Short intervals between bitewing examinations favor the timely detection of lesions on approximal surfaces. Long intervals reduce the exposure to radiation. Thus, the question arises which intervals between bite-wing examinations are appropriate. The length of intervals between bitewing examinations should be adapted to the caries risk on approximal surfaces of molars and premolars. In order to estimate the caries risk in the Swiss school population, longitudinal data of 591 schoolchildren from the Canton (County) of Zurich were analyzed. These schoolchildren had been examined at 4-year intervals. The proportion of 7-year-olds with caries increment on approximal surfaces within 4 years was 7.1%, i.e., the caries risk in the population was 7.1%. In the 11-year-olds, the caries risk was 17.60%. Seven-year-olds without caries experience on selected approximal surfaces had a low caries risk of 2.2%. However, 7-year-olds with caries experience on selected approximal surfaces had a high risk of 24.2%. The same applied to 11-year-olds: those without caries experience had a low risk (7.5%), and those with caries experience had a high risk (38.5%). For the 7-year-old schoolchildren without any caries experience, an x-ray interval of 8 years is proposed. For the 7-year-old schoolchildren with caries experience, an x-ray interval of 1 year is proposed.