Plasma chemical oxidation (PCO®) enhances implant fixation and boneimplant contact in a rat model
C. Schrader 1, J. Schmidt 1, M. Diefenbeck 2, T. Mückley 2, S. Zankovych 3, J. Bossert 3, K. D. Jandt 3, M. Faucon 4 and U. Finger 4
1
2
INNOVENT e.V. Technologieentwicklung Jena, Prüssingstraße 27B, D-07745 Jena, Germany
Klinik für Unfall-, Hand- und Wiederherstellungschirurgie, Universitätsklinikum Jena, Erlanger Allee 101,
D-07747 Jena, Germany
3
Institut für Materialwissenschaft und Werkstofftechnologie, Löbdergraben 32, 07743 Jena, Germany
4
Königsee Implantate GmbH, Am Sand 4 / OT Aschau, D-07426 Allendorf, Germany
Abstract: Metal surface properties can be modified by various methods like plasmaspraying, micro-spheres or µ-metal scaffolds to generate nano-, micro- and macroporous structures to enhance osseointegration and thus implant fixation. This paper
describes an electrochemical routine which covers the whole range of surface modifications from the nm- to the µm-scale. The plasma assisted process produces bioinert
and bioactive properties under typical plasma conditions in an electrolyte.
Keywords: plasma chemical oxidation, bioinert, bioactive, antibacterial
1. Introduction
Orthopaedic and dental implants rely on early
ridged fixation to the host bone, which is a prerequisite for good clinical outcome [1-2]. The implant
anchorage apparatus has two structural components.
The bone-implant bonding (osseointegration [OI])
and peri-implant trabecular bone [PIB]. OI is formed
with trabecular struts that are integrated into the PIB,
which bridges the implant to the bony cortex, thus
forming a structural unit between implant and skeleton [3-5]. In the past, different approaches have been
used to enhance osseointegration and peri-implant
bone formation. Hydroxyapatite coatings [6], often
in combination with growth factors [7-8] or bisphosphonates [9] have been shown to improve osseointegration of titanium implants. Some of the stimuli
used to enhance implant fixation might bear the risk
of complications [10-13]. Titanium and its alloys
were utilised as biomaterials in orthopaedics since
the end of the nineteen-seventies because of their
excellent corrosion resistance, advantageous mechanical properties and biocompatible interaction
with the human body [14-15]. Certain disadvantages
from biomaterials made of titanium and its alloys
take into account that cytotoxic elements can possibly diffuse into the surrounding body tissues and
cause irritations. Additionally, temporary implants
for short-time repositioning purposes, especially in
sophisticated bone geometries stabilised by selfdrilling screws in angle-stable plate combinations,
tend to increased removal torques. This leads on the
one hand to tissues irritations and on the other hand
to an escalated bone fracture risk in implant removal
resulting in extended hospitalisation. Our approach
to face these challenges is to modify the titanium
surface from the implant itself by plasma chemical
oxidation [PCO®] to a ceramic coating. A selected
element contribution of this coating can be combined
and varied with topographical properties for useful
applications [16]. For permanent implants porous
structured coatings are predestined. They deliver an
appropriate element contribution for fast OI with an
interlocking surface topography [17] for PIB. Temporary implants with an optimised surface topography to prevent OI and PIB can be removed after its
bone reposition duty. The structural and chemical
properties of the PCO®-coating can be varied over
quite a wide range by altering the process parameters, such as anode potential, electrolyte composition, temperature and current density [18].
2. Anodic oxidation (AO)
Under atmospheric conditions the high affinity of
titanium towards oxygen establishes a natural insulating titanium oxide film of only a few nanometres
on all titanium work pieces. This passivity oxide film
works as a dielectric barrier and inhibits e.g. corrosive charge carrier to pass the boundary layer. In an
ordinary electrolysis cell, it is possible to enlarge the
barrier thickness by connecting the chosen work
piece as anode and to deposit under galvanostatic
conditions (anodic oxidation).
Both interfaces:
Ti 4+ + 2O 2− ⇔ TiO2
(1.4)
The titanium and oxygen ions formed in these
electrochemical reactions have to be driven through
the oxide film. This is carried out by the externally
Power Supply
Power Supply
U/V
U/V
100 V
0V
Fig. 1: Products by courtesy of Königsee Implantate GmbH after anodic
oxidation
With a constant current density of about 100 A·m-2, it
can be observed, that the voltage increases and layer
forming mechanisms take place at the same time.
