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j o u r n a l o f d e n t i s t r y 4 0 ( 2 0 1 2 ) 6 7 0 6 7 7
Available online at www.sciencedirect.com
elsInternal adaptation, marginal accuracy and microleakage of apressable versus a machinable ceramic laminate veneers
Moustafa Nabil Aboushelib a, Waleed AbdelMeguid Elmahy b, Mohammed Hamed Ghazy c,*aDental Biomaterials Department, Faculty of Dentistry, Alexandria University, EgyptbRestorative Department, Faculty of Dentistry, Alexandria University, EgyptcConservative Dentistry Department, Faculty of Dentistry, Mansoura University, Egypt
1. Introduction
Ceramic laminate veneers are considered as conservative
solution for patients requiring improvement of the shape,
colour, or position of their anterior teeth.1,2 These thin and
brittle restorations are bonded using adhesive resin cements
which establishes a chemical bond between the ceramic and
the tooth structure using standard hydrofluoric acid etching
and silane application. Once properly cemented, ceramic
veneers become an integral part of the tooth structure and
share part of applied loading stresses during masticatory
a r t i c l e i n f o
Article history:
Received 6 December 2011
Received in revised form
19 April 2012
Accepted 20 April 2012
Keywords:
Laminate veneers
Margin
Gap
Leakage
Film thickness
a b s t r a c t
Objectives: The aim of this study was to evaluate the internal adaptation and marginal
properties of ceramic laminate veneers fabricated using pressable and machinable CAD/
CAM techniques.
Materials and methods: 40 ceramic laminate veneers were fabricated by either milling
ceramic blocks using a CAD/CAM system (group 1 n = 20) or press-on veneering using lost
wax technique (group 2 n = 20). The veneers were acid etched using hydrofluoric acid,
silanated, and cemented on their corresponding prepared teeth. All specimens were stored
under water (37 8C) for 60 days, then received thermocycling (15,000 cycles between 5 and
55 8C and dwell time of 90 s) followed by cyclic loading (100,000 cycles between 50 and 100 N)
before immersion in basic fuchsine dye for 24 h. Half of the specimens in each group were
sectioned in labio-lingual direction and the rest were horizontally sectioned using precision
cutting machine (n = 10). Dye penetration, internal cement film thickness, and vertical and
horizontal marginal gaps at the incisal and cervical regions were measured (a = 0.05).
Results: Pressable ceramic veneers demonstrated significantly lower (F = 8.916, P < 0.005)
vertical and horizontal marginal gaps at the cervical and incisal margins and lower cement
film thickness (F = 50.921, P < 0.001) compared to machinable ceramic veneers. The inferior
marginal properties of machinable ceramic veneers were associated with significantly
higher microleakage values.
Conclusions: Pressable ceramic laminate veneers produced higher marginal adaptation,
homogenous and thinner cement film thickness, and improved resistance to microleakage
compared to machinable ceramic veneers.
Clinical significance: The manufacturing process influences internal and marginal fit of
ceramic veneers. Therefore, dentist and laboratory technicians should choose a
manufacturing process with careful consideration.
# 2012 Elsevier Ltd. All rights reserved.
* Corresponding author. Tel.: +20 2 0105025275.E-mail address: mghazy@mans.edu.eg (M.H. Ghazy).
0300-5712/$ see front matter # 2012 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.jdent.2012.04.019journal homepage: www.intl. evierhealth.com/journals/jden
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structural defects. Nowadays, computer assisted design and
computer assisted milling technology (CAD/CAM) requires
nothing more than few keyboard clicks in order to design and
fabricate accurate restorations. Nevertheless, the shade and
colour of machinable ceramic produced ceramic veneers are
limited by the colour of the selected block used to mill these
restorations.2325
Up to the authors knowledges, there are no investigations
in the literature evaluating the influence of the fabrication
technique on the internal adaptation marginal accuracy and
microleakage of ceramic laminate veneers, Therefore, it was
the objective of this laboratory study to investigate these
parameters using pressable and machinable ceramics. The
null hypothesis to be tested was that neither the pressable nor
the machinable ceramic veneer fabrication technique would
have an effect on the internal adaptation, marginal accuracy
and microleakage of ceramic veneers.
