The purpose of this study was to compare the effectiveness of dental checkups incorporating tooth-brushing instruction (TBI) with that of conventional dental checkups. A team consisting of one dentist and three dental hygienists saw an average of 60 employees per day on-site at an airline company. The patient's teeth were stained with a disclosing tablet and the results recorded on a Plaque Control Record (PCR) chart. The patient was then given TBI. After recording the relevant data, including TBI given and PCR scores, the charts were stored. Checkups were performed in a total of 3,854 patients between 2001 and 2005 and changes in annual scores investigated. In addition, annual shifts in mean score in patients receiving checkups over all five years were compared with those in patients receiving checkups for the first time in each of the five years. The mean score in patients receiving a checkup in 2001 was 35.1%, declining by 2.6 points to 32.5% in 2005. Among patients receiving checkups over all five years, the mean score in 2001 was 34.0%, declining by 11.2 points to 22.8% in 2005. Over the five-year period, the mean score in patients receiving checkups was 34.1%. In patients receiving checkups over all five years, the proportion with PCR scores <30% increased each year. This was because the number of patients with PCR scores ≥60% decreased each year. These findings suggest that TBI is effective in reducing poor plaque control. When compared with in patients who had not received TBI, five consecutive years of checkups was clearly effective. These results indicate that checkups incorporating TBI are more effective than conventional dental checkups that simply check for caries. In future, this type of checkup should contribute to improved preventative dentistry with minimal intervention.