Osseointegration of zirconia implants: an SEM observation of the bone-implant interface.

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ssBioMed CentHead & Face Medicine
Open AcceResearch
Osseointegration of zirconia implants: an SEM observation of the
bone-implant interface
Rita Depprich†1, Holger Zipprich2, Michelle Ommerborn*3, Eduardo Mahn1,
Lydia Lammers4, Jörg Handschel†1, Christian Naujoks†1, Hans-
Peter Wiesmann4, Norbert R Kübler1 and Ulrich Meyer1
Address: 1Department for Cranio- and Maxillofacial Surgery, Heinrich-Heine-University Duesseldorf, Germany, 2Department for Prosthetic
Dentistry, Section of Materials Sciences, Johann Wolfgang Goethe University Frankfurt, Germany, 3Department for Operative and Preventive
Dentistry and Endodontics, Heinrich-Heine-University Duesseldorf, Germany and 4Department for Cranio- and Maxillofacial Surgery, Westfalian
Wilhelms-University Muenster, Germany
Email: Rita Depprich - depprich@med.uni-duesseldorf.de; Holger Zipprich - depprich@med.uni-duesseldorf.de;
Michelle Ommerborn* - ommerborn@med.uni-duesseldorf.de; Eduardo Mahn - depprich@med.uni-duesseldorf.de;
Lydia Lammers - depprich@med.uni-duesseldorf.de; Jörg Handschel - depprich@med.uni-duesseldorf.de;
Christian Naujoks - depprich@med.uni-duesseldorf.de; Hans-Peter Wiesmann - depprich@med.uni-duesseldorf.de;
Norbert R Kübler - depprich@med.uni-duesseldorf.de; Ulrich Meyer - depprich@med.uni-duesseldorf.de
* Corresponding author †Equal contributors
Abstract
Background: The successful use of zirconia ceramics in orthopedic surgery led to a demand for
dental zirconium-based implant systems. Because of its excellent biomechanical characteristics,
biocompatibility, and bright tooth-like color, zirconia (zirconium dioxide, ZrO2) has the potential
to become a substitute for titanium as dental implant material. The present study aimed at
investigating the osseointegration of zirconia implants with modified ablative surface at an
ultrastructural level.
Methods: A total of 24 zirconia implants with modified ablative surfaces and 24 titanium implants
all of similar shape and surface structure were inserted into the tibia of 12 Göttinger minipigs. Block
biopsies were harvested 1 week, 4 weeks or 12 weeks (four animals each) after surgery. Scanning
electron microscopy (SEM) analysis was performed at the bone implant interface.
Results: Remarkable bone attachment was already seen after 1 week which increased further to
intimate bone contact after 4 weeks, observed on both zirconia and titanium implant surfaces. After
12 weeks, osseointegration without interposition of an interfacial layer was detected. At the
ultrastructural level, there was no obvious difference between the osseointegration of zirconia
implants with modified ablative surfaces and titanium implants with a similar surface topography.
Conclusion: The results of this study indicate similar osseointegration of zirconia and titanium
implants at the ultrastructural level.
Published: 6 November 2008
Head & Face Medicine 2008, 4:25 doi:10.1186/1746-160X-4-25
Received: 30 July 2008
Accepted: 6 November 2008
This article is available from: http://www.head-face-med.com/content/4/1/25
© 2008 Depprich et al; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0),
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Page 1 of 7
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Head & Face Medicine 2008, 4:25 http://www.head-face-med.com/content/4/1/25
Background
Dental implants are a well-accepted and predictable treat-
ment modality for the rehabilitation of partially and com-
pletely edentulous patients. Ten-year survival rates > 95%
and 15-year survival rates > 92% have been reported [1].