2. Materials and methods
j o u r n a l o f d e n t i s t r y 4 0 ( 2 0 1 2 ) 6 7 0 6 7 7 671cycle. The adhesive resin cement is subjected to dynamic
loading, thermal cycling, and is influenced by the hydrolytic
effect of water and different chemicals present in the
mouth.3,4
External marginal adaptation of ceramic veneers, which is
defined as the vertical distance between the finish line of the
prepared tooth and the margins of the fabricated veneers5
plays an important role for their success. Close proximity
between the margin of the restorations and the tooth structure
protects the adhesive resin cement from excessive exposure to
the oral cavity leading eventually to slow process of gradual
disintegration of its chemical, physical, and mechanical
properties resulting in microleakage, recurrent decay, dis-
colouration of the tooth structure, and fracture of the
cemented veneers. On the other hand, internal marginal
adaptation is a direct measure of the cement film thickness
underneath the restoration and is significantly influenced by
the accuracy of fabrication process used.6,7
While external marginal adaptation could be measured
using different imaging methods as stereo or scanning
electron microscopy, internal marginal adaptation requires
sectioning of these restorations in order to assess the cement
film thickness underneath the cemented restorations.8,9
Holmes measured various points between the casting and
the tooth and clarified the terminology for misfit and defined
the internal gap as the perpendicular measurement from the
axial wall to the internal surface of the restoration.10 Non
destructive techniques which rely on measuring the thickness
of low viscosity impression silicon material used in place of
the resin cement were also used in previous investigations.11
13 Ucar et al. concluded that weighing the light body addition
silicon is a convenient method for 3 dimensional evaluation
the 3 dimensional internal fit of dental crowns.14 These
parameters play a significant role which directly influences
the clinical performance of ceramic veneers. From one hand,
these thin shells have supra-gingivally placed margins directly
exposed to the oral cavity and on the other hand the thickness
of resin cement is a parameter that significantly influences the
shade and colour of these restorations.1518
Traditionally, ceramic veneers are fabricated using layer-
ing technique which incorporates refractory dies used to
support the condensed layers of the ceramic slurry.19 This
technique gives the ceramist full control over the layers
incorporated resulting in a naturally looking restoration. On
the contrary, it requires investing time and effort in order to
produce accurately fitting restorations. Duplicating the work-
ing model with brittle refractory material is a sensitive process
and removal of the refractory material after firing the veneers
are sensitive procedures.20 A new generation of ceramic
materials were introduced to the dental field using pressing
technology.21,22 Pressable ceramics are fabricated by burning
out wax patterns using the conventional lost wax technique
and melting and pressing ceramic ingots under controlled
pressure, temperature, and vacuum using computer pro-
grammed press ovens. These ovens are equipped with a
pneumatic press that activates an alumina plunger used to
compress molten ceramic ingots. Press-on ceramics allow
accurate reproduction of the anatomical features carved in thewax pattern and controlled processing of the ceramic material
resulting in an accurate restoration with minimal internalA silicon index was made for a defect free maxillary right
central incisor in a student typodent (Frasaco, Tettnang,
Germany) with interchangeable hard resin teeth. Incisal lap
preparation for ceramic laminate veneers was made with
1.5 mm incisal edge reduction; 0.7 mm labial reduction
extended to proximal contact regions, and a chamfer finish
line placed 1.5 mm lingual to the incisal edge on the palatal
wall. Depth orientation grooves were cut followed by tapered
diamond point and finishing stones.2628 The sectioned
silicon index (Virtual Putty fastset, Ivoclar Vivadent, Schaan,
Liechtenstein) was used to ensure even tooth reduction, Fig. 1.
The tooth was polished with a nylon bristle brush and
polishing paste at 5000 rpm in a slow speed handpiece. A
heavy and light body impression (Virtual Putty fastset, Ivoclar
Vivadent) was taken for the full arch including the prepara-
tion and then poured in extra hard stone to produce the
working cast and die.
Fig. 1 Digital image demonstrating cut section of the
silicon index used to verify preparation dimensions andused as a reference using preparation and waxing
procedure.
