin
(cementum) aspects of restorations remains a problem
of clinical significance.1,4,5 Glass ionomers are alternaVOLUME 81 NUMBER 5
TOLEDANO ET AL
tive materials to composites for the conservative
restoration of these lesions because of their adhesion to
tooth structure, fluoride release, biocompatibility,
lower shrinkage values, reduced microleakage, and
acceptable esthetics.7-11 Light-cured resin-modified
glass ionomer cements were developed to improve the
handling and working characteristics of the original
glass ionomer formulation.12,13 Improved adhesion to
dentin is probably caused by both a chemical bond
from the polyacrylic acid component and formation of
a hybrid layer from the hydrophilic HEMA.14-21
Favorable adhesive and fluoride-releasing properties
of glass ionomer cements have lead to their widespread
use as restorative, lining, and luting materials. To overcome the problems of moisture sensitivity and low early
mechanical strengths associated with the conventional
glass ionomer cements (GICs) and at the same time
maintain their clinical advantages, some hybrid versions
of GIC were introduced that are light-cured, because
of their small quantity of resin components such as
HEMA or BIS-GMA. In some situations, the polyacid
also has been modified with side chains that can be
polymerized by light-curing mechanisms. The actual
formulations vary between manufacturers, but the
amount of resin in the final set restoration is between
4.5% to 6%, such as for Fuji II LC and Vitremer glass
ionomer cements. The addition of a resin component
to GIC and its effects on the development of the ionic
crosslink and the subsequent marginal seal against the
tooth structure needs further evaluation.
To overcome technique-sensitive mixing and handling properties of the resin-modified glass ionomer
cements, new materials containing acid-decomposable
glass and acidic polymerizable monomers substituting
the polyalkenoic acid polymer were developed. These
materials were termed polyacid-modified resin composites,22-26 commonly called compomers. Dyract polyacid-modified resin composite belongs to the new
materials that have either been marketed as multipurpose materials, or contain both of the essential components of a glass-ionomer cement but at levels that are
insufficient to produce an acid-base reaction.13 With
this material, the resin content is approximately 28%.
The purpose of this study was to compare the
microleakage of Class V restorations produced with the
3 materials, which differ in their resin content, to test
the hypothesis that resin content affects microleakage.
MATERIAL AND METHODS
Thirty noncarious human molars, which were stored
in a solution of 1% sodium hypochlorite for up to
4 months at room temperature, were test specimens.
After surface debridement with a hand-scaling instrument and cleaning with a rubber cup and slurry of
pumice, a standardized Class V cavity preparation was
placed in the buccal and lingual surface at the cemenMAY 1999
THE JOURNAL OF PROSTHETIC DENTISTRY
toenamel junction. Preparations were made with a
no. 329 carbide bur in a high-speed handpiece and a
template to a uniform kidney-shaped outline. Preparations measured 5 mm long, 3 mm wide, and 2 mm
deep with the occlusal margin in enamel and the gingival margin in dentin or cementum.
Subsequently, teeth were randomly assigned to
3 experimental groups of 10 teeth each. Buccal and lingual preparations of group 1 were restored with Fuji II
LC (GC Corp, Tokyo, Japan) resin-modified glass
ionomer cement; group 2 with Vitremer (3M, St Paul,
Minn.) resin-modified glass ionomer cement; and
group 3 with Dyract (De Trey Dentsply, Konstanz,
Germany) polyacid-modified resin composite.
In all cases, the manufacturers’ instructions for
dentin conditioning, powder/liquid proportioning and
mixing were strictly followed. For Fuji II LC glass
ionomer cement, the cavity wall was conditioned for
20 seconds with dentin conditioner (GC Dental Corp).
For Vitremer glass ionomer cement, Vitremer primer
(3M Dental Products) was applied on the cavity wall
for 20 seconds, gently air dried and light cured for
30 seconds. For Dyract composite restorations, the cavity wall was treated with PAS primer/adhesive (DeTrey
Dentsply) for 30 seconds, excess was removed with a
blast from an air syringe and the adhesive was cured for
20 seconds. A second coat of the primer/adhesive was
applied and immediately light cured for 20 seconds.