The process ends with a layer thickness of several
hundred nanometres. This layer thickness range
shows typical interference effects demonstrating the
interaction with the electromagnetic spectrum of
visible light by the impression of a coloured surface.
This is appreciated by the surgeon to differentiate
more easily between implants and their suggested
place of implantation or screw and plate combinations translated in colour codes. Different diluted
acids (H2SO4, H3PO4, acetic acid and others) can be
used as electrolyte for this process. The main technological advantage of these converted titanium surfaces is improved adhesion and bonding (> 20 MPa),
which is particularly relevant in the aerospace industry. It can also be used to increase the oxide thickness for corrosion protection, for decreased ion release, coloration and for dielectric coatings on electrode materials e.g. dielectric barrier discharges
[DBD].
Plasma
Ignition voltage
Steel cathode (-)
Elektrolyte
Titanium anode (+)
Steel cathode (-)
Power Supply
U/V
Steel cathode (-)
Elektrolyte
Titanium anode (+)
+ coating
Power Supply
U/V
200 V
300 V
Plasma
Ignition voltage
Plasma
Ignition voltage
Elektrolyte
Titanium anode (+)
+ coating
Steel cathode (-)
Elektrolyte
Titanium anode (+)
+ coating
Fig. 2: Schemes of anodic oxidation (0 V – 100 V) and Plasma chemical
oxidation (200 V – 300 V)
applied electric field and linearly increases the oxide
film thickness with approximately 1.5 nm·V-1 to
3.0 nm·V-1 [18] in an anodic oxidation process.
3. Plasma chemical oxidation (PCO®)
In this paper a special electrolyte composition is
presented that enlarges the deposition range from the
nm- to the µm-scale in combination with selected ion
implantation and finishing methods for evidentially
improved OI and PIB under typical clinical conditions. This is carried out by a process called Plasma
Chemical Oxidation (PCO®).
Fig. 3: Cross section of a PCO® coating (300 V)
Ti / Ti oxide interface:
Ti 0 ⇔ Ti 4 + + 4e −
(1.1)
Ti oxide / electrolyte interface:
2 H 2O ⇔ 2O 2− + 4H + (TiO2-formation)
(1.2)
2 H 2O ⇔ O2 + 4 H + + 4e − (O2 formation)
(1.3)
The applied voltage drop mainly occurs across the
oxide film because of its high resistivity compared to
the electrolyte or metallic parts of the electric circuit.
With a suitable electrolyte further layer growth beyond the coloration regime of the anodic oxidation
can be induced.
Fig. 4: PCO®-process on a distal palmar radius plate
Above a certain voltage, mainly determined by the
electrolyte, work piece and power supply settings,
the oxide will be no longer resistive enough to prevent further current flow. The result is an increased
oxygen formation (see equation 1.3) with local field
strengths above 106 V·m-1 - 109 V·m-1 that ignite a
thermal arc discharge in pure oxygen surrounded by
an aqueous electrolyte.The additional layer formation by a thermal arc discharge increases the deposition rate and leads to the storage of electrolyte compounds into the coating when the melted plasma
channels and - pores (Fig. 3) solidify again. Therefore, it is possible to create coatings doped with useful elements for osseointegration, antibacterial properties, etc. Furthermore, the longer the discharge
regime of the deposition process occurs the more
electrolyte material is incorporated into the ceramic
coating. In-vitro adhesion- and proliferation assays
of MC3T3 cells on these PCO® modified titanium
surfaces show enhanced growth. The purpose of the
present study is to determine, if surface modifications by PCO® have an effect on peri-implant bone
volume, bone-implant contact and implant fixation.
Fig. 6: Surface of a PCO®-bioinert coating (220 V, blasted)
A modified rat tibial implantation model, described
by Gao et al. [9] with bilateral implantation of titanium rods is used. Pure titanium, typ-III anodization
(blue) titanium implants and implants with two different surfaces modifications by PCO® (300 V [bioactive] and 200 V [bioinert]) were evaluated in histomorphometric analysis and mechanical pull-out
testing.
