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d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 545–552
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RD2 micro-diffraction analysis of the interface between-TZP and
veneering porcelain: Role of application methods
ichael J. Tholeya, Christoph Bertholdb, Michael V. Swainc,∗,
Norbert Thiela
Research and Development Department VITA Zahnfabrik, Bad
Saeckingen, GermanyDepartment of Geo Sciences, University of
Tuebingen, GermanyDepartment of Oral Sciences, School of Dentistry,
PO Box 647, Dunedin, New Zealand
r t i c l e i n f o
rticle history:
eceived 3 June 2009
eceived in revised form
7 November 2009
ccepted 1 February 2010
eywords:
irconia
-TZP
nterface
ll-ceramic
a b s t r a c t
Objectives. The metastability of the tetragonal crystal
structure of yttria partial stabilized
zirconia polycrystalline (Y-TZP) ceramics is a basis of concern
for dental restorations. Reac-
tions between the porcelain and the Y-TZP framework may result
in a reduction of the
stability of the zirconia and interface bonding caused by a
transformation from tetragonal
to monoclinic crystalline structure during veneering.
Methods. XRD2 micro-diffraction measurements were carried out on
tapered veneered cross-
sections of the interface area to generate locally resolved
information of the phase content
in this region. To get a high intensity X-ray beam for short
measurement times a focussing
polycapillary with a spot size of app. 50 �m was used to
evaluate the porcelain zirconia
interface.
Results. Under almost all conditions the phase composition of
zirconia grains at the interface
revealed both the monoclinic and tetragonal structure. These
observations indicate that
-ray diffraction
eneering material
destabilization of the tetragonal phase of zirconia occurs at
the interface during veneering
with porcelain.
Significance. These results and their relevance to the long-term
stability of the interface adhe-
sion between zirconia and veneering porcelain as well as the
tetragonal to monoclinic crystal
transformations at the interface are discussed.
emy
© 2010 Acad
. Introduction
irconia holds an exclusive place amongst dental restora-ive
materials compared with other oxide ceramics, such
s alumina, because of its excellent mechanical propertiess a
consequence of transformation toughening that wasdentified in the
mid-1970s [1]. Pure zirconia can exist inhree different crystal
structures depending on tempera-
∗ Corresponding author. Tel.: +64 3 479 4196; fax: +64 3 479
7078.E-mail address: [email protected] (M.V.
Swain).URL: http://www.otago.ac.nz (M.V. Swain).
109-5641/$ – see front matter © 2010 Academy of Dental
Materials. Puoi:10.1016/j.dental.2010.02.002
of Dental Materials. Published by Elsevier Ltd. All rights
reserved.
ture. At room temperature up to 1170 ◦C, the symmetry
ismonoclinic, the structure is tetragonal between 1170 and2370 ◦C
and cubic above 2370 ◦C up to the melting point[2]. The
transformation from tetragonal (t) to monoclinic(m) during a
cooling process is accompanied by a volume
increase (approximately 4%) and shear distortion, sufficientto
cause catastrophic failure. Alloying pure zirconia withstabilizing
oxides such as Y2O3 allows the preservationof the meta-stable
tetragonal structure at room tempera-
blished by Elsevier Ltd. All rights reserved.
mailto:[email protected]/10.1016/j.dental.2010.02.002
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546 d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 545–552
Table 1 – Preparation methods of the Y-TZP frameworks.
No. Liquid medium Porcelain Firing process
VVV
1. VITA VM liquid2. VITA VM liquid3. No
ture and therefore the potential to enable stress-inducedt → m
transformation, which can enhance resistance to crackextension
leading to higher toughness compared to alumina[1,3,4].
As a consequence of the metastability of tetragonal zir-conia,
stress-generating surface treatments, such as grindingor
sandblasting, are able to trigger the t → m transformationwith the
associated volume increase leading to the forma-tion of surface
compressive stresses, thereby increasing theflexural strength.
However such metastability of the materialalso increases the
susceptibility to aging [5]. The low tem-perature degradation (LTD)
of zirconia is a well-documentedphenomenon, dependent upon the
presence of moisture andmodest heat [6–11]. The consequences of
this aging pro-cess are multiple and include surface degradation
with grainpullout and micro-cracking as well as strength
degradation.Although LTD has been shown to be associated with a
seriesof orthopedic hip prostheses failures in 2001 and despite
awell established definition of the conditions under which
LTDoccurs, there is currently no clear relationship between LTDand
failure predictability when zirconia is used as a dentalbio-ceramic
[12].
