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ePaper created 2017-11-09, 09:28:26 | version 1.38.0
| research From titanium to zirconia implants Dr Sofi a Karapataki, Greece Zirconium is a metal with the atomic number 40. Zir- conium dioxide (ZrO2) or Zirconia is a ceramic material without any metal properties. It is electrochemically in- ert causing no galvanising or electro current disturbance effects at an inter- and intracellular level. It is the most bioinert and biocompatible material currently available in the market, with no detected allergies or intolerances. The material exhibits lower surface free energy that leads to hydrophilic reduced plaque (biofilm) accumulation, so, less inflammation is expected leading to superior soft tis- sue health. Zirconia fulfils highly desirable aesthetic results: healthy, pink and beautiful tissue can be created around an im- plant, with no tissue translucency. Its high aesthetics re- sembles natural tooth. Unlike titanium, it may stimulate bone growth in the long-term with ultimate osseointegra- tion for both bone and gum. In addition to the white co- lour, a low modulus of elasticity and thermal conductivity have made zirconia implants a very attractive alternative to titanium in implant dentistry.1–4 With its interesting microstructural properties, zirconia is the material of choice for the “new generation” of im- plants. Hashim et al. (2016) made a systematic review and evaluated the clinical success and survival rates of zirco- nia ceramic implants after at least one year of function- ing.5 They concluded that in spite of the unavailability of sufficient long-term evidence to justify using zirconia oral implants, zirconia ceramics could potentially be the alter- native to titanium for a non-metallic implant solution. This is also shown in the review made by Cionca et al. (2017), that through in vitro and in vivo studies, zirconia has man- aged to earn its place as a valuable alternative to titanium.6 Mechanical and physical properties Zirconia though, is a totally different material than tita- nium. The thorough knowledge of implantology using ti- tanium is not so easy to be transferred to zirconia, simply due to different physical and mechanical properties of the materials. Knowledge of the potentials of the material is the key of success and the only chance to minimise fail- ures. Zirconia (ZrO2) is a highly biocompatible material, but it needs to osseointegrate and withstand masticatory force without fracturing. A good product needs to be fab- ricated that would fulfil all the necessary requirements in order to be successfully implanted. ZrO2 is stable at room temperature at a monoclinic phase. Doped by yttrium oxide, when it cools down from 1,173 °C, a tetragonal phase stable at room tem- perature (metastable) is produced. This is the material used for implants. It is of major importance for the implant to be kept in the tetragonal phase to keep its mechan- ical and physical properties over time. It is well estab- lished that the stability of this phase is affected by several compositional parameters, including grain-size, process- ing conditions and quality control. Purity or rather contamination with impurities, density and porosity of the final product as well as pre-sintering and sintering process and time are also some of these parameters. Environment or conditions (loading-tempera- ture-humidity) in which the product will be used (it makes a difference whether zirconia is produced for a hip pros- thesis or for dental implants) are to be kept in mind. And last but not least, handling of the material is of outmost importance.7, 8 Lughi et al. (2010) suggested engineering guidelines for the use of zirconia as dental material.9 Producing zirconia implants There are two ways of producing zirconia implants: through moulding and through milling of prefabricated rods. The first method produces implants with specific shape and specific low roughness on their surface. Mill- ing of the rods on the other hand, is done either on par- tially or fully sintered zirconia. The fabrication of an im- plant through soft machining of partially sintered ZrO2 06 implants 1 2017 06 implants m o c . k c o t s r e t t u h S / r a T n v a N © i