The clinically-examined number of teeth significantly correlated with the self-reported number of teeth in both males (ρ = 0.70) and females (ρ = 0.67) of the present study. Thus, the present results suggested that the self-reported number of teeth is a valid reflection of the clinically-examined number of teeth. Our results showed a lower correlation coefficient than those previously reported [10–13]. A previous study of 40- to 56-year-old Japanese subjects reported a correlation coefficient of 0.80 , and a study comprised of 50 subjects older than 70 years reported a correlation coefficient of 0.97 . However, the latter study was a telephone survey, and had directed subjects to count their teeth with a mirror. In contrast, our subjects have high proportion of younger population who might not be careful for the oral health behavior than those previous reports. It may cause that our results indicated lower correlation coefficient.
The present results are consistent with previous studies reporting that the self-reported number of teeth is often lower than that determined during clinically-examined [11, 12]. This may be due to the use of the phrasing “natural teeth,” which may lead patients to not count teeth abutting a crown and bridge. The discrepancy between the number of self-reported and clinically-examined teeth was greatest in those with many prosthetic teeth (data not shown). Therefore, the validity of self-reported number of teeth may be improved if the wording of the questionnaire explicitly explained the characteristics of restorative and prosthodontic dental work, to allow subjects to have a better understanding of their restoration status.
Buhlin et al.  reported that older individuals show more concern for their oral health. Moreover, the average number of remaining teeth in the present study was higher than that of the average Japanese population , which may be possibly attributed to the subjects’ increased awareness of their oral health. Therefore, the correlation coefficient may increase with age.
Ueno et al.  reported that the correlation coefficient of patients with 1–19 teeth is higher than that of patients with 20–32 teeth. This result is in accordance with our result. Also, our results showed significantly negative correlation between CPI and the clinically-determined number of teeth (r = -0.13, data not shown). Therefore, the correlation coefficient may increase with CPI.
Some previous studies reported frequency of tooth brushing as a factor associated with the number of remaining teeth [16, 17]. These studies included the nonuse of tooth brushing; however our study did not assess this. Therefore, the subjects’ concern for their oral health may be more related to the choice of brushing their teeth or not, rather than the frequency of tooth brushing.
Nakayama et al.  reported that the association between the number of remaining teeth and regular dental check-ups was not significant. Therefore, the association between the frequency of dental scaling and awareness of oral health is not significant, and may have no effect on the correlation between the numbers of remaining and self-reported teeth.
One limitation of the present study is population bias; those voluntarily undergoing medical examination tend to be more conscious about their health. Furthermore, the present study included a higher proportion of both subjects of a regular company medical checkup and J-MICC Study having 20–32 teeth compared with the Japanese national average . Future studies including more patients with 0–19 teeth are warranted. However, our subjects were superior to previous reports that there were wide age bracket and great numbers of subjects.