Atmospheric plasma jets are being intensively studied with respect to potential applications in medicine. The aim of this in vitro study was to test a microwave-powered non-thermal atmospheric plasma jet for its antimicrobial efficacy against adherent oral microorganisms. Agar plates and dentin slices were inoculated with 6 log 10 c.f.u. cm "2 of Lactobacillus casei, Streptococcus mutans and Candida albicans, with Escherichia coli as a control. Areas of 1 cm 2 on the agar plates or the complete dentin slices were irradiated with a helium plasma jet for 0.3, 0.6 or 0.9 s mm "2 , respectively. The agar plates were incubated at 37 6C, and dentin slices were vortexed in liquid media and suspensions were placed on agar plates. The killing efficacy of the plasma jet was assessed by counting the number of c.f.u. on the irradiated areas of the agar plates, as well as by determination of the number of c.f.u. recovered from dentin slices. A microbekilling effect was found on the irradiated parts of the agar plates for L. casei, S. mutans, C. albicans and E. coli. The plasma-jet treatment reduced the c.f.u. by 3-4 log 10 intervals on the dentin slices in comparison to recovery rates from untreated controls. The microbe-killing effect was correlated with increasing irradiation times. Thus, non-thermal atmospheric plasma jets could be used for the disinfection of dental surfaces.

The decontamination of implant surfaces represents the basic procedure in the management of peri-implant diseases, but it is still a challenge. The study aimed to evaluate the degradation of oral biofilms grown in situ on machined titanium (Ti) discs by cold atmospheric plasma (CAP). ~200 Ti discs were exposed to the oral cavities of five healthy human volunteers for 72 h. The resulting biofilms were divided randomly between the following treatments: CAP (which varied in mean power, treatment duration, and/or the gas mixture), and untreated and treated controls (diode laser, air-abrasion, chlorhexidine). The viability, quantity, and morphology of the biofilms were determined by live/dead staining, inoculation onto blood agar, quantification of the total protein content, and scanning electron microscopy. Exposure to CAP significantly reduced the viability and quantity of biofilms compared with the positive control treatments. The efficacy of treatment with CAP correlated with the treatment duration and plasma power. No single method achieved complete biofilm removal; however, CAP may provide an effective support to established decontamination techniques for treatment of peri-implant diseases.

The removal of biofilms from microstructured titanium used for dental implants is a still unresolved challenge. This experimental study investigated disinfection and removal of in situ formed biofilms from microstructured titanium using cold atmospheric plasma in combination with air/water spray. Titanium discs (roughness (Ra): 1.96 µm) were exposed to human oral cavities for 24 and 72 hours (n = 149 each) to produce biofilms. Biofilm thickness was determined using confocal laser scanning microscopy (n = 5 each). Plasma treatment of biofilms was carried out ex vivo using a microwave-driven pulsed plasma source working at temperatures from 39 to 43°C. Following plasma treatment, one group was air/water spray treated before re-treatment by second plasma pulses. Vital microorganisms on the titanium surfaces were identified by contact culture (Rodac agar plates). Biofilm presence and bacterial viability were quantified by fluorescence microscopy. Morphology of titanium surfaces and attached biofilms was visualized by scanning electron microscopy (SEM). Total protein amounts of biofilms were colorimetrically quantified. Untreated and air/water treated biofilms served as controls. Cold plasma treatment of native biofilms with a mean thickness of 19 µm (24 h) to 91 µm (72 h) covering the microstructure of the titanium surface caused inactivation of biofilm bacteria and significant reduction of protein amounts. Total removal of biofilms, however, required additional application of air/water spray, and a second series of plasma treatment. Importantly, the microstructure of the titanium discs was not altered by plasma treatment. The combination of atmospheric plasma and non-abrasive air/water spray is applicable for complete elimination of oral biofilms from microstructured titanium used for dental implants and may enable new routes for the therapy of periimplant disease.

Tooth material surface chemical and micromechanical properties are important for success and sustainability in restorative dentistry. Modification by cold atmospheric plasma jet treatment may help to improve presently existing shortcomings as a part of future restorative therapies. The present study has been focused on changes of surface properties of tooth substances by this approach. Polished and etched enamel and dentin slices from the vestibular face of bovine incisors are used. A plasma jet modifies these surfaces at a distance of 2 mm and with a scan velocity of 5.5 mm Á s À1. The treatment parameters are: helium process gas flow 3.525 slm, plasma excitation by 2.45 GHz with an average pulsed microwave power of 2 W, single pulse power of 250 W, pulse width 5 ms. The surface modifications are subjected to laser scanning microscope roughness-measurement, contact angle measurements, X-ray photoelectron spectroscopy (XPS) analysis and morphological visualization by scanning electron microscopy (SEM). Plasma treatment causes changes of surface roughness and morphological alterations on dentin, while no such changes are measureable on etched dentin and polished and etched enamel surfaces. Plasma causes contact angle reductions for both, water and ethylene glycol. XPS analyses show significant carbon reduction on enamel surfaces after plasma treatment. Admixture of 30% of hydrogen peroxide or deionized water, respectively, as precursors in the plasma jet processing gas flow generates measureable amounts of CÀO-bindings at the surfaces assigned to hydrophilic groups. Surface modifications by plasma treatment might enable interesting new options for dental procedures in all areas of interaction between tooth substance and restorative materials.

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