22G02
Plasma Dental Treatment with the Reduced pH Method and the LF Plasma Jet~ Disinfection of Dentin~
低 pH 法を用いたプラズマ歯科治療～感染歯質の殺菌～

Hiromitsu Yamazaki1, Tomoko Ohshima1, Satoshi Ikawa2, Hiroyasu Yamaguchi1, Asiri
Jayawardena1, Yuji Tsubota1, Yasushi Nishimura1, Nobuko Maeda1 & Katsuhisa Kitano3
山崎弘光 1, 大島朋子 1, 井川聡 2, 山口博康 1 , アシリ ジャヤワルディナ 1, 坪田有史 1，西村康 1 前田伸子 1, 北野勝久 3
1 Dental Med. Tsurumi Univ. 2TRI Osaka, 3 Eng. Osaka Univ.
^1^鶴見大歯,^2^大阪産技研,^3^阪大工Tsurumi University School of Dental Medicine,
2-1-3 Tsurumi, Tsurumi-ku, Yokohama, Kanagawa 230-8501, Japan
鶴見大学歯学部 〒230-8501 神奈川県横浜市鶴見区鶴見2-1-3
In the dental treatment, methods for sterilization of infected dentine have not been established yet. In the presentstudy, we evaluated the bactericidal effect of low frequency atmospheric pressure plasma jets with low pH
against Enterococcus faecalis, an oral pathogen causing incurable root-canal infection, using the dentine
infection models. The results showed that the LF jet had bactericidal effects on E. faecalis in liquid with lower
pH condition than 4.5 in one minute irradiation, and reached to the detection limit in 3-5 minutes. In the similar
test using the infection model of hydroxyapatite pellets instead of dentine, the bactericidal effect was detected as99.9%. With the infection model using the dentine slices of human molar teeth, the bactericidal effect of 99%
was gained. These results indicate that LF jets might be applied to the clinical dentistry.

Introduction

progress, microorganisms gain entry into the dental

The dental caries is a disease caused bypulp, leading to pulpal inflammation. Eventually,

demineralization with organic-acids metabolicallythis requires a root canal treatment, but the successproduced by oral microorganisms, and the hard

rate of root canal treatment

tissue of tooth is decayed.

apparently

The therapeutic

due

to

is about 80%,

incomplete

intra-canaltreatment is removing the infected enamel andsterilization and obturation. Hence, in order todentine mechanically, and filling the cavity withobtain better results with caries and root canal

dental materials or replacing the lost crown bytreatment, it is necessary to invent new methods

prosthetic dentistry techniques. However, thethat can completely sterilize the infected dental

methods for sterilization of infected dentine havetissues. We have already studied about the bactericidal

not been established yet. If the removing of infected

effect on Streptococcus mutans, a major cariogenic

tooth is not enough or not adequate, it has beenbacteria [1]. In this study, we evaluated thereported that some bacteria remain inside thebactericidal effect of low frequency atmosphericdentinal tubules, and these remaining bacteria maypressure plasma jets with low pH against E. faecalis,

subsequently lead to secondary caries. As the caries

an oral pathogen causing incurable root-canalinfection, using the dentine infection models.

Effects of plasma irradiation on bacterial suspensions

Materials and methods

in the liquid phase

Preparation of dentine slices

As shown in Fig.1, after irradiation from 2 to 3

Dentine slices were pepared from human molar

minutes at pH 6.5 and in comparison with the control,

tooth by cutting into 2mm thick with micro-cutter.

there was a gradual reduction in viable cells which

The surfaces of slices were polished with

was not statistically significant. A 5-minute irradiationwater-resist polishing paper #1000 and treated withresulted in a significant reduction (p<0.001). No

ultrasonication.

The hydroxyapatite pellet was

viable cells could be detected at pH 4.5 or 3.5, for 2

high temperature calcinations to gain the sameand 3 minute irradiation times. When compared withdensity as dentine. The slices and pellets werethe control, there was a significant difference forsterilized by autoclave and kept in water until toirradiation times from 1 to 5 minutes (p<0.001). For E.

next step.

faecalis, the D values at pH 3.5, 4.5 and 6.5 were

Sterilization test

calculated to be 0.30, 0.47 and 2.00, respectively.
106

E. faecalis (ATCC19433 strain) was cultured and
5n=7* p<0.001

105

6CFU/mladjusted to 10 ～ 10 CFU/ml and 50μl of thismicrobial suspension was added to 450μl of citrate

104

**

103
102

buffer (2.0mM ) making a total volume of 500μl of*101

the suspension liquid in 24 well plate. E. faecalis was100****

also adjusted to 10 CFU/10μl in BHI broth and2
345
Plasma exposure time (min)Fig. 1 CFU assay of E. faecalis in various pH solutions.

inoculated onto the surfaces of slices or pellets for

Effects of plasma irradiation on inoculated dentin

overnight at 37 ℃.

models7

After slight washing with0*
*

pH3.5
pH4.5
pH6.5

1

distilled water, the slices and pellets were immersed

As shown in Fig2, in the results of tests using thein citrate-Na buffer of pH3.5 and 4.5. The liquid of

infection model of hydroxyapatite pellets instead ofsuspension or containing immersed slices anddentine, the bactericidal effect was detected as 99.9%.

pellets were exposed to LF jet (Gas: Helium, Flow

With the infection model using the dentine slices ofrate of Helium gas: 2.00l/min, High voltage: 7 kV,

human molar teeth, the bactericidal effect of 99% wasLow frequency: 16 kHz, consumption of electricalgained.

power: 22VA, inner and outer diameters of the glass

Hydroxyapatite pelltes

Dentine slicestube, 4mm and 2mm).
After irradiation, 100μl of suspension was plated on
the agar plates and the number of live cells wasdetermined by the colony forming unit (CFU) assay.

After removing buffer from slices or pellets, 100μl

Fig2. REDOX indicator assay after plasma irradiation
on dentine infection modelsof RPMI 1640 medium added by Alamar Blue(TREK Diagnostic Systems，CA，USA) as the redox

These results indicate that LF jets might be applied toindicator and aerobically incubated at 37ºC for 6-8

the clinical dentistry to sterilize dentine tissues.

hours, and the fluorescence was measured with a[1] H.Yamazaki, T.Ohshima, Y.Tsubota,

wavelength of Ex 530nm，Em：590nm.

H.Yamaguchi, A.Jayawardena Y.Nishimura:

Results and Discussions

Dent Mater J, 2011；30(3)：384-391