ABSTRACTImplants have been widely used indentistry since along time. Titanium and titanium alloys are a gold standardfor rehabilitation of edentulous spaces. However, with advancement intechnology and potential immunological and esthetic compromises with titaniumimplants need for neoteric material was perceived. The use of zirconia as analternative to titanium implants for oral rehabilitation is being considered aszirconia has better tissue acceptance and superior mechanical, biological andesthetic properties.
The following study aims to review clinical and researcharticles conducted on zirconia implants and their comparison with titaniumimplants and to analyze the creditability of zirconia implants over titaniumimplants as an alternative for rehabilitation.INTRODUCTIONThe rehabilitation of edentulous spacesin patients with an osseointegrated dental implant is a scientifically acceptedand well-documented treatment modality. Branemark in 1908, first discovered theconcept of osseointegration when blocks of titanium placed into the femur ofrabbit got ankylosed with the surrounding bone and could not be retrieved.Since then, numerous investigations and clinical studies have establishedtitanium as a reliable biomaterial for oral rehabilitation and reconstruction.Various modifications in the structure, composition, and design of titaniumimplants have been made since then to enhance its physical, mechanical andoptical properties 1–4.
However, the development of undesirableallergic reactions, cellular sensitization, galvanic current formation andaesthetics gray hue have raised demands for more aesthetic and biocompatibleimplant material 5–9. However, ceramics are known to be sensitive to shearand tensile loading, and surface flaws may lead to early failure. Theserealities imply a high risk for fracture 11.
Recently, high strength zirconiaceramics are considered as new materials for dental implants. They areconsidered to be inert in the body and exhibit minimal ion release compared withmetallic implants. Zirconia, is emerging as a promisingalternative to conventional titanium based implant system for oralrehabilitation with superior biological, aesthetic, mechanical and opticalproperties 10.However, it is important to understandthe similarities and differences between zirconia and titanium implant systemso as to enable the clinician to provide the best treatment outcomes for theirpatients. This review aims to analyze the reliability of zirconia as analternative to replace titanium based implant system.2.Material and methodsThis review started with a PubMed searchfrom 1975 to 2016.
The search was conducted using the following key words:zirconia or zirconium dioxide, dental, and implant. The full text of articleswas obtained where possible. If it was not possible to obtain a fulltext, the electronically available abstracts were collected.
Thus, theinclusion criteria for articles were as follows: (1) Articles were related tozirconia dental implants, and (2) abstracts were obtained when the full textscould not be obtained. Articles about zirconia implants for orthopedic usagewere excluded from the review.3.ResultsThe results will be discussed under thefollowing headings:a) Chemicalcomposition and structure of zirconia implantsb) Properties of zirconia implantsc) Osseointegrationand biocompatibility of zirconia implantd) Implanttissue compatibility and soft tissue healing around zirconia implantse) Clinicalstudies a) Chemicalcomposition and structure of zirconia implants:Theadvent of zirconia (ZrO2) as a high-performing ceramic has itsorigins in a classic paper by Garvie et al. (1975) and subsequent work ofothers in the materials science community. It has evolved into severalvariants, depending on powder selection, sintering additives, heat treatment,and other processing factors.
Three crystalline phases occur in zirconiaimplants: monoclinic (m), tetragonal (t) and cubic (c). The monoclinic phase ofZirconia exists at room temperature and is stable for up to 1170C.Above 1170C, the monoclinic phase changes to tetragonal phase with4-5% decrease in volume. At 2370C, the cubic phase starts appearing.
Upon cooling, a tetragonal to monoclinic transformation with a 3–4% increase involume takes place for about 1000C till 1070C. Thisincrease in volume and resultant expansion without a mass transfer upon coolinggenerates stress and causes it to become unstable at room temperature. Toprevent this phenomenon and to generate a Partially Stabilized Zirconia (PSZ)with stable tetragonal and/or cubic phases, various stabilizing oxides 16 mol%magnesia (MgO), 16 mol% of limestone (CaO) or 8 mol% Yttria (Y2O3)are added to zirconia implants. This martensitic-like phase transformationtoughening significantly increases the crack resistance, fracture toughness,and longevity of zirconia. (1). Aluminahas also been added to Yttria stabilized-tetragonal Zirconia polycrystal(Y-TZP) in low quantities (0.25 wt%) to yield tetragonal zirconia polycrystalwith alumina (TZP-A) with significant improvement in the durability andstability of zirconia crystals under high temperatures and humid environment.
