Bactericidal effects of tea tree oil on E. faecalis

Objective: This study evaluated the antibacterial effect of calcium hydroxide associated with different dressing vehicles (tea tree oil, propylene glycol, and distilled and deionized water) against Enterococcus faecalis. Methods: A single colony of E. faecalis (ATCC29212) was selected from Mueller-Hinton plates, which were incubated for 24 h at 37oC, and then inoculated in brain-heart infusion for the same period. The broth was adjusted to 1.0 McFarland standard. Nine agar plates with 20 ml of Mueller-Hinton were inoculated with E. faecalis (1:100 dilution), and experimental groups were as follows: GI: tea tree oil; GII: calcium hydroxide with propylene glycol; GIII: calcium hydroxide with tea tree oil; GIV: calcium hydroxide with distilled and deionized water. Combinations were mixed in 1:3 (p/v) ratio, until a paste consistency was obtained (except for tea tree oil alone). Four wells (one for each material on each plate) were made by removal of agar at equidistant points and then filled immediately with the substances, totaling 12 samples for each group. The zones of inhibition were measured from the periphery of the well after 24 h. Results: Calcium hydroxide dressings associated with water had a significantly higher antimicrobial effect (13.00 mm ± 0.81) than those associated with tea tree oil (10.66 mm ± 0.47) and propylene glycol (11.00 mm ± 0.0), which were similar at the level of 1% (Kruskal-Wallis test). The use of tea tree oil alone was not compared due to the difference in diffusibility, however, the present study showed that when used alone tea tree oil presented the highest bacterial inhibition (17.33 mm ± 0.47). Conclusions: Tea tree oil may be an alternative dressing for infected root canals, however, before introducing it into daily practice other physical properties should be evaluated.