Effects of a Novel Calcium Titanate Coating on the Osseointegration Of

Jo-Young Suh Effects of a novel calcium titanate Oh-Cheol Jeung Byung-Ju Choi coating on the osseointegration of Jin-Woo Park blasted endosseous implants in rabbit tibiae

Authors’ affiliations: Key words: calcium titanate coating, hydroxyapatite blasting, osseointegration, rabbit Jo-Young Suh, Oh-Cheol Jeung, Jin-Woo Park, tibia, titanium implant Department of Periodontology, College of Dentistry, Kyungpook National University, Daegu, South Korea Abstract Byung-Ju Choi, Department of Dental Pharmacology, College of Dentistry, Kyungpook Objective: The purpose of this study was to investigate the effects of a nanostructured National University, Daegu, South Korea calcium coating on the surfaces of blasted Ti implants on peri-implant bone formation in the rabbit tibiae. Correspondence to: Professor Jin-Woo Park Material and methods: Threaded implants (3.75 mm in diameter, 6 mm in length) were Department of Periodontology roughened by hydroxyapatite (HA) blasting (control; blasted implants). The implants were College of Dentistry Kyungpook National University then hydrothermally treated in a Ca-containing solution for 24 h to prepare Ca- 188-1, Samduk 2Ga, Jung-Gu, Daegu 700-412 incorporated Ti surfaces (experimental; blasted/Ca implants). Surface characterizations South Korea were performed by scanning electron microscopy and stylus profilometry before and after Tel.: þ 82 53 660 6913 Fax: þ 82 53 427 3263 Ca coating. Forty-two implants (21 control and 21 experimental) were placed in the e-mail: [email protected] proximal tibiae of seven New Zealand White rabbits. Each rabbit received six implants. To evaluate the effects of the nanostructured Ca coating on the peri-implant bone-healing response, removal torque tests and histomorphometric analyses were performed 6 weeks after surgery. Results: The Ca coating did not significantly change the surface properties produced by blasting at the micron level. Histologically, active bone apposition was observed in the blasted/Ca implants in the marrow space. Compared with the blasted implants, the blasted/ Ca implants showed significantly increased bone-to-implant contact over the total implant length (Po0.01) and greater mean removal torque values (Po0.05). Discussion and conclusion: The nanostructured, Ca-incorporated surface significantly enhanced the peri-implant bone-healing response of HA-blasted Ti implants. It may be concluded that the use of nanostructured, Ca-coated surfaces may have synergic effects in enhancing osseointegration of blasted Ti implants due to their micron-scaled surface properties and biologically active surface chemistry.

The predictability and long-term success success is greatly affected by local bone rates of dental endosseous implants have conditions, such as bone quality and quan- Date: been well documented (Adell et al. 1990; tity. Today, with their rough surfaces, im- Accepted 20 April 2006 van Steenberghe et al. 1990); however, plants have achieved high success rates in To cite this article: high implant failure rates have been re- poor bone by enhancing osseointegration Suh J-Y, Jeung O-C, Choi B-J, Park J-W. Effects of a novel calcium titanate coating on the osseointegration of ported in areas of poor quality bone such via increasing bone-to-implant contact blasted endosseous implants in rabbit tibiae. as in the posterior maxilla (Jafﬁn & Ber- compared with implants with smooth sur- Clin. Oral Impl. Res. 18, 2007; 362–369 doi: 10.1111/j.1600-0501.2006.01323.x man 1991). It is well known that long-term faces (Wennerberg et al. 1998; Trisi et al.

362 c 2007 Blackwell Munksgaard Suh et al . Calcium coating promotes osseointegration

