Biomedical Engineering Reference
In-Depth Information
cortical bone [
39
]. Results showed that friction logs transformed from partial slip
directly to gross slip without a mixed regime, and the friction coeffi cients in each
fretting regime went up with the displacement. The wear depths on the Ti ball were
only at the extent of several microns to tens of microns, which were much lower
than those of bone. In addition, the friction coeffi cient of the bone-TC4 pair was
higher than that of the bone-TA2 pair, and the maximum wear depth on bone against
TA2 was about 40 % of the value of that on bone against TC4. Therefore, the wear
adaptability of bone-TA2 pairs was better than that of bone-TC4 pairs. Abrasive
wear features and various microfractures were observed on the worn cortical bone
surfaces. Some surface modifi cation techniques of titanium may need to be adopted
to reduce the fretting damages of bone.
It also should be noted that commercially pure (CP) titanium and its alloys have
been increasingly applied to indirect dental restorations, especially implants, in
place of other metals due to their excellent biocompatibility, corrosion resistance,
and light weight [
40
-
44
]. Yang et al. used a WTM-11E microfriction- and wear-
testing machine to study and compare the tribological behaviors of three dental
restorative materials, TA2, TC4, and amalgam, against a Si
3
N
4
ceramic ball [
45
].
They found that the TA2 and TC4 possessed similar wear mechanics, and the
friction log of TA2 was consistent with that of TC4. The main wear mechanism of
TA2 was adhesive wear, while adhesive wear and abrasive wear were dominant on
the worn surface of TC4. The wear mechanism of amalgam was abrasive wear,
and it exhibited the biggest wear loss. The result is consistent with the clinical rule
that amalgam is only employed as a dental fi lling material. To the contrary, both
pure titanium (TA2) and its alloy (TC4) are relatively ideal dental restorative
materials due to their better wear resistance. Xu et al. investigated the fretting
wear behaviors of eight artifi cial dental materials and natural enamel against
porcelain plate [
46
]. The result showed that the sequence related to wear vol-
ume was as follows: Co-Cr alloy > Ni-Cr alloy > TC4 > Vata ceramic > IPS
d.Sign > Refl ex ceramic > TA2 > natural enamel > 55 % gold alloy. It indicated that
TA2 is an ideal dental restorative material because it has a similar wear property
as natural enamel.
6.3
Wear Behavior of Porcelains
Porcelain, with excellent mechanical properties, has been studied and applied
widely in medicine. As material technology develops rapidly, the concept of porce-
lain has been expanded into the whole inorganic nonmetallic material, which means
inorganic solid materials made of oxides, nitride, carbide, etc., can be called porce-
lain. Because of the extraordinary mechanical, biochemical, and aesthetic charac-
teristics, porcelain is now commonly used in dentistry.
Feldspathic porcelain is a kind of material sintered of feldspar mainly, and quartz,
kaolin clay, with a small amount of borax and colorants, which in dentistry is the
mixture of albite (Na
2
O · Al
2
O
3
· 6SiO
2
) and potash feldspar (K
2
O · Al
2
O
3
· 6SiO
2
).
