Feasibility of low temperature atmospheric pressure plasma
to aesthetics of teeth; teeth bleaching
Gyoo Cheon Kim1, Seoul Hee Nam1, Hyun Woo Lee2 and Jae Koo Lee2
1
Department of Oral Anatomy, School of Dentistry, Pusan National University,
Yangsan, 626-870, Republic of Korea
2
Department of Electronic and Electrical Engineering, Pohang University of
Science and Technology, Pohang, 790-784, Republic of Korea
Abstract: A low temperature atmospheric pressure, helium plasma jet device was
developed to enhance the tooth bleaching effect of hydrogen peroxide (HP;
H2O2). Therefore, the aim of the present study was to investigate the
combinational effect of low temperature atmospheric pressure plasma and HP on
external/internal tooth bleaching. As for the external tooth bleaching, plasma was
applied to teeth in combinational treatment with HP for 30 minutes. Furthermore,
the stained teeth by either coffee or red wine were bleached by 30 % HP plus
plasma for 20 minutes. The internal tooth bleaching, the combinational treatment
of plasma with 30% HP enhanced the whitening effect in discolored teeth by
human blood. Statistical analysis of overall color changes (ΔE) showed
significant difference (P < 0.05). The ΔE of external/internal bleaching the
combination of plasma with HP was at least 2 times larger than without plasma
treatment. The temperature inside the tooth was maintained at a low temperature
during the tooth bleaching with the applications of plasma (< 40°C). We suggest
that the improvement in tooth bleaching induced by plasma is due to the removal
of tooth surface proteins and to increased hydroxyl radicals (·OH) production.
Keywords: low temperature atmospheric pressure plasma, hydrogen peroxide,
tooth bleaching, low temperature, hydroxyl radical
1. Introduction
Recently, there has been increasing interest in tooth
bleaching because white teeth are being retained
longer [1]. Tooth discoloration results from various
and multifaceted causes that are classified into
extrinsic and intrinsic discoloration [2]. Extrinsic
discoloration is caused by the deposition of external
chromogens such as food, beverages, and tobacco on
the tooth surface. Intrinsic discoloration occurs when
the chromogens are deposited within the bulk of the
tooth, usually the dentine, and caused by systemic or
pulpal factors [3]. Hydrogen peroxide (HP; H2O2) is
a widely used bleaching agent that is highly effective
at removing chromgens deposited on teeth [4]. Inoffice bleaching, high concentration of HP is used in
combination with light sources [5]. The light source
might enhance the process of bleaching by heating
the HP and consequently accelerating the tooth
bleaching [6]. However, the temperature could
increase up to 50-60°C during this process [7]. In
this study, we demonstrate a tooth bleaching
procedure that uses low temperature plasma instead
of a light source in an in-office bleaching system.
Thus, the purpose of this study is to demonstrate
enhanced bleaching of extracted human teeth when
combining plasma with HP.
2. Materials and methods
Plasma Device
The low temperature atmospheric pressure plasma
jet (Fig. 1a, c) consists of a tube constructed of a
dielectric material (Teflon, 3 εr = 2.6) and 1 inner
and 1 outer electrode (both aluminum). The Teflon
tube has outer and inner diameters of 10 and 6.4 mm,
respectively. The outer electrode surrounds the
Teflon tube; it is 1 mm thick and is connected to a
sinusoidal voltage power source that has a frequency
of 20 kHz and a peak voltage of 10 kV. The inner
electrode, which is not connected to any external
power source, has capillary hole of 1 mm diameter.
To prevent electrical or physical damage to teeth or
gums, the outer and inner electrodes are set back 5
and 10 mm, respectively, from the outlet of the
Teflon tube. Helium gas with a flow rate of 2 L/min
was used as feeding gas at atmospheric pressure in
air. The plasma source is less than 10 cm long, and
the device can be hand-held. The plasma generation
occurs inside the Teflon tube near the powered outer
electrode. The device generates a low temperature
plasma jet that passes through the capillary hole of
the inner electrode (Fig. 1b, d) and extends up to 3
cm beyond the end of the Teflon tube.
with 30% HP (20 μL every 5 min) with the plasma
in the pulp chamber for 30 min, and group 2 was
treated with 30% HP (20 μL every 5 min) alone in
the pulp chamber for 30 min.
External bleaching experiments
Fifty-eight extracted human teeth were used for this
experiment. Twenty-eight tested were cut in half
longitudinally, and the pieces were placed in 2
groups as follows: the experimental group was
treated by using HP (28%, 20 μL, every 30 s) plus
plasma for 10 min, and the control group was treated
by using HP alone for the same duration.
Fifteen of the sectioned teeth were immersed in
coffee (Maxim original - coffee subgroup) for seven
days and fifteen were immersed in red wine (Palacio
De Anglona Tinto Semidulce - red wine subgroup)
for seven days. Teeth in the experimental group
were treated using HP (30%, 20 μL, every 30 s) plus
plasma for 20 min, and teeth in the control group
were treated using HP alone for the same duration.
Teeth were photographed before treatment and at 5
min-intervals during the 20 min treatment.
Internal bleaching experiments
Forty extracted single-root human teeth were used.
Standard endodontic access cavities were created
with a diamond-coated bur (BR-31 MANI Inc.,
Tochigi, Japan). All teeth were artificially stained by
human blood and teeth samples were immersed for 4
days and stored at 37 °C and 100% air humidity in
an incubator for 15 days. The teeth were randomly
assigned to two groups (n = 20): group 1 was treated
Figure 1. The process of tooth bleaching using low temperature
atmospheric pressure plasma. (a) Schematic diagram of the external
bleaching plasma device and (b) photograph of the process. (c)
Schematic diagram of the internal bleaching plasma device and (d)
photograph of the process.