1999; Khang et al. 2001; Cochran et al. Ti substrates, several studies have been using a hydrothermal method. Surface 2002; Stach & Kohles 2003; Glauser et al. reported so far, such as hydrothermal treat- characterizations were performed to deter- 2005). ment, hydrothermal electrochemical mine whether altered micron-scaled sur- Numerous approaches have been tried in treatment (Yoshimura et al. 1995; Fujishiro face properties, including changes in sur- order to improve clinical results with poor et al. 1998), and sol–gel coating (Kaciulis face roughness due to coating procedures, local bone conditions and to shorten heal- et al. 1998; Manso et al. 2003). However, affect the corresponding results. Peri- ing periods. Many trials have focused on those methods seem difficult to apply to Ti implant bone responses were evaluated providing enhanced osseous stability by implants with microroughened surfaces by removal torque testing and histological improving the quality of early biological without alteration of micron-scale surface and histomorphometric evaluations after events at the bone–implant interface. It is properties including microarchitectures and 6 weeks of implantation in rabbit tibiae. well known that microroughness and an surface microroughness, because of their increase in the implant surface area pro- thickness (4 50 mm) and the size of Ca- duced by blasting and/or acid etching TiO3 crystals (1 10 mm) in the coatings. Material and methods enhance biomechanical bonding by Most recently, we revealed the possibi- optimizing the biological response of the lity of a novel nanostructured Ca coating of Titanium implants and calcium coating bone and micromechanical interlocking Ti implants preserving the original micron- Screw-type implants (n ¼ 48) with an ex- (Davies 1998; Lossdorfer et al. 2004; scale topography, related to biomechanical ternal diameter of 3.75 mm and a length of Szmukler-Moncler et al. 2004a). interlocking with bone tissue, as an effec- 6 mm were turned from commercially pure One of the strategies used to improve tive surface modification method for im- titanium rods (ASTM Grade 2) and the osseointegration is to make the bioinert proving osseointegration (submitted, surfaces were roughened by hydroxyapatite surfaces of metallic implants bioactive, 2007). We were able to observe the forma- blasting. Implants roughened with hydro- thereby favoring bone–tissue reactions at tion of crystalline CaTiO3 coating with xyapatite particles were used in this study the interface. Titanium (Ti) induces os- nanometer dimension (approximately to obviate surface contamination resulting seointegration and as such it is not bioac- 100 nm or less in size) on Ti substrates, from blasting processes using alumina par- tive. Titanium is generally considered to be without alteration of surface microstruc- ticles (MegaGen Co. Ltd., Kyungsan, bioinert and not likely to form direct bonds ture at the micron-scale level, by control- Korea; Szmukler-Moncler et al. 2004b). with bone, so various kinds of bioactive ling the reaction parameters during The implants were then passivated in nitric materials have been coated onto the sur- hydrothermal treatment. We expect that acid according to ASTM specification F-86 faces of Ti implants in order to provide this nanostructured Ca coating of Ti im- (blasted implant). The Ca-coated implants optimal surface reactivity. Hydroxyapatite plants may have advantages over other were prepared using hydrothermal treat- (HA) plasma spraying is the most fre- coating methods such as HA plasma spray- ment according to our previous study (sub- quently used coating method to produce ing to confer bioactivity to Ti implants mitted, 2007) (blasted/Ca implants). potentially bioactive implant surfaces, but without the thick layers common with Briefly, Ti implants were treated in a Ca- several problems, such as delamination and HA coating. Based on the results of earlier containing solution – a mixed solution of unpredictable biodegradation, have been studies, which reported enhanced bone 0.2 M NaOH and 2 mM CaO (Sigma Che- reported (Hanisch et al. 1997; Albrektsson formation on calcium phosphate-coated mical Co., St. Louis, MO, USA) dissolved 1998; Morscher et al. 1998). surfaces of implants when compared with in deionized water (Milli-Q Ultra-Pure, Recently, many studies have demon- commercially pure titanium surfaces (Cau- Millipore, Billerica, MA, USA) – using a strated the advantages of Ti implants in- lier et al. 1997; Karabuda et al. 1999), the Teflon-lined hydrothermal reactor system corporating calcium ions in enhancing bioactive surface chemistry of the Ca may (ILSHIN Autoclave Co., Ltd., Daejeon, osseointegration. Sul (2003) reported that provide potential synergic effects for peri- Korea) at 1801C for 24 h under a water Calcium-deposited Ti implants produced implant bone formation around endosseous vapor pressure of 1 MPa. We used these by micro-arc oxidation achieved biochem- Ti implants beyond the effects of the mi- reaction parameters in order to preserve ical bone bonding in an animal study. croscale surface topography. surface microstructure because the surface Several studies have reported that an in- The purpose of this study was to inves- structure demonstrated relatively smooth creased calcium (Ca) composition in the tigate the effects of a nanostructured Ca features at a more higher pressure; the outer oxide layer affected increased cell coating on the surfaces of Ti implants on thickness of the CaTiO3 coating increased adhesion by increasing protein adsorption peri-implant bone formation in the rabbit on increasing the concentration of NaOH onto Ti surfaces at physiologic pH (Elling- tibiae. Additionally, we investigated the in our previous study. After treatment, Ti sen 1991; Klinger et al. 1997). Webster et effects of micron-scaled surface properties implants were ultrasonically cleaned in al. (2003) reported that calcium titanate of implants in relation to biomechanical deionized water for 2 5min and then

