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ePaper created 2017-11-09, 09:28:26 | version 1.38.0
| technology Shifting of dental implants through ISO standards Dr Aous Dannan, Richard Donaca & Philipp Rausch, Germany The introduction of cylindrical endosseous implants to dentistry have had a significant effect on restorative treat- ment planning.1 These advances can also affect treat- ment planning for teeth requiring endodontic treatment.2 The long-term success of titanium osseointegrated im- plants in periodontally healthy patients has been doc- umented in various studies.3 However, additional data are still needed to confirm the long-term predictability of dental implants in general. tal implants is not a frequent phenomenon, it can cause unfavourable clinical results. Green et al. reported a frac- ture of a dental implant four years after loading.13 The failure analysis of this implant revealed that the fracture was caused by metal fatigue and that the crown-metal, a NiCrMo alloy, exhibited corrosion. In another study, Yokoyama et al. concluded that titanium in a biological environment absorbs hydrogen and this may be the reason for delayed fracture of a titanium implant.14 Titanium as dental implant material Dental ceramics Titanium and titanium alloys are commonly used as dental implant materials. The process of integration of titanium with bone has been firstly termed by Brånemark4 as “osseointegration”. Currently, most of the commer- cially available implant systems are made of pure tita- nium or titanium alloy. Titanium and its alloys provide strength, rigidity, and ductility similar to those of other dental alloys. Whereas, pure titanium castings have me- chanical properties similar to type III and type IV gold alloys. Titanium and its alloys give greater resistance to corrosion in saline and acidic environments. However, even though titanium alloys were exceptionally corro- sion-resistant because of the stability of the TiO2 oxide layer, they are not passive to corrosive attack.5 Moreover, one of the most renowned problems regarding titanium is hypersensitivity.6, 7 Some reports have considered titanium hypersensitiv- ity as a risk factor in dental implant failure.8, 9 Even though titanium has been used as a biomaterial for more than 50 years, several reports have identified its potential tox- icity. Sakellariou and colleagues reported postoperative spinal infection due to titanium spinal implants.10 Simi- larly, Hettige and Norris documented a case of mortality after a suspected fatal local allergic response of the brain to a titanium cranioplasty.11 Patients sensitive to metals such as nickel, aluminium, or cobalt appear to be more susceptible to titanium-hypersensitivity reactions, and special care should be taken in the selection of implant biomaterial for such patients.12 Another relevant problem related to titanium dental im- plants is the potential fracture. Although fracture of den- Porcelain has been used in dentistry for 100 years. Aesthetics is the major advantage of porcelain, and brit- tleness is its weakest point for load-bearing restorations. Therefore, porcelain-fused-to-metal restorations to make “metal-ceramic restorations” have been the first choice of prostheses to satisfy requirements for aesthetics, dura- bility, and fit to the abutments.15, 16 Two main types of all-ceramic fixed dental prosthe- sis systems are proposed. The first system involves us- ing a single material for full-contour crowns. Reinforced glassy materials were successfully used to make sin- gle crowns for anterior and premolar regions. Inno- vatively, polycrystalline zirconia with improved trans- lucency has been used for full-contour crowns in the molar region.17 The second system is to fuse aesthetic ceramics, such as porcelain and other glassy materials, to frameworks made of high-strength ceramics instead of alloys. Dense sintered polycrystalline zirconia- based material is promising for frameworks of fixed dental prostheses.18 Industrial dense polycrystalline ceramics such as alumina, zirconia, and alumina-zirconia composites are currently available for use with CAD/CAM technol- ogy via a networked machining system. In particular, Yttrium partially-stabilised Tetragonal Zirconia Poly- crystalline (Y-TZP) shows better mechanical properties and superior resistance to fracture. Y-TZP has a high fracture toughness, from 5 to 10 MPa m1/2, and a flex- ural strength of 900 to 1,400 MPa.19, 20 The positive clin- ical performance of Y-TZP has been recently confirmed through several reports.21, 22 34 implants 1 2017