## 3 Results
### Processing and Bacteriological Analysis of Infected Tenth
Without instrumentation, AqEOs decreased the bacterial load (clove and oregano down to no bacterial growth, as seen in the direct paper-points assessment), but viable bacteria still persisted. Oregano and thyme EO are known as having one of the best antibacterial effects. The antibacterial effect of oregano extract on _E. faecalis_, observed in our study, was also reported in previous studies, where a concentration 1% and NaOCl had similar antibacterial effect, and better effect than ethylenediaminetetraacetic acid. Moreover, at this concentration, oregano EO is less cytotoxic than NaOCl [47; 48]. Oregano AqEO content was mostly composed of carvacrol, followed by 5-10% of each para-cymene, gamma-terpinene and linalool. Carvacrol was generally found to be main constituent of oregano EO, with very good antibacterial effect [21; 49]. In this study, from all the oils evaluated, thyme EO presented the lowest MIC against _E. faecalis_, as previously reported [49; 50; 51]. In concordance with other findings [52], our HPLC analysis showed thymol, para-cymene, gamma-terpinene and linalool as main bioactive constituents of thyme EO. The other tested AqEOs (lemongrass, clove, melaleuca) presented high MIC values (50%_v/v_), supposedly making them ineffective as antibacterial substances. As a reminder, in our study aqueous solutions of EO were used, so a lower activity is expected than compared with whole EO effect. Nevertheless, clove AqEO (in synergism with instrumentation) was capable of completely neutralizing _E. faecalis_ from the root canal. The major bioactive constituent of clove is eugenol and eugenyl-acetate (with broad-spectrum antimicrobial activity against Gram-positive, Gram-negative, fungi and viruses, and widely used as sedative dressing, cement formulations or endodontic sealer), comprising more than 95% of all detected compounds [53; 54]. This makes us conclude that even small amounts of these compounds are enough to exert the bioactive effects, and thus may explain the difference between the high MIC versus the good ex vivo efficiency in treating infected root canals. Because of its bioactive potency (good antibacterial effect, but also tissue irritant), clove EO is recommended to be used in small concentration, to protect the vital tissues [55], but still to provide an effective result. The failure of root canal therapy due to _E. faecalis_ infection is associated with microbial-related factors such as proton pump activity, collagen adherence or inter- and intraspecies horizontal gene transfer [56] which makes the treatment difficult; this is the reason of choosing this study to search for more bio-friendly and biocompatible irrigants. Complementary to this, other studies confirmed the usefulness of probiotics for dental health [57; 58]. However, other studies suggest new approaches that might be used for the treatment of _E. faecalis_ infections, such as transcriptome sequencing for identification of genes that are associated with bacterial survival and adaptability [59]. Another therapeutic approach is the use of isolated phages for targeting _E. faecalis_ in dental infections [60]. These perspectives could offer a more effective therapeutic approach that excludes the use of both natural and chemical substances alike. Rather than by just studying the MIC and MIB of natural substances on _E. faecalis_, another aspect that needs to be further explored in order to precisely find a naturally derived bactericidal compound, is the specific array of characteristics that enables _E. faecalis_ to escape chemo-mechanical instrumentation. These mechanisms include activation of some survival genes, the targeting of highly nutritional tooth areas, or the presence of strong bacterial synergism [61]. Given these facts, since the root canal treatment is constantly evolving, we can assert that natural products, particularly essential oils, can be alternative intracanal irrigants against bacteria.