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Effects of implant geometry, surface properties, and tgf-β1 on peri-implant bone response: an experimental study in goatsEffects of implant geometry, surface properties, and TGF-b1 on peri-implant J. J. J. P. van den BeuckenP. H. M. Spauwen bone response: an experimental study Authors' affiliations: Key words: calcium phosphate coating, electrostatic spray deposition, goat study, implant C. Schouten, G. J. Meijer, J. J. J. P. van den Beucken, J. A. Jansen, Department of Periodontology &Biomaterials, Radboud University NijmegenMedical Center, Nijmegen, The Netherlands P. H. M. Spauwen, Department of Plastic & Objectives: Despite the high success rates in implantology, the desire to use oral implants in Reconstructive Surgery, Radboud UniversityNijmegen Medical Center, Nijmegen, The more challenging clinical situations drives the need for continuing refinements in implant design and surface properties. In the present study, the effect of implant geometry on Correspondence to: implant bone response was evaluated using two geometrically different implant types, i.e.
screw type (St) and push-in type(Pi). Furthermore, the potential beneficial effect of an Department of Periodontology & BiomaterialsNijmegen Medical Center Radboud University electrosprayed calcium phosphate (CaP) coating, either or not enriched with the osteoinductive growth factor TGF-b1, on the osteogenic response was examined.
Material and methods: A total of 54 implants, divided into six groups (n ¼ 9), were inserted The NetherlandsTel.: þ 31 24 3614006 into the femoral condyles of nine goats. After an implantation period of 12 weeks, retrieved Fax: þ 31 24 3614657 specimens were evaluated histologically and histomorphometrically. Measurements were statistically evaluated using SPSS 14.0 and analyzed using a linear regression model.
Results: With respect to implant design, St-implants showed an overall superior biological healing response compared with Pi-implants. Considering surface properties, the deposition of an electrosprayed CaP (2–3 mm) coating onto implants significantly increased the amount of bone–implant contact for both implant types. Additional enrichment of the CaP coating with the osteoinductive growth factor TGF-b1 did not significantly affect peri-implant bone Conclusions: The results of this study indicate that a substantial improvement of the osteogenic response to titanium implants can be achieved by the deposition of an electrosprayed CaP coating. The enrichment of the coating with 1 mg TGF-b1 has only a marginal effect.
For decades, an uneventful healing period for et al. 1994; Testori et al. 2002; Del Fabbro several months has been advocated for oral et al. 2006), optimization of the initial bone- implants to avoid fibrous tissue formation, healing response after implant placement is which should result in an appropriate fixa- still an important issue. In addition, the tion of the implant within the native bone desire to use oral implants in more challen- tissue (Adell et al. 1981). As during this ging clinical situations drives the need for Date:Accepted 29 September 2008 healing period the implants should be pre- continuing refinements in implant design, vented from any form of loading, patients surface characteristics, and optimization of To cite this article:Schouten C, Meijer GJ, van den Beucken JJJP, Spauwen experience this ‘waiting period' as very in- the biological healing response following PHM, Jansen JA. Effects of implant geometry, surfaceproperties and TGF-b1 on peri-implant bone response: convenient (Gapski et al. 2003). Therefore, implant placement (Davies 2003).
an experimental study in goats.
despite the high clinical success rates of oral Over the last few decades, many differ- Clin. Oral Impl. Res. 20, 2009; 421–429.
doi: 10.1111/j.1600-0501.2008.01657.x implants (Albrektsson et al. 1988; Buser ent implant designs have been introduced 2009 The Authors. Journal compilation c 2009 John Wiley & Sons A/S Schouten et al . Effects of implant geometry, surface properties and TGF-b1 to optimize the anchorage of an implant in may result in coating delamination and bone tissue, i.e. the rapid achievement and fragmentation, thus influencing the long- maintenance of direct bone–implant contact term stability of the implants (Sun et al.
