What exactly is “plasma”?
When we talk about plasma, we usually mean a gas with ions, electrons and neutral particles (atoms, molecules, radicals). Plasma has e.g. B. proven to be effective for the sterilization of medical devices, packaging in the food industry, implants or blood coagulation. It is generated, for example, by radio or microwave frequencies and high voltage. Recently, plasma has also been recommended in dentistry to improve bond strength, especially in conjunction with the new monomer-free material PAEK.
What does “surface modification using plasma pretreatment” mean for prosthetic restorations?
In the dental literature, plasma pretreatment is increasingly recommended for improved bond strength between two or more materials (e.g. for attachment or repair). The material surface is “bombarded” with ionized gases: free radicals are formed. A surface coating develops through the refraction of the polar groups. The process gas between two electrodes after the energy supply is ionized and a plasma jet is created. The thickness and quality of the plasma coating depends on the type and purity of the gas used, the pressure and the position of the restoration during pretreatment. In general, plasma pretreatment is defined as a process that uses partially or fully ionized gas with approximately equal numbers of positively and negatively charged particles.
Can plasma pretreatment really increase bond strength?
There are different research results on this. Theoretically, the material surface should be activated by the plasma and functional groups should be formed at the same time. One study initially showed significantly higher bond strength values after pretreatment with helium plasma. However, the composite could not withstand its stability after thermal aging. In contrast, other studies observe no increase in bond strength between various polymers (PMMA, composite, PAEK) or zirconium oxide and dental composites based on dimethacrylate after plasma pretreatment - regardless of time, gas used and pressure of the plasma. However, a negative effect on the bond strength is not measured in any in-vitro study.
All studies unanimously report that there is a higher wettability (surface tension) after plasma pretreatment. The plasma pretreatment activates the surfaces on an atomic and molecular level, producing a hydrophilic surface and thus improving wettability. The plasma pretreatment has no influence on the surface roughness and topography. Further investigations and further developments are clearly necessary here.
SAVE: It is important to ensure that the surface only remains active for a few minutes after the plasma pretreatment and therefore must be continued quickly.
What does the term “cold plasma” mean?
There are two types of plasma treatment. A distinction must be made between warm and cold plasma. In dentistry, cold plasma is generally used for surface modifications. This is not warmer than 40 °C at the time of application. Devices that can produce cold plasma include, for example, the dielectric barrier discharge device, the atmospheric pressure plasma jet, the plasma needle and the plasma pen.
In addition to surface modification, are there other dental indications for plasma treatment?
Yes, cold plasma is used e.g. B. also for eliminating various types of bacteria in the biofilm and in the root canals or for pure disinfection. In addition, when teeth whitening, plasma can be used together with other agents (e.g. hydrogen peroxide or carbamide peroxide) to increase effectiveness. Cold plasma can also be used to treat oral mucosa infections such as herpes simplex, aphthous ulcers or even stomatitis. An attempt has already been made to use the plasma jet to clean teeth or as a toothbrush. However, further studies in this area are needed.
Bogna Stawarczyk, Annett Kieschnick, Anja Liebermann