Majority of New Onset of Dental Caries Occurred from Caries-Free Students: A Longitudinal Study in Primary School Students

Abstract

We examined Rose's axiom that a large number of people exposed to a small risk may generate more cases than a small number exposed to a high risk, using data on caries incidence. This longitudinal study was based on the records of annual dental checks conducted in primary schools in Okinawa, Japan. Participants were students aged 6-11 years at baseline in 2014, and a follow-up survey was conducted after one-year. The outcome variable was the increased number of decayed, missing, and filled teeth (DMFT). The predictor variable was the baseline DMFT score. Gender, grade, and affiliated school variables were adjusted. A negative binomial regression model was used to obtain the estimated increase of DMFT score. Among 1542 students, 1138 (73.8%) were caries-free at baseline. A total of 317 (20.6%) developed new caries during the follow-up. The predicted number of new carious teeth in a caries-free students and students with DMFT = 1 at baseline were 0.26 (95% CI, 0.22-0.31) and 0.45 teeth (95% CI, 0.33-0.56), respectively. However, among the total of 502 newly onset of carious teeth, 300 teeth (59.7%) occurred from the caries-free students at baseline. Hence, prevention strategies should target the low-risk group because they comprise the majority of the population.

Keywords: dental caries; longitudinal study; population approach; prevention paradox; universal health coverage.

Figure 1

The participants flow for analytic sample (n = 1542).

Figure 2

(a) Number of newly onset carious teeth at the one-year follow-up by DMFT at baseline. Most of the carious teeth occurred in students previously caries-free at baseline. (b) Number of participants with caries incidence during one-year follow-up by DMFT at baseline. MDFT: decayed, missing, and filled teeth.

Figure 3

(a) The number of newly onset carious teeth per participant and the total number of carious teeth by DMFT at baseline. As DMFT at baseline rises, the number of newly onset carious teeth increases. However, the total number of newly onset caries is highest in the caries-free population (DMFT = 0) at baseline. (b) Individual caries incidence and the total number of students experiencing caries incidence by DMFT at baseline. Similar to the number of newly onset carious teeth, when DMFT ≥ 1 at baseline, the individual caries incidence rate is higher than DMFT = 0. However, the total number of individual caries incidence is highest in caries-free (DMFT = 0) at baseline.