In the first few days after surgery, all implants are subjected to attacks from cells in charge of defending the integrity of the organism (multinucleate giant cells, macrophages, monocytes, etc.). The main cell involved in this degradation is the macrophage. They are cells which can, initially, create detrimental conditions of pH and oxidation for materials. It has thus been shown that ceramics in bioactive calcium phosphates deposited on metallic
in the first few days after the implantation. These phenomena however stop naturally when these implants are not toxic in nature and do not generate particle inflammation. However, in the opposite case, the local inflammatory reaction can take place and deteriorate the implant and neighboring biological tissues.
12.3.3.4. Toxicity of constituting elements
Several elements present in ceramics, either as impurity or as constitutive elements, may cause toxicity. It is customary to distinguish essential trace elements, oligoelements necessary for the life, from toxic trace elements. It appears, however, that all these elements have different toxic limits. The latter are difficult to
determine in an absolute manner and in the case of implanted substances, the local effect on tissues should be distinguished from the remote effect of the implant on other tissues or organs (Table 12.2).
The toxicity of alumina, lead, arsenic, mercury and cadmium are well documented. These studies however often relate to the elements ingested in nutriments. Very few studies have been made on the toxicity of elements associated
with implants and in their immediate neighborhood and the standards in vigor are not often based on any experimental data.
The solubility of phases and their reactivity in a biological environment is evidently a determining factor. Thus, for example, alpha alumina implants have never shown toxicity associated with aluminum, despite the large quantities of aluminum introduced into the organism, while degradable glasses containing smaller
proportions of aluminum may considerably impair the formation of bone tissue [NIZ 99]. Similarly, fluorapatite, which is very insoluble, does not induce any negative reaction despite
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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