3Y-TZP is now widely used in dentistry for the fabrica-tion of
dental restorations, mostly processed by machining ofpartially
sintered blanks followed by sintering at high temper-ature. The
mechanical properties of 3Y-TZP strongly dependon its grain size
[13–15]. Above a critical size, Y-TZP is less sta-ble and more
vulnerable to spontaneous t → m transformationthan smaller grain
sizes (
-
d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 545–552 547
F hema al sc
cpdmdlmspt[
wabwTilssispttal
rttptconfd
mvsits
completely tetragonal and had no observable monoclinic peak.The
GADDS frame in Fig. 2 shows only the tetragonal crystal
structure on the surface of the Y-TZP sample. In all
samplesreflections no monoclinic Baddeleyite structure of Zr02
was
Fig. 2 – Typical GADDS frame of the diffraction pattern
ig. 1 – Measurement points on the samples, on the left a sccross
the interface while on the right hand side the elliptic
ollimators to generate a small analysis spot on the sam-le
surfaces. The use of such pinhole collimators howeverecreases the
intensity of the X-ray beam on the sample dra-atically, which
results in long measurement times. In the last
ecade pinhole collimators have been replaced by monocapil-ary
optics and in the last few years by focussing polycapillary
icro-lenses in order to focus the generated X-ray beam on
theample. This has increased the localized intensity on the sam-le
by orders of magnitude depending on the X-ray source andype of
optics in comparison to a standard pinhole collimator19].
The X-ray micro-diffractometer (�-XRD2) used in this studyas a
modification of typical powder diffractometer withfocussing
micro-lens to achieve a micrometer-sized X-ray
eam and a 2-dimensional detector system (BRUKER-HiStar),hich
covers app. 30◦ in 2� and app. 30◦ � at the same time [19].he
advantage of such a focussing polycapillary micro-lens
nstead of the common pinhole collimator or a monocapil-ary is
the short measurement time required, down to a feweconds, due to
the high brilliance of the X-ray beam on theample combined with a
spot size currently down to approx-mately 50 �m diameter FWHM. A
general disadvantage ofmall spot sizes in powder diffraction setups
is the potentiallyoor crystallite statistics in the analyzed volume
depending onhe crystallite size. In addition and to avoid this
disadvantagehe additional 2-dimensional HiStar-detector provides
directssessment of texture effects and crystallite size in the
ana-yzed sample.
Before commencing the �-XRD2-analysis of the interfaceegion
various sample preparation methods of the taper sec-ions were
examined by locally scanning the surface withhe
micro-diffractometer. This indicated that the cutting andolishing
preparation [18] did not generate significant t → mransformation of
the zirconia grains on the surface. Mono-linic peaks and broadening
of the tetragonal/cubic peak werenly observed on the ground surface
of the prepared area andot on the polished area in the vicinity of
the veneered inter-
ace with the relatively low spatial resolution of the
X-rayiffraction system used in the former study [18].
All three preparation procedures were scanned with
theicro-diffractometer in the manner shown in Fig. 1. The
eneered part and the polished zirconia surfaces were mea-
ured at 8 different positions in steps of 50 �m across
thenterface with a measurement time of 120 s per pattern usinghe 50
�m micro-lens and Co K� (radiation with 30 kV/30 mAetting) with a
fixed incident angle of 10◦ to the flat interface.
atic illustration vertically through the tapered sampleanned
surface locations are shown.
Due to this incident angle the measurement spot has an
ellip-tical geometry with a length of app. 400 �m and a width of
app.50 �m. Three of the scanning positions are shown as an exam-ple
for the working area in Fig. 1 where the middle positionfocuses on
the location directly at the interface between Y-TZPand porcelain
and the others on the adjacent positions. Theschematic on the left
hand side vertically through the taperedinterface sample shows
positions of the spots indicated bythe elliptical areas on the
right hand side. No etching processsuch as HF content gel was used
to ensure that other potentialinfluences on the framework material
were minimized.
3. Results
The zirconia surfaces were scanned, as described above,before
the veneering process to ensure that the zirconia was
observed for untreated Y-TZP with a solid angle ofincidence of
10◦. The major peak is associated with the 1 0 0tetragonal/cubic
peaks while the less intense peaks to theright are of the 2 2 0
series of tetragonal and cubic peaks.
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548 d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 545–552
Fig. 3 – X-ray scans across the interface area of the
Wash-Dentin (method 1) prepared sample measured using a 50
�mmicro-lens, Co K�, 30 kV/30 mA, fixed incident angle 10◦, 120
s/frame.
