Stress distributions in ceramic and composite inlays with different resin cements

Stress distributions in adhesively cemented
ceramic and resin-composite Class II inlay
restorations: a 3D-FEA study
Pietro Ausielloa,*, Sandro Rengoa
, Carel L. Davidsonb
, David C. Wattsc
a
Department of Cariology, School of Dentistry, University of Naples ‘Federico II’,
Policlinico Edificio 14, Via Pansini 5, Naples 80131, Italy
b
University of Amsterdam, Amsterdam, The Netherlands
c
University of Manchester Dental School, Manchester, UK
Received 4 November 2003; received in revised form 13 April 2004; accepted 11 May 2004
KEYWORDS
Dental materials;
3D finite elements
analysis;
Occlusal loading;
Stress-distribution
simulation;
Class II MOD inlay
restorations;
Resin cements
Summary Objectives: The purpose of this study was to investigate the effect of
differences in the resin-cement elastic modulus on stress-transmission to ceramic or
resin-based composite inlay-restored Class II MOD cavities during vertical occlusal
loading.
Methods: Three finite-element (FE) models of Class II MOD cavity restorations in an
upper premolar were produced. Model A represented a glass–ceramic inlay in
combination with an adhesive and a high Young’s modulus resin-cement. Model B
represented the same glass–ceramic inlay in combination with the same adhesive and
a low Young’s modulus resin-cement. Model C represented a heat-cured resin-
composite inlay in combination with the same adhesive and the same low Young’s
modulus resin cement. Occlusal vertical loading of 400 N was simulated on the FE
models of the restored teeth. Ansyse FE software was used to compute the local von
Mises stresses for each of the models and to compare the observed maximum
intensities and distributions. Experimental validation of the FE models was
conducted.
Results: Complex biomechanical behavior of the restored teeth became
apparent, arising from the effects of the axial and lateral components of the
constant occlusal vertical loading. In the ceramic-inlay models, the greatest von
Mises stress was observed on the lateral walls, vestibular and lingual, of the cavity.
Indirect resin-composite inlays performed better in terms of stress dissipation.
Glass–ceramic inlays transferred stresses to the dental walls and, depending on its
rigidity, to the resin-cement and the adhesive layers. For high cement layer
modulus values, the ceramic restorations were not able to redistribute the stresses
properly into the cavity. However, stress-redistribution did occur with the resin-
composite inlays.
Dental Materials (2004) 20, 862–872
www.intl.elsevierhealth.com/journals/dema
0109-5641/$ - see front matter Q 2004 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
* Corresponding author. Tel.: C39-81-7462089; fax: C39-81-7462197.
E-mail address: pietausi@unina.it (P. Ausiello).

