SUZUKI, KURASHIGE, AND TANAKAINT CHIN J DENT

In vitro evaluation of marginal degradation of composite restorations
Shiro Suzuki, DDS, PhD,a Hisanori Kurashige, DDS,b and Takuo Tanaka, DDS,
PhDba

Department of Prosthodontics and Biomaterials, University of Alabama at
Birmingham School of Dentistry, Birmingham, AL, USA, and bDepartment of Fixed
Prosthodontics, Kagoshima University Dental School, Kagoshima, Japan
Purpose: The purpose of this study was to evaluate the effect of occlusal stressing on marginal integrity ofmultiple composite restorations in the same tooth.
Materials and Methods: Class V cavities were prepared on buccal and lingual surfaces of 42 extracted
human maxillary premolars. Cavo-surface margins were placed in enamel on the incisal wall and in
cementum on the gingival wall. Class II (MOD) cavities were also prepared on the same tooth. Class V
cavities were restored with a direct composite. For Class II cavities, one-half numbers of the specimens
were restored with the direct composite, and the remainders were restored with an indirect composite. The
specimens were mounted on two different loading devices (vertical and sliding types) and repetitively
loaded with 75 N at 1.2 Hz for 100,000 cycles. Seven specimens were used for each simulation. The tested
specimens were immersed into 5% methylene blue solution for two hours, and the lengths of marginal
staining and depth of dye penetration were evaluated. The values at each area were averaged, and the data
were statistically analyzed by analysis of variance (ANOVA). The differences between gingival andocclusal microleakage; vertical loading and vertical with sliding; and direct and indirect restorations were
determined with Fisher’s PLSD test (p<0.05).
Results: The results indicated that all of the gingival margins on Class V restorations exhibited greater
deterioration compared to occlusal margins.
Conclusion: It is suggested that the cementum/restoration interface had less durability compared toenamel/restoration interface. (Int Chin J Dent 2002; 2: 143-150.)
Clinical Significance: Clinicians need to realize that cementum margin of Class V composite restoration
will be affected by occlusal stress when Class II restoration is placed on the same tooth.
Key words: class V restoration, composite, in vitro test, marginal degradation, occlusal stress.

INTRODUCTION
In clinical situations, a single tooth is sometimes restored with resin composite materials via multiple
cavity preparations. Although a complete-coverage cast restoration is often recommended as a durable
restoration, the cavity preparation is advantageous when minimization of tooth reduction is a primary143

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concern. Therefore, enhancement of longevity is essential to make composite restorations more reliable.
Although restorative dentistry has significantly changed since the introduction of enamel etching,1
polymerization shrinkage of resin composite is still an unsolved problem.

Microleakage aroundrestorations needs to be minimized to prevent microbial invasion as well as other clinical problems.
Deficiency in perfect sealing of restorative materials to tooth structure leads to gap formation between therestorative material and cavity walls, resulting in postoperative sensitivity, plaque accumulation, recurrent
caries, pulpal degeneration and sometimes necrosis.2,3Ongoing development of new adhesive systems and increasing understanding of the dentin substrate4-6
together with extensive investigation of the smear layer,7,8 surface phenomenon,9-12 makes bonding to bothenamel and dentin simultaneously possible as evidenced by currently available adhesive systems. The
micromechanical interlock of etched enamel with bonding resin has long been established as a majormechanism for enamel bonding.13 Encapsulation of enamel crystallites of the etched enamel surface withbonding resin, has been reported to be the most significant factor in promoting surface protection from aciddissolution.14,15 With the advent of newer generation adhesive systems, bonding to tooth structure bothenamel and dentin, is attainable.16-20 In vitro study has demonstrated that the marginal sealing ability ofcurrent bonding resin composite systems has been improved.18 While other in vitro study has shown thatthe use of dentin bonding agents reduces the marginal gap formation in composite resin restorations.19 The
dentin hybrid layer resulted from interpenetration of monomers into dentin substrate followed bypolymerization and is responsible for a functional monomer group for subsequent chemical bonds of theresin composite.20 Encapsulation of hydroxyapatite in the hybrid layer by impregnated resin also relates thebonding durability.21,22
Extensive and continuous occlusal stresses could possibly create marginal degradation of resin composite
restorations. Although several in vitro studies on microleakage using occlusal-like loading have been
attempted,24-25 the effect of loading on marginal integrity was not clearly demonstrated. This indicates thedifficulty in simulating clinical conditions by an in vitro testing system. Therefore, the purpose of thisstudy was to develop a new in vitro system to simulate the marginal degradation of resin composite
restorations after a long period of masticatory stressing. It was also the purpose of this study to evaluate
the effect of occlusal stressing on marginal integrity of resin composite restorations when they were placedin the same tooth.