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j o u r n a l o f d e n t i s t r y 4 0 ( 2 0 1 2 ) 6 7 0 6 7 76722.1. Pressing fabrication technique
20 ceramic laminate veneers were fabricated using the
pressing technique (IPS e.max press A3; Ivoclar Vivadent). A
single layer of die spacer material (20 mm) was applied on
gypsum dies of the prepared tooth and allowed to dry. A wax
pattern was manually built on each gypsum die to restore the
anatomical features of the unprepared tooth using the
sectioned silicon index as a reference, Fig. 1. Five wax patterns
were attached to the pressing ring using a 3 mm round wax
sprue and a freshly vacuum mixed investment material was
cast on a vibrating table. Following chemical setting of the
investment, 45 min, the ring was transferred to a preheated
burn out oven (800 8C) after removal of the plastic base. After
2 h, preheated ceramic ingots were placed inside the ring and
transferred to the pressing oven (P500; Ivoclar Vivadent) which
was automatically programmed to complete the pressing
cycle. Pressable ceramic laminate veneers were devested by
gentle airborne particle abrasion using 50 mm glass particles
and cutting and finishing the location of the sprue.
2.2. Machining fabrication technique
Multichromatic blocks (Multishade A3; Ivoclar Vivadent) were
used to mill 20 veneers (CEREC 3D1 3.0, CEREC Mc XL, Sirona
dental system, Charrlotte, USA). A powder imaging spray was
thoroughly applied on the surface of the gypsum die of the
prepared tooth in order to form a reflection medium that is
necessary for the optical impression. 3D camera (Charge-
Coupled Device) was positioned over the powdered die and the
3D image was captured for each specimen in labial, palatal and
incisal directions. The acquired optical image was transferred
into the CAD software and the preparation finish line was
marked on the digital model. After selection of the required
anatomy, the contours were adjusted by labelling the
curvature lines.
2.3. Cementation procedure
Each ceramic laminate veneer was etched using 9.6% hydro-
fluoric acid gel for 30 s (Porcelain Etch Gel, Pulpdent Corp.,
Watertown, MA, USA), washed, dried, and finally coated with a
silane primer (Variolink S bond primer; Ivoclar Vivadent)
which was left to completely dry for 3 min. A freshly mixed
resin cement (Variolink A3) was applied on the fitting surface
of each laminate veneer which was then seated on the
prepared tooth using fixed pressure of 250 g for one min.
Excess cement was wiped off and the resin cement was light
polymerized for 60 s first from the lingual surface then from
the Labial surface.29
2.4. Artificial ageing programme
The cemented laminate veneers were stored under water for
60 days then received thermo-cycling (15,000 cycles between 5
and 55 8C with 90 s immersion time at each temperature) using
water as transfer medium followed by cyclic loading (100,000
cycles between 50 and 100 N at 4 Hz). Up on completion ofartificial ageing, the entire external surface of the restorations
and the supporting tooth was coated with two layers of nailvarnish without covering the margins before immersion in
penetration dye (15% basic fuchsine dye) for 24 h.
2.5. Sectioning technique
The root portion of each restoration was sectioned 2 mm below
the cervical line and the coronal section was imbedded in
transparent chemically polymerized acrylic resin. For each
fabrication technique, half of the specimens were vertically
sectioned in a labio-lingual direction (n = 10) and the other half
was sectioned in a horizontal direction using a diamond coated
disc and a precision cutting machine (Mikracut 120, Metkon,
Germany). At least two intact mid sections (0.5 mm thick) were
obtained from each specimen. Each section was polished on a
rotating metallographic polishing device (M3000, Buehler, Ltd.,
Evanston, IL, USA) using ascending grit tungsten carbide coated
paper. The polished sections were ultrasonically cleaned in
distilled water for 60 s to remove surface contaminants.
2.6. Internal adaptation, marginal accuracy andmicroleakage
The cut sections were examined under stereo microscope (SZ
11, Olympus, Japan) under different magnifications and using
scanning electron microscope (XL 30; Philips, Eindhoven, the
Netherlands). On vertical sections, marginal accuracy was
measured as the maximum distance between the finish line of
the underlying prepared tooth and the margin of the ceramic
laminate veneer on both the cervical and the incisal margins.