To achieve long-term success, rigid fixation of the
implants within the host bone site is required [2]. This
biological concept of osseointegration was first intro-
duced by Branemark et al. in the 1960s [3]. Since its intro-
duction the term osseointegration has been successively
redefined, the common denominator being an inanimate
metallic structure anchored long-term in living bone
under functional loading [4]. Nowadays, commercially
pure (cp) titanium and its alloys are the materials most
often used in implant manufacturing because of their
excellent biocompatibility, favourable mechanical prop-
erties and well-documented beneficial results. When
exposed to air titanium immediately develops a stable
oxide layer which forms the basis of its exceptional bio-
compatibility. The properties of the oxide layer, i.e. its
chemical purity and surface cleanliness, are of great
importance for the biological outcome of the osseointe-
gration of titanium implants [5]. According to Albrekts-
son et al., the quality of the implant surface is one major
factor that influences wound healing at the implantation
site and subsequently affects osseointegration [6]. In
recent years, much effort has been made to improve
implant anchorage in bone tissue by modifying the sur-
face characteristics of titanium implants. Various studies
have demonstrated that the success of integration of
implants into bone tissue correlates positively with a spe-
cial roughness of the implant surface [7]. Another advan-
tage of a roughened titanium surfaces is a shorter healing
period and the option of utilizing shorter implants, still
with a good long-term prognosis because of the better
bone anchorage [8]. Therefore, many surface modifica-
tions of titanium implants have been developed to
achieve better osseointegration (machined, plasma-
sprayed, grit blasted and/or acid etched).
In recent years, high-strength ceramics have become
attractive as new materials for dental implants. They are
considered to be inert in the body and exhibit minimal
ion release compared to metallic implants. Zirconium
oxide partially stabilized with yttrium (yttrium-stabilized
tetragonal polycrystals [Y-TZP]) appears to offer advan-
tages over aluminium oxide for dental implants due to its
higher fracture resilience and higher flexure strength [9].
Zirconia ceramics have also been successfully used in
orthopedic surgery to manufacture ball heads for total hip
replacements and this is still the current main application
of this biomaterial [10,11].
ceramics. As the surface topography of zirconia implants
seems to influence the bone implant interface, the aim of
this study was to investigate the osseointegration of zirco-
nia implants with modified ablative surfaces at the
ultrastructural level.
Materials and methods
Experimental animals
Twelve minipigs (> 5 years, average body weight 66.5 kg)
were used in this study. The investigation was approved by
the Animal Ethics Committee of the University of Dues-
seldorf. The animals were kept in small groups in pur-
pose-designed sties and fed on a standard diet. Twelve
hours before surgery, the animals received no more feed
while water was accessible ad libitum.
Implant system
Twenty-four screw-type zirconia implants (yttrium-stabi-
lized tetragonal polycrystals) with roughened surfaces
produced by acid etching were compared to 24 implants
of commmercially pure titanium with acid etched sur-
faces. Implants were supplied by Konus Dental Implants
(Bingen, Germany). All implants had the same geometry
with a standardized diameter of 3.5 mm and a length of 9
mm.
Surgical procedure
All surgery was performed under sterile conditions in a
veterinary operating theatre. The animals were sedated by
intramuscular injection (10 mg/kg) of ketamine (Ket-
avet®, Pfizer, Karlsruhe, Germany), 1 ml atropine (Atro-
pinsulfat Braun®, Braun, Melsungen, Germany) and 5 mg/
kg azaperone (Stresnil®, Janssen-Cilag, Neuss, Germany).
Anaesthesia was induced with an intravenous bolus of 3–
5 ml thiopental (Thiopental inresa®, Inresa Arzneimittel,
Freiburg, Germany) followed by intubation and mainte-
nance of anaesthesia by inhalation of 1.5% isoflurane. For
analgesia, animals received 0.5 ml piritramide (Dipido-
lor®, Janssen-Cilag, Neuss, Germany). In the areas exposed
to surgery 5 ml of local anaesthesia [articain hydrochlo-
ride, (Ultracain® DS, 1:200.000), Aventis, Frankfurt, Deut-
schland] was injected. The tibias were exposed by skin
incisions and via fascial-periosteal flaps. Thereafter, four
implants were inserted into the tibia. The implant sites
were sequentially enlarged with two drills according to the
standard protocol of the manufacturer. Implants were
inserted using continuous external sterile saline irrigation
to minimize bone damage caused by overheating. At the
surgical site, the skin and the fascia-periosteum were
closed in separate layers with single resorbable sutures
(Vicryl®2-0, Ethicon, Norderstedt, Germany). Periopera-
tively, the animals received amoxicillin (10 mg/kg KG)
(Duphamox LA®, Fort Dodge, Würselen, Germany) as
®Page 2 of 7
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Up to now, only few studies have investigated the
osseointegration of dental implants made of zirconia
antibiotic and carproven p.o. (4.4 mg/kgKG) (Rimadyl ,
Pfizer, Karlsruhe, Germany) as antiphlogistic medication

Head & Face Medicine 2008, 4:25 http://www.head-face-med.com/content/4/1/25
for three days. The animals were inspected after the first
few postoperative days for signs of wound dehiscence or
infection and, thereafter, weekly to assess general health.
