Zirconia doped with yttrium oxide has also been proposed as a substitute for alumina in the heads of osteoarticular prostheses. Important developmental studies have been made [CAL 95] and these heads have been commercialized. The main advantages of zirconia compared to alumina are a greater failure strength, mainly
bending strength, as well as a good resistance to fatigue [DRO 97]. These properties make the use of prostheses heads of very small dimensions possible, thus reducing the wear debris. Besides, zirconia has a better coefficient of friction and a better
wear resistance, despite the quite controversial results. One of the unknowns is the role of zirconia in the nucleation of calcium phosphates from supersaturated body fluids. Moreover, as we have mentioned, alumina has the advantage of a longer use
and currently gives satisfactory results.
12.2.2.4. Vitreous carbon and diamond carbon
Vitreous carbon has several interesting physicochemical and biological properties: it is light, resistant to wear and haemocompatible. It is essentially used for making cardiac valves and replaces natural valves taken from pigs which have a tendency to calcify and have a more limited life. Essential problems which remain are the formation of thromboses and bleeding due to the degradation of the junction between the prosthesis and the artery. Mechanical valves appear, however, to be tolerated in the long term [PET 99].
Diamond is an interesting coating from a biological point of view: it does not induce any cytotoxic or haemolytic effects and can be used for various vascular applications or in cardiac surgery [DIO 92].
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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