Q ui
by N ht
pyrig No Co t fo rP ub lica tio n te ss e n c e
Assistant Professor, Department of Prosthodontics, School of Dentistry, National and Kapodistrian University, Athens, Greece Private practice, Athens, Greece
Maria Koumanou, DDS, Ms Prosthodontist, Private practice, Athens, Greece
Spiridon-Oumvertos Koutayas, Dr med dent, DDS, CDT Adjunct Senior Lecturer, Department of Prosthodontics, School of Dentistry, Albert-Ludwigs University, Freiburg, Germany Private practice, Corfu, Greece
Spiridon Zinelis, PhD Lecturer, Department of Prosthodontics, School of Dentistry, National and Kapodistrian University, Athens, Greece
George Eliades, DDS, Msc, PhD Professor and Chairman, Department of Biomaterials, School of Dentistry, National and Kapodistrian University, Athens, Greece Private practice, Athens, Greece
Correspondence to: Dr Stavros Pelekanos Department of Prosthodontics, School of Dentistry, National and Kapodistrian University, Thivon Str. 2, 79106 Athens, Greece Tel: +30-210-9578925; Fax: +30-210-9532691; e-mail:
[email protected]
278 THE EUROPEAN JOURNAL OF ESTHETIC DENTISTRY VOLUME 4 • NUMBER 3 • AUTUMN 2009
fo r
Stavros Pelekanos, Dr med dent, DDS
n
Micro-CT Evaluation of the Marginal Fit of Different In-Ceram Alumina Copings
ot
EAED RESEARCH COMPETITION
n
Abstract
fo r
The aim of the study was to evaluate the
tions the marginal gap (MG) and the ab-
marginal fit of different In-Ceram alumina
solute marginal discrepancy (MD) were
ceramic cores manufactured by four differ-
measured in microscale (μm).
ent techniques.
ot
Q ui
by N ht
PELEKANOS ET ALopyrig No C t fo rP ub lica tio n te ss e n c e
The slip-cast and the electro-deposition
Four groups of four In-Ceram alumina
dipping techniques presented the best re-
core specimens (Vita), each 0.6 mm in
sults of MG with 22 μm and 35 μm, respec-
thickness, were fabricated from a master
tively (α < 5%). The CAD/ CAM system pre-
die using four different techniques: Group
sented an MG of 55 μm. In addition, the
SL, the slip-cast technique (In-Ceram sys-
slip-cast and the electro-deposition dip-
tem); Group CL, the copy-milling technique
ping techniques presented the best results
(Celay system); Group CR, a CAD/CAM
of MD with 50 μm and 60 μm, respectively
system (Cerec inLab system) and Group
(α < 5%).
WO, the electro-deposition dipping tech-
The slip-cast technique and the Wol-Ce-
nique (Wol-Ceram). After the core speci-
ram system presented the best marginal fit,
mens were fitted on the master die, they
followed by Cerec inLab, which presented
were scanned with the use of a microto-
clinically acceptable results. Microtomog-
mography device (1072 micro-CT, Sky-
raphy analysis seemed to be a reliable
Scan). Datasets were processed by soft-
method of evaluating the marginal fit of
ware (TView v1.1, SkyScan) and 10 vertical
dental restorations.
sections from each core were generated. On these microtomographic cross-sec-
(Eur J Esthet Dent 2009;4:278–292.)
279 THE EUROPEAN JOURNAL OF ESTHETIC DENTISTRY VOLUME 4 • NUMBER 3 • AUTUMN 2009
EAED RESEARCH COMPETITION
Q ui
by N ht
pyrig No Co t fo rP ub lica ti te and on importance, ss e n c e
ot
fo r
Despite its documented
n
Introduction
unlike physical and mechanical properThe progress in material technology and
ties of materials, the fit of a restoration has
manufacturing procedures has extended
never been strictly defined. The term “fit” is
the clinical use of all-ceramic restorations.
