Fig. 1

Decision tree of the Markov model. The subsequent structure of the control was identical to fluoride treatment. Subjects in both groups would be at risk of developing new root caries based on corresponding probabilities in each cycle. The decayed teeth could be restored (with or without endodontic treatment), extracted or remain untreated. A proportion of endodontically treated teeth would undergo crown restoration afterward. The decayed teeth that did not receive any treatment would transition to untreated root caries status in the next cycle and faced the same possible transitions as the previous cycle. Teeth in direct restoration status would have a risk of restoration failure in each cycle and require refilling. Crown restoration teeth as well as extracted teeth were regarded as constant. Abbreviation endo, endodontic treatment; restor, restoration