Treatment The subjects will be randomly assigned to three groups: a Magnolia and Xylitol group (MX group) using a chewing gum containing MBE and xylitol, a Xylitol group (X group) using a chewing gum with the same content of xylitol but free of MBE and finally and a Control group (C group), using a sugar-free chewing gum without MBE and xylitol. Each subject will be instructed to chew 1 or 2 pellets for 5 minutes, 3 times a day (2 in the morning, 2 after the midday meal and 1 in the afternoon). Thus, the total daily intake of magnolol and honokiol in MX group will be 11.9 mg/day. The daily use of the three different chewing gums will be carried out for 12 months.