Implants alumina

The chemical stability of alumina is related to its phase stability, whereas the phase changes of zirconia result in degradation in strength and wear resistance. Release of substances from zirconia and alumina implants to the surrounding tissue is very low and neither local nor systemic effects have been reported. 

Isotropic carbon is obtained by the pyrolysis of a hydrocarbon, usually methane, at high temperature (1200-1500°C) in a fluidized bed on a graphite substrate.Under these conditions, a turbostratic structure is obtained which is characterized by very little ordering and an essentially random orientation of small crystallites. In contrast to graphite which is highly anisotropic, such a structure has isotropic properties (see Ch. 7). Isotropic carbon is completely inert biologically. Its properties are compared to alumina, another common implant material, in Table 17.8. Notable is its high strain to failure. 

In addition to the loss of GAD staining (i.e. GABA) neurons and inhibitory symmetrical synapses around an alumina focus in primates (see above), studies with a chronically implanted cortical cup over a cobalt lesion (focus) in rats show an increased release of glutamate that is associated with spiking (Dodd and Bradford 1976). 

Li, P., Ohtsuki, C., Kokubo, T., Nakanishi, K, Soga, N. and de Groot, K (1994) The role ofhydrated silica, titania and alumina in inducing apatite on implants. Journal of Biomedical Materials Research, 28, 7-15. 

Considerable development has occurred on sintered ceramics as bone substitutes. Sintered ceramics, such as alumina-based ones, are uru eactive materials as compared to CBPCs. CBPCs, because they are chemically synthesized, should perform much better as biomaterials. Sintered ceramics are fabricated by heat treatment, which makes it difficult to manipulate their microstructure, size, and shape as compared to CBPCs. Sintered ceramics may be implanted in place but cannot be used as an adhesive that will set in situ and form a joint, or as a material to fill cavities of complicated shapes. CBPCs, on the other hand, are formed out of a paste by chemical reaction and thus have distinct advantages, such as easy delivery of the CBPC paste that fills cavities. Because CBPCs expand during hardening, albeit slightly, they take the shape of those cavities. Furthermore, some CBPCs may be resorbed by the body, due to their high solubility in the biological environment, which can be useful in some applications. CBPCs are more easily manufactured and have a relatively low cost compared to sintered ceramics such as alumina and zirconia. Of the dental cements reviewed in Chapter 2 and Ref. [1], plaster of paris and zinc phosphate... 

Alumina is a well-known bioinert ceramic material which can be used in total hip prosthesis and dental implants since it exhibits good biocompatibility, strength, and excellent corrosion resistance.70,71 The application of alumina has some limitations due to poor fracture toughness. The incorporation of ductile phase may lead to the... 

Dental Dental implant for tooth fixation Titanium, alumina, calcium phosphate... 

Some ceramics exhibit biocompatibility in the human body. Alumina and zirconia are employed as the ball for hip replacements. Hydroxyapatite (Caio(P04)6(OH)2) is used as bone replacements, as ocular implants, and as a coating for metallic implants. Ceramics also find application in dentistry for restorative work. 

Figure 2.2 Classification of biomaterials according to their bioactivity (a) bioinert single crystal alumina dental implant, (b) bioactive hydroxyapatite [Ca10(PO4)6(OH)2]...

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