Effect Of PH On Antibacterial Activity And Soft Tissue Dissolving Property Of Sodium Hypochlorite

Root canal therapy is an effect measure to cure pulpities and apical periodontitis.The fundamental principle of it is controling infection and eradicating reinfection.But there also exsits failure rate in the treatment process. In all the pathogenic bacteria that could lead to reinfection, Enterococcus faecalis is a primary one,whose detection rate is relatively high.Enterococcus faecalis possesses the peculiarity of small volumn and strong survival ability,subsequently,it becomes the refractory bacteria in the root canal system. Calcium hydroxide could not resist the infection of Enterococcus faecalis.Residual pulpities is one form of failure in root canal therapy.Because residual pulps locate hiddenly,it is difficult to clean the root canals in the machanical way.Denatured and necrotic pulps are also difficult to be thoroughly cleaned,using the machanical method.Thus it is necessary to use an efficient endodontic irrigation solution to clean the root canals in auxiliary.Sodium hypochlorite is a widely used root canal irrigation solution in the clinical operation.lt owns the characteristics of broad spectrum of antimicrobial and powerful antiseptic effect,and also could dissolve the dental pulps,which is benifical to the root canal cleaning.Although the antibacterial activity of high concentration is stronger than the low concentration one,the irritation is relatively stronger.Once the irrigation solution exceeds the apical foramen,it would cause greater damage to the periapical tissue.In addition,it cannot completely kill Enterococcus faecalis in the root canals within a time of irrigating,whether it is the high concentration one or the low one.Since pH could effect the quality and proportion of active ingredients in the sodium hypochlorite solution,it can be a significant factor which could influence the antibacterial activity and soft tissue dissolving property of sodium hypochlorite.The purpose of these experiments is investigating the effect of pH on antibacterial activity and soft tissues dissolving property of sodium Hypochlorite solution by adjusting the pH,and finding an effective irrigation solution which could maintain the antibacterial activity and soft tissues dissolving property of it,but also create less damage to the periapical tissue.Objective:To evaluate the antibacterial activity of sodium hypochlorite against Enterococcus faecalis within root canals and the dissolving effect on soft tissues by altering the pH.Methods:①Root canal irrigation:Two hundred single root canals from extracted human teeth that had already contaminated with Enterococcus faecalis were randomly divided into11groups.Group1to Group9contained20teeth per group,and Group10and Group11,10per group. The canals from Group1to Group9were irrigated by sodium hypochlorite with the following configuration:5.25%,pH12;5.25%,pH7.5;5.25%,pH6;2.5%,pH12;2.5%,pH7.5;2.5%,pH6;1.25%,pH12;1.25%,pH7.5;1.25%,pH6;Group10was underwent the normal saline,and Group11,5%sodium thiosulfate.Microbiological samples were collected from root canals before and after irrigation,transformed the amount of bacteria into the form of lg(CFU/ml+l),and operated the variance analysis of factorial design to the data from Group1to Group9.②Filter paper dispersion:Filter paper were put on the solid culture medium that had been coated Enterococcus faecal is. Added the solutions from Group1to Group9on the filter paper.Group1to Group9solutions were sodium hypochlorite with the following configuration:5.25%,pH12;5.25%,pH7.5;5.25%,pH6;2.5%,pH12;2.5%,pH7.5;2.5%,pH6;1.25%,pH12;1.25%,pH7.5;1.25%,pH6;Group10solution was normal saline.After the48h culturing,measured the diameter of the antibacterial loop,and operated the variance analysis of factorial design to the data from Group1to Group9.③Dissolution:Porcine muscle tissues was equally cut into70pieces with their original weight been noted.Put the pieces into the2.5%sodium hypochlorite with the pH were respectively12(Group1),7.5(Group2) and6(Group3),the forth group was normal saline.After5min,15min and30min,weighted the pieces and calculated the weight variation, and operated the multivariate variance analysis of repeated measurement to all the data.Results:①Enterococcus faecalis within all the11groups was decreased;Results of variance analysis from each level of pH in each level of concentration showed that, antibacterial activity of sodium hypochlorite with different level of pH was markedly different (P<0.01),and the pH6groups were more effective than those of pH12and7.5groups,and the pH12groups were the least effective, pH7.5groups was situated in the middle;There was significant difference between every group of irragation solutions (P<0.01) except Group1and Group6,Group4and Group9(P=0.7084、 P=0.6280).②Evident antibacterial loops were observed from Group1to Group9,but those from Group10were not. Results of variance analysis from each level of pH in each level of concentration showed that, antibacterial activity of sodium hypochlorite with different level of pH was markedly different (P<0.01),the diameter of antibacterial loops were the longest from pH6groups,and then the antibacterial activity was the most effective,while the pH12groups,the least effective,pH7.5groups was situated in the middle;There was significant difference between each group of solutions (P<0.01).③All groups of sodium hypochlorite from3pH levels could dissovle porcine muscles and bring weight variation,while normal saline could not.Results from repeated measurement multivariate variance analysis showed,dissolving activity of sodium hypochlorite with different level of pH was markedly different (P<0.01),the pH12group dissolved the most tissues,and then the dissolving activity was the most effctive, while the pH6group,the least effective,the pH7.5group was situated in the middle.Conclusions:①The antibacterial activity is enhanced while the pH becomes lower, when the pH is6, antibacterial activity is the most effective.②The dissolving activity is enhanced while the pH bocomes higher,when the pH is12, dissolving activity is the most effective.