This improves the resistance of implant to low temperature degradation (LTD)and “ageing”. Studies have shown that implants without alumina when exposed tothe artificial mouth have a survival rate of 50%, whereas implants with aluminahave a survival rate of 87–100%.12 b) Propertiesof zirconia implants:Themechanical and physical properties of zirconia implants depend upon itscomposition, nature of crystals, metastable polymorphic structure, ratio of themonoclinic to tetragonal phase, percentage of stabilizing metal oxide, ageingprocess, macro and micro design of the implant, nature of the finish line onthe implant abutment, characteristics of implant abutment, and amount ofocclusal load.
Though transformation toughening improves the fracture strengthand toughness of Y-TZP implant, it hampers the phase integrity and makes theimplant susceptible to LTD or ageing. An increase in moisture or stress cancause transformation of zirconia crystals to a monoclinic phase with microcrack formation that increases the water penetration, crack propagation,surface deterioration, phase destabilization and decreased resistance to load. Themacro design of zirconia implants such as the depth of thread, diameter, andimplant neck design of the implant are important criteria’s that should beevaluated before selecting a zirconia implants system. The thread design of theimplant plays a critical role in crack initiation and propagation. A profoundthread depth should be avoided as it may hinder bone clearance during thesurgical implant placement and generate unnecessary bending forces on theimplant body, especially in the patients with dense bone. Any sharp or pointedthread design with a narrow diameter, notched edges, minor scratches, and anysurface modifications including grinding, acid etching, sandblasting etc.
should be avoided to prevent local stress concentration, mechanical overloading,and subsequent implant fracture. Since mechanical overloading is considered asone of the main reasons for the implant fracture, zirconia implants with adiameter less than or equal to 3.25 mm are not recommended for clinical use. Animportant advantage of zirconia implant over titanium is in relation to itsexcellent aesthetics.
The optical behavior of zirconia varies with itscomposition, crystal size, grain distribution and methods of machining. Theenhanced aesthetics of zirconia is attributed its ability to mask darksubstrates with good opacity in the visible and infrared spectrum andcontrolled translucency. The masking ability is due to its grain size beinggreater than the length of light, high refractive index, low absorptioncoefficient, high density with low residual porosity (<0.05%) even in thinsections, the presence of various additives, stabilizers and pigments. c) Osseointegrationand biocompatibility of zirconia implants:Zirconia-basedceramics are chemically inert biomaterials with minimal local or systemicadverse reactions; good cell adhesion; excellent tissue response and a highdegree of biocompatibility with the surrounding bone and soft tissues. Animaland human clinical studies have evaluated and confirmed the deposition of newlyformed mature bone in close proximity to zirconia implant surfaces with fewmarrow spaces, minimal inflammation and numerous small actively secretingmultinucleated osteoblasts 14– 18. Various in vitro and in vivo studies haverevealed the osteoconductive nature of zirconia with no cytotoxic, oncogenic ormutagenic effects on the bone and fibroblasts after implantation into musclesor bones 16-22.
Scarano et al. demonstrated a good bone response to zirconiaimplants at four weeks with Bone to Implant contact (BIC) of nearly 68.4% 21.Dubruille et al. compared the BIC in titanium, alumina, and zirconia implantsand found no statistically significant difference between the three types ofimplants.
The BIC was found to be 68% for alumina, 64.6% for zirconia, and 54%for titanium. When osseointegration of zirconiaimplant is compared to titanium implant, minimal difference in the BIC anddistribution of stress patterns were observed 22 d) Implanttissue compatibility and soft tissue healing around zirconia implants:The bio-inert properties ofzirconia help in rapid proliferation of the human gingival fibroblasts over theimplant surface and formation of a good mucosal barrier 23.
However, variousfactors such as surface characteristics and design, nature of implant materialand degree of roughness influence the nature and amount of the mucosal sealaround zirconia implants. A smooth implant surface promotes a good soft tissueseal in comparison to a rough implant surface. Various differences have beenobserved in the peri implant mucosa around zirconia implants as compared totitanium. The expression of chemical mediators such as integrin alpha2,integrin alpha5 and type I collagen are found to be more up-regulated on smoothzirconia implants as compared to titanium. However, the pattern of connectivetissue adhesion and transgingival collar around zirconia implants is similar tothat seen around machined titanium surface (collagen fiber orientationpredominantly in a parallel oblique pattern).
The color of the peri implantmucosa, the amount of bleeding on probing and probing depth is similar aroundzirconia implants as compared to titanium implants. Zirconia implant has alsoshown to inhibit bacterial adhesion and biofilm formation on its surface becauseof its hydrophobicity, bio-inert properties, optimal smoothness, reducedsurface free energy and surface wettability 24-35. e) Clinical Studies:Three clinical studiesinvestigated zirconia implants. Blaschke et al reported that dental implants made from zirconia are a feasiblealternative to titanium dental implants. In addition to excellent cosmeticresults, zirconia implants allow a degree of osseointegration and soft tissueresponse that is superior to that of titanium dental implants. Oliva et al47reported the first clinical evaluation of 100 zirconia implants (CeraRoot,Barcelona, Spain) with 2 different surface roughness in humans after 1 year offollow-up. Two implants failed after15 days.