Internal adaptation (also defined as cement film thickness) was
measured as the maximum distance (perpendicular line to the
prepared surface) between the inner surface of the labial wall of
veneer and the outer surface of the prepared tooth at five fixed
locations. Measurements were also made on the horizontal
sections. Microleakage was defined as the distance the dye was
able to penetrate at both the cervical and the incisal margins.
One way analysis of variance was used to analyse the data
and based on the sample size (n = 10), chosen level of
significance (a = 0.05), and medium effect size difference
(F = 0.25) the chosen statistical test had adequate power to
detect significant differences which could be used to interpret
clinical recommendations.
3. Results
Because of limitations related to sample size used in this study
(n = 10), Levenes test of homogeneity of variables was used (8.8)
which indicated homogenous distribution of data confirming
also acceptable standard error of Skewness of data (0.37). Also
Data was analysed with ShapiroWilk test to confirm the
assumption of normal distribution of the data (0.165), therefore,
parametric statistics were used to evaluate the data.
Statistical analysis revealed that machinable ceramic
veneers, Fig. 2, were associated with significantly higher
marginal gap values compared to pressable ceramic veneers,
Fig. 3. Significantly higher horizontal (F = 8.916, P < 0.005) and
vertical (F = 43.393, P < 0.001) gaps were observed with machin-able ceramic veneers compared to the pressable veneers.
Moreover, machinable ceramic veneers were associated with
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j o u r n a l o f d e n t i s t r y 4 0 ( 2 0 1 2 ) 6 7 0 6 7 7 673significantly higher (F = 50.921, P < 0.001) cement film thickness
which was irregular compared to pressable veneers. Cement
film thickness values were almost identical when measured in
either vertical or horizontal sections made for the same
specimen.
Higher marginal gaps resulted in significantly higher
microleakage at incisal (F = 37.708, P < 0.001) and cervical
(F = 18.245, P < 0.001) margins observed for machinable ce-
ramic veneers, Fig. 2. Few specimens belonging to both groups
demonstrated micro-cracks after completion of cyclic loading
programme. Previous data are summarized in Table 1.
4. Discussion
The results of the present investigation justify rejection of the
null hypothesis as there was significant influence of the
Fig. 2 (A) Horizontal cut section of machinable veneer demons
associated microleakage. (B) Vertical cut section of machinable
microleakage. Distance between two red lines represent vertica
demonstrating uneven cement film thickness, marginal gap, an
surface of the veneer. Red line represent internal cement film tfabrication technique on the internal adaptation, marginal
accuracy, and microleakage of the tested ceramic veneers. For
many decades, fabrication of refractory die material was used
for the production of porcelain laminate veneers where the
porcelain slurry was directly built on the heat resistant
material. After firing, the refractory material was removed
using airborne particle abrasion incorporating glass beads
which may also compromise marginal accuracy of the
veneers.30 This technique required extensive laboratory work
in order to duplicate the working die with a refractory one and
during building the porcelain slurry. The marginal quality of
laminate veneers fabricated using refractory technique
depends on the accuracy and skill of the dental ceramist.
In the pressable ceramic technique, wax patterns are
directly built on the prepared working model giving the dentist
more control during shaping, carving, and sealing the
margins. During pressing, the molten porcelain ingot is
trating uneven cement film thickness, marginal gap, and
veneer demonstrating cervical marginal fit and associated
l misfit. (C) Vertical cut section of machinable veneer
d associated microleakage. Notice angle lines on the fitting
hickness at incisal edge.