Significance: Application of low modulus luting and restorative materials do
partially absorb deformations under loading and limit the stress intensity,
transmitted to the remaining tooth structures.
Q 2004 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
Introduction
Resin-composites are limited for direct restoration
of the larger stress-bearing posterior Class II
cavities, on account of polymerization shrinkage
effects and some limitations in mechanical proper-
ties. Thermally post-cured resin-composite inlays,
however, are recommended in preference [1].
Thermal post-curing does improve the mechanical
qualities of composites [2,3]. Another advantage of
resin-composite inlays, instead of direct place-
ment, is that effects from the bulk curing-shrinkage
can be evaded.
As a further option for restoring large Class II
MOD restorations, strong ceramics are now avail-
able that can function properly without metal
support [4]. For both ceramic and composite
materials, adhesive cementation is imperative to
ensure reliable coherence of inlay and tooth
structure. Moreover, the cementation with (dual-
cure) cements has to be accompanied by appli-
cation of dentin bonding agents [5]. It is now
customary to use resin-based luting cements in
combination with dentin bonding agents for com-
posite and all-ceramic inlay restorations to enhance
(adhesive) retention and survival rates [6,7].
Unfortunately, luting also induces a significant
adverse effect. Luting creates a long and narrow
restoration, analogous to a Class I, made in
materials that are principally inferior to the usual
resin-composite restorative materials. This means
that a weaker and higher shrinking material is
inescapably present, that will set, moreover, in a
most unfavorable configuration (high C-value)
within the restored tooth [9]. Yet, with respect to
wall-to-wall adaptation, adhesively luted resin-
composite inlays score slightly better than direct
composite restorations, whilst ceramic-inlays per-
form as well as cast-gold inlays [4].
Notwithstanding their widespread application,
marginal integrity of tooth-colored direct or indir-
ect restorations remains a major problem in today’s
dentistry [8]. The cement layer is not only subject
to stresses that originate from curing shrinkage, but
also from mastication. Therefore, marginal and
internal adaptation of composite and ceramic inlays
should also be studied after loading and fatiguing
[10]. As a variety of materials with diverse
mechanical properties are involved in inlay design
and placement, analysis of the wall-to-wall integ-
rity of inlay-restored teeth requires that attention
be given to the elastic properties of the various
materials at the interfaces. For instance, it has
been demonstrated that incorporation of some
elasticity (lining) to the restoration may decrease
or even prevent interfacial separation [11–13].
However, particularly the fragile ceramic-inlays
still require rigid support. In indirect adhesive Class
II inlays, leakage often depends on the resin-
cement properties and on its mechanical behavior
[14]. Not only the shrinkage-strain, but the shrink-
age-stress magnitude and kinetics [15], the Young’s
modulus and the thickness of the cement determine
the totality of the developing stresses [16].
Ausiello et al. [17] showed, by means of a 3D
finite element analysis (FEA) model analysis, the
influence of occlusal loading and polymerization
shrinkage-strain on the stress-distribution in an
adhesive Class II MOD direct restoration for resin-
composites of different elastic modulus. Also the
influence of the adhesive-layer thickness on stress-
distribution was illustrated by 3D FEA [18].
The aim of the present study was to analyze by
3D FEA the stress-distribution in all materials
involved in adhesively luted Class II MOD inlay
restorations, of both ceramic and resin-composite
types.
Materials and methods
Finite element models
A 3D model of a human upper premolar, as used in a
previous study [18] was reused for this study. It was
realized by digitizing a plaster human upper-
premolar model on the scale of one to five with a
laser scanner (Cyber-ware). Crown and roots were
constructed in two different phases and sub-
sequently assembled.
For the crown, over 200 profiles were generated
at 0.33 mm increments by vertical and horizontal
scanning. Of these profiles, only 34 were selected,
17 vertical and 17 horizontal, at 2 mm increments,
for use in the external shape definition of the solid-
tooth model. Literature data on the tooth
Ceramic and composite inlay Class II behavior 863

morphology for the definition of the dentine and
enamel volumes [20] were used. The model data
were assembled in a 3D wire-frame structure by
means of a 3D CAD (Autocad 12, Autodesk, Inc.,
Neuchatel, Switzerland, 1992). The 3D curves were
exported into Pro-Engineer 16.0 (Parametric Tech-
nology Co., Waltham, MA, USA, 1994), where a solid
model was generated by fitting the horizontal and
vertical profiles. The model was cut in the cervical
area to obtain the final crown.
The roots were modeled by their mesial-distal
and buccal-lingual representations taken from
literature. The two representations were scanned
and eight vertical profiles were generated imitating
the scanned images. The roots were constructed by
fitting the vertical profiles. The pulp region was
obtained in an analogous way and subtracted from
the roots. The crown and the roots, with the pulp
chamber, were assembled in the final model.
A parametric cutting plane was chosen to
generate different cavities and MOD preparations.
In Fig. 1, the Class II MOD is shown (3.5 mm occlusal
width). The cavity design was characterized by flat
floor and sharp internal line angles. No bevel was
considered at the proximal and occlusal margins.
The preparation derived was flat from proximal to
proximal surface.
The solid model was transferred into a FEA
program (ANSYS Rel. 6.0, ANSYS, Inc., Houston,
TX, USA, 1994) where a 3D mesh was created. In the
previous work [18], we explained the volumes that
were redefined and meshed with 8-node-brick and
4-node-tetrahedral elements, resulting in 7282
elements (3376 hexahedral and 3906 tetrahedral
shape elements) and 5236 nodal structures.
Different material properties were now assigned
to the elements, according to the volume defi-
nition. In particular, in the previous study, the
adhesive layer was modeled in the FEM program
using spring elements connecting the nodes from
the cavity wall of the natural tooth with those of
the composite restoration [18]. In the present
study, technical enhancements in the finite
element model generation were used to increase
the structural relevance of the model itself.
The modeling of the adhesive area in the Class II
MOD preparation was differently realized. In this
case, where an indirect Class II MOD restoration-
type was simulated, one part of the adhesive area
was modeled to be the adhesive layer, contacting
the dental walls. The other part was modeled to be
the resin luting cement, contacting from one side
this adhesive layer and from the other side the
filling material (Fig. 2).
The new Class II MOD FE model used a different
element mesh-size (the size of all the elements was
reduced to obtain more detailed analysis results)
and a different methodology to simulate the resin
bonding and the luting cement layers. To investi-
gate the strain-status of the total adhesive area
under occlusal vertical loading simulation, shell
elements (with membrane behavior) were
employed both for the adhesive layer and for the
luting cement layer (Fig. 1), instead of the spring
elements used previously [18].
The volumes were redefined and meshed with
8-node brick and 4-node tetrahedral elements,
resulting in a 27,140-element and 18,244-node
structure, for a total solid elements number of
24,818. In particular, 1160 shell membrane
elements were used (Fig. 2). In Ansys 6.0 software
these elements are called shell 41 and they are 3D
characterized for each of the 4 nodes of the single
Figure 1 Finite element model of Class II MOD indirect
restoration of an upper premolar with particulars relative
to the shell modeling of the adhesive resin bonding and of
the cement layers.
Figure 2 Finite elements models of the cement and
adhesive layers.
P. Ausiello et al.864