(CaTiO3) promoted osteoblast adhesion, interlocking and bioactive chemical com- air-dried for 24 h. In this study, two groups and suggested CaTiO3 as a strong candi- position, and biochemical bonding with of implants were used: blasted implants as date for increasing osseointegration. They bone tissue on osseointegration of titanium the control, and blasted/Ca implants as the conﬁrmed the formation of CaTiO3 on the implants. experimental group. All implants were surfaces of Ti-coated HA discs annealed For this purpose, nanostructured Ca- sterilized by gamma irradiation before use. in air. To deposit CaTiO3 coatings on coated blasted implants were prepared To evaluate the crystalline structure and

c 2007 Blackwell Munksgaard 363 | Clin. Oral Impl. Res. 18, 2007 / 362–369 Suh et al . Calcium coating promotes osseointegration chemical composition of the Ti oxides after The implant site osteotomies were pre- inspection, and the surfaces of implants surface treatment, rectangular Ti samples pared in the usual manner. A final drill were observed by SEM for failure analysis. (20 10 1 mm) were treated in the diameter of 3 mm was used. All drilling manner described above. procedures were carried out under profuse Specimen preparation and histomorpho- sterile saline irrigation. Six screw-shaped metric evaluation Surface characterization implants were placed in one animal; a set The most proximal implant in each leg was The experimental and control implants of three control implants and a set of three selected for histomorphometric evaluation. were subjected to surface analysis. Surface experimental implants were randomly The proximal tibiae containing the im- morphology was observed by scanning placed in the right and left rabbit tibiae. plants were removed en bloc,fixedin4% electron microscope (SEM; S-4200; Hita- Blasted/Ca experimental implants (n ¼ 21) neutral-buffered formaldehyde, dehydrated chi, Tokyo, Japan) to evaluate the micron- and blasted control implants (n ¼ 21) were using an ascending series of alcohols, and scaled surface structure before and after the inserted with self-tapping. All implants embedded in methyl methacrylate for un- Ca-coating procedure. Implant surface penetrated the first bone cortex only. decalcified sectioning. Undecalcified cut- roughness measurement was performed After surgery, surgical sites were closed and-ground sections containing the central by stylus profilometry (Form Talysurf Ser- in layers and sutured using Vicryl (Ethicon, part of the implants were produced at a ies 2; Taylor Hobson, London, UK). Two of Somerville, NJ, USA). Antibiotics (Baytril; final thickness of 20 mmusingaMacro each implant were measured, and three Bayer Korea) and analgesics (Nobin; Bayer cutting and grinding system (Exakt 310 measurements were performed on each Korea) were injected intramuscularly for 3 CP series; Exakt Apparatebau, Norder- implant. All measurements were per- days to prevent postsurgical infection and stedt, Germany). The sections were stained formed at the lateral flat surface of the to control pain. The animals were killed by with toluidine blue, and histomorpho- lower part of the implants. The crystalline intravenous injection of air 6 weeks after metric analysis was carried out using a structure was evaluated by thin-film X-ray surgery and tissues were taken for removal light microscope (Axioplan 2; Carl Zeiss, diffractometry (XRD, X’Pert-APD; Philips, torque tests and histomorphometric eva- Oberkochen, Germany) with an image the Netherlands), and the surface chemical luation. analysis system (i-Solution, iMTechnology compositions of coating were analyzed by Inc., Daejeon, Korea) under 50 magni- X-ray photoelectron spectroscopy (XPS, Removal torque tests fication. The image was captured using a MT 500/1; VG Microtech Inc., UK) and Removal torque tests were performed to digital camera (AxioCam MRc 5; Carl Auger electron spectroscopy (AES, PHI 680 evaluate implant stability in the bone bed. Zeiss) attached to the microscope and dis- Auger Nanoprobe; Physical Electronics, The removal torque value in Newton cen- played on a computer monitor. The per- USA) using rectangular Ti samples. timeter (N cm) reflects the interfacial shear centage of bone-to-implant contact (BIC%) strength (Johansson et al. 1998). Two of the in the first three threads and the percentage Animals and surgical procedure distal implants from each leg were sub- of bone area inside the same threads were Seven adult male New Zealand White jected to removal torque testing (seven measured (seven rabbits; blasted/Ca experi- rabbits weighing 3–3.5 kg were used in rabbits; blasted/Ca experimental implants, mental implants, n ¼ 7; blasted control this study. This experiment was approved n ¼ 14; blasted control implants, n ¼ 14). implants, n ¼ 7). BIC% was measured as by the Institutional Animal Care and Use The implants were surgically exposed and the percentage of the length of bone in Committee of Kyungpook National Uni- implant removal mounts were securely direct contact with the implant surface. versity Hospital, Daegu, Korea. connected. The leg was stabilized and the We evaluated BIC% and bone area in the General anesthesia was induced by in- peak removal torque force was measured first three threads because the lower parts tramuscular injection of a combination of using a digital torque meter (MG series; of the implants were surrounded by the 1.3 ml of ketamine (100 mg/ml) (Ketara; Mark-10 Corporation, New York, NY, marrow space, in which bony structures Yuhan, Seoul, Korea) and 0.2 ml of xyla- USA) with a measuring range of 0– are almost absent. Additionally, the BIC% zine (7 mg/kg body weight; Rompun; 135 N cm. A single blinded examiner re- in the total length of the implant except the Bayer Korea, Seoul, Korea). The medial corded measurements of peak torque to apical part was measured. This is a useful surfaces of proximal tibiae were used as initiate reverse rotation. parameter in evaluating the osteoconduc- the surgical sites. The surgical areas were tivity of the implants, especially in the shaved and the skin was washed with a Surface analysis of the torqued implants marrow region. mixture of iodine and 70% ethanol before After removal torque tests, the implants surgical draping. Local anesthesia with were completely removed from the tibiae Statistical analysis 1 ml of 2% lidocaine (1 : 100,000 epinephr- and were ultrasonically cleaned in 5% The surface roughness value, removal tor- ine; Yuhan, Seoul, Korea) was adminis- sodium hypochlorite solution for 10 min que value, and histomorphometric data tered to control bleeding and to provide in order to remove the soft tissue and the were processed with the SAS statistical additional local anesthesia. Surgical sites nonattached bone. The implants were system. The significance of the differences were exposed with an incision through the fixed in 4% neutral-buffered formaldehyde, between the two groups was analyzed skin, fascia, and periosteum at the medial dehydrated using ascending series of alco- using Student’s t-test. P-values less than surface of proximal tibiae using sterile hols, and dried. The surface color of tor- 0.05 were considered to be statistically surgical techniques. qued implants was examined by optical significant.

