The Bone-Biomaterial Interface for Load-Bearing Implants
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TIN/SEPTEMBER1991
engineering, physical, and biological sciences hâve significantly improved patient treatment with bone-interfacing surgical implants, little fundamental knowledge concerning the bone-implant interface and the conditions essential for establishing successful implant fixation has been acquired. During the past three décades, four différent methods for achieving fixation of load-bearing implants to bone hâve been used clinically: (1) mechanical fixators such as screws and threaded components,1 (2) acrylic bone cernent (polymethyl methacrylate),2 (3) porous-coated implants for bone ingrowth, 3 and (4) bioactive ceramic coatings on suitable substrates. 4 Currently, ail four methods are used in orthopedics. While anatomic constraints preclude using cernent for dental implant fixation, the other three methods are used for endosseous dental implant fixation within the mandible and maxilla. Some novel expérimental approaches hâve been introduced recently for the purpose of developing a better understanding of bone-biomaterial interface reactions, with particular emphasis on the influence of preparative methods on surface topography and composition of current implant materials. In vitro methods that hâve been developed allow bone-forming cells (osteoblasts) and bone-resorbing cells (osteoclasts) to grow on well-characterized substrates.49 Light and scanning électron microscopy and also analytical transmission électron microscopy (imaging EELS) hâve been used to examine interface régions."111 Récent observations from in vivo experiments hâve shown structures at the bone-implant interface very similar in appearance to those observed previously in vitro.12,13 Thèse récent findings are described below.
Bonding and Nonbonding Implant Materials The high loads that must be borne by orthopédie and dental implants require that the materials used to fabricate thèse devices, as well as their overall design, provide adéquate fracture résistance during use14 in addition to being "biocompatible." For this reason, current orthopédie and dental implants are, for the most part, metallic (titanium, titanium alloys, and cobalt-based and stainless steel alloys), with high strength ceramics (alumina and zirconia) and polymers (ultrahigh molecular weight polyethylene) used for bearing components that are primarily loaded in compression and for which the major requirements are good wear résistance and provision of low friction surfaces. Surface modification of métal implants by coating has been studied and is used to provide bénéficiai surface characteristics for bone-interfacing implants without sacrificing important mechanical properties such as fatigue and fracture résistance. This approach has resulted in the clinical use of porous coatings on implants. Metals, polymers, ceramics, and composites hâve been used to form thèse coatings, although porous métal coatings on métal substrates are most commonly used at présent.345"17 Of great interest in récent years has been the use of "bioactive" ceramic coatings over métal substrate
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