USES OF COLD PLASMA IN CONSERVATIVE DENTISTRY AND ENDODONTICS

Aim: To recapitulate the possible applications of non dentistry and endodontics. Objective: Nonthermal plasma is lately being researched for its applications in dentistry and cancer therapy. The objective of this review is to summarize the possible role of Non thermal plasma in conservative dentistry and endodontics. Background: Plasma is the fourth state of matter and also the most form, the other three being air, water and solid. Plasma is ionised form of gas and is of two types: thermal and nonthermal or cold atmospheric plasma. The cold atmospheric plasma based dental applications is being investigated recently in fields such as root canal disinfection, tooth whitening, sterilization, deactivation of oral biofilms, enhancement of strength of light cure restorations and cancer therapy. Reason: Cold atmospheric plasma may be of a great use in dentistry due to its properties. This review is to recapitulate and bring to light the possible uses of cold atmospheric plasma in conservative dentistry and endodontics.


INTRODUCTION
The three states of matter, solid, liquid and gas are relatively well known. Plasma which is an ionised gas is considered as the fourth state of matter. It is found naturally (upper part of earth's atmosphere) and can also be produced artificially. It is a mixture of ions, electrons, neutral atoms and molecules Based on their temperature plasmas can be categorized into thermal (high temperature) and non-thermal plasmas (cold or low temperature). In thermal plasma, the component particles are in thermal equilibrium with each other. I cold plasmas the larger molecules comprising the gas, ions and atoms remain at low temperatures while the electrons are accelerated. Thermal plasmas are associated with electric sparks, flames, lightening, the sun and the stars. Cold plasm are seen in fluorescent lighting tubes, neon tubes and plasma TVs 2 .
Plasmas operated at lower temperatures have attracted a lot of interest due to its use in applications such as surface treatment, food processing, thin-film deposition and biomedicine. In the medical field, the use of non plasma in applications such as sterilization of living tissues, sterilization of non-living objects for medical applications, blood coagulation, wound healing and tissue regeneration and cancer therapy have been studied 3 . Apart from these applications, studies have been carried out to find out the solid, liquid and gas are relatively well known. Plasma which is an ionised gas is considered as the fourth state of matter. It is found naturally (upper part of earth's atmosphere) and can also be produced artificially. It is neutral atoms and molecules 1 . Based on their temperature plasmas can be categorized into thermal plasmas (cold or low temperature). In thermal plasma, the component particles are in thermal equilibrium with each other. In non-thermal or cold plasmas the larger molecules comprising the gas, ions and atoms remain at low temperatures while the electrons are accelerated. Thermal plasmas are associated with electric sparks, flames, lightening, the sun and the stars. Cold plasmas are seen in fluorescent lighting tubes, neon tubes and plasma Plasmas operated at lower temperatures have attracted a lot of interest due to its use in applications such as surface film deposition and e. In the medical field, the use of non-thermal plasma in applications such as sterilization of living tissues, living objects for medical applications, blood coagulation, wound healing and tissue regeneration and . Apart from these applications, studies have been carried out to find out the possible uses of cold plasma in dentistry. The dental applications that have been experimented are inactivation of oral microorganisms associated with periodontal diseases, dental caries, root canal disinfection, surface modifications of dentine and implants, polymerization and tooth bleaching

Cold plasma/ Non-thermal atmospheric pressure plasma
The temperature of non-thermal plasma is 104ºF at the point of application. Energy is required to produce plasma. Electric, light or thermal energy can be used. Cold plasma can be produced using different gases such as Helium, Argon, Nitrogen, Heliox (a mix of helium and oxygen), and air. Some methods used to produce cold atmospheric plasma are Dielectric Barrier Discharge (DBD), Atmospheric Pressure Plasma Jet (APPJ), plasma needle, and plasma pencil The non-equilibrium nature of atmospheric plasma wi phase at low temperatures and highly reactive particles, allows it to be directly applied to living tissues at safe temperatures. The highly reactive plasma species clean, etch, modify, form a thin layer of plasma coating or react with the surface they come into contact with, depending on the gas composition. This characteristic feature of plasma has been used in various fields 12,13 .
The surface interaction is based on the excited particles produced by the ionised gas with an essential equal positive and negative charges. These excited particles will decay and excite other particles, thus reacting with the surface in a dry chemical way 14