4. Materials and methods
4.1 Preparation of implants
The power supply in the experimental setup in
Fig. 2 consists of a pulsed rectifier set D400 G500/50
WRG-TFKX from Munk Ltd. in Hamm, Germany.
The electric supply is realised by three feed cables
(3 x 400 V / 50 Hz / 100 A) and delivers a positively
pulsed directed current of 50 A and a negatively
pulsed directed current of 30 A with voltages from
0 V to 500 V. The system control with a digital output provides constant voltages and currents with an
accuracy of ±1% (± 1.5%) and a ripple content of
w = 0.5 %. The adjustable pulse frequency ranges
from 10 Hz to 2 kHz.
The implants were divided into four groups:
(1) Ti: Grinded and ceramic-blasted pure titanium
implants
(2) Ti-blue: Grinded and ceramic-blasted pure titanium implants coated by type III anodisation
(blue)
Fig. 5: Surface of a PCO®-bioactive coating (280 V)
(3) bioinert TiOB®: Grinded and ceramic-blasted
pure titanium implants with PCO®-bioinert coating (220 V, 1000 Hz, blasted)
(4) bioactive TiOB®: Grinded and ceramic-blasted
pure titanium implants with PCO®-bioactive coating (280 V, 1000 Hz)
tioned above. Before implantation, the implants were
sterilised in a steam autoclave (Vacuklav 44B, Melag, Berlin, Germany) for 35 minutes at
134°C - 138°C and 2.16 · 105 Pa.
4.2 Cell biological investigation
To monitor cytotoxic-, proliferation- or any other
growth inhibiting effects a very useful in-vitro cytotoxicity assay for biomaterials, the live/dead assay, is
performed. Therefore, direct inoculation with culture
medium (25.000 cells·cm-2 MC3T3-E1) on autoclaved specimen (HiClave HV-50, HMC Europe
GmbH, Tüssling, Germany), incubation for 24h and
96h at 37°C (Revco Ultima, Revco Technologies,
NA-Ashville, U.S.A) and examination with a fluorescence microscope (Axiovert 25 / filter 44 with
beam splitter FT 500 / filter 14 with beam splitter FT
580, Carl Zeiss GmbH, Jena, Germany) after staining
with a diluted solution of Fluoresceindiacetate
(FDA) and Ethidiumbromide (EtBr) in phosphate
buffer solution (PBS) is carried out. The amount of
green fluorescent cells indicates vital, FDA metabolising organisms in contrast to orange-red fluorescent
cells indicating dead organisms with perforated cell
membranes and subsequent diffusion of EtBr into the
nuclei.
4.3 Animal model and implantation
Animals
All experiments were approved by the Animal Care
Committee of Thuringia (Reg. No. G 02-008/10).
Sixty-four, 3-month-old male Sprague Dawley rats
(Harlan Laboratories GmbH, Eystrup, Germany)
weighing 300 g - 389 g were used. All were given
free access to standard rat-chow and water and were
raised in relative steady temperature and humidity in
an air-conditioned environment with lighting controlled in a cycle of light 12h / dark 12 h. Institutional guidelines for the care and treatment of laboratory animals were followed.
Implants
128 custom Ti6Al4V rods (Königsee Implantate
GmbH, Aschau, Germany), measuring 0.8 mm in
diameter and 10 mm in length were used. All implants were pre-treated with aluminium oxide abrasives and finished with spherical ceramic particles.