(Pilliar et al. 1991). Implant designs range 2001). Moreover, the crystallinity, composi- from threaded to non-threaded, cylindrical or tion, and thickness of the coatings are not conical, either or not combined with addi- uniform. Using the magnetron sputter tech- tional features, such as vents, grooves, in- nique, thinner (o5 mm), more dense and dentations, or perforations (Siegele & Soltesz adherent coatings can be obtained (Jansen 1989; Misch 1999; Sykaras et al. 2000; et al. 1993), but it is still challenging to vary Steigenga et al. 2003). Despite the available the coating composition. These problems data on the effect of single implant designs, can be overcome using the Electrostatic the number of studies that directly compare Spray Deposition (ESD) technique, which different implant geometries is limited.
is a simple and versatile technique that In addition to implant design, implant allows deposition of thin (2–3 mm) CaP surface properties are an important factor coatings with a wide variety of chemical Fig. 1. Representation of implant designs used in this in the biological healing response. Conse- (Leeuwenburgh et al. 2004, 2005) and study: Screw type (St; left) and Push-in (Pi; right).
quently, surface modifications represent a tool to enhance the biological response into burgh et al. 2005, 2006).
a desired direction. The main conse- Bone-healing responses can be further and with a smooth surface (Fig. 1) were quences of the available surface modifica- stimulated using appropriate growth factors provided by Dyna Dental Engineering BV tion techniques can be reduced to effects on (Fischer et al. 2003). Among these factors, (Bergen op Zoom, the Netherlands): surface topography (roughness or texture) or members of the TGF-b superfamily appear surface chemistry (or a combination thereof) to play the most critical role in bone heal- 4.2 mm; length: 10 mm) (Puleo & Thomas 2006). It has been claimed ing (Gombotz et al. 1993). For example, Cylindrical, Pi-implant with grooves that a certain degree of roughness leads to an TGF-b1 has been shown to stimulate bone (diameter: 3.6 mm; length: 10 mm) increased mechanical stability through sur- healing in several animal models (Joyce face enlargement and mechanical interlock- et al. 1990; Beck et al. 1998). Moreover, Recombinant human TGF-b1 was ob- ing with the surrounding bone (Shalabi et al.
previous studies have reported on the abi- tained from R&D Systems Inc. (Minneapo- 2006; Duyck et al. 2007). In addition, some lity of TGF-b1 to enhance bone healing lis, MN, USA). Fluorochromes Alizarin studies indicate that rougher surfaces in- around ceramic-coated implants in un- (Alizarin Complexon dehydrate), Calcein crease the degree and rate of peri-implant loaded gap-healing models (Sumner et al.
(Fluorexon), and Tetracycline were acquired bone formation (Puleo & Thomas 2006).
1995; Lind et al. 1996a, 1996b, 2001).
from Acros Organics (Geel, Belgium).
Regarding surface chemistry, beneficial In view of the described effects of im- effects on bone response have been ascribed plant design, surface properties, and enrich- to the deposition of ceramic materials, such ment with biologically active factors, the Electrostatic spray deposition (ESD) process as calcium phosphates (CaP) (Jansen et al.
present study aimed at evaluating these Before CaP coating deposition, implants 1991; Dorozhkin & Epple 2002) and bio- parameters in a comparative study design.
were cleansed ultrasonically in nitric acid glass (Turunen et al. 1998; Wheeler et al.
Therefore, two geometrically different den- 10% (15 min), acetone (15 min), and etha- 2001). These so-called ‘bioactive' materials tal implants [screw type (St) and push-in nol (15 min) successively. For CaP coating have the ability to bond bone directly, with- type(Pi)] were used in an implantation study deposition, a vertical ESD setup (Advanced out an intervening layer of soft tissue, in goats. Additionally, these implants were Surface Technology, Bleiswijk, the Nether- thereby making them suitable as coatings modified using an electrosprayed CaP coat- lands) was used, as described previously by onto bone-anchored implants (Ducheyne ing, either enriched or not with the osteoin- Leeuwenburgh et al. (2003). In brief, the et al. 1992; Dorozhkin & Epple 2002).
ductive growth factor TGF-b1. Implants basic principle of ESD is the generation of a Various techniques have been used to deposit were inserted into the trabecular bone at so-called electrospray of organic solutions CaP coatings onto an implant surface, the medial side of both femoral condyles containing the inorganic precursors Ca and among which plasma spraying and mag- for 12 weeks. Evaluation consisted of quali- P. This is accomplished by pumping this netron sputtering are the most widely used.
