MATERIALS AND METHODS: Matured, healthy and disease-free leaves of Eucalyptus globulus were collected. The leaves were washed under tap water and finally dried in an oven at a temperature of 45°C for 48 hours. The dried plants were ground in an electric blender to make them into a powder. The powder was mixed with 100% ethanol and kept it inside a shaker overnight at 35°C. The mixture was centrifuged for 10 minutes at 2,500 rpm. Three different concentrations (10%, 50%, and 100% v/v) were used as antibacterial agents. Chlorhexidine (0.2%) was considered as positive control and dimethyl formamide was considered as negative control against P. gingivalis and A. actinomycetemcomitans. The disc diffusion method was used to determine the extract's antibacterial activity against the test organisms. A digital Vernier caliper was used to measure the diameter of antibacterial activity showing the zone of inhibition in millimeters.

RESULTS: Eucalyptus globulus with 100% concentration showed a maximum zone of inhibition against A. actinomycetemcomitans and P. gingivalis (5.38 ± 0.32 mm, 4.82 ± 0.11 mm) followed by 50% and 10% accordingly. The negative control of dimethyl formamide showed a zone of inhibition of 0.48 ± 0.96 mm and 0.63 ± 0.20 mm against A. actinomycetemcomitans and P. gingivalis. The positive control of 0.2% chlorhexidine showed a zone of inhibition of 8.46 ± 1.02 mm and 7.18 ± 0.54 mm against A. actinomycetemcomitans and P. gingivalis. The ANOVA test showed a highly significant antibacterial efficacy in 0.2% chlorhexidine and 100% concentration Eucalyptus globulus.

CONCLUSION: A significant maximum zone of inhibition against A. actinomycetemcomitans and P. gingivalis was showed by 100% concentration of Eucalyptus globulus.