After 1, 4 or 12 weeks animals were sacrificed (4 minipigs
each) with an overdose of pentobarbital (Eutha 77® ad us.
vet, Essex Pharma, München, Germany) given intrave-
nously. Following euthanasia, tibia block specimens con-
taining the implants and surrounding tissues were
dissected from all of the animals. The block samples were
sectioned by a saw to remove unnecessary remnants of
bone and soft tissue and were prepared for the subsequent
investigations.
Scanning electron microscopy (SEM)
Utilizing the fracture technique [12] the block samples
were dissected into two halves (Figure 1). Samples con-
taining the implants were used for scanning electron
microscopy (SEM), the corresponding bone samples for
EDX analysis. After fixation in 4% glutaraldehyde, the
specimens were dehydrated in a graded series of ethanol
and critical-point dried. Samples were then sputter-coated
with gold and examined under a JEOL 6300F (JEOL, Ech-
ing, Germany) high-resolution field emission scanning
electron microscope.
Results
All surgical procedures were performed without complica-
tions and the animals recovered well after surgery. Daily
investigation showed no clinical signs of infection during
the observation period. Scanning electron microscopy
demonstrated that, already after one week, osseous matrix
adhered to the implant surfaces of the zirconia and tita-
nium implants (Figure 2). At higher magnification, differ-
ences in matrix composition were observed. On the
zirconia implants, a dense matrix mainly consisting of
fibrinous and collagenous filaments in combination with
corpuscular and cellular components was found in direct
contact with the ZrO2 surface (arrows in Figure 3 left). On
the titanium implants, less osseous matrix was seen on the
surface. Extracellular matrix was anchored particularly in
the cavities of the titanium surface (Figure 3 right). After 4
weeks, intimate contact with bone cells embedded in a
mineralized collagen-rich extracellular matrix was present
on both titanium and zirconia implant surfaces. Although
a slightly higher degree of mineralization was detected on
the titanium surface, there were no significant differences
between the bone-implant interfaces of the two implant
materials (Figures 4 and 5). After 12 weeks, successful
osseointegration of the zirconia as well as the titanium
implants was visualized at the ultrastructural level. Scan-
ning electron microscopy showed newly developed bone
integrated at the implant surfaces and confirmed the inti-
mate contact of the mature lamellar bone with the zirco-
nia and titanium surfaces. No interposition of an
interfacial layer or foreign-body reaction was detected in
any of the samples examined (Figures 6 and 7).
Discussion
In the study presented, osseointegration of zirconia
implants with a modified ablative surface was investigated
at the ultrastructural level and compared to titanium
implants with a similar surface structure. One week after
implantation, SEM analysis demonstrated a firm attach-
ment of collagen-rich extracellular bone matrix to both
implant surfaces. Three weeks later, both titanium and zir-
conia implant surfaces had made intimate contact with
mineralized tissue, osteoid, and dense collagen-rich extra-
cellular matrix. After 12 weeks, ultrastructural evidence of
a successful osseointegration of both implant systems was
found.
