Influence of resin cement viscosity on m

dental
materials
Dental Materials 17 (2001) 191±196
www.elsevier.com/locate/dental

In¯uence of resin cement viscosity on microleakage of ceramic inlays
P. Hahn*, T. Attin 1, M. GroÈfke, E. Hellwig
Department of Operative Dentistry and Periodontology, Dental Clinic, University of Freiburg, Hugstetterstrasse 55, 79106 Freiburg, Germany
Received 16 September 1999; revised 10 May 2000; accepted 1 June 2000

Abstract
Objectives. The aim of the present investigation was to evaluate the effect of the different viscosities of two resin luting cements on
microleakage of ceramic inlays at dentinal margins. The effect of the width of the space between inlay and tooth, on the quality of the
marginal seal was also investigated.
Methods. Mesial and distal class V cavities were prepared in 48 extracted third molars. The incisal margins of the cavities were in enamel
and the cervical margins in dentin. Subsequently, Empresse inlays with different cervical margin gap dimensions were fabricated. The mean
cervical gap dimensions in the respective groups were as follows: group 1 (27 mm); group 2 (232 mm); group 3 (406 mm). Half the inlays in
each group (16) were cemented with a low viscous resin luting cement, and half (16) with a highly viscous resin luting cement. The teeth were
subjected to occlusal loading with synchronized thermal cycling in a masticatory simulator. Then, the specimens were immersed in basic
fuchsin solution, and dye penetration along the cavity walls was measured. In addition, marginal adaptation was analyzed in the SEM at
baseline and after loading, using a replica technique.

Results. With regard to dye penetration at dentinal margins, the highly viscous cement performed statistically signi®cantly better at dentin/
composite margins than the low viscous cement …p ˆ 0:0158†: These ®ndings are supported by SEM analysis.
Signi®cance. It is assumed that polymerization stress within the luting cement could not be completely compensated for by larger luting
spaces. Highly viscous luting cements are recommended for cementing class V inlays in larger luting spaces. q 2001 Academy of Dental
Materials. Published by Elsevier Science Ltd. All rights reserved.
Keywords: Viscosity; Microleakage; Ceramic inlay

1. Introduction
Composite restorative materials undergo signi®cant volumetric shrinkage when polymerized [1]. It has been suggested
that this property leads to poor margin quality in composite
restorations. Various techniques have been recommended to
compensate for this shortcoming, for example, acid etching
and incremental technique, or the use of inlay restorations
instead of direct composite ®llings [2]. Ceramic inlays are
adhesively cemented using composite materials. It has been
claimed that a small volume of luting composite is desirable
[3] in order to reduce stress formation caused by polymerization shrinkage of the luting material [4]. However, it has also
been stated [5±8] that the narrower the luting space is, the
more polymerization stress occurs, due to shrinkage of the
material. This stress is increased when the cavity design

* Corresponding author. Tel.: 149-761-270-4756; fax: 149-761-270-4762.
E-mail address: hahn@zmk2.ukl.uni-freiburg.de (P. Hahn).
1
New address: Department of Operative and Preventive Dentistry,
Dental Clinic, University of GoÈttingen, Robert-Koch Strasse 40, 37075
GoÈttingen, Germany.

shows an unfavorable con®guration factor (C-factor). With
respect to adhesively cemented ceramic inlays it is important
to note that the C-factor of cavities prepared for ceramic inlays
is high, i.e. unfavorable [7].
Shrinkage of composite materials also depends on their
composition and viscosity [9,10]. Moreover, composites
with a low viscosity show better ¯ow properties thereby
reducing the stress created within the material during
early setting [5]. However, the opportunity for ¯ow in
light cured composites is small as the material hardens
quickly when exposed to the polymerization light [11].
Additionally, light polymerization is initiated at the surface
of the restoration. This further prevents ¯ow of the composite material at the surface and prevents this portion of the

®lling from acting as a source of stress relief for deeper
composite layers during polymerization [12].
To date, no adhesive technique is available which results
in predictably good marginal adaptation, when margins of
the restoration are located cervical to the dentin±enamel
junction [13±15]. Taking the above-mentioned aspects
into consideration, it is conceivable that larger luting spaces
and low viscosity luting cements may improve the quality of

