| Microorganisms and their by-products are the main pathogenic factors of endodontic therapy failure.Enterococcus faecalis（E.faecalis）is generally considered to be closely related to persistent/secondary root canal infections.It can harbor in root canal wall and invade into dentinal tubules.It can resistant to the nutrient deficiency environment.Hence,elimination or reduction of E.faecalis is of prime importance in preventing treatment failure and secondary infections.The elimination of infection consists of mechanical instrumentation,root canal irrigation,and intracanal medicament.The root canal system have complex internal anatomy and variations.Root canal preparation leaves untouched area and produces hard-tissue debris,which can be packed into root canal irregularities such as isthmuses,lateral canals and other irregular areas.The dentin debris could affect the physical,chemical and biological functions of irrigation solution and compromise the disinfection of the root canal system.It is necessary to remove the dentin debris,enhance the disinfection of the inaccessible areas,and improve the long-term prognosis.Irrigation plays a key role in root canal cleaning.Sodium hypochlorite（Na OCl）is the most widely used solutions with antibacterial effect and the ability to dissolve organic tissues.The conventional syringe and needle irrigation is influenced by the flow rate of fluid,the diameter of the needle,and the volume of irrigation.It is difficult for the solution to penetrate into the complex three-dimensional root canal system,especially in the apical third or the irregular areas.Therefore,various irrigation activation techniques have been implemented to improve the efficacy of root canal debridement,such as ultrasonically activated irrigation（UAI）,sonic irrigation,and laser-activated irrigation.Laser-activated irrigation is the use of erbium lasers（2780 nm Er,Cr:YAG and 2940 nm Er:YAG）to agitate water-based fluids.Vapor bubbles are formed in fluids,which expand and then collapse,inducing cavitation and photoacoustic phenomenon.The intensive shock waves can enhance the flow of the fluid,improving the removal of smear layer,debris and microorganisms.The technique has gradually become one of the most effective methods for root canal irrigation.The wavelength of Er:YAG laser is consistent with the highest absorption band of water,which has a good application prospect in laser-activated irrigation.Photon-induced photoacoustic streaming（PIPS）has attracted much attention due to its high efficiency and safety.It delivers single pulse into the liquid.Recently,the novel shock wave enhanced emission photoacoustic streaming（SWEEPS）has been introduced into clinical practice.The SWEEPS technique,which delivers synchronized laser pulses,was intended to enhance the cleaning and disinfection of PIPS.Until now,few study has assessed the new SWEEPS technology,and the effect on the root canal cleaning is still unclear.Therefore,the purpose of this study was to evaluate the cleaning efficiency of the SWEEPS for the removal of biofilm,dentin debris,and intracanal medicament,to analyze its possible mechanism of action,and provide a reference for related studies and clinical practice of endodontists.Part Ⅰ:Antibacterial efficacy of the novel SWEEPS against Enterococcus faecalis biofilmObjective:To compare the new SWEEPS technique with UAI and PIPS for the elimination of E.faecalis biofilm.Methods:Forty-eight human premolars were selected and prepared to Protaper F3,autoclaved,and incubated with E.faecalis for 4 weeks.Three specimens were randomly selected and visualized by scanning electron microscopy（SEM）to confirm the presence of biofilm on the canal wall and in the dentinal tubules.The negative and positive control groups were established.The remaining teeth were randomly divided into three experimental groups（n=13）:UAI,PIPS,and SWEEPS.Irrigation was performed by 2.5%Na OCl for each tooth with an activation time 2*30s.The bacterial count before and after irrigation was performed.The root canal walls were observed by using SEM.The ratio of dead/total bacteria in the dentinal tubules was determined by using confocal laser scanning microscope（CLSM）.Data were analyzed by one-way analysis of variance and nonparametric tests at a significance level of 5%.Results:All activation regimens significantly reduced bacterial counts（P<0.05）.The bacterial counts after irrigation was significantly different between UAI and SWEEPS groups（P<0.05）,but it was not significantly different between SWEEPS and PIPS groups and UAI and PIPS groups（P>0.05）.Residual