Effect Of Different Irrigation Solutions On The Repair Of Apical And Periapical Tissues Of Dog's Teeth With Periapical Lesion

Chronic periapical periodontitis is a long-standing non-specific inflammation of the periapical tissues .The source of the inflammation is in the root canal. The decline of immunity or the reinforcement of irritation can lead to acute attack; when the immunity is enhanced or the irritation is attenuated, acute inflammation can be transformed into chronic inflammation, impaired periapical tissues can be repaired. The lesions often involve periapical alveolar bone and cementum.Root canal therapy is a method of treating pulp necrosis and periapical diseases. it is also an important way to conserve dental tissues. The source of irritation can be eliminated through the following steps: preparation, disinfection and obturation of the root canal. And it will be cured with the help of abundant blood supply and strong repair and regeneration capacity of periapical tissues. However, there still lack of relatively systematic reports about the effect of root canal irrigation solutions on the repair of apical and periapical tissue.In this study, dogs were used to establish experimental chronic periapical periodontitis model with bone resorption. Through the root canal therapy, the antimicrobial effect of different root canal irrigation solutions and their effects on the repair of periapical tissues were observed. The study is divided into four parts:1. Establishment of dog models of chronic periapical periodontitis by different methodsEighty premolar roots from four mongrel dogs were selected for the study, and were randomly divided into four groups of twenty roots each. Standardized preoperative Periapical radiographs were taken of all the roots. Crown access was made under anesthesia, and then the root canals were filled with bacterial endotoxin, mixed bacteria, Enterococcus faecalis and normal saline in different group. Apical periodontitis was radiographically confirmed after 30, 45, 60, 75,90days.The results are as follows: LPS group showed apical shadow at 30days; mixed bacteria group showed apical shadow at 45 days, which showed a rapid progress; Enterococcus faecalis group showed apical shadow at 90 days; the control group (NS group) didn't show any apical shadow during the experiment. These results indicated that the mixed bacteria or LPS can cause periapical inflammation rapidly and effectively, however, the developments of periapical periodontitis induced by Enterococcus faecalis were milder than that of the other two experimental groups.2. The research of antimicrobial activity of two combinations of root canal irrigation solutions on predominant bacteria from periapical periodontitis in vivoThe animal model of periapical periodontitis induced by mixed bacteria were selected, and randomly divided into three groups, treated with three different combinations of root canal irrigation solutions during the root canal preparation (two experimental groups: 5.25% Sodium hypochlorite plus EDTA group and 3% hydrogen peroxide plus NS group; the blank control group was NS group).The bacteria in each canal were sampled and counted under light microscope before and after the root canal preparation. The data revealed that: (1) the bacteria in root canals of each group reduced significantly after root canal preparation(P<0.01); (2) After treated by 5.25% Sodium hypochlorite plus EDTA and 3% hydrogen peroxide plus the difference between the two groups against obligate anaerobes was not significant(P>0.05), however, compared with the blank control group, both experimental groups showed significant differences (P<0.05); (3) 5.25% Sodium hypochlorite plus 17% EDTA group showed better antimicrobial activity than 3% hydrogen peroxide plus NS group and the blank control group on facultative anaerobes(P<0.05), and the difference between the latter two groups was not significant(P>0.05). These results indicated that 5.25% Sodium hypochlorite plus 17% EDTA as a combination of root canal irrigation solutions has a stronger antimicrobial efficacy on several predominant bacteria.3. The research of antimicrobial activity of two combinations of root canal irrigation solutions on Enterococcus faecalis in vivoThe animal model of periapical periodontitis induced by Enterococcus faecalis were selected, and randomly divided into three groups, treated with three different combinations of root canal irrigation solutions during the root canal preparation (two experimental groups: 5.25% Sodium hypochlorite plus EDTA group and 3% hydrogen peroxide plus NS group; the blank control group was NS group).The bacteria in each canal were sampled and counted under light microscope before and after the root canal preparation. The results showed that: (1) the bacteria in root canals of each group reduced significantly after root canal preparation(P<0.01); (2) After irrigating with 5.25% Sodium hypochlorite plus 17% EDTA, Enterococcus faecalis were all cleared, the two experimental groups had no significant difference(P>0.05), however, compared with the blank control, the difference was significant (P<0.05). These results indicated that 5.25% Sodium hypochlorite plus 17% EDTA has a stronger antimicrobial efficacy against Enterococcus faecalis.4. Effect of different root canal irrigation solutions on the repair of periapical tissues of teeth with periapical lesion after endodontic treatmentAll the teeth were submitted to root canal therapy as in Part 2and Part 3. After three months, the animals were sacrificed by anesthetic overdose, and the obtained histological sections were stained weith hematoxylin and eosin for optical microscopic analysis of apical and periapical repair. The results revealed that in the animal model induced by LPS the inflammatory responses among all the groups were the same(P>0.05); in the animal model induced by mixed bacteria there was better histological repair(P<0.05)in the goups with 5.25% Sodium hypochlorite plus 17% EDTA than the groups with 3% hydrogen peroxide plus NS group or the blank control group ;in the animal model of periapical periodontitis induced by Enterococcus faecalis, there were no noticeable differences between the 5.25% Sodium hypochlorite plus 17% EDTA group and the 3% hydrogen peroxide plus NS group(P>0.05), they both have better histological repair ( P<0.05 ) than the blank control group(P<0.05).Therefore it can be concluded that biomechanical preparation with 5.25% Sodium hypochlorite plus 17% EDTA showed better results in apical and periapical tissue repair of teeth with chronic apical periodontitis in short period. It still need longer period to examine its long-term effect.