This study was conducted to determine the age at which bitewing radiograph data may become important for research studies that involve measuring decay on permanent teeth. The National Preventive Dentistry Demonstration Program provided the database for the study. The general results indicated that the amount of additional DMFS (decayed, missing, and filled surfaces) and DFS (decayed and filled surfaces) information that is detected on permanent teeth by bitewing radiographs only starts to become of practical significance at the fifth grade level in nonfluoridated communities and at the sixth grade level in fluoridated communities. Therefore the use of radiographs to detect caries on permanent teeth has little or no benefit for research purposes below the sixth grade. This conclusion does not pertain to studies including the primary teeth or to the use of radiographs in clinical dental practice.