Purpose: To investigate the effects and mechanisms of lemon essential oil products on dental caries prevention.
Materials and methods: Lemon essential oil microemulsions (LEOM) with concentrations of 1/8 minimum inhibitory concentration (MIC), 1/4 MIC, and 1/2 MIC were applied to S. mutans at concentrations of 0.2%, 1%, and 5% glucose, respectively. Changes in acid production capacity of S. mutans were measured based on changes in pH. The effect of the reductive coenzyme I oxidation method on LDH activity was examined. The effect of lemon essential oil microemulsion on the expression of the lactate dehydrogenase gene (ldh) was detected by a quantitative real-time polymerase chain reaction.
Results: Lemon essential oil microemulsion at 1/2 MIC concentration reduced the environmental pH value at different glucose concentrations, compared to those observed in the control group (p < 0.05). LDH activity of S. mutans was decreased at three subinhibitory concentrations of lemon essential oil microemulsions (p < 0.05). The effect of lemon essential oil microemulsions on S. mutans LDH activity and bacterial acid production were positively correlated (r = 0.825, p < 0.05). Lemon essential oil microemulsion at 1/2 MIC concentration downregulated the expression of the ldh gene of S. mutans at different glucose concentrations (p < 0.05). In different glucose environments, lemon essential oil microemulsions at subminimum inhibitory concentrations can inhibit the acid production of S. mutans by reducing ldh expression and LDH activity in the glycolytic pathway, proving its anti-caries potential.
Conclusions: LEOM can effectively prevent dental caries and maintain the microecological balance of the oral environment.
Keywords: Streptococcus mutans; acid production; dental caries; lactate dehydrogenase; lemon essential oil microemulsion.