often used to refer to different measure-
Due to the growing awareness of esthetics
ments, or different terms are used to refer
and biocompatibility, the demand for all-
to the same measurement. Holmes et al11
ceramic restorations in all quadrants has
supported the idea that misfit is a combi-
increased. In addition to fracture resist-
nation of gap error and extension error. In
ance and esthetics, marginal fit is one of
an attempt to define those terms it was
the most important criteria of all-ceramic
suggested the fit of a casting would be best
crowns and affects both periodontal status
described in terms of the misfit measured
and longevity. Clinical trials have under-
at various points between the casting sur-
lined the importance of marginal accura-
face and the tooth. This suggestion was il-
cy for clinical success.1–4 An inadequate fit
lustrated through figures, and each dis-
is potentially damaging to both the abut-
tance
ment and the periodontal tissues, causing
different term (Fig 1).
measured
was
defined
with
a
deterioration of the luting agent in the gap
The perpendicular measurement from
and permitting the percolation of bacte-
the internal surface of the casting to the ax-
ria.5,6,7 Caries and periodontal disease are
ial wall of the preparation is called the in-
often complications.8,9 In addition, the
ternal gap (a). The same measurement at
strength of the restoration can be influ-
the margin is called the marginal gap (b).
enced by a poor marginal fit.10
Another important measurement, the absolute marginal discrepancy (g), is the angular combination of the marginal gap and extension error (over-extension or underextension), in other words, it is the combination of the vertical marginal discrepancy and horizontal marginal discrepancy.12 In the literature, a variety of methods for measuring marginal discrepancies have been suggested, each having advantages and disadvantages. Sorensen et al,13 suggested a classification of the available methods in four basic categories: direct view, cross sectional, impression technique, and explorer and visual examination (x-rays). Qualitative techniques such as explorer and visual examination14 are not accurate, and are often subjective, unavoidably introducing the bias of the investigator as they
Fig 1
Casting misfit terminology.11
280 THE EUROPEAN JOURNAL OF ESTHETIC DENTISTRY VOLUME 4 • NUMBER 3 • AUTUMN 2009
depend on experience and tactile sensitiv-
fo r
margins are subgingival.15 Concerning the
n
ity. The technique is less reliable when the
ot
Q ui
by N ht
PELEKANOS ET ALopyrig No C t fo rP ub lica tio n te procedure can also cause distortions ss e n c e which may affect the results. Additionally,
radiographic techniques, apart from not
this method only allows for the evaluation
being precise, they are not always applica-
of a limited area of the crown (not of the
ble to ceramics as most are not radio-
complete margin or the internal surface of
paque enough to show in a radiograph in-
the crown), as the sections should have a
detail.16
minimum thickness.
A popular technique to evaluate marginal misfit is the impression technique, using low viscosity impression materials.17–20 This is a non-invasive technique that presents
Computerized x-ray microtomography
some difficulties in cases of crowns with very good internal and marginal fit, as there
In computerized x-ray microtomography
is the possibility of distortion or damage of
(micro-XCT), multiple projections of an ob-
the material that can affect the results.21–22
ject are taken as the source is rotating
Another non-destructive quantification
around it. These multiple projections are
of crown margins is suggested in the use
received by an x-ray charge-coupled de-
23
of profilometry.
A profilometer is a device
vice (ccd) camera and transferred to a
used to evaluate the roughness of the sur-
computer. The projections are reconstruct-
face. It is an accurate method, but consid-
ed with special software to produce sever-
ering that it cannot give images in cases of
al small slices of the object’s internal struc-
vertical over-extension, the results are sub-
ture, which can be added to the object’s
jected to false interpretation.
3-D image. Micro-XCT and computerized 24–28
or
x-ray tomography share the same basic
and measurement
principles. An x-ray tomographic system
of the misfit of the restoration using mi-
allows the visualization and measurement
crophotography is a commonly applied
of complete 3-D object structures without
technique. Its main advantage is that it is
sample preparation or chemical fixation.
non-destructive for the restoration and very
Typically, the spatial resolution of conven-
accurate. On the other hand, if a slight de-
tional medical computed tomography (CT)
viation occurs in the angle the photographs
scanners is in the range of 1.25 to 2 mm,
are taken, this greatly influences the meas-
which corresponds to 1 to 10 cubic voxel
urements, and in several cases it is not
size. Computerized x-ray microscopy and
clear if the measurement refers to the mar-
microtomography provide the possibility to
gin or to the vertical projection of one to the
improve the spatial resolution by seven to
other.