tative (histology and fluorochrome labeling) solvent through a nozzle, which is con- Although the osteoconductive and bone- as well as quantitative (histomorphometry) nected to a high-voltage supply. As a result bonding behavior of plasma-sprayed and analyses of the peri-implant bone response.
of the applied potential difference, a spray magnetron sputter coatings has been con- consisting of charged, micron-sized drop- firmed by numerous studies (Jansen et al.
lets is formed, which are attracted towards 1993; Dhert 1994; Hulshoff & Jansen 1997; Material and methods a grounded and heated substrate. Conse- Lacefield 1998, 1999; Geesink 2002), there quently, the droplets impinge onto the are still some important limitations related heated substrate, where they lose their to these techniques. Plasma-sprayed coat- Prototypes of two geometrically different charge. After complete solvent evapora- ings are relatively thick (430 mm), which oral implants, made of Ti-6AL-4V alloy, tion, a thin layer (2–3 mm) consisting of 422 Clin. Oral Impl. Res. 20, 2009 / 421–429 2009 The Authors. Journal compilation c 2009 John Wiley & Sons A/S Schouten et al . Effects of implant geometry, surface properties and TGF-b1 the inorganic product is left on the sub- Pi þ CaP þ TGF-b1 (Push-in type with strate surface.
a CaP coating loaded with TGF-b1).
In this study, implants were coated in three runs (in turns of 120 Sterility was obtained through autocla- each, at a substrate holder temperature vation of non-coated and CaP-coated im- plants. TGF-b1 enrichment of CaP-coated 1C, a nozzle-to-substrate distance of 20 mm, and a precursor liquid flow rate implants was performed after autoclavation of 2.0 ml/h. Coatings were prepared using under aseptic conditions.
precursor solutions with a Ca/P ratio of 1.8(Ca(NO3)2 4H2O and H3PO4 were precur- Surgical procedure sors for Ca and P, respectively). Subse- All in vivo work was conducted in accor- quently, all coated implants were subjected dance with ISO standards, and protocols of to an additional heat treatment for 2 h at the University Medical Center, Nijmegen, Fig. 2. Location of implant sites in the medial femoral 1C in order to transform the amorphous the Netherlands. National guidelines for condyle. The black bars represent the implants.
coatings into crystalline carbonated hydro- the care and use of laboratory animals were xyapatite (CHA) coatings (Siebers et al.
observed, and approval of the Experimental 2007). The morphology of the CaP coatings Animal Ethical Committee was obtained.
Table 1. Scheme for subcutaneous fluoro- was characterized using scanning electron A total of 54 implants (nine implants of chrome administration at timed intervals microscopy (SEM, Jeol, SEM6310, Tokyo, each experimental group; n ¼ 9) were im- Fluorochrome Color Japan). In addition, X-ray diffraction (XRD) planted into nine female Saanen goats (2–4 using a thin-film Philips X-ray diffrac- years of age), with a mean body weight of tometer (PW3710, Almelo, the Nether- about 50–60 kg. Surgery was performed lands) and Fourier Transform Infrared under general inhalation anesthesia and Spectrometry (FTIR; Perkin Elmer Instru- sterile conditions. To reduce the peri- ments, Zoetermeer, the Netherlands) were operative infection risk, the prophylactic used in order to characterize the crystal antibiotic Albipen was administered sub- structure and the molecular structure of cutaneously (Albipen 15%, 3 ml/50 kg pre- the deposited coatings, respectively.
operative and Albipen LA, 7.5 ml/50 kg for three holes were made on the medial side of 3 days post-operative, Intervet BV, Boxm- the condyle (proximal, medial, and distalwith an interimplant distance of 1 cm).
