Effects Of Root Canal Preparation On Infected Root Canal Formation Periapical Biofilm：a Vitro Study

Pulpitis and periapical periodontitis is a type of inflammatory disease,mainly caused by bacteria infections and occurred in the pulp andperiapical tissue. It is a common disease, accounting for60%of the oralmedicine clinic. Root canal therapy is the preferred method for thetreatment of pulpitis and periapical periodontitis. At present, the successrate of root canal treatment is more than68~85%. The failures of root canaltreatment are mainly as refractory apical periodontitis and post-treatmentendodontic diseases. Apical biofilm is considered to be the main cause ofthe refractory periapical disease and post-treatment endodontic disease.Currently, more scholars have studied the structure and source ofperiapical biofilm. Scholars have reached a consensus that periapicalbiofilm comes from infected root canal. However, the study of mechanismfrom infected root canal to apical biofilm is little and inconclusive. Themain methods of periapical specimen collection are extraction of teeth andapical surgery. But coverage by these two methods is limited. It limits theresearch on these issues. Therefore, in this study we expect to establish a root canal-apical complex model in vitro, to discover the effects of rootcanal preparation on infected root canal formation periapical biofilm andguide clinical treatment.Purpose:1. This study will be proposed to establish a root canal-apical complexmodel in vitro.2. This study will discover the effects of root canal preparation oninfected root canal formation apical biofilm.Methods:1. Premolar with one root, extracted for orthodontic, was sealed insterile vial containing LB solid medium, making the culture medium reachone third of apical. Totally25root canal-apical complex models wereprepared. Five models were randomly selected to detect bacteria inperiapical tissues by PCR immediately after modeled. The remaining20models were randomly subjected to a control group (n=10) and experimentalgroup (n=10). Extracted teeth were opened in experimental group and thecontrol group received no treatment. All models were exposured to air. On21d, bacteria were detected through PCR in root canal and apical of the twogroups; endotoxin content in apical was assayed by chromogenic end-pointlimulus test.2. Root canal-apical complex models (n=115) were prepared accordingto the above method. Five models were randomly selected to detect bacteria in periapical tissues by PCR immediately after modeled. The remaining110models were randomly subjected to a control group (n=25) and experimentalgroup (n=85). Extracted teeth were opened in experimental group and thecontrol group received no treatment. All models were exposured to air21days. In experimental group, five models were randomly selected to detectthe presence or absence of bacteria in root canal to determine infection rootcanal has been formed. In the control group, five models were randomlyselected to detect the presence or absence of bacteria in periapical tissue todetermine the closure effect of the models. The remaining80experimentalmodels were divided into four groups. Group1: not treated, group2: cordpulled, group3: root canal prepared according to the working length of theisolated tooth, group4: root canal prepared beyond the apical foramen.Immediately,7d,14d and21d after root canal preparation, the presence orabsence of bacteria at apical were detected by PCR. Extraradicular biofilmwas observed using a scanning electron microscope when bacteria weredetected. Immediately,7d and21d after root canal preparation, endotoxincontent in apical was assayed by chromogenic end-point limulus test.Results:1. In apical, bacteria was not detected in all groups, but detected in rootcanal of the experimental group. The endotoxin content was increasedsignificantly in experimental group compared with control group (P<0.01).2. Immediately,7d and14d after root canal preparation, bacteria was not detected in all groups;21d after root canal preparation, bacteria wasdetected in group3and group4. In addition, extraradicular biofilm wasobserved in group3and group4.Endotoxin content: Immediately,7d,14d and21d after root canalpreparation, there were no significant differences between group1andgroup2. Compared with control group1, immediately after root canalpreparation, the endotoxin content was decreased significantly in group3and group4, and more significant reduction in group4;7d,14d and21dafter root canal preparation, the endotoxin content was increasedsignificantly in group3and group4, and more significant increase in group4.Conclusion:1. Root canal-apical complex was established in vitro through thismethod. Bacteria were not easy to reach the apical when root canal was notdisturbed. Bacteria in the infected root canal caused apical periodontitisthrough the secretion of virulence factors such as endotoxin.2. When root canal was prepared full-length or beyond the apicalforamen, bacteria in infected root canal were more likely to spread to theapical than just marrow was pulled, and endotoxin content increased more significantly in periapical tissues.