The United Kingdom Defence Dental Agency assesses United Kingdom servicemen as being at low, moderate, or high risk of developing morbidity during the next year, based on the examining dental officer's assessment of their dental status. The most frequent reason for assessing a patient as being at high risk of experiencing a dental emergency is the presence of extensive caries; however, dental officers' perceptions of which caries render a patient at high risk vary considerably. An investigation was carried out with records for Royal Air Force recruits who had been assessed as needing restorative work at their initial dental inspections but for whom this treatment had not been provided for >= 1 year. Intraoral radiographs taken at the initial dental inspection were examined, and the width of apparently sound dentine remaining between the edge of the carious lesion and the pulp was measured. The results indicate that, when there is >= 2 mm of apparently sound dentine remaining, there is very little risk that the patient will experience symptoms during the next year. Personnel with a carious tooth with <2 mm of sound dentine remaining should be classified as high risk.