Biomedical Engineering Reference
In-Depth Information
Change in pH during hydration
The results of the measurement of pH development during hydration of the Ca-aluminate
based are shown in Table 7. The initial
in vitro
-pH is 10.5 in saliva. After 1 week, pH after 1 h
dissolution time in saliva is approx. 8.
Test No.
At start
1h
24 hrs
7 days
14 days
28 days
1
10.5
10.3
10.7
10.3
9.9
9.8
2
10.5
10.2
10.2 (7.7)
9.9 (7.8)
9.5 (8.1)
9.2 (8.1)
Table 7. Change of pH during initial hydration of Ca-aluminate based materials
The pH is high during the early stage of the hydration, but decreases with time and
approaches neutrality. The reason for the high pH in the beginning is the general basic
character of the material and the formation of OH
-
during the hydration process. In the
clinical situation saliva is produced in a dynamic way, creating an environment capable of
buffering surrounding solution to neutrality. In the clinical studies performed so far no
adverse reactions have been reported from a possible elevated pH during the early part of
the hydration.
When Ca-aluminate material is combined with glass ionomer system the pH-system
becomes initially acidic. However after 10 min the pH is above neutral, but will not exceed
pH 9 (Jefferies et al 2009).
Cytotoxicity testing
The
in vitro
MTT reduction test of the experimental Ca-aluminate dental filling material in
human oral fibroblast culture showed no obvious cytotoxicity. The average level of MTT
reduction of the experimental dental filling material was close to 100% of the control values.
The maximal variation (SD) was less than 30%. Different curing times of the test material
did not seem to affect the cytotoxicity test results although one week curing produced the
most stable testing results both in the short and long term tests. After a week the material
can be considered as fully cured, i.e. stable.
Morphological changes were not observed in any of the test groups at different MTT
reduction testing points. As shown in Figure 3, the cell culture was typically fibroblastic
with a slender and elongated form in both the control group and the group exposed to the
examined material. In the exposed picture B even some precipitated hydrates are seen.
Fig. 3. Morphological observation of human oral fibroblasts on an experimental Ca-
aluminate based material. A: Normal control. B: After exposure to the experimental filling
material for one week (Liu et al 2002).