element. Because of their low-thickness, they do
not show flexural deformation. In this way, it was
possible to better simulate the mechanical behavior
of these two different layers.
Experimental model validation
To validate this new Class II MOD FEM model,
compression loading measurements were per-
formed on sets of differently restored teeth until
fracture of the samples. These were the Class II
MOD designs, corresponding to Models A and C,
described below. Ten caries-free human upper
premolars were used for each test group. Class II
MOD cavities were prepared with a diamond bur at
high speed under water coolant. Axial and gingival
walls were cut non-retentively, at approximately
1008 angles. No bevels were prepared at the cavo-
surface enamel angles. For the Class II MOD
restoration, a heat-cured resin-composite with a
Young’s modulus of about 50 MPa (Gradia, GC,
Japan) was used. Unifil Bond adhesive (GC, Japan)
with a Young’s modulus of 4.5 MPa was applied on
the cavity walls. Unifil Flow (GC, Japan) with a
Young’s modulus of 9.6 MPa was used as resin luting
material.
The samples were inserted, as far as the
cementum–enamel junction, into steel cylindrical
rings with the apical root area in contact with the
steel-ring floor. Subsequently, spaces between
roots and steel walls were filled with rigid resin-
composite, so that only material deformation
within the tooth would be measurable. The test-
rings were clamped to the universal testing machine
and loading was applied vertically via a 6 mm
diameter steel cylinder, with the axis normal to
the tooth axis. To simulate one major occlusal
force, a 1 mm/min compression rate was used. The
vertical displacement and the axial load were
recorded until each restored tooth fractured. This
loading situation was also simulated using the FE
analysis, generating closely matched results
(Graph 1).
An important parameter to be considered was
the rigidity of the restored teeth, expressed under
the loading conditions used in this analysis. Two
components of rigidity were considered: axial and
lateral. Axial rigidity directly measures the resist-
ance to compressive forces. Lateral rigidity
measures cuspal-displacement under flexural load-
ing. Thus, the effect of the applied masticatory
loading was to provide both a compressive load to
the system and also displacement of the cusps.
The FE analysis performed was linear and static.
It used the over-position effect principle to
determine the axial rigidity comparative par-
ameter (%RCPA) and lateral rigidity comparative
parameter (%RCPL). They represent, in percentage,
the perceived rigidity variation of a system with
respect to an other reference rigidity. If they are
positive it means that the test system is more rigid
than reference system. In formulas:
%RCPA Z 1 K
axial ÿ movementperceived
axial ÿ movementreference