Analysis of Bleaching Efficacy
Teeth were photographed at 5 or 10 min-intervals
during plasma treatment. The images of teeth were
captured with 10× magnification digital imaging
system consisting of a stereomicroscope (SZ-CTV,
OLYMPUS, JAPAN) connected to a camera (Pixel
link PL-B686 CU, CANADA). The images were
stored in a personal computer with the Image-Pro
Plus 5.1 software (Media cybernetics Inc,
Washington, DC, USA). The overall color changes
(ΔE) were assessed on the basis of the Commission
Internationale de L’Eclairage (CIE, 1979) Lab Color
System [8]. The L *, a *, and b *, which represent
lightness, redness-greenness, and yellownessblueness, respectively. The ΔE was calculated for
each tooth by using the CIELAB equation:
E 
 L *    a *   b *
2
2
2
Measurement of tooth temperature
The pulp chamber temperature during bleaching was
measured using a fibre optic temperature
measurement system (FTI-10 fibre optic signal
conditioner, FOT-L-SD fibre optic temperature
sensor; FISO Technologies Inc., Quebec, Canada).
The distance between the emitting tip of the plasma
source (end of the Teflon tube) and the fibre optic
temperature sensor was set at 1 cm during ‘plasmaon’ for 30 min and thereafter set at ‘plasma-off’ for
20 min.
group but not in the control group (Fig. 2). The
differences in brightness and color tone between the
experimental and the control groups did not differ
before treatment (Fig. 2Ia), but the teeth in the
experimental group were clearly brighter than those
in the control group after treatment (Fig. 2Ic, b). The
average (n = 28) of the ΔE was 19.7±6.6 for the
experimental group and 6.1±4.6 for the control
group.
These stained teeth were significantly bleached by
plasma plus HP treatment compared with HP
treatment alone in the manner of time dependence
(Fig. 3a). Remarkable color change occurred over
time in the experimental group, whereas no
significant color change occurred in the control
group (Fig. 3b). ΔE for the experimental groups
were 3.1 (coffee) and 3.7 (red wine) times larger
than those of the control groups. (P < 0.05).
Protein Removal from Tooth Surface
After treatment, teeth were rinsed with deionized
water and stained with 0.1% Ponceau S in acetic
acid for 5 min. Protein stained in red was observed
with a stereomicroscope and the surface of tooth was
observed with SEM (S-4200 SEM; Hitachi, Tokyo,
Japan) at 8 kV.
Measurement of ∙OH
The amounts of hydroxyl radicals (∙OH) generated
from HP before and after the plasma treatment were
measured by using electron spin resonance (ESR)
spin-trapping method. Samples from each group
were exposed to the plasma for 1 min at a distance
of 1 cm from the outlet of the plasma source.
Figure 2. I, The external bleaching effect of plasma treatment.
Photographs of canine tooth used (a) before, (b) after treatment for the
experimental group only, (c) followed by treatment for control groups,
demonstrating typical results in the experimental group (A’/A) and the
control group (B’/B). The experimental group was treated by using HP
(28%, 20 μL every 30 s) plus plasma (5 W) for 10 min; the control group
was treated by using HP alone for the same duration.
Statistical analysis
The difference in ΔE values between two groups
was determined using Student’s t-test. Differences
with P values < 0.05 were considered statistically
significant.
3. Results and Discussion
Effects of external tooth bleaching
Bleaching can occur when pigments on the tooth
surface are destroyed [9]. Photographs showed
increased brightness of teeth in the experimental
Figure 3. a) Photographs of tooth used before treatment and at every 5
min during the 20 min treatment. b) The change of ΔE with time during
the 20 min treatment.
Effects of internal tooth bleaching
Figure 4 represented high efficacy for the plasma
and HP bleaching compared with HP bleaching
alone in discolored teeth stained by blood. The mean
ΔE values of group 1 were approximately 2.07 times
larger than that of group 2 at the end of 30 min.
There was a significant difference in the bleaching
efficacy (P < 0.05) between group 1 and group 2.
12
Overall Color Change Δ E
10
8
Figure 5. Measurement of the pulp chamber temperature. The cavity
temperature increased after the plasma jet was turned on and then it
6
4
stabilized near 37.5 °C (5 kV) in three independent experiments.
2
4. Conclusion
0
10 min
20 min
Group 1
30 min
Group 2
Figure 4. The treatment effect of plasma on internal bleaching. The ΔE
of groups 1 and 2 was measured after plasma treatment for 30 min
Protein removal from tooth surface
The color-producing materials on a tooth surface are
typically organic compounds that possess extended
conjugated chains of alternating single or double
bonds [10]. After treatment, uniformly distributed
red color indicating the presence of proteins and
many dust-like materials were observed on the
surfaces of the teeth; these were much more
prominent in the control group than in the
experimental group. SEM images showed
remarkable reduction in the quantity of extraneous
substances on the tooth surface.
Quantification of ∙OH
∙OH is widely known as the main substance
responsible for tooth bleaching [11]. We showed that
the production of ∙OH doubled after plasma
treatment and claimed that this abundant ∙OH caused
the enhanced tooth bleaching.
Temperature Measurement in a Dental Cavity
The temperature of the pulp chamber increased from
room temperature (25°C) and stabilized near 37°C (5
kV) after plasma treatment (Fig. 5).
The external/internal tooth bleaching technique
using low temperature atmospheric pressure plasma
could be complementary to the conventional method
because combining the plasma jet and HP improved
the bleaching efficacy under low temperature
conditions (< 40°C). We suggest that the application
of low temperature atmospheric pressure plasma to
tooth bleaching may be a novel and efficient therapy
for tooth bleaching.
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