Biomedical Engineering Reference
In-Depth Information
Ball specimen
Movement
Supporting frame
Flat specimen
Piston
Force extensometer
Balance weight
Artificial saliva
F
n
Fig. 3.1
Schematic diagram of friction and wear-testing rig [
19
]
Table 3.1
Composition of artifi cial saliva
NaCl
KCl
CaCl
2
.2H
2
O
NaH
2
PO
4
.2H
2
O
Na
2
S. 9H
2
O
Urea
Distilled water
0.4 g
0.4 g
0.795 g
0.78 g
0.005 g
1 g
1,000 ml
so that the polished surface intersected the cusp tips and exhibited the maximized
enamel thickness (this orientation is referred to as the “axial section”). Samples
were fi rst ground using abrasive papers and then followed by diamond paste pol-
ishing. After polishing, the samples were stored in distilled water at 4 °C. The
teeth were dehydrated partially during preparation, but efforts were made both to
shorten the dry time and to keep the preparation time approximately the same for
each sample.
The microhardness of each tooth contact surface was tested before the wear test.
Ten to twenty indentations under a 50-g load were produced for each polished sur-
face. In vitro wear tests were conducted in a ball-on-fl at confi guration using a recip-
rocating apparatus containing an artifi cial saliva solution; see Fig.
3.1
. Pure titanium
has often been used clinically as a dental material recently due to its excellent bio-
compatibility. Thus, high-purity titanium (C 0.10 %, Si 0.15 %, H 0.02 %, O 0.20 %,
N 0.05 %, Fe 0.30 %, Ti the balance) with a hardness of 240 HV
50g
and 40 mm in
diameter was used as a ball counterpart. For the occlusal section of each tooth, wear
test was fi rst performed on sample surface. After microscopic examinations on the
morphology of the wear scar and measurements of wear depth, the worn surface
was removed by about 0.5 mm through the grinding and polishing process. A new
surface was obtained as a result, ready for a second wear test. According to this
method, wear tests were performed gradually from the outer enamel to the dentin in
every sample. For the axial section, wear tests were conducted in the enamel, DEJ,
and dentin, respectively, with the three wear scars aligned.
The artifi cial saliva (its composition is listed in Table
3.1
) was prepared accord-
ing to Fusayama's guidelines with Holland's modifi cation [
20
,
21
]. In order to avoid
the effect of acidity on wear, artifi cial saliva was neutralized to a pH of 7. A normal
force of 20 N, a reciprocating amplitude of 500
m, and a frequency of 2 Hz were
used for all the wear tests. To better simulate the real wear conditions of human
teeth, the choice of these parameters is based on clinical experience and the litera-
ture. During humans' normal chewing process, the magnitude of the masticatory
μ