Next, surface modifications were performed as men-
Implantation procedure
Surgery was performed under general anaesthesia
by weight-adopted intraperitoneal injection of Domitor® (Meditomidin) 0.15mg / kg BW(Pfizer, Berlin,
Germany), Dormicum® (Midazolam) 2.0 mg / kg
BW (Ratiopharm, Ulm, Germany) and Fentanyl®
(Fentanyl) 0.005 mg / kg BW (Janssen-Cilag, Neuss,
Germany). Animals were prepared for surgery as
follows: Both hind legs were shaved and disinfected
with alcohol. To provide sterile conditions during
surgery animals were placed on sterile drapes and
bodies were covered with sterile sheets. Both hind
legs were draped with a sterile incision foil (Raucodrape, Lohmann & Rauscher, Rengsdorf, Germany). A medial incision to expose the knee joint in
both hind limbs was made over 5 mm longitudinally,
a pilot hole marked at the intercondylar eminence. A
custom-made awl with a tip in the size of 0.9 mm
diameter and 10 mm length was gradually twisted to
make a channel from the proximal tibia epiphysis
into the medullary canal. The implants were inserted
into this channel and positioned 2 mm beyond the
articulating cartilage. Soft tissue was irrigated with
sterile saline and fascia and skin incisions were
closed in single-knot technique (Vicryl 5/0 and
Prolene 5/0, Ethicon, Norderstedt, Germany). Prophylactic i.m. antibiotic (Terramycin, Pfizer GmbH,
Berlin, Germany) and analgesics (Buprenovet,
Bayer, Leverkusen, Germany) was administered once
at the time of surgery. Correct position of implants
was controlled by x-ray. After x-ray control general
anaesthesia was antagonised by Antisedan® (Atipamezol) 0.75mg / kg BW (Pfizer, Berlin, Germany),
Flumazenil-hameln® (Flumazenil) 0.2mg / kg BW
(Invera Arzneimittel GmbH, Freiburg, Germany) and
Naloxon (Naloxon) 0.12mg / kg BW (Deltaselect
GmbH, Dreieich, Germany).
Explantation and bone processing
The animals were sacrificed after three weeks and
eight weeks. Tibiae were harvested and denuded of
soft tissues prior to further analyses. From eight animals per group, five tibiae were fixed in formalin
(5%) for histological and ten frozen at – 20°C for
biomechanical examination (all in a blinded manner).
4.4 Biomechanical testing
The biomechanical property of bone–implant interface was assessed using a pull-out test. The tibia epiand metaphysis was trimmed with a bur (Minimot
40IE, Proxxon, Niersbach / Eifel, Germany) to expose the proximal tip of the implant (2 mm - 3 mm).
Afterwards the samples were again stored at -20°C.
The distal part of the tibia was embedded in a special
polyester resin (CEM 2000, Cloeren Technology
GmbH, Wegberg, Germany) with a comparable low
polymerisation enthalpy. For embedding a custom
made fixture was used to permit coaxial alignment of
the implant in the direction of force. The tibial implant-bone interface were tested in a commercial
material testing system (Tiratest 2710, Tira GmbH,
Schalkau, Germany) after thawing in air at room
temperature. The distraction speed was set at
1 mm·min-1 throughout the test, and the loaddisplacement curve was recorded simultaneously.
From these curves, maximum force was determined
and interfacial shear strength was calculated by dividing the force (N) at the point of failure by the
surface area of the implant in contact with tissue
(mm2).
4.5 Histological examination
Proximal tibiae with implant in situ (n=5/group)
were fixed in 5% neutral buffered formalin for
10 days, dehydrated with increasing concentrations
of alcohol, then impregnated with a mixture of alcohol/Technovit 7200VLC = 1:1, followed by infiltration with pure Technovit 7200VLC (Heraeus Kulzer,
Wehrheim / Ts, Germany) and embedded into this
methacrylate-based resin without decalcification.
200 µm thick cross-sections were performed using an
EXAKT 300 diamon band saw.
Fig. 7: X-ray image of the tibia (a) cross-section of the implant MassonGoldner stain, 40-fold magnification (b)
Next, the slices were grinded with the EXAKT
400CS grinding system and special grinding papers
down to a thickness of 10 µm – 20 µm. Four sections
(proximal (1), median I (2), median II (3) and distal
implant (4)) were selected and stained with modified
Masson-Goldner without removing the polymethacrylate (Fig. 7). Histomorphometric analysis of
the percentages of bone contact and bone area were
performed with a semi-automated digitizing image
analyzer system, consisting of a Nikon ECLIPSE
E600 stereomicroscope, a computer-coupled Nikon
Digital Camera DXM1200 and NIS-Elements F 2.20
image software. Bone contact (BC) was calculated as
a length percentage of the direct bone-implant interface to total implant surface. Bone area (BA) was
defined as the area percentage of the newly formed
bone within a circle of 0.1 mm around the implant to
the whole area.
4.6 Statistical analysis
All data are presented as box- and whisker plots indicating median, quartiles, whiskers and outliers.
StatGraphics Centurion (Statpoint Technologies, Inc.