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Results implants at a magniﬁcation of 1000 was observed on the surface of the blasted/ (Fig. 1a, c). Typical irregular indentations Ca implants (Fig. 1d). The XRD analysis Surface characteristics produced by blasting were observed on of the blasted/Ca samples exhibited a

SEM observation showed no micron-scale the surfaces of both groups of implants. set of peaks of reflection from CaTiO3 morphological differences between the sur- However, at a relatively higher magnifica- (JCPDS #22-0153; Fig. 2). The blasted faces of blasted implants and blasted/Ca tion ( 30,000), nanostructure formation surfaces consisted primarily of Ti and O. Carbon was detected as a surface contami- nant in the XPS survey spectra; no traces of Ca in the surfaces of blasted samples were detected. AES depth profiles showed a graded surface structure of a Ca-incorporated Ti oxide layer of the blasted/ Ca samples; the relative atomic concentration of Ca was approximately 40% at the outermost surface (Fig. 3). Based on profilometry, the mean values of the roughness parameters of the blasted/Ca implant surfaces were slightly lower than those of the blasted implants (Po0.05; Table 1).

Removal torque testing The mean removal torque of the blasted/ Ca implants was 42.3 7.9 N cm, significantly higher than that of the blasted implants (35.1 5.6 N cm; Po0.05).