Dyract composite was placed in 1 increment. The teeth
were prevented from dehydration by remaining in
deionized water storage at room temperature when not
being prepared for restoration.
Immediately after the restorative material was placed,
a clear cervical matrix (Clear Thru, Premier Dental
Products, Norristown, Pa.) was adapted over the resinmodified GIC restorations and the materials cured with
a visible light source (Optilux 400, Demetron Research
Corp, Danbury, Conn.) in accordance with the manufacturers’ recommended time. The light was tested for
light output (>600 mW/cm2) before each use with a
Demetron radiometer (model 100, Demetron Research
Corp). When the matrix was removed, the unfinished
restorations were immediately coated with the respective
manufacturer’s sealer or varnish, and this was either
cured with a visible light source or allowed to dry before
returning the tooth to deionized water storage at room
temperature. After 24 hours, the teeth were finished to
contour and to the cavosurface margins with a no. 7901
carbide finishing bur (SS White, Lakewood, N.J.) with
air and water spray in a high-speed handpiece (Star Dental, Lancaster, Pa.) and medium, fine, and super fine SofLex disks (3M Dental Products), which were first lubricated with water and used in sequence with air-water
spray in a slow-speed handpiece (Star Dental). The
apical portions of all specimens were filled ad retrum
with a zinc oxide-eugenol paste.
611
THE JOURNAL OF PROSTHETIC DENTISTRY
TOLEDANO ET AL
Table I. Microleakage of the different groups
Occlusal
Group
Fuji II LC (n = 17)
Vitremer (n = 18)
Dyract (n = 22)
Gingival
Overall
0
1
2
3
0
1
2
3
0
1
2
3
14
9
7
1
3
4
0
2
6
2
4
5
12
8
6
2
1
3
0
4
0
3
5
13
10
4
5
3
4
3
0
4
1
4
6
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 restorative 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.
Teeth were prepared for microleakage evaluation by
coating the entire tooth with 1 application of nail varnish, except for 1 mm around the restoration margins.
These specimens were then subjected to 1000 temperature cycles as suggested in a previous study.27 Each
cycle consisted of 30 seconds at 6°C and 30 seconds at
60°C. After thermocycling, teeth were placed in a solution of 2% basic fuchsin dye (Fisher Scientific, Fair
Lawn, N.J.) for 24 hours at room temperature.
After removal of the specimens from the dye solution, the superficial dye was removed with a pumice
slurry and rubber cup. Teeth were then mounted in a
light-curing 1-component methacrylate-based resin
(Technovit 7200 VLC, Kulzer, Norderstedt, Germany)
to facilitate handling during sectioning. The resin was
cured for 24 hours (Histolux, EXAKT, Norderstedt,
Germany), then teeth were sectioned longitudinally
with a hard tissue microtome (Exakt-apparerteban,
Otto Herrman, Norderstedt, Germany) in 0.6-mm
thick sections to evaluate the dye penetration.28 The
sections were then separated, and the cut surfaces corresponding to the most mesial, central (mesial and distal), and most distal portion of the tooth restoration
interface were examined at the occlusal and gingival
margins with a stereomicroscope (Olympus Co, Tokyo,
Japan) at ×16 magnification. Examination of the specimens was undertaken at random, and the investigators
were unaware of the exact nature of the restorative
material.
Staining along the tooth restoration interface was
recorded by 2 evaluators, according to the following
criteria: 0 = no dye penetration; 1 = partial dye penetration; 2 = dye penetration along the occlusal or
gingival wall, but not including the axial wall; and 3 =
dye penetration to and along the axial wall. If disagreement occurred between the evaluators, a consensus was
obtained after reexamination of the specimen by both
investigators. Occlusal, gingival, and overall scores for
each group of restoration were compared with the
Kruskal-Wallis 1-way analysis of variance (ANOVA)
nonparametric statistical test to identify any statistical
612
significant differences between the materials, and the
Wilcoxon test was performed to compare each matched
pair of restorative materials. Significance was considered at the .05 level.