Insights into cellular processes occurring at the bone-
implant interface are important for the understanding of
biocompatibility and osseointegration. The resulting
knowledge will contribute to the production and testing
of biomaterials with specific and desired biological
responses [13,14]. According to Büchter and co-workers
[15], probe processing by sample fracturing for the SEM
investigation is indicative of the fact that the bonding
strength between the implant and the adjacent bone layer
seems to reach bonding values in the bone itself. After one
week, firm anchorage of the extracellular matrix at the
complete titanium surface was evident particularly at the
interdigitation of titanium peaks on the implant demon-
strating that implant anchorage is dependent on surface
topography [16]. Rougher surfaces are predicted to pro-
mote mainly osteoconduction by increasing available sur-
face area for fibrin attachment and by providing surfaceDissection of the block samples into two halvesFigure 1
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features with which fibrin could become entangled [17].
The results of the present study are in agreement with Sim-
Dissection of the block samples into two halves.

Head & Face Medicine 2008, 4:25 http://www.head-face-med.com/content/4/1/25
mons et al. [18] who investigated the early healing
response of porous-surfaced implants compared to Ti
plasma-sprayed implants inserted in rabbit femoral con-
dyles. After four days, the necrotic bone that had been cre-
ated during surgery had been resorbed and a well-defined
interface zone had formed adjacent to both investigated
implant designs. Scanning electron microscopical analysis
revealed a fibrinous and collagenous matrix extensively
interdigitated with the three-dimensional interconnected
porous structure in contrast to the plasma-sprayed
implants. After 8 days of healing, coverage and interdigi-
tation of the healing tissue had increased on both sur-
faces. However, the matrix around porous-surfaced
implants appeared more dense and extensive compared
with plasma-sprayed implants. After 16 days, both
implant surfaces were well covered and extensively inte-
grated into a mixture of mineralized tissue, osteoid, and
dense matrix. No significant differences in strength and
stiffness of attachment between the two implant designs
were detected at this time point. Similar results are shown
by Büchter et al. [15]. They demonstrated complete
Bone matrix adherent to the implant surface after one week healing timeFigure 2
Bone matrix adherent to the implant surface after one week healing time. Zirconia implant (left), titanium implant
(right) (2 kV, magnification 50-fold).

zirconia titanium
One week healing time: dense fibrinous and collagenous bone matrix in direct contact with the zirconia implant surface (arro s) (left)Figure 3
One week healing time: dense fibrinous and collagenous bone matrix in direct contact with the zirconia
implant surface (arrows) (left). Anchorage of bone matrix in the cavities of the titanium implant surface (##) (right) (2 kV,
zirconia titaniumPage 4 of 7
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magnification 1000-fold).

Head & Face Medicine 2008, 4:25 http://www.head-face-med.com/content/4/1/25
osseointegration of differently loaded titanium implants
after 28 days by SEM observation.
A recent SEM evaluation of the human bone-oxidized tita-
nium interface showed ingrowth and anchorage of bone
independant of the pore size. In contrast to previously
published studies, intimate bone contact was present in
pores with a diameter of less than 2 μm [19].
Only one recent study investigated the bone implant
interface of titanium and zirconia implants with different
surface modifications [9]. Sennerby et al. detected no sig-
nificant differences after six weeks of healing time.
Ultrastructural analysis revealed intimate contact of bone
tissue with the material surfaces in their study, indicated
by the observation of fracture of the bone rather than sep-
aration of the interface. These results are in agreement
with our findings presented in this study, confirming that
the surface texture positively influences bone integration.
4 weeks healing time: zirconia implant well covered with mineralized tissue, osteoid, and dense matrix (left) (2 kV, magnifica-tion 250-fold)Figure 4
4 weeks healing time: zirconia implant well covered with mineralized tissue, osteoid, and dense matrix (left) (2
kV, magnification 250-fold). Enlarged detail: fibrous matrix in the artifical gap resulting from the dissection of the specimen
(right) (2 kV, magnification 1000-fold).
zirconia zirconia
4 weeks healing time: coverage of the titanium implant with mineralized tissue and dense bone matrix (left) (2 kV, magnification 250-fold)Figure 5
4 weeks healing time: coverage of the titanium implant with mineralized tissue and dense bone matrix (left) (2

titanium titaniumPage 5 of 7
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kV, magnification 250-fold). Enlarged detail (right) (2 kV, magnification 1000-fold).