eight orders in terms of volume, reaching a
The use of an optical microscope a stereomicroscope
29,30
The sectioning of the specimens and 12,31,32
their study under an optical
or scan-
spatial resolution of 5 μm corresponding near to a 1x10-7 cubic mm voxel size.37
ning electron microscope33–36 is not affect-
Micro-XCT, has wide-ranging applicabil-
ed by the angle from which the photograph
ity in dental research. In endodontics it is
is taken, but is a destructive technique as
used for the evaluation of root canal sys-
the restoration with the abutment has to be
tems,38 and preparation39 and sealing pro-
embedded, sectioned, and polished. The
cedures.40 In periodontology, it has been
281 THE EUROPEAN JOURNAL OF ESTHETIC DENTISTRY VOLUME 4 • NUMBER 3 • AUTUMN 2009
EAED RESEARCH COMPETITION
Q ui
by N ht
pyrig No Co t fo rP ub lica tio n te Fabrication of the master die ss e n c e
42,43
fo r
several guided bone regeneration proce-
ot
mandibular bone microstructure41 and for
n
used for the study of the maxillary and
A lateral incisor (12) made from a hard thermosetting acrylic material (standard
as well as for assessment of im-
tooth for AG-3 model, Frasaco, Tettnang,
plant osseointegration.44 It is also used for
Germany) was circumferentially prepared
the qualitative assessment of biomaterials
with 6 degrees of convergence, 6.0 mm in
in restorative dentistry.45
height, 2.0 mm incisal reduction and a
dures
1.2 mm 360 degree chamfer with rounded inner angles using appropriate diamonds
Purpose
(Brasseler, Lemgo, Germany) in order to receive an all-ceramic crown (Fig 2). The
The aim of the study was to evaluate the
prepared acrylic incisor die was copied in-
marginal fit of different In-Ceram® alumina
to a glass-infiltrated alumina one (master
ceramic cores (Vita, Bad Säckingen, Ger-
die) using a special pre-sintered Al2O3
many) with techniques developed by four
cube (Celay® alumina blanks, AC-12, Vita)
different manufacturers using innovative
and a copy-milling system (Celay system,
and non-destructive methods such as mi-
Mikrona). After milling the cube a hole was
cro-XCT analysis.
manually inserted in the center of the die base to facilitate a uniformly distributed glass infiltration. The specific master die
Materials and methods
served for both the fabrication of all the
Study outline
ings into the microtomography device
Sixteen aluminum oxide (Al2O3) speci-
(Fig 3).
Al2O3 copings and for scanning the cop-
mens (copings), 0.6 mm in width, were fab-
A custom acrylic base that can be both
ricated using a master die and four differ-
easily fixed into the special socket of the
ent techniques: Group SL, the slip-cast
microtomography device (1072 Micro CT,
technique (In-Ceram system, Vita); Group
SkyScan) and accommodate the master
CL, the copy-milling technique (Celay sys-
die was fabricated to facilitate the scanning
tem, Mikrona, Spreitenbach, Switzerland);
process.
Group CR, a CAD/ CAM system (Cerec inLab®, Sirona Dental Systems, Bensheim,
Fabrication of the copings
Germany); and Group WO, the electro-
Sixteen high accuracy impressions of the
®
deposition dipping technique (Wol-Ceram
master die were made, with a polyether im-
system,
Ger-
pression material (ImpregumTM Penta, 3M
many). All specimens, were scanned with
ESPE, Seefeld, Germany) using a mixing
a microtomography device (1072 micro-
device (PentamixTM 2, 3M ESPE) and spe-
CT, SkyScan, Kontich, Belgium) and both
cial impression rings (Fig 3). After the set-
marginal gap (MG) and absolute marginal
ting time (6 minutes) of the impression ma-
discrepancy (MD) were evaluated using
terial, 16 working dies were cast with class
microtomographic cross-sections generat-
IV dental stone (Esthetic-base® gold, Den-
ed after the processing of datasets by soft-
tona AG, Dortmund, Germany) according
ware (TView v1.1, SkyScan).
to manufacturer’s instructions.