!100
%RCPL Z 1K
lateralÿmovementperceived
lateralÿmovementreference

!10
The sound tooth has been chosen as a reference
model in numerical calculations [20]. Results are
shown in Table 1.
Numerical simulation
The simplest approximation to the probable nature
of occlusal loading is where forces to the teeth are
applied statically and vertically. In all the FE
models investigated here, the external roots
nodes were constrained in all the spatial directions.
Adhesive mechanical properties are listed in Table 2
for all the restored tooth models.
The compression test with a 400 N occlusal load
was conducted. The loading cylinder was modeled
Graph 1 Validation data: showing the theoretical plot,
determined numerically, and the experimental plot of
axial load versus displacement.
Table 1 Rigidity comparison of the systems.
Model
G-lC
Model
G-hC
Model C Sound
tooth
%RCPA 4.29 5.00 K0.54 0.00
%RCPL 8.60 8.60 K2.10 0.00

as a 3D elastic beam (Fig. 3). End rotations were not
constrained. The common end was displaced in the
central position of the loading cylinder section in
the experimental test. The load was applied on the
tooth at two points (Fig. 3) through the beams
elements on the cusps (red areas). The resulting
force F crossing the central position of the loading
cylinder section was 400 N (Fig. 3, red arrow). The
beam elastic properties were treated as being
infinitely rigid compared to the tooth. Resin-
composite support was not modeled and it was
considered to be as rigid as the loading system.
Moreover, the following assumptions were made:
† A static linear numerical analysis was performed.
Thus, all materials were considered elastic
throughout the entire deformation, which is a
reasonable assumption for brittle materials in
non-failure conditions.
† Dentin is an elastic and isotropic material.
† Enamel was treated as mechanically homo-
geneous and isotropic, as in Refs. [19,20].
In Fig. 2, the different thicknesses of the two
interfacial layers is shown. The elements simulating
the luting cement and the adhesive are positioned
between the tooth and the filling material. We
hypothesize the perfect and absolute bonding
between the two materials. In the FE analysis
different conditions were simulated, modifying the
thickness of the cement, not varying the adhesive
resin bonding one, and including different filling
materials properties (Fig. 2). Three different
models of Class II MOD inlay restorations were
considered in order to simulate three different
clinical indirect restorations types.
Model A (G-hC, Glass-core ceramic with ‘high
modulus’ Cement), in which an high
modulus glass–ceramic filling material
was considered in combination with an
high modulus cement;
Model B (G-lC, Glass-core ceramic with ‘low mod-
ulus’ Cement), in which an high modulus
glass–ceramic filling material was con-
sidered in combination with a low modulus
cement;
Model C (Composite restoration), in which a heat-
cured resin-composite inlay was con-
sidered in combination with a low modulus
cement.
In all the combinations, one resin bonding system
was considered. Physical properties of the used
materials are presented in Table 2.
Results
Inspection of the results revealed critical zones
with particular stress behavior. The results are
presented in terms of von Mises stress maps in MPa,
which were computed within Ansys using the von
Mises shear-strain-energy failure criterion, as an
outcome of the 400 N occlusal loading. The figures
utilize a false-color non-linear scale for stress. It
should be understood that von Mises stress is
essentially an aggregate stress, sometimes termed
an octahedral stress. As such, it cannot be directly
decoded into specific contributions from tensile,
compressive or shear stress. However, other types
of output from most FE programs can provide such
information.
Figs. 4–6 show the varying biomechanics arising
from the differing rigidity of the three models: A, B
and C. These figures show, respectively, stresses
computed: at the surface of each model (Fig. 4a–c),
within each model cavity preparation (Fig. 5a–c),
within each MOD restoration (Fig. 5d–f) and (in
Fig. 6) from the interfacial areas (adhesive layerC
resin-cement layer) between the inlay restoration
Figure 3 The model structure is blocked avoiding
movement in the three directions of the space.
Table 2 Materials properties.
Material Elastic
modulus,
E (GPa)
Poisson
ratio
Thickness,
T (mm)
*Enamel 48 0.23
Dentine 18 0.2
Composite 50
Ceramic 90
Cement hm 10 70
Cement lm 6 70
Adhesive 4.5 10
*Verluis, 1996 [20]. Co., data.