Warrenton, Virginia, USA) was used for statistical
analysis. One-way analysis of variance (ANOVA)
following multiple comparisons with Fishers´s least
significant difference (LSD) procedure at the 95.0 %
confidence level was performed to determine which
means were significantly different from each other.
5. Results
5.1 In vitro testing
Fig. 8 - Fig. 11 present the results of the vital / dead-assay for biomaterials via cell staining
(Fluoresceindicacetate/Ethidiumbromide). In comparison with a referenced petridish (Fig. 10 - Fig. 11)
the bioinert TiOB®-surface (Fig. 8 - Fig. 9) shows
neither cytotoxic nor any other proliferation- and
growth inhibiting effects.
Fig. 8: Image of dead cells on bioinert TiOB® after 24 h (l) and 96 h (r)
of incubation
Fig. 9: Image of vital cells on bioinert TiOB® after 24 h (l) and 96 h (r)
of incubation
groups have been included in this analysis. The biomechanical data revealed significant influences of
the bioinert and bioactive coating either on maximum force required to pull out the implant or on the
corresponding interfacial shear strength after three
and eight weeks (Fig. 12 and Fig. 13). Bioactive
TiOB® surface modification induced a marked increase in the maximum force and the interfacial
shear strength, whereas bioinert modification showed
a trend towards a higher interfacial shear strength.
Fig. 10: Image of dead cells on a reference after 24 h (l) and 96 h (r) of
incubation
Fig. 12: Shear strength after 3 weeks
Fig. 11: Image of vital cells on a reference after 24 h (l) and 96 h (r) of
incubation
5.2 Clinical outcome of osseointegration
During explantation and sample preparation for
mechanical testing, some implants were not integrated in the bone and could be remove by a forceps
without using any force. Others fell out of the bone
during embedding of the tibiae. Theses implants
were defined as not osseous integrated (nonintegrated). In the three week group, only four of
eleven pure titanium implants were fixed, whereas
all of the bioactive modified implants were integrated (Tab. 1). After eight weeks eight of ten pure
titanium, nine of ten bioactive and all of the bioinert
modified implants were integrated.
Tab. 1: Status of implants during explantation and sample preparation.
Osseointegration OI / %: Number of integrated implants vs. total number of implants
Ti
Ti blue
bioinert
TiOB®
bioactive
TiOB®
3 weeks
4/11
(36.4 %)
4/10
(40.0 %)
7/11
(63.6 %)
10/10
(100 %)
8 weeks
8/10
(80%)
9/11
(81.8 %)
10/10
(100 %)
9/10
(90 %)
5.3 Biomechanical analysis
A total of four to ten tibiae in the three week
groups and eight to ten samples in the eight week
Fig. 13: Shear strength after 8 weeks
5.4 Histology evaluation
Light microscope images of implant–bone interfaces eight weeks after implantation are shown in
Fig. 14. Histomorphometric analysis revealed the
results of bone contact (BC) and bone area (BA)
(Fig. 15 and Tab. 2).
Tab. 2: Histomorphometric analyses: Bone area (BA) after three and
eight weeks in percent (± SEM)
3
weeks
8
weeks
Ti
Ti blue
27,5
(±2,55)
69,0
(±2,67)
39,9
(±1,65)
67,5
(±3,23)
bioinert
TiOB®
34,3
(±3,42)
60,4
(±4,77)
bioactive
TiOB®
47,4
(±4,07)
60,8
(±3,59)
One is the length ratio of direct bone–implant interface to total implant surface, the other is the area
ratio of newly formed bone area to the whole area
within a circle of 0.1 mm width [6]. BA showed a
dynamic increase in all groups from three to eight
weeks, but no significant difference within the
groups after eight weeks (Tab. 2).
Fig. 14 Implant-bone interfaces after 8 weeks
However, BC showed significant increased values
for the bioactive TiOB® group after eight weeks,
followed by bioinert TiOB® surfaces (Fig. 15).
Fig. 15 Bone contact after 8 weeks of implantation
6. Discussion
To our knowledge, this is the first time that bioactive- and bioinert TiOB® surfaces have been tested in
an animal model. The bioactive TiOB® surface demonstrates a significantly stronger implant fixation in
mechanical testing and a significant increased bone
contact. The modification of titanium surfaces by
PCO® provides three features, which might act in a
synergistic way for a stable implant / bone- interface.