RESULTS
Microleakage scores for the occlusal, gingival, and
overall walls are presented in Table I. Kruskal-Wallis
1-way ANOVA indicated significant differences
between the restorative materials for overall, occlusal,
and gingival scores (P=.03; P=.01; P=.01, respectively).
Further matched analysis by Wilcoxon test was undertaken to compare occlusal, gingival, and overall scores
of each material, which revealed statistically significant
differences between Fuji II LC glass ionomer cement
and Dyract resin composite, both for the occlusal
(P=.005) and gingival (P=.005) margins and also as an
overall evaluation (P=.01) (combining the occlusal and
gingival margins scores) with Fuji II LC demonstrating
the least dye penetration between these 2 products.
Vitremer glass ionomer cement revealed dye penetration scores between Fuji II LC glass ionomer cement
and Dyract resin composite, with no statistically significant differences between Vitremer glass ionomer
cement and the other 2 products.
DISCUSSION
Polymerization shrinkage of resin-containing restorative materials may result in marginal discrepancies that
lead to microleakage, marginal discoloration, and sensitivity.2-4 Hygroscopic expansion can compensate, to
some degree, for polymerization shrinkage. Water sorption can help to reduce marginal gaps3; 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 al7 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 volumetric loss. Thus, they concluded that water expansion
is 1 factor that reduces the leakage.
VOLUME 81 NUMBER 5
TOLEDANO ET AL
Our results disagree with those of Yap et al8 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 difference between enamel and dentin; in our study, even if
microleakage was less common in enamel, the difference was not significantly different. These differences
between the studies could be because Yap et al8 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 thermally cycled for approximately 2 days, and the material
may not have expanded completely. Yap et al8 also suggested that 1 of the unique features of the resin that
releases fluoride to enamel is the omission of acid etching, 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 formulated 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 completely resisted microleakage at the occlusal or gingival 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 (enamel and gingival scores pooled together). However,
only with the overall evaluation did Fuji II LC glass
ionomer cement reveal a statistically significant difference with Dyract resin composite. The lack of statistically significant difference in microleakage between
resin-modified glass ionomers has also been previously reported.15 Uno et al16 concluded that the superior
adaptation of Fuji II LC glass ionomer cement to the
cavity walls was responsible for the lower dye penetration, 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 different rates of polymerization shrinkage during light
curing (as it is a dual-cure material) compared with
Dyract resin composite.
MAY 1999
THE JOURNAL OF PROSTHETIC DENTISTRY
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 Vitremer, in addition to being a simple mixture of HEMA
with polyalkenoic acid, is also modified by the attachment 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 adaptation 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 structures 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 composite tested had orthophosphoric acid to condition
the dentin, it also contained TGDMA and elastomeric
resins, which have chemical affinity with the resin contained in the material. When these resins shrink during
polymerization, they could generate a gap where
microleakage could be detected. The extent of the curing 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 permit the tooth and restorative material to come into intimate interfacial contact.18 Charlton and Haveman20
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 composite because it does not have an acid-base cure reaction.13 These differences in bond strength values could
contribute, among other factors, to explain the differences 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.
613
THE JOURNAL OF PROSTHETIC DENTISTRY
However, this bonding is not so strong and does not
produce an adequate marginal sealing.20,21
The increase in leakage of Dyract resin composite
also could be attributed to thermal expansion mismatch
with tooth substance, which is reported to be significantly higher than that of conventional cements and
also less than that of composites,9,10 perhaps due to
their different chemical composition. Leakage of composite resin restorations may be attributed to a contraction gap produced by polymerization shrinkage and
expansion and contraction with temperature changes,
because the coefficient of thermal expansion of composites is different from that of the dental hard tissues.
