## 3 Results
### Processing and Bacteriological Analysis of Infected Tenth  
After the first processing that included instrumentation, bacterial growth was observed in the enrichment media for oregano, lemongrass and melaleuca. In a synergism with mechanical treatment, thymme and clove completely inhibited _E. faecalis_ growth. After the second processing which involved only irrigation and no instrumentation, after enrichment in broth, bacterial growth was observed in all the samples except NaOCl. Nevertheless, the turbidity of the enrichment media was lower for the samples irrigated with AqEOs thanfor control (Figure 3) considering the same incubation time, which suggests a degree of inhibitory effect. During the second processing, the persistence of bacteria in the root canals after irrigation with AqEO, without instrumentation was also evaluated by the semi-quantitative method. The results showed a complete clearance of _E. faecalis_ (no bacterial growth on agar plates) by clove and oregano EO, as well as by NaOCI. Thyme was also highly effective, with only a few colonies being observed on the culture medium after irrigation. Lemongrass showed also an important effect, decreasing the bacterial load with more than 75%. Melaleuca AqEO presented an effect similar to that obtained by irrigation only (with  
Figure 3: Bacterial growth in enrichment media after irrigation with AqEOs, with and without instrumentation. Figure 2: Assessment of minimum inhibitory concentrations (MICs) for aqueous extracts of essential oils (AqEOs) against _E. faecalis_: A—Oregano; B—Thyme; C—Lemongrass; D—Clove; E—Melaleuca; H11- positive control; H12—negative control. The concentration of AqEOs in columns 1–12 (v/o) are: 50%, 25%, 12.5%, 6.25%, 3.125%, 1.56%, 0.78%, 0.4%, 0.2%, 0.1%, 0.05% and 0.025%. To increase the success of root canal treatment it is necessary to use a biocompatible intracranial irrigant able to reduce or eliminate the bacteria from the root canal [28]. Despite the qualities of NaOCl, it has clinical disadvantages, especially cytotoxicity. The search for bio-friendly and more biocompatible irrigants made us determined to undertake this study, also considering the rising interest in natural alternatives to chemical antiseptics and antimicrobials, in particular EO and probiotics. Herbal products, due to their biocompatibility are used in many medical fields [32]. Plants are able to defend themselves against microbial aggressors due to their secondary metabolites which are present. Also, the leaves, the bulbs, and the seeds of the plants contain antimicrobial active compounds, which contribute to the antibacterial properties of the plants [13]. _E. faecalis_ has the ability to invade dentinal tubules and resist even in the presence of calcium hydroxide dressings for more than 10 days, as reported by some authors, due to its power to adapt to harsh environmental conditions [9; 10; 33]. Also, _E. faecalis_ is an initiator of endodontic biofilm, being able to form microcolonies on the root canal dentin surface [33]. Antibacterial agents present either bactericidal (act aggressively on key bacterial structures), or inhibitory effects (interfere with bacterial structures or metabolic pathways, being a reversible phenomenon). Current chemical compounds such as NaOCl or chlorhexidine are highly effective, but do not persist at their action site. Sodium hypochlorite (NaOCl) is commonly used for root canal disinfection, as a root canal irrigant, which in concentration of 1-6% is able to reduce bacterial infection [27; 28; 30]. Although NaOCl is commonly used for root canal disinfection, it presents disadvantage such as chlorinated odor, which can be unpleasant for both doctor and patient. This odor is a result from the reaction of NaOCl with water [34].