This study analyzes the bone response to zirconia ceramic implants inserted in New Zealand white mature male rabbits. The implants were inserted into the tibia, and each rabbit received 4 implants. All the animals were euthanatized after 4 weeks. A total of 20 implants were retrieved. Implants and surrounding tissues were immediately fixed in 4% paraformaldehyde and 0.1% glutaraldehyde in 0.15 molar cacodylate buffer at 4°C and pH 7.4 to be processed for histology. The specimens were processed to obtain thin ground sections with the Precise 1 Automated System. The slides were observed in normal transmitted light under a Leitz Laborlux microscope. A great quantity of newly formed bone was observed in close contact with zirconia ceramic surfaces; in some areas, many osteoblasts were present directly on the zirconia. Percentage of bone-implant contact was 68.4% ± 2.4%. Mature bone, with few marrow spaces, was present. Small actively secreting osteoblasts were present in the most coronal and apical portions of the implant. No inflamed or multinucleated cells were present. This study concluded that these implants are highly biocompatible and osteoconductive.

RESEARCHBONE RESPONSE TO ZIRCONIA CERAMICIMPLANTS: AN EXPERIMENTAL STUDY INRABBITSAntonio Scarano, DDSFabio Di Carlo, DDSManlio Quaranta, MD, DDSAdriano Piattelli, MD, DDSKEY WORDSBone growthBone healingImplantsZirconiaAntonio Scarano, DDS, is a research fellowand Adriano Piattelli, MD, DDS, is aprofessor of Oral Pathology and Medicine inthe Dental School, University of Chieti, Chieti,Italy. Address correspondence to Dr Piattelli atVia F. Sciucchi 63, Chieti, Italy 66100 (e-mail:apiattelli@unich.it).Fabio Di Carlo, DDS, is a research fellow andManlio Quaranta, MD, DDS, is a professorof Prosthetic Dentistry in the Dental School,University of Rome, Rome, Italy.8 Vol. XXIX/No. One/2003This study analyzes the bone response to zirconia ceramic implants inserted inNew Zealand white mature male rabbits. The implants were inserted into thetibia, and each rabbit received 4 implants. All the animals were euthanatizedafter 4 weeks. A total of 20 implants were retrieved. Implants and surroundingtissues were immediately fixed in 4% paraformaldehyde and 0.1%glutaraldehyde in 0.15 molar cacodylate buffer at 48C and pH 7.4 to be processedfor histology. The specimens were processed to obtain thin ground sections withthe Precise 1 Automated System. The slides were observed in normal transmittedlight under a Leitz Laborlux microscope. A great quantity of newly formed bonewas observed in close contact with zirconia ceramic surfaces; in some areas,many osteoblasts were present directly on the zirconia. Percentage of boneimplantcontact was 68.4% 6 2.4%. Mature bone, with few marrow spaces, waspresent. Small actively secreting osteoblasts were present in the most coronaland apical portions of the implant. No inflamed or multinucleated cells werepresent. This study concluded that these implants are highly biocompatible andosteoconductive.and have excellent resistance to corrosionand wear, good biocompatibility,and high bending strength and fracturetoughness.2-9 Moreover, zirconiapossesses high fracture resistance dueto its energy-absorption property durpb are im nia Tlants.1 Zircobe usedplantsas dentalioinimertradiographs, and its ivory color, simiol zirconia (ZrO2), which can nia is radiopaque and clearly visibZirco- 4,10 umina. o ngth stre n be ) o 3 O (Al al suresochrbasableuminametal2oxidesrones.ding4 Zirconia ceramif alcs have twiceethnec oclini o m into ti par nal o tetrag o n r i b s e u in rialsIhNTRODUCTIONe familclydof ceramioinectmateningthe martensiticlesc transformantion oflar to the color of the natural tooth,6renders it extremely useful in aestheticallycritical areas of