eer, the Netherlands). Anesthesia was For growth factor loading, TGF-b1 was initiated by an intravenous injection of After preparation, the holes were irrigated dissolved in sterile 4 mM HCl containing (AUV Wholesale, Cuijk, and the implants were inserted. In each 1 mg/ml bovine serum albumin (BSA; the Netherlands). Subsequently, the goats femur, three implant sites were located, Sigma Aldrich, Zwijndrecht, the Nether- were intubated and connected to an inhala- resulting in six sites per goat (Fig. 2). To lands). Administration was achieved by tion ventilator with a constant volume of a ensure complete randomization, the im- direct adsorption of the growth factor onto mixture of nitrous oxide, isoflurane, and plants were placed according to a balanced the CaP-coated implants. Aseptic condi- oxygen. Before the insertion of the im- split-plot design. However, to avoid cross- tions were maintained throughout the plants, each animal was immobilized on over effects, all implants containing TGF- adsorption process. A volume of 6 ml of its back and the hind limbs were shaved, b1 were grouped together and placed in left the HCl/BSA solution (containing 1.0 mg washed, and disinfected with povidone– femurs only. After insertion of the im- TGF-b1) was pipetted onto each implant.
iodine. For implantation of the implant in plants, the soft tissues were closed in After loading, implants were immediately the femur, a longitudinal incision was separate layers, and the skin was closed made on the medial surface of the left and transcutaneously using resorbable Vicryl 1C for 1 h, and placed in a 24-well plate for overnight lyophilization.
the right femur. Subsequently, landmarks 4 0 sutures (Ethicon Products, Amers- were placed in the femoral condyle, and a foort, the Netherlands). To reduce pain radiographic image was made to localize after surgery, all goats received Finadyne Experimental animal groups the trabecular bone. After exposure of the (AUV Wholesale, Cuijk, the Netherlands) In the animal study, a total of six different femoral condyle, a 2 mm pilot hole was for 2 days postoperatively. Postoperative experimental groups were used: drilled, which was gradually widened with radiographs were conducted to check 1. St (Screw type), non-coated; drills of increasing size until the final implant placement.
2. St þ CaP (Screw type with a CaP diameter was reached. The final drill, For dynamics of bone growth, four goats re- both the St and the Pi implants had a ceived sequential fluorochrome labels at 1, 3. St þ CaP þ TGF-b1 (Screw type with a diameter of 4 mm. The bone defect pre- 6, 9, and 11 weeks postoperatively (Table 1).
CaP coating loaded with TGF-b1); paration was performed with a gentle sur- All labels were administered subcuta- 4. Pi (Push-in type), non-coated; gical technique, using low rotational drill 5. Pi þ CaP (Push-in type with a CaP speeds (800–1200 rpm) and continuous At 3 months postimplantation, euthanasia external cooling with saline. In this way, was performed with an overdose of 2009 The Authors. Journal compilation c 2009 John Wiley & Sons A/S 423 Clin. Oral Impl. Res. 20, 2009 / 421–429 Schouten et al . Effects of implant geometry, surface properties and TGF-b1 Nembutal , and the implants with sur- the implant: for the St-implant, starting at rounding tissue were retrieved for histolo- the first coronal screw thread, and for the Pi- gical evaluation.
implant, starting at the beginning of the firstconcave thread (total standardized distance of interest of 4000 mm).
After the animals were sacrificed, thefemoral condyles were retrieved, excess Fluorochrome labeling tissue was removed, and, using a diamond For fluorochrome labeling analysis, a circular saw, the condyles were divided reflectant fluorescence microscope was into smaller specimens suitable for histo- used (Leica Microsystems AG). In addi- logical processing. Finally, each specimen tion, a Zeiss filter No. 05, consisting of a contained only one implant with surround- 395–440 nm band-pass excitation filter, Fig. 3. Scanning electron micrograph of the porous ing bone. Subsequently, the tissue blocks was used for visualization of the different CaP coating as deposited using electrostatic spray were fixed in 10% neutral-buffered forma- deposition (ESD).
lin solution, dehydrated in a graded seriesof ethanol (70–100%), washed with acet- Statistical analysis one, and embedded in methyl methacrylate Measurements were statistically evaluated retrieved and used for histological and for 4 weeks. After polymerization, non- using SPSS 14.0 (SPSS Inc., Chicago, IL, USA). Data obtained with histomorphome- (10–20 mm) of the implants were prepared try regarding bone–implant contact were implants implants implants (at least three of each implant), using a analyzed using a linear regression model.
retrieved used for modified sawing microtome technique The dependent variable was represented by (van der Lubbe et al. 1988), and stained ‘bone contact,' whereas the independent with methylene blue and basic fuchsin.
