Evaluating The Role Of Plasma In The Disinfection Of The Resin Base And The Cleanliness Of Endodontic Files

Part Ⅰ Inactivation of Candida albicans on the surface of resin base by plasmaTest 1 Antifungal efficacy of plasma against planktonic Candida albicans on the surface of resin baseObjective:To investigate the fungicidal effects of different plasma（argon,30%H₂O₂ and 50%H₂O₂ plasma）on planktonic Candida albicans on the surface of resin base.Methods:Candida albicans were inoculated on polymethyl methacrylate specimens with the size of 9mm×9mm×2mm.Fifty-six resin specimens were randomly divided into fourteen groups（n=4）.The specimens in control group did not receive any treatment and the other groups were exposed to argon,30%H₂O₂ and 50%H₂O₂ plasma for different durations.Each specimen was immersed into phosphate bufffered saline（PBS）for 2h and sonicated for 5 min in an ultrasonic bath sonicater.PBS cell suspensions of corresponding specimens were serially diluted.Then aliquots of appropriate dilutions（200μl）were inoculated on Sabouraud dextrose agar（SDA）and incubated at 37℃ for 48h before the colonies were counted.The anticandidal efficacy of plasma was evaluated by the reduction of colony forming units（CFU）in log10.Reduction of 4 log10 CFU was regarded as the threshold of clinical relevance in accordance with EN 1275-2005.Results:The reduction of viable Candida albicans on the resin was 4.016 log10CFU with 100s of argon plasma treatment.The inactivation efficacy of 4.220 log10CFU was observed after 15s for 30%H₂O₂ plasma treatment.The reduction of viable fungi was 4.442 log10 CFU with the prolonged exposure time of 20s.The Antifungal efficacy of 4.306 log10 CFU was achieved after 15s for 50%H₂O₂ plasma treatment.The reduction of Candida albicans cells was increased further up to 4.618 log10CFU when 50%H₂O₂ plasma treatment time extended to 20s.Conclusions:Argon,30%H₂O₂ and 50%H₂O₂ plasma are effective in killing the planktonic Candida albicans on the resin base.The anticandidal effects of 30%H₂O₂ and 50%H₂O₂ plasma are better than that of argon plasma.Test 2 Inactivation of Candida albicans biofilms on the surface of resin base by plasmaObjective:To evaluate the fungicidal efficacy of different plasma（argon,30%H₂O₂ and 50%H₂O₂ plasma）on Candida albicans biofilms on the surface of acrylic resin.Methods:Candida albicans biofilms were cultivated for 48h on sixty-eight polymethyl methacrylate specimens with the size of 9mm×9mm×2mm.Sixty-four resin specimens were randomly divided into sixteen groups（n=4）.The specimens in control group did not receive any treatment and the other groups were exposed to argon,30%H₂O₂ and 50%H₂O₂ plasma for different durations.Each specimen was immersed into phosphate bufffered saline（PBS）for 2h and sonicated for 5 min in an ultrasonic bath sonicater.PBS cell suspensions of corresponding specimens were serially diluted.Then aliquots of appropriate dilutions（200μl）were inoculated on Sabouraud dextrose agar and incubated at 37℃ for 48h before the colonies were counted.The anticandidal efficacy of plasma was evaluated by the reduction of colony forming units（CFU）in log10.One of the remaining four samples was not treated by plasma and the others were exposed to Argon,30%H₂O₂ and 50%H₂O₂ plasma for 300s.Then the morphological changes of Candida albicans cell in biofilms were assessed by scanning electron microscopy.Results:The reductions of viable Candida albicans in biofilms did not reach the predefined threshold within 240s for argon plasma,80s for 3 0%H₂O₂ plasma and 60s for 50%H₂O₂ plasma treatment.The killing efficacy of Candida albicans in biofilms was 4.100 log10CFU after 300s argon plasma treatment.The inactivation efficacy of 5.161 log10CFU was observed with 30%H₂O₂ plasma treatment time of 100s.The anticandidal efficacy of 4.064 log10CFU was achieved after 80s 50%H₂O₂ plasma treatment.The killing efficacy was increased further up to 5.462 log10 CFU when 50%H₂O₂ plasma treatment time extended to 100s.Distinct micromorphological alterations and cells with pores were detected after exposure to plasma.Conclusions:Argon,30%H₂O₂ and 50%H₂O₂ plasma are effective in inactivation of Candida albicans biofilms formed on the surface of the denture base.The anticandidal effects of 30%H₂O₂ and 50%H₂O₂ plasma are superior to that of argon plasma.Part Ⅱ Evaluating the cleaning effect of argon plasma on the residual debris on the surface of endodontic filesObjective:To evaluate the cleaning effect of argon plasma on the residual debris on the surface of endodontic files after cleaning and disinfection.Methods:Thirty endodontic files after cleaning and disinfection were randomly divided into control group and four treatment groups（n=6）.The control group did not receive any treatment,and the other groups were exposed to argon plasma for different durations.Then the samples were observed using scanning electron microscopy to assess the cleaning effectiveness of argon plasma on the debris remaining on the surface of endodontic files.The adherent debris was analyzed by energy dispersive X-Ray spectroscopy（EDX）to determine the components of the residual debris.Results:The residual debris was effectively removed from the endodontic files after argon plasma treatment extended to 20min.Conclusions:Argon plasma can effectively remove the adherent debris from the surface of endodontic files and it can be applied to the cleaning procedures of contaminated endodontic files in the dental practice.