Wol-Dent,
Ludwigshafen,
282 THE EUROPEAN JOURNAL OF ESTHETIC DENTISTRY VOLUME 4 • NUMBER 3 • AUTUMN 2009
n
fo r
Fig 2
The master die after glass infiltration is com-
Fig 3
Circle with 10 diameters positioned onto a 2-D
pleted.
sagittal image.
Specifically, these dies were used for the
0.6 mm coping. The alumina coping fol-
fabrication of 16 Al2O3 copings which were
lowed a sintering firing at 1,120°C (Incera-
randomly divided into four groups of four
mat, Vita) and then a glass infiltration firing
dies each according the fabrication tech-
under vacuum at 1,100°C (Vacumat®, Vita).
nique: i) Group SL, ii) Group CL, iii) Group
Excess glass was removed using a coarse-
CR, and iv) Group WO.
grit diamond and an airborne particle abra-
Apart from the last millimeter above the preparation finishing line, dies of Groups
ot
Q ui
by N ht
PELEKANOS ET ALopyrig No C t fo rP ub lica tio n te ss e n c e
sion apparatus with Al2O3 (50 μm) at 3-bar compressed air.
SL and CL were coated with two layers of
For the copy-milling technique (Group
spacer varnish (Yeti, Yeti Dental, Engen,
CL), after a resin analogue of each coping
Germany). In Group CR appropriate space
was modeled with a light-polymerized
was maintained digitally and dies of Group
resin (Celay Tech, 3M ESPE), copings were
WO received a special wax spacer (Wol-
fabricated using prefabricated porously
Ceram spacer wax, Wol-Dent).
sintered Al2O3 blocks (Vita Celay alumina
For the slip-cast technique (Group SL), a
blanks, A-12, Vita) and the Celay copy-
special Al2O3 slip (In-Ceram alumina pow-
milling machine (Mikrona). Glass-infiltra-
der, Vita) was mixed to a homogeneous
tion and excess glass removal were per-
consistency (Vitasonic, Vita) and then ap-
formed as above.
plied to the working die to build-up a
283 THE EUROPEAN JOURNAL OF ESTHETIC DENTISTRY VOLUME 4 • NUMBER 3 • AUTUMN 2009
EAED RESEARCH COMPETITION
Q ui
by N ht
pyrig No Co t fo rP ub lica tio n te na coping and master die) of the object of ss e n c e
ot
fo r
na copings (Group CR) using the inLab
n
For the fabrication of the CAD/CAM alumi-
interest from 2-D x-ray shadow projec-
system (Sirona Dental Systems), working
tions. It consists of a combination of an x-
dies were prepared for scanning (or opti-
ray shadow microscopic system, a tomo-
cal) impression by the application first of a
graphic reconstruction package, software,
special covering layer (Cerec liquid, Vita)
and computer.
and then of an opaque powder (Cerec
The custom acrylic base with the master
powder, Vita) which conform a sharply
was positioned precisely within the x-ray
contrasting image for an optimal digitaliza-
beam into a special socket and all 16
tion of the die surface. Each die was insert-
Al2O3 copings were successively placed
ed into the inLab system (Sirona Dental
onto the master die for scanning. After a
Systems) and was automatically scanned
micro-focused x-ray source (100kV / 98Ua)
with the laser scanner. After designing the
illuminated the alumina coping and mas-
coping with the provided software (Cerec
ter die, the x-ray shadow images were ac-
3D V3.00, Sirona Dental Systems), copings
quired by a sensitive x-ray camera. During
were milled out from prefabricated porous-
image acquisition, each specimen was ro-
ly sintered Al2O3 blocks (In-Ceram alumi-
tated one step (0.9 degrees) at a time
na for inLab, CA-12, Vita). Copings were in-
through 180 degrees and images were
filtrated in a furnace (Vacumat, Vita) at
recorded at each rotation, and 960 2-D
1,140°C and excess glass was removed as
sagittal
described above.
1024x1024, pixel size and slice width were
images
(or
slices)
(resolution
dipping
both 8.85 μm), based on x-ray density,
technique (Group WO), copings were
were reconstructed from the x-ray shadow
fabricated after immersion of the working
images.
