Biomedical Engineering Reference
In-Depth Information
Tabl e 9. 4
Properties of Y-TZP compared to ISO 13356 (data from Table III in [
288
])
Units
Desmarquest
a
Metoxit
b
Kyocera
c
ISO
kg/m
3
>
Density
6,000
6,080
6,080
6,080
Grain size (av.)
m
0.6
<
0.5
0.4
0.2
Hardness HV1
GPa
n.s.
d
n.s.
12
13
Bending strength
1,500 1,200 1,200
E modulus GPa n.s. n.s. 210 210
K
IC
MPa m
1=2
n.s.
8-10 8 5
a
J.M. Arnaud et al. in 30e Meeting de la Societe Orthopedique de l'Ouest, Pont l'Aubee (France,
June 1997)
b
W. Rieger, on p. 283 in
World Tribology Forum in Arthroplasty
(Hans Huber, Bern, 2001)
c
H. Oonishi et al. on p. 7 in
Reliability and long-term results of ceramics in orthopedics
(Thieme,
Stuttgart, 1999)
d
n.s.: nonspecified
MPa
>
800
>
progressing third body wear. Immunological effects of wear debris will be discussed
later. An interesting in depth analysis of a zirconia head broken 34 months after
surgery is published by Piconi and colleagues with similar conclusions [
288
]. In a
paper of 1999, Allain and colleagues reported a survivorship of eight years for only
63% of the total hip replacements they implanted using a zirconia head/polyethylene
cup. Abundant osteolysis near the implantation site was observed, something they
did not see for alumina heads. Consequently, they abandoned the use of zirconia
heads [
289
]. The ceramics world, however, did not stop here. The company Mathys
(Bettlach, Switzerland) uses for their heads and cups a composite, tradename
Cer-
amys
, which is, compared to BIOLOX
R
delta, positioned at the other end of the
composition line. It consists of a nanocrystalline homogeneous dispersion of 20%
alumina with 80% zirconia and no other elements involved. We are not aware of
long-term studies about the use of this composite.
The Story Does not End Here
From foregoing discussion, it should be clear that ceramic composites and not the
single oxide ceramics, pure Al
2
O
3
or ZrO
2
, are the future. A weak point of zirconia
remains wear resistance. Figure
9.8
illustrates what is going on in the field of techni-
cal ceramics and the composite ZrO
2
-WC-Al
2
O
3
meets the weak wear resistance
of zirconia and might find application in the biomedical field. The fracture tough-
ness of ZrO
2
-TiCN composites prepared from nanopowders is about 3.9 MPa m
1=2
and it has a Vicker's hardness of HV
10
kg mm
2
, and although not bad,
the toughness is still lower than that of Y-TZP (Table
9.4
). A ceramic with exquisite
properties, probably to be situated in the upper right corner of Fig.
9.8
is silicon
nitride Si
3
N
4
. It does not suffer from low temperature degradation (zero water
absorption), is not sensitive to stress corrosion, is hard (2,200 kg mm
2
Knoop)
and has high compressive strength (360-434 MPa) and excellent fracture toughness
D 1;630
