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Prosthodontist, Private practice, Athens, Greece ... suggested the fit of a casting would be best described in terms .... IV dental stone (Esthetic-base® gold, Den-.

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

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EAED RESEARCH COMPETITION

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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.

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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

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pyrig No Co t fo rP ub lica ti te and on importance, ss e n c e

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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-

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margins are subgingival.15 Concerning the

n

ity. The technique is less reliable when the

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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

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pyrig No Co t fo rP ub lica tio n te Fabrication of the master die ss e n c e

42,43

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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

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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

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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

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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

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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

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(a) Vertical cut of a coping on

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Fig 4

the master die (left down: designated area shown is in Figure 4b). (b) DM: die

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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

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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

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200

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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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