variables were represented by ‘implant Specimens from the four goats that design', ‘presence of CaP,' and ‘presence received fluorochromes were processed of TGF-b1.' Using this model, the effect of to obtain both unstained and stained the independent variables on bone–implant contact could be evaluated. The signifi- cance level was set at a probability (P) value nDuring implantation one St þ CaP þ TGF-b1 smaller than 0.05.
implant was lost, and replaced by one To evaluate the trabecular bone response to wDuring explantation one non-coated the implants, histological as well as histo- Pi-implant could not be retrieved.
zDuring histological preparation one morphometrical analyses were performed.
Coating characterization non-coated St-implant, one St þ CaP þ TGF-b1, Histological evaluation using a light micro- SEM observations showed a uniform sur- one Pi þ CaP, and one Pi þ CaP þ TGF-b1 scope DMRD (Leica Microsystems AG, face coverage of the implant. The electro- implant were damaged.
Wetzlar, Germany) consisted of a concise sprayed CaP coatings revealed a porous, description of the observed tissues reaction, reticular surface morphology (Fig. 3). Heat including the structure and arrangement of treatment increased coating crystallinity number of implants placed, retrieved after cells, implant, and tissue–implant inter- and yielded in a CHA structure as con- implantation, and included in the histolo- face. In addition, a computer-based image firmed with XRD and FTIR (data not gical and histomorphometrical analyses.
analysis technique (LEICA QWIN PRO- shown). Additionally, XRD measurements Of the 54 installed implants, a total of 53 IMAGE analysis software; Leica Imaging showed reflection peaks of TiO implants could be retrieved. One implant Systems, Cambridge, UK) was used for was not found during retrieval. Throughout 1 2y for heat-treated CaP histomorphometrical evaluation. The quan- coatings, which were absent in non-heat- the histological processing, five implants titative measurement was performed for treated CaP coatings. The coatings were were damaged, and hence not included for three different sections per implant, on crack free after the heat-treatment at analyses. A total of 48 implants were used each side of the 2D histological image. The for analyses.
average of these six measurements was usedfor statistical analysis. The quantitative Descriptive histological evaluation parameter assessed was the bone–implant Light microscopic examination of the contact (at magnification 25). Therefore, All nine goats remained in good health the amount of bone contact was defined as during the experimental period without sections of the implants and its surround- the percentage of implant length at which any postoperative wound-healing compli- ing tissue demonstrated that one of the there is direct bone-to-implant contact with- cations. At sacrifice, no signs of inflamma- implants (non-coated Pi) was inserted out intervening soft tissue layers. Measure- tion or adverse tissue reaction could be seen very close to the growth plate cartilage, ments were performed along the length of around the implants. Table 2 depicts the but no contact between the implant and 424 Clin. Oral Impl. Res. 20, 2009 / 421–429 2009 The Authors. Journal compilation c 2009 John Wiley & Sons A/S Schouten et al . Effects of implant geometry, surface properties and TGF-b1 the growth plate was seen. Also, for an-other implant (St þ CaP þ TGF-b1), in-flammatory the implant surface. Generally, in allsections, bone apposition, bone remodel-ing, and ingrowth of newly formedbone into the threads of the implantswere observed.
In all St-implants, except for one, a close contact between the implant and surround-ing bone was observed. The screw threadswere almost completely filled with bone(Fig. 4, St-implants), but around one non-coated St-implant, an intervening fibroustissue layer was present at the crestal areaof the implant. In the sections of four Fig. 4. Representative histological sections of Screw-type (St) and Push-in (Pi) implants after 12 weeks of Pi-implants (three non-coated, and one implantation in the femoral condyles of goats.
CaP coated), a gap was observed betweenthe surrounding bone and the implant sur-face (Fig. 4, Pi-implants), resulting in noimplant–bone contact at all. In all other Pi-implants a close bone-to-implant contactwas observed.
For all St- and Pi-implants, except for one, the CaP-coated equivalents, whetheror not enriched with TGF-b1, showeda close bone-to-implant contact (Fig. 4,CaP coated implants). In these sections,the presence of bone on top of the threadand conducting over the implant surfaceinto the threads was observed.