For
the
electro-deposition
die and a direct apposition of an Al2O3
For the evaluation of the marginal fit
ceramic material (In-Ceram alumina, Vi-
mean values of the MG and the MD were
ta) using the Wol-Ceram system (Wol-
determined according the criteria stated
Dent). The Electro-Layered Ceramic (ELC)
by Holmes et al.11 Measurements of both
process of this specific system is based on
MG and MD were made after computed
the difference in polarity between the die
reconstruction (TView v1.1, SkyScan)46 of
and the ceramic material and leads to an
10 vertical cuts (jpeg files) to the axial wall
extremely dense and uniform coping. The
of the prepared die. For this reason, a cir-
copings were sintered at 1,140°C, (Incera-
cle with 10 different diameters (each step
mat,
1,120°C
18 degrees) was centered at the centre of
(Vacumat, Vita) and excess glass was re-
the same image position of every scanned
moved as described above.
specimen (Fig 3). One diameter was di-
Vita),
glass-infiltrated
at
rected from the middle of the buccal and
Tests and statistics
the lingual surface while another perpen-
A compact desktop system for non-de-
dicular to the latter was directed from the
structive high-resolution x-ray microscopy
middle of the mesial and the distal surface.
and microtomography (1072 micro-CT,
Therefore, in every vertical reconstruction
SkyScan) was used to obtain a 3-D recon-
of each specimen, ten measurements re-
struction of the inner microstucture (alumi-
garding MG and another 10 regarding MD
284 THE EUROPEAN JOURNAL OF ESTHETIC DENTISTRY VOLUME 4 • NUMBER 3 • AUTUMN 2009
n
(a) Vertical cut of a coping on
fo r
Fig 4
the master die (left down: designated area shown is in Figure 4b). (b) DM: die
ot
Q ui
by N ht
PELEKANOS ET ALopyrig No C t fo rP ub lica tio n te ss e n c e alumina coping
margin (contact point of the tangential lines between prepared and unpre-
MG
pared surface of the die near to the marDM
gin); CM: coping margin (contact point of the tangential lines between the inner and outer surface of the coping near to MD
the margin); MD: absolute marginal discrepancy (the distance between the DM
master die
CM
and the CM); MG: marginal gap (the distance of the vertical projection of DM to the inner surface of a hyperextended
b
a
coping or the distance of the vertical projection of CM to the prepared surface of a hypoextended coping).
were obtained. All values, either for over-
values of 21 μm and 35 μm respectively
extended
margins
(95 μm and 158 μm being the highest
were gathered as positive values. Mea-
or
under-extended
measurements for each system). For Celay
surements were performed under certain
and Cerec inLab systems the respective
magnification using digital image editing
values were 139 μm and 55 μm. Overall
software (Photoshop CS2, Adobe Systems
the results were statistically significant (H
Incorporated, San Jose, CA, USA) and with
(3, N = 320) = 122,2314 P = 0.000). Indi-
a reduction ratio of the given size of the pix-
vidual Mann–Whitney tests revealed that
el (8.85 μm) (Fig 4).
CL differed significantly from WL, and also
Statistical analysis of the data was per-
from CR and CL. All MG values were sta-
formed regarding the fabrication tech-
tistically different from each other for the
nique (or system), the margin location
four methods. The MG results are pre-
(buccal/lingual, mesial/distal) and the
sentedin detail in Table 1.
over- or under-extension of the copings.
WO had the lowest MD value (50 μm)
Kruskal–Wallis analysis of variance by
followed by SL (60 μm) whereas CR had
ranks was used to assess overall statisti-
the highest, followed by CL (188 μm and
cal significance and consequently the
179 μm respectively). Overall the results
Mann–Whitney U test was used to evalu-
were statistically significant (H (3, N = 320)
ate statistical significance comparisons
=
between the four methods.
Mann–Whitney tests revealed that WO did
73,5043
P
=
0.000).
