الفهرس 
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Abstract
The aim of this study was to develop an intracanal polymicrobial biofilm and testing its susceptibility to different antibacterial medications in vitro
A total of seventy single rooted human teeth were used in this study .Teeth were decoronated to a length of 16 mm, cleaned and shaped , longitudinal grooves were made along the entire length of the teeth before preparation and the teeth were divided into 9 groups , 7 experimental groups (n=8) and 2 control groups ,the positive control group (n=10) and the negative control group (n=4).The positive control group and the experimental groups were incubated with previously cultured Enterococcus faecalis,Staphylococcus epidermidis and Candida albicans to form a multispecies biofilm for 3 weeks at 37°C incubator.
Six samples were scanned for evaluating the biofilm development by SEM examination at three time intervals (days 7,14,21).
The 3-week-old bacterial biofilm grown on samples was observed for thickness, homogeneity, and presence of an extracellular polymeric substance using scanning electron microscopy.
After 21 days of incubation, calculated MICs of antimicrobials tested were applied to the experimental groups.
group 1: received 0.5 ml of 0.04 mg ciprofloxacin.
group 2: received 0.5 ml of 10 mg Doxycycline.
group 3: received 0.5ml of 30 mg Clindamycin.
group 4: received 0.5 ml of 0.1 mg of metronidazole.
group 5: received 0.5 ml of 24 mg Augmentin.
group 6: received 0.5 ml of 300 mg triple antibiotic paste, consisting of equal ratios of (Doxycycline, Ciprofloaxcin and metronidazole).
group 7 received 0.5 ml of calcium hydroxide.
After one week, all samples were irrigated with 20 ml sterile saline solution to remove the root canal contents, bacterial samples were taken using a standard method of collection and collected in sterile tubes containing saline for CFU, the effect of tested drugs on the biofilm dissolution was assessed with scanning electron microscope.
Results showed that all the experimental groups demonstrated significantly less CFU counts as compared to the positive control group (p <0.0001).As regard to the antimicrobial effectiveness of tested drugs, it was found that the most effective were Metronidazole and TAP with no statistical difference between them (p≥0.05), Followed by Clindamycin and Ciprofloxacin with no statistical difference between them (p≥0.05) and the least effective were Calcium hydroxide, Doxycycline and Augmentin respectively with no significant differences between them (p≥0.05).
Within the limitations of this study it can be concluded that:
1.None of the antimicrobial agents used was able to completely eradicate microorganisms from the root canal system.
2.The multispecies biofilm model is a better indicator for the nature of complex root canal infections than monospecies models.
3. The local application of antibacterial agents can be beneficial in resistant cases of apical periodontitis but only after culture and sensitivity testing to choose the appropriate agents against existing flora.
4.For the selected microbes, Metronidazole and TAP showed better antimicrobial efficacy compared to other drugs.
Recommendations: In order to obtain the maximum clinical benefit of antimicrobial agents, additional research should be directed to investigate the best drug delivery form, drug substantivity &the feasibility of using drug combinations.
Also, novel strategies should be directed to target the biofilm matrix which constitute the major bulk of the biofilm structure.