Fig. 5. Fluorescence microscopy images of histological sections of fluorochrome-administered experimentalanimals. Colors indicate bone formation at 1 (blue; calcein blue), 6 (red; alizarin-complexon), 9 (green; calceingreen), and 11 (yellow; tetracycline) weeks post-implantation.
Fluorescence microscopyConsecutive fluorochrome markers, laiddown in the form of bands, were observedaround the implants in the sequenceof their administration (Fig. 5a and b).
In contrast to the labels, alizarin com-plexon (red), calcein (green), and tetracy-cline (yellow), the presence of the calceinblue label, administered 1 week afterimplantation, could not be clearly identi-fied.
Detailed observation of the images showed the yellow line to be very close tothe implant surface and bone marrowspaces in the trabecular bone, and the greenand red lines more towards the peripheralareas (away from the implant surface) withabout equal distances between the lines.
Fig. 6. Fluorescence microscopy images of histological sections of fluorochrome-administered experimental This band formation was absent in images animals. The color indicates bone formation at 9 weeks post-implantation (green; calcein green). Images of the non-coated groups.
indicate bone formation predominantly in the implant vicinity.
Fluorochromes in the non-coated groups of both implant types, i.e. St and Pi,showed a less intense fluorescence signal TGF-b1 or not (Fig. 6a and b). In general, a more pronounced signal was seen at sites The results of the bone–implant contact groups, i.e. CaP coated, enriched with where new bone was formed.
measurements and the outcome of the 2009 The Authors. Journal compilation c 2009 John Wiley & Sons A/S 425 Clin. Oral Impl. Res. 20, 2009 / 421–429 Schouten et al . Effects of implant geometry, surface properties and TGF-b1 roborates published data of other experi-ments, in which different animal modelswere used (Steigenga et al. 2003; Watzaket al. 2005). An explanation for the higherimplant–bone contact for St-implants isthat, relative to their length, St-implantsoffer the surrounding bone a larger surfacearea compared with Pi-implants. Moreover,the manufacturer's recommendations forinsertion of the St-implants actually involvescrewing implants into an undersized defect,whereas the advice for Pi-implants is to pushthe implants into an oversized defect. Con-sequently, the placement of St-implants isassociated with shear forces at the interface, Fig. 7. Results of histomorphometric analyses of Screw-type (St) and Push-in (Pi) implants in femoral condyles hence loosening small bone fragments.
of goats. Bone-implant contact of St- and Pi-implants after 12 weeks of implantation is displayed for thedifferent experimental groups. Bars represent the mean þ standard deviation. No interaction between the These bone fragments are likely to be experimental variables was found. Significantly higher bone implant contact for St-implants compared with Pi- pressed in between the trabecular voids and implants. nSignificantly different compared with non-coated controls.
in between the screw threads during implantplacement, enhancing new bone formation(Shalabi et al. 2006). In addition, during Table 3. Bone contact percentages and statistical testing of the experimental variables implant placement, a degree of compression Bone-implant contact 95% Confidence Interval will take place along the implant–bone inter-face, which further enhances implant stability (O'Sullivan et al. 2004). When such an undersized approach is used for Implant design (Pi ¼ 1, St ¼ 0) CaP (with ¼ 1, without ¼ 0) cylindrical Pi-implants, there may be an TGF-b1 (with ¼ 1, without ¼ 0) increased risk of (i) failing to place the implant fully into the drill hole and (ii) Indicates statistically significant effect (Po0.05).
CaP, calcium phosphate; TGF-b1, transforming growth factor-b1.
detrimental effects of bone tissue compres-sion, potentially causing local cellular da-mage, resulting in cell death, necrosis, and statistical analyses are depicted in Fig. 7 The results of this study showed a signifi- ultimately bone resorption (O'Sullivan et al.
