1448 Volume 27, Number 6, 2012

estoration of missing teeth in dentistry can be
achieved with a variety of treatment options. In
particular, restoration of the esthetic zone remains a
challenge for clinicians. Although the least minimally
invasive option is the application of resin-bonded
fxed dental prostheses (FDP), their long-term survival
rate is not predictable.
On the other hand, the con-
ventional full-coverage FDP requires the preparation
of abutments that result in more tissue loss.
Clinical efcacy of osseointegrated implants for
single-tooth replacement has been well documented.

Several studies have demonstrated a high incidence
of prosthetic complications associated with FDPs
supported by implants such as screw or abutment
loosening, screw or abutment fracture, or fractures in
the framework or veneer parts of the FDPs.
Implant abutments are usually fabricated from
commercially pure titanium due to its well-documented
biocompatibility and mechanical properties.
Associate Professor, Department of Buccofacial Prosthesis,
Faculty of Odontology, University Complutense of Madrid,
Madrid, Spain.
Research Student, Department of Buccofacial Prosthesis,
Faculty of Odontology, University Complutense of Madrid,
Madrid, Spain.
Professor, Head of Dental Materials Unit, University of Zürich,
Center for Dental and Oral Medicine, Clinic for Fixed and
Removable Prosthodontics and Dental Materials Science,
Zurich, Switzerland.
Researcher, Department of Biomaterials and Bioinspired
Materials, Materials Science Institute of Madrid, Spanish
Research Council, Madrid, Spain.
Professor, Associate Dean, Department of Buccofacial
Prosthesis, Faculty of Odontology, University Complutense of
Madrid, Madrid, Spain.
Correspondence to: Prof Mutlu Özcan, Center for Dental and
Oral Medicine, Clinic for Fixed and Removable Prosthodontics
and Dental Materials Science, University of Zürich,
Plattenstrasse 11, CH-8032, Zürich, Switzerland. Fax: +41-44-
6344305. Email: mutluozcan@hotmail.com
Fracture Resistance of Crowns Cemented on Titanium and
Zirconia Implant Abutments: A Comparison of Monolithic
Versus Manually Veneered All-Ceramic Systems
Francisco Martínez-Rus, DDS, PhD
/Alberto Ferreiroa, DDS
Mutlu Özcan, DDS, Dr Med Dent, PhD
/José F. Bartolomé, PhD
/Guillermo Pradíes, DDS, PhD
Purpose: To evaluate the fracture resistance of all-ceramic crowns cemented on titanium and zirconia implant
abutments. Material and Methods: Customized implant abutments for maxillary right central incisors made
of titanium (Ti) and zirconia (Zr) (n = 60, n = 30 per group) were fabricated for an internal connection implant
system. All-ceramic crowns were fabricated for their corresponding implant abutments using the following
systems (n = 10 per group): (1) monolithic computer-aided design/computer-assisted manufacture (CAD/
CAM) lithium disilicate (MLD); (2) pressed lithium disilicate (PLD); (3) yttrium stabilized tetragonal zirconia
polycrystal (YTZP). The frameworks of both PLD and YTZP systems were manually veneered with a fuorapatite-
based ceramic. The crowns were adhesively cemented to their implant abutments and loaded to fracture in a
universal testing machine (0.5 mm/minute). Data were analyzed using two-way analysis of variance (ANOVA)
and Tukey’s test (α = 0.05). Results: Both the abutment material (P = .0001) and the ceramic crown system
(P = .028) signifcantly affected the results. Interaction terms were not signifcant (P = .598). Ti-MLD (558.5
± 35 N) showed the highest mean fracture resistance among all abutment −crown combinations (340.3 ±
62 − 495.9 ± 53 N) (P < .05). Both MLD and veneered ceramic systems in combination with Ti abutments
(558.5 ± 35 − 495.9 ± 53 N) presented signifcantly higher values than with Zr abutments (392.9 ± 55 −
340.3 ± 62 N) (P < .05). MLD crown system showed signifcantly higher mean fracture resistance compared
to manually veneered ones on both Ti and Zr abutments (P < .05). While Ti-MLD and Ti-PLD abutment-crown
combinations failed only in the crowns without abutment fractures, Zr-YTZP combination failed exclusively
in the abutment without crown fracture. Zr-MLD and Zr-PLD failed predominantly in both the abutment and
the crown. Ti-YTZP showed only implant neck distortion. Conclusions: The highest fracture resistance was