Fig. 4 – X-ray scans across the interface area of the thin layer
of porcelain coated zirconia (preparation procedure 1)measured
using a 50 �m micro-lens, Co-K�, 30 kV/30 mA, fixed incident angle
10◦, 120 s/frame. An arrow at position 2correlates the intense
single crystal reflection with the corresponding monoclinic (−1 1
1)-reflection in the XRD-pattern.
-
d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 545–552 549
Fig. 5 – (a) Area a in the veneered part of preparationmethod
no. 1; 500 �m monocapillary optic with 300 �mpinhole Co K�, 30
kV/30 mA, fixed incident angle 10◦,600 s/frame. (b) Diffraction
pattern from Spot a showing thetetragonal diffraction rings and
isolated spots caused bys
dwp
s1p1bzwiz
sna
t
Fig. 6 – (a) Area b in the veneered part of preparationmethod
no. 2; 500 �m monocapillary optic with 300 �mpinhole Co K�, 30
kV/30 mA, fixed incident angle 10◦,600 s/frame. (b) Diffraction
pattern from Spot b againhighlighting the presence of intense
monoclinic single
ingle crystal (1 1 1)-reflections of the monoclinic
structure.
etectable. After the phase composition of the Y-TZP surfacesas
established they were veneered using the different sam-le
preparation methods listed in Table 1.
The result of the �-XRD2-measurements from one typicalample
prepared with a Wash-Dentin (preparation method no.) coating and
prepared as schematically shown in Fig. 1 areresented in Fig. 3.
The black arrow on the left side at positionidentifies the location
of the interface of the taper section
etween the veneered zirconia grain surface and the
polishedirconia. Scans of intensity versus 2� at 8 measurement
pointsere performed, starting in the veneered surface, proceed-
ng across the interface region and ending in the
substrateirconia.
Both measurements at position 1 (green coloured patterns)how
only low intensities of both, monoclinic and tetrago-
al/cubic Zirconia due to the overlying veneering glass,
whichbsorbs the X-ray beam.
At the locations 2 and 3 (red patterns) the intensities fromhe
zirconia surface beneath the porcelain layer were sig-
crystal (1 1 1)-reflections of the monoclinic structure.
nificantly increasing, due to the decreasing thickness of
theoverlying veneering. It should be pointed out that the
observedmonoclinic (−1 1 1)-reflection which appears at app. 33◦
2�seems to be significantly more intense than for the other
loca-tions. Also in both green patterns (positions 1 and 2) there
isa significantly intense monoclinic reflection at this
position.
At positions 4–7 (black patterns) no porcelain is coveringthe
zirconia substrate due to the geometry of the sample,therefore the
information comes from the ground and pol-ished zirconia at areas
below the interface. These areas arebeneath the veneered zirconia
interface and so they providea basis for comparison with the
diffraction patterns near the
interface. These results are similar to positions 2 and 3
(redpatterns). The X-ray patterns show broader
tetragonal/cubicpeaks and weak and significantly broad monoclinic
peaks at 2�33◦ in all of these areas. As such the influence of the
veneering
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550 d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 545–552
Fig. 7 – Interface area of the without liquid veneered zirconia
(preparation procedure 3) measured using a 50 �m micro-lens,nly
d
Co-K�, 30 kV/30 mA, fixed incident angle 10◦, 120 s/frame, o
observable.
process can be compared with the grinding/polishing prepa-ration
of the taper section.
The right hand side of Fig. 3 presents the scan from 2� 32◦
to 37◦ at a higher magnification superimposing results fromall
locations. The slight broadening in width of the
knowncubic/tetragonal peak at about 2� 35◦ is evident for the
blacktraces and an increase in intensity and sharpness of the
mon-oclinic peak at 2� 33◦ for some of the green and red traces
isalso obvious.
Another feature evident in Fig. 3 is the two reflections inthe
range around 70◦ 2�, the cubic (3 1 1)/tetragonal (0 1 3 and1 2 1)
peaks. Both show a switch of tetragonal peaks inten-sity (1 2 1 to
0 1 3), starting under the veneering (red patterns2, 3). This
grinding induced intensity flip phenomenon ofthese tetragonal
intensities is well known on zirconia surfaces[20].
The �-XRD2-results for the “normal” Wash-Dentin layer-ing
technique (preparation method no. 1) coating and thethicker
veneered specimen (preparation method no. 2) showsimilar results.
