As indicated in Chapter 2, simple oxides were a primary focus of the
development of modern bioceramics in the late 1960’s (Hulbert et al. 1982-83). The development of dense, high-purity (>99.5%)Al2O3 structural ceramics by sophisticated sintering technology was well established by that point, and Al2O3 was the first bioceramics widely used clinically. (Hench 1993).
Alumina ceramics are used for orthopaedic surgery as hip prostheses and in dentistry as dental implants. Their widespread use is based on a combination of good strength, modest fracture toughness, high wear resistance, good biocompatibility and excellent corrosion resistance. In addition to the polycrystalline, sintered aluminas, some dental implants have been fabricated from single-crystal sapphire. To ensure maximum strength and fracture toughness, materials processing is critical. It is desirable to maintain an average grain size less than 4 ?m and a chemical purity greater than 99.7%. Similarly, the extremely low coefficient of
friction and wear rate for alumina is dependent on a small grain size combined with a narrow grain-size distribution. The inherently high level of chemical inertness is, of course, intimately associated with the successful performance of alumina in regard to corrosion resistance and biocompatibility. Experience with alumina in orthopaedic surgery for more than twenty years demonstrates its high degree of biocompatibility.
More specifically, alumina is associated with minimal scar formation , scar formation prevents the mechanical bonding of bone to a porous implant surface.
The specifics of hip replacement surgery will be described . In essence, the natural ball-and-socket geometry of the hip is replaced by synthetic materials. In Europe, both the ball and socket are often fabricated of alumina. This design is stimulated by the exceptionally low friction and wear of the alumina-on-alumina system. To properly utilize these properties, the ball and socket must have a high degree of sphericity which is produced by grinding and polishing the mating surfaces together. The wear rate in this system can be ten times lower than that of the conventional metal alloy ball against a polymeric socket.
Although well-engineered alumina/alumina ball-and-socket systems in Europe have demonstrated long-term performance
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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