Surface analysis of the torqued implants All torqued, experimental implants exhibited a homogeneous color of deep blue, Fig. 1. Scanning electron microscope images of blasted (a, b) and blasted/Ca (c, d) implants at magniﬁcations of 1000 (a, c) and 30,000 (b, d). Nanostructure formation (arrows) can be seen on the surface of blasted/ which was the same as that of original Ca implant (d). Scale bars ¼ 30 mm (a, c) and 1 mm (b, d). blasted/Ca implants produced by hydrothermal treatment in this study. In SEM observation, a considerable quantity of attached bone was observed on the surfaces of blasted/Ca implants, indicating that fracture had often occurred in the bone (Fig. 4b, c). In contrast, a very limited quantity of attached bone was observed on the surfaces of blasted implants (Fig. 4a) after thorough cleaning in sodium hypochlorite solution. These results indicate that active bone apposition with strong attachment was achieved on the surfaces of blasted/Ca implants in the medullary Fig. 2. X-ray diffraction pattern of a blasted/Ca sample. space, which may be the reason for the

Table 1. Surface roughness parameters of the implants (Mean SD)

Implant Ra (mm) Rq (mm) Rt (mm) RzDIN (mm) Sm (mm) Blasted 1.7080 0.1401 2.1989 0.2261 11.5765 0.8561 10.1375 1.0031 56.92 9.83 Blasted/Ca 1.3011 0.0720n 1.6797 0.1129n 9.4054 0.0894n 8.2917 1.0439 43.77 2.69

Ra , the arithmetic average of the absolute height values of all points of the proﬁle; Rq , the root mean square of the values of all points of the proﬁle; Rt ,the

maximum peak-to-valley height of the entire measurement trace; RzDIN , the arithmetic average of the maximum peak to valley height of the roughness,

values of five consecutive sampling sections over the filtered profile; Sm , the arithmetic average spacing between the falling flanks of peaks on the mean line. n significantly different between the two groups at Po0.05.

c 2007 Blackwell Munksgaard 365 | Clin. Oral Impl. Res. 18, 2007 / 362–369 Suh et al . Calcium coating promotes osseointegration

The lower threads were in contact with either newly formed bone or marrow tissue (Fig. 6). The blasted/Ca implants showed more active bone formation, and new bone was frequently observed in contact with the lower parts of most implants (in the medullary space). In contrast, very limited bone–implant contact was observed with the blasted implants.

Histomorphometric analysis The mean BIC% over the total implant length was 29 7.8% for the blasted implants, and 46.9 8.2% for the blasted/Ca implants. In the first three threads, the mean BIC% was 66.1 9.4% for the blasted implants, and 69.4 13.6% for the blasted/Ca implants (Fig. 7). Over the total implant length, the blasted/Ca implants showed a Fig. 3. Auger electron spectroscopy depth profile of a blasted/Ca sample (sputter rate at 23.8 nm/min significantly greater mean BIC% compared in SiO ). 2 with the blasted implants (Po0.01). There was no statistical difference when comparing the mean BIC% between the two groups in the first three threads (P40.05). Within the first three threads, the mean bone area percentage was 61.8 5.2% for the blasted implants, and 70.9 7.1% for the blasted/Ca implants (Fig. 7). There was a statistical difference between the two groups (Po0.05).

Discussion

In this study, Ca coatings induced active bone apposition on the implant surfaces in the medullary space, which is almost devoid of bony components, and resulted in an increased BIC% over the total length of Fig. 4. Scanning electron microscope images of torqued blasted (a) and blasted/Ca (b, c, d) implants at the implants, while the BIC% of the magnifications of 50 (a, b), 3000 (c), and 30,000 (d). Bars equal 1 mm (a, b), 10 mm (c), and 1 mm(d). blasted implants and blasted/Ca implants A considerable amount of attached bone (arrows) can be seen on the surface of blasted/Ca implant (b). The surface of blasted/Ca implant was filled with closely attached bone (asterisk); arrows delineate the borderline were similar within the first three threads. between attached bone and implant (c). These results were the same as those in earlier reported in vivo studies in which it was reported that the benefit of a bioactive higher removal torque value. No signs of Histological evaluation coating produced by hydroxyapatite plasma surface alteration after removal torque test- Six weeks after implantation, all implants spraying is maximized in spongy bone, ing were found at either the surfaces of the in the control and experimental groups with enhanced bone apposition not seen experimental or the control implants. The were histologically in direct contact with in cortical bone (Oonishi et al. 1989; torqued blasted/Ca implants showed the the surrounding bone along their upper Jansen et al. 1993). Therefore, these results original surface nanostructures (Fig. 4d), threads, with no signs of inflammation or indicate that the use of this type of indicating that CaTiO3 layer has relatively connective tissue interposition at the bone– Ca coating is expected to be most relevant good mechanical properties including coat- implant interface in the cortical region under conditions of poor quality bone, ing adhesion and mechanical strength. (Fig. 5). such as in areas of low bone content, where