Individual
not differ significantly from SL, but did differ significantly from CR and CL. The same
Results
result was observed for SL, whereas CR did not differ significantly from CL. The MD
The slip-cast technique and the Wol-Cer-
results are presented in detail in Table 2.
am system were the techniques that pre-
Mean MG values buccolingually were
sented the best results of MG with mean
68 μm and mesiodistally 57 μm, whereas
285 THE EUROPEAN JOURNAL OF ESTHETIC DENTISTRY VOLUME 4 • NUMBER 3 • AUTUMN 2009
EAED RESEARCH COMPETITION
Q ui
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pyrig No Co t fo rP ub lica tio n t e Minimum, maximum, and mean values of the marginal gap (MG) s se nc e
fo r
Measurements/ method
Marginal gap
Table 2
ot
n
Table 1
Distance in μm N
Mean
SD
SE
-95%
+95%
Wol-Ceram
79
34.86
33.49
3.77
27.36
42.36
Slip cast
80
21.04
25.08
2.80
15.46
26.62
Cerec inLab
80
55.09
49.06
5.49
44.17
66.01
Celay
81
139.27
85.46
9.50
120.38
158.17
Minimum, maximum, and mean values of the marginal discrepancy (MD)
Measurements/ method
Distance in μm N
Mean
SD
SE
-95%
+95%
80
49.86
36.97
4.13
41.64
58.09
Slip cast
80
60.09
39.47
4.41
51.30
68.87
Cerec inLab
80
187.64
82.49
9.22
169.28
205.99
Celay
80
179.36
86.78
9.70
160.05
198.67
Marginal Wol-Ceram discrepancy
mean MD values buccolingually were
Discussion
125 μm and mesiodistally 121 μm. Furthermore the buccal-lingual measurements
In this study, scanning with micro-XCT was
did
the
used to compare the marginal fit of In-Ce-
mesiodistal measurements regarding the
not
differ
significantly
from
ram alumina ceramic cores. The applica-
MG or the MD values (Figs 5 and 6).
tion of this technique for this study is inno-
Cores manufactured by the slip-cast
vative. The main advantages are that it is a
technique presented only under-extension
non-destructive method that provides im-
of the margin in 68.75% of measure-
ages of the internal structure of the speci-
68,75
ments.
Celay cores presented under-
men, in section form, and at the same time
extension in 23.75% and over-extension in
it is the only method that allows for a 3-D
17.5% of measurements taken. Cerec in-
reconstruction in each selected position.
Lab cores presented only over-extension
Furthermore, even very proximate sections
(87.5%), whereas the Wol-Ceram cores
are possible. As a result, micro-XCT pro-
presented over-extension in 12.5 % and
vides the ability to measure different dis-
under-extension in 13.75 % of measure-
tances in marginal area.
ments taken (Fig 7).
286 THE EUROPEAN JOURNAL OF ESTHETIC DENTISTRY VOLUME 4 • NUMBER 3 • AUTUMN 2009
n
fo r
200
ot
Q ui
by N ht
PELEKANOS ET ALopyrig No C t fo rP ub lica tio n te ss e n c e
150 100 50 Fig 5
Regarding the mar-
ginal gap (MG), buccolin-
0
gual measurements did not
mesiodistal
buccolingual
mesiodistal
buccolingual
differ significantly from the mesiodistal measurements.
200 150 100 50 Fig 6
Regarding the mar-
ginal discrepancy (MD), buc-
0
colingual measurements did not differ significantly from the mesiodistal measurements.
12.50%
17.50% 31.25%
87.50% 73.75%
58.75%
68.75%
Fig 7 per-
Percentages of hyand
hypo-extended
23.75 13.75%
12.50%
copings between the different fabrication techniques (or systems).
287 THE EUROPEAN JOURNAL OF ESTHETIC DENTISTRY VOLUME 4 • NUMBER 3 • AUTUMN 2009
EAED RESEARCH COMPETITION
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pyrig No Co t fo rP ub lica tio n te intraorally prepared ss e n c e
ot
n
The disadvantage of the technique is the
both laboratory and
low capacity of discrimination of CT micro-
abutments.