0109-5641/01/$20.00 + 0.00 q 2001 Academy of Dental Materials. Published by Elsevier Science Ltd. All rights reserved.
PII: S 0109-564 1(00)00067-1

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P. Hahn et al. / Dental Materials 17 (2001) 191±196

ceramic inlay restorations at dentinal margins by producing
lower stress contractions. The objective of the present study
was, therefore, to investigate the in¯uence of two luting
cements with different viscosities and various luting space

dimensions on adaptation of ceramic inlays at dentinal
margins.

2. Materials and methods
Forty-eight extracted caries free third molars of comparable dimension were selected for the experiments. The teeth
were cleaned, using scalers and rotating brushes to completely remove soft tissue remnants, and stored in Ringer's
solution (Delta-Pharma, Pfullingen, Germany). The teeth
were then randomly divided into three groups. Each tooth
was ®xed in a custom-made specimen holder. Box-shaped
non-beveled class V cavities were prepared in the mesial
and distal aspects of each tooth, using a 6-degree conical
diamond bur (30 mm, No.: 8959KR.314.016, Gebr.Brasseler, Lemgo, Germany) in a high-speed handpiece with air±
water spray. The bur was renewed after 16 preparations. The
preparation extended incisally to enamel and cervically to
dentin. Standardization of the cavity size was accomplished
by ®xing the handpiece in a parallelometer during preparation. The handpiece was carried along using a template with
the corresponding preparation form. The cavity had an
asymmetric design, which ensured correct positioning of
the inlay after fabrication with different cervical luting
spaces (Fig. 1). Subsequently, Empresse inlays were

produced using plaster casts and the lost wax technique.
In group 1, the control group, Empresse inlays were fabricated according to the manufacturer's instructions. In order
to reproduce the dentinal margin gap in the remaining
groups, tin foil was placed at the cervical cavity wall before
wax modulation. The thickness of the tin foil (Fino, DT
Dental Trading, Bad Kissingen, Germany) used in group 2
amounted to 200 mm and in group 3 to 400 mm. The remaining fabrication steps were in accordance with group 1.
Before luting, the ®t of the inlays was checked by measuring the discrepancy between cavity wall and inlay using a
light microscope (40 £ , Zeiss, Oberkochen, Germany).
Measurements were performed at three locations along the
enamel margins. Five measurements were taken at dentinal
margins (Fig. 1).
Prior to cementation, the ceramic inlays were etched with
10% ammonium hydrogen di¯uoride (Biodent Retention
Gel w, DeTrey Dentsply, Dreieich, Germany) and silanised
(Monobond S w, Vivadent, Schaan, Liechtenstein). The
enamel margins of the cavities were etched with phosphoric
acid for 60 s (DeTrey Conditioner 36 w, DeTrey Dentsply,
Dreieich, Germany). Afterwards, dentin was treated with
the dentin bonding agent Syntac classic w (Vivadent,

Schaan, Liechtenstein) according to the manufacturer's
instructions. A thin layer of the un®lled resin (Heliobond w,
Vivadent, Ellwangen, Germany) was then applied to dentin,

Fig. 1. Schematic drawing of asymmetrical class V inlay preparation.
Measuring points prior to cementation ( ! ) and of dye penetration analysis
are marked (W).

enamel and the bottom of the inlays. In each group 16 inlays
were cemented into 8 teeth with a low viscous composite
luting cement (Variolink II w, Vivadent, Schaan, Liechtenstein) and 16 inlays into 8 teeth with a highly viscous
composite luting cement (Variolink ultra w, Vivadent,
Schaan, Liechtenstein). The inlays ®xed with the low
viscous cement were positioned conventionally by ®nger
pressure only, while the inlays luted with the highly viscous
cement were inserted using an ultrasonic insertion technique
[16]. Excess highly viscous cement was removed with
scalers, and low viscous material with foam pellets. In
order to avoid oxygen inhibition, glycerin gel was applied
to the margins. The luting cement was then light cured for