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plant. However, many coating methods providing bioactivity to the metallic implants need a minimum coating thickness before bioactivity is seen, and these coatings obstruct the underlying micron- scale surface structure, a situation that is unavoidable with HA plasma spraying. The surface morphology of blasted/Ca implants and blasted implants was almost identical at the micron-scale level. The blasted/Ca implants showed slightly Fig. 5. Histological sections of blasted (left) and blasted/Ca (right) implants at equivalent thread positions smoother surfaces compared with blasted below the original cortex. In the blasted implant, incompletely mineralized osteoid matrix (arrow) can be seen implants (Ra 1.3 mm for blasted/Ca im- in contact with the implant surface. More mature bone can be seen in contact with the blasted/Ca implant. plants, 1.7 mm for blasted implants), and The distance between the threads is 600 mm (stained with toluidine blue). therefore the enhanced bone response to the blasted/Ca implants cannot be ex- plained by the effects of micron-scale surface properties. The possible explanation for this finding is that the Ca surface chemistry effectively influenced osseointegration. These results coincide with the findings of other studies, which reported that Ca-incorporated titanium implants showed rapid and strong osseointegration in animal models (Sul et al. 2002; Sul 2003; Jinno et al. 2004). The blasted/Ca implants showed higher Fig. 6. Histological sections of blasted (left) and blasted/Ca (right) implant 6 weeks after implantation in rabbit mean peak values for removal torque com- tibiae. The blasted/Ca implant shows active bone formation – new bone apposition can be observed on the lower part of the implant, located in the marrow space, which is devoid of surrounding bone. The distance pared with the blasted implants, which has between the threads is 600 mm (stained with toluidine blue). the slightly decreased value of Ra.The higher removal torque value may be inter- preted as an increase in the strength of bony thickness, have been claimed, which may integration at the bone–implant interface. cause some problems as delamination The increased mean peak removal torque (however, this is thickness and manufac- value of the blasted/Ca implants is prob- turer dependent; Hanisch et al. 1997; Bur- ably due to the surface Ca chemistry, gess et al. 1999; Sun et al. 2001). In which appeared to improve bone minerali- contrast to HA plasma-sprayed coatings, zation at the interface, and to the additional this type of Ca coating has several advan- effect of the increased BIC% in the marrow tages in terms of the mechanical properties space. of the coating itself. In particular, it does The nanostructured Ca coating used in not induce the activation of phagocytic this study may have several advantages in

Fig. 7. Mean percentage of the bone-to-implant con- cells by delaminated or dissolved HA par- enhancing the bone response around tact (BIC%) and bone area in the first three threads ticles from coatings, which may impede endosseous titanium implants. of implants. The BIC% was not significantly differ- bone healing and might initiate subsequent The surface has more abundant Ca ent between the two groups (P40.05). There was a cascades of bone resorption (Gottlander et compared with that reported in other stu- significant difference in bone area between the two n al. 1997; Sabokbar et al. 2001; Sun et al. dies (Ca 40% at the outer surface). Sul groups ( Po0.05). 2002). However, particulate-induced osteo- (2003) reported a maximum of 11% of Ca lysis has not been reported as a major incorporation into a Ti oxide matrix using an enhanced bone-healing response is re- finding in dentistry. Hayashi et al. (1994) micro-arc oxidation. It is believed that quired for successful osseointegration. reported that HA coatings enhance early integrin function is critically dependent It is known that calcium phosphate- bone growth on the surface of implants; on the concentration of divalent cations. coated implants induce faster bone forma- however, long-term stability depends on It may be possible that the increased tion. Nevertheless, some drawbacks of bone anchoring to micron-scale surface amount of Ca may facilitate integrin- plasma spraying associated with the lack structure. They suggested that bioactive mediated attachment of bone-forming cells of reproducibility in their coatings, such as coatings should be developed that do not through enhanced ligand binding of the phase composition, crystallinity, and obstruct the surface structure of the im- integrin receptor (Ajroud et al. 2004).

