The effect of chewing gums containing MBE and xylitol on different variables related to caries and gingivitis in a sample of adult volunteers with a high risk for caries will be evaluated. The main result of that double-blind randomized controlled interventional trial will be that chewing gum containing MBE was more effective in reducing plaque acidogenicity, salivary mutans streptococci concentration and gingival bleeding compared to a xylitol and sugar-free chewing gum.