First, the natural passive titaniumoxide film on a
titanium implant of a few nanometers is increased to
a TiOB® layer up to several micrometers. This conversion layer is defined by its compactness, uniform-
ity and excellent anchoring properties between implant material and surface. It provides a diffusion
barrier for metallic ions and body fluids. Second, a
finishing porous cover layer with a specific pore
density is processed by a temporary thermal arc discharge. Depending on the dielectric barrier characteristics of the TiOB® coating and the applied voltage, these discharges generate temperatures of
1.000 K to 50.000 K in an electrolyte at room temperature. Where these oxygen plasmas occur, the
previously built TiOB® layer melts and creates a
nano-porous surface. Third, the electrolyte itself can
be modified by adding different electrolyte compounds. These compounds are embedded in the porous surface by PCO®. In the bio-active TiOB® layer
a high concentration of phosphorous and calcium
was integrated. Both elements are important for synergetic bone growth mechanism with osteoblastic
cells [13]. Thus, PCO® has a different mechanism of
action than the commonly used coatings of implants
with hydroxyapatite. PCO® is solely a modification
of a titanium surface, compared to the local application of growth factors, bisphosphonats or other
medication by different other coatings. To show the
effects of TiOB® layers, a modified rat tibial implantation model, described by Gao et al. [9] with bilateral implantation of titanium rods was used. Since
we present the first in-vivo results of TiOB® surfaces, we used animals with a normal bone structure
[7] and not osteoporotic animals after bilateral ovariectomization [5, 9, 19]. We plan those experiments
at a later stage. In the literature, different time intervals of the mechanical testing of implants are discussed; animals are sacrificed between two weeks
[20], four weeks [7], six weeks [3] and three months
[9, 13]. We decided to elevate implant fixation at
three weeks and eight weeks, which was well chosen
to assess the dynamic process of the formation of the
bone / implant-interface. Implant fixation was analysed by mechanical pull out tests. Compared to the
Ti control, the bioactive TiOB® layer increased
maximum pull-out force 7.3-fold after 3 weeks and
12.1-fold after 8 weeks. Gao Y et al. reported in their
study of different hydroxyapatit-bisphosphonate
coatings in an osteoporotic rat model an increase of
maximum force between 2.9- and 6.8-fold [9]. From
our point of view, it is remarkable that the TiOB®
surface modification revealed results in a comparable
range than the local treatment with hydroxyapatite
plus bisphosphonates. De Raniery et al. could not
show significant differences in mechanical pull out
tests for the local application of rhTGF-β2 growth
factor compared to titanium implants in his animal
model [7]. The bioinert TiOB® layer showed a
0.9-fold reduced maximum pull-out force after
3 weeks and a 3.2-fold increase after 8 weeks compared to Ti. Since the bio-inert layer has a smooth
surface and almost no phosphorus and calcium components, this may show a time-dependent effect:
Probably the nano-porous structure of the bioactive
layer is responsible for the earlier implant fixation
after three weeks. For the histomorphometric measurements an established method was used [9, 19].
We found for all groups a dynamic increase of the
bone area (BA) (e.g. Titanium: 27.5 % after three
weeks vs. 69.0 % after eight weeks) from three to
eight weeks, but no significant difference within the
groups after eight weeks. BA is a parameter for the
amount of the de-novo bone formation. Our interpretation of the BA results is that the de-nove bone formation is not influenced by PCO®. Bone contact
(BC) was significantly increased by bioactive TiOB®
surfaces about 2.5 fold and by bioinert TiOB® surfaces 1.5-fold compared to titanium after eight
weeks. This correlates well with the enhanced shear
strength in both groups. From our point of view, BC
is the more important parameter for implant ancorage
than BA. Gao et al. report a stronger correlation between BC and sheer force than for BA and sheer
force [19], which is in general agreement with our
findings.
7. Conclusion
The results of our study demonstrate that the surface modification of titanium implants by PCO® can
promote osseointegration and implant fixation. Bioactive TiOB® surfaces have a nano-porous structure,
are enriched with phosphorus and calcium and show
comparable results in biomechanical test to the local
treatment with hydroxyapatite, bisphosphonates and
growth factors without their known disadvantages.
