The Antibacterial Effect of Eight Selected Essential Oils Against Streptococcus mutans: An In Vitro Pilot Study

Background/Objectives: As antimicrobial dental treatments, based on chemical products, long tested for their efficacy, have been lately associated with developing antimicrobial resistance, there is a growing interest to identify and develop efficient alternatives. The aim of this paper is to assess the antimicrobial potential of eight selected essential oils (EOs): Cinnamon (Cinnamomum verum), Tea tree (Melaleuca alternifolia), Spearmint (Mentha spicata), Rosemary (Rosmarinus officinalis), Clove (Eugenia caryophyllata), Eucalyptus (Eucalyptus radiata), Cedarwood (Juniperus virginiana), and Lemongrass (Cymbopogon flexuosus), more or less recognized and investigated for this particular therapeutic effect, on Streptococcus mutans (S. mutans), a key pathogen involved in oral pathology. Materials and methods: The chemical constituents of the EOs were identified and quantified by Gas Chromatography-Mass Spectrometry (CG-MS) method. Saliva samples, collected from nine patients with active dental caries, were tested in vitro. To assess the bacterial susceptibility of the selected EOs against S. mutans, the inhibition zones (IZ), minimum inhibitory concentrations (MIC), and minimum bactericidal concentrations (MBC) were determined. Results: All EOs tested showed antimicrobial activity against S. mutans, with IZs over 20 mm. The highest antimicrobial efficacy was observed for spearmint, followed by Eucalyptus, Tea tree, and Lemongrass. The next in descending order were Cinnamon Bark, Clove, Rosemary, and Cedarwood. Considering the mean MIC and MBC values, the spearmint EO proved to be the most effective in inhibiting the growth of S. mutans, as well as in annihilating it, followed by the Eucalyptus EO, Tea tree EO and Lemongrass EO. The less effective were determined to be Cinnamon, Clove, Rosemary and Cedarwood EOs. Conclusions: The eight selected EOs demonstrated antimicrobial activity against S. mutans, with Spearmint and Eucalyptus showing the most significant effects, advocating for their potential in dental caries prevention and treatment, and their potential role in oral hygiene applications.