MATERIALS AND METHODS
Materials used in this study are presented in Table 1. They included an enamel/dentin bonding agent(Bond 3), a direct composite restorative (Simile), an indirect composite restorative (Sculpture), and acomposite luting cement (Cement-It!).

All of the materials were manufactured by Jeneric/Pentron(Wallingford, CT, USA).
Forty-two extracted human maxillary premolars were selected for evaluation. The approval for use of
extracted human teeth was obtained from the Institutional Review Board for Human Use (IRB) at the144

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University of Alabama at Birmingham. Class V cavities (3 mm high, 4 mm wide, and 1.5 mm deep) wereprepared on buccal and lingual surfaces of all teeth with a #4 carbide round bur. The cavo-surface margin
was placed in enamel on the incisal wall and in cementum on the gingival wall. The margin was beveled(0.5 mm wide) entirely with a white stone (Dura-White Stone, #0244, Shofu Inc, Kyoto, Japan). Class II(MOD) cavities were prepared with a #271 carbide fissure bur on the same tooth. Proximal extension
included removal of marginal ridges. The dimension of the cavity was 1.5 mm wide at central fossa, 0.8
mm wide at gingival wall, and 2.5 mm deep at occlusal surface. No bevel was prepared on occlusal margin.
The gingival margin was placed in enamel and beveled with 0.5 mm width. Each tooth received a total ofthree preparations.
Table 1. Materials used.
Material Type

Product Name

Manufacturer

Batch number

Bonding agent

Bond 3

Jeneric/Pentron

59011

Direct composite

SimileJeneric/Pentron

S8414

Indirect composite

Sculpture

Jeneric/Pentron

44339

Luting cement

Cement-It!

Jeneric/Pentron

550962

Class V cavities were restored with Simile direct composite with Bond 3 adhesive. The cavities were
etched with a 37% phosphoric acid for 20 s, followed by rinsing with tap water for 20 s. Bond 3 adhesive
was applied and polymerized by visible light irradiation for 10 s. The cavities were restored with the resin
composite with two increments. The resin composite was polymerized by visible light irradiation for 20 son the first increment and for 40 s on the second increment. Class II cavities were restored with both thedirect and indirect composite materials. One-half of the specimens were directly restored with the Simile,
and the remainders were restored with Sculpture indirect composite. The direct restorations were restoredwith three increments. The first and second increments were polymerized for 20 s each, and the third
increment was polymerized for 40 s. Sculpture inlays were fabricated by light polymerization, followed byheat polymerized at 110°C for 10 minutes in a vacuum oven (Conquest oven, Jeneric/Pentron). The inlays
were cemented with Cement-It! dual-cure composite cement. The cement was polymerized by visible lightirradiation for 40 s on each surface.
All restorations were finished and polished with silicon points (Brown point, #0413, and Blue point,#414B, Shofu Inc.) with copious amounts of irrigation.

