A Matter of Fact: Cold Atmospheric Plasma in Periodontics

Introduction

The three states of matter are well established and are a no-brainer: Solid, liquid and gas. The fourth state of matter is plasma which may be news to many. It is a form of ionized gas and makes up 99% of the universe (Figure 1). Components of the stars, lightening and aurora borealis include plasma. Although present in abundance in nature, acquiring it directly from these sources is not a feasible option. However, it can be synthesized in laboratories. This is accomplished by subjecting gases to heat or running them through electromagnetic field until they become ionized.

Plasma is generally produced by an electric discharge in noble or molecular gases, such as argon (Ar), helium (He), oxygen (O2), and nitrogen (N2), using different excitation schemes, such as microwaves, radiofrequency and direct current (DC) or alternating current (AC) electric fields.¹

There are two variation of plasma: Thermal and nonthermal plasma (NTP). In thermal plasma, both the heavy particles (atoms, molecules and ions) and the electrons are in thermal equilibrium and are present in very high temperatures whereas non-thermal or cold plasma are partially ionized gases, where the electrons are of higher temperature but the heavy particles have a much lower temperature, approximating to that of room temperature (<40°C).²

History William Crooks first discovered plasma in 1879 in Crookes tube. The term plasma was introduced by Irving Langmuir. He portrayed plasma as a fluid with electric charge that transports electrons and ions, similar to blood plasma which transports white and red cells. The Siemens Company utilized plasma release to create ozone in the 1850s.³

The idea of using Cold Atmospheric Pressure (CAP) for innovative dental procedures was first proposed by Stoffels and colleagues, where they proved its efficacy against Streptococcus mutans.⁴

Pioneer research involving Periodontics goes back to 1992 with observations by Swartz et al. ⁵ At the time, CAP was used for cleaning and sterilisation of titanium surfaces. The story of how CAP found its way from the sterilization rooms into the operating rooms is contained in this article.

Production of CAP

Plasma output sources can be divided into indirect, direct plasma devices and hybrid devices. In an indirect plasma device, which is commonly fabricated as a jet design, plasma is produced by ionization of the working gas between two electrodes and continuously pushed out by the gas flow. In a direct plasma device, plasma is generated between the electrode of the device and the treated surface, which functions as a grounded electrode. These devices can operate by utilizing ambient air:⁶ Hybrid devices are still at an experimental level.⁷

The forms of energy required to generate plasma can be, thermal, light, or the commonly used electric discharge.

Direct Devices

These consist of Direct barrier discharge, Plasma brush and Corona discharge device.

Direct Barrier Discharge (DBD)

It was made by Siemens in 1857 and possesses two metal electrodes. One electrode is a high voltage, and another is a grounded electrode. Gas passing between electrodes is ionized and plasma is formed. Alternative current of high voltage is required, and the power consumption is 10–100W (Figure 2A).⁸

More recently, Friedman et al. developed the floating electrode DBD (FE-DBD).⁹ It is comparable to the original DBD except that the second electrode is not grounded. The second electrode can be human skin, or any organ which is considered ‘active’. The powered or active electrode needs to be at least < 3 mm of the biological sample to create the discharge (Figure 2B).

However, it is not advisable for therapeutic application in the internal organs of the human body such as tooth root canals.

Atmospheric Plasma Pressure Jet (APJJ)

Atmospheric Plasma Pressure Jet (APPJ) are the plasma jets having the gas temperature ranges from 25–200 °C with a charged-particle density of 10¹¹–10¹² cm^-3 and reactive species at high concentrations, i.e., 10–100 ppm. It can be made up with different setups in which a gas mixture is pushed to flow quickly between two electrodes. The mixture may contain oxygen, helium and/or other gases. One of the common setup is shown in Figure 3A, where a RF of 13.56 MHz at a power of 50–100 W is applied on the discharge creating a central (cathode) electrode, and the outer electrode (anode) is grounded.¹⁰

In 1992, Koinuma et al. pioneered the Radiofrequency (RF) cold plasma jet. Later in the year 2002, Stoffels et al. constructed a miniature version of the atmospheric plasma jet and called it ‘Plasma needle’. A new model was made in 2004. Samples were placed inside the box in the earlier version because the needle was confined in it. The plasma needle consists of a 0.3 mm diameter of metal wire with a sharp tip inside of a Perspex tube (Figure 3B) and a 2 mm diameter of plasma glow is generated as a result. Its small size enables accuracy and precision.¹¹

Plasma Needle/Plasma Pen

Laroussi et al. presented a miniature jet and called it ‘Plasma pencil’ (Figure 4). A tube in the shape of a cylinder with 2.5 cm diameter is taken and two electrodes of equal diameter as the tube are inserted. These electrodes are placed with a distance of 0.3 – 1 cm and a thin copper ring is attached to the dielectric copper disk. To produce plasma, the two electrodes are subjected to a sub microsecond high voltage pulses. The holes in the electrodes are used to inject gas. Once adequate discharge is produced, a plasma plume is launched through the hole of the outer electrode into the air. Because the plasma plume remains at low temperature (290K), it can be touched safely. The high voltage is supplied to the pulse generator by a DC voltage supply with variable output.¹² It has various application owing to its transportable size. 

