Since natural alternatives are needed in dentistry for the treatment of root canal, where the standard irrigant is NaOCl with significant toxicity, the aim of the study was to assess the antibacterial properties of non-chemical root-canal irrigants (aqueous extracts of oregano, thyme, lemongrass, melaleuca and clove essential oils) against Enterococcus faecalis. For this, aqueous extracts of each essential oil (AqEO) were prepared. A solution of sodium hypochlorite (NaOCl) was used as a positive standard against which the antimicrobial effects of AqEO could be reported. The root canals of seven teeth were inoculated with 20 µL of Enterococcus faecalis ATCC29212 inoculum and incubated overnight at 37 °C. All the teeth canals were instrumented and were irrigated with the corresponding AqEO, NaOCl and saline solution, then rinsed with saline. Bacteriological samples for each canal post-instrumentation were collected with sterile paper points which were inoculated on culture media. A second processing followed the same methodology but involved only irrigation and no instrumentation. Using instrumentation, thyme and clove completely inhibited Enterococcus faecalis growth. Without instrumentation, clove and oregano AqEOs completely reduced the bacterial load as seen in direct inoculation, but bacterial growth was observed in all the samples after enrichment, except for NaOCl. Nevertheless, the turbidity of the enrichment media was lower for the samples irrigated with AqEOs than for control. In conclusion, AqEOs of thyme, oregano and clove showed a promising antibacterial effect, especially when teeth instrumentation was performed.

The aim of the study is to evaluate antibacterial properties of commercial essential oils (Oregano, Black pepper, Coriander, Cinnamon) against oral pathogens (Streptococcus mutans, Enterococcus faecalis). Nevertheless, we want to asses if the price of the essential oils (EO) which were purchased from 2 different retailers, can influence the quality of essential oil and the antimicrobial effect. Materials and methods: Essential oils from two different Producers (A-high price range, respectively B-low price range) with two opposite price ranges were purchased from local retailers. The inhibitory effect was assessed by disk diffusion. Bacterial inoculums of 0.5 McFarland units (~1.5 x 108 CFU/ml) were prepared from Streptococcus mutans Enterococcus faecalis. Muller-Hinton agar plates were inoculated with bacterial inoculums. Sterile paper disks with the diameter of 6 mm (Bioanalyse Ltd, Turkey) were dispensed on the medium surface. Five μl of essential oils were pipetted on corresponding disks. After 10 minutes (time needed for a proper diffusion of active components), the plates were incubated in normal atmosphere at 37°C. After 24 hours of incubation, the inhibition zone diameters (in millimeters) were read and noted in spreadsheet software, aside the average price in €/ml of essential oil. A cost-efficiency antibacterial activity index was also calculated.Results:With regard to EO from Producer A, the inhibition zone against Enteroccocus ranged from the weakest 14mm(Black pepper), 28mm(Coriander) to the strongest over 40 mm(Oregano and Cinnamon). With regard to volatile essential oils from Producer B, against the Enteroccocus, the smallest inhibition zone was observed for Coriander (10 mm), followed by Black pepper(11 mm); on the opposite side, the strongest inhibition zone presented both Oregano EO and Cinnamon EO (34 mm). Against S. mutans, the weakest inhibition zone showed Black pepper(6 mm), followed by Coriander EO(12 mm) and the strongest inhibition zone had Oregano EO(38 mm) and Cinnamon EO (40 mm). All the EO from the Producer A managed to successfully inhibit S. mutans growth. In both producers, Origanum vulgare EO was the most cost-efficient against E. faecalis (index=0.06 for Producer A and 0.03 for Producer B). In the case of Producer A, against S.mutans the best index was seen at Coriandrum sativum EO (0,05) and the weakest at Cinnamonum zeylanicum (0,14). In the case of Producer B, against E. faecalis, the lowest index was seen at Piper nigrum(0,13). The same pattern was seen against S. mutans, the highest index had Origanum vulgare(0,03) and the lowest Piper nigrum (0,23) Conclusions:Most of essential oils studied from both Producers, had better antibacterial effect against S. mutans compared to E. faecalis.All the EO from the Producer A managed to successfully inhibit S. mutans growth.The high price EO had a better antimicrobial effect compared to the low price EO.The strongest antimicrobial effect against E.faecalis had the high-price Oregano and Cinnamon EO and the weakest antimicrobial effect had low-price Coriander EO. Against S. mutans, the greatest efficacy had all high-price EO, and the lowest had the low-price Black pepper EO.The high price of some EO (Piper nigrum) does not make any difference regarding the antibacterial effect. Lower price EO may be still suitable in regards of antibacterial effect if considering the associated costs, even if the effect does not reach the potency of the higher-price alternatives.