8. Acknowlegement
This work was supported by a grant from the “Europäischer Fonds für regionale Entwicklung”
[EFRE] (2006 FE 0183).
9. References
[1] Bauer TW, Schils J. The pathology of total joint athroplasty: 1.
Mechanisms of implant fixation. Skeletal Radiol 1999; 28: 423-432.
[2] Mjöberg B. The theory of early loosening of hip prostheses. Orthopedics 1997; 20: 1169-1175.
[3] Gabet Y, Kohavi D, Kohler T, Baras M, Müller R, Bab I. Trabecular
bone gradient in rat long bone ketaphyses: mathematical modelling and
application to morphometric measurements and correction of implant
positioning. J Bone Miner Res 2008; 23: 48-57.
[4] Davies JE. Understanding peri-implant endosseous helaing. J Dent
Educ 2003; 57:932-949.
[5] Gabet Y, Kohavi D, Voide R, Mueller TL, Müller R, Bab I. Endosseus implant anchorage is critically dependent on mechanostructural
determinants of peri-implant bone trabeculae. J Bone Miner Res 2010;
25: 575–583
[6] Wermelin K, Suska F, Tengvall P, Thomsen P, Aspenberg P.
Stainless steel screws coated with bisphosphonates gave stronger fixation
and more surrounding bone. Histomorphometry in rats. Bone 2008; 42:
365 – 371
[7] De Ranieri A, Virdi AS, Kuroda S, Shott S, Leven RM, Hallab NJ,
Sumner DR. Local application of rhTGF-ß2 enhances peri-implant bone
volume and bone-implant contact in a rat model. Bone 2005; 37: 55 – 62
[8] Sachse A, Wagner A, Keller M, Wagner O, Wetzel WD, Layher F et
al. Osseointegration of hydroxyapatite-titanium implants coated with
nonglycosylated recombinant human bone morphogenetic protein-2
(BMP-2) in aged sheep. Bone 2005; 37:699-710
[9] Gao Y, Zou S, Liu X, Bao C, Hu J. The effect of surface immobilized
bisphosphonates on the fixation of hydroxyapatite-coated titanium
implants in ovariectomized rats. Biomaterials 2009; 30: 1790 – 1796
[10] Silverman SL, Landesberg R. Osteonecrosis of the jaw and the role
of bisphosphonates: a critical review. Am J Med 2009; 122(2 Suppl):
S33-45.
[11] Mroz TE, Wang JC, Hashimoto R, Norvell DC. Complications
related to osteobiologics use in spine surgery: a systematic review. Spine
2010; 35 (9 Suppl): S86-104
[12] Vaidya R, Sethi A, Bartol S, Jacobson M, Coe C, Craig JG.
Complications in the use of rhBMP-2 in PEEK cages for interbody spinal
fusions. J Spinal Disord Tech. 2008; 21: 557-62
[13] Li LH, Kong YM, Kim HW, Kim YW, Kim HE, Heo SJ, Koak JY.
Improved biological performance of Ti implants due to surface modification by micro-arc oxidation. Biomaterials. 2004 Jun;25(14):2867-75.
[14] Williams DF, Brunette DM, Tengvall P,Textor M, Thomsen P.
Titanium in Medicine 2001; 13.
[15] Steinemann SG, Müsle PA, Lacombe P, Trocit R, Beranger G.
Proceedings of the 6th World Conference on Titanium, Les Editions de
Physique 1988; 535.
[16] Nebe B, Lüthen F, Lange R, Becker P, Beck U and Rychly J. Materials Science and Engineering: C 2004; 25/5: 619-624.
[17] Song WH et al. Biomaterials 2004 ; 25 : 3341-3349.
[18] Liu X et al. Materials Science and Engineering R 2004; 47: 49-121.
[19] Gao Y, Luo E, Hu J, Xue J, Zhu S, Li J. Effect of combined local
tratment with zoledronic acid and basic fibroblast growth factor on
implant fixation in ovariectomized rats
[20] Tengvall P, Skoglund B, Askendal A, Aspenberg P. Surface immobilized bisphosphonate improves stainless-steel screw fixation in rats.
Biomaterials 2004; 25: 2133 – 2138