27pC02「プラズマの歯科治療応用-感染歯質の殺菌-」
Dental Application of LF Plasma Jet –Sterilization of Infected Dentin–
大島朋子 1, 山崎弘光 1，井川聡 2，山口博康 1，Asiri Jayawardena1，
前田伸子 1，北野勝久 3
Tomoko Ohshima1, Hiromitsu Yamazaki1, Satoshi Ikawa2,Hiroyasu Yamaguchi1, Asiri Jayawardena1, Nobuko Maeda1, Katsuhisa Kitano3
1

鶴見大学歯学部, 2 大阪府立産業技術総合研究所, 3 大阪大学工学研究科
1
School of Dental Medicine, Tsurumi University
2
Technology Research Institute of Osaka Prefecture
3
Graduate School of Engineering, Osaka University
E-mail:ohshima-t@fs.tsurumi-u.ac.jp◆ Objectives
In dental treatment, the control of infectious
microorganisms is very important, however,effective sterilization methods for infected
dentine have not been established yet. In thedental caries treatment, surface grinding alone
does not eliminate the infected site, because
multiplication of the remaining microbes whichhave invaded into the depths of dentine causes
morbidity again. When caries progresses andreaches the pulp, the pulpitis develops and inorder to save the tooth the pulp must be removed.
However, even after this treatment, remaining
bacteria in a root canal wall or the fine structureof the dentin may cause root canal infection again.
Therefore, it is necessary to remove and sterilize
the bacteria of root canal walls or dental tubules
completely.

structure of dentine. Therefore, we need to find anovel sterilizing method that is more effective
than currently employed antiseptics. In thepresent study, we evaluated the bactericidal effectof low frequency atmospheric pressure plasma
jets (LF plasma jet), which is expected to be
having excellent sterilizing properties, osmoticstrength and residual toxicity in comparison withthe existing drugs. Generally, the sterilization in
the liquid phase with LF plasma jet is difficult
because it is not irradiated to bacteria directly, but
adaptation of the reduced pH method [1] wasexpected effective against pathogens in the oralcavity.

Generally, in the treatment of infected root-canals,
caustic disinfectants such as H2O2 and sodium
hypochlorite are used, but according to thesystematic review published in 2007-2008, a◆ The sterilization test against oral bacterial
suspension in vitro
In order to evaluate the sterilizing properties ofplasma jet against, the oral pathogens including
Streptococcus mutans, Enterococcus faecalis andCandida albicans, which are causes of dental
caries and resistant root-canal infection, asterilization test with CFU assay using eachfailure rate, as high as 30% has been reported.
One reason considered was the difficulty ofdisinfectant reaching the complicated finebacterial suspension of 1.0 x 106 CFU/mL wascarried out. The results showed that the LF jetirradiation had bactericidal effects on oral

pathogens in liquid suspension when the pH wasless than 4.5. As shown in Fig.1, after irradiation
at pH 6.5, the number of viable cells wasgradually reduced. On the other hand, no viable
cells could be detected at pH 4.5 or 3.5, for 2 and3minute irradiations, and it was significantly
different from the control (p<0.01). For E.
faecalis, the D values at pH 3.5, 4.5 and 6.5 were
calculated to be 0.30, 0.47 and 2.00, respectively[2].
Fluorescent levels◆ The sterilization test using an infected toothmodel in vitro
In a similar test using the infected model ofhydroxyapatite pellets or dentine slice models, asignificant bactericidal effect of 99-99.9% on E.
faecalis was detected by metabolical REDOX
indicator assay (Fig.2).
** p<0.010 min

5 min

Irradiation

Fig 2. REDOX indicator assay after plasma
time
irradiation on dentine infection models in the bufferof pH3.5◆ The sterilization test of root canal infection
model using Wistar rats
Under anesthesia, the pulp of mandibular firstmolar of Wister rats (Male, 8-10 weeks age) wasextracted and then 1.0 x 104-6 CFU/μL of E.

faecalis was inoculated with filing. After washingwith 0.2M citrate buffer (pH3.5), LF plasma jet
was irradiated for 30 seconds on the canal.
Subsequently, the root canal contents werecollected with paper points and cultured in BHI
broth. The results showed that the success rate ofsterilization of root canal was around 50%.
◆ Conclusion
As results were obtained by in vitro sterilization
tests, it was indicated that LF plasma jets might
be applied to the clinical dentistry. For
verification of the effective condition in vivo, thefurther trials using animal models should beconducted.
References[1] S. Ikawa, K. Kitano, S. Hamaguchi, Plasma
Process. Polym., 7, 1, pp.33, (2010).
[2] H. Yamazaki, T. Ohshima, Y. Tsubota, H.
Yamaguchi, A. Jayawardena, Y.Nishimura, Dent.
Mater. J 30(3) : 384-391 (2011).