Page 45 - Academic Press Encyclopedia of Physical Science and Technology 3rd BioTechnology

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Encyclopedia of Physical Science and Technology EN002G-62 May 19, 2001 19:27

Biomaterials, Synthetic Synthesis, Fabrication, and Applications 185

FIGURE 7 Clinical use of inorganic bioceramics in the human body.

being one of the first oxide materials to be developed cause the materials show excellent machinability, translu-
for use in load-bearing orthopedic prostheses. Cermam- cency, and good bending strength. BIOVERIT ® II is a
ics based on alumina mixed with beta-silicon nitride (β- phlogopite-type glass–ceramic with two major crystal
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Si 3 N 4 ) known as Sialon are also used with the mixture phases, mica and cordierite, present in the glassy ceramic.
havinghigherfracturetoughnessthaneithercomponenton The translucency, mechanical properties, and thermal ex-
its own. Zirconia (ZrO 2 ) and yttrium and magnesium sta- pansion coefficient can all be regulated in accordance with
bilized zirconias are also used when applications require a the required medical usuage. The material is biocompat-
fully densified material. Machinable glass–ceramics con- ible but not bioactive and is used in middle ear implants
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taining mica as the main crystal phase such as Macor ® and in dental work. BIOVERIT I has a different compo-
with a base glass composition of 47.2 SiO 2 , 8.5 B 2 O 3 , 16.7 sition being a mica-apatite glass–ceramic and offers the
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Al 2 O 3 , 14.5 MgO, 9.5 K 2 O, and 6.3 F , and DICOR , possibility of a machinable glass together with bioactiv-
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which contains significant amounts of the alkaline earth ity. Both of BIOVERIT materials have successfully been
oxides are used in the production of dental crowns be- used in head and neck surgery and in orthopedic surgery.