Geoscience Reference
In-Depth Information
Table 10.6 Types of Bioceramic Tissue Attachment and Bioceramic Classification
[257]
Type of Attachment
Type of Bioceramic
Dense, nonporous, almost inert ceramics
attach by bone growth by cementing the
device into the tissue, or by press-fitting
into a defect (morphological fixation)
Al
2
O
3
ZrO
2
For porous implants, bone ingrowth occurs,
which mechanically attaches the bone to
the material (biological fixation)
Porous HAp and HAp-coated porous metals
Surface-reactive ceramics, glasses, and
glass
ceramics attach directly by chemical
bonding with the bone (bioactive fixation)
Bioactive glasses, bioactive glass
ceramics,
dense HAp
Resorbable ceramics and glasses in bulk or
powder form designed to be slowly
replaced by bone
Calcium sulfate (plaster of Paris), tricalcium
phosphate, calcium phosphate salts,
bioactive glasses
gives the types of bioceramics and also the tissue attachment and bioceramic classi-
fication
[259]
. Bioceramics are also widely used in dentistry as restorative materials,
gold porcelain crowns, glass-filled ionomer cements, dentures, and so on.
High-density, high-purity (
.
99.5%) Al
2
O
3
(
α
-alumina) was the first biocera-
mic, widely used for clinical purposes during the 1960s. It is used in total hip
prostheses and dental implants because of its combination of excellent corrosion
resistance, good biocompatibility, low friction, high wear resistance, and high
strength
[260,261]
. Other clinical applications of Al
2
O
3
include knee prostheses,
bone screws, alveolar ridge (jaw bone), and maxillofacial reconstructs, ossicular
(middle ear) bone substitutes, keratoprostheses (corneal replacements), segmental
bone replacements, and blade and screw and post-type dental implants
[260,261]
.
Zirconia (ZrO
2
), in tetragonal form, stabilized by either magnesium or yttrium,
has also been developed as a medical-grade bioceramic for use in total joint pros-
theses. The interest in ZrO
2
is derived from its high fracture toughness and tensile
strength. These improved properties make it possible to manufacture femoral heads
for total hip prostheses that are smaller than the present generation of Al
2
O
3
heads.
ZrO
2
implants are now used clinically; however, only implant survivability data
over a 10-year period will establish clinical advantages
[261,262]
.
These materials are prepared by hydrothermal techniques such as hydrothermal
sintering, HHP, and under hot isostatic pressure.
The most significant area of growth for bioceramics, however, involves a more
complex material—HAp {Ca
10
(PO
4
)
6
(OH)
2
}, which is the main mineral constituent
of teeth and bones, representing 69% by weight. HAp-based bioceramics have been
in use in medicine and dentistry for 20 years
[261
264]
. It has the physicochemi-
cal advantages of stability, inertness, and biocompatibility. However, its relatively
low strength and toughness produced little interest among researchers searching for
bulk structural materials. HAp ceramics do not exhibit any cytotoxic effects, and
