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ePaper created 2017-11-09, 09:28:26 | version 1.38.0
| technology Fig. 4 Fig. 4: Eight electronic components can be integrated into the control unit DORA CONTROL. and, even more important, accelerate the aging kinet- ics.55 Therefore, ISO 13356 does not account for the real transformation rate of samples with roughened surface and a non-porous bulk, whereas ISO 14801 requires a dynamic loading procedure subjecting the implants to different loads, to finally obtain a fatigue resistance curve.56 Regrettably, only the latter standard evaluates the “market-ready” product but it misses to provide any environmental condition that induces aging. Since complex geometries, manufacturing procedures and surface modifications of zirconia oral implants are known to compromise the original mechanical material properties and aging kinetics measured by the use of bending bars or discs,57 long-term thermomechanical loading in a hot aqueous environment of the finally de- signed implant should be mandatory before its market re- lease. This method validates the functionality and safety of the product prior to the clinical application. Otherwise, the patient might be the one who suffers from poten- tially predictable early fatigue. Y-TZP is prone to low tem- perature degradation (LTD; “aging”) in presence of water vapour.58 Aging can result in intergranular micro-crack- ing, surface-roughening and, up from a certain level, in reduced strength.59 To simulate intraoral aging to the extent possible and, in particular, address the degradation susceptibility of metastable zirconia ceramics, an experimental setup by Spies et al. (2016) tried to add some modifications that differed from ISO 14801.54 The mentioned norm does not include horizontal loading components or degrada- tion accelerating environmental factors. By placing the samples of the mentioned study in a warm fluid of 60 °C during the dynamic loading procedure, the applied test- ing protocol was designed to account for the specific nature of zirconia ceramics and its behaviour in aque- ous environments. Furthermore, ISO 14801 dictates the simulation of a 3 mm bone recession. According to a clinical observation,60 the implants of the investigation by Spies et al. were embedded simulating 0.5 to 1 mm of bone recession. Moreover, the authors wanted the area assumed to be the most fragile (i.e. the transition zone from abutment to implant) near the point of entry to the embedding material, since maximum loads occur in this zone.40 Therefore, the calculated pure fracture load val- ues of the final static loading test were not comparable to other investigations adapting ISO 14801. More recently, Spies et al. (2017) conducted a study aiming at investigating a new testing protocol considering environmental conditions adequately inducing aging during dynamic fatigue when using zirconia dental implants.61 It was shown that phase transformation was only detect- able after hydrothermally induced aging. Strength of the investigated zirconia prototype implant was not reduced by aging, fatigue or simultaneous treatment. However, in- creased fracture load of solely dynamically loaded implants indicated localised stress-induced transformation. The au- thors argued that the presented protocol might serve as a reference for the discussion on how to specify the current testing standards. In another important trial to enhance the testing condi- tions of ISO 14801, Castolo et al. (2017) tried to use finite element analysis to assess the influence of design pa- 38 implants 1 2017