These failed implants were placedin situations where sinus elevation was required. The overall success rate wasreported as 98%. Given the sinus elevation requirement, future investigatorsmay exclude patients with less than 5 mm residual bone. Pirker et al48 placed azirconia implant to the maxillary first premolar region immediately andevaluated the clinical outcome of this implant. At 2-year follow-up, a stableimplant and an unchanged peri-implant marginal bone level were observed. Nobleeding was detected on probing.
4. Conclusion:Studies have proved zirconiaimplants is a potential alternative to titanium having better soft-tissueresponse, biocompatibility, and aesthetic with comparable osseointegration. Theearly fracture of zirconia implant, especially in the posterior region is acritical factor to be considered regarding its use and acceptance in allclinical situations. Since most clinical studies on zirconia implants areshort-term, substantial evidence supported by long-term clinical trials are requiredbefore zirconia based implant systems can completely replace titanium forprosthetic rehabilitation. Further research to prevent the ageing, improvingsurface characteristics, structure and osseointegration of zirconia implant areneeded. 5. REFRENCES:1GahlertM, Röhling S, Wieland M, Eichhorn S, Küchenhoff H, Kniha HA.
Biomechanical andhistomorphometric comparison between zirconia implants with varying surfacetextures and a titanium implant in the maxilla of miniature pigs. Clin OralImplants Res 2007;18:662–8.2Depprich R, Zipprich H, Ommerborn M, Naujoks C, Wiesmann HP, KiattavorncharoenSirichai, et al. Osseointegration of zirconia implants compared with titanium:an in vivo study. Head Face Med 2008;4:30.3Steinemann SG.
Titanium—the material of choice? Periodontol 2000 1998;17:7–21. 4Sykaras N, Iacopino AM, Marker VA, Triplett RG, Woody RD. Implant materials,designs, and surface topographies: their effect on osseointegra- tion. Aliterature review. Int J Oral Maxillofac Implants 2000;15:675–90.
5Bianco PD, Ducheyne P, Cuckler JM. Local accumulation of titanium released froma titanium implant in the absence of wear. J Biomed Mat Res 1996;31:227–34. 6Weingart D, Steinemann S, Schilli W, Strub JR, Hellerich U, Assenmacher J, etal. Titanium deposition in regional lymph nodes after insertion of titaniumscrew implants in the maxillofacial region. Int J Oral Maxillofacial Surg1994;23:450–2.7Lalor PA, Revell PA, Gray AB, Wright S, Railton GT, Freeman MA.
Sensitivity totitanium. A cause of implant failure? J Bone Joint Surg 1991;73:25–8.8Sicilia A, Cuesta S, Coma G, Arregui I, Guisasola C, Ruiz E, et al. Titaniumallergy in dental implant patients: a clinical study of 1500 consecutivepatients. Clin Oral Implants Res 2008;19:823–35.
9 TschernitschekH, Borchers L, Geurtsen W. Non-alloyed titanium as a bioinert metal—a review.Quintessence Int 2005;36:523–30. 10McLean JW. Evolution of dental ceramics in the twentieth century. J ProsthetDent 2001;85:61–6.11Yilmaz H, Aydin C, Gul BE. Flexural strength and fracture toughness of dentalcore ceramics.
J Prosthet Dent 2007;98:120–8. 12 K.Sivaraman, et al., Is zirconia a viable alternative to titanium for oralimplant? A critical review, J Prosthodont Res (2017)13ZhangY, Lawn BR. Novel Zirconia Materials in Dentistry. Journal of dental research.2017:2203451773748314 DeMedeiros RA, Vechiato-Filho AJ, Pellizzer EP, Mazaro JV, dos Santos DM, GoiatoMC. Analysis of the peri-implant soft tissues in contact with zirconiaabutments: an evidence-based literature review.
J Contemp Dent Pract2013;14(3):567–72. 15Akagawa Y, Ichikawa Y, Nikai H, Tsuru H. Interface histology of unloaded andearly loaded partially stabilized zirconia endosseous implant in initial bonehealing. J Prosthet Dent 1993;69:599–604.
16Nevins M, Camelo M, Nevins ML, Schupbach P, Kim DM. Pilot clinical andhistologic evaluations of a two-piece zirconia implant. Int J PeriodonticsRestorative Dent 2011;31:157–63. 17Stadlinger B, Hennig M, Eckelt U, Kuhlisch E, Mai R. Comparison of zirconia andtitanium implants after a short healing period: a pilot study in minipigs.
