Efficacy Of The Photon-initiated Photoacoustic Streaming Combined With Different Solutions On Enterococcus Faecalis In The Root Canals

BackgroundChronic periapical periodontitis(CAP),which is associated with long-term root canal infections,can cause chronic and progressive destruction of the periapical tissue of the affected tooth.Currently,root canal therapy is the most commonly used and effective treatment method.Mechanical preparation combined with chemical irrigation is the main method to disinfect the root canal in the process of root canal therapy,which can effectively remove the bacteria,dentin debris and necrotic pulp tissue in the root canal.Mechanical preparation is mainly for the root canal wall containing bacteria and their toxins,but more than 50% of the root canal wall is still unprepared,so chemical irrigation is an indispensable step.However,due to the complex anatomical structure of the root canal system,the lateral accessory root canals in the root canal structure often become blind spots for mechanical debridement and chemical irrigation due to their small features.The combined use of sodium hypochlorite,chlorhexidine and MTAD and other irrigation solutions cannot be used.To achieve a complete sterilization effect,the infectious substance stays in the root canal,leading to long-term prolonged periapical inflammation.Enterococcus faecalis is usually an isolated bacterium associated with persistent periapical lesions,and most of them exist in the root canal system in the form of biofilms.Studies have shown that nickel titanium instrument preparation combined with 5.25%Na OCl irrigation can only remove 50–75% of bacteria in infected root canals.In order to improve the removal effect of bacteria in root canals,researchers are looking for a new type of root canal irrigation method and propose the supplementary use of laser-activated irrigation technology,which can improve the distribution of root canal irrigation fluid in the root canal system and improve irrigation efficiency.Photon-induced photoacoustic technology(PIPS),a form of laser-activated irrigation,can activate the root canal irrigation solution by producing intense photoacoustic shock waves under low pulse energy,and the velocity of fluid flow caused by cavitation is ten times higher than that produced by ultrasonic stirring,inducing efficient three-dimensional flow irrigation in the whole root canal system.It has been proven that PIPS has the potential to eliminate the smear layer.However,the antimicrobial effect of different root canal irrigators combined with a PIPS laser is not very clear;thus,the following three experiments were designed for this study.Objective(1)To study the effect of PIPS combined with different irrigation solutions in the resin root canal models,and to determine the suitable root canal irrigation solution.(2)To study the effect of PIPS in different tapers and diameters of root canal models,and to explore the appropriate taper and diameter of the root canal.(3)To evaluate the bactericidal effect of PIPS combined with Na OCl at different diameters or root canal tapers in vitro.Materials and methods(1)A total of 240 artificial root canal samples were included in the study.The models were split and incubated for two days to form the E.faecalis biofilm.Six different irrigation solutions were distilled water,1% Na OCl,2% Na OCl,5.25% Na OCl,MTAD,and CHX,combined with conventional needle irrigation(CNI)or Photon induced Photoacoustic Streaming(PIPS)for root canal irrigation.Finally,adenosine5’-triphosphate(ATP)was used to detect planktonic bacteria,fluorescence microscopy,to observe the biofilm,and Image Pro Plus to analyze the average fluorescence intensity to explore the most suitable root canal irrigation solution.(2)Artificial root canal samples(n=480)were randomly divided into three groups(n=160/group).The canals were prepared to fit file size #10/.02,#25/.02,or #25/.06.The size #10/.02 group was incubated for seven days.Size #25/.02 or #25/.06 was incubated for two days.A stable biological model of E.faecalis infection was established.The root canals were irrigated with distilled water,1%,2%,or 5.25%Na OCl combined with CNI or PIPS,respectively.Bacterial suspensions and biofilms were assessed using an ATP assay kit and fluorescence microscopy.Image Pro Plus was used to analyze the average fluorescence intensity to determine the most suitable root canal irrigation solution.(3)Twenty-three maxillary first molars with three independent root canals were included in this study.The mesiobuccal(MB),distalbuccal(DB),and palatal(P)root canals were prepared with file sizes #10/.02,#25/.02,and #25/.06,respectively.After incubation with a bacterial suspension for 4 w,the specimens were irrigated with 2%Na OCl activated by CNI(n=10)or PIPS(n=10).Three specimens were not treated(control group).Before and after irrigation,the presence of bacteria was assessed using an ATP assay kit,and biofilms were assessed using confocal laser scanning microscopy(CLSM)and scanning electron microscopy(SEM).Results(1)In the CNI and PIPS groups,the ATP value immediately decreased after irrigation,and there was no significant difference between the six subgroups(P>0.05).The ATP level in the PIPS group was significantly lower than that in the CNI group(P<0.05).After incubation,the ATP value of each subgroup increased significantly,but the ATP value in the PIPS group was lower than that in the CNI group(P<0.05).There was no statistical difference in the intensitye intensity of 5.25% Na OCl + PIPS and 2%Na OCl + PIPS after irrigation and after incubation(P>0.05).(2)In the CNI and PIPS groups,the ATP value of the 5.25% Na OCl subgroup was the lowest,followed by that in the 2% Na OCl and 1% Na OCl subgroups.The ATP value of the distilled water subgroup was the highest(P<0.05).When the root canal taper was 0.02,the ATP value of #10/.02 + PIPS group was significantly lower than that of the #25/.02 + CNI group(P<0.05).The average fluorescence intensity of the #10/.02+ PIPS group was lower than that of the #25/.02 + CNI group(P<0.05).When the apical diameter was #25,the ATP value of the 0.02 taper in the PIPS group was lower than that of the 0.06 taper in the CNI group(P<0.05),and the average fluorescence intensity of the 0.02 taper + PIPS group was lower than that of the 0.06 taper + CNI group(P<0.05).The 2% and 5.25% Na OCl combined with PIPS can effectively improve the long-term antibacterial effect after root canal irrigation and re-culture for6 h.(3)In the specimen prepared using PIPS irrigation,ATP was reduced by more than 98%.When the root canal taper was 0.02,the size #25 root canals had a higher percentage of dead bacteria than the size #10 root canals in all regions(P<0.05)in the PIPS group.When the root canal diameter was #25,the 0.02 taper group had a higher percentage of dead bacteria than the 0.06 taper group in the apical region(P<0.05),and no significant differences were observed between the coronal and middle regions(P>0.05).PIPS irrigation resulted in a greater percentage of dead bacteria and reduction of ATP in size #10/.02 root canals than CNI in size #25/.06 root canals in three regions(P<0.05).Conclusion(1)PIPS-assisted Na OCl root canal irrigation can achieve a better irrigation effect.In the CNI group,5.25% Na OCl showed the best antibacterial and bacteriostatic effects,followed by 2% Na OCl.The antibacterial and bacteriostatic effects of 5.25% Na OCl and 2% Na OCl were the same after using PIPS.(2)Compared with CNI,PIPS has a greater ability to remove bacteria in root canals with a small preparation diameter and a small taper.PIPS with 2% and 5.25% Na OCl exhibited superior antibacterial and bacteriostatic effects.(3)Increasing the diameter of the root canal improves the bactericidal effect of PIPS when the same taper is used.Increasing the taper had no positive effect on the antibacterial effect of PIPS in the #25 root canals.PIPS had a greater bactericidal effect in root canals with a smaller taper and diameter.PIPS effectively cleaned the smear layer and opened the dentinal tubules in the coronal region of the root canals.