The restored teeth were immersed into 5%

methylene blue solution at 37°C for two hours to confirm an intact marginal integrity. They were thencleaned and evaluated for subsequent testing. The completed specimens were secured in specimen holders
with an auto-polymerized acrylic resin (Unifast II, GC Corp., Tokyo, Japan) 2 mm below the gingival
margin. These specimens were mounted on two different loading devices. A UAB wear simulator26-29 was

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used as a vertical loading type, and a modified wear simulator30 was used as another type of in vitro test
that has vertical loading with a sliding motion. A custom made stylus was prepared for each individual
tooth using two hemi-spherical metal screws (Zinc round-head, Hillman, Cincinnati, OH, USA) and theauto-polymerized acrylic resin (Fig. 1). The screw heads were designed to contact both buccal and lingual
triangular ridges, and four contact points were obtained on each specimen.

The screw heads werepositioned to exclude contact with the restorations. A 75 N load was applied in both simulators (Fig. 2). A
schematic illustration of the loading system is presented in Fig. 3. Only vertical loading was employed tothe original device (arrow A), and a sliding movement (arrow B) was combined with vertical loading in themodified device. The stylus directly contacted the tooth surface at 1.2 Hz, and the loading was repeated for
100,000 cycles. Seven specimens were used for each condition in each type of loading system.

Acrylic

Metal screw headFig. 1. Custom made stylus for loading.

Fig. 2. Cyclic loading.

Load
Stylus

Tip

B
A

A
mm

Fig. 4. Measurement of marginal staining length.
Fig. 3. Illustration of loading system. A: Vertical loading; B: Sliding.
The tested specimens were immersed into 5% methylene blue solution at 37°C for two hours to evaluatemarginal leakage. Fourteen specimens without the stressing were used as control groups. The lengths ofmarginal staining at both gingival and occlusal margins of Class V restorations were evaluated (Fig. 4).

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The values of respective sites were averaged independently. The gingival margins of both mesial and distal
proximal surfaces of Class II restorations were also evaluated on each restoration, and the values on eachcondition were averaged.
After the measurements of staining length were made, the specimens were sectioned buccolinguallyalong the tooth axis. However, the control groups were not sectioned, as they exhibited no marginal
staining. Depth of dye penetration along the cavity wall was then evaluated. The deepest dye penetrations
were measured in millimeter by a light microscope. The values at each area were averaged, and the data
were statistically analyzed by three-way analysis of variance (ANOVA). The differences between gingival
and occlusal margins, vertical loading and vertical with sliding, direct and indirect Class II restorations
were determined with Fisher’s PLSD test (p<0.05).

RESULTS
Table 2. Results of marginal stain lengths in mm with standard deviations in parentheses.
Direct class II group
No stressing

Bucco-gingival

0

Vertical

4.43 (1.10)
a, *Bucco-occlusal

02.43 (1.90)a,Linguo-gingival0

4.43 (1.34)bLinguo-occlusal

02.00 (2.25)bProximal-gingival0

3.09 (1.13)

Indirect class II group

Vertical/Sliding

No stressing

5.00 (0.96)

0c1.64 (1.38)

0c4.43 (0.84)

05.93 (0.93)

4.50 (1.78)

e, *, #

g, #2.21 (2.48)

1.71 (2.58)

5.50 (1.04)

g
4.64 (0.85)f0d2.44 (1.53)

Vertical/Slidinged0.29 (0.76)

Vertical

0.57 (1.13)
f0

2.11 (1.31)h0h1.21 (0.76)

Values with the same letters and symbols indicate significant differences (p<0.05).
a-h: gingival/occlusal, *: direct/indirect, #: vertical/vertical + sliding.

The results of marginal staining lengths are presented in Table 2. The control groups exhibited no
marginal staining at all, while occlusally stressed groups showed various amount of staining. The values ofClass V gingival margins (cementum margins) ranged 4.43 to 5.93 mm, while those of occlusal margins(enamel margins) ranged 0 to 2.43 mm. The values of Class II gingival margins (enamel margins) ranged
1.21 to 3.09 mm. The statistical analysis indicated that all of the gingival margins exhibited greater
deterioration as compared to occlusal margins on Class V restorations regardless of stressing modes. The
difference between direct and indirect Class II restoration groups was only detected at bucco-gingival
margin when they were subjected to vertical stressing. The difference between vertical loading group andvertical with sliding movement group was only seen at bucco-gingival margin of Class V restorations when147

