Dental caries and periodontitis are initiated by specific bacteria and modified by host and environmental factors. Individuals have great differences in their rates of disease progression, but a small set of risk factors, such as smoking and diabetes, can distinguish patients at high risk for more severe disease. The application of information about factors that influence disease can be used to improve disease prevention and management. Knowledge of when specific information may be valuable should lead to the optimal management of individual patients. The use of diagnostic and prognostic tests and their application to the assessment and management of dental caries and periodontitis are the focus of this review.