Glass ionomer cements exhibit limited shrinkage during setting and their coefficient of thermal expansion is
similar to that of dentin.4 Mitra and Conway9 reported
that Fuji II LC and Vitremer materials had coefficients
of thermal expansion of 31.5 and 11.5 ppm/°C,
respectively, and Silux Plus microfilled composite 56.6
ppm/°C 7 days after curing. Dyract has a composition
closely related to the microfilled composites and has a
coefficient of thermal expansion of 40.52 ppm/°C
(P Hammesfahr, verbal communication, 1998). This
may explain why Dyract resin composite is more susceptible to thermal stresses than the other materials.
Also, because the resin component of the material
adheres poorly to the cervical dentin than to enamel,
this justifies, in part, that the Dyract resin composite
revealed more leakage at the gingival margin than at
the enamel margin.
Although Vitremer glass ionomer cement displayed
microleakage values between those of Fuji II LC and
Dyract materials, there was no statistically significant
difference among the 3 materials. Some authors have
pointed out that significant dimensional changes and
surface hardening can occur after initial light curing of
the resin component of resin-modified glass ionomers,
and further contraction continues for the first 24 hours
as the material matures.10,11 Because both Vitremer
and Fuji II LC glass ionomer cements contain approximately the same percentage of resin, which is less than
that for Dyract composite, it could be thought that this
is another reason to explain the different microleakage
patterns.10,11 Uno et al16 considered that the differences observed between Vitremer and Fuji II LC glass
ionomer cements might be due to differences in maturation of setting reactions.
Although the results obtained from this study may
not be directly extrapolated to the clinical situation,
they provide some information regarding the performance of the restorative system evaluated. Independent
long-term clinical data are still required.
CONCLUSIONS
Within the limits of this study, the following conclusions were drawn:
614
TOLEDANO ET AL
1. The resin-modified glass ionomers showed less or
similar microleakage than the polyacid-modified composite resin tested.
2. The amount of resin content and filler particles of
the materials may influence the degree of microleakage.
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4. Kaplan I, Mincer HH, Harris EF, Cloyd JS. Microleakage of composite
resin and glass ionomer cement restorations in retentive and nonretentive
cervical cavity preparations. J Prosthet Dent 1992;68:616-23.
5. Gordon M, Plasschaert AJM, Stark MM. Microleakage of several toothcolored restorative materials in cervical cavities. A comparative study in
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6. Mount GJ. Atlas práctico de cementos de ionómero de vidrio. Barcelona:
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7. Attin T, Buchalla W, Kielbassa AM, Helwig E. Curing shrinkage and volumetric changes of resin-modified glass ionomer restorative materials.
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8. Yap AU, Lim CC, Neo JC. Marginal sealing ability of three cervical restorative systems. Quintessence Int 1995;26:817-20.
9. Mitra SB, Conway WT. Coefficient of thermal expansion of some
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10. Cárdenas HL, Burgess JO. Thermal expansion of glass ionomers. J Dent
Res 1994;73:220 (abstr 946).
11. Hallett KB, García-Godoy F. Microleakage of resin-modified glass
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306-11.
12. Antonucci JM, Mckinney JE, Stansbury JW. Resin-modified glass-ionomer
cement restoration. US Patent 160856, 1988.
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14. Ferrari M, Davidson CL. Interdiffusion of a traditional glass ionomer
cement into conditioned dentin. Am J Dent 1997;10:295-7.
15. Sidhu SK. Sealing effectiveness of light-cured glass ionomer cement liners. J Prosthet Dent 1992;68:891-4.
16. Uno S, Finger WJ, Fritz UB. Effect of cavity design on microleakage of
resin-modified glass ionomer restorations. Am J Dent 1997;10:32-5.
17. Trushkowsky RD, Gwinnett AJ. Microleakage of Class V composite, resin
sandwich, and resin-modified glass ionomers. Am J Dent 1996;9:96-9.
