The improvement of dental hygiene is considered to be one of the most important measures in dental health education. Hence, it was the aim of the present study to investigate the influence of two similar preventive programmes on oral hygiene performed in adults and schoolchildren. In the adult study, the oral hygiene indices PI (Quigley-Hein) and API (Lange) could be significantly improved after six months by an individualized preventive programme performed every three months. Besides repeated instructions and motivations in oral hygiene, the programme included professional toothcleaning. In contrast, nine-year old schoolchildren showed no improvement in the oral hygiene indices PI and PBI (Mühlemann and Son) after applying a similar programme over three years. For the PI, even a deterioration from 1.86 at the beginning of the study to 2.65 at the final examination was seen. Other authors were more successful by applying a programme without professional toothcleaning but with inclusion of the parents. It is therefore concluded that children should be educated to oral self-care by including their parents and by taking their status of psychological development into account.