Colonization Patterns Of Bacteria In Infected Root Canals And Susceptibility To Antibiotics In Vitro

Bacterial biofilms are microorganisms colony embedding in the extracellular matrix, adhering to the animate and inanimate substrata irreversibly. Dental plaque is un-mineralized bacterial sediment, adhering to the surface of teeth or prosthesis, constitute of viscous matrix and bacterium, as typical biofilm structure. In recent years, with the development of microbiology and molecular-biology technology, it is confirmed that dental plaque is closely related to caries and periodontitis, which has significant differences to planktonic bacteria in pathogenicity and drug resistance. Pulpitis and periapical periodontitis are bacterial infectious diseases, although the treatment methods update continuously, it is difficult to avoid the complications such as pain, reinfection, sinus not healing. In order to explore the pathogenesis of pulpitis and periapical periodontitis, improve treatment methods, this study planned to investigate the ultrastructure of microorganisms colonization in the teeth with pulpitis and periapical periodontitis, constructe root canal biofilm, and determine the MIC and MBEC of MNZ and TNZ on intracanal contents, to provide a reference for clinical application.MethodsText 1, healthy teeth (n=6), teeth with irreversible pulpitis(n=10), necrotic pulp (n=20), chronic periapical periodontitis (n=20), refractory periapical periodontitis (n=6)were divided equally into 2 groups to examine the presence of bacteria on the surface of dentin(Group A) and cementum(Group B) by using a scanning electron microscope respectively.Text 2,collected 15 intracanal contents of chronic periapical periodontitis , multiplying, regulated to 2×106 CFU /ml, selected orthodontic premolars or impaction third molar, intercepted 5mm of root, prepared to 40#, syringed, splitted, rinsed and disinfected,made to root discs,soaked into saliva overnight,inoculated standardized bacteria, constructed root canal biofilms. Observed bacterial biofilm formation in root discs at different- time-stages by SEM. Broth dilution method was used to determine the MIC and MBEC of MNZ and TNZ, statistical analysis.ResultsText 1, Group A, dentin surface of 28 infected root canals covered with dense bacterial aggregates with sticky matrix and among them 26 teeth exhibited microorganisms penetrating into the dentinal tubules , while the healthy teeth did not show detectable bacterium. Fungus infections were found in 2 teeth which were difficult to heal. In Group B, 13 of teeth with periapical periodontitis had root absorption and biofilms formed, while the healthy teeth and the teeth with irreversible pulpitis and necrotic pulp had no these changes. Three teeth with over-filled gutta-percha were also covered with biofilms. The ultrastructure of biofilm differed from the size of matrix and the composition of bacterium.Text 2, bacterial biofilms were readily formed on the root discs under selected condition (observed by SEM). Coccis colonized onto root canal wall on the first day of inoculation., different types of bacterial colonized on the root canal wall with time. First, cells just connected , and then developed to three-dimensional structure, embedding in dense matrix, covered dentinal tubule openings, penetrating into the dentinal tubules, formed mature biofilms. MIC of MNZ, TNZ on bacteria were 0.125～4.000μg /ml, 0.125～2.000μg /ml,MIC50 were 0.500μg /ml, 0.250μg /ml , respectively; MBEC of MNZ, TNZ were 8.000～>128.000μg /ml, 4.000～>128.000μg /ml, MBEC50 were 32.000μg /ml, 12.000μg /ml, respectively. Statistical analysis to compare MIC of MNZ and TNZ, MBEC of MNZ and TNZ, MIC and MBEC of MNZ, MIC and MBEC of TNZ, datas had a significant difference. A test bacteria remained survival at the highest concentration , MIC>32.000μg /ml, identified as resistant.Conclusion1. Microorganisms related with pulpitis,necrotic pulp and periapical periodontitis in the surface of dentin, those with periapical periodontitis in the surface of cementum, were implanted in biofilms , penetrating into the dentinal tubules or hid in the cementum resorption lacunae.2. Bacteria in infected root canals of chronic periapical periodontitis can colonize on the dentin soaked in saliva overnight, formed a mature biofilm structure gradually with the time in vitro.3. Bacteria growing as planktonic was sensitive to MNZ at concentrations greater than 4.000μg / ml and TNZ at concentrations greater than 2.000μg / ml. Once bacteria forming biofilms, drug at higher concentration should be demanded to eliminate them.4. Against bacteria of chronic periapical periodontitis (planktonic, biofilm), TNZ was significantly effective than MNZ.