Comparative analysis of the inhibitory effects of natural cinnamon leaf oil, clove oil, and commercial eugenol on Streptococcus mutans

Dental caries remains one of the most prevalent chronic diseases worldwide and imposes a substantial burden on healthcare systems. Streptococcus mutans is recognized as a primary etiological agent in the initiation and progression of carious lesions. While eugenol-based materials such as zinc oxide-eugenol (ZOE) are widely used in caries management, reliance on expensive, imported commercial eugenol creates vulnerabilities in resource-limited settings like Sri Lanka. Consequently, there is an urgent need for cost-effective, locally sourced alternatives. This study evaluated and compared the antibacterial activity of commercial eugenol with essential oils extracted from Ceylon cinnamon leaves, a sustainable agricultural byproduct, and clove buds, against S. mutans. To our knowledge, this is the first report comparing Sri Lankan-origin clove and Ceylon cinnamon leaf oils against commercial eugenol. Essential oils were extracted by steam distillation from commercially available and home-dried clove buds, as well as Ceylon cinnamon leaves. Antibacterial activity of these extracts and commercial eugenol, which is generally used in dental clinics, was tested against S. mutans using the disc diffusion assay. Data were analyzed using one-way ANOVA. The mean zones of inhibition for commercial eugenol, clove oils from commercial clove buds, clove oil from home-dried clove buds,  and cinnamon leaf oil were 20.33 ± 0.94 mm, 20.50 ± 1.48 mm, 20.31 ± 1.56 mm, and 20.61 ± 1.11 mm, respectively, with no significant differences observed among the tested products (p > 0.05). Essential oils from commercial clove buds, home-dried clove buds, and Ceylon cinnamon leaf demonstrated antibacterial activity against S. mutans comparable to commercial eugenol, suggesting that these locally sourced oils represent promising alternatives to commercial eugenol that warrant further investigations. However, further studies evaluating minimum inhibitory and bactericidal concentrations, cytotoxicity, formulation compatibility, and clinical performance are required to confirm their suitability for use in dental practice.