bacteria or colonies was observed in all experimental groups.SWEEPS group resulted in a cleaner root canal surface.CLSM showed that SWEEPS had the highest level of dead bacteria in the dentinal tubules,but it was not significantly different between PIPS and UAI groups（P>0.05）.Conclusions:Compared with PIPS and UAI,SWEEPS had a better performance in dentinal tubules disinfection.The SWEEPS was similar to PIPS and was superior to UAI in root canal walls disinfection.Part Ⅱ:Debris removal from the root canal system of mandibular molars with a novel laser-activated irrigationObjective:To compare the efficacy of UAI,PIPS and SWEEPS for the removal of accumulated hard-tissue debris（AHTD）from the root canal system of mandibular molars by using microcomputed tomography（micro-CT）.Methods:A total of 30 mandibular first and second molars with joining mesial root canals containing an isthmus were selected.Mesial canals were prepared up to a Pro Taper F3 rotary file,and distal canals were prepared up to a F4 rotary file.No irrigation was carried out during preparation.Teeth were randomly assigned to three groups according to the irrigant activation method（n=10）:UAI,PIPS and SWEEPS.The final irrigation procedures were performed using a total of 15.5 m L of 1%Na OCl for each tooth with an activation time of3*30 s.All teeth were subjected to three micro-CT scans（before and after canal instrumentation and after final irrigation）at a resolution of 15μm.After three-dimensional model reconstruction,the volume of root canals and debris were measured and the percentage reduction（%Rd）of AHTD was calculated.The%Rd of AHTD was analyzed statistically using one-way analysis of variance and nonparametric tests at a significance level of 5%.Results:There were no significant differences between the three groups in terms of root canal volume before or after preparation,or the volume of debris after preparation（P>0.05）.In the mesial canals,irrigation with SWEEPS reduced the overall debris by 84.31%,which was significantly more than the reduction associated with PIPS and UAI（58.79%and 50.27%,respectively）.A significant difference was also observed between PIPS and UAI groups（P<0.05）.In the distal canals,The SWEEPS has a greater%Rd of AHTD than the PIPS and UAI groups,but was not significantly different between PIPS and UAI groups（P>0.05）.None of the groups was able to completely remove AHTD from the root canal.Conclusions:The SWEEPS was associated with significantly less debris compared than PIPS and UAI,especially in isthmus-containing mesial roots.None of the activation techniques completely removed debris from root canal systems.Part Ⅲ:Efficacy of different irrigation technique to remove calcium hydroxide from mandibular molar root canalsObjective:This study aimed to compare the efficacy of conventional needle irrigation（CI）,UAI,PIPS,and SWEEPS in removing calcium hydroxide[Ca（OH）2]from root canals of mandibular molars using micro-CT.Methods:A total of 40 mandibular molars with joining mesial root canals containing isthmus were selected.Mesial canals were instrumented to Protaper F3,and distal canals were prepared to F4.All teeth were subsequently filled with Ca（OH）2.Four irrigation groups（CI,UAI,PIPS,and SWEEPS）were established.All teeth were subjected to three micro-CT scans（after canal instrumentation,before and after final irrigation）at a resolution of 30μm.The volume of the canal after instrumentation and the volume of Ca（OH）2 before and after removal in each third of the root canal were measured,and the percentage reduction of Ca（OH）2 volume（%Rd）was calculated.Data were analyzed by one-way analysis of variance and Kruskal-Wallis analysis of variance at a significance level of 5%.Results:The volume of the canal after instrumentation and the volume of Ca（OH）2before removal showed no significant difference in each portion of the root canal between groups（P>0.05）.The residual Ca（OH）2 in the apical third was higher than those in the cervical and middle thirds in all groups（P<0.05）.Significant differences in%Rd of Ca（OH）2 were noted between CI and other groups in the apical third of mesial and distal canals（P<0.05）,but there were no significant differences between the three groups.No group demonstrated complete removal of Ca（OH）2.Conclusions:UAI and laser-activated irrigation significantly improved Ca（OH）2 removal in the apical third of mesial and distal canals.The SWEEPS and PIPS regimens performed similarly in terms of their cleaning effect.No irrigation technique could completely remove Ca（OH）2. |
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