60 s from the inlay surface. The margins of the restorations
were ®nished and polished using ®nishing diamonds (Gebr.Brasseler, Lemgo, Germany) and ¯exible discs of decreasing grain (So¯ex discs, 3M Dental Products, St. Paul, USA).
The materials used in this study are listed in Table 1.
After the inlays were placed, teeth were subjected to arti®cial aging by exposing them to a chewing simulator
(Kausimulator
N6C41/N6W26,
Willytec,
Munich,
Germany). This simulator mimics occlusal loading and thermal cycling simultaneously. The device is more precisely
speci®ed by Kern et al. [17]. The loading procedure
comprised 120 000 cycles with 100 N (frequency 1.6 Hz).
The parameters of the 520 thermal cycles were: 60 s at
either 5 or 558C, with 12 s break in between. After arti®cial
aging, the specimens were stored in Ringer's solution for
nine months.
A quantitative scanning electron microscope (SEM)
analysis of margin adaptation at the restoration surface
was carried out [18]. For this purpose epoxy resin replicas
of the cemented inlays were fabricated before and after
processing in the chewing simulator, and after water

storage, respectively. The margins were evaluated in increments of 200 mm each at 100 £ magni®cation. The interfaces between ceramic and luting composite, and between
luting composite and dentin were evaluated separately. A
clearly visible loss of adhesion was described as a gap and
expressed as a percentage of the entire length of the evaluated interface.

P. Hahn et al. / Dental Materials 17 (2001) 191±196

193

Table 1
Materials used for the restorations
Material
Empress

w

Biodent Retention Gel w
Monobond-S w
DeTrey conditioner 36 w
Syntac classic w

Heliobond w
Variolink II w

Variolink Ultra w

Manufacturer

Essential ingredients (batch numbers)

Ivoclar, Ellwangen,
Germany
DeTrey Dentsply, Dreieich,
Germany
Vivadent, Schaan,
Liechtenstein
DeTrey Dentsply, Dreieich,
Germany
Vivadent, Ellwangen,
Germany

Leucite strengthened glass cermaic (920838)

Vivadent, Ellwangen,
Germany
Vivadent, Schaan,
Liechtenstein
Vivadent, Schaan,
Liechtenstein

Ammonium hydrogene di¯uoride (10)
3-Methacryloxypropyl-trimetoxysilane, water ethanol (906891)
36% Phosphoric acid (9707000425)
Primer:
Tetraethylene glycol dimethacrylate, maleic acid in aqueous aceton solution
(730193)
Adhesive:
Polyethylene glycol dimethacrylate, glutaraldehyde 50% in aqueous solution
(902168)
Bispheylglycidyl methacrylate, triethylene glycol dimethacrylate (904711)

Bis-GMA, urethane dimethacrylate, triethylene glycol dimethacrylate, barium
glass, ytterbium tri¯uoride. Ba±Al-¯uorosilicate glass, spheriod mixed oxide
(Base 824319, Catalyst 918863)
Bis-GMA, urethane dimemthacrylate, triethylene glycol dimethacrylate, barium
glass, ytterbium bi¯uoride, spheroid mixed oxide (Base 914051, Catalyst 914049)

For dye penetration analysis, tooth surfaces (except for
the area of the restoration) were covered with nail varnish.
Specimens were immersed in 0.5% basic fuchsin solution, at
378C for 24 h. Then, the teeth were embedded in acrylic
resin (Technovit 4071, Heraeus Kulzer, Hanau, Germany)
and bisected bucco-orally resulting in two halves containing
one inlay each. These samples were sectioned twice mesiodistally using a band saw (EXAKT 300 CL, Exakt Apparatebau GmbH, Germany). Cutting the specimens resulted in
sections, which allowed for evaluation of dye penetration
depths along the cavity walls. Thus, four interface sites per
inlay were evaluated (Fig. 1). The extension of the dye
penetration (in mm) was measured with a light microscope
at 40 £ magni®cation (Zeiss, Oberkochen, Germany).
Analysis of variance (ANOVA) was used to detect
differences between the experimental groups. Signi®cance
was set at a level of a ˆ 0:05. Luting space and luting
composite material were chosen as ªinter-specimen
factorsª for variables in the ANOVA test. Time of
measurement (SEM analysis: before and after loading)
and interface were regarded as ªintra-specimen factorsª.
Repeated measures of ANOVA tested the hypothesis of
effects between different variables. One way ANOVA and
Kruskal Wallis tests were used to detect for differences at
dentinal margins.