and Table 3, respectively. Considering cant effect on the bone-healing response 2004). Because of the visco-elastic properties geometry, a significantly higher (12.5%) of both implant geometry and CaP of bone, an oversized bone cavity is always bone–implant contact was observed for coating, whereas additional enrichment of drilled for cylindrical implants, implicating St-implants compared with Pi-implants CaP-coated implants with TGF-b1 did less primary stability as compared with (P ¼ 0.004). Furthermore, surface modifi- not further enhance peri-implant bone To improve bone–implant contact, bio- coating showed a significantly higher A prerequisite for successful orthopedic active materials, such as CaP ceramics, (19.7%) bone contact (Po0.001) compared and dental implant placement is to obtain have been used successfully. These materials with their non-coated equivalents. The a good primary stability of the implant in the are characterized by their potential to form a enrichment of CaP-coated implants with surrounding bone (Albrektsson et al. 1981).
very tight, chemical bond with the surround- TGF-b1, however, was not statistically The establishment of such a mechanically ing bone, i.e. ‘bone–bonding' (Ducheyne significant (8.0%; P ¼ 0.147) compared stable interface prevents the development et al. 1992). Because of their favorable bio- with CaP-coated implants.
of an intervening layer of fibrous tissue logical behavior, bulk CaP ceramics have (Shalabi et al. 2006). In view of the currently been widely used in the orthopedic and available implant systems, it needs to be dental field. As bulk materials, however, emphasized that the degree of primary the mechanical properties of CaP ceramics stability, besides bone quality, largely are too weak, limiting their use in load- The aim of this study was to evaluate depends on implant design and insertion bearing situations. Consequently, CaPs are the effect of implant geometry on bone- modality. For this reason, the current study applied as coatings onto mechanically strong healing responses in an in vivo goat included two geometrically different implant (metallic) implants. Numerous studies have femoral condyle model. Furthermore, the designs (St; Pi). With respect to implant already confirmed the osteoconductive and potential beneficial effect of an electro- geometry, the results of this study indicate bone–bonding behavior of CaP coatings (Jan- sprayed CaP coating, enriched or not with that bone–implant contact is superior for sen et al. 1991; Hulshoff & Jansen 1997).
TGF-b1, on bone healing was evaluated.
St- over Pi-implants. This observation cor- Similar positive data were obtained in an 426 Clin. Oral Impl. Res. 20, 2009 / 421–429 2009 The Authors. Journal compilation c 2009 John Wiley & Sons A/S Schouten et al . Effects of implant geometry, surface properties and TGF-b1 animal gap study, showing that gaps of the combination of TGF-b1 with a non- phate-coated implants. Loading an electro- 1 mm can only be bridged by bone if a coated implant was not included. It should sprayed b-tricalcium phosphate coating with CaP coating is applied, whereas uncoated be realized that most growth factors, includ- TGF-b1 also resulted in a burst release of implants demonstrated no bone contact at all ing TGF-b1, are very expensive. Only a 490% (Siebers et al. 2006). Analogous to (Clemens et al. 1997).
significant extra effect, beyond the effect of this relatively fast and almost complete in Various deposition methods have been a CaP coating alone, may value these high vitro release of TGF-b1, the release in the proposed to apply CaP coatings onto im- costs. To prove such an effect, only the current study may have resulted in subopti- plants, among which plasma spraying and combination of CaP-coated implants and mal amounts of TGF-b1 both spatially and magnetron sputtering are the most widely TGF-b1 was selected. Over the last decade, temporarily. Therefore, the need for a slow used. A major drawback of both coating several studies have been performed to eva- and more gradual release still exists and has techniques is the lack of control over the luate the effects of TGF-b1 in vitro and in to be investigated. A possible solution can be final coating composition and morphology.
vivo, which obtained rather mixed results.
found by the incorporation of the growth Consequently, promising CaP phases, like For example, 2 mg TGF-b1 applied in a 3% factor into the carrier material, as proposed carbonate apatite, which comprise a chemi- methylcellulose gel was able to regenerate a by Liu et al. (2004), who incorporated BMP- cal composition closest to bone and teeth, critical-size defect in a rabbit skull within 28 2 during the deposition of a biomimetic cannot be deposited (Jansen et al. 1993; De days; 0.1- and 0.4 mg showed less bone for- CaP coating onto a titanium implant by Groot et al. 1994; Leeuwenburgh et al.
