Biomedical Engineering Reference
In-Depth Information
Below the gum, the dentine of the root is covered with a thin layer of cementum, rather than
enamel. Cementum is a hard bone-like substance onto which the periodontal membrane
attaches. This membrane bonds the root of the tooth to the bone of the jaw. It contains elastic
fibres to allow some movement of the tooth within its bony socket.
The pulp forms the central chamber of the tooth. The pulp is made of soft tissue and
contains blood vessels to supply nutrients to the tooth, and nerves to enable the tooth to
sense heat and cold. It also contains small lymph vessels which carry white blood cells to the
tooth to help fight bacteria.
The extension of the pulp within the root of the tooth is called the root canal. The root canal
connects with the surrounding tissue via the opening at the tip of the root. This is an
opening in the cementum through which the tooth's nerve supply and blood supply enter
the pulp from the surrounding tissue.
Unfortunately, dental caries is one of the most important problems in human oral diseases
(Namba et al., 1982). It is known that
streptococcus mutans
play one of most important roles
in dental caries (Jessica et al., 2007). During metabolizing carbohydrates,
streptococcus mutans
produces organic acid, which can induce the demineralization of tooth surface and results in
dental caries (Ooshima et al., 2000).
Some literatures disclosed that the dental plaque pH after a sucrose rinse can decrease to 4.5
or even 4 (Hefferren et al., 1981; Thylstrup et al., 1986). A pH of higher than 6 is considered
to be the safe area, a plaque pH of 6.0~5.5 is the potentially cariogenic area, and pH of 5.5~4
is the cariogenic or dangerous area for cavity formation. Therefore, the maintenance of a
higher pH value in the plaque is very important for the anticaries.
The fluoride has been used for about five decades in caries prevention. However, it is
difficult to control its quantity to a proper level (Nakajo et al., 2008); excessive fluoride is
harmful to human body and insufficient fluoride will not take effect for anticaries action. In
recent years much attention has been paid to developing fluoride-free techniques that can
prevent human teeth from caries(Scherp et al., 1971; Allakera and Ian Douglas, 2009).
Some natural products were reported to be candidates of new anticariogenic substances
(Shouji et al., 2000; Matsumoto et al., 1999). However, there is not scientific evidence about
the effect of natural tourmaline on the
streptococcus mutans
.
Tourmaline is a kind of electropolar mineral belonging to the trigonal space group of R3m,
whose general chemical formula can be written as XY
3
Z
6
Si
6
O
18
(BO
3
)
3
W
4
, where X is Na
+
,
Ca
2+
, K
+
, or vacancy; Y is Mg
2+
, Fe
2+
, Mn
2+
, Al
3+
, Fe
3+
, Mn
3+
, Cr
3+
, Ti
4+
or Li
+
; Z is Al
3+
, V
3+
,
Cr
3+
, or Mg
2+
; and W is OH
-
, F
-
, or O
2-
(Castañeda et al., 2006). Its Crystal structure of
tourmaline is shown in Figure 4 (Fuchs et al., 1998).
The most important feature among the electric properties of the tourmaline is the possession
of spontaneous and permanent poles, which would produce an electric dipole, especially in
a small powder with a diameter of several microns or less (Jin et al., 2003). Therefore, a
strong electric field exists on the surface of a tourmaline powder (Nakamura et al., 1994; Zhu
et al., 2008). The electric field effect of tourmaline powders can influence the redox potential
of water and regulated the pH value of solution (Xia et al., 2006). The maintenance of pH
value is very important for the growth and metabolism of bacteria (Esgalhado et al., 1995).
Therefore, the graded composite materials were fabricated with nano-tourmaline and
nano-hydroxyapatite powders by direct inkjet colour printing for the study of inhibiting
function on
streptococcus mutans
. Moreover, the mechanism by which tourmaline inhibits
the growth and acid production of
streptococcus mutans
was also explained from the view
of pH value.