It was impossible with the diffraction methodto recognize
dissimilar effects between the zirconia samplesfrom these two
preparation methods as anticipated from other
studies [18]. In both cases clear monoclinic zirconia peakswere
detectable directly under the porcelain layer from thezirconia
surface, but they were not stronger or more clearlyrecognizable
from those associated with the preparation with
iffraction rings caused by the tetragonal ZrO2 are
the thicker layer (method no. 2) than the layering
technique(method no. 1).
To understand the reason for the sharp and increasing(−1 1
1)-reflection of the monoclinic phase especially in theinterface
region in Fig. 3 the related GADDS–frames from theHi-Star detector
are shown in Fig. 4 for the 6 patterns whichare in the direct
neighbourhood of the interface region.
The GADDS frame especially for position 2 shows a verystrong
single crystal reflection which is the reason for themonoclinic (−1
1 1) reflection in the corresponding pattern(The arrow indicates
this single crystal diffraction spot withinthe corresponding
reflection pattern).
Higher magnification X-ray patterns provide a better
appre-ciation of the structural phase change with the
Wash-Dentincoating and the thicker layer of the porcelain on top of
Y-TZP(preparation no. 1 and no. 2). Figs. 5 and 6 present
azimuthalprojections from positions at similar distances from the
inter-face region with preparation methods 1 and 2 within
theveneered areas measured in this case with a 500 �m
mono-capillary optic with a 300 �m exit pinhole to analyse a
largersurface area for better statistics. Again in both cases
similarsingle crystal reflection spots from the monoclinic phase
are
detectable in the area under the porcelain independent of
thepreparation method.
A clearly identifiable difference in the Y-TZP surface
regionprepared in the absence of a liquid medium by the
veneered
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d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 545–552 551
Table 2 – Monoclinic volume percentage from the analysis of
Garvie and Nicholson [3].
Preparation Monoclinic V% @ red line position 2 Monoclinic V% @
black line position 5
pat
4
Tpatewwlutpegfva
vtfIoloasF
pftud
o2ug(mfcitdp
Method 1 (wash-firing) 11.5%Method 2 (thick layer) 13%Method 3
(no liquid)
-
l s 2
r
2008;27(3):448–54.
552 d e n t a l m a t e r i a
achieve a 50 by 200 �m-sized localized beam had the advan-tage
to enable phase stability of the near surface layer of thezirconia
interface to be evaluated. This specially designed X-ray
polycapillary micro-lens system also enabled detection ofthe
zirconia through thin layers of the porcelain surface.
This structural t → m change at the interface creates local-ized
residual stresses as a consequence of the volume dilationas well as
the different coefficient of thermal expansion of theframework
material. Such localized residual stresses at theinterface may
weaken the porcelain to zirconia adhesion andmay have influenced
the shear interfacial strength tests by Fis-cher et al. [24].
However to date there have been no publishedreports of clinical
adhesion failure between porcelain and Y-TZP frameworks despite
increasing observations of chippinginduced failures within the
porcelain on such frameworks [25].
The localized stresses developed between the veneeringand the
reliability of the dental restoration in the clinical situa-tion
are not completely established and further investigationswith a
focus on these topics need to be undertaken.
5. Conclusions
The present observations using the locally resolved
�-XRD2-technique have clearly established that the
porcelainveneering process, especially with a wet veneer during
firing,results in a localized tetragonal to monoclinic structural
trans-formation at the surface of the zirconia framework
materialduring preparation of these all-ceramic dental
restorations.
In the case of moist veneering porcelain a highly texturedor
oriented monoclinic crystalline phase was observed at
thezirconia/porcelain interface. In the absence of moisture
withinthe veneering porcelain no transformation of the Y-TZP
tetrag-onal phase was identified.
As a consequence of the findings in this study, it is
stronglyrecommended to use a porcelain layering technique that
isvery thin and as dry as possible for the initial layering
applica-tion to prevent destabilization of the tetragonal crystals
of theY-TZP framework at the interface, which will otherwise
inducelocal mechanical stress into the overlying porcelain layer
andtherefore could decrease the mechanical stability of the
finalproduct.
e f e r e n c e s
[1] Garvie RC, Hannink RH, Pascoe RT. Ceram Steel
Nat1975;258:703–4.
[2] Subbarao EC. Zirconia-an overview. In: Heuer AH, Hobbs
LW,editors. Science and technology of zirconia. Columbus, OH:
The American Ceramic Society; 1981. p. 1–24.