obtained with titanium abutments restored with MLD crowns, but the failure type was more favorable with
Ti-YTZP combination. INT J ORAL MAXILLOFAC IMPLANTS 2012;27:1448–1455
Key words: CAD/CAM, lithium disilicate, monolithic crowns, pressed ceramics, titanium, YTZP
Martínez-Rus et al
The International Journal of Oral & Maxillofacial Implants 1449
studies demonstrated excellent survival rates for
fxed implant reconstructions supported by titanium
Despite the numerous improvements
in the fabrication and design of titanium abutments,
their metallic color may still shine through the mucosa,
impairing the esthetic outcome. Even when placed
subgingivally, a dull gray background may give the soft
tissue an unnatural bluish appearance. The presence
of a gray gingival discoloration may also be partially
attributed to a thin gingival tissue thickness around
the abutment that is incapable of blocking refective
light from the metal abutment surface.
although they are very stable from a biomechanical
point of view, titanium abutments have limitations in
esthetically delicate areas.
Especially in the anterior zone, the success of sin-
gle-implant therapy is dictated by a number of factors
that involve the appearance of the peri-implant soft
The harmony of the crown-implant complex
in terms of color and form with the mucosa and neigh-
boring teeth is essential. In that respect, tooth-colored
ceramic abutments such as yttrium tetragonal zirconia
polycrystals (hereon, zirconia) have been proposed as
an alternative material to titanium abutments. Zirconia
has superior mechanical properties, presenting frac-
ture resistance as high as 900 to 1,200 MPa.
abutments not only induce signifcantly less mucosal
discoloration than metal abutments,
but also yield
to less bacterial adhesion than titanium.
the soft tissue integration of zirconia was found to be
similar to that of titanium.
However, not only im-
plant abutments but also implant restoration materi-
als should be considered during prosthetic treatment
planning. Metal-ceramic FDPs are commonly indicated
for implant-supported reconstructions. Since dental
implants do not have periodontal ligament (PDL) in-
terposed between the bone and implant surface that
eliminates the special proprioceptive nerve endings,
the sensitivity and mobility of natural dentition cannot
be duplicated in endosseous implants.
Therefore, in
the absence of a neurosensory mechanism that ade-
quately compensates for the PDL proprioception and
compressibility, the stability of the prosthesis-implant
complex is impaired resulting in FPD complications.
Recent developments in high strength ceramic
materials and manufacturing techniques try to fulfll
the expectations from both optical and biomechani-
cal perspectives on implant reconstructions.
the many options, in the late 1990s, lithium disilicate
glass-ceramics (SiO
- Li
O) was introduced to dentistry
as a framework material. Its fexural strength ranges be-
tween 300 and 400 MPa and its fracture toughness be-
tween 2.8 and 3.5 MPa/m
Lithium disilicate glass
ceramics could be typically fabricated through a com-
bination of the lost-wax and heat-pressed techniques
or milled with computer-aided design/computer-
assisted manufacture (CAD/CAM) systems and used for
the same indications. Using this material in conjunc-
tion with the pressed technique allows the dental tech-
nician to achieve better morphology and eliminate
the purchase of CAD/CAM devices. Because of its high
strength, this material ofers versatile applications and
can be used for the fabrication of monolithic crowns
(chairside or labside) with subsequent staining and
characterization. With lithium disilicate glass ceram-
ics, limited information is available on artifcial dies

but no information is present on implants. In fact, one
clinical study reported a 93% survival rate of three-unit
FDPs using pressed lithium disilicate glass-ceramics up
to 8 years
but the survival of such ceramics on im-
plant abutments is not known. Also, one of the most
signifcant advances in this feld has been the intro-
duction of zirconia as a framework material that can
be processed using CAD/CAM techniques. Compared
to other all-ceramic systems, zirconia exhibits superior
mechanical properties, owing to the transformation
toughening mechanism.