tomography when compared with an opti-
crowns that are manufactured in the lab on
cal or electron microscope (1.8 μm for mi-
prefabricated abutments, 18 measure-
crotomography and 0.3 μm and 0.25 nm
ments in spots that are equidistant (the ini-
for optical and electron microscope re-
tial reference point does not affect the re-
spectively).37,47 In addition, considering that
sult), are enough so the result does not
the images result from radiation, there may
vary numerically more than ± 5 μm. The
be artifacts from refraction. The more ma-
number rises to 50 for crowns that are
terials with different coefficients of absorp-
manufactured from impressions made in-
tion that exist, the more difficult it is to clear-
traorally. According to these findings, in
ly define the lines between those materials
the present study, 20 measurements in
using x-rays. Of course it is not possible to
equidistant spots were performed for each
discriminate between the line of two differ-
specimen.
concluded
fo r
They
that
for
ent materials with the same coefficients of
To evaluate the marginal fit, MG and MD
absorption when they are in contact. This
were measured. MG refers to the surface of
has to be considered when planning to
the cement that is left exposed intraorally
use microtomography in a study.
and can be dissolved, leading to second-
For this study, alumina was the material
ary carries and pulp implications due to mi-
of choice for the initial abutment, because
croleakage. MD is indicative of proper ex-
of its wear-resistance, radiopacity, and be-
tension of the crown margins compared
cause it is the same material used for the
with the margins of the abutment, and is of
manufacture of the cores. In this, the mar-
great importance mainly in overextension
gins of the abutment and the core, as well
cases as it enhances plaque accumulation
as the space in between, are easier to dis-
and compromises health.11
criminate with the use of CT microtomography.
In the present study the slip-cast technique and the Wol-Ceram system were the
There is no agreement in the literature
methods that presented the best results in
concerning the number of measurements
MG with 22 μm and 35 μm respectively.
that are necessary to evaluate the margin-
The Cerec inLab technique presented an
al fit of prostheses. Groten et al48 suggest-
MG of 55 μm whereas the Celay technique
ed taking 50 measurements of marginal fit,
presented a 140 μm MG. All MG values
to limit the numerical variance between
were statistically different from each other
± 5 μm, whereas with fewer measure-
for the four methods. In the literature, mean
ments there was a greater variance and
values that vary between 78 μm30 and
the result was not credible. However, in
83 μm25 for non-cemented In-Ceram alu-
Groten’s study, there was not a standard-
mina crowns were reported when fabricat-
ized method of taking photographs for the
ed with the Celay technique. The difference
microscope evaluation, and this factor in-
in results in the authors’ study may be due
27
troduced an error. Gassino et al standard-
to improper usage of the technique or even
ized the angulation that the photographs
problems relating to the Celay device.
were taken. In addition they evaluated the
The slip-cast technique is not machine
number of measurements necessary for
dependent and MG values are indicative
288 THE EUROPEAN JOURNAL OF ESTHETIC DENTISTRY VOLUME 4 • NUMBER 3 • AUTUMN 2009
n
of the technician’s ability, whereas for
Since the
Cerec inLab and the Wol-Ceram system,
turing have developed, and supposing that
MG is indicative of the ability of the system.
the clinical procedures for preparation and
In order to evaluate the present results
impression are ideally performed, the fit
fo r
it is critical to define the clinically accept-
depends on the thickness of the cement.
able MG. There is much controversy in the
The selection of the cement greatly in-
literature concerning this matter. While
fluences the final fit of the restoration. Many
studies by McLean and von Fraunhofer49
studies support that the cementation of a
and McLean50 support the idea that 120 μm
crown increases the MG.29,30 Beschnidt
MG is clinically acceptable, a recent litera-
and Strub,30 comparing the marginal fit be-
ture review supports a maximum gap of
fore and after cementation using resin ce-
21
100 μm.
ot
Q ui
by N ht
PELEKANOS ET ALopyrig No C t fo rP ub lica tio n te techniques for crown manufacss e n c e
ments, concluded that the greater increase
All-ceramic restorations with alumina
in MG was presented in slip-cast manufac-
cores can be cemented with both conven-
tured crowns and the lowest in Celay tech-
tional and resin cements.51 The advantage
nique manufactured crowns. Their re-
of resin cements is less dissolution and in-
search suggests that this is the result of
creased resistance to microleakage.36,52 On
easier escape of excessive cement in
the other hand, they present polymeriza-
crowns with greater internal gap (Celay).