the mouth.10Also, zirconia can transmit light, whichmakes it an ideal candidate for use inaesthetic restorations.10 Zirconia ceramicshave been used as femoralheads in total hip replacement as analternative to metal devices, althoughsome researchers have reported poorperformance for zirconia heads comparedwith alumina femoral heads.11,12Microscopical studies in animalshave demonstrated that zirconia implantspossess good biocompatibility,and direct bone apposition to the implantwas observed in zirconia implantsinserted in monkeys5 with abone-implant contact percentage between66% and 81%. In a comparativestudy of unloaded and early loadedzirconia implants, Akagawa et al4found high bone-implant contact percentagein both groups, with no fi-brous tissues at the interface. The mechanicalproperties and the elasticmodulus of zirconia might also contributeto bone healing.4 The purposeof the present study was to analyze invivo cellular reactions and bone healingaround zirconia implants insertedin rabbit tibia.MATERIALS AND METHODSImplants made of zirconia ceramic(Norton Desmarquest, Evreux, France)were used in this study. The implantswere then passivated (ASTM A380)and cleaned using the following steps:water rinses, 3 ultrasonic cleaningsteps, additional water rinses, distilledwater agitation, alcohol agitation, andair-blown drying. Five New Zealandwhite mature male rabbits were usedfor this study. The implants were insertedinto tibia according to a previouslydescribed technique.13 Each rabbitreceived 4 implants, 2 in the left tibiaand 2 in the right tibia. A total of 20implants were inserted.The rabbits were anesthetized withintramuscular injections of fluanisone(0.7 mg/kg body weight) and diazepam(1.5 mg/kg body weight), and localanesthesia was given using 1 mL of2% lidocaine/adrenalin solution. Askin incision with a periosteal flap wasused to expose the tibia. The preparationof the bone site was done withburs under generous saline irrigation.The zirconia implant insertion wasperformed by hand. The periosteumand fascia were sutured with catgutand the skin with silk. There were nopostoperative complications or deaths;all animals were euthanatized with anoverdose of intravenous pentobarbitalafter 4 weeks.A total of 20 implants were retrieved.The implants and surroundingtissues were washed in saline solutionand immediately fixed in 4% paraformaldehydeand 0.1% glutaraldehyde in0.15 molar cacodylate buffer at 48C andpH 7.4 to be processed for histology.The specimens were processed to obtainthin ground sections with the Precise1 Automated System (Assing,Rome, Italy).14 The specimens were dehydratedin an ascending series of alcoholrinses and embedded in a glycolmethacrylateresin (Technovit 7200VLC, Kulzer, Wehrheim, Germany).After polymerization, the specimenswere sectioned along their longitudinalaxis with a high-precision diamonddisc at about 150 mm and grounddown to about 30 mm with a speciallydesigned grinding machine.A total of 3 slides were obtainedfor each zirconia implant. The slideswere stained with acid fuchsin and toluidineblue, then observed in normaltransmitted light under a Leitz Laborluxmicroscope (Leitz, Wetzlar, Germany)at magnifications of 350. Thepercentage of bone contact was calculatedusing a Laborlux-S light microscope(Leitz, Wetzlar, Germany)connected to a high-resolution videocamera (3CCD, JVC KY-F55B, JVC ProfessionalProducts, Milan, Italy) andinterfaced to a monitor and an IntelPentium III 1200 MMX (Intel IrelandLtd, Kildare, Ireland). This optical systemwas associated with a digitizingpad (Matrix Vision GmbH, Oppenweiler,Germany) and a histometrysoftware package with image-capturingcapabilities (Image-Pro Plus 4.5,Media Cybernetics, Inc, ImmaginiComputer Snc, Milan, Italy).RESULTSFrom a radiographic (Figure 1) andclinical (Figures 2 and 3) point of view,Antonio Scarano et alall implants appeared to be osseointegrated.No clinical signs of inflammationor mobility were present. It waspossible to observe the presence ofnewly formed bone trabeculae in directcontact with the implant surface (Figure4), but in a few areas unmineralizedmatrix was present. Newlyformed bone surrounded the implantsurfaces, and many osteoblasts secretingosteoid matrix were observed. Inother areas of the implant perimeter, itwas possible to observe the formationof osteoid matrix directly on the implantsurface (Figure 5). Resorption areasand inflammatory or multinucleatedgiant cells were not present.Percentage of bone-implant contactwas 68.4% 6 2.4%. No gaps or fibroustissue were present at the interface. Noforeign-body reaction was found at thebone-implant interface. No epithelialdowngrowth was observed at the interface.Wide marrow spaces were present,with some of them abutting onthe implant surface (Figure 6). Thenewly formed bone showed many viableosteocytes.DISCUSSIONCeramic implants have been demonstratedto be chemically stable, mechanicallyhard, and highly resistant todegradation. This combination of mechanicalproperties and excellent biocompatibilitymakes zirconia ceramicone of the best biomaterials for prostheticjoints, including hip joints.7 Zirconiamay have better affinity to bonetissue than other biocompatible ceramics.4 The values of elastic modulus ofzirconia are half that of single-crystalsapphire, which may contribute to biomechanicalintegration of the bone-implantinterface.6The addition of a fraction of zirconiato alumina resulted in a composite materialof increased toughness.15 In an experimentalstudy in minipigs, Schultze-Mosgau et al8 found that alveolar boneapposed exactly the steps and lacunaeon the surface of the implants, and theseauthors concluded that the interfacearound zirconia implants was similar toJournal of Oral Implantology 9BONE RESPONSE TO ZIRCONIA IMPLANTSFIGURES 1-3. FIGURE 1. Radiography of a retrieved zirconia implant inserted in rabbit tibia. FIGURE 2. Zirconia implant (Z) inserted inrabbit tibia after removal of the surrounding soft tissues. FIGURE 3. Cut surface of the implant and bone: the bone (arrow) is closelyadapted to the implant.that seen around titanium implants. Thebiocompatibility of zirconia ceramicswas investigated in vivo by implantingthem in bone and soft tissues; in zirconiaimplants inserted into subcutaneous tissue,only a small inflammatory cell infil-10 Vol. XXIX/No. One/200345 to 150 mm and as nonporous materials,into rabbit muscles. Histologicalanalysis of all the materials tested didnot reveal signs of toxic, immunological,oncogenic effects in vitro.7trate was found, and the implant wascompletely encapsulated by a thin fi-brous connective tissue.6 Hulbert et al16implanted discs and tubes of CaO 1Al2O3, CaO 1 TiO2, and CaO 1 ZrO2, as or carcinogenic effects.16 Zirconia has noporous materials with a pore size fromFIGURES 4-6. FIGURE 4. Newly formed bone (B) is in close contact with the implant surface (Z). No gaps or fibrous tissues are present atthe interface (Toluidine blue and acid fuchsin, original magnification 3100). FIGURE 5. Osteiod matrix is deposited directly on the implantsurface (arrow). Z 5 Zirconia implant (Toluidine blue and acid fuchsin, original magnification 3100). FIGURE 6. Newly formed bone (B)and wide marrow spaces are present at the bone-implant interface. Z 5 Zirconia implant (Toluidine blue and acid fuchsin, originalmagnification 3100).In our study, the presence of maturecompact lamellar bone and osteocytesnear the implant surface indicatedgood biocompatibility, and certainlythe presence of the implant didnot disturb the processes of bone formationat the