Since the fracture resistance of lithium disilicate
glass-ceramics is in general less than zirconia, higher
fracture resistance could be anticipated with the lat-
ter on implant abutments. On the other hand, due to
a delamination problem related to bilayered ceramic
structures, monolithic ones are considered proper alter-
natives. Due to the ductility of metals, bending resist-
ance could compensate for the fracture of the ceramic
restoration. Thus, less fracture resistance could be ex-
pected from zirconia abutment–ceramic compared
with titanium abutment–ceramic crown combinations.
The objectives of the present study were therefore
to evaluate (1) the fracture resistance of titanium and
zirconia implant abutments restored with monolithic
CAD/CAM lithium disilicate, manually veneered press-
able lithium disilicate, and manually venered zirconia
all-ceramic crowns, and (2) to identify the failure types.
The tested hypotheses were that fracture resistance of
crowns on titanium abutments would be higher than
for the zirconia abutments, and that zirconia crowns
would be more fracture resistant than lithium disilicate
Sample Preparation
Sixty internal connection implants with a diameter of
4.1 mm and length of 12 mm (Straumann Standard Plus
Implant) were obtained for this study. A clinical case
was selected for the design of the master abutment
with a height of 7 mm and taper of 6 degrees. This abut-
ment was digitally designed for the patient’s situation
Martínez-Rus et al
1450 Volume 27, Number 6, 2012
using three-dimensional abutment fabrication soft-
ware (inLab 3D for Abutments, version 3.80, Sirona
Dental Systems) (Fig 1).
The data generated were sent to the Straumann
production center in Markkleeberg, Germany, for the
construction of two groups of identical customized
abutments (n = 60, 30 per abutment type), namely zir-
conia abutments (Straumann CARES Abutment Ceram-
ic, Straumann) and titanium abutments (Straumann
CARES Abutment Titanium, Straumann) (Fig 2).
The abutments were randomly divided into three
subgroups (n = 10 per group) for the fabrication of all-
ceramic crowns using the following systems: (1) mono-
lithic CAD/CAM lithium disilicate (MLD; IPS e.max CAD,
Ivoclar Vivadent); (2) heat-pressed lithium disilicate
(PLD; IPS e.max Press); and (3) yttrium stabilized te-
tragonal zirconia polycrystal (YTZP; IPS e.max ZirCAD).
Standardized maxillary central incisor crowns (height,
11 mm; mesiodistal width, 8.5 mm; wall thickness, 2
mm) were fabricated with the help of a silicone index.
All ceramic crowns were fabricated according to their
manufacturer’s recommendations by one experienced
dental technician.
Fully anatomically shaped MLD and YTZP frame-
works were designed and milled with a CAD/CAM
system (CEREC InLab, Sirona Dental Systems) from
presintered blocks. After the milling procedure, MLD
crowns and YTZP frameworks were sintered accord-
ing to the manufacturer’s guidelines. PLD frameworks
(thickness, 0.6 mm) were fabricated using the heat-
pressing technique. YTZP and PLD frameworks were
then veneered manually using a fuorapatite veneer-
ing ceramic (IPS e.max Ceram, Ivoclar Vivadent).
Thereafter, all implants were embedded in special
specimen holders using epoxy resin (Epoxicure Resin,
Buehler) with 3 mm of vertical distance from the most
coronal bone-to-implant border to the top of the holder,
simulating vertical bone resorption of 3 mm according
to ISO Norm 14801.
The implants were placed in the
center of the specimen holders and at an angle of
90 degrees to the horizontal plane. The embedding
resin had a modulus of elasticity of approximately
12 GPa, which approximates that of human bone
(18 GPa).