USES OF COLD PLASMA IN CONSERVATIVE DENTISTRY AND ENDODONTICS
Vellapanchavadi, Chennai-77 To recapitulate the possible applications of non-thermal plasma in conservative thermal plasma is lately being researched for its applications in dentistry summarize the possible role of Nonthermal plasma in conservative dentistry and endodontics.
Plasma is the fourth state of matter and also the most form, the other three being air, water and solid. Plasma is ionised form of gas and is of two types: thermal and thermal or cold atmospheric plasma. The cold atmospheric plasma based dental cations is being investigated recently in fields such as root canal disinfection, tooth whitening, sterilization, deactivation of oral biofilms, enhancement of strength of light cure f a great use in dentistry due to its properties. This review is to recapitulate and bring to light the possible uses of cold atmospheric possible uses of cold plasma in dentistry. The dental applications that have been experimented are inactivation of oral microorganisms associated with periodontal diseases, dental caries, root canal disinfection, surface modifications of ts, polymerization and tooth bleaching [4][5][6][7][8][9][10] .
mal atmospheric pressure plasma thermal plasma is 104ºF at the point of application. Energy is required to produce plasma. Electric, light or thermal energy can be used. Cold plasma can be produced using different gases such as Helium, Argon, x of helium and oxygen), and air. Some methods used to produce cold atmospheric plasma are Dielectric Barrier Discharge (DBD), Atmospheric Pressure Plasma Jet (APPJ), plasma needle, and plasma pencil 11 . equilibrium nature of atmospheric plasma with gas phase at low temperatures and highly reactive particles, allows it to be directly applied to living tissues at safe temperatures. The highly reactive plasma species clean, etch, modify, form a thin layer of plasma coating or react with the hey come into contact with, depending on the gas composition. This characteristic feature of plasma has been plasma are short lived 15 . Thus, surface treatment by plasmas can clean and improve the bonding characteristics of polymers by changing the surface energy of materials 16 .

Applications of cold plasma in endodontics
The non-thermal atmospheric plasma was effective in disinfection of root canals. The conventional methods of disinfecting the root canals include mechanical debridement, chemical irrigation, laser irradiation, and ultrasound. These methods cannot achieve complete disinfection of endodontic sites 17 . The failure of endodontic treatment is frequently caused by Enterococcus faecalis 18 . Many studies have been done to investigate the disinfection of root canals using plasma-based approaches.
The study by Jiang C et al was the first to demonstrate the effectiveness of plasma mediated removal of bacterial biofilms from root canal surfaces and dentinal tubules. He and He/ (1%) O2 plasmas were used. Complete inhibition of Bacillus atrophaeus on nutrient agar plates on exposure to He and He/ (1%) O2 plasmas for 60 seconds was observed. He/ (1%) O2 plasma was shown to be more effective than He alone for eradication of Bacillus atrophaeus. A 180 seconds treatment with He/ (1%) O2 plasma disinfected human tooth root canal with saliva-derived biofilms 6 .
The antibacterial effects of cold plasma against Enterococcus faecalis in vitro was evaluated by Du T et al. The study showed that treatment of E.faecalis biofilms on tissue culture plates for 5 minutes with atmospheric pressure nonequilibrium plasma or 2% chlorhexidine killed majority of the bacteria in biofilms. Infected single rooted teeth were also exposed to atmospheric pressure non-equilibrium plasma or 2% CHX for 5, 10 and 15 minutes. Bacterial survival remarkably reduced with increased exposure times with atmospheric pressure non-equilibrium plasma and 2% CHX. ANAP was found to be as effective as 2% chlorhexidine for inactivating bacteria in infected root canals 19 .
Jie Pan et al also studied the disinfection of tooth root canal with E. faecalis biofilms in vitro using cold plasma. Seventy single rooted teeth infected with E.faecalis biofilms were divided into 7 groups. The group 1 was the negative control group which received no treatment. Group 7 was treated with calcium hydroxide intracanal medication for 7 days. Groups 2 to 6 were treated with cold plasma for 2,4,6,8 and 10 minutes respectively. A single electrode nonthermal atmospheric pressure plasma jet was used to treat the E. faecalis biofilms. The results of the study showed that, compared with the positive control group, cold plasma treatment of 8 or 10 minutes (groups 5 and 6) had a significantly higher anti microbial efficacy 20 .

