| Refractory periapical periodontitis is a disease that cannot be easily cured by repeated applied root canal therapy. Undoubtably, patients with this kind of disease become the emphasis and difficulty of clinical treatment. There usually exists the vitality tenacious Enterococcus faecalis who has unique biological characteristics from other oral bacteria in the infected root canals. By now, from the so many imperfectly study designations in this area, we cannot draw a certain conclusion about detection rate of E.f in refractory periapical periodontitis cases, the differences of biological characteristics of the clinical E.f isolates and the standard strains and the antibacterial effect of laser to the clinical strains. Thus, this study improved the experimental design basing on the preliminary experiment research in our team aimed to solve the three questions above.1. Isolation and characterization of Enterococcus faecalisThis study included the patients with refractory periapical periodontitis which is already treated twice by a standard root canal treatment came to our department for treatment between December 2014 and March 2015. A pre-designed inclusion and exclusion criteria were used. After the collection of the patient’s information, we sampled the bacteria in infected root canals with Reciproc Ni-Ti rotaries. Then the different samples went into the process of isolated culture and 16 sr RNA sequencing identification. Finally several positive samples were selected, and we further determined their biological characteristics with Crystal Violet staining in combination with the OD570 determining method, the CFU counting method accompanied the OD600 determining and 96-well plate method. In addition, we analyzed the relationship between the isolation of E.f and clinical symptoms, and compared the differences between the clinical isolates and the standard strains.This totally included 39 cases with refractory periapical periodontitis and 18 positive clinical E.f isolates. The detection rate of E.f is 46.15%. Meanwhile, we found that the clinical isolates were homologous with E.f V583( with a similarity about 99%). The detection of E.f is not related to the clinical symptoms of pain, swelling, antrum and asymptomatic( P>0.05). Even though the standard E.f strains V583 and the 18 clinical isolates all possessed the ability of biofilm formation, but the ability between them is different( P<0.05). In addition, there were totally 7 samples possessed the significant difference in crystal violet staining experiment. However, there showed no difference when comparing the growth curve and acid and alkali resistant ability between the isolate strains and the standard strains. Besides, no obvious correlation between the bacterial biofilm formation ability and the clinical symptoms(P>0.05).2. Root canal disinfection methods on the clinical isolatesUltrasonic disinfection technique has been introduced into the normal application for the root canal therapy. Now, laser technology, with its good disinfection efficacy, has also been welcomed by more clinical doctors and researchers. Conclusions from current studies about the disinfection efficacy between lasers and ultrasonic technique are still controversial. So we planned to solve this clinical problem by a systematic review or a meta analysis. Even though there were some shortcomings among studies in this field, we can also concluded that the laser activated irrigation technique including the PIPS have their many unique advantages. Thus, we consider the laser treatment group is better than ultrasonic group before more studies with high quality come out.Then, in the last part of our study, we built up the ex-vivo E.f in hunger stage infected root canal model to examine different root canal disinfecting methods to the E.f clinical isolates. We take the Er:YAG laser with Na OCl group as the best match just as a former research of our team proved. In this study, we concluded that no matter in standard strains group or in the clinical isolates group, Er:YAG laser accompanied by Na OCl has a significant better effect in the surface and different depth of the root canal than the negative group( P<0.05). Er:YAG laser group owned better antibacterial effect than 5.25%Na OCl group. Additionally, as the depth increasing, the bacteria reduce rate has the tendency to reduce. When compared the two strains in this studies, we can draw that the clinical isolates is more resistant to the antibacterial methods.Above all, on the basis of the existing experiment we concluded that E.f has a higher detection rate in refractory periapical periodontitis root canals. Additionally, when we come across this kind of cases, Er:YAG laser may help us better disinfect the roots. Last but not least, further studies should notice that the most popular used standard strains ATCC 29212 which is isolated from the intestinal tract may have different characteristics from the E.f in infected root canals. |
