The Xylitol for Adult Caries Trial (X-ACT) is a three-year, multi-center, randomized, placebo-controlled, double-blind study to determine the effectiveness of xylitol lozenges in reducing the incidence of coronal and root caries in caries-active adults. The intervention is the daily use of xylitol lozenges. Participants will be 750 adults (ages 25-75) with current or recent caries lesions who are dental school patients at one of three Clinical Centers in Chapel Hill, NC, Birmingham, AL, and San Antonio TX. These Clinical Centers offer diverse populations with substantial proportions of minority populations that enhance the generalizability of the findings. The Study Chair is located at the University of North Carolina-Chapel Hill, and the Data Coordinating Center is at the Kaiser Permanente Center for Health Research in Portland, OR.