Numerous studies have related dental caries experience of children with the frequency of their toothbrushing or with their oral cleanliness at the time of examination. Conflicting results were obtained and, therefore, no conclusions may be drawn from these studies. In other studies, the incidence of new carious lesions over a number of years was related to oral cleanliness during the same period of time. These studies showed that children with good oral hygiene had a lower caries incidence than those with poor oral hygiene, but the differences were small. Toothbrushing with a fluoridated toothpaste, which is now the usual practice, is effective in reducing caries incidence. Flossing can remove plaque from approximal tooth surfaces, and there is some evidence that it can reduce caries incidence. Dental caries can be largely prevented by highly efficient removal of plaque by toothbrushing and flossing. However, the available evidence suggests that regular prophylaxis by dental personnel is essential to maintain the necessary high level of efficiency. It is not known to what extent individuals are capable of removing their own plaque to the same high level of efficiency. It is probable that only highly-motivated individuals can maintain such a high standard of plaque control.