interface. Dubruille et al1found that the mean percentage of implant-bone contact was better for ceramicimplants than for titanium im-Antonio Scarano et alplants. Our results confirm the data alreadyreported that the bone-implantinterface around zirconia implants issimilar to that observed around titaniumimplants. The surface of the zirco-Journal of Oral Implantology 11BONE RESPONSE TO ZIRCONIA IMPLANTSnia implants appeared to be highlybiocompatible, and no gaps, fibrous tissue,multinucleated cells, or inflammatorycell infiltrate were found at thebone-implant interface.ACKNOWLEDGMENTSThis work was partially supported bythe National Research Council (CNR),Finalized Project ''Materials Tailoredfor Advanced Technologies,'' PF MSTAII, Rome, Italy; and by the Ministry ofEducation, University, and Research(MIUR), Rome, Italy.REFERENCES1. Dubruille JH, Viguier E, LeNaour G, Dubruille MT, Auriol M, LeCharpentier Y. Evaluation of combinationsof titanium, zirconia, and aluminaimplants with 2 bone fillers in thedog. Int J Oral Maxillofac Implants. 1999;14:1-7.2. Rosengren A, Pavlovic E, OscarssonS, Krajewski A, Ravaglioli A,Piancastelli A. Plasma protein adsorptionpattern on characterized ceramicbiomaterials. Biomaterials. 2002;23:1237-1247.3. Jackson MC. Restoration of posteriorimplants using a new ceramicmaterial. J Dent Technol. 1999;16:19-22.4. Akagawa Y, Ichikawa Y, NikaiH, Tsuru H. Interface histology of unloadedand early loaded partially sta-12 Vol. XXIX/No. One/2003bilized zirconia endosseous implant ininitial bone healing. J Prosthet Dent.1993;69:599-604.5. Akagawa Y, Hosokawa R, Sato Y,Kameyama K. Comparison betweenfreestanding and tooth-connected partiallystabilized zirconia implants aftertwo years function in monkeys: a clinicaland histological study. J ProsthetDent. 1998;80:551-558.6. Ichigawa Y, Akagawa Y, NikaiH, Tsuru H. Tissue compatibility andstability of a new zirconia ceramic invivo. J Prosthet Dent. 1992;68:322-326.7. Covacci V, Bruzzese N, MaccauroG, et al. In vitro evaluation of themutagenic and carcinogenic power ofhigh purity zirconia ceramic. Biomaterials.1999;20:371-376.8. Schultze-Mosgau S, SchliephakeH, Radespiel-Troger M, Neukam FW.Osseointegration of endodontic endosseouscones: zirconium oxide vs titanium.Oral Surg Oral Med Oral PatholOral Radiol Endod. 2000;89:91-98.9. Josset Y, Oum'Hamed Z, ZarrinpourA, Lorenzato M, Adnet J, Laurent-Maquin D. In vitro reactions of humanosteoblasts in culture with zirconiaand alumina ceramics. J Biomed MaterRes. 1999;47:481-493.10. Ahmad I. Yttrium-partiallystabilized zirconium dioxide posts: anapproach to restoring coronally compromisednonvital teeth. Int J PeriodontRestor Dent. 1998;18:455-465.11. De Aza AH, Chevalier J, FantozziG, Schehl M, Torrecillas R. Crackgrowth resistance of alumina, zirconiaand zirconia toughened alumina ceramicsfor joint prostheses. Biomaterials.2002;23:937-945.12. Allain J, Le Mouel S, GoutallierD, Voisin MC. Poor eight-year survivalof cemented zirconia-polyethylene totalhip replacement. J Bone Joint Surg Br.1999;81:835-842.13. Piattelli A, Scarano A, PiattelliM. Detection of alkaline and acid phosphatasesaround titanium implants: alight microscopical and histochemicalstudy in rabbits. Biomaterials. 1995;16:1333-1338.14. Piattelli A, Scarano A, QuarantaM. High-precision, cost-effectivesystem for producing thin sections oforal tissues containing dental implants.Biomaterials. 1997;18:577-579.15. Affatato S, Testoni M, CacciariGI, Toni A. Mixed oxides prosthetic ceramicball heads. Part 1: effect of theZrO2 fraction on the wear of ceramicon polyethylene joints. Biomaterials.1999;20:971-975.16. Hulbert SF, Morrison SJ, KlawitterJJ. Tissue reaction to three ceramicsof porous and non-porousstructures. J Biomed Mater Res. 1972:6:347-374.