While the zirconia abutments were
connected to the implants using secondary titanium
abutments (SynOcta 1.5 mm, Straumann), the titanium
abutments were directly connected to the implants.
All abutments were torqued to 35 Ncm according to
the manufacturer’s recommendation using a torque
control system (no. 046.049 Straumann). The screw
cavities were flled with polytetrafuoroethylene (PTFE)
tape and provisional restorative material (Fermit N,
Ivoclar Vivadent).
To ensure maximum adhesion between the all-
ceramic crowns and the abutments, the abutment
surfaces of all groups and the inner surfaces of the
zirconia crowns were air-abraded with Al
(100 μm, 1 bar). The inner surfaces of lithium disilicate
crowns were etched with 4.5% hydrofuoric acid (IPS
Ceramic Etching Gel, Ivoclar Vivadent) for 20 seconds
and rinsed thoroughly. Bonding areas of abutments
and crowns were silanized (Monobond Plus, Ivoclar
Vivadent) and the crowns were cemented using
adhesive resin cement (Multilink Implant, Ivoclar
Vivadent) according to the manufacturer’s instructions.
Finally, the restorations were stored at 37°C for 48
hours until testing.
Fracture Resistance Measurement and Failure
Type Analysis
All specimens were mounted in a steel holder at an
angle of 30 degrees in relation to the loading cell in
the universal testing machine (Shimadzu AG-X Series,
Shimadzu) (Fig 3). A piece of tin foil with a thickness of
0.5 mm was applied on the crowns. With this procedure,
an even distribution of the load was achieved until
fracture or deformation occurred. The load was applied
at a crosshead speed of 0.5 mm/minute at the incisal
edge according to ISO Norm 14801.
The fracture load
was registered as soon as fracture load decreased by
10% of the maximum load (Fmax). The fracture load
was noted in Newton (N) calculated by the specifc
software (Trapezium X Software, Shimadzu).
After fracture resistance tests, the failure types were
observed by two operators and categorized as fol-
lows: Score 1, complete crown fracture without abut-
ment fracture; Score 2, only abutment fracture without
any destruction in the crown; Score 3, screw fracture;
Score 4, crown and abutment fracture; and Score 5, im-
plant neck distortion.
Fig 1 The digital design of the master abutment for the
maxillary right central incisor using three-dimensional abutment
fabrication software.
Martínez-Rus et al
The International Journal of Oral & Maxillofacial Implants 1451
Fig 2 Customized titanium and zirconia abutments for the maxillary right cen-
tral incisor with identical dimension.
Statistical Analysis
Statistical analysis was performed using SPSS 14.0
software for Windows (IBM). The data were submit-
ted to two-way analysis of variance (ANOVA) with the
fracture resistance as the dependent variable and the
abutment type (two levels) and all-ceramic crown ma-
terial (three levels) as independent variables. Multiple
comparisons were made using Tukey’s post hoc test. P
values < .05 were considered to be statistically signif-
cant in all tests.
Both the abutment material (P = .0001) and the all-ce-
ramic crown system (P = .028) signifcantly afected the
results. Interaction terms were not signifcant (P = .598)
(Table 1).
Ti-MLD (558.5 ± 35 N) showed the highest mean frac-
ture resistance among all abutment–crown combina-
tions (340.3 ± 62 − 495.9 ± 53 N) (P < .05) (Table 2, Fig 4).
Both monolithic and veneered ceramic systems in com-
Fig 3 Representative photo of an implant with
its abutment and the cemented crown mounted
in the holder at the universal testing machine at
an angle of 30 degrees in relation to the loading
cell. To ensure an even distribution of the static
forces, a tin foil (thickness, 0.5 mm) was placed
on the crowns.