18. Pachuta SM, Meiers JC. Dentin surface treatments and glass ionomer
microleakage. Am J Dent 1995;8:187-90.
19. Van Meerbeek B, Inokoshi S, Braem M, Lambrechts P, Vanherle G. Morphological aspects of the resin-dentin interdiffusion zone with different
dentin adhesive systems. J Dent Res 1992;71:1530-40.
20. Charlton DG, Haveman CW. Dentin surface treatment and bond strength
of glass ionomers. Am J Dent 1994;7:47-9.
21. Zyskind D, Frenkel A, Fuks A, Hirschfeld Z. Marginal leakage around Vshaped cavities restored with glass-ionomer cements: an in vitro study.
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22. McLean JW, Nicholson JW, Wilson AD. Proposed nomenclature for glassionomer dental cements and related materials. Quintessence Int 1994;25:
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23. Van Dijken JW. 3-year clinical evaluation of a compomer, a resin-modified glass ionomer and a resin composite in Class III restorations. Am J
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24. Abdalla AI, Alhadainy HA, García-Godoy F. Clinical evaluation of glass
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25. García-Godoy F, Hosoya Y. Bonding mechanism of Compoglass to dentin
in primary teeth. J Clin Pediatr Dent 1998;22:217-20.
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THE JOURNAL OF PROSTHETIC DENTISTRY
27. Crim GA, García-Godoy F. Microleakage: the effect of storage and cycling
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Copyright © 1999 by The Editorial Council of The Journal of Prosthetic
Dentistry.
0022-3913/99/$8.00 + 0. 10/1/96694
Reprint requests to:
DR. FRANKLIN GARCIA-GODOY
DEPARTMENT OF RESTORATIVE DENTISTRY
UNIVERSITY OF TEXAS HEALTH SCIENCE CENTER
7703 FLOYD CURL DR
SAN ANTONIO, TX 78284-7850
FAX: (210) 567-3522
E-MAIL: godoy@uthscsa.edu
Noteworthy Abstracts
of the
Current Literature
Shear stresses in the adhesive layer under porcelain veneers
Troedson M, Derand T. Acta Odontol Scand 1998;56:257-62.
Purpose. In vitro studies into which part of the enamel-resin–composite-porcelain laminate system breaks have shown that the luting interface is the weakest part of the lamination and that it
will fail due to sheer stresses. This study calculated sheer stress in the composite cement and
enamel bond with the facing loaded in the incisal area under different angles and adhesive conditions.
Material and methods. Two-dimensional finite element models of veneers on teeth with an
intermediate layer of resin were designed according to the size of an average maxillary central
incisor. The abutment was considered to be homogenous, and the remaining enamel layer under
the buccal surface of the veneer and the pulp were treated as dentin with regard to material properties. Three models of the tooth were created with different margin designs, while all designs
had preparations that covered the incisal edge. Porcelain facings were made to be 0.5 mm thick:
composite cement layer, 25 µm; enamel bond layer, 1 µm. Three adhesive conditions were tested: (1) lack of polymerization in the facing’s periphery, (2) lack of polymerization in the middle,
and (3) total bonding of the facing. All models were loaded at 0, 30, and 60 degrees to the long
axis of the tooth.
Results. Rather extensive tables presented the numeric results of the study. Maximum sheer
stresses did not exceed the stress level for debonding, but great differences in maximum shear
stress appeared with varying loss of bond and different loading angles. Fully laminated facing
showed stress levels in the composite cement to be only 1⁄5 of those in the facing with a lack of
adhesion in the periphery and 1⁄15 of those in the enamel bond. Maximum stresses increased about
4 times when the load angle was 30 degrees compared with 0 degrees, and increased 1.5 times
from 30 to 60 degrees.
Conclusions. A porcelain veneer that is kept inside the enamel, with full lamination, demonstrated fairly low shear stresses in the enamel bond and composite cement and thus should indicate good long-term prognosis. 13 References.—ME Razzoog
MAY 1999
615