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j o u r n a l o f d e n t i s t r y 4 0 ( 2 0 1 2 ) 6 7 0 6 7 7674pressed under controlled pressure, temperature, and vacuum
insuring accurate reproduction of fine details especially at the
margins. On the other hand, software limitations in designing
restorations, and hardware limitations of the camera, scan-
ning equipment, and milling machines could produce errors in
the CAD/CAM technique especially during manual tracing and
fine milling of the finish line which justifies the findings of this
study.31 An additional problem with computer-milled ceramic
restorations is that the cutting tool may be larger in diameter
than some parts of the tooth preparation, such as the inner
surface of the incisal edge causing misfits, Fig. 2C, resulting in
a inferior marginal properties.32
Marginal fit, accuracy or adaptation is synonymous for a
key criterion used in the evaluation of fixed restorations and
could be defined as a parameter that measures the proximity
between the margin of the restoration and the finish line on
the prepared tooth in two directions.33,34 In this study, all
Fig. 3 (A) Horizontal section of pressable veneer ceramic demo
the finish line. Distance between blue and red lines represent v
pressable veneer demonstrating marginal fit at the cervical reg
demonstrating marginal fit at the incisal region. Observe roundspecimens were fabricated on working dies directly repro-
duced from a single master tooth which eliminated any
possible differences between the specimens. In cut sections, it
was possible to precisely measure marginal accuracy in both
horizontal and vertical dimensions. In vertical sections, higher
marginal adaptation at the incisal and cervical regions were
observed for press-on veneers. Similar finding were observed
at the mesial and distal margins in horizontal sections. These
results are directly related to the fabrication technique of
choice like previously reported by Tinschert in 200435 and
Reich et al.32 Nevertheless, marginal adaptation and cement
film thickness values reported in this study were higher
than those observed for conventional porcelain veneers
(50195 mm).36Potincy and Klim,37 presented an overview of
the CEREC Acquisition Center with Bluecam system (Sirona
Dental Systems, Charlotte, NC) and available materials. The
results showed that on the basis of the growth of CAD/CAM,
nstrating even cement film thickness and marginal gap at
ertical and horizontal marginal gap. (B) Vertical section of
ion. (C) Vertical cut section of pressable veneer
ation of the veneer in this region.
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ole
e at
j o u r n a l o f d e n t i s t r y 4 0 ( 2 0 1 2 ) 6 7 0 6 7 7 675the manufacturer has made substantial improvements to all
aspects of the CEREC AC system-including hardware, software
and materials-during the past 25 years. They concluded that
the dentists can create laboratory-grade restorations in their
offices with little disturbance to work-flow patterns. This is
possible, because of innovations to the system that make CAD/
CAM feasible for most dental practices.
In a step towards improving production accuracy of
machinable ceramics, blue light was incorporated in the
scanning device of the CEREC system which has improved
scanning potentials especially in highly curved areas claiming
an accuracy to capture 19 mm details without the need to
powder the teeth. The newly released version of the designing
software (3D 4.0) has improved features related to automatic
detection of the margins of the restorations which is also a
step towards preparing an accurate digital model. Compared
to earlier versions, these new improvements are expected to
improve final fit of the milled restorations as manufacturer
claim a scanning and cutting accuracy of (19 mm). However,
limited access at incisal edge or internal channels of implant
abutment may restrict full access of the milling tool in these
regions.38 Additionally, the type and curvature of finish line
are parameters that directly influences vertical misfit at finish
line region.39
An interesting observation for both pressable and machin-
able ceramic veneers was that the value of vertical misfit was
much higher than horizontal misfit, almost double the value,
indicating that it was more difficult to seat the veneers in
Table 1 Internal adaptation, marginal accuracy, and micr
Variable Fabrication technique
Cement film thicknessa Pressable
Machinable
Horizontal misfit Pressable
Machinable
Vertical misfit Pressable
Machinable
Incisal microleakage Pressable
Machinable
Cervical microleakage Pressable
Machinable
SD: standard deviation; F: frequency; P: significant at P > 0.5.a Cement film thickness was presented as the average value measurvertical direction. This observation could be related to the
labially applied pressure which neglected adequate vertical
seating or due to premature contact at the incisal edge of the
restoration which was commonly observed for machinable
ceramic laminate veneers, Fig. 2C. Milling of the fine details
present on the inner surface of the incisal edge presents a
challenge for CAD/CAM technique due to the limited access of
the milling tool in this narrow region.