Influence of cold plasma in bond strength of composite resin restoration
In conventional composite resin restorations, the connection between resin and intact dentin is brought about by the adhesive or bonding agent. The penetration and subsequent polymerization of the adhesive monomers increases the bond strength. Incomplete penetration will lead to leakage and disruption of the hybrid layer 21 . Resin adhesive penetration into the demineralised dentin under the influence of plasma treatment was studied by Y Zhang et al. Extracted, non-carious, unerupted human third molars were used. The prepared dentin surfaces were etched and sectioned perpendicularly. The separated halves were randomly treated with argon plasma brush or gentle argon air blowing for 30 seconds. The specimens were then applied with a model adhesive containing BisGMA and HEMA, gently air dried for 5 seconds and light cured for 20 seconds. The results revealed higher content of adhesive at the adhesive/dentin interface in plasma treated specimens as compared to controls. The penetration of HEMA was especially enhanced. Plasma treatment could also improve the polymerization at the interface 7 .
Other similar studies by Dong X et al and Ritts AC et al also revealed that plasma treatment improved the interfacial bonding strength 22,23 .
The effectiveness of cold plasma for inducing polymerization of model self -etch adhesives was studied by Chen M et al. Monomer/water mixtures with varying mass ratios of monomers were treated with non-thermal atmospheric plasma brush for 40 seconds at 32º to 35ºC. For comparison, photoinitiators were added to the mixtures, which were light-cured for 40 seconds. The results of the research indicated that nonthermal atmospheric plasma exposure induced polymerization of the photo initiator-free self-etch adhesives. The presence of water did not negatively affect the degree of conversion (DC) of plasma cured samples but caused decline in the DC of the light-cured samples. The study showed that the possibility of having dental composite restorations with enhanced properties and performance by polymerization with non-thermal atmospheric plasma brush 9 .
Composite resins are relatively hydrophobic when compared to enamel and wet dentin which are hydrophilic. This makes adhesion between the resin and the tooth substrate difficult. Good wettability is needed to enhance adhesion between these two substrates. Chen M et al studied the surface modification of dental substrates including dentin, enamel and two composites using non-thermal, atmospheric plasma brush. The study demonstrated that this device could be used effectively to improve the surface wettability of these substrates clinical setting. SEM images also indicated no significant changes in the morphology of these dental substrates 24 .
Cho B et al investigated the shear bond strength of composite resin to ceramic with plasma polymer coating using nonthermal atmospheric -pressure (NAP) glow discharge. A small pencil-type NAP glow discharge plasma torch was used. The study revealed that the shear bond strength (SBS) of the adhesive to ceramic surface pre-treated sequentially with water plasma and TEGDMA plasma in helium gas was significantly higher than that of the adhesive to the untreated surface 25 .

Tooth bleaching
Lee et al demonstrated tooth bleaching with nonthermal atmospheric pressure plasma. A helium plasma jet device was used. Teeth were sectioned sagitally into halves and assigned to experimental and control groups randomly. The experimental group was treated with hydrogen peroxide plus plasma for 10 minutes while the control group was treated with hydrogen peroxide for the same duration. The results showed improved bleaching efficacy with hydrogen peroxide and plasma compared with using hydrogen peroxide alone. The surface temperatures of the teeth did not exceed 40ºC during plasma treatment. Tooth surface proteins were seen to be noticeably removed with plasma treatment 10 . In addition, teeth stained with coffee or red wine could be effectively whitened using plasma jet in combination with hydrogen peroxide compared with using hydrogen peroxide alone 26 .
Tooth whitening using hydrogen peroxide with direct current cold atmospheric plasma microjet was demonstrated by Sun P et al 27 .
Intracoronal tooth bleaching using nonthermal atmospheric pressure plasma was studied by Park JK et al. Forty extracted, single rooted and blood stained human teeth were randomly divided into two groups. One group was treated with 30% hydrogen peroxide with nonthermal atmospheric plasma intra coronally for 30 minutes. Other group received hydrogen peroxide alone intracoronally for the same duration. The efficacy of bleaching with hydrogen peroxide and plasma was significantly higher compared to using hydrogen peroxide alone. The temperature was approximately 37ºC during treatment with plasma 28 .
Kim MS et al used hybrid Ar gas-liquid plasma to produce tooth whitening. It was confirmed that tooth whitening in this study was primarily due to OH radicals 29 .
Nam et al investigated tooth bleaching using non thermal atmospheric pressure plasma (NAAP) with low concentration of hydrogen peroxide. Forty human teeth were randomly divided into four groups: 15% carbamide peroxide (CP) with NAAP, CP plus plasma arc lamp, CP plus diode laser, CP alone. 15% carbamide peroxide with NAAP showed highest bleaching efficacy with temperature during treatment around 37ºC 30 .
Claiborne et al investigated the use of low temperature atmospheric pressure plasma (LTAPP) delivered using plasma pencil with hydrogen peroxide gel. Thirty extracted human teeth were randomly divided into two groups. One group received LTAPP with 36% hydrogen peroxide and the other group received 36% hydrogen peroxide gel only at 10, 15 and 20 minutes duration in both groups. The effectiveness was significantly higher with LTAPP and 36% hydrogen peroxide compared to hydrogen peroxide alone in 10 and 20 minutes groups. The temperature in both the groups remained under 80ºF with no possibility of thermal injury 2 .

CONCLUSION
The above evidence suggests that plasma may be used in conservative dentistry and endodontics for increased effectiveness of treatment using it. It is due to its non thermal nature, anti-microbial properties and ability to modify the surfaces that comes in contact. It can be used to disinfect the root canal, increase bond strength in composite restorations and in tooth bleaching.