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teeth were restored with indirect Class II restoration. Class II gingival margins showed no differences
regardless of the restoration modes.
The results of dye penetration along the cavity wall are presented in Table 3. The values of Class V
gingival margins ranged 0.85 to 1.25 mm, while those of occlusal margins ranged 0 to 0.46 mm. The
values of Class II gingival margins ranged 0.14 to 0.60 mm. The statistical analysis demonstrated that allof the values for gingival margin on Class V were significantly greater than those of occlusal margin.
There were no differences between vertical loading and vertical with sliding motion. The differences
between direct restoration and indirect inlay were only seen at the gingival margin of Class II restorations.
The inlay groups showed less dye penetrations compared to the direct restoration groups.
Table 3. Results of dye penetration (mm).
Direct class II group
VerticalVertical/Sliding

Indirect class II group
VerticalVertical/Sliding

Bucco-gingival

1.25 (0.43) a

0.92 (0.49) c

0.97 (0.34) e

0.90 (0.36) g

Bucco-occlusal

0.32 (0.47) a

0.32 (0.58) c

0.10 (0.19) e

0.20 (0.52) g

Linguo-gingival

1.03 (0.46) b

0.85 (0.58) d

1.12 (0.13) f

1.12 (0.21) h

Linguo-occlusal

0.30 (0.54) b

0.06 (0.16) d

0.46 (0.61) f

0 (0) hProximal-gingival

0.48 (0.25) *0.60 (0.31) **0.14 (0.12) *0.18 (0.23) **Values with the same letters and symbols indicate significant differences (p<0.05).
a-h: gingival/occlusal, *, **: direct/indirect.

DISCUSSION
There are many clinical problems of Class V composite restorations. One of them is the interfacialdebonding that is provoked by numerous factors including the polymerization shrinkage of composite,
contamination by oral fluids, failure of polymerization, operator error, and longitudinal degradation.31 The
degradation of tooth/restoration interface is inevitable under a functional oral environment even with theappropriate clinical procedures.

The results indicated that all of the gingival margins on Class V

restorations were deteriorated after cyclic loading regardless of the type of loading. This was probably due
to fatigue of bonding interface by the continuous stressing created by this cyclic loading system. The moststress is perhaps concentrated at the tooth/restoration interface of gingival margins as can be speculated
from the mechanism of abfraction defects.32 The results also indicated that the cementum/restorationinterface had less durability compared to the enamel/restoration interface. It can be speculated that thebond strengths of the adhesive system to cementum could be weaker than to enamel. This assumption is
supported by the results of other in vitro studies, showing dentin or cementum margins exhibited weakerbonding compared to enamel.23-25,33,34 From the results of this study, it can be concluded that the in vitro
system used in this study may simulate the clinical situation in terms of marginal breakdown by long-term

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occlusal stressing.
Although the marginal integrity of the Class V restorations was significantly deteriorated by the cyclicloading, little influence was obtained under different loading modes.

Therefore, further research iswarranted to investigate the improved experimental designs to simulate the clinical conditions more
precisely.

CONCLUSIONS
Based upon the results of this study, it is concluded that the in vitro cyclic loading system used in thisstudy has a potential to simulate the marginal degradation of resin composite restorations by means ofcontinuous occlusal stressing. It is concluded that occlusal stressing considerably affected the gingival
marginal integrity of resin composite restorations, and the cementum/restoration interface had lessdurability as compared to enamel/restoration interface.

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Reprint request to:
Dr. Shiro Suzuki
Department of Prosthodontics and Biomaterials, University of Alabama at Birmingham School of Dentistry
1919 7th Avenue South, Birmingham, AL 35294-0007, USA
FAX: +1-205-975-6108
E-mail: Shiro@mail.dental.uab.edu
Received on October 9, 2002. Revised on October 22, 2002. Accepted on November 19, 2002.
Copyright ©2002 by the Editorial Council of the International Chinese Journal of Dentistry.

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