tin foil) the gap was 232 mm …^26† and in group 3 (with the
400 mm tin foil) the gap was 406 mm …^38†:
3.1. Dye penetration analysis
The results of the dye penetration analysis (mm) are
summarized in Fig. 2. The values are plotted separately
with regard to the different luting cements, the cervical
composite/ceramic interface and the composite/dentin interface.
Assessing penetration data for all groups together, penetration depths at dentin/composite interfaces …221 mm ^
166† were higher as compared to ceramic/composite interfaces …53 mm ^ 68†: The in¯uence of the interface location
was signi®cant …p ˆ 0:0001†:
Luting space and kind of luting cement had no signi®cant
in¯uence on dye penetration at the ceramic/composite interfaces. However, at dentin/composite interfaces the variable
luting cement signi®cantly in¯uenced margin quality.
When inlays had ideal luting spaces (group 1), luting
cements did not signi®cantly in¯uence marginal seal at
the dentin/composite interface. However, dye penetration
depths for larger luting spaces were deeper for inlays
cemented with low viscous material than for those cemented
with highly viscous material at the dentinal margins. The
in¯uence of luting cement on dye penetration depths was
signi®cant for the 400 mm luting space …p ˆ 0:0106†:

3. Results

3.2. SEM analysis

The gap between inlay and enamel cavity margin prior to
cementation was 47 mm …^8†; In group 1 the dentin cavity
margin gap was 27 mm …^8†; in group 2 (with the 200 mm

Results of SEM analysis concerning the parameter gap
are summarized in Figs. 3a and b. Means and standard
deviations are recorded with regard to the interfaces

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P. Hahn et al. / Dental Materials 17 (2001) 191±196

Fig. 2. Dye penetration depths (means and standard deviations) at ceramic/composite and dentin/composite interfaces. Group 1 ideal gap; Group 2, 200 mm
gap; Group 3, 400 mm gap.

(composite/ceramic interface, composite/dentin interface),
the time before and after arti®cial loading, and the different
luting spaces for both resin cements used.
Repeated measures of variance were performed for the
factors; localization of interface, luting space, luting
cement, and time. This analysis revealed that the location
of the interface …p ˆ 0:001†; the luting cement …p ˆ 0:001†;
and time …p ˆ 0:001† in¯uenced gap formation signi®cantly. Luting space had no signi®cant in¯uence.
Luting cement was found to have an in¯uence at the
ceramic margin after loading …p ˆ 0:0496; Fig. 3a). Inlays
cemented with low viscous cement showed greater gap
formation than inlays cemented with the highly viscous
cement at the composite/ceramic interfaces.
In accordance with these results, larger gap values were
found at dentin/composite interfaces after luting inlays with
low viscous cement. This was signi®cant before …p ˆ
0:0037† and after loading …p ˆ 0:0085; Fig. 3b).

4. Discussion
The marginal integrity of the ceramic inlay/composite
resin system was assessed according to the hypothesis
that gap formation, and therefore also dye penetration
are in¯uenced by the degree of contraction stress within
the composite luting cement, which itself is modulated
by polymerization shrinkage and compensation phenomena [20]. It has been debated, that this stress can be
compensated for when low viscous composite cements
and wider luting spaces between inlay and tooth are