mation (Beck et al. 1991). In a non-critical- co-precipitation. More research is needed to 2004). To overcome these problems, the size rabbit skull model, the combination of a find a suitable technique for the incorpora- ESD technique was used in the present Ti fiber mesh implant with 2 mg TGF-b1 tion of biologically active compounds in study to deposit carbonated apatitic CaP induced orthotopic bone formation (Vehof order to create a more gradual release, or an coatings. Leeuwenburgh et al. (2003) al- et al. 2002). Further, in a canine model, optimized combination of a burst and sus- ready confirmed the feasibility of the ESD porous coated implants showed a more tained release profile.
technique for the deposition of thin CaP effective bone ingrowth with a dose In summary, this study demonstrates coatings with a defined surface morphology, of 120 mg TGF-b1, compared with a dose of that the peri-implant healing response fol- by varying the deposition parameters. More- 335 mg TGF-b1 (Sumner et al. 1995). In the lowing implant placement is dependent on over, by varying the Ca/P precursor solution present study, no significant effects of TGF- both implant design and surface modifica- ratio, and applying an additional heat treat- b1 on bone healing were observed. The tion. With respect to implant design, ment, this technique is able to control the reason for this lack of beneficial effects of St-implants show an overall better bio- coating composition and crystallinity (Leeu- TGF-b1 remains unclear. A possible expla- logical healing response over Pi implants.
wenburgh et al. 2004). Despite the im- nation may be the dose–response effect for Considering surface modification, the de- proved mechanical strength and interfacial TGF-b1. However, as shown in the available position of an electrosprayed CaP coating adhesion, no data are available yet that can literature, higher doses do not necessarily onto implants significantly increased the provide information regarding whether the generate more bone formation, as there is an amount of bone–implant contact. Further, coating remains stable after implantation.
optimum dose. Therefore, in the present enrichment of the CaP coating with the However, the observed biological response study, it was decided to load the implants osteoinductive growth factor TGF-b1 did in the present study proves that during the with 1 mg TGF-b1. In addition to the dose- not show an additional effect on peri-im- initial bone-healing process, the CaP coat- response effect, data have been published plant bone response. The results of this ing exerted its biological effect by enhancing suggesting a positive correlation between study consequently indicate that a substan- the bone formation around the implanted the in vivo osteoinductive activity of TGF- tial improvement of the osteogenic re- materials. Additionally, as a result of the b1 and the amount of protein retained at the sponse to titanium implants can be heat-treatment, oxidation of the titanium site of implantation. Consequently, if less obtained by the deposition of an electro- substrate occurred, which was demon- growth factor is retained, a higher dose is sprayed CaP coating. The enrichment of strated through XRD analysis. Although the coating with 1 mg TGF-b1 has only a the authors are aware of the effects of heat- response. Although growth factor retain- marginal effect.
treatment on the mechanical properties of ment was not assessed in this study, the titanium, the current study did not evaluate amount of TGF-b1 remaining on the im- this parameter.
plants in the present study might have been In addition to the deposition of a CaP below the optimal osteoinductive level. Sev- would like to acknowledge Dr E.M.
coating, the potential beneficial effect of eral in vitro studies have been performed to Bronkhorst for his assistance with the TGF-b1 on the peri-implant bone response determine the release characteristics of TGF- statistical analyses, and Dyna Dental was also evaluated in this study. It is recog- b1. For instance, a burst release of 70% of Engineering BV (Bergen op Zoom, nized that TGF-b1 might have effects in the TGF-b1 was observed from a titanium fiber the Netherlands) for providing the vicinity of the implant; however, thorough mesh implant (Vehof et al. 2002). Lind et al.
implants. This study was financially histological observations did not support this (1996b) found a burst release of 80% of supported by the Dutch Program for suggestion. With respect to the study design, TGF-b1 adsorbed onto tricalcium phos- Tissue Engineering (DPTE; NGT. 6730).
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UNIVERSITE LUMIERE LYON II - 2006-2007 Institut d'Etudes Politiques de Lyon Mémoire de fin d'études : Section Relations Internationales La gouvernance du VIH/Sida en Thaïlande : Etude du réseau PHPT (Program for HIV Prevention and Treatment) Soutenu le 6 juin 2007 Directeur de mémoire : Gwenola Le Naour séminaire gestion des risques et politiques publiques