Mechanism of Action

Plasma is considered an electrically conducting medium that reacts to electric and magnetic fields. These are also known to contain huge amounts of electrons, ultraviolet photons, active radicals that are highly reactive in nature.¹ These highly reactive species, especially those of nitrogen and oxygen contain free radicals that cause oxidative stress and biological destruction of pathogens.

The liquid environment, in which the cells are normally located, acts as an interface between plasma and living matter. CAP can activate a liquid interface with reactive species which then act as a carrier agent to deliver the antibacterial effects onto the underlying target surface.¹³

In general, the production of reactive oxygen and nitrogen species affect various microbial structures. The cell wall could be etched and the membrane damaged by disruption and lipid peroxidation. Genetic material of the bacteria is destroyed by oxidative damage, protein denaturation or breaking of strands. Many factors determine the anti-microbial effects including the device parameters and the experimental setup, and especially the treated pathogens.¹⁴

The interaction of CAP with prokaryotic cells can cause loss of cellular content due to resultant cell rupture caused by formation of pores. The destruction of covalent bonds in the polymeric matrix of microbial biofilms favours their disruption.¹⁵ This interaction enhances the anti-microbial activity of CAP and has determined its place in periodontal therapy.

Figure 5 represents the device and method of application of CAP into the oral cavity.¹⁶

CAP in Periodontics

The various treatment options in Periodontics fan out with a preliminary non-surgical treatment followed by appropriate surgical techniques with regeneration being the cornerstone of periodontal procedures. The role of CAP is outlined in each of these interventions.

Non-surgical therapy

The utility of CAP as an adjunct to scaling and root planing (SRP) was documented by Küçük et al. ¹⁶ They demonstrated a significant increase in CAL gain and reduction in colonization of periodontal pathogens.

The effect of application of CAP on periodontal pathogens including P. gingivalis, A. actinomycetem comitans were extensively studied. The results showed decrease in these pathogens that was time-dependent. Observations differed depending on the variety of noble gas used as well.⁶

Anti-viral agent

The possibility of use of CAP as an anti-viral agent was ventured based on its ability to induce release of hydrogen peroxide in contact with water. Plasma-activated water was used for de-activation of phages. Further, their purpose against adenovirus led the investigators to study its effect against herpes virus.¹⁷ Interestingly, with further research, CAP could prove to be a one-stop-shop for both viral as well as bacterial infections.

Role in regeneration

Fibroblast: Kwon et al., evidenced the association of non-thermal atmospheric pressure plasma jet (NTAPPJ) on gingival fibroblasts and the results demonstrated that NTAPPJ increased mRNA expressions of growth factors in human gingival fibroblasts.¹⁸

Cementoblast: The value of CAP and its outcome on cementoblasts were noted in which therapeutic measures with CAP was shown to stimulate regeneration associated processes in dental cementoblasts.¹⁹

Osteoblast: Increased alkaline phosphatase activity and enhanced mineralization was noted when plasma irradiation was conducted under specific conditions. The yield of radicals was also increased in a time-dependent manner.²⁰

In guided bone regeneration, the potency of CAP used with titanium meshwork reduced the surface energy, thereby improving wettability of the material.²¹ This had a positive response when judged by speed and amount of bone augmentation.

CAP as the magic wand of healing

The performance of CAP in terms of healing has been long established. Studies show that upregulation of matrix, proliferation, inflammation, and degradation genes, and downregulation of apoptotic genes, a higher cell proliferation, and wound closure were observed after the application of CAP.²²

CAP in Implantology

Dental implants have become a routine treatment option in the field of dental prosthesis. However, the success of dental implants depends upon a lot of factors. So, the clinician aspires to take steps to completely eradicate the possibilities of post-operative complications; the most feared of them is peri-implantitis. Removal of biofilm is the determining factor of controlling or preventing peri-implantitis. Decontamination of implant surfaces can be achieved by subjecting the implant to CAP as evidenced by Flörke et al. ²³

The antimicrobial effect and biofilm reduction was investigated on two different types of implant surfaces and observations revealed a promising therapeutic option for the treatment of peri-implantitis.²⁴

The healing capacity provided through CAP treatment could enhance osseointegration of dental implants and has the potential to serve as an effective treatment option in peri-implantitis therapy.²⁵

Application of CAP significantly increased the adhesion of gingival fibroblasts to the titanium surface with no cytotoxic effect on gingival fibroblasts.¹⁴

Study by Yan et al. showed that the activated titanium has beneficial effects on cell adhesion and proliferation, and meanwhile has no adverse effects on cytocompatibility.²⁶

Modified Forms of CAP

The efficacy of CAP has been increased by integrating 2% chlorhexidine to enhance its versatility in the treatment of peri-implantitis.²⁷

In addition to this, atmospheric air has been used by Yan et al. as opposed to use of novel gases which proves to be a more feasible option.

Limitations in the Use of CAP

With advent of new state-of the-art technology, considerations need to be given to the downside as well. Availability could be a major factor in this regard. Use of natural resources such as noble gases cannot be considered as an eco-friendly choice.

Cost could be a restraining factor when it comes to utility in routine dental practice.

Conclusion

The application of CAP in Periodontics is still at its cradle. The idea of a magic pen that could erase wounds seems all but impossible. It is a minimally invasive option that can work wonders. With further research it could be a promising tool in the future for Periodontics and dental implants.

Conflict of Interest

None