IntJ Oral Maxillofac Surg 2010;39:585–92. 18Depprich R, Ommerborn M, Zipprich H, Naujoks C, Handschel J, Wiesmann HP, etal. Behavior of osteoblastic cells cultured on titanium and structured zirconiasurfaces. Head Face Med 2008;4:29. 19Cranin AN, Schnitman PA, Rabkin SM, Onesto EJ. Alumina and zirconia coatedvitallium oral endosteal implants in beagles. J Biomed Mater Res 1975;9:257–62. 20Covacci V, Bruzzese N, Maccauro G, Andreassi C, Ricci GA, Piconi C, et al.
Invitro evaluation of the mutagenic and carcinogenic power of high purityzirconia ceramic. Biomater 1999;20:371–6.21Scarano A, Di Carlo F, Quaranta M, Piattelli A. Bone response to zirconiaceramic implants: an experimental study in rabbits. J Oral Implantol2003;29:8–12.
22Dubruille JH, Viguier E, Le Naour G, Dubruille MT, Auriol M, Le Charpentier Y.Evaluation of combinations of titanium, zirconia, and alumina implants with 2bone fillers in the dog. Int J Oral Maxillofac Implants 1999;14:271–7.23 WelanderM, Abrahamsson I, Berglundh T. The mucosal barrier at implant abutments ofdifferent materials.
Clin Oral Implants Res 2008;19:635–41.24Calvo-Guirado JL, Ramos-Oltra ML, Negri B, Delgado-Ruíz RA, Ramirez- FernándezP, MateSánchez JE, et al. Osseointegration of zirconia dental implants modifiedby femtosecond laser vs.
zirconia implants in healed bone: a histomorphometricstudy in dogs with three-month follow-up. J Osseointegr 2013;5:39–44. 25Nakazato G, Tsuchiya H, Sato M, Yamauchi M. In vivo plaque formation on implantmaterials. Int J Oral Maxillofac Implants 1989;4:321–6. 26Yamano S, Kwok-Yui Ma A, Shanti RM, Kim S-W, Wada K, Sukotjo C. The influenceof different implant materials on human gingival fibroblast morphology,proliferation, and gene expression. Int J Oral Maxillofac Implants2011;26:1247–55.
27Noro A, Kaneko M, Murata I, Yoshinari M. Influence of surface topography andsurface physicochemistry on wettability of zirconia (tetragonal zirconiapolycrystal). J Biomed Mater Res B Appl Biomater 2013;101:355–63.28Cionca N, Hashim D, Cancela J, Giannopoulou C, Mombelli A. Pro-inflammatorycytokines at zirconia implants and teeth: a cross-sectional assessment. ClinOral Investig 2016;20:2285–91.29Van Brakel R, Cune MS, van Winkelhoff AJ, de Putter C, Verhoeven JW, van derReijden W. Early bacterial colonization, and soft tissue health around zirconiaand titanium abutments: an In vivo study in man.
Clin Oral Impl Res2011;22:571–7.30Van Brakel R, Meijer GJ, Verhoeven JW, Jansen J, de Putter C, Cune MS. Softtissue response to zirconia and titanium implant abutments: an in vivowithinsubject comparison. J Clin Periodontol 2012;39:995–1001. 31Degidi M, Artese L, Scarano A, Perrotti V, Gehrke P, Piattelli A. Inflammatoryinfiltrate microvessel density, nitric oxide synthase expression, vascularendothelial growth factor expression, and proliferative activity inperi-implant soft tissues around titanium and zirconium oxide healing caps.
JPeriodontol 2006;77:73–80.32Rimondini L, Cerroni L, Carrassi A, Torricelli P. Bacterial colonization ofzirconia ceramic surfaces: an in vitro and in vivo study. Int J Oral MaxillofacImplants 2002;17:793–8. 33Salihoglu U, Boynuegri D, Engin D, Duman AN, Gokalp P, Balos K. Bacterialadhesion and colonization differences between zirconium oxide and titaniumalloys: an in vivo human study.
Int J Oral Maxillofac Implants 2011;26:101–7. 34Quirynen M, van der Mei HC, Bollen CM, Schotte A, Marechal M, Doornbusch GI, etal. An in vivo study of the influence of surface roughness of implants on themicrobiology of the supra and subgingival plaque.
J Dent Res 1993;72:1304–9. 35Nascimento CD, Pita MS, Fernandes FHNC, Pedrazzi V, de Albuquerque Junior RF,Ribeiro RF. Bacterial adhesion on the titanium and zirconia abutment surfaces.Clin Oral Implants Res 2014;25:337–43.