Table 1 Results of Two-way ANOVA ( = 0.05)
Effect df Sum of squares Mean square F P
Abutments 1 194011.1 194011.1 65.1 .0001*
All-ceramic crowns 2 23767.4 11883.7 3.9 .028*
Interaction 2 3110.9 1555.4 0.5 .598
Residue 54 101225.5 2977.2
Total 59 350125.6
Martínez-Rus et al
1452 Volume 27, Number 6, 2012
bination with Ti abutments (558.5 ± 35 − 495.9 ± 53 N)
presented signifcantly higher values than with Zr
abutments (392.9 ± 55 - 340.3 ± 62 N) (P < .05). MLD
crown system showed signifcantly higher mean frac-
ture resistance compared to manually veneered ones
on both Ti and Zr abutments (P < .05).
While Ti-MLD and Ti-PLD abutment–crown combi-
nations failed only in the crowns without abutment
fractures, Zr-YTZP combination failed exclusively in the
abutment without crown fracture (Table 3). Zr-MLD
and Zr-PLD failed predominantly in both the abutment
and the crown. Ti-YTZP showed neither crown nor
abutment fracture where only implant neck distortion
was observed. In none of the samples was screw frac-
ture observed.
This study evaluated the fracture resistance of titanium
and zirconia implant abutments restored with mono-
lithic CAD/CAM lithium disilicate, manually veneered
pressable lithium disilicate, and manually venered zir-
conia all-ceramic crowns. The results showed signif-
cantly higher fracture resistance values for all types of
all-ceramic crown systems when they were cemented
on the titanium abutments. Thus, the frst hypothesis
could be accepted. Since the mean fracture resistance
of the monolithic lithium disilicate all-ceramic crowns
presented signifcantly higher results compared to the
veneered lithium disilicate and zirconia ceramic sys-
tems, the second tested hypothesis was rejected.
The critical load of implanted-supported ceramic
and metal abutments restored with all-ceramic crowns
has been evaluated in previous studies, with the re-
sults ranging between 170 N and 1454 N.
et al
investigated the fracture resistance of leucite
reinforced heat-pressed glass ceramic (IPS Empress 1,
Ivoclar Vivadent) crowns adhesively cemented on alu-
mina and zirconia abutments on the external connec-
tion implants. Similar to the present study, in that study
no artifcial aging was practiced. The results showed
signifcant diferences between the mean fracture load
of crowns cemented on alumina abutments (280 N)
and those cemented on zirconia abutments (737 N).
Although stronger ceramic systems were used com-
pared to leucite reinforced ceramic, the mean fracture
resistance of all-ceramic systems on zirconia abutments
(340 to 393 N) in the present investigation was lower
than those reported by Yildirim et al.
This might be
due to diferences in the testing protocols. In this study,
the implants were embedded in the epoxy resin molds
simulating vertical bone loss of 3 mm, according to ISO
Norm 14801,
whereas in the former investigation,

the implants were embedded in autopolymerizing
composite up to the implant shoulder. Consequently,
the loads applied in these two studies might have
caused diferent lever arms. Furthermore, diferent to
that study where external connection implants were
used, in the present study internal connection implants
with a neck height of 1.8 mm were used, possibly fur-
ther increasing the bending moment.
The embedding parameters simulating vertical
bone loss of 3 mm described in ISO Norm 14801
resents the worse-case scenario. In fact, marginal bone
level can move apically following implantation to a rel-
atively steady-state level in clinical practice, marginal
bone loss > 3 mm are fortunately rare.
Therefore, this
simulated bone loss can be considered excessive as it
exposes the implant threads, making it more suscepti-
ble to early failure. It is possible that the results would
have been diferent in this study if the implants had
been placed at the nominal bone level, which requires
further investigation.
Table 2 Mean (Standard Deviation) Fracture Resistance Values (N) Recorded for the Experimental
All-ceramic crown type
Monolithic CAD/CAM
lithium disilicate (MLD)
Manually veneered
pressable lithium disilicate (PLD)
Manually veneered
zirconia (YTZP)
Titanium (Ti) 558.5 (35.2)
482.2 (58.4)
495.9 (53.4)

Zirconia (Zr) 392.9 (55.3)
363.0 (50.5)
340.3 (61.8)
*Same superscripts do not show signifcant differences in the column and row (P < .05).