used [5±8]. The in¯uence of these parameters on
marginal quality of ceramic inlays at dentinal margins
should be evaluated.
Class V cavities have an unfavorable C-factor, resulting
in high contraction stress within an adhesively ®xed resin
material. For this reason, ceramic inlays in class V cavities
were evaluated, to simulate a particularly disadvantageous
situation and also because it is easier to standardize the
preparation of class V cavities than class II cavities. The
cavities were prepared on both approximal sides of the teeth
to reduce the number of the teeth needed for the experiments. Since the morphology of buccal and oral surfaces
is often very different, mesial and distal approximal surfaces
were prepared. The box-shaped preparation design without
beveling is related to the geometrical form of the proximal
portion of class II inlay preparations. For this reason, the
results of the present study should, in principle, also be
applicable for the proximal parts of class II inlays.
Occlusal forces may cause tooth de¯ections and vertical
tooth deformations resulting in tensile ¯exure stresses and
shear stresses at the margins of restorations [19]. Therefore,
a chewing simulator was chosen to age the restorations in
the present investigation.
Only the results referring to the gap formation aspect
were reported, facilitating the comparison between SEM
analysis and the results of dye penetration.
As expected, dye penetration and SEM analysis revealed
better restoration margin quality at ceramic/composite interfaces than at dentin/composite interfaces. Additionally, arti®cial loading resulted in a signi®cant increase in gap
formation and penetration depths.

P. Hahn et al. / Dental Materials 17 (2001) 191±196

195

Fig. 3. Results of SEM analysis before and after arti®cial loading (means and standard deviations). Group 1, ideal gap; Group 2, 200 mm gap; Group 3, 400 mm
gap. (a) Gap formation at the ceramic/composite interface. (b) Gap formation at the dentin/composite interface.

Larger cervical luting spaces created higher penetration
depths at margins below the dentin±enamel junction, when
inlays were cemented with low viscous luting material, but
not when luted with highly viscous cement. According to
the present results, further studies could demonstrate that
low viscous luting cements are unfavorable in combination
with ceramic inlays with larger luting spaces for class II
cavities surrounded by enamel. Additionally, larger luting
spaces had no in¯uence on marginal quality at enamel
margins when inlays were cemented with highly viscous
luting cement [21,22].
In contrast to these results Dietschi et al. [20] found no
interaction between cement thicknesses, different luting
cements and marginal seal, in a model of simply shaped
bonded ceramic onlays with dentinal margins. It is conceiva-

ble that free vertical movement of onlay restorations compensated for polymerization stress within luting cement, while
for class V inlays this movement is restrained by the high
ratio of bonded to unbonded surfaces [20,23,24]. In the clinical situation free vertical movement of class II inlays for
polymerization stress relaxation is unlikely, therefore interaction between cement viscosity and luting space should be
similar to the results found in the present investigation.
Larger luting spaces did not increase marginal leakage
when inlays were luted with highly viscous luting cement.
This is in agreement with Alster et al. [25] who found a
decreased contraction stress with increasing cement layer
thickness of a highly viscous, chemically hardening composite (Clear®l F2, Kuraray, Japan). Moreover, composite
cements, which are mixed from two pastes, have an

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P. Hahn et al. / Dental Materials 17 (2001) 191±196

additional effect on remaining contraction stress. They
contain air voids increasing ¯ow capacity [24]. In highly
viscous materials this porosity may be greater than in low
viscous materials contributing to a higher ¯ow and therefore,
a better marginal seal in inlays with larger luting spaces.
Therefore, in the present investigation bond strength
between dentin and highly viscous cement was suf®cient
to compensate for the remaining polymerization stress and
to withstand the aging procedure. For inlays cemented with
low viscous composite resin, the increased polymerization
shrinkage in larger luting spaces resulted in loss of adhesion
at dentinal margins under the present experimental
conditions.
5. Conclusions
With well ®tting inlays viscosity of luting cements had no
signi®cant in¯uence on marginal quality at dentinal margins.
If inlays extend beyond the dentin±enamel junction, good
marginal ®t is still desirable. For inlays with larger luting
spaces extending into dentin, for example Cerec inlays or
prefabricated ceramic inlays, luting composites with higher
viscosities should be preferred.
Acknowledgements
We acknowledge gratefully the support of Professor
JuÈrgen Schulte-MoÈnting, Department of Medical Biometrics,
University of Freiburg, who did the statistical analysis of the
results of this study.
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