Formulation of Mouthwash Utilising Knobweed Leaf Essential Oil (Hyptis capitata Jacq.) and Evaluation of Antibacterial Efficacy against Streptococcus mutans, the Etiological Agent of Dental Caries

Background: Dental caries is associated with acid-producing oral microorganisms, including Streptococcus mutans. This study aimed to formulate mouthwash preparations containing knobweed (Hyptis capitata Jacq.) leaf essential oil and evaluate their physicochemical properties and in vitro antibacterial activity against S. mutans.Methods: Essential oil was obtained from dried knobweed leaves by steam distillation, and phytochemical screening was performed. Three mouthwash formulations containing 0.5% (F1), 1% (F2) and 2% (F3) essential oil were prepared. Organoleptic characteristics, homogeneity, pH, viscosity and sedimentation were evaluated. Antibacterial activity against S. mutans ATCC 25175 was assessed using an agar-well diffusion assay with positive and negative controls. Inhibition-zone measurements were analysed by one-way analysis of variance and Tukey's post hoc test.Results: The reported essential-oil yield was 3.05%. Phytochemical screening indicated the presence of flavonoids, alkaloids and terpenoids. All three preparations were homogeneous, and no visible sedimentation was recorded. Formulation pH ranged from 6.89 to 7.07, while viscosity ranged from 2.79 to 3.40 cP. Mean inhibition-zone diameters were 8.93 ± 1.79 mm for F1, 9.79 ± 1.28 mm for F2 and 12.77 ± 0.78 mm for F3. The positive and negative controls yielded 17.68 ± 1.33 mm and 7.23 ± 0.29 mm, respectively. Overall differences among groups were statistically significant (p < 0.001).Conclusion: The 2% formulation produced the largest inhibition zone among the tested mouthwashes, although the negative control also exhibited inhibitory activity. These in vitro findings warrant further evaluation of the essential oil's specific contribution.