Fig 4 Mean fracture resistance (N) and standard deviations of
all experimental groups.
Martínez-Rus et al
The International Journal of Oral & Maxillofacial Implants 1453
In another study
with similar testing conditions
and the abutments (CARES), milled leucite reinforced
glass-ceramic crowns adhesively cemented on zirconia
abutments presented a mean fracture resistance value
(283 N) lower than that reported by Yildirim et al.
Since stronger ceramics were used in the present study,
the results were higher than that investigation.

Sundh and Sjögren
evaluated the bending
resistance of implant-supported titanium and zirconia
abutments restored with all-ceramic copings. They
reported that the bending resistance of the magnesia
and yttrium stabilized zirconia ceramic specimens
was equal or superior to that of the titanium control
(> 300 N). These results are not in accordance with the
present fndings. The diference may be due to the
mode of load application. In the present investigation,
the fracture load was applied at 30 degrees to the long
axis of the implants, whereas in the former study, the
load was applied perpendicular to the long axis of the
specimens by means of a chisel-shaped steel blade,
which probably aggravated the stress on the coping-
implant assembly. Since the tests were performed on
copings only, the lack of anatomical restoration might
have also contributed to the diferences between the
two studies. According to Cho et al,
under vertical
loading, the fracture resistance of restorations on
titanium abutments was almost twice that of those on
ceramic abutments. However, under oblique loading
(45 degrees) no statistically signifcant diferences in
fracture resistance were seen between the restorations
on titanium and ceramic abutments.
In the present investigation, no artifcial aging or
dynamic loading was applied to the test specimens
that could be considered as the limitation of the study.
Dynamic loading might lead to crack propagation in
the ceramics and if it were involved, it could have af-
fected the outcome of the study or ranking of the ma-
terials tested. Therefore, the results in its current form
Table 3 Distribution of Failure Types after Fracture Resistance Test
Failure types
Experimental groups
Score 1 10 10 0 0 0 0
Score 2 0 0 0 0 1 10
Score 3 0 0 0 0 0 0
Score 4 0 0 0 10 9 0
Score 5 0 0 10 0 0 0
Score 1 = complete crown fracture without abutment fracture; Score 2 = only abutment fracture without any destruction in the crown;
Score 3 = screw fracture; Score 4 = crown and abutment fracture; Score 5 = implant neck distortion.
Martínez-Rus et al
1454 Volume 27, Number 6, 2012
could represent possible early clinical failures that may
result not as a consequence of fatigue.

Cyclic loading
or thermo-mechanical fatigue conditions could re-
duce the fracture resistance of zirconia implant abut-
ments signifcantly. Gehrke et al
reported decreased
strength of zirconia abutments from 672 N without
cyclic loading, to less than 405 N after 5,000,000 cy-
clic loading. In two other studies, the static fracture
resistance of diferent implant-supported all-ceramic
restorations was tested after chewing simulation.

Ninety-six implants with an internal connection design
received titanium, alumina, and zirconia abutments.
