Page 375 - Biomedical Engineering and Design Handbook Volume 1, Fundamentals
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352 BIOMATERIALS
FIGURE 14.6 Carbon-fiber-reinforced thermoplastic hip prosthesis, with and
without hydroxyapatite coating, shown alongside conventional titanium equiva-
lent. (Courtesy of Orthodesign, Ltd., Christchurch, U.K.)
Bone cements used to fill the void and improve adhesion between implants and the host bone
tissue have been reinforced with various fibers to prevent loosening and enhance shear strength. The
typical bone cement is PMMA powder mixed with a methacrylate-type monomer that is polymer-
ized during fixation. Low volume fractions of graphite, carbon, and Kevlar fibers have been added
to PMMA matrices to increase fatigue life and reduce creep deformation. 17
14.8.2 Dental
Composites have been by far the most successful in dental applications by meeting several stringent
design requirements difficult to achieve with homogeneous materials such as ceramics and metal
alloys. Whether it is preparation of crowns, repair of cavities, or entire tooth replacement, the product
needs to be aesthetically matched in color and translucence with other teeth and retain its gloss. It
must match the hardness of the opposing tooth and be resistant to wear or fatigue fracture. It must
be dimensionally stable and withstand the largely varying thermal stresses in the mouth. It also has