Cement film thickness is measure of the internal fit or
adaptation of the restoration. Not only lower cement film
thickness was observed for pressable ceramic veneers in this
study but an even thickness as well, Fig. 3, which indicated
better seating compared to irregular and thicker cement film
thickness observed for machinable ceramic veneers. These
findings were in agreement with May et al.40who stated that the
cement space should be uniform to facilitate seating without
compromising retention or resistance forms. Application oftwo coats of die spacer material could facilitate easier seating of
the veneers, maintain even cement film thickness, and reduce
polymerization stresses.41 In a previous study, it was observed
that polymerization stresses resulted in strengthening the
bonded veneers due to generation of compressive forces on the
external surface, however, thermo-cycling could eliminate
such strengthening effect.42
According to CAD/CAM milling technology, restorations
with adequate marginal adaptation may not necessarily
demonstrate adequate internal adaptation.43 Reich et al.32
also reported that systems which depend on optical impres-
sion experience problems with rounded edges due to the
scanning resolution and positive error, which simulates peaks
at the edges. A thick cement film beneath the bonded veneer
could interfere with the mechanical integrity of the restora-
tion, increase polymerization pre-stresses, or influence final
shade and translucency of the restoration. Several incidences
of bulk cracks could be related to lack of rigid support under
the bonded veneers or extension of surface flaws under the
influence of thermo-cycling and dynamic fatigue.44 Under
clinical conditions, it is recommended to maintain prepara-
tion finish line in enamel in order to reduce chances of fracture
under functional loads.45
The artificial ageing programme used in this study
accelerated mechanical fatigue plus thermal and chemical
degradation of the restoration and resin cement.46,47 Increased
dye penetration was associated with inferior marginal
accuracy and thicker cement film thickness of the machinable
akage of tested veneers.
Mean (mm) SD (mm) F P
106.7380 29.5838 50.921 0.001
340.3569 143.3908
105.5820 63.2381 8.916 0.005
230.9664 176.8251
242.4017 36.9710 43.393 0.001
545.8161 195.8031
308.4561 95.3308 37.708 0.001
831.7576 368.9927
233.5116 66.5306 18.245 0.001
509.9443 281.6729
five fixed locations.ceramic veneers. While several studies questioned the
correlation between marginal adaptation and microleak-
age,48,49 the high horizontal and vertical misfits exposed more
area of the resin cement to hydrolytic effect of water under the
influence of thermo-cycling and this is might be the plausible
cause of cement degradation and increased microleakage. For
an aesthetic restoration as laminate veneers, microleakage is
considered as a direct failure requiring remake of the
restoration.33 Location of the margin,50,51 polymerization
method and type of adhesive resin,52 and type of finish line
and preparation design53 are factors that must be considered
in order to reduce microleakage under porcelain veneers.
In the present investigation, the maxillary central incisor
was selected to represent the most commonly indicated tooth
requiring a laminate veneer.21 Two fabricating techniques;
pressable and machinable ceramic, were compared as
regards to their internal adaptation, marginal accuracy,
-
j o u r n a l o f d e n t i s t r y 4 0 ( 2 0 1 2 ) 6 7 0 6 7 7676and microleakage properties. All veneers were first seated
on their corresponding prepared die using finger pressure to
achieve proper seating followed by a constant load to insure
accurate measurements of cement film thickness, A point of
concern was whether similar microleakage pattern could be
achieved if natural teeth were used in place of the resin dies.
Nevertheless, it is the restoration resin cement interface
that was of interest for this study as exploring the resin
cementtooth interface was beyond the scope of this
investigation.
5. Conclusion
Under the conditions of this investigation the following
conclusion could be drown: pressable ceramic laminate
veneers produced higher marginal adaptation, homogenous
and thinner cement film thickness, and improved resistance
to microleakage compared to machinable ceramic veneers.
Clinical implications
Pressing technique produced porcelain veneers with precise
marginal and internal adaptation which resulted in reduced
microleakage compared to CAD/CAM produced porcelain
veneers.
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Internal adaptation, marginal accuracy and microleakage of a pressable versus a machinable ceramic laminate veneersIntroductionMaterials and methodsPressing fabrication techniqueMachining fabrication techniqueCementation procedureArtificial ageing programmeSectioning techniqueInternal adaptation, marginal accuracy and microleakage
ResultsDiscussionConclusionClinical implicationsReferences
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