[3] Garvie RC, Nicholson PS. Phase analysis in zirconia
systems.J Am Ceram Soc 1972;55:303–5.
[4] Heuer AH, Lange FF, Swain MV, Evans AG.
Transformationtoughening: an overview. J Am Ceram Soc
1986;69:1–4.
6 ( 2 0 1 0 ) 545–552
[5] Deville S, Chevalier J, Gremillard L. Influence of
surfacefinish and residual stresses on the ageing sensitivity
ofbiomedical grade zirconia. Biomaterials 2006;27:2186–92.
[6] Sato T, Ohtaki S, Shimada M. Transformation of
yttriapartially stabilized zirconia by low-temperature annealing
inair. J Mater Sci 1985;20:1466–70.
[7] Sato T, Shimada M. Crystalline phase-change
inyttria-partially-stabilized zirconia by low-temperatureannealing.
J Am Ceram Soc 1984;67:C212–3.
[8] Sato T, Shimada M. Transformation of yttria-dopedtetragonal
ZrO2 polycrystals by annealing in water. J AmCeram Soc
1985;68:356–9.
[9] Lange FF, Dunlop GL, Davis BI. Degradation during aging
oftransformation-toughened ZrO2–Y2O3 materials at 250 ◦C. JAm Ceram
Soc 1986;69:237–40.
[10] Chevalier J, Cal‘es B, Drouin JM. Low-temperature aging
ofY-TZP ceramics. J Am Ceram Soc 1999;82:2150–4.
[11] Guo X. On the degradation of zirconia ceramics
duringlow-temperature annealing in water or water vapor. J PhysChem
Solids 1999;60:539–46.
[12] Chevalier J. What future for zirconia as a
biomaterial?Biomaterials 2006;27:535–43.
[13] Green D, Hannink R, Swain M. Transformation tougheningof
ceramics. Boca Raton, FL: CRC Press; 1988.
[14] Burger W, Richter HG, Piconi C, Vatteroni R, Cittadini
A,Boccalari M. New Y-TZP powders for medical grade zirconia.J Mater
Sci Mater Med 1997;8:113–8.
[15] Ruiz L, Readey MJ. Effect of heat-treatment on grain
size,phase assemblage, and mechanical properties of 3 mol%Y-TZP. J
Am Ceram Soc 1996;79:2331–40.
[16] Heuer AH, Claussen N, Kriven WM, Ruhle M. Stability
oftetragonal ZrO2 particles in ceramic matrices. J Am CeramSoc
1982;65:642–50.
[17] Cottom BA, Mayo MJ. Fracture toughness of
nanocrystallineZrO2–3 mol% Y2O3 determined by Vickers indentation.
ScrMater 1996;34:809–14.
[18] Tholey MJ, Swain MV, Thiel N. The interface
betweendifferent Y-TZP and their veneering materials. Dent
Mater2009, doi:10.1016/j.dental.2009.01.006.
[19] Berthold C, Bjeoumikhov A, Brügemann L. Fast
XRD2microdiffraction with focusing X-ray microlenses. Part PartSys
Charact 2009;26:107–11.
[20] Kao HC, Ho FY, Yang CC, Wei WJ. Surface machining
offine-grain Y-TZP. J Eur Ceram Soc 2000;20:2447–55.
[21] Coldea A, Stephan M, Tholey M, Thiel N. Untersuchung
desEinflusses verschiedener Keramikschleifersysteme
aufZirkoniumdioxid. Quintessenz Zahntech 2009;35(4).
[22] Denry IL, Holloway JA, Microstructural and
crystallographicsurface changes after grinding zirconia-based
ceramics,Online publication; 2005. www.interscience.wiley.com.
[23] Chevalier J, Gremillard L, Deville S.
Low-temperaturedegradation of zirconia and implications for
biomedicalimplants. Annu Rev Mater Res 2007;37:1–32.
[24] Fischer J, Grohmann P, Stawarczyk B. Effect of
zirconiasurface treatments on the shear strength
ofzirconia/veneering ceramic composites. J Dent Mater
[25] Larsson C, Vult von Steyern P, Sunzel B, Nilner K.
All-ceramictwo- to five-unit implant-supported reconstructions.
Arandomized, prospective clinical trial. Swed Dent
J2006;30(2):45–53.
http://www.interscience.wiley.com/
XRD2 micro-diffraction analysis of the interface between Y-TZP
and veneering porcelain: Role of application
methodsIntroductionMaterials and
methodsResultsDiscussionConclusionsReferences