tion shrinkage,53 which can be partly bal-
The Wol-Ceram system and the slip-cast
anced by displacement of the material to-
technique were the techniques that pre-
wards the inner surface of the crown, due
sented the best results of MD with 50 μm
to its low viscosity. Therefore, the weak link
and 60 μm respectively. The slip-cast tech-
in margin is the area with high MG values.
nique presented 68.75% under-extension,
The SL group presented no measurement
whereas Wol Ceram presented 13.75%
higher than 100 μm, the CR group pre-
under- and 12.5% over-extension. This re-
sented 12 measurements higher than
sult may be because the determination of
100 μm (223 μm being the highest), and
the finishing line in the slip-cast technique
WO presented 3 measurements higher
is made before the sintering of alumina,
than 100 μm (158 μm being the highest).
using a scalpel on the duplicated master
The Cerec inLab system presented 15% of
die made by Vita In-Ceram special plaster.
the measurements higher than 100 μm
Using the Wol-Ceram system the same
with the highest value being much higher
procedure is performed on the master die
than what is clinically acceptable.
using elastic rotary instruments. Therefore,
It is also of great importance to study the
one possible explanation could be that the
distribution of MG values. For values low-
duplication material (Vita In-Ceram special
er than 10 μm, the SL and WO groups pre-
plaster) is not as reinforced as the type IV
sented 45% (36 values) and 28% (22 val-
plaster.
ues) respectively, and between 11 to
In an attempt to compare the results of
40 μm, 33% (26 values) and 39% (31 val-
this study with others reported in the liter-
ues) of measurements respectively. The
ature, there were no available studies re-
corresponding values for the CR group
ferring to the Wol-Ceram system and
are 25% (20 values) lower than 10 μm and
Cerec inLab using In-Ceram alumina ma-
18% (14 values) between 11 and 40 μm.
terial. Regarding the slip-cast technique
289 THE EUROPEAN JOURNAL OF ESTHETIC DENTISTRY VOLUME 4 • NUMBER 3 • AUTUMN 2009
EAED RESEARCH COMPETITION
Q ui
by N ht
pyrig No Co t fo rP ub lica tio n required to t eassess ss e n c e
with
great
variance,
fo r
results
ot
Further research is
n
there are several studies54,25,29,30 presenting between
more factors that can influence the mar-
9.31 ± 3.7 μm29 and 112 ± 55 μm25 for non-
ginal fit, such as cementation, layering of
cemented crowns. In those studies the
the veneering material, and/or functional
misfit was evaluated using an optical mi-
loading and thermocycling.
croscope or stereo-microscope and the external margin was measured, with all the disadvantages of the method. So al-
Conclusions
though the MD is defined as a reference measurement, it is not clear whether it is
Within the limitations of the present in vitro
the actual distance measured because it
study the following conclusions can be
is influenced by different angulations of
drawn.
observation.30,54 In conclusion, it is not pos-
I
The different manufacturing techniques
sible to directly compare the results, espe-
of the same all-ceramic material affect-
cially as the slip-cast technique mainly de-
ed the marginal fit of the restoration.
pends on the skills of the technician, a
I
The slip-cast technique and the Wol-
great variance of the results could be ex-
Ceram system presented the best MG
pected.
and MD results followed by the Cerec inLab and Celay systems.
In the literature there are two studies of all-ceramic In-Ceram zirconia crowns man-
I
There was no difference between the
ufactured by the Cerec inLab system. The
marginal measurements in any system
techniques used are different and the mean
or technique used in the present study
values of the crowns vary from 43 μm35 to
regarding the location of the margin
17
77 μm,
(buccal/lingual, mesial/distal).
whereas in the present study the
mean MG is 55 μm. The first study35 meas-
I
The Wol-Ceram system presented the
ured the marginal fit of 12 cemented cores,
highest percentage of accuracy regard-
(in vitro study), taking 8 measurements of
ing the over- and/or under-extended
each. An electron microscope is used, but the parameter measured is not clearly de-
margin. I
17
Micro-XCT may be a reliable method for
fined. The second study measured the MD
further evaluation of the marginal and in-
of 8 fixed dental prostheses, supported by
ternal fit.
16 natural abutments using an impression technique and 4 to 6 measurements at nonequidistant points and an optical micro-
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