All abutments were restored with alumina and zirco-
nia all-ceramic crowns. The specimens were exposed
to 1,200,000 cycles in a chewing simulator to simulate
5 years of clinical service. The median fracture loads
after aging were 1251 N and 457 N for titanium abut-
ment-zirconia crown and zirconia abutment-zirconia
crown combinations, respectively. Although speci-
mens in the present study were not aged, the results
were surprisingly lower than those obtained by Att et
Theoretically, the aging efect through environ-
mental stresses could alter the metastable tetragonal
crystalline phase of the YTZP-based ceramics. The con-
sequences of this process are multiple and include sur-
face degradation with grain pullout and microcracking
and degradation in strength. Long-term exposure
of zirconia ceramics to humidity and thermal cycling
leads to a low-temperature degradation (LTD) of the
However, there is controversy over whether
this would lead to a reduction in the fracture resistance
of zirconia. Although it may be speculated that no wa-
ter could seep into the implant body during chewing
the presence of water is necessary to
initiate the LTD. Therefore, even though no aging was
practiced in this study, the lower results may be ex-
plained on the grounds that in the above mentioned
studies, the implants were placed at the nominal bone
level. In the present study, the vertical bone loss of
3 mm together with the 1.8 mm implant neck resulted
in the bone level almost 4.8 mm below the upper im-
plant shoulder. All this makes a direct comparison dif-
cult between studies on fracture resistance of implant
supported reconstructions. Future studies should sug-
gest some more standardization.
The fracture resistance results should also be cou-
pled with the failure type analysis. The failure types
were fairly uniform in each group. When monolithic or
manually veneered lithium disilicate crowns were used
on titanium abutments, only the crowns fractured. In
bilayered ceramic structures, veneering ceramic is ex-
pected to fracture more frequent than the monolithic
However, the exclusive crown fracture failure
type in the monolithic crowns cemented on titanium
abutments indicates that these ceramics do not pres-
ent advantages over bilayered ones even though the
highest mean fracture resistance value was obtained
with this ceramic. Due to lower load-bearing capac-
ity of glass-ceramics than titanium, lithium disilicate
crowns were identifed as the weakest components in
abutment-crown assemblies. From the clinical point
of view, using glass-ceramic crowns on titanium abut-
ments may not fulfl the esthetic requirements in the
anterior region. Hence, the performance of lithium di-
silicate crowns on zirconia abutments may be of more
relevance. In these groups, unfortunately both the
crowns and their corresponding abutments showed
Among all testing groups, manually veneered zir-
conia on zirconia abutments failed exclusively in the
abutments without any destruction in the crowns. The
esthetic outcome would probably be better with zir-
conia abutments in combination with zirconia crowns.
However, this failure type also indicates that the risk of
zirconia abutment damage is more likely to occur. Inter-
estingly, the same manually veneered zirconia crowns
did not demonstrate any crown fractures on titanium
abutments. In this group, no fractures of the crowns and
the abutments but only implant neck distortions were
observed. Since the translucency of zirconia ceramics
are less than that of lithium disilicate ceramics, esthetic
outcome on titanium abutments may be perhaps not
perfect, but acceptable. Therefore, considering both the
fracture resistance values and failure types, the most
stable abutment-ceramic crown combination seem to
be manually veneered zirconia on titanium abutments.
It is not always possible to extrapolate the fndings
of in vitro studies to clinical situations since the stresses
and strains of dental restorations in vivo are complex.
However, with the increasing number of implants,
abutments, and ceramic systems in the dental market,
in vitro studies may help ranking material combina-
tions before they are experimented clinically. The tests
were performed only in maxillary central incisors and
the results may vary in posterior teeth due to morpho-
logical diferences. Early and long-term clinical failure
types in implant dentistry should be reported in more
detail in order to verify the fndings of in vitro studies.
Based on the results of the present study, overall tita-
nium abutments showed better durability than zirconia
abutments. Titanium abutments restored with mono-
lithic lithium disilicate crowns presented the highest
fracture resistance with complete crown fractures with-
out abutment fractures. Titanium abutment–manually
veneered zirconia crown combinations presented no
crown fracture but only implant neck distortion.
Martínez-Rus et al
The International Journal of Oral & Maxillofacial Implants 1455
This investigation was partially supported by grant No. 320-2008
from the University Complutense of Madrid. The authors grate-
fully acknowledge Mr Javier Pérez (Técnica Dental Studio VP,
Lugo, Spain) for the fabrication of the abutments and crowns.
Furthermore, they thank the companies Straumann and Ivoclar
Vivadent for the support of the study with implants, abutments,
and ceramic ingots/blocks. The authors reported no conficts of
interest related to this study.
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