and the cavity preparation. In these interfacial
areas, the biomechanical differences were
especially critical.
Experimental and theoretical validation curves
are compared in Graph 1. The two similar stress–
strain behaviors gave good support to the validity of
the model. Even the extreme (high strain) proper-
ties could be rather well approximated by the
theoretical curve. The experimental curve shows a
mild non-linear behavior near to the origin and a
linear behavior thereafter. This apparent non-
linearity was not due to a real material or
geometrical non-linearity but to the initial system
assessment that included effects due to contact and
sliding. These phenomena were unimportant in the
FE model validation.
The glass–ceramic-restored teeth, respectively
cemented with a high (10 GPa) and low (6 GPa)
modulus cement material (Models A and B; Fig. 4a
and b) may be compared with the behavior shown
in Fig. 4c of the composite-restored tooth (Model
C), luted with the low modulus cement. The
highest stress values of about 400–500 MPa for all
three models were concentrated on the cuspal
loading points. At the center of the occlusal
surface, for Models A and B, a stress value of
100–500 MPa was computed while for Model C it
was generally much lower, ranging from 40 to
100 MPa. All the tooth models were low-stressed
mesial-distally, with values of only 10–15 MPa. On
the vestibular and lingual sides, depending on the
displacement of cusps, stresses appeared higher,
about 20–40 MPa.
In Fig. 5a–c, analysis was conducted within the
cavity preparation, while the ﬁlling material was
extracted from the cavity itself. This was possible
Figure 4 (a) von Mises stress-distribution of Model A (G-hC). (b) von Mises stress-distribution of Model B (G-lC). (c) von
Mises stress-distribution of Model C.

because of the CAD/FE model conﬁguration. Stres-
ses were particularly intense in Models A and B
(10–40 MPa) compared with Model C (1–5 MPa),
speciﬁcally localized on the vestibular and lingual
cavity walls of Models A and B (Fig. 5a and b).
In Model C, a lower modulus (50 GPa) heat-cured
composite resin was simulated.
In Fig. 5d–f is displayed the stress behavior within
the core of the restoration of Models A–C. Slight
differences are evident between the ceramic
restorations of Models A and B, where von Mises
stress values appear elevated but similar, irrespec-
tive of the modulus of the cement material used in
the two simulations. Stress is concentrated in the
core of the restoration, extending to the vestibular
and lingual sides of the restoration itself and totally
transmitted to the cavity walls, as already shown in
Fig. 5a and b.
In Fig. 5f, by contrast, where lower modulus
(50 GPa) resin-composite was used for restoration,
stress gradients from the internal area to the cavity
walls were lower, matching the distribution seen in
Fig. 5c.
In Fig. 6 are shown for the three models the stress-
distributions, as successive pairs, for the adhesive
and the resin-cement. The change of stress scale
(0–10 MPa) should be noted.
For the adhesive layer, no differences are evident
between ceramic Models A and B (Fig. 6a-1 and b-1).
For the cement layer, higher stress was apparent
with the higher modulus cement (Fig. 6a-2) com-
pared with the lower modulus lute (Fig. 6b-2).
Fig. 6c-1 and c-2 illustrates the interfacial stresses
for the adhesive and cement layers within composite
Model C. The lowest stress values were recorded for
this condition.
Figure 5 (a) von Mises stress-distribution within Model A (G-hC). (b) von Mises stress-distribution within Model B (G-lC).
(c) von Mises stress-distribution within Model C. (d) von Mises stress-distribution within the restoration of the Model A
(G-hC). (e) von Mises stress-distribution within the restoration of the Model B (G-lC). (f) von Mises stress-distribution
within the restoration of the Model C.

In Graph 1, a linear analysis on Model A and C
is represented in which it can be seen that
with increasing the loading from 400 to 800 N,
the stresses proportionally increase, leading to
a critical stress concentration in Model A, particu-
larly on the lingual cusp.
Discussion
Teeth in posterior regions are subject to functional
and para-functional forces of varying magnitudes
and directions. In vitro mechanical tests on Class II
adhesive posterior restorations revealed the differ-
ent aspects related to the stress-distribution
regarding the marginal and internal adaptation
of adhesive Class II restoration [21]. The role of
the ﬁlling material, of the adhesive resin and of the
resin cement was clearly demonstrated and results
indicated various important points to observe to
obtain high performance of the restoration itself.
The rigidity or elastic modulus of dental restorative
materials was considered extremely important at
the adhesive tooth-restoration interface.
In the present work, the FEA method was used to
investigate the stress-distribution resulting from
occlusal loading within the restoration and in
correspondence to that of the interfacial layers
(adhesive and cement) between the cavity walls
and the inlay materials.
An arbitrary load of 400 N was applied in this
test, which is probably lower than can be applied by
the teeth in vivo. Different data are reported on
this aspect. Tortopidis [22] found that 580 N was
Figure 5 (Continued)

the maximum bite force of healthy people in
posterior areas. Other investigations [23] suggested
that these values differ between males (522 N) and
females (441 N).
Under laboratory conditions, varied loading rates
can be applied to the samples to investigate
biomechanics of natural and restored teeth. In
particular, fracture resistance of Class II
Figure 6 (a-1) von Mises stress on Model G-hC, adhesive. (a-2) von Mises stress on Model G-hC, cement. (b-1) von Mises
stress on Model G-lC, adhesive. (b-2) von Mises stress on Model G-lC, cement. (c-1) von Mises stress on Model C, adhesive.
(c-2) von Mises stress on Model C, cement.

