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Implant Tribune Middle East & Africa Edition No. 2, 2018

D2 ◊Page D1 closest match to the original missing tooth (Figs. 9–11). This tooth design is then positioned digitally within an e.max meso block. This meso block has a predetermined hole within it that acts as the access hole for the screw-retained crown, as well as the orifice into which a TiBase will be bonded (Fig. 12). This restoration is then milled from Fig. 21 IMPLANT TRIBUNE Dental Tribune Middle East & Africa Edition | 2/2018 the low translucency monolithic e.max CAD Block in its purple phase (taking around 18 minutes) and checked for precision of fit on the TiBase (Figs. 13 & 14). It is tried in intraorally to assess contacts and occlusion in static and dynamic function (Figs. 15 & 16). The restoration is then stained us- ing Ivoclar e.max Crystall Glaze so as to provide an aesthetically har- monious restoration and glazed with Glaze Spray. It is placed in an Ivoclar Vi- vadent Programat CS2 fir- ing furnace for 15 minutes to crystalise the ceramic, turning it from purple to tooth-coloured (Fig. 17). The ceramic restoration is then bonded onto the TiBase extraorally. The fit surface of the ceramic is treated with 5 % Hy- drofluoric acid and silanated with Monobond Plus (Ivoclar Vivadent). The TiBase is sandblasted and also silanated. Finally, the ceramic and TiBase are bonded with multilink hy- brid resin cement (Ivoclar Vivadent; Figs. 18–21). Following the bonding, the restora- tion is steam cleaned to remove any residue. The final restoration (Fig. 22) is now ready to be inserted, approxi- mately 2 hours after the patient ar- rived in the practice (Fig. 23). The restoration is finally torqued down to 25 Ncm. Following this, occlusion is rechecked, but no ad- justment is required at this stage following the try-in adjustments. PTFE is placed in the access cavity and the access hole filled with opa- cious composite (OMC Venus Pearl) and stained with Venus tints (Figs. 24–26). In conclusion, as you can see in the final result (Figs. 27–29) an aesthetic, biologically designed and durable restoration has been fabricated. The patient has been delivered the final restoration in a single visit without the need for traditional analogue im- pressions. Editorial note: A list of references is available from the publisher. The article was originally published in CAD/CAM International Magazine 2/2017. Dr Simon Chard BDS(Hons) BSc(Hons) qualified with Hon- ours from King’s Col- lege London Dental Institute in 2012. He is director of member- ship for the British Academy of Cosmetic Dentistry, was voted the Best Young Den- tist in the Dentistry Awards 2015 and is a member of the Association of Dental Implantology. Dr Chard is very passionate about providing beautiful, healthy smiles for his patients and is a big promoter of using digital technology to simplify cos- metic and implant dentistry. Dental education is something that is a major part of his professional career and he has dedicated thousands of hours to advanced training from the best dentists around the world. Fig. 22 Fig. 23 Fig. 24 Fig. 25 Fig. 26 Fig. 27 Fig. 28 Fig. 29 From titanium to zirconia implants By Sofia Karapataki, Greece Zirconium is a metal with the atom- ic number 40. Zirconium dioxide (ZrO2) or Zirconia is a ceramic ma- terial without any metal properties. It is electrochemically inert causing no galvanising or electro current disturbance effects at an inter- and intracellular level. It is the most bioinert and biocompatible mate- rial currently available in the market, with no detected allergies or intoler- ances. The material exhibits lower surface free energy that leads to hy- drophilic reduced plaque (biofilm) accumulation, so, less inflammation is expected leading to superior soft tissue health. Zirconia fulfils highly desirable aes- thetic results: healthy, pink and beau- tiful tissue can be created around an implant, with no tissue translucency. Its high aesthetics resembles natural tooth. Unlike titanium, it may stimu- late bone growth in the long-term with ultimate osseointegration for both bone and gum. In addition to the white colour, 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 inter- esting microstructural properties, zirconia is the material of choice for the “new generation” of implants. Hashim et al. (2016) made a system- atic review and evaluated the clinical success and survival rates of zirconia ceramic implants after at least one year of functioning.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 alternative 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 managed to earn its place as a valu- able alternative to titanium.6 Mechanical and physical properties Zirconia though, is a totally different material than titanium. The thor- ough knowledge of implantology using titanium is not so easy to be transferred to zirconia, simply due to different physical and mechanical properties of the materials. Knowl- edge of the potentials of the mate- rial is the key of success and the only chance to minimise failures. Zirconia (ZrO2) is a highly biocompatible ma- terial, but it needs to osseointegrate and withstand masticatory force without fracturing. A good product needs to be fabricated that would ful- fil 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 sta- ble at room temperature (metasta- ble) is produced. This is the material used for implants. It is of major im- portance for the implant to be kept in the tetragonal phase to keep its mechanical and physical properties over time. It is well established that the stability of this phase is affected by several compositional parame- ters, including grain-size, processing conditions and quality control. Purity or rather contamination with impurities, density and porosity ZrO2 is a highly biocompatible material that needs to osseointegrate and withstand masticatory force without fracturing. of the final product as well as pre- sintering and sintering process and time are also some of these param- eters. Environment or conditions (loading-temperature-humidity) in which the product will be used (it makes a difference whether zirconia is produced for a hip prosthesis or for dental implants) are to be kept in mind. And last but not least, han- dling of the material is of outmost importance.7,8 Lughi et al. (2010) sug- gested engineering guidelines for the use of zirconia as dental material.9 Producing zirconia implants There are two ways of producing zir- conia implants: through moulding and through milling of prefabricated rods. The first method produces im- plants with specific shape and spe- cific low roughness on their surface. Milling of the rods on the other hand, is done either on partially or fully sintered zirconia. The fabrication of an implant through soft machining of partially sintered ZrO2 provides the advantage of easier milling than the fully sintered ZrO2. It requires less milling time and causes less wear of the cutting tools.10, 11 In hard machining of fully sintered ZrO2, no sintering shrinkage is ex- pected and there is no need for a sin- tering oven. However, microcracks maybe introduced.10 Since diamond zirconia is known as the toughest material existing, only diamond tools are used for cutting sintered zirconia. The grinding of the fully sintered ZrO2 causes a certain degree of transformation (from tetragonal to monoclinic phase) in the surface of this material.12 When comparing the final surface of the soft machined ZrO2 to the hard machined ZrO2, it is expected that the former will have a more consistent final state, given that it is left intact (no sandblasting or grinding) after the final sintering.13 The implants that are produced need to be roughened in order to be osse- ointegrated. Question arises what is the optimal roughness and surface that is produced after it, in order for zirconia implants to be successfully osseointegrated in any of the afore- mentioned production methods. It seems that the rougher the body, the better the odds for osseointegra- tion.14 This though should not be the goal for the head of the implant in case that it is visible in the mouth— it could favour bacteria colonisation. The best method to achieve the op- timal roughness as well as the mo- ment that this should be realised with respect to the material’s prop- erties is also not established. Finally, depending on the procedure, the roughened surface needs to be to- tally clean, free of all foreign bodies. Ageing of titanium vs zirconia Ageing of titanium implants is a not widely known phenomenon and starts four weeks after their produc- tion which decreases dramatically the osseointegration potential.15–18 Ageing of zirconia (Low Temperature Degradation LTD, i.e. the slow trans- formation of the metastable tetrago- nal crystals to the stable monoclinic structure in the presence of water or water vapour) on the other hand is quite well investigated. ÿPage D3

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