c 2007 Blackwell Munksgaard 367 | Clin. Oral Impl. Res. 18, 2007 / 362–369 Suh et al . Calcium coating promotes osseointegration

Nayab et al. (2005) reported that Ca im- effects on cultured osteogenic cells. It was Moreover, it is suggested that the use of plantation in Ti significantly affected the reported that the nanoscale surface struc- nanostructured Ca-coated surfaces may spreading of the MG-63 cells, both qualita- ture enhanced osteoblast adhesion and sub- have a synergic effect in enhancing osseoin- tively and quantitatively. They indicated sequent cellular function due to increased tegration of blasted Ti implants due to the that an increased dose of Ca enhanced the present optimal sites for osteoblast adhe- micron-scale surface properties and biolo- network of fibrillar processes between cells sion on the surface (Elias et al. 2000; gically active surface chemistry. However, and toward the Ti surface. Several studies Webster & Ejiofo 2004). The enhanced further studies are needed to better under- have suggested that an increased Ca com- early deposition of bone sialoprotein and stand the effects of this nanostructured Ca- position in the outer oxide layer increases osteopontin, containing RGD sequences, incorporated surface on bone responses. the adsorption of polyanionic proteins, in- on nanotextured Ti surfaces was reported cluding proteoglycans, onto Ti surfaces by in osteogenic cell culture (de Oliveira & ionic bonding at physiologic pH, which Nanci 2004). It may be considered that subsequently increases cell adhesion and nanoscale surface structures may provide provides nucleation sites for mineral for- a potential approach for enhancing peri- mation (Lindhe et al. 1989; Ellingsen 1991; implant bone responses in clinical use. Klinger et al. 1997). The increased amount However, more research is needed to pro- of Ca in the Ti oxide layer of the Ti vide a definite mechanism and confirm the implants may be the possible reason for results in vivo. the enhanced bone responses seen in this Although it is not clear which surface study. property – Ca chemistry or nanoscale sur- The coating preserves micron-scaled surface structure – more greatly affected the face properties, including microroughness enhanced quality and quantity of peri-im- and topography.Mostmethodsforprovid- plant bone formation around the blasted/ ing bioactivity to metallic implants need a Ca implants in this study, this coating minimum coating thickness to show bioac- layer positively increased the osteoconduc- tivity (Wolke et al. 1999). These coatings tivity of blasted Ti implants. The nanos- obscure the underlying micron-scale sur- cale surface structure also increases the face properties produced by surface pre- surface area, which subsequently increases treatment such as blasting and/or etching the area of the Ca coating exposed to the and related to biomechanical interlocking. biological environment and increases the The Ca-coating method used in this study reactivity of the implant surface, influen- produces the surface layer by a dissolution– cing the initial protein adsorption, subse- reprecipitation mechanism, not as a simple quent bone cell adhesion, and mineral additive coating (Eckert et al. 1996). This formation. This may be another reason may be the possible reason for the unique for the improved peri-implant bone re- surface characteristics of this coating layer, sponse, as measured by biomechanical with preservation of the microarchitecture. tests and histomorphometric evaluation. This Ca-coating method may be consid- Surface modification with a nanostruc- ered a promising approach of providing tured Ca coating could thus prove to be an bioactivity to endosseous Ti implants effective tool for improving bone formation with microroughened surfaces, replacing in vivo and the clinical efficacy of bioinert plasma-sprayed HA coatings. endosseous titanium implants. The coating layer has a surface nanos- In summary, the use of bioconductive tructure. Although there are no proven Ca coatings is expected to have advantages advantages for a surface nanostructure in in suboptimal situations involving poor- enhancing implant stabilization in clinical quality bone, such as in areas of low bone use, several in vitro studies reported that content, where an enhanced bone response nanotopography has significant biological is required for successful osseointegration.

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