Calcium phosphate-based ceramics constitute, at present, the preferred bone substitute in orthopedic and maxillofacial surgery. They are very similar to the mineral phase of the bone, by their structure and/or their chemical composition. Calcium phosphates usually found in ceramics are:
– hydroxyapatite (HAP): Ca10(PO4)6(OH)2;
– tricalcium phosphate ? (? TCP
These ceramics are bioactive and can be degraded to various degrees.
The stoichiometric HAP, characterized by an atomic ratio Ca/P = 1.67 and a hexagonal structure, is the nearest relative of biologic apatite crystals. Moreover, the HAP is the least soluble and the least resorbable calcium phosphate. When an HAP ceramic is implanted in a bone site, the bone tissue formation is observed on its contact (osteoconduction) . Besides, in certain conditions, calcium phosphate ceramics can induce the formation of bone tissue in ectopic sites. HAP implants appear in the form of dense ceramics or with variable porosity or again, in the case of prostheses, as thin coatings deposited by plasma sprayed on a metal The ? TCP, characterized by an atomic ratio Ca/P = 1.5, is perfectly biocompatible and bioresorbable. Like HAP, it is capable of developing a chemical bond with the bone and to stimulate its growth, but its resorption is more rapid. It is difficult to make pure HAP or ? TCP and biphasic materials HAP-? TCP have been developed initially by accident and later deliberately; they combine the physicochemical properties of each of the compounds. These can be advantageously used to prepare materials with controlled resorption and bone substitution .
The presence of pores in materials provides anchor points for the bone and improves the mechanical quality of the bone/implant interface; the increase in the specific surface further encourages cell colonization and the revascularization. While calcium phosphate-based bioceramics are excellent materials for bone
reconstruction, they have a low mechanical strength (less than that of the bone), not lending themselves to machining. This resistance diminishes while porosity increases, making the utili
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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