restorations in upper premolars submitted to
vertical loading has been experimentally investi-
gated [24]. It ranged for resin-composites in
combination with dentin bonding systems between
700 and 800 N. These data were also confirmed
recently [25], where the use of resin-composite and
ceromers as restorative materials was considered.
However, it was not the objective of this study to
determine the absolute numerical stress levels
created within the restoration but to examine
their distribution and localization. The software
used in this study was not programmed for evaluat-
ing the model to failure and therefore higher or
lower loads would only change the magnitude of the
stresses in the distribution pattern.
In the ceramic Models A and B, where a ceramic
inlay of high modulus (90 GPa) was used in
combination with 70 mm thick resin-cements of
two different Young’s moduli, no major differences
were found in terms of stress-distribution within
the restoration. However, when the inlay modulus
was reduced to 50 GPa, still in combination with the
same parameters for the cement layer, the stress-
distribution significantly changed. Comparing
Fig. 5d and e with Fig. 5f (respectively, Model A
and B, with Model C) the stress-distribution was
more intensive where the 90 GPa modulus inlay was
used and these stresses are almost totally trans-
ferred to the cavity walls, as shown in Fig. 5a and b;
whilst for the 50 GPa inlay (Fig. 5f), the stresses are
partially absorbed and partially transfered to the
cavity walls.
From the load-strain values as represented in
Fig. 3, it can be derived that a 400 N loading in
horizontal direction, when flexural deflections will
take place in the prepared brittle tooth structure,
destructive damage will occur earlier than with
vertical, occlusal loading.
Recently, Abu-Hassan et al. [26], used 3D-FEA to
investigate stress-distributions associated with
loaded ceramic onlay restorations with different
designs of marginal preparation. It was possible to
establish how vertical and horizontal forces act
differently in correspondence with the total mar-
gins of the restoration. Hence interesting con-
clusions could be drawn regarding the optimum
morphology of the butt-joint onlay preparation.
In our investigation, the 400 N axial simulations
showed that ceramic Models A and B transmitted
higher stress to the cavity walls than composite
Model C.
Fig. 4a and b shows that Class II MOD prep-
arations, restored by a 90 GPa ceramic inlay with
the same 4.5 GPa adhesive but with either a 10 or
6 GPa resin-cement, do not show a substantially
different stress-distribution after axial loading.
By contrast, in Model C, a 50 GPa resin-compo-
site inlay, with the same adhesive and the 6 GPa
resin-cement, showed a lower stress with a more
homogenous distribution. This indicates a greater
stress-dissipating effect of the relatively compliant
resin-composite than the more rigid glass–ceramic
inlay.
Sorensen and Munksgaard [5] concluded from
clinical trials that none of the dentin adhesives they
tested were able to completely prevent interfacial
gaps developing when inlays were cemented with a
dual-cure resin-cement. But in absence of the
adhesive, the failure rate was significantly higher.
The investigation of the interfacial zone
between the cavity and inlay margins has always
represented an important tool in laboratory inves-
tigations as well as in clinical reports.
A low-modulus poly-acid-modified glass-ionomer
cement used with ceramic-inlays resulted in a high
fracture rate and loss of marginal adaptation. The
marginal adaptation of the lute was more durable at
the enamel interface than that at the ceramic
interface [27].
When comparing Fig. 6a-2 and b-2, the higher
stresses in the contact area of the 10 GPa resin-
cement is clear. Further studies on the role of
cement layer thickness and minimal modulus to still
sufficiently support the ceramic inlay are in
progress.
Conclusions
From this FE analysis on stress-distribution in inlay-
restored Class II MOD cavities under axial load, it is
evident that both optimum stress magnitude and
distribution are best served with low modulus
restorative materials. FEA enabled investigation of
optimal conditions, material selection and their
interaction when adhesively restoring teeth. Class II
MOD restorations by glass core inlay materials
created higher stress levels at the cusp and at the
internal sides. Thermally post-cured resin-compo-
site Class II restorations presented elastic biome-
chanics similar to that of the sound tooth.
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