Dental caries incidence in adults is similar to that in children and adolescents, but few caries preventive agents have been evaluated for effectiveness in adult populations. Magnolia bark extract (MBE) is a plant extract obtained from the bark of magnolia that has been widely used in traditional Chinese medicine for 2,000 years, Magnolia officinalis has been used for the treatment of acute pain, diarrhea, coughs and urinary problems. The two main constituents of the bark of this medicinal plant are magnolol and honokiol. They are known to possess a variety of pharmacological properties, including therapeutic-related activities central nervous system inhibition anti-inflammatory effects, antimicrobial activity, antioxidative activity and freeradical scavenging activity. Magnolol andhonokiol have also been reported to inhibit the growth of Streptococcus mutans, Streptococcus sobrinus, Porphyromonas gingivalis, Fusobacterium nucleatum, Aggregatibacter actinomycetemcomitans, Capnocytophaga gingivalis and Veillonella disper in vitro and reduce the dental caries values in rats. Consequently, the antimicrobial properties of MBE against cariogenic and plaque bacteria have showed promising results. 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.